U.S. patent application number 11/819270 was filed with the patent office on 2008-07-24 for biometric piezo scanner.
This patent application is currently assigned to Cross Match Technologies, Inc.. Invention is credited to Walter G. Scott.
Application Number | 20080175450 11/819270 |
Document ID | / |
Family ID | 22521801 |
Filed Date | 2008-07-24 |
United States Patent
Application |
20080175450 |
Kind Code |
A1 |
Scott; Walter G. |
July 24, 2008 |
Biometric piezo scanner
Abstract
A piezoelectric thin film sensor array is used to scan and
capture biometric data, for example, a fingerprint image. In one
embodiment, a multi-layer structure includes a PVDF layer in
between two conductor grids arranged orthogonally to one another.
Urethane can be added to one side where a finger is placed. A foam
substrate can be used as a support. In one feature, the PVDF, and
grids can be peeled off like a label for easy replacement.
Multiplexers are switched to scan the sensor. A single pixel or a
group of pixels can be detected and output to an image memory. The
presence of a fingerprint ridge is detected by virtue of a
ring-down oscillation that arises from reflection when an electric
field is applied to the piezoelectric thin film sensor array at a
pixel in contact with the fingerprint ridge. For example, such a
ring-down value associated with a fingerprint ridge can be detected
at about 150 ns. (or 5 cycles at 30 MHZ). Other reflections
indicative of additional biometrics (e.g. from tissue, blood, bone,
fingernail, etc.) can also be detected. A Doppler effect due to
reflections from circulating blood can also be detected. Such a
Doppler effect can provide further information about direction and
speed of blood circulation. An instantaneous pyroelectric effect
can also be detected to indicate a live finger presence.
Inventors: |
Scott; Walter G.; (North
Palm Beach, FL) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX P.L.L.C.
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
Cross Match Technologies,
Inc.
Palm Beach Gardens
FL
|
Family ID: |
22521801 |
Appl. No.: |
11/819270 |
Filed: |
June 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10049100 |
Feb 8, 2002 |
7236616 |
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PCT/US00/21658 |
Aug 9, 2000 |
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11819270 |
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60147497 |
Aug 9, 1999 |
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Current U.S.
Class: |
382/124 |
Current CPC
Class: |
A61B 8/06 20130101; G06K
9/00053 20130101; G06K 9/00899 20130101; G06K 9/0002 20130101 |
Class at
Publication: |
382/124 |
International
Class: |
G06K 9/00 20060101
G06K009/00 |
Claims
1. A biometric sensing device, comprising: a first conductor grid
including a first set of conductors; a second conductor grid
including a second set of conductors arranged orthogonally to said
first set of conductors such that pixels within an array of pixels
correspond to regions where ones of said first set of conductors
cross ones of said second set of conductors; and a piezoelectric
film disposed between said first and second conductor grids;
wherein biometric data can be produced by applying an electric
pulse to a pixel through said first and second conductor grids and
measuring a voltage across said first and second conductor grids at
said pixel subsequent to said application of said electric
pulse.
2-17. (canceled)
Description
[0001] This application claims the benefit of the filing date of
U.S. Provisional Application Ser. No. 60/147,497, filed 9 Aug.
1999, which is hereby incorporated by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to fingerprint
scanning and imaging. More specifically, this invention relates to
a piezoelectric film used within a fingerprint scanner.
[0004] 2. Related Art
[0005] Biometrics are a group of technologies that provide a high
level of security. Fingerprint capture and recognition is an
important biometric technology. Law enforcement, banking, voting,
and other industries increasingly rely upon fingerprints as a
biometric to recognize or verify identity. See, Biometrics
Explained, v. 2.0, G. Roethenbaugh, International Computer Society
Assn. Carlisle, Pa. 1998, pages 1-34 (incorporated herein by
reference in its entirety). A number of companies are currently
active in biometric finger technologies. See, a listing of
companies published by Biometric Technology Today (Btt.TM.), two
pages, 1999 (http://www.sjbresearch.com).
[0006] Optical fingerprint scanners are available that detect a
reflected optical image of a fingerprint. To capture a quality
image at a sufficiently high resolution, optical fingerprint
scanners require at minimum optical components (e.g., lenses), an
illumination source, and an imaging camera. Such components add to
the overall cost of a fingerprint scanner. Mechanical structures to
maintain alignment also increase manufacturing and maintenance
costs.
