U.S. patent application number 11/409936 was filed with the patent office on 2006-11-09 for method and apparatus for measuring temperature.
This patent application is currently assigned to Glucon, Inc.. Invention is credited to Gabriel Bitton, Allan C. Entis, Benny Pesach.
Application Number | 20060251146 11/409936 |
Document ID | / |
Family ID | 11075535 |
Filed Date | 2006-11-09 |
United States Patent
Application |
20060251146 |
Kind Code |
A1 |
Pesach; Benny ; et
al. |
November 9, 2006 |
Method and apparatus for measuring temperature
Abstract
A method for determining concentration of at least one component
of the material, the method comprising: measuring at least one of
the real and imaginary parts of the permittivity of the material at
each of a first plurality of frequencies for which substantially
only a second plurality of known components of the material
contributes to the dielectric permittivity of the material, wherein
for each of the known components the permittivity as a function of
temperature is known and the first plurality is greater than the
second plurality; determining the concentration of at least one of
the known components responsive to a solution of a set of
simultaneous equations determined by the first plurality of
measurements and the dependence of the permittivities of the known
components on temperature.
Inventors: |
Pesach; Benny;
(Rosh-Ha'ayin, IL) ; Bitton; Gabriel; (Jerusalem,
IL) ; Entis; Allan C.; (Tel-Aviv, IL) |
Correspondence
Address: |
WOLF, BLOCK, SCHORR & SOLIS-COHEN LLP
250 PARK AVENUE
NEW YORK
NY
10177
US
|
Assignee: |
Glucon, Inc.
Boulder
CO
|
Family ID: |
11075535 |
Appl. No.: |
11/409936 |
Filed: |
April 24, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10481215 |
Dec 17, 2003 |
7056011 |
|
|
11409936 |
Apr 24, 2006 |
|
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|
Current U.S.
Class: |
374/142 ; 374/45;
374/E13.002; 374/E7.038 |
Current CPC
Class: |
G01K 7/343 20130101;
G01K 13/20 20210101 |
Class at
Publication: |
374/142 ;
374/045 |
International
Class: |
G01K 1/14 20060101
G01K001/14; G01N 25/00 20060101 G01N025/00; G01K 13/00 20060101
G01K013/00; G01K 1/08 20060101 G01K001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2001 |
IL |
143904 |
Claims
1. A method for determining temperature of a material comprising:
measuring at least one of the real and imaginary parts of the
permittivity of the material at each of at least one frequency for
which substantially only a plurality of known components of the
material contributes to the dielectric permittivity of the
material, wherein for each of the known components the permittivity
as a function of temperature is known and concentration of the
component relative to the others of the plurality of known
components is known; and using at least one of the determined real
and imaginary parts of the permittivity at each of the at least one
frequency and the dependence of the permittivities of the known
components on temperature to determine temperature of the
material.
2. A method for determining an amount of radiation absorbed by a
material comprising: illuminating the material with the radiation
between a first time and a second time; measuring at least one of
the real and imaginary parts of the permittivity of the material at
first and second temperatures at each of at least one frequency for
which substantially only at least one known component of the
material contributes to the dielectric permittivity of the
material, wherein for each of the at least one known component the
permittivity as a function of temperature is known and
concentration of the component relative to the others of the at
least one known component is known; using at least one of the
measured real and imaginary parts of the permittivity at the first
and second times at each of the at least one frequency, the
dependence of the permittivity of each of the at least one known
components on temperature and their relative concentrations, to
determine a difference of temperature between the first and second
times; and using the difference to determine an amount of energy
absorbed from the radiation by the material.
3. A method for determining concentration of at least one component
of the material, the method comprising: measuring at least one of
the real and imaginary parts of the permittivity of the material at
each of a first plurality of frequencies for which substantially
only a second plurality of known components of the material
contributes to the dielectric permittivity of the material, wherein
for each of the known components the permittivity as a function of
temperature is known and the first plurality is greater than the
second plurality; and determining the concentration of at least one
of the known components responsive to a solution of a set of
simultaneous equations determined by the first plurality of
measurements and the dependence of the permittivities of the known
components on temperature.
4. A method according to claim 3 and further comprising determining
the temperature of the material.
5. A method according to claim 3 wherein the material is living
tissue.
6. A method according to claim 3 wherein the component is
water.
7. A method for determining temperature and concentration of a
component of a material, the method comprising: measuring at least
one of the real and imaginary part of the permittivity of the
material at each of at least one frequency for which substantially
only a single known component of the material contributes to the
dielectric permittivity of the material and for which known
component the permittivity as a function of temperature is known;
using at least one of the determined real and imaginary part of the
permittivity at each of the at least one frequency and the
dependence of the permittivity of the known component on
temperature to determine temperature of the known component and
thereby of the material; and determining the concentration of the
component responsive to the determined temperature and dependence
of the permittivity of the component on temperature.
8. A method according to claim 7 wherein using at least one of the
measured real and imaginary part of the permittivity to determine
temperature, comprises determining a value for a ratio between the
real and imaginary parts of the permittivity measured at a same
frequency of the at least one frequency and determining temperature
from the value.
9. A method according to claim 7 wherein the at least one frequency
comprises a plurality of frequencies.
10. A method according to claim 9 wherein using the measured real
and/or imaginary part of the permittivity to determine temperature
comprises determining a value for a ratio between the real or
imaginary part of the permittivity at a first frequency of the
plurality of frequencies and the real or imaginary part of the
permittivity at the second frequency of the plurality of
frequencies and determining temperature from the value.
11. A method according to claim 7 wherein the material is living
tissue.
12. A method according to claim 7 wherein the component is water.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation-in-part of U.S.
patent application Ser. No. 10/481,215 filed on Dec. 17, 2003,
which is a national phase of PCT/IL02/00482 filed on Jun. 19, 2002,
the disclosures of which are incorporated by reference.
