U.S. patent application number 10/512087 was filed with the patent office on 2005-08-18 for method of detecting biological pattern, biological pattern detector, method of biological certificate and biological certificate apparatus.
Invention is credited to Takiguchi, Kiyoaki.
Application Number | 20050180620 10/512087 |
Document ID | / |
Family ID | 29422383 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050180620 |
Kind Code |
A1 |
Takiguchi, Kiyoaki |
August 18, 2005 |
Method of detecting biological pattern, biological pattern
detector, method of biological certificate and biological
certificate apparatus
Abstract
The present invention enables permanent biometric authentication
without the risk of forgery or the like. The present invention
enables living-tissue discrimination as well as biometric
authentication. The roughness distribution pattern of deep-layer
tissue of the skin covered with epidermal tissue is detected,
thereby extracting a unique pattern of the living tissue. Then,
biometric authentication is performed based upon the detected
pattern. The roughness distribution pattern of the deep-layer
tissue of the skin is optically detected using difference in
optical properties between the epidermal tissue and the deep-layer
tissue of the skin. In this case, long-wavelength light, e.g.,
near-infrared light is used as illumination light cast onto the
skin tissue. A fork structure of a subcutaneous blood vessel is
used as the portion which is to be detected, for example. The
portion which is to be detected is determined based upon the
structure of the fork structure. In this case, the living-tissue
discrimination may be made using the subcutaneous blood vessel.
Inventors: |
Takiguchi, Kiyoaki; (Tokyo,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
29422383 |
Appl. No.: |
10/512087 |
Filed: |
April 7, 2005 |
PCT Filed: |
May 7, 2003 |
PCT NO: |
PCT/JP03/05696 |
Current U.S.
Class: |
382/128 ;
382/115 |
Current CPC
Class: |
G01N 21/49 20130101;
G06K 2009/0006 20130101; G06K 2009/00932 20130101; G06K 9/0012
20130101; G06K 9/00087 20130101; G06K 9/00013 20130101; G06T
2207/30088 20130101; G06K 9/00114 20130101; G06T 7/42 20170101;
G06T 7/0012 20130101; G06T 2207/30101 20130101; G06K 9/00067
20130101; G06K 9/00885 20130101 |
Class at
Publication: |
382/128 ;
382/115 |
International
Class: |
G06K 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 9, 2004 |
JP |
2002-134534 |
May 9, 2002 |
JP |
2002-134569 |
Claims
1. A living-tissue pattern detecting method wherein the roughness
distribution pattern of deep-layer tissue of skin covered with
epidermal tissue is detected for extracting a unique pattern of
living tissue.
2. A living-tissue pattern detecting method according to claim 1,
wherein said deep-layer tissue of the skin is dermal tissue.
3. A living-tissue pattern detecting method according to claim 1,
wherein said roughness distribution pattern is optically detected
using difference in optical properties between said epidermal
tissue and said deep-layer tissue of the skin.
4. A living-tissue pattern detecting method according to claim 3,
wherein polarized light is cast on said tissue, and reflected light
is detected through a polarizing filter with a polarizing plane
orthogonal to that of said polarizing light, for detecting said
roughness distribution pattern.
5. A living-tissue pattern detecting method according to claim 4,
wherein long-wavelength light is used as said polarizing light.
6. A living-tissue pattern detecting method according to claim 5,
wherein near-infrared light is used as said long-wavelength
light.
7. A living-tissue pattern detecting method according to claim 4,
wherein wavelength components changed due to reflection are
selected by means which allow light with a predetermined frequency
to pass through, or means which reflect light with a predetermined
frequency.
8. A living-tissue pattern detecting method according to claim 4,
wherein incident angle of said polarized light is controlled so as
to adjust the depth for detecting the object which is to be
detected.
9. A living-tissue pattern detecting method according to claim 3,
wherein illumination light is cast onto said tissue so as to cause
interference between a part of said illumination light and
reflected light for detecting change in wavelength components of
the reflected light in the form of an interference pattern, thereby
extracting a unique pattern of living tissue.
10. A living-tissue pattern detecting method according to claim 1,
wherein said roughness distribution pattern is electrically
detected using difference in electric properties between epidermal
tissue and deep-layer tissue of the skin.
11. A living-tissue pattern detecting method according to claim 10,
wherein the electric potential of the skin is measured using
electrostatic induction so as to detect the depth at which dermal
tissue beneath epidermis is positioned, thereby detecting the
tissue structure beneath epidermis.
12. A living-tissue pattern detecting method according to claim 11,
wherein a plurality of fine electrodes are arrayed in parallel at a
predetermined pitch for being fit to the skin which is to be
detected.
13. A living-tissue pattern detecting method according to claim 12,
wherein capacitance coupling is formed between each fine electrode
and dermal tissue, and distance distribution regarding the
conductive layer beneath epidermis is calculated based upon
electrostatic capacitance thus formed underneath each fine
electrode, thereby detecting said tissue structure beneath the
epidermis.
14. A living-tissue pattern detecting method according to claim 13,
wherein said fine electrodes each of which are stored in a metal
casing through an insulating member are disposed at a predetermined
pitch, and said metal casing includes a dielectric thin film for
being fit to the skin so as to be introduced between said metal
casing and the skin.
15. A living-tissue pattern detecting method according to claim 13,
wherein an electret film is provided on the surface of said fine
electrode, and electrostatic capacitance is formed between said
fine electrode and dermal tissue with a bias voltage due to
permanent polarization of said electret film.
16. A living-tissue pattern detecting method according to claim 12,
wherein change in charge on living tissue due to motions is
detected with said fine electrode, and difference in the amplitude
of waveforms due to change in charge between said fine electrodes
is converted into distance between the surface of the skin and
tissue beneath epidermis.
17. A living-tissue pattern detecting device including means for
detecting the roughness distribution pattern of deep-layer tissue
of skin covered with epidermal tissue.
18. A living-tissue pattern detecting device according to claim 17,
wherein said means for detecting said roughness distribution
pattern have a function for optically detecting said roughness
distribution pattern.
19. A living-tissue pattern detecting device according to claim 18,
comprising: an illumination optical system including a light source
for casting light onto a portion which is to be detected, and a
polarizing filter for aligning the polarizing plane of illumination
light; and an imaging optical system including a light-receiving
unit for receiving reflected light from said portion which is to be
detected, and a polarizing filter with a polarizing plane
orthogonal to that of said polarizing filter.
20. A living-tissue pattern detecting device according to claim 19,
wherein said light source comprises a near-infrared light
source.
21. A living-tissue pattern detecting device according to claim 19,
further comprising means for selecting wavelength components of
said reflected light, changed due to reflection.
22. A living-tissue pattern detecting device according to claim 19,
further comprising a moving reflecting mirror for controlling the
incident angle of light cast from said light source.
23. A living-tissue pattern detecting device according to claim 18,
comprising: an illumination optical system including a light source
for casting light onto a portion which is to be detected; a
reference optical system for causing an interference pattern for
detecting change in wavelength components of the reflected light;
and an imaging optical system for detecting said interference
pattern.
24. A living-tissue pattern detecting device according to claim 23,
wherein said light source comprises a white light source.
25. A living-tissue pattern detecting device according to claim 23,
wherein a plurality of detecting units each of which includes said
illumination optical system, said reference optical system, and
said imaging optical system, are arrayed.
26. A living-tissue pattern detecting device according to claim 23,
further comprising a moving mirror for controlling the incident
position at which light is cast from said light source.
27. A living-tissue pattern detecting device according to claim 17,
wherein said means for detecting the roughness distribution pattern
have a function for electrically detecting the roughness
distribution pattern.
28. A living-tissue pattern detecting device according to claim 27,
wherein the electric potential of the skin is measured using
electrostatic induction for detecting the depth at which dermal
tissue beneath epidermis is positioned, thereby detecting tissue
structure beneath epidermis.
29. A living-tissue pattern detecting device according to claim 28,
further comprising a plurality of fine electrodes arrayed in
parallel at a predetermined pitch upon the skin which is to be
detected, wherein the distance distribution regarding a conductive
layer beneath epidermis is calculated based upon electrostatic
capacitance underneath each fine electrode, thereby detecting the
tissue structure beneath epidermis.
30. A living-tissue pattern detecting device according to claim 29,
wherein said fine electrodes each of which are stored in a metal
casing through an insulating member are arrayed at a predetermined
pitch, and wherein said metal casing includes a dielectric thin
film to be introduced between said metal casing and the skin.
31. A living-tissue pattern detecting device according to claim 29,
wherein each fine electrode includes an electret film on the
surface thereof.
32. A biometric authentication method wherein the roughness
distribution pattern of deep-layer tissue of the skin covered with
epidermal tissue is detected, and said roughness distribution
pattern thus detected is compared to a pattern which has been
registered beforehand, whereby biometric authentication is
performed.
33. A biometric authentication method according to claim 32,
wherein said deep-layer tissue of the skin is dermal tissue.
34. A biometric authentication method according to claim 32,
wherein said roughness distribution pattern is optically detected
using difference in optical properties between said epidermal
tissue and said deep-layer structure of the tissue.
35. A biometric authentication method according to claim 34,
wherein polarized light is cast on said tissue, and reflected light
is detected through a polarizing filter with a polarizing plane
orthogonal to that of said polarizing light, for detecting said
roughness distribution pattern.
36. A biometric authentication method according to claim 34,
wherein illumination light is cast onto said tissue so as to cause
interference between a part of said illumination light and
reflected light for detecting change in wavelength components of
the reflected light in the form of an interference pattern, thereby
extracting a unique pattern of living tissue.
37. A biometric authentication method according to claim 32,
wherein a fork structure of a subcutaneous blood vessel is used as
the portion which is to be detected, and wherein said portion which
is to be detected and the direction of the principal axis are
determined at the time of authentication, based upon said fork
structure using the relation between said principal axis and said
fork structure registered beforehand.
38. A biometric authentication method according to claim 37,
wherein living-tissue discrimination is made using said
subcutaneous blood vessel.
39. A biometric authentication method according to claim 38,
wherein living-tissue discrimination is made using change in
absorbance due to change in blood flow in said subcutaneous blood
vessel.
40. A biometric authentication method according to claim 32,
wherein said roughness distribution pattern is electrically
detected using difference in electric properties between epidermal
tissue and deep-layer tissue of the skin.
41. A biometric authentication method according to claim 40,
wherein the electric potential of the skin is measured using
electrostatic induction so as to detect the depth at which dermal
tissue beneath epidermis is positioned, thereby detecting the
tissue structure beneath epidermis.
42. A biometric authentication method according to claim 32,
wherein the tissue structure beneath epidermis covered with
epidermal tissue is detected using difference in temperature
between epidermal tissue and deep-layer tissue of the skin.
43. A biometric authentication method according to claim 42,
wherein fine temperature detecting devices are arrayed, and wherein
said tissue structure beneath epidermis is detected based upon
difference in temperature between said temperature detecting
devices.
44. A biometric authentication method according to claim 43,
wherein said difference in temperature is detected in the form of
difference in magnitude of infrared light.
45. A biometric authentication device including means for detecting
the roughness distribution pattern of deep-layer tissue of the skin
covered with epidermal tissue, wherein said roughness distribution
pattern thus detected is compared to a pattern which has been
registered beforehand, whereby biometric authentication is
performed.
46. A biometric authentication device according to claim 45,
wherein said means for detecting the roughness distribution pattern
has a function for optically detecting said roughness distribution
pattern.