[0007] Solid-state silicon-based transducers are also available in
commercial fingerprint scanners sold by Seimens, Lucent, and Harris
Semiconductor. Such silicon transducers measure capacitance. This
requires the silicon transducers to be thin, reducing their
durability. To detect a rolled fingerprint, the sensing array of
the solid-state transducer needs to have an area of sufficient
size, for example one-inch by one-inch with a thickness of about 50
microns. A silicon array with such a large size increases the base
cost of a fingerprint scanner and leads to greater maintenance
costs. Durability and structural integrity are also more likely to
suffer in such a large silicon geometry.
[0008] What is needed is an inexpensive, durable fingerprint
scanner with low maintenance costs.
SUMMARY OF THE INVENTION
[0009] The present invention provides a piezoelectric film
biometric sensing device. A piezoelectric film sensor array is used
to detect biometric data, for example, a fingerprint image. In one
embodiment the piezo film sensor array is a multi-layer structure
that includes a piezo layer sandwiched by two conductor grids. The
conductor grids are oriented orthogonally to one another. A shield
layer can be added to one side where a finger is placed to provide
a protective coating. A foam substrate can be used as a
support.
[0010] In one example, the piezo layer comprises a polarized
fluoropolymer film, such as polyvinylidene fluoride (PVDF) film or
its copolymers. Conductor grids are silver ink electrodes printed
on opposite sides of the PVDF film. A shield layer is made of
urethane or other plastic. A foam substrate is made of Teflon.TM..
An adhesive holds the shield layer and foam substrate on opposite
sides of the printed PVDF film.
[0011] In one feature, the PVDF film, including the printed
electrodes, can be peeled off like a label for easy
replacement.
[0012] According to one embodiment, a fingerprint scanner uses a
piezo film sensor array to scan and capture an image of a
fingerprint. The fingerprint scanner further includes an
oscillator, gate counter, pulser, two multiplexers, controller,
detector, filter and image memory. An input pulse of one cycle of
the oscillator frequency (e.g., 30 MHZ) is applied by the pulser
through a multiplexer to a single pixel or group of pixels in the
piezo sensor array. A reflection from a ridge can be detected
within a number of cycles after the input pulse is applied by the
pulser. The presence of a fingerprint ridge is detected by virtue
of a ring-down oscillation. The ring-down oscillation arises from
reflections that occur when an electric field is applied to the
piezoelectric thin film sensor array at a pixel in contact with the
fingerprint ridge. A single pixel or a group of pixels is then
detected and output to an image memory. The controller switches the
multiplexers to scan the piezo film sensor array in coordination
with the cycles of pulses output from the pulser and the detected
pixel readings made by the detector.
[0013] Other reflections indicative of additional biometrics
related to the finger (e.g. from tissue, blood, bone, fingernail,
etc.) can also be detected. A Doppler effect due to reflections
from circulating blood can also be detected. Such a Doppler effect
can provide further information about direction and speed of blood
circulation.
[0014] According to another embodiment, an instantaneous
pyroelectric effect can also be detected by the piezoelectric film
sensor array to indicate a live finger presence. A signal
indicative of the live finger detection can then be used to
automatically initiate or "awaken" the fingerprint scanner to scan
and capture an image of the fingerprint using the same
piezoelectric scanner array.
[0015] Further features and advantages of the present invention, as
well as the structure and operation of various embodiments of the
present invention, are described in detail below with reference to
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings, which are incorporated herein and
form part of the specification, illustrate the present invention
and, together with the description, further serve to explain the
principles of the invention and to enable a person skilled in the
pertinent art to make and use the invention.
[0017] FIG. 1A is a cross-sectional view of a piezoelectric film
sensor array according to one embodiment of the present
invention;
[0018] FIG. 1B is an overhead diagram illustrating the conductor
grids of a piezoelectric film sensor array according to one
embodiment of the present invention;
[0019] FIG. 2 is a flowchart showing a routine for capturing a
fingerprint image in a piezoelectric film sensor array scan
according to one embodiment of the present invention;
[0020] FIG. 3 is a block diagram of a piezoelectric film
fingerprint scanner having a piezoelectric film sensor array
according to one embodiment of the present invention;
[0021] FIGS. 4A and 4B are plots of an example input pulse and
detected output signal with ring-down oscillation according to the
present invention;
[0022] FIG. 5 is a cross-sectional view of a piezoelectric film
sensor array having a fingerprint ridge (not to scale) in contact
with the sensor array; and
[0023] FIG. 6 is a plot of an example output signal with an
extended range that shows other reflections indicative of further
biometric information according to another embodiment of the
present invention.
[0024] The present invention is described with reference to the
accompanying drawings. In the drawings, like reference numbers
indicate identical or functionally similar elements. Additionally,
the left-most digit(s) of a reference number identifies the drawing
in which the reference number first appears.