FIELD OF THE INVENTION
[0002] The invention relates to methods and apparatus for
determining temperature and in particular to determining
temperature of a material from measurements of the complex
dielectric permittivity of the material.
BACKGROUND OF THE INVENTION
[0003] Temperature measurement is required by an enormous range of
activities and processes, and a large variety of devices are
available for measuring temperature for different applications,
temperature ranges and environmental conditions. Non-invasive
devices for measuring temperature of a material usually measure
temperature of the material at or near to a surface of the
material. Generally, measuring internal temperature of a material
involves accessing an internal region of the material invasively
and determining a temperature for the internal region. There is an
ongoing need for new and alternative methods and devices for
measuring temperature conveniently and accurately.
[0004] It is well known to use measurements of the complex
dielectric permittivity of a material to determine properties of
the material and various methods and devices are known for
measuring the dielectric permittivity of a material. For example,
it is known to measure the dielectric permittivity of a material to
determine its composition or its water content and to use
measurements of dielectric permittivity to monitor rate of
polymerization. PCT publication WO 99/58965, the disclosure of
which is incorporated herein by reference, describes an example of
using dielectric spectroscopy to evaluate properties of oil. The
publication describes measuring the dielectric permittivity of oil
by flowing the oil through a capacitor and measuring the
capacitance of the capacitor. U.S. Pat. No. 5,744,971, the
disclosure of which is incorporated herein by reference, describes
a probe for measuring the dielectric permittivity of a material by
reflecting electromagnetic waves from the material. The inventors
of the probe suggest that it can be used for depth profiling of
paintings or to determine how rapidly methanol applied to a region
of a painting to de-acidify paint in the region evaporates.
[0005] It is also well known that in general, the dielectric
permittivity of a material is dependent on the material's
temperature. To provide meaningful results, an assay or testing
process that measures the dielectric permittivity of a material to
determine a property of the material generally performs the
measurements at known and carefully controlled temperatures. For
example, in the processes described in WO 99/58965, to determine
properties of an oil, the dielectric permittivity of the oil is
measured as a function of temperature over a controlled range of
temperatures.
[0006] However, whereas, it is known to determine many different
properties of materials by measuring their dielectric
permittivities, and it is known that values of dielectric
permittivities depend on temperature, it appears not to be known to
determine temperature of materials by measuring their dielectric
permittivities. In addition, it has not appeared to be practical to
use measurements of the dielectric permittivity of a material to
determine the material's temperature.
[0007] The dielectric permittivity of a material is in general a
complicated function of the types and relative amounts of
components that make up the material and contaminants found
therein. As noted in WO 99/58965, for example, the ratio of the
imaginary part to the real part of the dielectric permittivity of
an oil can be a function of acid content and water content of the
oil. Therefore, since the exact composition of a material whose
temperature is to be measured is often not known, it is not obvious
how to relate a measurement of the material's dielectric
permittivity to the temperature of the material.
[0008] In addition, measuring the dielectric permittivity of a
material typically involves applying a changing, often high
frequency, electric field to the material. Not only is the
dielectric permittivity of a material in general a function of the
frequency of the applied field, but the applied field also loses
energy to the material and tends to heat the material. Since the
very act of measuring the dielectric permittivity of a material
tends to change the material's temperature, it does not appear to
be advantageous to attempt to measure temperature of a material by
measuring its dielectric permittivity.
SUMMARY OF THE INVENTION
[0009] An aspect of the present invention relates to providing
methods of measuring temperature of an object by determining a
(generally complex) dielectric permittivity of the object. The
terms "dielectric permittivity" or "permittivity" of a material as
used herein refer to the complex permittivity of a material
relative to the permittivity of free space, which is real and equal
to about 8.85.times.10.sup.-12 F/m.
[0010] An aspect of some embodiments of the present invention
relates to determining the dielectric permittivity of a single
known component of a material in order to determine the temperature
of the material. In accordance with various embodiments of the
present invention the dielectric permittivity of the single known
component is determined by measuring the dielectric permittivity of
the material for a frequency at which only the single component
contributes to the dielectric permittivity of the material.
[0011] As noted above, the dielectric permittivity of a material is
a function of frequency of an applied field used in measuring the
dielectric permittivity and in general, at any particular
frequency, a number of different components of the material
contribute to the dielectric permittivity. However for some
materials, a range of frequencies, hereinafter referred to as
"isolation frequencies", can be found, for which substantially only
one of the components, hereinafter an "indicator component",
contributes to the dielectric permittivity of the material.
Measurements of the dielectric component of the material at an
isolation frequency of the indicator component can therefore be
used to determine the dielectric permittivity of the indicator
component. Assuming that the dependence of the dielectric
permittivity of the indicator component on temperature is known,
the determined dielectric permittivity can be used to determine a
temperature of the material.
[0012] However, the dielectric permittivity of a material at an
isolation frequency is a function not only of the dielectric
permittivity of an indicator component associated with the
isolation frequency but also of the concentration of the indicator
component in the material. Since the concentration is generally
unknown, in accordance with an embodiment of the present invention,
a ratio between measurements of the dielectric permittivity of the
material is used to determine the material's temperature. In some
embodiments of the present invention, the ratio is a ratio between
real or imaginary parts of the dielectric permittivity at two
different isolation frequencies of an indicator component. In some
embodiments of the present invention the ratio is a ratio between
the real and imaginary part of the dielectric permittivity at a
same isolation frequency of an indicator component. The ratios are
independent of concentration of the indicator component and if
dependence of the dielectric permittivity of the indicator
component of the material on temperature is known, the dependence
of the ratios on temperature is known.
[0013] A suitable indicator component for many materials, in
accordance with an embodiment of the present invention, is water,
which is ubiquitously found in various amounts in many materials
and is a component of all living organisms. Water is a dipolar
molecule that interacts with electromagnetic fields and contributes
to the dielectric permittivity of a material in which it is found.