47. A biometric authentication device according to claim 46,
comprising: an illumination optical system including a light source
for casting light onto a portion which is to be detected, and a
polarizing filter for aligning the polarizing plane of illumination
light cast from said light source; and an imaging optical system
including a light-receiving unit for receiving reflected light from
said portion which is to be detected, and a polarizing filter with
a polarizing plane orthogonal to that of said polarizing
filter.
48. A biometric authentication device according to claim 46,
comprising: an illumination optical system including a light source
for casting light onto a portion which is to be detected; a
reference optical system for causing an interference pattern for
detecting change in wavelength components of the reflected light;
and an imaging optical system for detecting said interference
pattern.
49. A biometric authentication device according to claim 45,
including means for determining the position which is to be
detected and the direction of the principal axis based upon the
structure of a subcutaneous blood vessel.
50. A biometric authentication device according to claim 49,
comprising: an interference-light detecting unit for detecting the
roughness distribution pattern of deep-layer tissue of the skin
covered with epidermal tissue; a moving mirror for controlling the
incident angle of illumination light cast from said
interference-light detecting unit; a blood-vessel position
detecting unit for detecting the positions of subcutaneous blood
vessels based upon information from said interference-light
detecting unit; a blood-vessel data storage unit for storing an
images of subcutaneous blood vessels; a blood-vessel position
comparison unit for comparing the positions of the detected blood
vessels to blood-vessel data stored beforehand; a mirror control
unit for controlling the angle of said moving mirror based upon
control information from said blood-vessel position detecting unit
and said blood-vessel position comparison unit; an
interference-pattern storage unit for storing the interference
pattern due to deep-layer tissue of the skin; a matching unit for
performing matching of the positions of blood vessels and said
interference pattern; and an interference-pattern comparison unit
for comparing interference-pattern information received from said
interference-light detecting unit to the interference pattern
stored in said interference-pattern storage unit.
51. A biometric authentication device according to claim 45,
wherein said means for detecting the roughness distribution pattern
have a function for electrically detecting the roughness
distribution pattern.
52. A biometric authentication device according to claim 51,
wherein the electric potential of the skin is measured using
electrostatic induction for detecting the depth at which dermal
tissue beneath epidermis is positioned, thereby detecting tissue
structure beneath epidermis.
53. A biometric authentication device according to claim 52,
wherein further comprising a plurality of fine electrodes arrayed
in parallel at a predetermined pitch upon the skin which is to be
detected, wherein the distance distribution regarding a conductive
layer beneath epidermis is calculated based upon electrostatic
capacitance underneath each fine electrode, thereby detecting the
tissue structure beneath epidermis.
54. A biometric authentication device according to claim 45,
wherein said means for detecting the roughness distribution pattern
have a function for detecting tissue structure beneath epidermis
covered with epidermal tissue using difference in temperature
between said epidermal tissue and said deep-layer tissue of the
skin.
55. A biometric authentication device according to claim 54,
including a plurality of temperature detecting devices arrayed upon
the skin which is to be detected, wherein the roughness
distribution regarding the tissue beneath epidermis is detected
based upon difference in temperature between said temperature
detecting devices, whereby the tissue structure beneath epidermis
is detected.
56. A biometric authentication device according to claim 54,
including a plurality of infrared detecting devices arrayed upon
the skin which is to be detected, wherein the roughness
distribution regarding the tissue beneath epidermis is detected
based upon difference in the magnitude of infrared light between
said infrared detecting devices, whereby the tissue structure
beneath epidermis is detected.
57. A biometric authentication method wherein near-infrared light
is cast onto the tissue through a polarizing filter, as well as
detecting reflected light through a polarizing filter with a
polarizing plane orthogonal to that of said polarizing filter, so
as to detect an image of blood capillaries beneath epidermis or the
three-dimensional distribution pattern thereof, and wherein
comparison is made between: said image of blood capillaries beneath
epidermis or said three-dimensional distribution pattern thereof
thus detected; and a pattern registered beforehand, whereby
biometric authentication is performed.
58. A biometric authentication device comprising: an illumination
optical system including a light source for casting near-infrared
light onto a portion which is to be detected, and a polarizing
filter for aligning the polarizing plane of illumination light cast
from said light source; and an imaging optical system including an
imaging unit for taking an image of reflected light from said
portion which is to be detected, and a polarizing filter with the
polarizing plane orthogonal to that of said polarizing filter;
wherein comparison is made between: an acquired image of blood
capillaries beneath epidermis or the three-dimensional distribution
pattern thereof; and a pattern registered beforehand, whereby
biometric authentication is performed.
Description
TECHNICAL FIELD
[0001] The present invention relates to a new biometric pattern
detecting method and biometric pattern detecting device for
acquiring the pattern of a deep skin layer such as dermis or the
like, and particularly to a biometric authentication method and a
biometric authentication device.
BACKGROUND ART
[0002] Fingerprints, palm patterns, or the like, are widely used
for person authentication. These patterns are skin ridge patterns
wherein a part of the epidermal tissue is embedded in the roughness
structure of the dermis, and accordingly, the patterns can be
directly observed from the outside. That is to say, the
aforementioned pattern essentially corresponds to the deep layer
structure of the skin such as dermis or the like. The skin of the
portion such as a palm, a sole, or the like, has a special
structure wherein the epidermal structure corresponds to the
structure of the dermis beneath the epidermal tissue, unlike the
skin of other portions, leading to the physiological advantages
such as high sensitivity of the touch sensory nerves of which ends
are positioned in the deep layer of the skin to external
stimulation, great toughness regarding friction, and so forth.
Conventionally, the fingerprints have been used for person
authentication since the fingerprints exhibit sufficient stability
essentially due to the high stability of the deep layer structure
therebeneath.
[0003] However, the aforementioned biometric authentication using
the fingerprints does not provide sufficient security against
so-called "spoofing" or the like. That is to say, the fingerprints
are readily left on various objects, and the fingerprints left on
the object can be easily observed, leading to a risk that other
persons would forge the fingerprints.
[0004] On the other hand, it is expected that biometric
authentication using the epidermal tissue of other portions avoids
the aforementioned risk of forgery, for example. However, the
epidermal tissue changes due to metabolism thereof in a 28-day
cycle. Furthermore, the epidermal tissue readily exhibits various
conditions due to rough skin, dry skin, or the like. Accordingly,
the epidermal tissue of other portions does not have sufficient
stability. Furthermore, it has become clear from measurement that
the patterns of the epidermal tissue of the base portion of a
finger, the thenar region, and the like, do not correspond to the
patterns thereunderneath at all, rather, in some cases, the
patterns of the epidermal tissue thereof are formed orthogonal to
the patterns thereunderneath, except for a special case such as the
fingerprints, leading to difficulty in biometric authentication
using such a portion.
[0005] That is to say, a large part of the epidermal tissue of the
human body, including the palm portion such as the thenar region
and so forth, the base portion of a finger, the skin of the back of
the hand, and the like, has patterns different from the patterns of
the deep-layer structure therebeneath, except for a special case
such as the fingerprints which are fingertip impressions, wherein
the epidermal tissue directly corresponds to the deep-layer
structure, allowing external observation thereof. Furthermore, it
is difficult to make external observation of the deep-layer
structure therebeneath due to scattering of visible light from the
6-layer epithelial structure and absorption thereof by the melanin
pigment in basal cells or the like. This leads to difficulty in
development of a finger-ring-type authentication device wherein
person authentication is performed using the pattern of the skin in
contact with the inner face of the finger ring at the time of being
fit by the user.
[0006] On the other hand, the deep-layer structure beneath the
epidermal tissue is essentially unique to an individual, and
exhibits sufficient stability over time, as with a well-known
example of fingerprints or the like. Note that a tattoo wherein a
pigment is injected into the deep-layer structure, and a stretch
mark caused by pregnancy, also have the same stability due to the
properties of the deep-layer structure beneath the epithelium
tissue. Accordingly, it is expected that the pattern beneath the
epithelium tissue, i.e., the deep-layer structure of the epithelium
tissue is suitably used for biometric authentication. However, the
aforementioned patterns cannot be directly observed, neither left
on an object by contact with the object, and accordingly,
development of the authentication device using the pattern of the
deep-layer structure has not been made, although the pattern of the
deep-layer structure has the same performance of biometric
authentication as with fingerprints.
[0007] The present invention has been made in order to solve the
aforementioned problems, and accordingly, it is an object thereof
to provide a biometric pattern detecting method and biometric
pattern detecting device for acquiring the roughness structure
distribution of the deep-layer structure beneath the epithelium
tissue (patterns beneath the epithelium tissue) or the blood-vessel
pattern beneath the epithelium tissue, which cannot be directly
observed. Furthermore, it is an object of the present invention to
provide a biometric authentication method and a biometric
authentication device which enables stable biometric authentication
while preventing a risk of "spoofing", e.g., forgery or the
like.
DISCLOSURE OF INVENTION
[0008] The present inventor has made various study in order to
achieve the aforementioned object. As a result, it has become clear
that discrimination can be made between epidermal tissue and
deep-layer tissue of the skin using difference in properties
(optical properties, electric properties, and temperature
difference) therebetween, and the roughness distribution pattern of
the deep-layer tissue of the skin wherein visual observation is
difficult due to shielding with epidermis is clearly detected.
Accordingly, it has become clear that the pattern of any desired
portion of the skin and subcutaneous tissue over the entire body of
the user can be detected, as well as a special portion where the
epidermal pattern corresponds to the dermal pattern such as
fingerprints or the like, and the pattern thus detected can be
applied to biometric authentication (person authentication).
[0009] The present invention has been made based upon the
information thus obtained. That is to say, with a living-tissue
pattern detecting method according to the present invention, the
roughness distribution pattern of the deep-layer tissue of the skin
covered with the epidermal tissue is detected using difference in
properties (optical properties, electric properties, and
temperature difference) therebetween, thereby extracting a unique
pattern of the living tissue. Furthermore, a living-tissue pattern
detecting device according to the present invention includes means
for detecting the roughness distribution pattern of the deep-layer
tissue of the skin covered with the epidermal tissue. Furthermore,
with a biometric authentication method according to the present
invention, the roughness distribution pattern of the deep-layer
tissue of the skin covered with the epidermal tissue is detected so
as to be compared to a pattern registered beforehand, whereby
biometric authentication is performed. Furthermore, a biometric
authentication device according to the present invention includes
means for detecting the roughness distribution pattern of the
deep-layer tissue of the skin covered with the epidermal tissue,
and the pattern thus detected is compared to a pattern registered
beforehand, whereby biometric authentication is performed.
[0010] The present invention has been made based upon the basic
concept that authentication is performed not using an epidermal
pattern, but using the pattern of the deep-layer tissue of the
skin, e.g., a dermal pattern. The roughness distribution pattern
(pattern) of the deep-layer tissue is unique to individual living
tissue as with fingerprints, palm pattern, sole pattern, and so
forth, and exhibits small change over time, i.e., exhibits high
stability. Furthermore, the deep-layer tissue of a large part of
the skin has a different pattern from that of the epidermal layer,
except for special portions such as a fingertip having fingerprints
which can be observed from the outside, or the like. Furthermore,
the pattern of the deep-layer tissue is covered with the epidermal
tissue, leading to difficulty in visual observation from the
outside. Furthermore, no impression is left on any object even if
the tissue comes in contact with the object. Accordingly, it is
almost impossible for other persons to forge such a pattern.