DETAILED DESCRIPTION OF THE EMBODIMENTS
1. Overview and Terminology
[0025] According to the present invention, a piezoelectric film
biometric data sensing device is provided. The biometric sensing
device can be, for example, a fingerprint scanner. A piezoelectric
film sensor array is used to detect biometric data, for example, a
fingerprint image.
[0026] The terms "piezoelectric" and "piezo" are used
interchangeably herein to refer to the piezoelectric effect found
in certain materials, including but not limited to piezoelectric
polymer materials.
[0027] The term "conductor grid" as used herein is meant to refer
to a pattern of conductors and includes, for example, a plurality
of conductors arranged in parallel.
2. Piezoelectric Film Sensor Array
[0028] FIG. 1A is a cross-sectional view of a piezoelectric film
sensor array 100 according to one embodiment of the present
invention. Piezoelectric film sensor array 100 is a multi-layer
structure that includes a piezo film 120 sandwiched between two
conductor grids 115, 125. Piezo film in one example of the instant
invention is a polarized fluoropolymer film, such as polyvinylidene
fluoride (PVDF) or its copolymers.
[0029] Conductor grids 115 and 125 each include parallel
electrically conductive lines. Preferably, the lines of grid 115
are oriented orthogonally with respect to the lines of grid 125.
This relationship is shown in FIG. 1B. FIG. 1B is an overhead
diagram illustrating the conductor grids of a piezoelectric film
sensor array according to one embodiment of the present invention.
As seen in FIG. 1B, the two conductor grids are arranged
orthogonally to one another such that a first of the two grids may
be characterized as including conductive rows 1 to n, while a
second of the two grids may be characterized as including
conductive columns 1 to m. These conductive rows and columns are
connected to respective associated row and column multiplexers,
which will be discussed in greater detail below. Pixels within the
array are the regions associated with points where ones of the rows
cross ones of the columns. For example, the region where row n
crosses column m corresponds to a pixel (n,m). In one example,
conductor grids 115, 125 are silver ink electrodes printed on
opposite sides of the PVDF film 120.
[0030] Returning to FIG. 1A, shield layer 110 can be added as a
protective coating to a side where a finger is placed. Shield layer
110 can be made of urethane or another plastic capable of acting as
a protective coating. Shield layer 110 can be affixed to conductor
grid 115 and piezo film 120 with an adhesive 142. Materials
suitable for use as such an adhesive are known to those skilled in
the art and so the selection of an appropriate adhesive material is
within the ordinary level of skill in the relevant art given this
disclosure.
[0031] Foam substrate 130 can be used as a support within the piezo
sensor array 100. Foam substrate 130 can be made of Teflon.TM..
Other types of supportive material can be used in place of foam
substrate 130, as would be apparent to a person skilled in the
relevant art given this disclosure. Foam substrate 130 can be
affixed to the conductor grid 125 and the piezo film 120 with an
adhesive layer 144. Materials suitable for use as such an adhesive
are known to those skilled in the art and so the selection of an
appropriate adhesive material is within the level of skill in the
art given this disclosure.
[0032] The above description is illustrative and not intended to
limit the present invention. For example, piezo layer 120 can be
any material exhibiting a piezoelectric effect including, but not
limited to, piezoelectric polymers. Conductor grids 115, 125 can be
any electrically conductive material including, but not limited to,
metals. Likewise, other types of protective material can be used
for shield layer 110 as would be apparent to a person skilled in
the art given this description.
[0033] Piezoelectric polymer film sensors are further described in
Piezo Film Sensors: Technical Manual, available from Measurement
Specialties, Inc. Norristown, Pa., Apr. 2, 1999 REVB (incorporated
by reference herein in its entirety).
3. Peel-Off Application
[0034] As an additional feature of the present invention, the PVDF
film, including the printed electrodes, can be peeled off like a
label for easy replacement. As shown in FIG. 1, piezo sensor array
100 can be mounted by adhesive 146 onto wax-paper or other material
(not shown) for easy peel off. Materials suitable for use as such
an adhesive are known to those skilled in the art and so the
selection of an appropriate adhesive material is within the level
of skill in the art given this disclosure. This allows the piezo
sensor to be installed and/or replaced simply and easily at minimum
cost. Indeed, compared to optical and silicon technologies
maintenance of the piezo sensor array 100 is trivial.
4. Piezoelectric Film Fingerprint Scanner
[0035] The present invention further uses piezo film technology to
detect and capture biometric data. For example, a fingerprint image
can be detected.