In addition, generally, a range of frequencies for an applied
electromagnetic field can be found for which substantially only
water contributes to the dielectric permittivity of a material in
which the water is found.
[0014] The dielectric relaxation time of a dipolar molecule in a
material is correlated with a time that it takes the molecule to
become aligned with a direction of an electric field applied to the
material. Let a "dielectric relaxation frequency" of a molecule be
the inverse of its dielectric relaxation time. For an applied field
having a frequency that is substantially greater than the
dielectric relaxation frequency of a molecule in a material, the
molecule does not "follow" changes in direction of the applied
field and therefore does not contribute substantially to the
dielectric permittivity of the material at the frequency.
[0015] Water, that is in a liquid state and not bound to another
molecule, because of its relatively small size and weight generally
has a dielectric relaxation frequency substantially greater than
larger and heavier molecules or relatively large structures of
matter, such as for example lymphocytes in blood. Therefore, at a
frequency close to the dielectric relaxation frequency of liquid
"unbound" water, generally referred to as "free water", free water
is generally substantially the only dipole molecule that
contributes to the dielectric permittivity of a material in which
free water is found. In accordance with an embodiment of the
present invention, water therefore is a convenient and
substantially "universal" indicator component for use in measuring
temperature of materials. Typically, the dielectric relaxation
frequency for free water is on the order of 20 GHz. Water that is
bound to heavier molecules, referred to as "bound water", or
"hydrate water" has a relaxation frequency that generally varies
from between 10.sup.8 Hz to about 10.sup.9 Hz. Hereinafter, the
term "water" refers to "free water".
[0016] In accordance with an embodiment of the present invention, a
temperature of a surface region of a material is measured by
measuring the dielectric permittivity of the material at the
surface region. Electromagnetic waves at at least one isolation
frequency of an indicator component of the material are directed so
that they are incident on the surface region. Amplitude and phase
of electromagnetic waves reflected by the surface region of the
material from the incident waves are measured. The measured
amplitudes and phases are used to determine the complex dielectric
permittivity of the material for each of the at least one isolation
frequency. The dielectric permittivity or permittivities are used
to determine the temperature of the material at and close to the
surface region.
[0017] In accordance with an embodiment of the present invention an
internal temperature of a material is determined by measuring the
imaginary part of the dielectric permittivity of the material.
Electromagnetic waves at at least one an isolation frequency of an
indicator component of the material are directed so that they are
incident on the material. An amount of energy from each incident
wave that passes through the material is measured. The measured
amount of transmitted energy at a given isolation frequency is a
function of and is used to determine the average imaginary part of
the dielectric permittivity of the material at the isolation
frequency along the path length of the transmitted energy through
the material. The determined imaginary part of the dielectric
permittivity for each of the at least one isolation frequency is
used to determine an average internal temperature of the material
along the path length of the transmitted energy.
[0018] An aspect of some embodiments of the present invention
relates to limiting energy of an applied field used to measure the
dielectric permittivity of a material so that during measurement of
the dielectric permittivity, the field does not substantially
change the temperature of the material.
[0019] An aspect of some embodiments of the present invention
relates to correcting measurements of temperature of a material for
heating of the material by an electromagnetic field used in
determining the dielectric permittivity of the material and thereby
the temperature.
[0020] The determined imaginary part of the permittivity is used to
estimate energy deposited by the field in the material during
measurement of the permittivity. The amount of deposited energy,
density and specific heat of the material are used to estimate
heating of the material during the measurement and to correct a
temperature of the material determined from the permittivity.
[0021] There is therefore provided in accordance with an embodiment
of the present invention, a method for determining temperature of a
material comprising: measuring at least one of the real and
imaginary part of the permittivity of the material at each of at
least one frequency for which substantially only a single known
component of the material contributes to the dielectric
permittivity of the material, for which known component the
permittivity as a function of temperature is known; and using at
least one of the determined real and imaginary part of the
permittivity at each of the at least one frequency and the
dependence of the permittivity of the known component on
temperature to determine temperature of the known component and
thereby of the material.
[0022] Optionally using at least one of the measured real and
imaginary part of the permittivity to determine temperature,
comprises determining a value for a ratio between the real and
imaginary parts of the permittivity measured at a same frequency of
the at least one frequency and determining temperature from the
value.
[0023] Additionally or alternatively, the at least one frequency
optionally comprises first and second frequencies and using the
measured real and/or imaginary part of the permittivity to
determine temperature comprises determining a value for a ratio
between the real or imaginary part of the permittivity at the first
frequency and the real or imaginary part of the permittivity at the
second frequency and determining temperature from the value.
[0024] In some embodiments of the present invention, measuring the
real and/or imaginary part of the permittivity of the material at
each of the at least one frequency comprises measuring the
dielectric permittivity near a surface region of the material and
determining a temperature comprises determining a temperature of
the material at or in the neighborhood of the surface region.
[0025] Optionally, measuring the real and/or imaginary part of the
permittivity near the surface region comprises measuring
reflectance of the surface region for an electromagnetic wave
incident thereon and determining the real and/or imaginary part of
the permittivity in a region of the material at or in the
neighborhood of the surface region from the reflectance.
[0026] There is further provided in accordance with an embodiment
of the present invention, a method comprising measuring the
temperature of each of a plurality of surface regions of a material
in accordance with an embodiment of the present invention and using
the temperatures determined at the plurality of surface regions to
generate a thermal surface map of the material.
[0027] In some embodiments of the present invention, measuring the
real and/or imaginary part of the permittivity at each of the at
least one frequency comprises measuring the real and/or imaginary
part of the permittivity inside the material and determining a
temperature comprises determining an internal temperature of the
material.