[0011] Furthermore, with the present invention, the system does not
detect the structure of dead tissue having no nucleus such as the
horny layer of the skin, specifically, fingerprints, and so forth,
but detects deep-layer tissue of the skin which is living tissue,
as described above. The deep-layer tissue of the skin does not
maintain the pattern thereof if the deep-layer tissue is cut off
from the living human body. For example, the deep-layer tissue of
the skin has blood capillaries therein, and the pattern formed of
the blood flow within the blood capillaries is unique to the living
tissue. Furthermore, if the tissue is cut off from the living human
body, the aforementioned pattern is immediately lost due to
contraction of blood vessels, retention of blood, lost of blood,
and so forth. This affects the pattern of the entire deep-layer
tissue of the skin. Thus, with the present invention, the biometric
authentication and the living-tissue discrimination are integrated,
thereby suppressing the risk of "spoofing" using the tissue of the
user to an unrealistic level, and thereby realizing true "biometric
authentication".
[0012] The aforementioned deep-layer tissue of the skin, e.g., the
roughness distribution pattern of dermal layer can be optically
detected using the fact that difference in the structure between
epidermal tissue formed of simple cells or dead cells thereof and
dermal tissue which is dense connective tissue causes difference in
scattering properties and refraction properties therebetween, and
this leads to depolarization or difference in frequency between the
incident light and the returning light.
[0013] Specifically, first, polarized light is cast onto the
tissue, as well as detecting the reflected light through a
polarizing filter with the polarizing plane orthogonal to that of
the aforementioned polarized light, thereby detecting the
aforementioned roughness distribution pattern. In this case, the
polarized light is cast on the surface of the tissue, and the
reflected light is filtered with the polarizing filter with the
polarizing plane orthogonal to the aforementioned polarized light,
and accordingly, only the depolarized light due to scattering in
the living tissue, such as back-scattered light, light split due to
birefringence, and so forth, is detected, thereby extracting the
pattern of the tissue having the nature which causes scattering of
light, such as a dermal layer beneath epidermis and so forth. In
particular, an arrangement may be made wherein long-wavelength
light such as near-infrared light and so forth, which has the
nature that the light readily passes through the epidermal tissue,
and is readily scattered in dermal tissue, is employed as the
aforementioned polarized light, thereby reducing adverse effects
due to absorption of the polarized light in the living tissue, and
thereby effectively detecting the pattern of the subcutaneous
tissue beneath epidermis due to desirable optical properties
(scattering properties, birefringence properties, and so forth) of
the subcutaneous tissue beneath epidermis.
[0014] Second, an arrangement may be made wherein the illumination
light is case onto the tissue, as well as causing interference
between a part of the illumination light and the reflected light so
as to detect change in wavelength components of the reflected light
in the form of an interference pattern, thereby extracting a unique
pattern of the living tissue. In this case, the system causes
interference between the reflected or scattered light from the skin
and the incident light split by a half mirror or the like serving
as reference light, thereby detecting change in wavelength
components due to birefringence or scattering in the internal
structure of the skin in the form of a beat pattern (interference
pattern). Such a beat pattern has properties unique to an
individual living tissue, thereby enabling authentication using the
beat pattern.
[0015] Furthermore, with the biometric authentication method and
the biometric authentication device according to the present
invention, an arrangement may be made wherein the subcutaneous
tissue structure covered with epidermal tissue is electrically
detected using difference in electric properties between the
epidermal tissue and the deep-layer tissue of the skin, and the
subcutaneous tissue structure thus detected is compared to a
pattern registered beforehand, thereby enabling biometric
authentication. Furthermore, an arrangement may be made wherein the
subcutaneous tissue structure covered with epidermal tissue is
detected using difference in temperature between the epidermal
tissue and the deep-layer tissue of the skin, and the subcutaneous
tissue structure thus detected is compared to a pattern registered
beforehand, thereby enabling biometric authentication.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic diagram which shows skin tissue.
[0017] FIG. 2 is a schematic diagram which shows an example of a
detecting device (authentication device) for acquiring an image of
dermal tissue using depolarization due to back-scattering of
light.
[0018] FIG. 3 is a schematic diagram which shows an example of a
detecting device (authentication device) for taking an image of
scattering light from the skin at a desired depth.
[0019] FIG. 4 is a schematic diagram for describing a mechanism of
birefringence measurement with the optical heterodyne
interferometry.
[0020] FIG. 5 is a schematic diagram which shows an example of a
detecting device (authentication device) for detecting the tissue
pattern beneath epidermis using the scattering property pattern
obtained due to interference of the light returning from the
skin.
[0021] FIG. 6 is a schematic diagram which shows an example of a
detecting device (authentication device) having a configuration
wherein multiple beat detecting devices are arrayed.
[0022] FIG. 7 is a schematic diagram which shows an example of a
detecting device (authentication device) having a configuration
wherein a moving mirror is provided to an illumination unit for
casting light onto the skin.
[0023] FIG. 8 is a schematic diagram which shows an example of a
detecting device (authentication device) having a function for
determining a portion which is to be authenticated, based upon a
vein pattern.
[0024] FIG. 9 is a property chart which shows absorption spectra of
oxidized hemoglobin and reduced hemoglobin.
[0025] FIG. 10 is a property chart which shows difference in
transmissivity between hemoglobin and water in living tissue.
[0026] FIG. 11 is a schematic diagram which shows an example of a
detecting device (authentication device) for performing pattern
detection with the differential interference method using
near-infrared light.
[0027] FIG. 12 is a schematic diagram which shows an example of a
skin-surface electric-potential detecting device.
[0028] FIG. 13 is another schematic diagram which shows an example
of a skin-surface electric-potential detecting device.
[0029] FIG. 14 is a schematic diagram which shows a
subcutaneous-tissue pattern detecting device having a configuration
wherein the multiple skin-surface electric-potential detecting
devices are two-dimensionally arrayed.
[0030] FIG. 15 is a waveform chart which shows an example of an
electric-potential waveform observed when walking.
BEST MODE FOR CARRYING OUT THE INVENTION
[0031] Detailed description will be made below regarding a
biometric pattern detecting method, a biometric pattern detecting
device, a biometric authentication method, and a biometric
authentication device, according to the present invention with
reference to the drawings.
[0032] For example, the biometric authentication using the
fingerprints has a risk of forgery by other persons since the
impressions (fingerprints) are readily left on another object, and
can be easily observed. As a countermeasure, there is the need to
perform living-tissue discrimination for determining whether or not
the detected fingerprints have been acquired from the live tissue
without unauthorized means. The reason is that the biometric
authentication using the fingerprints is essentially measurement
wherein the tissue structure of the dead tissue having no nucleus
such as the horny layer of the skin is optically or electrically
detected.
[0033] The security performance of the biometric authentication
using the aforementioned fingerprints, the iris, or the like, does
not only depend upon the detection precision, but also the
aforementioned living-tissue discrimination. For example, let us
say that other persons can breach the living-tissue discrimination
at the time of the biometric authentication using the fingerprints,
as well as having obtained the tissue used for the biometric
authentication. This allows the other persons to easily make
"spoofing", resulting in deterioration in the security of the
system to zero. Furthermore, the aforementioned "spoofing" using
the tissue leads to a new additional risk of a serious hazard to
the body and the life of the user, as well as the financial risk in
a case wherein the security of the conventional credit card is
breached. The aforementioned serious hazard to the body and the
life of the user will be referred to as "surgical hazard"
hereafter.
[0034] The biometric authentication needs to provide not only the
sufficient limitation security performance which has been proposed
in the conventional authentication techniques, but also the
sufficient security performance against the surgical hazard for
securing the safety of the user, which has been hardly proposed in
the conventional techniques.
[0035] That is to say, the security performance of the biometric
authentication consists of two kinds of the security performance.
One security performance depends upon the precision of the
"authentication" for identifying whether or not that the tissue
which is to be authenticated matches the tissue of the user. The
other security performance depends upon the precision of the
"living-tissue discrimination" for determining whether or not the
tissue used for authentication is live tissue, i.e., for confirming
that the tissue is not dead tissue cut off from the body of the
user. The conventional biometric authentication techniques have
provided only the precision and reliability of the former security
performance. In this case, the "biometric authentication" used here
essentially means authentication without "living-tissue
discrimination", and accordingly, does not mean true biometric
authentication. Accordingly, from the practical perspective, the
conventional security system having such a problem may lead to the
additional hazard, i.e., the surgical hazard.
[0036] With the simplest spoofing method without any particular
technique and equipment, spoofing is made using the tissue such as
a finger, arm, eyeball, or the like, which has been cut off from
the body of the user. Such a simple method for breaching the
biometric authentication security leads to a new additional and
serious hazard to the life and body of the user, of which money
cannot replace, even in a case of small finance loss. Accordingly,
the conventional biometric authentication methods using the
fingerprints, iris within the eyeball, or the like, remain
accessory means used with other main authentication means, or
remain accessory means in a limited form for unimportant matter, or
the like. This leads to difficulty in wide use of the conventional
biometric authentication.
[0037] On the other hand, forgery of the fingerprints or the like
can be relatively easily made. As a countermeasure against forgery
of the fingerprints, electrostatic capacity or electrostatic
induction is measured between the finger and the electrode so as to
detect the distance between the surface of the skin and the
electrode, thereby detecting the pattern of the fingerprints, using
the fact that the surface of the skin serves as a conductive
material due to moisture (water) containing salt from sweat or the
like secreted from the live tissue. This is a kind of an example of
the biometric authentication with the "living-tissue
discrimination". The reason is that the aforementioned measurement
is impossible without moisture which is an electrolyte containing
salt from sweat or the like secreted from the live tissue.
[0038] However, while the aforementioned detecting method requires
moisture serving as an electrolyte on the surface of the object
which is to be authenticated, the aforementioned object does not
need to be alive. That is to say, with the aforementioned detecting
method, the "living-tissue discrimination" is not performed for
confirming that the object which is to be authenticated has not
been cut off from the body of the user, for example. Accordingly,
with the aforementioned detecting method, it is difficult to reject
unauthorized means such as forgery of the fingerprints formed of a
gel material having water retentivity, or the finger which has been
cut off from the body of the user and subjected to spraying with or
soaking in a physiological salt solution.
[0039] Furthermore, with the biometric authentication using DNA or
the like, while forgery of the DNA is difficult, it is essentially
impossible to discriminate whether the DNA sample which is to be
authenticated belongs to the live body of the user or is formed of
DNA mass-produced by replicating the DNA obtained from the dead
body or a hair of the user with the PCR (Polymerase Chain
Reaction). Accordingly, the biometric authentication using DNA does
not include "living-tissue discrimination". Accordingly, the
biometric authentication using DNA needs some sort of a
countermeasure such as a new separate sensor for discriminating
whether or not the sample belongs to the live body of the user with
a suitable method such as detection of the blood flow in the finger
using infrared light and so forth, as well as "biometric
authentication".
[0040] In this case, the "biometric authentication" is performed by
two means. One is "authentication", and the other is "living-tissue
discrimination". That is to say, the conventional "biometric
authentication" does not only depend upon the "authentication"
serving as a "front door" as if it were, but also "living-tissue
discrimination" serving as a "back door" as if it were, which is
performed in separate detection means using a different physical
principle. Accordingly, the conventional "biometric authentication"
has a problem that if other persons breach the security of the
"living-tissue discrimination" serving as a back door, the security
of the biometric authentication security is breached, leading to a
risk of "spoofing", and further leading to a risk of surgical
hazard. With the "living-tissue discrimination", the system
discriminates whether the tissue which is to be authenticated is
alive or dead. However, the living tissue has great diversity, and
accordingly, the "living-tissue discrimination" must be performed
for a single tissue sample with a sufficiently wide threshold
range, as can be understood from the standing theory (central
dogma) what life is. This leads to an essential problem of the poor
security of the conventional "biometric authentication" against
"spoofing". That is to say, with the conventional "biometric
authentication" having separate means formed of the means of
"authentication" and the means of "living-tissue discrimination",
other persons can easily find and analyze the discrimination
mechanism for discriminating whether the tissue is alive or dead.