[0036] The operation and structure of a piezoelectric film
fingerprint scanner according to one embodiment of the present
invention is described further with respect to FIGS. 2 and 3. FIG.
2 is a flowchart showing a routine 200 for capturing a fingerprint
image in a piezoelectric film sensor array scan according to one
embodiment of the present invention (steps 210-290). FIG. 3 is a
block diagram of a piezoelectric film fingerprint scanner 300 that
includes piezo film sensor array 100 according to one embodiment of
the present invention. Piezo film fingerprint scanner 300 includes
oscillator 310, gate counter 320, pulser 330, row multiplexer 340,
column multiplexer 350, controller 360, filter 362, detector 370,
memory controller 380 and image memory 385. For clarity and in the
interest of brevity, the steps of routine 200 are described in
further detail with respect to the structure of FIG. 3. However,
routine 200 is not so limited and other structure can be used as
would be apparent to a person skilled in the art given the
description herein.
[0037] In step 210, piezo film sensor array 100 is switched to
detect an initial pixel or a group of pixels. In the example of
FIG. 3, controller 360 switches row multiplexer 340 to a particular
row or rows and column multiplexer 350 to a particular column or
columns. In this manner, a particular associated pixel or group of
pixels is designated as the initial pixel or group of pixels. For
example, as shown in FIG. 1B, if the row multiplexer is switched to
row n and the column multiplexer is switched to column m, pixel (n,
m) is designated. In one example, piezo film sensor array is a
512.times.512 pixel array. Multiplexers 340 and 350 are each
addressed by nine digit binary numbers to select a particular grid
line at a designated address of the initial pixel or group of
pixels being detected.
[0038] In step 220, a pulse is applied in one 30 MHz cycle.
Oscillator 310 generates an oscillation signal at 30 MHz. This
oscillation signal is applied to gate counter 320. Gate counter 320
then initiates pulser 330 to send an input pulse to row multiplexer
340. Gate counter 320 also sends a signal to controller 360 and
detector 370 indicating a count of the number of cycles. Controller
360 is coupled to row multiplexer 340 and a column multiplexer 350.
Controller 360 sends signals to row multiplexer 340 and 350 that
cause an initial particular pixel or group of pixels to be selected
by the multiplexers 340, 350. Row multiplexer 340 forwards the
input pulse to the initial pixel or group of pixels. Due to the
piezoelectric characteristic of the piezo film, the pulse causes an
oscillation at the pixel or pixels where the pulse is applied.
[0039] In step 230, piezo fingerprint scanner 300 waits a number of
cycles before detecting a signal at the pixel. For example, in
response to the signal sent from gate counter 320, detector 370
waits a number of cycles after the pulse is applied to the pixel
(or group of pixels). Detector 370 is coupled to column multiplexer
350 and a filter circuit 362. In step 240, when the wait is
complete the voltage at the initial pixel or group of pixels
selected by column multiplexer 350 is evaluated at detector
370.
[0040] For example, one 30 MHz cycle corresponds to approximately
33 nanoseconds. The wait can be approximately 5 cycles or 150
nanoseconds. Other wait durations (e.g. a greater or smaller number
of periods) can be used depending upon the oscillator frequency
and/or other design considerations that would be apparent to a
person skilled in the relevant art given this disclosure. This wait
allows the ring down oscillation due to the presence of a
fingerprint ridge to occur in response to the applied electrical
pulse at the pixel.
[0041] In step 240, a filtered voltage is evaluated by detector 370
and a gray scale or a binary pixel value is output representative
of the detected voltage (step 250). Filter circuit 362 is a
band-pass filter that filters the output voltage to detect an
output voltage signal in a passband centered about a frequency of
approximately 30 MHz. The gray scale or binary pixel value is
output to memory controller 380 for storage in an image memory 385.
In one example, the output gray scale or binary pixel value is
stored in an address in image memory 385 that corresponds to the
detected pixel.
[0042] In step 260, a check is made to determine if the scan is
complete. In other words, a check is made to determine whether each
pixel in the 512.times.512 sensor array 100 has been scanned and a
corresponding output value has been stored and accumulated in image
memory 385. If the scan is complete, then the routine ends (step
290). A signal or other indication can then be generated and output
from scanner 300 to indicate that a fingerprint image has been
successfully captured. If the scan is not complete, then the piezo
film sensor array 100 is switched to detect the next pixel or next
group of pixels (step 270). Control then returns to perform steps
220 through 250 at the next pixel or next group of pixels.
Multiple Pixel Hits
[0043] As described above in steps 210 and 270, piezo film sensor
array 100 can be switched by multiplexers 340 and 350 to detect
voltage values at a single pixel or a group of pixels. In general,
any pattern for scanning pixels can be used. For example, a raster
scan of pixels can be performed. Pixels can be scanned row by row
or column by column.