[0028] Optionally, measuring the real and/or imaginary part of the
permittivity inside the material comprises measuring amounts of
energy reflected by the material and transmitted through the
material from energy of an electromagnetic wave incident on the
material and determining from the reflected and transmitted
energies an average imaginary part of the permittivity inside the
material.
[0029] Alternatively or additionally, measuring the real and/or
imaginary part of the permittivity inside the material optionally
comprises: directing an electromagnetic wave so that it is incident
on the material; measuring amplitude and phase of an
electromagnetic wave reflected by the material from the incident
wave; measuring amplitude and phase of an electromagnetic wave
resulting from the incident wave that is transmitted through the
material; and determining an average for the real and imaginary
parts of the permittivity inside the material from the measured
amplitudes and phases.
[0030] There is further provided in accordance with an embodiment
of the present invention, a method comprising determining the
internal temperature of a material at a plurality of internal
locations of the material in accordance with an embodiment of the
present invention, and using the temperatures determined at the
plurality of locations to generate a thermal map of an internal
region of the material.
[0031] In some embodiments of the present invention, the method
comprises limiting power in the incident electromagnetic wave so
that during a time that it takes to measure the real and/or
imaginary part of the dielectric permittivity, an amount of energy
absorbed by the material from the incident wave does not
substantially change the temperature of the material.
[0032] Optionally, the power is determined so that a rate of
temperature change is less than about 0.05 degrees Celsius per
second. Optionally, the power is determined so that a rate of
temperature change is less than about 0.02 degrees Celsius per
second.
[0033] In some embodiments of the present invention, determining
temperature of the material comprises estimating an amount by which
energy absorbed by the material from the incident electromagnetic
wave changes temperature of the material during measurement of the
real and/or imaginary part of the permittivity and using the
estimated change to determine the temperature.
[0034] In some embodiments of the present invention, the known
component of the material is a dipolar molecule that is not bonded
to another molecule. Optionally, the dipolar molecule is water.
[0035] Optionally, the at least one frequency is a frequency in a
range from about 10.sup.10 Hz to about 50.times.10.sup.10 Hz.
[0036] There is further provided, in accordance with an embodiment
of the present invention, a method for determining an amount of
radiation absorbed by a material comprising: illuminating the
material with the radiation between a first time and a second time;
measuring temperature of the material at the first and second times
according to the present invention; and using a difference between
the measured temperatures at the first and second times to
determine an amount of energy absorbed from the radiation by the
material.
[0037] Optionally, the radiation is electromagnetic radiation.
Optionally, the electromagnetic radiation is light. Optionally, the
light is IR light. Optionally, the radiation is acoustic
radiation.
[0038] There is further provided, in accordance with an embodiment
of the present invention, a method comprising determining an amount
of radiation absorbed by a material at each of a plurality of
regions of the material according to the present invention and
using the amounts of absorption at the plurality of regions to
provide a spatial map of the absorption of the radiation by the
material.
[0039] There is further provided, in accordance with an embodiment
of the present invention, a method for assaying a component of a
material comprising: determining an amount of radiation absorbed by
the material in accordance with the present invention; determining
an absorption coefficient of the component for the radiation from
the amount of absorbed energy; and determining a concentration of
the component in the material from the determined absorption
coefficient and a known absorption cross-section of the
component.
[0040] There is further provided, in accordance with an embodiment
of the present invention, a method of mapping concentration of a
component in a material comprising: assaying the component in
accordance with the present invention at a plurality of regions of
the material; and using the assays at the plurality of regions to
map concentration of the material as a function of position.
[0041] There is further provided, in accordance with an embodiment
of the present invention, a method for determining temperature of a
material comprising: measuring at least one of the real and
imaginary part of the permittivity of the material at each of at
least one frequency for which substantially only a plurality of
known components of the material contributes to the dielectric
permittivity of the material, wherein for each of the known
components the permittivity as a function of temperature is known
and concentration of the component relative to the others of the
plurality of known components is known; and using at least one of
the determined real and imaginary part of the permittivity at each
of the at least one frequency and the dependence of the
permittivities of the known components on temperature to determine
temperature of the material.
[0042] There is further provided, in accordance with an embodiment
of the present invention, a method for determining an amount of
radiation absorbed by a material comprising: illuminating the
material with the radiation between a first time and a second time;
measuring at least one of the real and imaginary part of the
permittivity of the material at first and second temperatures at
each of at least one frequency for which substantially only at
least one known component of the material contributes to the
dielectric permittivity of the material, wherein for each of the at
least one known component the permittivity as a function of
temperature is known and concentration of the component relative to
the others of the at least one known component is known; using at
least one of the measured real and imaginary part of the
permittivity at the first and second times at each of the at least
one frequency, the dependence of the permittivity of each of the at
least one known components on temperature and their relative
concentrations, to determine a difference of temperature between
the first and second times; and using the difference to determine
an amount of energy absorbed from the radiation by the
material.
[0043] In accordance with some embodiments of the present invention
the material is living tissue.
[0044] In accordance with some embodiments of the present invention
the living tissue is tissue in an ear.
[0045] There is further provided in accordance with an embodiment
of the invention, a method for determining concentration of at
least one component of the material, the method comprising:
measuring at least one of the real and imaginary parts of the
permittivity of the material at each of a first plurality of
frequencies for which substantially only a second plurality of
known components of the material contributes to the dielectric
permittivity of the material, wherein for each of the known
components the permittivity as a function of temperature is known
and the first plurality is greater than the second plurality;
determining the concentration of at least one of the known
components responsive to a solution of a set of simultaneous
equations determined by the first plurality of measurements and the
dependence of the permittivities of the known components on
temperature. Optionally, the method further comprises determining
the temperature of the material. Optionally, the material is living
tissue. Optionally, the component is water.