Accordingly, there is demand for the "true" biometric
authentication integrating the means of "authentication" and the
means of "living-tissue discrimination", i.e., the biometric
authentication without the aforementioned "back door".
[0041] With the present invention, biometric authentication is
performed based upon the detected roughness distribution pattern of
the epithelial deep-structure tissue, e.g., dermal layer, instead
of patterns of the epidermal tissue such as fingerprints described
above.
[0042] FIG. 1 is a schematic diagram which shows skin tissue which
is roughly classified into epidermis 1 and dermis 2. The epidermis
1 is keratinized stratified flattened epithelium formed of a horny
layer 11, a lucid layer 12, a granular layer 13, a prickle layer
14, a basal layer 15, and a basement membrane 16. Note that a layer
formed of the granular layer 13, the prickle layer 14, a basal
layer 15, is referred to as "Malpighian layer".
[0043] The horny layer 11 has a lamellar liquid crystal structure
formed of a bilayer membrane formed of a horny-layer intercellular
lipid. The lucid layer 12 has a cholesteric liquid crystal
structure, and the granular layer 13 is formed of cells of which
cytoplasm contains basic structures which are referred to as
"keratohyalin granule" having optical properties which cause
reflection and scattering of light, like beads. On the other hand,
the basal layer 15 has melanin granules. As described above, the
skin tissue has a multi-layer structure having various optical
scattering/absorption properties due to each layer, leading to the
advantage of preventing the living tissue from exposure to
ultraviolet light or the like. In particular, the epidermis 1 has a
kind of dichroic properties for ultraviolet light due to the
multi-layer structure formed of thin membranes each of which has a
different refractive index. However, the epidermis 1 is translucent
tissue having relatively high scattering properties in a range of
visible light, except for absorption of the light due to the
melanin pigment. Note that the epidermis 1 has high transparency in
a longer wavelength range than with red visible light or
near-infrared light. Accordingly, the light reflected from the
blood flow in the blood capillaries within the dermis 2 beneath the
epidermis 1 is scattered. The scattered light is observed as a
complexion or the color of the skin. Note that the color of the
skin essentially depends upon the distribution of the melanin
pigment and the blood flow within the blood capillaries in the
dermis 2. The flow of an electrolyte fluid such as blood or lymph
does not occur in the epidermis 1, and accordingly, the epidermis 1
essentially serves as a dielectric as exemplified by the horny
layer 11.
[0044] On the other hand, the dermis 2 has essentially different
structure as compared with the epidermis 1. The dermis 2
essentially comprises the dense fibrous connective tissue formed of
collagen or elastin, and a blood capillary pattern, unlike the
epidermis 1 formed of simple cells having no blood capillaries.
[0045] The dermis 2 is classified into a papillary layer and a
reticular layer. The dermal papillary layer is in contact with the
epidermal tissue through the basement membrane serving as the
lowermost layer of the epidermal tissue, is formed of the
connective tissue and the blood capillary pattern, and has the end
of the sensory nerve. The reticular layer is formed of collagen
having an array structure, elastin for connecting the collagen
structures one to another, and a matrix which fills the space
therebetween. The dermis 2 contains a great amount of the
electrolyte fluid due to great amount of blood capillaries and the
flow of lymph or the like, leading to extremely high electric
conductivity as compared with the epidermis 1.
[0046] Method Using the Optical Properties]
[0047] While the collagen and elastic fibrous tissue forming
connecting tissue of the dermis 2 exhibits high optical
birefringence, the epidermal tissue does not exhibit birefringence.
On the other hand, the epidermis 1 has optical properties which
cause scattering of light, and polarization properties which cause
depolarization of light due to scattering thereof. In a basic
mechanism, the tissue exhibits a unique vertical/horizontal
polarization ratio dependent upon the size and shape of the
scattering particles therewithin.
[0048] In a case wherein the wavelength of the electromagnetic wave
is far greater than the particle size, Rayleigh scattering
occurs.
[0049] In a case wherein the wavelength of electromagnetic wave
generally matches the particle size, Mie scattering occurs. (which
causes the color of cloud particles, aerosol, and cumulonimbus, to
appear white)
[0050] In a case wherein the wavelength of electromagnetic wave is
far smaller than the particle size, the electromagnetic wave
geometrically passes through the object. (e.g., rainbow formed of
rain particles, diamond dusts)
[0051] The dermis 2 having a thickness greater than a certain
thickness appears white, like milk agar. Furthermore, the dermis 2
has optical properties wherein the longer the wavelength of light
is, the more readily the light passes through the dermis 2. On the
other hand, the shorter the wavelength of the light is, the more
readily the light is scattered. Let us say that the dermis 2
contains a significant amount of absorption pigment. In this case,
the short-wavelength light scattered at a shallow portion returns
to the eyes of the observer with a high probability. However, the
long-wavelength light returns to the observer with a low
probability due to absorption of the light in the pigment.
Accordingly, the blood capillaries at the shallow portion of the
skin appear vivid red from external observation, and the vein and
hemangioma positioned at relatively deep portion appears relatively
blue. Note that while the nevus (birthmark) due to melanocyte,
which is positioned at the boundary between the dermis and the
epidermis appears relatively brown from the external observation,
the blue nevus positioned in the dermis appears relatively blue
from the external observation, wherein the name agrees with the
color. Furthermore, the Ota's nevus and Mongolian spot due to
dermal melanocyte appear relatively blue from the clinical
observation.
[0052] With the present invention, the system detects the roughness
distribution pattern or the like of the deep structure of the skin
(e.g., dermal tissue) using difference in optical properties or
electric properties between the dermal tissue and the epidermal
tissue, whereby biometric authentication is performed. For example,
the reflected light from the tissue sample is subjected to
filtering so as to discriminate the dermal layer formed of the
connecting tissue, collagen fibrous tissue, or the like, in a
deeper portion, from the epidermal tissue, using the difference in
the scattering/polarization properties of the reflected light as to
the incident white light between the dermal tissue and the
epidermal tissue. This enables the user to clearly discriminate the
dermal tissue wherein observation is difficult due to shading by
the epidermal tissue, from the epidermal tissue. In particular, the
present invention has the advantage of enabling person
authentication by detecting the pattern of the dermal tissue, even
using the skin or the subcutaneous tissue of any portion of the
body of the use, as well as a special portion such as fingerprints
and so forth, where the dermal tissue pattern matches the epidermal
tissue pattern.
[0053] FIG. 2 shows an configuration example of a detecting device
for acquiring an optical image of the dermis 2 beneath the
epidermis having a great diversity of scattering mechanisms as
described above. The detecting device has a configuration which
allows the light returning due to scattering and birefringence to
pass through the receiver of the detecting device while preventing
the light reflected from the epidermal layer from being received,
by polarizing means including polarizing plates at the
light-emitting unit and the light-receiving unit with planes of
polarization orthogonal one to another.
[0054] Description will be made below regarding a specific
configuration. First, an illuminating optical system includes a
light source 21, optical lens 22, and an illumination-unit
polarizing plate 23. Any suitable light source such as an LED or
the like can be employed as the light source 21. Note that a light
source for emitting long-wavelength light such as near-infrared
light or the like is preferably employed as the light source 21
since such long-wavelength light has the nature to readily pass
through the epidermal tissue, as well as being reflected by the
dermal tissue. Such a configuration enables acquisition of the
pattern of the tissue using the optical properties such as
scattering properties, birefringence properties, and so forth.
[0055] On the other hand, an imaging optical system includes an
imaging device (solid-state image sensor, e.g., CCD) 24 serving as
a light-receiving device, an imaging lens set 25, and a
receiving-unit polarizing plate 26. Furthermore, a half mirror 27
is disposed on a light path between the aforementioned illuminating
optical system and the imaging optical system. Note that the
aforementioned illuminating optical system and the imaging optical
system are disposed with the polarizing planes orthogonal one to
another.
[0056] With the aforementioned detecting device, the illumination
light is cast from the light source 21 onto the skin with a single
polarizing plane determined by the illumination-unit polarizing
plate 23. On the other hand, the imaging optical system includes
the receiving-unit polarizing plate 26 with the polarizing plane
orthogonal to that of the illumination-unit polarizing plate 23.
Accordingly, the reflected light from the epidermal tissue through
simple reflection passes through with a polarizing plane orthogonal
to the polarizing plane of the receiving-unit polarizing plate 26,
whereby such reflected light is intercepted by the receiving-unit
polarizing plate 26.
[0057] The illumination light cast onto the skin from the
illumination optical system reaches the deep-layer tissue of the
skin (e.g., dermal tissue), leading to scattering of the light or
birefringence thereof due to various kinds of tissue, resulting in
depolarization thereof. The reflected light, e.g., back-scattered
light, passes through the half mirror 27, and is introduced to the
aforementioned imaging optical system. In this case, depolarization
has occurred for the reflected light, thereby allowing the
reflected light to pass through the receiving-unit polarizing plate
26, whereby the back-scattered light reaches the imaging device
24.
[0058] The aforementioned scattered or reflected light exhibits
phase shift as to the incident light due to birefringence thereof
caused by reflection or scattering in the dermal tissue containing
connecting tissue, collagen, and so forth, having properties which
cause birefringence of the light. Note that the epidermal tissue
does not contain the aforementioned materials having properties
which cause birefringence of the light. With the present
embodiment, the system discriminates between the
scattered/reflected light from the epidermal tissue and from the
dermal tissue (which causes birefringence of the light) by
detecting the difference in the phase of the light
therebetween.
[0059] Furthermore, an arrangement may be made wherein the system
allows only the reflected light with a phase shift in a
predetermined wavelength range due to birefringence in the dermal
tissue, to pass through a band-pass filter such as a dichroic
filter or the like, and detects only the light thus selected,
thereby selectively detecting only the tissue which causes
birefringence of the light, and thereby enabling external
observation of the dermal tissue in a noninvasive manner.
[0060] On the other hand, as an example of measurement of the skin
using the polarizing light, a method is known in the field of the
beauty industry, wherein the skin is observed with polarized light
using the optical properties of a polarizing filter in a range of
the visible light. For example, a measurement method for evaluating
the surface of the skin is known, wherein the beauty factors such
as the glossiness of the skin, the brightness thereof, and so
forth, are measured (see Japanese Examined Patent Application
Publication No. 3,194,152, or Japanese Examined Utility Model
Registration Application No. 7-22655).
[0061] However, such conventional measurement methods are not
configured in order to observe the tissue beneath the epidermis,
such as the dermal tissue or the like, but are configured in order
to evaluate the surface of the skin using visible light from the
perspective of beauty and appearance. That is to say, the disclosed
arrangement is nothing but a method wherein an image of the skin is
obtained from scattered light from the skin using visible light
while preventing deterioration in image quality due to the
excessive brightness of the reflected light directly reflected from
the horny layer of the epidermis or the like, using the well-known
nature that depolarization of the light occurs due to scattering,
thereby obtaining a stable image of the skin.
[0062] While such conventional methods using visible light have a
function of detecting the scattered light from the epidermis, use
of the visible light leads to difficulty in precise detection of
the state of the dermal layer due to absorption or interception of
the visible light by the prickle cells or basal cells containing
melanin pigment. Furthermore, this leads to difficulty in forming
an image by extracting light wherein birefringence thereof has
occurs due to the dermal tissue. No method has yet been proposed
whatsoever wherein the structure of the dermal tissue is observed
using the fact that the dermal layer containing the connective
tissue, the collagen tissue, and so forth, exhibits great
anisotropic optical properties which cause birefringence of the
light as compared with the epidermis, and the fact that the
epidermal tissue exhibits high transmissivity of near-infrared
light, unlike visible light, i.e., using the scattering properties
and the birefringence properties of the dense connective tissue
forming the dermal tissue; this is being newly proposed in the
present specification.