[0044] In one preferred example, when multiple groups of pixels are
read out at a given instant, each pixel in a group of pixels are
separated by a predetermined distance. In this way, interfering
effects from the ring down oscillation in neighboring pixels are
minimized or avoided. In one example, pixels detected in a given
cycle are separated by a minimum distance of at least 8 pixels. In
this way any ring down oscillations between neighboring pixels are
attenuated significantly.
Other Implementations
[0045] Piezoelectric fingerprint scanner 300 as described above
with respect to FIG. 3 is illustrative and not necessarily intended
to limit the present invention. As it would be apparent to a person
skilled in the art other implementations are possible given this
description. For example, filter circuit 362 can be tuned as
desired to remove noise and other oscillations. Filter circuit 362
can be a LC circuit or other type of filter circuit. Multiplexers
340 and 350 can be any type of multiplexer. For example, a single 1
to N multiplexer or multiple stages of multiplexers can be used.
Oscillator 310 can be any type of oscillator, including but not
limited to, a simple LC oscillator, variable-frequency oscillator,
tunable oscillator, or crystal oscillator. In one preferred
example, the oscillator is a radio-frequency 30 MHz oscillator.
Other oscillation frequencies could be used as would be apparent to
one skilled in the relevant art given this disclosure. Detector 370
can include an analog-to-digital converter (ADC) for output to a
processor (e.g. a CPU) to support additional processing and
control.
[0046] In general, control for carrying out routine 200 can be
implemented in software, firmware, hardware, or any combination
thereof. Such implementation would be apparent to a person skilled
in the relevant art given this disclosure.
Fingerprint Ridge Detection
[0047] FIGS. 4A, 4B and 5 illustrate how fingerprint scanner 300
uses ring-down oscillation in piezo film sensor array 100 to detect
a fingerprint ridge at a pixel C according to the present
invention. Multiplexers 340 and 350 are switched to the address of
pixel C (step 210 or 270). An input pulse in one 30 MHZ cycle is
applied by pulser 330 (step 220). As shown in FIG. 4A, the voltage
of the pulse (and consequently the electric field applied to pixel
C) varies sinusoidally. The varying electric field causes the piezo
layer 120 to likewise stress and unstress in an oscillating
fashion. The stress on the piezo layer 120 creates wave energy.
Such wave energy is reflected on the substrate side of piezo sensor
array 100 at the interface with air. The wave energy is likewise
reflected at the shield layer boundary when air is present.
However, when a fingerprint ridge is present at pixel C, as shown
in FIG. 5, creating a non-reflecting or transmissive boundary for
the wave energy is created. This causes a ring-down oscillation to
occur. This ring-down oscillation dampens over time due to inherent
friction in the piezo film sensor array 100.
[0048] FIG. 4B shows a plot of an example detected output signal at
pixel C with ring-down oscillation according to the present
invention. The plots of FIGS. 4A and 4B are illustrative sketches
and are not drawn to scale to represent actual signal outputs. As
shown in FIG. 4B, after a wait of approximately five 30 MHZ cycles
(or about 150 ns), a detector signal output can be filtered and
detected to indicate the presence of a fingerprint ridge at pixel
C. If the fingerprint ridge were not in contact at pixel C,
ring-down oscillation would not occur. The filtered detector signal
output would equal zero or at least be below a minimum voltage.
Extended Range and Other Biometric Information
[0049] Other reflections indicative of additional biometrics
related to the finger (e.g. from tissue, blood, bone, fingernail,
etc.) can also be detected. A Doppler effect due to reflections
from circulating blood can also be detected. Such a Doppler effect
can provide further information about direction and speed of blood
circulation. FIG. 6 is a plot of an example output signal with an
extended range that shows other reflections indicative of further
biometric information according to another embodiment of the
present invention.
Live Finger Presence Detection Based on Pyroelectric Effect
[0050] According to another embodiment, an instantaneous
pyroelectric effect can also be detected by the piezoelectric film
sensor array to indicate a live finger presence. A signal
indicative of the live finger detection can then be used to
automatically initiate or "awaken" the fingerprint scanner to scan
and capture an image of the fingerprint using the same
piezoelectric scanner array.
CONCLUSION
[0051] While various embodiments of the present invention have been
described above, it should be understood that they have been
presented by way of example only, and not limitation. It will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention as defined in the appended claims. Thus,
the breadth and scope of the present invention should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the following claims and
their equivalents.
* * * * *
References