[0046] There is further provided in accordance with an embodiment
of the invention, a method for determining temperature and
concentration of a component of a material, the method comprising:
measuring at least one of the real and imaginary part of the
permittivity of the material at each of at least one frequency for
which substantially only a single known component of the material
contributes to the dielectric permittivity of the material and for
which known component the permittivity as a function of temperature
is known; using at least one of the determined real and imaginary
part of the permittivity at each of the at least one frequency and
the dependence of the permittivity of the known component on
temperature to determine temperature of the known component and
thereby of the material; and determining the concentration of the
component responsive to the determined temperature and dependence
of the permittivity of the component on temperature.
[0047] Optionally, using at least one of the measured real and
imaginary part of the permittivity to determine temperature,
comprises determining a value for a ratio between the real and
imaginary parts of the permittivity measured at a same frequency of
the at least one frequency and determining temperature from the
value.
[0048] Optionally the at least one frequency comprises a plurality
of frequencies. In some embodiments of the invention, using the
measured real and/or imaginary part of the permittivity to
determine temperature comprises determining a value for a ratio
between the real or imaginary part of the permittivity at a first
frequency of the plurality of frequencies and the real or imaginary
part of the permittivity at the second frequency of the plurality
of frequencies and determining temperature from the value.
[0049] In some embodiments of the invention the material is living
tissue. In some embodiments of the invention wherein the component
is water.
BRIEF DESCRIPTION OF FIGURES
[0050] Non-limiting examples of embodiments of the present
invention are described below with reference to figures attached
hereto. In the figures, identical structures, elements or parts
that appear in more than one figure are generally labeled with a
same numeral in all the figures in which they appear. Dimensions of
components and features shown in the figures are chosen for
convenience and clarity of presentation and are not necessarily
shown to scale. The figures are listed below.
[0051] FIG. 1 schematically shows dielectric relaxation frequencies
for different types of molecules and structures of matter;
[0052] FIGS. 2A and 2B are graphs of the real and imaginary parts
of the dielectric permittivity of water at three different
isolation frequencies;
[0053] FIG. 3A is a graph of a ratio between the real parts of the
dielectric permittivity of water at 20 GHz and 2.5 GHz as a
function of temperature, which is used to determine temperature of
a material, in accordance with an embodiment of the present
invention;
[0054] FIG. 3B is a graph of a ratio of the real to imaginary part
of the dielectric permittivity of water for a frequency of 20 GHz
as a function of temperature, which is used to determine
temperature of a material, in accordance with an embodiment of the
present invention;
[0055] FIG. 3C is a graph of a ratio of the real part of the
dielectric permittivity of water at 20 GHz to the imaginary part of
the dielectric permittivity at 10 GHz as a function of temperature,
which is used to determine temperature of a material, in accordance
with an embodiment of the present invention;
[0056] FIG. 4 schematically shows determining temperature of a
surface region of a material, in accordance with an embodiment of
the present invention; and
[0057] FIG. 5 schematically shows determining an internal
temperature of a material, in accordance with an embodiment of the
present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0058] FIG. 1 schematically shows dielectric relaxation frequencies
for types of molecules and structures commonly found in biological
systems. Dielectric relaxation frequency is shown along an axis 20.
Below and along axis 20 are witness bars 22, each labeled with a
molecule type or structure. Each witness bar 22 indicates a range
of dielectric relaxation frequencies that is characteristic of the
type of molecule or structure that labels the witness bar. A
structure or molecule contributes to the dielectric permittivity of
a material in which it is found at frequencies below its dielectric
relaxation frequency. For frequencies above its dielectric
relaxation frequency, the contribution of the structure or molecule
to the dielectric permittivity of the material decreases rapidly
and for frequencies substantially greater than its dielectric
relaxation frequency the contribution to the dielectric
permittivity is substantially zero.
[0059] From FIG. 1 is seen that water, in liquid form, has the
highest dielectric relaxation frequency among molecules and
structures commonly found in biological systems. Similarly, for
non-biological materials in which water is present, the water
generally has a dielectric relaxation frequency that is greater
than the dielectric relaxation frequencies of other components and
structures of the materials. Therefore, for many materials in which
water is present, for frequencies in the range of the dielectric
relaxation frequencies of water, the dielectric permittivities of
the materials are due primarily to the dielectric permittivity of
water. For these materials, water is a suitable indicator component
for measuring temperature of the materials, in accordance with an
embodiment of the present invention. Isolation frequencies for
water in the materials are frequencies that fall in the range of
dielectric relaxation frequencies of water.
[0060] The dielectric properties of water are well known and the
complex dielectric permittivity ".epsilon.*(.omega.,T)" of water as
a function of frequency ".omega." and temperature "T" is relatively
accurately approximated by
.epsilon.*(.omega.,T)=.epsilon.'(.omega.,T)+i.epsilon.''(.omega.,T)=.epsi-
lon..sub..infin.+(.epsilon..sub.S-.epsilon..sub..infin.)/(1+i.omega..tau.(-
T)), where i is the imaginary i. In the expression for
.epsilon.*(.omega.,T), .epsilon..sub.S is the "static" value of
.epsilon.*(.omega.,T) for .omega.=0, .epsilon..sub..infin. is the
value of .epsilon.*(.omega.,T) for .omega.=.infin. and dependence
of .epsilon.*(.omega.,T) on temperature T is through a relaxation
time .tau.(T). Various theoretical models for dependence of
.tau.(T) on temperature are known and values for .tau.(T) as a
function of temperature for pure water are tabulated. The inverse
of .tau. is the dielectric relaxation frequency of water at the
temperature T. FIGS. 2A and 2B are graphs of the real part
.epsilon.'(.omega.,T) and imaginary part .epsilon.''(.omega.,T)
respectively of the complex dielectric permittivity
.epsilon.*(.omega.,T) of water as a function of temperature for
"isolation" frequencies 2.5 GHz, 10 GHz and 20 GHz.