[0063] As described above, the aforementioned detecting device has
a function for detecting the dermal-layer structure (e.g., the
roughness distribution pattern) using the scattering properties or
the birefringence properties of the dense connective tissue forming
the dermal layer. Note that the detecting device having a
configuration as shown in FIG. 2 has the disadvantage of reduction
of the SN ratio due to increased noise due to scattered light from
the epidermal layer, and scattered light from the dermal tissue,
subcutaneous tissue, and so forth, beneath the surface of the
dermal layer which is to be detected. FIG. 3 shows an effective
configuration example of the detecting device for solving the
aforementioned problem, wherein the illumination light is cast onto
the skin with a shallow angle, as well as limiting the aperture of
the imaging optical system.
[0064] The detecting device shown in FIG. 3 further includes a
moving reflecting mirror 28, and has a configuration wherein the
illumination is cast onto the skin in a slant direction from the
illumination optical system. Furthermore, the detecting device
includes the imaging optical system disposed just above the tissue
which is to be measured, thereby enabling direct detection of the
back-scattered light and side-scattered light without the half
mirror 27. Furthermore, the detecting device includes a shield 29
for limiting the aperture, thereby allowing only the light
returning from the portion just underneath the aperture, to reach
the imaging device 24.
[0065] With the detecting device having such a configuration, the
illumination light cast from the illumination optical system passes
through the tissue toward the deep-layer structure of the skin
(dermal layer) from the epidermal layer in a slant direction. In
this case, scattering of light due to an excessively shallow
portion, i.e., the epidermal tissue, occurs in the region on the
right side shown in the drawing, thereby preventing the scattered
light from the excessively shallow portion from reaching the
imaging optical system with the aperture limited by the shield 29.
In the same way, scattering of light due to an excessively deep
portion occurs in the region on the left side shown in the drawing,
thereby preventing the scattered light from the excessively deep
portion from reaching the imaging optical system with the aperture
limited by the shield 29. On the other hand, with the detecting
device wherein the angle of the aforementioned moving reflecting
mirror 28 is adjusted such that the position of the dermal tissue
onto which the incident light is cast, is positioned just
underneath the aforementioned imaging optical system, only the
scattered light from this region (dermal tissue) reaches the
imaging optical system.
[0066] Next, description will be made regarding a detecting method
using the birefringence of the dermal tissue. First, an arrangement
may be made using a well-known method for detecting the
birefringence, e.g., using the optical heterodyne interferometry
for converting the phase difference between the illumination light
and the reflected light or transmitted light into the phase
difference in the beat signals, instead of a method using a
band-pass filter as described above.
[0067] FIG. 4 is a diagram which shows a mechanism of such an
arrangement. The detecting device has a configuration wherein the
oscillating light is cast to a sample 33 from a light source, e.g.,
a Stabilized Transverse Zeeman Laser (STZL) 31 through a half
mirror 32, and the transmitted light (signal light) passing through
a polarizing plate 34 is detected with a photo-detector 35. At the
same time, a part of the oscillating light emitted from the
Stabilized Transverse Zeeman Laser 31 is reflected by the half
mirror 32, following which the reflected light (reference light)
passes through a polarizing plate 36, whereby the reference light
is detected with a photo-detector 37. Then, the phase difference in
the light detected by the aforementioned photo-detectors 35 and 37
is measured with an electronic phase meter 38.
[0068] Here, the linear polarizers (polarizing plates 34 and 36 )
are used for causing interference between two light waves. Note
that this mechanism enables measurement of the birefringence of the
light with precision determined by the electronic phase meter 38.
In general, the electronic phase meter 38 exhibits the measurement
precision of 0.1 degree (or more), thereby enabling measurement of
the birefringence of the light with high precision of approximately
{fraction (1/4000)} of the wavelength of the light.
[0069] Description will be made below regarding a mechanism of the
optical heterodyne interferometry. First, the electric-field
component of the reference light Er and the electric-field
component of the signal light Es are represented as follows.
E.sub.r=a.sub.r cos(2.pi.f.sub.rt+.phi..sub.r) (1)
E.sub.s=a.sub.s cos(2.pi.f.sub.st+.phi..sub.s) (2)
[0070] Here, a.sub.r and a.sub.s represent the amplitude of the
reference light and the amplitude of the signal light,
respectively. In the same way, f.sub.r and f.sub.s represent the
frequency of the reference light and the frequency of the signal
light, respectively, and .phi..sub.r and .phi..sub.s represent the
phase of the reference light and the phase of the signal light,
respectively.
[0071] In general, the light intensity I is represented by the
square of the electric-field component, and accordingly, the light
intensity I obtained by superimposing the two light waves is
represented as follows. 1 I = E s + E r 2 = a s 2 + a r 2 2 + 2 a s
a r cos ( 2 ( f s - f r ) t + ( s - r ) ) = a s 2 + a r 2 2 + 2 a s
a r cos ( 2 f b t + ) ( 3 )
[0072] Note that in the above expression, the reference symbol
"< >" represents the average over time. On the other hand,
f.sub.b (=f.sub.s-f.sub.r) represents the optical-beat frequency,
and the reference character ".DELTA." (=.phi..sub.s-.phi..sub.r)
represents the phase difference between two light components.
[0073] The photoelectric current detected with the photo-detector
is classified into the DC component represented by the first term
and the second term of the Expression (3), and the AC component
which changes in the shape of a sine wave with the frequency fb as
represented by the third term thereof. The AC signal will be
referred to as "optical-beat signal". With the optical heterodyne
interferometry, the amplitude of the optical-beat signal
(2a.sub.s.multidot.a.sub.r), the frequency (f.sub.b), or the phase
(.DELTA.), is electrically measured, and the information is
obtained based upon the amplitude (as) of the light signal, the
frequency (f.sub.s), or the phase (.phi..sub.s).
[0074] Specifically, with the measurement of the dermal tissue,
with the refractive indexes of the skin tissue which causes
birefringence of the light as n.sub.x and n.sub.y, and with the
thickness of the tissue which the light passes through as d, the
phase lags .phi..sub.x and .phi..sub.y are represented by the
following Expressions (4) and (5). 2 x = 2 n x d ( 4 ) y = 2 n y d
( 5 )
[0075] With the present embodiment, the light having two frequency
components slightly different one from another, such as STZL
(Stabilized Transverse Zeeman Laser) oscillating light or the like,
is cast onto the sample. In this case, the light intensity signal I
detected by the photo-detector is represented as follows. 3 I = E x
+ E y 2 = a x 2 + a y 2 2 + 2 a x a y cos ( 2 ( f x - f y ) t + ( x
- y ) ) = a x 2 + a y 2 2 + 2 a x a y cos ( 2 f b t + ) = a x 2 + a
y 2 2 + 2 a x a y cos ( 2 f b t + 2 n ( n x - n y ) d ) = a x 2 + a
y 2 2 + 2 a x a y cos ( 2 ( f b t + nd ) ) ( 6 )
[0076] Note that reference character ".DELTA." represents the phase
difference between the two components of the light, and reference
character ".delta.n" represents the difference in the refractive
index (=magnitude of the birefringence). As can be understood from
Expression (6), the phase difference between the two light
components is represented by the phase difference of the beat
signals. This enables measurement of the magnitude of the
birefringence by measuring the phase of the optical-beat signals
with the electronic phase meter 38 or the like.
[0077] Note that with the aforementioned measurement, there is the
need to detect the direction of the principal axis beforehand, and
to adjust the polarizing plane of the STZL oscillating light so as
to precisely match the direction of the principal axis.
Accordingly, there is the need to make measurement wherein the
phase difference is detected while rotating the polarizing plane of
the STZL oscillating light around the optical axis, thereby
detecting the magnitude of the birefringence as well as the
direction of the principal axis. However, such a measurement method
leads to problems of an extremely complicated configuration of the
authentication device, complicated user operations, and an
excessively long detecting period of time. Furthermore, in this
case, there is the need to stringently fix the position and the
direction of the authentication device at the time of being fit by
the user. Furthermore, the authentication device needs to be
closely fit to the body of the user without looseness so as not to
deviate from the fitting position even if the user moves.
[0078] With the present embodiment, the skin containing a fork
structure of the subcutaneous blood vessel is used as the skin
which is to be authenticated. The direction of the aforementioned
principal axis can be easily obtained using the fork structure. For
example, an arrangement may be made wherein the positional relation
between the direction of the principal axis and the fork structure
is determined and stored beforehand at the time of user
registration, thereby enabling adjustment of the principal axis at
the time of user authentication based upon the position and the
direction of the blood-vessel fork structure in a simple
manner.
[0079] On the other hand, an arrangement may be made wherein the
deep-layer structure of the skin is detected using interference of
the light, thereby solving the aforementioned problems, as well.
That is to say, the object of the present invention is not to
provide measurement of the magnitude of the birefringence, but it
is an object thereof to provide a detecting method for detecting
the unique properties of the user by measuring the internal
structure of the skin through birefringence of the light or
scattering thereof. With the present arrangement, the system causes
interference between the incident light and the scattered light
from the skin without any polarizer, and obtains the change in the
frequency therebetween in the form of beat signals by detecting the
interference of the light, using the fact that upon casting the
light onto the skin, the frequency of the light changes due to
back-scattering of the light or birefringence thereof occurring in
the internal structure of the skin such as the dermal layer or the
like.
[0080] FIG. 5 shows a configuration example of such a detecting
device. The detecting device has the same configuration as with the
detecting device shown in FIG. 2 wherein an illumination optical
system formed of an illumination light source 41 and an optical
lens 42, and an imaging optical system formed of an imaging device
43 such as a CCD or the like and an imaging lens 44, are disposed
orthogonal one to another through a half mirror 45. Note that with
the present arrangement, neither of the illumination optical system
and the imaging optical system include a polarizing plate. Instead
of the polarizing plates, the present detecting device includes a
reference mirror 46 for introducing a part of the illumination
light cast from the light source 41 of the illumination optical
system to the imaging device 43 of the imaging optical system.
[0081] A part of the light emitted from the light source 41 such as
a white LED or the like is cast on the surface of the skin through
the half mirror 45. Upon casting the aforementioned part of the
illumination light onto the skin, various kinds of scattering of
the light and birefringence thereof occur in the internal structure
of the skin, and the scattered light returns to the half mirror 45.
The system causes a beat phenomenon (interference) between the
returning light and the light which is reflected from the half
mirror 45 onto the reference mirror 46, and is reflected by the
reference mirror 46, at the same time of illumination, whereby an
interference pattern is formed on the imaging device 43.
[0082] Furthermore, an arrangement may be made wherein the
aforementioned beat is detected for each region in a detecting
range for the skin, thereby obtaining a continuous pattern of the
internal structure beneath the epidermis based upon the beat
pattern thus obtained. Specific arrangement examples for obtaining
the aforementioned continues pattern include: an arrangement
wherein multiple beat detecting devices are arrayed as shown in
FIG. 6; and an arrangement wherein the illumination unit includes a
moving mirror for casting the light onto each region of the skin as
shown in FIG. 7. The former arrangement has a configuration wherein
the multiple beat detecting devices 50 are arrayed in the shape of
a so-called "array", each of which comprise the illumination
optical system formed of the aforementioned illumination light
source 41 and the optical lens 42, and the imaging optical system
formed of the imaging device 43 such as a CCD or the like and the
optical lens 44, disposed orthogonal one to another through the
half mirror 45, thereby obtaining a continues pattern of the
internal structure beneath the epidermis based upon the signals
detected with each beat detecting device 50.