[0061] As noted above, at an isolation frequency of water, the
dielectric permittivity of a material containing water is not a
function only of the dielectric permittivity of the water, but is
also a function of the concentration of the water in the material.
Therefore, to determine temperature of the material from
measurement of its dielectric permittivity and known values of the
dielectric permittivity of water, in accordance with an embodiment
of the present invention, a function of .epsilon.*(.omega.,T) that
is independent of concentration is determined from the measured
dielectric permittivity of the material. Dependence of the function
on temperature is used to determine temperature of the
material.
[0062] Let .epsilon.*.sub.mat(.omega.,T) represent the complex
dielectric permittivity of the material and let the material have a
concentration "k" g/m.sup.3 of water. It is expected that in
general, at an isolation frequency for water,
.epsilon.*.sub.mat(.omega.,T) will be equal to
k.epsilon.*(.omega.,T). Therefore, ratios between measurements of
real and imaginary parts of .epsilon.*.sub.mat(.omega.,T) can be
used to determine suitable functions of .epsilon.*(.omega.,T) that
are independent of concentration and can be used to determine
temperature, in accordance with an embodiment of the present
invention.
[0063] For example, a ratio between the real and imaginary parts of
.epsilon.*.sub.mat(.omega.,T) at a same frequency determines a
ratio between the real and imaginary parts of .epsilon.*(.omega.,T)
at the frequency and can be used to determine temperature of the
material from known values of .epsilon.*(.omega.,T). Similarly, a
ratio between real and/or imaginary parts of
.epsilon..sub.mat(.omega.,T) at different frequencies determines a
ratio between corresponding real and/or imaginary parts of
.epsilon.*(.omega.,T) at the frequencies and can be used, in
accordance with an embodiment of the present invention, to
determine temperature of the material.
[0064] FIG. 3A is a graph of a ratio
"R20/R2.5"=Re[.epsilon.*(20,T)]/Re[.epsilon.*(2.5,T)] between the
real part, Re[.epsilon.*(20,T)], of .epsilon.*(.omega.,T) and the
real part, Re[.epsilon.*(2.5,T)], of .epsilon.*(.omega.,T) at 2.5
GHz as a function of temperature in a range of temperatures from
0-60.degree. C. From the graph it is seen that the ratio is a
single valued function of temperature and if the value of R20/R2.5
for a material is known, a temperature for the material can be
determined.
[0065] Presently available sensors for determining the real part of
the dielectric permittivity of a material can determine
.epsilon.'(.omega.,T) to an accuracy of about 0.1%. The ratio
R20/R2.5 can therefore be determined to about 0.14% and temperature
of the material to about 0.13.degree. C.
[0066] FIG. 3B is a graph of a ratio
"R20/I20"=Re[.epsilon.*(20,T)]/Im[.epsilon.*(20,T)] between the
real part, Re[.epsilon.*(20,T)], of .epsilon.*(.omega.,T) and the
imaginary part, Im[.epsilon.*(20,T)], of .epsilon.*(.omega.,T) at
20 GHz as a function of temperature in the range of temperatures
from 0-60.degree. C. FIG. 3C is a graph of "I20/I10" between the
imaginary part of .epsilon.*(.omega.,T) at 20 GHz and the imaginary
part of .epsilon.*(.omega.,T) at 10 GHz as a function of
temperature. From these graphs it is seen that values R20/I20 and
I20/I10 determined for a material can also be used to determine
temperature of the material, in accordance with an embodiment of
the present invention.
[0067] Whereas the imaginary part of the dielectric permittivity of
a material and/or the real parts of the permittivity are used in
accordance with embodiments of the present invention to determine
temperature of the material, it is noted that for the imaginary
part of the dielectric permittivity of a material, present day
methods for measuring dielectric permittivity provide accuracy of
measurement of only about 0.5%. As a result, accuracy of
temperature measurement using R20/I20 or I20/I10 is generally less
than accuracy of temperature measurement using R20/R2.5. For
example, using R20/I20 and assuming that Im[.epsilon.*(20,T)] is
measured to an accuracy of about 0.5% and Re[.epsilon.*(20,T)] to
an accuracy of about 0.1%, accuracy of temperature measurement for
temperatures near 30.degree. C. is about 0.1.degree. C. On the
other hand, by using the ratio R20/R2.5, temperatures near
30.degree. C. can be determined to an accuracy of about 0.4.degree.
C. It is noted that accuracy of temperature measurement can be
improved by determining temperature from suitable ratios between
real and/or imaginary parts of the dielectric permittivity at a
plurality of different frequencies.
[0068] In accordance with an embodiment of the invention, once a
temperature is determined for a material using for example a ratio,
or ratios, between real and/or imaginary parts of the dielectric
permittivity of a material as discussed above, a concentration of
the indicator component or components of the material are
determined. By way of example, assume that water is an only
indicator component of a material and measurements of the real
and/or imaginary parts of the permittivity of the material are
acquired at a suitable isolation frequency, or frequencies, to
determine temperature of the material as discussed above. Given the
temperature, and permittivity of water known as a function of
temperature the concentration "k" of the indicator component is
determined optionally responsive to the expression referred to
above: .epsilon.*.sub.mat(.omega.,T)=k.epsilon.*(.omega.,T). In the
expression .epsilon.*.sub.mat(.omega.,T) is the measured
permittivity (or real or imaginary part thereof), .omega. is an
isolation frequency at which the measurement is made, T the
determined temperature and .epsilon.*(.omega.,T) is the known
permittivity (or real or imaginary part thereof) of the indicator
material at frequency .omega. and temperature T. The concentration
k may of course also be determined responsive to measurements at a
plurality of isolation frequencies.
[0069] Practice of the invention is not limited to determining
temperature of a material and concentration of a single indicator
material whose concentration substantially determines permittivity
of the material. Assume that N indicator substances and their
respective concentrations determine the permittivity of a material
in accordance with an expression of the form mat * .function. (
.omega. , T ) = n = 1 N .times. .times. k n .times. n * .function.