[0083] On the other hand, with the latter arrangement, illumination
of the light and detection of the returning light with each beat
detecting device 50, are performed using the aforementioned moving
mirror 51. The latter arrangement has a configuration wherein a
mirror control unit 52 controls the angle of the moving mirror 51
according to control information from an angle/interference-pattern
adjusting unit 53. The aforementioned angle/interference-pattern
adjusting unit 53 receives interference-pattern information from
the aforementioned beat detecting device 50. Then, the received
interference pattern is compared to an interference pattern which
has been stored and registered beforehand in a skin-interference
pattern storage unit 54, in a skin-interference pattern
storage/comparison unit 55, thereby enabling biometric
authentication.
[0084] The aforementioned methods do not require a polarizer which
is indispensable for detection of the phase difference or the like,
thereby having the advantage of enabling authentication without
precise adjustment of the optical axis. This allows stable
authentication even if the direction of a wristwatch-type
authentication device or the like, fit by the user, changes due to
failure in being fit by the user, looseness at the time of being
fit by the user, or the like, for example.
[0085] In practical situations, there is the need to adjust the
authentication device so as to face the tissue which is to be
authenticated in a case wherein the authentication device is fit by
the user with some looseness, or the like. On the other hand, an
arrangement may be made wherein the interference pattern is
registered for a wide skin region including the target region.
However, such an arrangement requires pattern matching processing
for searching the aforementioned wide region for a matched pattern,
leading to a great processing load. Such a great load is
undesirable for a mobile authentication device from the perspective
of power consumption and so forth.
[0086] For example, let us consider a special case of the biometric
authentication using the skin pattern, such as fingerprints or the
like. In this case, the center of a whirl-shaped pattern, a
horseshoe-shaped pattern, or the like, can be easily detected, and
furthermore, the area of the surface of the finger having such a
structure is narrow, thereby facilitating search for the position
which is to be authenticated. However, other ordinary portions have
relatively large area as compared with the fingertip, and have fine
skin pattern having no geometric structure which facilitates search
for the position which is to be authenticated, unlike the
whirl-shaped pattern of the fingerprints, except for limited
special portions, leading to extreme difficulty in search for the
region which is to be authenticated.
[0087] In order to solve the aforementioned problem, an arrangement
may be made wherein the skin pattern is registered for a wide
region beforehand as described above, and the system determines
whether or not the pattern detected at the time of authentication
is included in the aforementioned registered pattern. However, such
an arrangement leads to registration for an excessively large area,
which is troublesome, and leads to a problem of excessive
processing load and excessive processing period of time of the
authentication device at the time of authentication. With an ideal
arrangement, the skin pattern is preferably registered for the
whole body. However, such an arrangement is not undesirable from
the practical perspective as described above. Furthermore, in this
case, it is difficult to determine the "wide region". In practical
situations, the authentication device may deviate from the region
at the time of authentication due to flexibility of the human body,
or difference in the position to which the authentication device is
fit for each authentication.
[0088] Description will be made below regarding an effective method
for searching for the target region of the skin which is to be
authenticated. With the present method, the near-infrared light is
employed as the incident light instead of white light, which has a
wavelength range which allows the light to pass through the tissue
with high transmissivity, and causes exceptional absorption of the
light by reduced hemoglobin contained in venous blood or the like.
The authentication device detects a vein pattern using the detected
back-scattered light from the subcutaneous tissue, and searches for
the target region which is to be authenticated based upon the vein
pattern thus obtained. With the present arrangement, the target
region which is to be authenticated is a region containing a
distinctive pattern or a vein fork structure. This allows stable
search for the same skin region which is to be authentication in a
sure manner, even if a wristwatch-type person authentication device
is fit by the user with some displacement or looseness on a contact
face between the authentication device and the skin of the
user.
[0089] FIG. 8 shows an example of a detecting device having a
function for searching for the target region which is to be
authenticated based upon the vein pattern. The detecting device
shown in FIG. 8 has the same configuration as in FIG. 7, except for
a configuration wherein a near-infrared light source is employed as
the light source 41 for the beat detecting device 50, and a
subcutaneous vein position detecting unit 61, a subcutaneous vein
position comparison unit 62, and a vein data storage unit 63 for
storing vein data, are further included. Such a configuration
allows acquisition of an image of blood capillaries of a
subcutaneous vein 60 extending along the dermal layer, which is a
vein positioned at the shallowest portion of the skin.
[0090] The tissue exhibits marked low absorbance for the infrared
light in a wavelength range of 700 to 1200 nm, i.e., the tissue has
properties which allow the light to readily pass therethrough, and
accordingly, the wavelength range is referred to as "the window of
spectroscopic analysis". Note that while the epidermal tissue has
the properties which cause reflection and scattering of visible
light and ultraviolet light, nearly approximately 80% of the light
in the aforementioned wavelength range passes through the tissue.
On the other hand, of the near-infrared light in such a wavelength
range having such properties, the near-infrared light at a
particular wavelength is selectively absorbed by hemoglobin
contained in blood. Specifically, as shown in FIG. 9, the oxidized
hemoglobin (HbO.sub.2) exhibits the same absorbance as with the
reduced hemoglobin (Hb) at a wavelength of 805 nm. On the other
hand, the reduced hemoglobin (Hb) exhibits higher absorbance than
with the oxidized hemoglobin (HbO.sub.2) at a wavelength of 660 nm,
and the oxidized hemoglobin (HbO.sub.2) exhibits higher absorbance
than with the reduced hemoglobin (Hb) at a wavelength of 940 nm.
Furthermore, the hemoglobin has different spectroscopic properties
from those of water in the tissue, as shown in FIG. 10.
[0091] Accordingly, a blood-vessel image can be obtained by
detecting difference between hemoglobin and water within the tissue
using the aforementioned properties. Furthermore, difference
between an artery and a vein can be detected using difference in
absorbance therebetween at a suitably-selected wavelength. In order
to detect a vein pattern, an arrangement may be made wherein the
light source includes illumination means for illuminating
near-infrared light with a wavelength of 805 nm, and the
near-infrared light is cast onto the tissue through a polarizing
plate, for example. The incident light causes three kinds of
phenomena of reflection of the light, scattering thereof, and
birefringence thereof, and the returning light due to the
aforementioned kinds of phenomena is detected. In this case, the
reflected light from the surface of the skin deteriorates the
quality of the image of the internal structure beneath the skin
surface. Accordingly, with the present arrangement, an image of the
internal structure is taken with a CCD camera or the like through
the polarizing plate 26 disposed with the polarizing plane
orthogonal to that of the polarizing plate 23. This allows image
taking using only depolarized light such as scattered light and
light split due to birefringence while filtering the reflected
light with the same polarizing plane as with the incident light,
which has been reflected by the horny layer, the lucid layer, the
granular layer, and so forth, forming the epidermal tissue.
[0092] While description has been made regarding the detecting
devices shown in FIG. 2 and FIG. 3, wherein the dermal layer is
detected by eliminating the returning light other than the
scattered light from the tissue which is to be detected, with the
present arrangement, the incident light with a suitably-selected
wavelength is selectively absorbed in blood capillaries within the
dermal layer since the materials in blood vessels within skin
tissue other than hemoglobin exhibit low absorbance, i.e., have
high transmissivity at the wavelength, unlike a case of using the
white light source, thereby obtaining a clear image of a
blood-capillary pattern within the dermal layer with
back-scattering of the light at a deeper portion as a
background.
[0093] The pattern formed of blood flow in the blood capillaries is
unique to individual tissue. Furthermore, in the event that the
tissue is cut off from the body of the user, the aforementioned
pattern is immediately lost due to contraction of blood vessels,
retention of blood, lost of blood, and so forth. Furthermore, an
arrangement may be made wherein the system detects change in
absorbance corresponding to the heart beat using the absorbance of
oxidized hemoglobin at a wavelength of 940 nm, thereby enabling
living-tissue discrimination, as well as acquisition of an image of
the pattern of the subcutaneous blood capillaries. Furthermore, the
present arrangement may include an additional method wherein
determination is made whether the tissue belongs to normal live
tissue or dead tissue cut off from the user by detecting reduction
or loss of the absorbance of oxidized hemoglobin at a wavelength of
940 nm due to extreme reduction of oxygen concentration within the
tissue due to failure in pulmonary circulation, using the fact that
different types of hemoglobin exhibit different absorbance, e.g.,
the fact that the deoxidized hemoglobin exhibits higher absorbance
than with the oxidized hemoglobin at a wavelength of 660 nm, the
fact that the oxidized hemoglobin exhibits higher absorbance than
with the deoxidized hemoglobin at a wavelength of 940 nm, and so
forth.
[0094] The aforementioned methods integrate the biometric
authentication and the living-tissue discrimination. That is to
say, the system can discriminate and reject the tissue cut off from
the body of the user by detecting absence of blood flow even if the
tissue is alive by soaking in a physiological salt solution. In
this case, the tissue which is to be authenticated needs to exhibit
normal pulmonary circulation, normal heart beat, normal blood flow,
and normal hemoglobin ratio in blood. Accordingly, if other persons
cut off the arm of the user with a surgical method for "spoofing",
there is the need to connect the blood vessels of the arm to a
heart-lung machine, and to precisely reproduce the heat-beat wave.
Accordingly, it would be difficult to make "spoofing" in the
present situation wherein mobile heart-lung machines are
unavailable. Even if mobile heart-lung machines become available in
the future, such "spoofing" would require advanced surgical
techniques and surgical equipment for performing: cutting off of
the arm from the body; connection of the blood vessels of the arm
to a heart-lung machine; treatment for fine blood vessels and
nerves; prevention of change in the tissue due to vital reaction
caused due to cutting off of the arm; stabilization of the tissue
after resumption of blood flow; and so forth, which is far from
being realistic. On the other hand, it is even more difficult to
create a forgery of the tissue having precisely the same
three-dimensional structure of fine blood capillaries which causes
the same scattering of the light, instead of the tissue cut of from
the body of the user.
[0095] Next, description will be made regarding a detecting method
for detecting a pattern beneath the epidermis using the
differential interference method. The differential interference
method is one of observation methods using a microscope, wherein
the phase difference between the illumination light and the
returning light, which is dependent upon the thickness of the
sample and the difference in the refractive indexes, is converted
into contrast or contrast in color, thereby enabling observation
which provides impression of solidity. In general, it is difficult
to detect the dermal layer through a bright field optical system or
visual observation. The present arrangement has been made using the
fact that a differential interference optical system allows the
user to observe even cell nuclei wherein observation is difficult
using an ordinary microscope without staining. Note that while the
aforementioned differential interference optical system allows
detection of the dermal layer in a case wherein the dermal layer
appears as a top layer, it is difficult to detect the dermal layer
in normal situations. That is to say, in normal situation wherein
the dermal layer is covered with the epidermal layer, while the
surface of the epidermal layer can be observed with such a method,
detection of the epidermal layer is difficult due to reflection of
light, scattering thereof, and shielding thereof, without some
particular method.
[0096] While a white light source is employed for an ordinary
differential interference optical system, with the present
invention, a near-infrared light source and a near-infrared CCD are
employed as well as a differential interference optical system,
using the fact that the epidermal layer exhibits high
transmissivity in a wavelength length of red light to near-infrared
light. This enables detection of the roughness pattern of the
dermal layer beneath the epidermis in a noninvasive manner.
[0097] FIG. 11 shows a specific arrangement example. A detecting
device comprises an illumination optical system including a
near-infrared light source 71, a polarizing prism 72, and an
imaging optical system including an imaging device 73 such as a CCD
or the like, and a polarizing prism 74. The illumination optical
system and the imaging optical system are disposed with the optical
paths orthogonal one to another through a half mirror 75. The
illumination light is cast onto the skin from the illumination
optical system through reflection by the half mirror 75, and the
returning light (reflected light) passes through the half mirror
75, whereby the light reaches the imaging optical system. Note that
a Wollaston prism 76 and an objective lens 77 are disposed on the
optical path between the aforementioned half mirror 75 and the
skin.
[0098] The illumination light cast from the near-infrared light
source 71 is converted into light with the same polarizing plane by
the polarizing prism 72, and is reflected by the half mirror 75
toward the Wollaston prism 76. The illumination light cast onto the
Wollaston prism 76 is split into two beams (beam A and beam B) with
the polarizing planes orthogonal one to another, following which
the two beams are cast onto the object (tissue). Note that the
distance between the beam A and the beam B is equal to or less than
the resolution of the objective lens. Subsequently, the two beams
reflected by the object are recombined into a single beam by the
Wollaston prism 76. The single beam thus recombined passes through
the half mirror 75, and is converted into the light with the same
polarizing plane by the polarizing prism 74. With such a
configuration, reflection of the two beams A and B at a stepped
portion leads to optical-path difference therebetween, leading to
interference thereof at the time of the beam passing through the
polarizing prism 74. Note that in a case wherein the optical-path
difference matches half the wavelength of the beams A and B, the
light appears brightest due to interference. The interference
pattern can be observed with an ordinary differential interference
optical system employing a white light source, thereby enabling the
user to make visual observation of a transparent object with
impression of solidity. However, with the present arrangement using
near-infrared light, visual observation is difficult. Accordingly,
the present arrangement includes the imaging device 73 such as a
CCD for taking a near-infrared image.
[0099] [Method Using the Electric Properties]
[0100] Next, description will be made regarding another method
according to the present invention, wherein the roughness pattern
or the like of the deep-layer structure (e.g., the dermal tissue)
beneath the epidermis using the difference in the electric
properties, whereby biometric authentication is performed.
[0101] FIG. 12 shows an arrangement example of a detecting device
wherein the electric potential of the skin is detected using
electrostatic induction, and the depth at which the dermal tissue
is positioned is detected based upon the detected electric
potential, whereby the internal pattern beneath the epidermis is
obtained. With the present detecting device, the electrostatic
capacitance between the detecting electrode and the dermal layer is
detected using the fact that the epidermal layer relatively
exhibits a nature near being dielectric while the dermal layer
exhibits high electric conductivity.
[0102] In order to detect the electrostatic capacitance, the
detecting device shown in FIG. 12 includes multiple fine electrodes
121 two-dimensionally arrayed with micromachining technology so as
to form a detecting electrode plane for being in contact with the
surface of the skin. At the time of measurement, electrostatic
capacitance is formed between each fine electrode 121 on the
detecting electrode plane and the dermal layer. Then, the distance
distribution regarding the subcutaneous electric-conductive layer
underneath each fine electrode 121 is calculated based upon the
electrostatic capacitance which is dependent upon the distance
between the electrode and the electric-conductive layer, thereby
obtaining the subcutaneous tissue structure. That is to say, with
the present detecting device, electrostatic capacitance is formed
between: each of the fine electrodes 121 forming the detecting
electrode plane positioned parallel to the skin; and the skin, and
the terminal voltage of each electric capacitance is measured,
whereby the dermal-layer structure is obtained.
[0103] A cylindrical metal casing 22 stores the aforementioned fine
electrode 121 held by an insulating support member 123. The fine
electrode 121 is electrically connected to the casing 22 through a
resistor 24 having high electrical resistance. There is a gap
between the fine electrode 121 and the casing 122. At the time of
the casing 122 being in contact with the skin, the aforementioned
fine electrode 121 faces the skin with a predetermined gap
therebetween at an opening 122a of the casing 122.
[0104] Note that the present detecting device has a problem of
extremely unstable output signals since the surface of the skin
having the nature near a dielectric is readily affected by
electrostatic induction due to noise or the like from an external
AC power supply or a fluorescent lamp, and the surface structure of
the skin readily exhibits various conditions due to separation of
the horny layer, or the like. In order to solve the aforementioned
problem, a method is known for detecting fingerprints or the like,
wherein output signals are detected while applying high-frequency
electric signals to the human body. Such a method may be applied to
detection of the tissue structure wherein the epidermal pattern
corresponds to the dermal pattern, such as the fingerprints or the
like. However, the aforementioned method cannot be applied to
detection of the dermal pattern of other skin tissue wherein the
epidermal pattern does not correspond to the dermal pattern. The
reason is that in this case, the detecting device detects the
epidermal pattern. The epidermal pattern which does not correspond
to the dermal pattern does not exhibit sufficient stability, unlike
the fingerprints, and accordingly, the aforementioned method cannot
be employed for the biometric authentication using detection of
such tissue.
[0105] Accordingly, in order to solve the aforementioned problems,
the detecting device according to the present arrangement includes
a dielectric thin film 125 disposed at the opening of the metal
casing 122 as shown in FIG. 13, for example. At the time of
measurement, the dielectric thin film 125 is positioned between the
metal casing 122 and the skin with which the detecting device is
pressed into contact. At the same time, the dielectric thin film
125 is in contact with the metal casing 122 which stores the fine
electrode 121 and is connected to the ground, whereby electrostatic
capacitance is formed between casing 122 and the skin, as well.
Furthermore, such a configuration has the advantage of suppressing
adverse effects due to unstable conditions of the surface structure
of the horny tissue of the skin.
[0106] Furthermore, the detecting device includes an electret film
126 on the surface of each fine electrode 121 forming the detecting
electrode plane. The electret film 126 is formed of a
tetrafluoroethylene film or the like and semi-permanently holds
electric charges. With the present arrangement, the electrostatic
capacitance is formed between the fine electrode 121 and the dermal
tissue (electrically conductive tissue) with a bias voltage due to
the permanent polarization of the electret film 126 without
externally applying high frequency bias voltage, thereby enabling
detection of the distribution of difference in the electrostatic
capacitance between the fine electrodes 121, and thereby enabling
detection of the deep-layer structure of the skin such as the
dermal layer or the like covered with the epidermal tissue of the
skin in a noninvasive manner.
[0107] With the detecting device having a configuration shown in
FIG. 13, the fine electrode 121 having the electret film 126 is
disposed at the opening 122a of the aforementioned casing 122. At
the time of measurement, the detecting device is positioned such
that the opening 122a faces the tissue, whereby electrostatic
capacitance is formed between the fine electrode 121 and the skin
through the dielectric thin film 125. On the other hand, the casing
122 serves as a counter electrode as to the skin, and is grounded.
On the other hand, the electrode within the opening 122a serves as
a detection electrode. Accordingly, change in the electric
potential due to the epidermal tissue is common to both the
electrodes, and accordingly, the components thereof exhibit reverse
polarity between both the electrodes, leading to canceling out one
another.
[0108] On the other hand, change in the electric potential at a
deep portion of the skin causes electrostatic capacitance between
the dermal layer having electric conductivity and the fine
electrode 121 serving as a detection electrode, thereby enabling
detection of change in the electric potential at the deep portion
of the skin. On the other hand, no bias voltage due to an electret
film or the like is applied to the capacitance formed by the casing
122, and accordingly, change in the electric potential of the deep
layer of the skin is not detected by measuring the capacitance
formed by the casing 122 due to charges on the surface of the skin.
Thus, the present arrangement allows the detecting device to
precisely detect changes in the electric potential of the deep
layer of the skin alone, while canceling out adverse effects due to
electrostatic induction of the skin surface, charges thereon, or
the like.
[0109] With an arrangement wherein the change in the electric
potential is measured by extracting from change in the
electrostatic capacitance at each point on the tissue, different
amplitude is detected for each point due to variation in the
electrostatic capacitance dependent upon the thickness of the
epidermis. FIG. 14 shows an arrangement having a configuration
wherein the aforementioned detection electrodes (fine electrodes
121) are two-dimensionally arrayed in the form of a matrix, and
having a function wherein the conductive-layer structure beneath
the epidermis is obtained using the amplitude of the electric
potential which is changed synchronously with the entire human body
due to walking or the like.
[0110] As shown in FIG. 15, at the time of walking, change in the
electric charge occurs with a single phase, synchronously with the
entire human body due to grounding and electrical floating between
the foot and the floor. Description will be made below regarding
change in charge on the human body due to walking. That is to say,
the waveform which is formed on the skin due to walking and is
detected by an electrostatic-capacitanc- e sensor, is formed
according to two mechanisms as follows.
[0111] The first mechanism is essentially the same as with a
capacitor microphone. The capacitor microphone has a mechanism
wherein the gap between a diaphragm and an electret electrode
changes due to vibration of the diaphragm, the electrostatic
capacitance (C) of the gap changes due to the vibration, and the
signals due to change in the electrostatic capacitance are
subjected to impedance conversion through the gate of an FET,
whereby the vibration of the diaphragm is detected. The detecting
device according to the present invention has the same
configuration as with the capacitance microphone, except for the
configuration wherein a dielectric film is included instead of the
diaphragm, which is pressed into contact with the tissue of the
human body at the time of measurement, whereby charge coupling
occurs between the detecting device and the tissue of the human
body through the dielectric film. At the same time, capacitance
(electrostatic capacitance) is formed by the gap between the
electret electrode and the dielectric film, and furthermore, the
electrostatic capacitance of the human body and the electrostatic
capacitance of the gap are combined due to charge coupling. In this
state, change in the electrostatic capacitance due to interaction
between the human body and the external environment (e.g., grounded
object), e.g., walking or the like, is directly detected by the
detecting device in the form of waveform signals, like the
capacitance microphone.
[0112] Here, the electrostatic capacitance (C) of the human body
changes corresponding to the distance between the ground and the
position of the foot in the space. That is to say, in a case
wherein the foot is in contact with the ground, the capacitance of
the human body is great. On the other hand, in a case wherein the
foot is positioned away from the ground, the electrostatic
capacitance of the human body is extremely small due to an air
layer having a low dielectric constant between the sole (of a shoe)
and the ground. On the other hand, the greater the contact area
between the foot and the ground, the grater the electrostatic
capacitance is. Note that the electrostatic capacitance C is
represented by the following Expression.
C=.epsilon..multidot.S/d[F]
[0113] (.epsilon. represents dielectric constant of a medium with
which the gap between the electrodes is filled, S represents the
area of the electrode, and d represents the distance between the
electrodes)
[0114] As can be understood from the above Expression, the greater
the contact area between the foot and the ground is, i.e., the
greater the area of the electrode (S) is, the greater the
electrostatic capacitance is.
[0115] The second mechanism is that the electrode itself makes an
action serving as a charge sensor. That is to say, the electrode
stored in the metal casing of the detecting device, which faces the
tissue through the dielectric film, detects change in the electric
potential induced on the dielectric film due to charge of the human
body in the form of a waveform.
[0116] It is assumed that the waveform detected on the human body
is formed according to the two mechanisms as described above, i.e.,
it is assumed that the waveform is essentially formed not due to
the electric potential, but due to charge. That is to say, it is
assumed that the phenomenon represented by the following Expression
occurs. Note that the assumption has been confirmed by reproducing
the observed waveform by simulation using the equivalent circuit
method.
Q (charge)=C (electrostatic capacitance).multidot.V (voltage of the
electrode)
[0117] While change in the aforementioned charge exhibits generally
the same waveform over the entire human body, the waveform exhibits
different amplitude corresponding to the fine structure of the skin
tissue, in particular, corresponding to the relation between the
epidermis and the dermal layer. The waveform due to change in
charge changes synchronously over the entire human body.