( .omega. , T ) , ##EQU1## where .epsilon.*.sub.n(.omega.,T) is the
known permittivity of the n-th indicator material and k.sub.n its
unknown concentration. Then temperature T and the concentrations
k.sub.n can be determined by measuring
.epsilon.*.sub.mat(.omega.,T) at at least (N+1) suitable isolation
frequencies and solving a set of simultaneous equations comprising
at least (N+1) equations of the form given in the preceding
sentence that are determined by the measurements.
[0070] FIG. 4 schematically shows measuring temperature of a
surface region 30 of a material 32 that has a concentration of
water, in accordance with an embodiment of the present invention.
An appropriate probe 34, such as a probe described in U.S. Pat. No.
5,744,971 is used to generate an electromagnetic wave represented
by a solid wavy line 36 at at least one isolation frequency of
water that is incident on surface region 30. Energy from incident
wave 36 that is reflected by surface region 30 in a reflected wave
that is represented by a dashed wavy line 38 is sensed by probe 34,
which determines the amplitude and phase of the reflected wave
using methods known in the art.
[0071] A processor (not shown) in probe 34 uses the measured
amplitude and phase of reflected wave 38 to determine a
reflectance, "R(.omega.)", of surface region 30 at the isolation
frequency .omega. that characterizes incident wave 36. The
reflectance in turn is used to determine a value for the dielectric
permittivity .epsilon.*.sub.mat(.omega.,T) of material 32 at
surface region 30. For example, assuming that incident wave 36 is
normal to surface region 30, the dielectric permittivity of region
30 can be determined from the reflectance from the usual formula
R(.omega.)=[1-.epsilon.*.sub.mat(.omega.,T).sup.0.5]/[1+.epsilon.*.sub.ma-
t(.omega.,T).sup.0.5]. A suitable ratio, as discussed above,
between real and/or imaginary parts of the dielectric permittivity
.epsilon.*.sub.mat(.omega.,T) at at least one isolation frequency
is used to determine temperature of surface region 30.
[0072] In accordance with an embodiment of the present invention,
intensity of incident wave 36 is limited to prevent the wave from
heating surface region 30 during a time that the dielectric
permittivity of the region is being measured.
[0073] Assume that all energy that is not reflected from incident
wave 36 by material 32, is absorbed in a region of material 32 that
extends from surface region 30 to a depth equal to about one
absorption length "d(.omega.)" for wave 36 into material 32. Under
this assumption, energy from incident wave 36 that is not reflected
in reflected wave 38 heats a volume of material per square
centimeter of surface region 30 equal to about d(.omega.) cm.sup.3.
Let density of the material be represented by ".rho." and the
specific heat of the material be represented by "J". Then
temperature T of surface region 30 has a time rate of change dT/dt
during exposure to the incident wave that may be approximated by
dT/dt=P.sub.in(1-|R(.omega.).sup.2|)/(d(.omega.).rho.J), where
P.sub.in is the intensity of incident wave 36.
[0074] Assume that the specific heat J of material 32 is equal to
the specific heat of water, that .rho. is about 1 gm/cm.sup.3, that
the frequency of the incident wave is 20 GHz and that to prevent
the wave from distorting the temperature measurement, dT/dt must be
less than or equal to 0.02.degree. C./s. The absorption length
d(.omega.) for the wave may be estimated by the expression
d(.omega.)=.lamda..sub.o(.omega.)/[2.pi.Im(.epsilon.*(.omega.,T).sup.0.5)-
] where .lamda..sub.o(.omega.) is the free space wavelength of
incident wave 36. For .omega.=20 GHz, and a temperature of about
35.degree. C., d(.omega.).apprxeq.0.1 cm and
|R(.omega.).sup.2|.apprxeq.0.65. Then in order for dT/dt to satisfy
the relation dT/dt.ltoreq.0.02.degree. C./s, P.sub.in must satisfy
the relation P.sub.in.ltoreq.24 milliwatts/cm.sup.2.
[0075] In some embodiments of the present invention, measurements
of temperature are corrected for energy deposited by incident wave
36 in material 32 during measurement of temperature of surface 30.
The imaginary part of .epsilon.*.sub.mat(.omega.,T) is used to
estimate energy deposited by wave 36 in material 32 during
measurement of the temperature of surface 30. The amount of
deposited energy is used to estimate heating of material 32 during
the measurement of .epsilon.*.sub.mat(.omega.,T) and correct a
temperature of surface 30 determined from
.epsilon.*.sub.mat(.omega.,T). For example, in some embodiments of
the present invention, the imaginary part of
.epsilon.*.sub.mat(.omega.,T) is used to estimate energy deposited
in a region of material 32 extending from surface 30 to an
absorption length d(.omega.) inside the material during the
measurement. The estimated amount of deposited energy, specific
heat and density of material 32 are used to estimate by how much
the region is heated during the measurement. The amount of heating
is used to correct the temperature determined for surface 30 from
.epsilon.*.sub.mat(.omega.,T).
[0076] FIG. 5 schematically illustrates measuring an internal
temperature of a material 40 having a concentration of water, in
accordance with an embodiment of the present invention.
[0077] A probe 42 comprising an appropriate power supply,
circuitry, a network analyzer (none of which are shown) and two
antennas 44 is used to determine the internal temperature of
material 40, in accordance with an embodiment of the present
invention. Antennas 44, which may be, for example, strip or horn
antennas, or any other antennas suitable for radiating and/or
receiving electromagnetic waves at an isolation frequency of water
are placed so that they substantially sandwich a volume region 46
of material 40 between them.
[0078] The power supply and circuitry in probe 42 generate
electromagnetic waves at at least one isolation frequency of water
that are radiated from one towards the other of antennas 44. The
circuit analyzer, using methods known in the art, determines
amplitudes and optionally phases of waves that are reflected by
material 40 from a radiated wave and waves that are transmitted
through material 40 from the radiated wave. From the amplitudes and
phases of the reflected and transmitted waves the circuit analyzer
determines an average dielectric permittivity
.epsilon.*.sub.mat(.omega.,T) for volume region 46. A suitable
ratio between real and/or imaginary parts of the dielectric
permittivity .epsilon.*.sub.mat(.omega.,T) at at least one
isolation frequency is used to determine an average temperature for
volume region 46, which is an average internal temperature of the
volume region. Optionally, once the average temperature of the
volume region is determined, the concentration of water in the
volume region may be determined, similarly as noted above,
responsive to the determined temperature, the real and/or imaginary
parts of the permittivity determined at the at least one isolation
frequency and the known permittivity of water as a function of
temperature.
[0079] For example, in some embodiments of the present invention,
the circuit analyzer determines only amplitudes, or energies, of
reflected and transmitted waves and a value for an amount of energy
absorbed by volume 46 from the radiated wave determined. The amount
of absorbed energy is used to determine an average value for the
imaginary part of .epsilon.*.sub.mat(.omega.,T) for volume region
46. A ratio between average values of the imaginary part of
.epsilon.*.sub.mat(.omega.,T) at two isolation frequencies of water
can be used to determine the average internal temperature of volume
region 46 and the concentration of water in the volume region
determined from the temperature and permittivity measurements.
[0080] It is noted that by moving antennas 44 to different regions
of material 44 or by positioning an array of antenna pairs similar
to antennas 44, internal temperatures for different regions of
material 44 and water concentrations in the regions can be
determined and a thermal and water assay map of material 44
provided. Similarly, by moving probe 34 shown in FIG. 4 or by
positioning a plurality of probes 34 opposite the surface of
material 32 surface temperatures of different surface regions 30
and concentrations of water near the surface of the material can be
determined and a thermal and "surface water" assay map of the
material's surface provided.
[0081] In accordance with some embodiments of the present
invention, dielectric permittivity measurement of temperature is
used to determine absorption coefficients of a material for light.
The material is illuminated with light at an appropriate wavelength
between a first and a second time. Temperature of the material is
measured by measuring dielectric permittivity in accordance with an
embodiment of the present invention at the first and second times
to determine by how much the material is heated by the light. The
amount of heating is used to determine an absorption coefficient of
the material for the light.
[0082] It is known in the art to assay components of a material by
measuring absorption coefficients of the material for light.
Generally, to perform an assay, absorption coefficients of the
material are measured at a plurality of different wavelengths. For
example, U.S. Pat. No. 5,452,716 to V. Clift, the disclosure of
which is incorporated herein by reference, describes measuring
absorption coefficients of blood at a plurality of wavelengths to
assay blood glucose. In accordance with embodiments of the present
invention, absorption coefficients of a material for light
determined from dielectric permittivity measurement of temperature
is used to assay components of the material.
[0083] Whereas the above discussion describes determining
absorption coefficients of a material for light similar methods, in
accordance with embodiments of the present invention, may be used
for determining absorption coefficients for other types of
radiation. Absorption coefficients for substantially any type of
radiation that is absorbed by a material can be similarly
determined. For example, absorption coefficients for acoustic
radiation may be determined from dielectric permittivity
temperature measurements, in accordance with an embodiment of the
present invention.
[0084] In the above description temperature of a material is
measured by determining at least one isolation frequency of an
indicator component of the material and measuring the dielectric
permittivity of the material at the at least one isolation
frequency. In some embodiments of the present invention, an
isolation frequency is determined for which a plurality of known
indicator components of a material contribute to the dielectric
permittivity of the material, and other components of the material
do not substantially contribute to the dielectric permittivity.
Temperature of the material can be determined, in accordance with
an embodiment of the present invention, from known dependence of
the dielectric permittivity of each of the indicator components by
measuring at least one of the real or imaginary parts of the
dielectric permittivity of the material at the at least one
isolation frequency. Measurements of dielectric permittivity at an
isolation frequency corresponding to a plurality of indicator
components are used to determine temperature similarly to the way
in which measurements of dielectric permittivity at an isolation
frequency corresponding to a single indicator component is used to
determine temperature. However, for the case of an isolation
frequency of a plurality of indicator components, relative
concentrations of the known components must be known in order to
determine a dependence of the dielectric constant of the material
at the isolation frequency on temperature.
[0085] It is noted that determining temperature from measurements
of dielectric permittivity, in accordance with embodiments of the
present invention, is applicable to determining temperature of
various different types of materials. In particular, dielectric
temperature measurement, in accordance with an embodiment of the
present invention, is useable for measuring temperature of living
tissue. For example, a person's temperature can be measured in
accordance with an embodiment of the present invention by measuring
dielectric permittivity of a region of the person's ear. Or
dielectric temperature measurement, in accordance with an
embodiment of the present invention, can be used to measure
temperature of a region of a person's body undergoing ultrasonic,
hyperthermia or cryogenic treatment for cancer.
[0086] In the description and claims of the present application,
each of the verbs, "comprise" "include" and "have", and conjugates
thereof, are used to indicate that the object or objects of the
verb are not necessarily a complete listing of members, components,
elements or parts of the subject or subjects of the verb.
[0087] The present invention has been described using detailed
descriptions of embodiments thereof that are provided by way of
example and are not intended to limit the scope of the invention.
The described embodiments comprise different features, not all of
which are required in all embodiments of the invention. Some
embodiments of the present invention utilize only some of the
features or possible combinations of the features. Variations of
embodiments of the present invention that are described and
embodiments of the present invention comprising different
combinations of features noted in the described embodiments will
occur to persons of the art. The scope of the invention is limited
only by the following claims.
* * * * *