Accordingly, with the present arrangement, comparison is made for
the amplitude of the waveform detected by each of the fine
detecting electrodes arrayed in the form of a two-dimensional
matrix, thereby measuring the distance between the electrode and
the dermal layer for each electrode, and thereby obtaining the
structure beneath the epidermis.
[0118] As described above, with the present arrangement, change in
charge occurring due to walking or other motions is detected with
each fine electrode 121 without active charge generating means such
as an electrode for applying charges or the like, using the fact
that charge changes on the human body due to interaction between
the foot and the ground by motions wherein the foot is off the
ground and touches the ground at the time of walking or the like.
Then, the difference in the amplitude between the waveforms
occurring due to change in charge synchronously over the entire
human body due to motions of the user is converted into the
distance between the surface of the skin and the tissue beneath the
epidermis, thereby detecting the deep-layer structure beneath the
epidermis such as the dermal layer or the like underneath the
detecting electrode.
[0119] In general, it is assumed that conventional
electrostatic-capacitan- ce methods have been applied to a
stationary authentication device which is grounded. Accordingly, at
the time of a wearable authentication device employing such a
conventional method being fit by the user for performing
authentication of the user, in a case wherein the user walks on a
carpet in a low humidity environment in winter, both the detecting
electrode and the grounded portion may be greatly charged, leading
to difficulty in precise detection. The reason is that with the
wearable authentication device, the grounded portion is positioned
on the human body.
[0120] In order to solve the aforementioned problems, a method or
the like has been proposed, wherein additional transmission means
such as an electrode, a transducer, or the like, is provided for
being in contact with the human body in addition to the detecting
electrodes, a predetermined ultrasonic waves or high-frequency
signals are actively applied with the transmission means so as to
propagate on the human body, the signals thus propagating on the
human body are detected with fine electrodes on the skin, and
determination is made whether or not the face of each fine
electrode is in contact with the skin, thereby obtaining the
fingerprint pattern of the user. However, such a method leads to a
complicated configuration, as well as leading to a problem that the
tissue which is to be authenticated is restricted to a special
portion such as fingerprints, a part of the skin of the palm, and
so forth. For example, let us consider an authentication method
wherein the authentication is performed using the skin underneath a
ring including a built-in authentication device. In this case, the
pattern of the epidermal layer at such a portion, such as wrinkles
or the like, tends to be formed different from the pattern of the
dermal layer, in some cases, orthogonal thereto. That is to say,
with such a method, the epidermal pattern having poor stability is
detected, leading to problem of poor precision of
authentication.
[0121] On the other hand, with an arrangement according to the
present invention, the epidermal pattern is not detected, but the
structure of the tissue beneath the epidermis (e.g., the roughness
pattern of the dermal layer) is detected by measuring electrostatic
capacitance as described above, thereby solving all the
aforementioned problems.
[0122] That is to say, with the present invention, biometric
authentication is performed by detecting the structure of the
tissue beneath the epidermis, and accordingly, the "biometric
authentication"and the "living-tissue discrimination" are
integrated. Accordingly, the system can discriminate and reject the
tissue cut off from the body of the user by detecting absence of
blood flow even if the tissue is alive by soaking in a
physiological salt solution. Furthermore, the tissue which is to be
authenticated needs to exhibit normal pulmonary circulation, normal
heart beat, normal blood flow, and normal hemoglobin ratio in
blood. Accordingly, if other persons cut off the arm of the user
with a surgical method for "spoofing", there is the need to connect
the blood vessels of the arm to a heart-lung machine, and to
precisely reproduce the heat-beat wave. Accordingly, it is
difficult to make "spoofing" in the current situation wherein
mobile heart-lung machines are unavailable. If the mobile
heart-lung machine becomes available in the future, such "spoofing"
would require advanced surgical techniques and surgical equipment
for performing: cutting off of the arm from the body; connection of
the blood vessels of the arm to a heart-lung machine; treatment for
fine blood vessels and nerves; prevention of change in the tissue
due to vital reaction caused due to cutting off of the arm;
stabilization of the tissue after resumption of blood flow; and so
forth, which is far from practical. On the other hand, it is more
difficult to create a forgery of the tissue having precisely the
same three-dimensional structure of fine blood capillaries which
causes the same scattering of the light, instead of the tissue cut
of from the body of the user.
[0123] Furthermore, the present invention may be applied to an
wearable arrangement. For example, an arrangement may be made
wherein a wearable information device or a mobile information
device includes detecting means for detecting the pattern of
tissue, blood vessels, or the like, beneath the epidermis wherein
visual observation is difficult under natural light, on the face
thereof for being in contact with the skin of the user at the time
of the user holding or wearing the information device, the
skin-tissue pattern beneath the epidermis on the contact face
between the body of the user and the information device is detected
at the time of the user holding or wearing the information device,
the detected pattern is compared to the patterns which have been
registered in the information device or a server computer connected
to the information device via network, thereby enabling the system
to permit or restrict at least a part of the service provided from
the information device or the network system based upon the
detection results, i.e., thereby enabling so-called "access
control".
[0124] Let us consider that the present invention is applied to a
wearable authentication device such as wristwatch-type
authentication device, or the like, for example. In this case,
there is the need to strictly fix the position and the direction of
the authentication device at the time of being fit by the user.
Furthermore, the authentication device needs to be closely fit to
the body of the user without looseness so as not to be deviated
from the fitting position even if the user moves. Specifically, the
system needs to determine the portion of the skin which is to be
authenticated. On the other hand, an arrangement may be made
wherein the interference pattern is registered for a wide skin
region including the target region. However, such an arrangement
requires pattern matching processing for searching the
aforementioned wide region for a matched pattern, leading to a
great processing load. Such a great load is undesirable for a
mobile authentication device from the perspective of power
consumption and so forth.
[0125] For example, let us consider a special case of the biometric
authentication using the skin pattern, such as fingerprints or the
like. In this case, the center of a whirl-shaped pattern, a
horseshoe-shaped pattern, or the like, can be easily detected, and
furthermore, the area of the surface of the finger having such a
structure is narrow, thereby facilitating search for the position
which is to be authenticated. However, other ordinary portions have
relatively large area as compared with the fingertip, and have fine
skin pattern having no geometric structure which facilitates search
for the position which is to be authenticated, unlike the
whirl-shaped pattern of the fingerprints, except for limited
special portions, leading to extreme difficulty in search for the
region which is to be authenticated.
[0126] In order to solve the aforementioned problem, an arrangement
may be made wherein the skin pattern is registered for a wide
region beforehand as described above, and the system determines
whether or not the pattern detected at the time of authentication
is included in the aforementioned registered pattern. However, such
an arrangement leads to registration for an excessively large area,
which is troublesome, and leads to a problem of excessive
processing load and excessive processing period of time of the
authentication device at the time of authentication. With an ideal
arrangement, the skin pattern is preferably registered for the
whole body. However, such an arrangement is not undesirable from
the practical perspective as described above. Furthermore, in this
case, it is difficult to determine the "wide region". In practical
situations, the authentication device may deviate from the region
at the time of authentication due to flexibility of the human body,
or difference in the position to which the authentication device is
fit for each authentication.
[0127] In order to solve the aforementioned problems, the skin
containing a fork structure of the subcutaneous blood vessel is
preferably used as the skin which is to be authenticated. The
direction of the aforementioned principal axis can be easily
obtained using the fork structure. For example, an arrangement may
be made wherein the positional relation regarding the fork
structure is determined and stored beforehand at the time of user
registration, thereby enabling adjustment of the portion of the
skin which is to be authenticated at the time of user
authentication based upon the position of the blood-vessel fork
structure in a simple manner.
[0128] [Method Using Temperature Difference]
[0129] Next, description will be made regarding detection of the
tissue pattern and authentication using temperature difference. The
skin structure comprises the epidermal tissue which has no blood
vessels and is passive to the body temperature, and the dermal
tissue which has blood vessels and actively affects the temperature
through blood flow. This causes a relatively high temperature in
the dermal tissue as compared with the epidermal tissue, except for
special situations wherein heat is externally applied, such as
exposure of direct sunlight to the body surface. A detecting device
according to the present embodiment detects the structure of tissue
beneath the epidermis using the aforementioned mechanism.
[0130] For example, the detecting device according to the present
embodiment has a configuration wherein fine devices for detecting
temperature such as thermistor bolometers, thermopiles, or the
like, are two-dimensionally arrayed instead of the fine electrodes
described above, and temperature is measured at each point. In this
case, difference in temperature is detected between the fine
devices corresponding to the thickness of the epidermal layer or
the like underneath each fine device. The detecting device
according to the present embodiment detects the roughness structure
of the dermal layer beneath the epidermis using the aforementioned
mechanism. In particular, thermopiles having a sensitive range
corresponding to infrared light emitted from the human body are
preferably employed as the fine devices for detecting temperature,
thereby enabling detection while preventing adverse effects due to
an external heat source such as sunlight or the like.
[0131] Furthermore, an arrangement may be made wherein
infrared-light detecting means, which is a temperature detecting
means, are disposed in the form of a matrix, and the detecting face
thus formed is positioned close to the surface of the skin, thereby
detecting the dermal layer pattern beneath the epidermal tissue,
using the fact that the living tissue emits infrared light with a
unique wavelength (e.g., wavelength of around 10 .mu.m) due to the
body temperature. With the present arrangement, difference in the
infrared magnitude is detected between the infrared detecting
sensor units forming the matrix-shaped infrared detecting means,
corresponding the thickness of the epidermis or the distance
between the sensor unit and the dermis serving as an infrared
source. The detecting device according to the present arrangement
detects the structure of the subcutaneous tissue, e.g., the
roughness pattern of the dermal layer, based upon the infrared
magnitude distribution.
[0132] Furthermore, an arrangement may be made wherein the
positions of the blood vessels are detected using the fact that a
portion containing the subcutaneous blood vessels exhibits a
relatively high temperature as compared with the other portions,
thereby enabling biometric authentication. Furthermore, an
arrangement may be made wherein the position or the direction of
the portion which is to be authenticated is determined based upon a
detected image of blood capillaries. Furthermore, living-tissue
discrimination may be performed based upon a detected image of
blood capillaries, as well.
INDUSTRIAL APPLICABILITY
[0133] As can be clearly understood from the above description, the
present invention enables ubiquitous biometric authentication using
not only a special portion such as the fingertip or the like, but
also any desired portion of the skin of the user. Furthermore, such
a portion which is to be authenticated cannot be observed from the
outside, unlike the fingerprints, and accordingly, it is difficult
for other persons to identify the portion of the user body which is
used for authentication. Thus, the present invention has the
advantage of high security of privacy, as well as the advantage of
high security against forgery.
[0134] Furthermore, the present invention provides an
authentication method using the portion having active blood flow or
active circulation of body fluid, such as the dermal tissue. The
properties of such a portion exhibits high sensitivity to change in
the blood flow or circulation of body fluid, thereby providing
essential and complete integration of biometric authentication
means and living-tissue discrimination. Thus, the present invention
provides biometric authentication while suppressing the risk of
surgical hazard, i.e., improving safety of the user.
[0135] Furthermore, the present invention may be applied to a
wearable detecting device and a wearable authentication device
having a detecting portion for being in contact with the skin of
the human body, thereby enabling biometric authentication using
daily actions of the user without any special user operations.
Furthermore, even in the event that detection error or
authentication error occurs, retry processing is performed without
any particular user operations, and is not troublesome.
* * * * *