U.S. patent number RE31,832 [Application Number 06/456,330] was granted by the patent office on 1985-02-12 for temperature probe.
Invention is credited to Thaddeus V. Samulski.
United States Patent |
RE31,832 |
Samulski |
February 12, 1985 |
Temperature probe
Abstract
A temperature probe measures temperature changes within
biological material while the tissue is being irradiated with
microwaves. In order to measure tissue temperatures accurately a
probe must be designed to function in a microwave field while
causing minimum perturbation to the microwave field. This generally
requires a probe being constructed of dielectric (non-metallic)
material which utilizes physical phenomena which are thermally
dependent yet unaffected by electromagnetic fields at the field
strength and frequencies of interest. In one embodiment the
structure of the probe basically includes an optical fiber bundle
for conducting light both toward and away from a temperature
sensitive luminescent element located at one end of the optical
fiber bundle, the source for exciting the temperature sensitive
element and a light responsive detection element located at the
output end of the optical fiber bundle for detecting light emitted
from the temperature sensitive element which is temperature
dependent. The light received by the light responsive detection
element can be analyzed with regard to several parameters
(intensity, frequency and phase) and thereby used for indicating
the temperature of the biological sample or tissue.
Inventors: |
Samulski; Thaddeus V. (Palo
Alto, CA) |
Family
ID: |
26754947 |
Appl.
No.: |
06/456,330 |
Filed: |
January 6, 1983 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
073841 |
Sep 10, 1979 |
04245507 |
Jan 20, 1981 |
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Current U.S.
Class: |
374/131;
250/459.1; 374/137; 250/458.1; 356/44; 374/159 |
Current CPC
Class: |
G01K
11/3213 (20130101); G01K 13/20 (20210101); G01K
1/024 (20130101) |
Current International
Class: |
G01K
11/32 (20060101); G01K 1/02 (20060101); G01K
13/00 (20060101); G01K 1/00 (20060101); G01K
11/00 (20060101); G01K 011/20 () |
Field of
Search: |
;250/461.1,459.1,458.1
;351/96.25 ;356/44,45,43 ;374/159,121,137,130,129,131 ;313/475,474
;315/145 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2755713 |
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Jun 1978 |
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DE |
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2064107A |
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Nov 1979 |
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GB |
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Other References
NASA Report No. NAS 3-21005; 1-23-79, entitled "Analysis and
Preliminary Design of Optical Sensors for Propulsion Cont.", pp.
63-86. .
Control Engineering, Feb. 1979, pp. 30-33. .
Sholes and Small, Rev. Sci. Instrum., vol. 1, No. 7, Jul. 1980, pp.
882-884. .
"Photoluminescent . . . Probes . . . "; Science, vol. 208, 4-11-80,
pp. 193, 194. .
"Photoluminescent Thermometry . . . " Phys. Med. Biol., 1980, vol.
27, No. 1, pp. 107-114. .
"Remote Optical Measurement . . . ", Electronic Letters, 9-3-81,
vol. 17, No. 18, pp. 631, 632. .
Curie, Luminescence in Crystals, 1960, pp. 1-9..
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Primary Examiner: Woodiel; Donald O.
Attorney, Agent or Firm: Majestic, Gallagher, Parsons &
Siebert
Claims
I claim: .[.1. A temperature probe adapted to be implanted in a
material whose temperature is to be measured, said temperature
probe comprising:
an optical fiber bundle having at least one distinct group of optic
fibers for optically conducting light between one end thereof and
the other;
a temperature sensitive element located at one end of said optical
fiber bundle, said temperature sensitive element having temperature
sensitive luminescent properties and being adapted to be implanted
in such material whose temperature is to be measured;
means located at one of said optical fiber bundle for exciting said
temperature sensitive element; and
1ight responsive detection means located at the other end of said
optical fiber bundle from said temperature sensitive element for
detecting light directed from said temperature sensitive element
and passed through said optical fiber bundle..]. .[.2. A
temperature probe adapted to be implanted in a material whose
temperature is to be measured, said temperature probe
comprising:
an optical fiber bundle having a first group and a second group of
optical fibers which are physically separated at one end of said
bundle;
a temperature sensitive element having temperature sensitive
luminescent properties, said temperature sensitive element being
located at the other end of said bundle and being adapted to be
implanted in such material whose temperature is to be measured;
1ight source located proximate said first group of optical fibers
at said one end of said bundle, said light from said source
optically passing through said first bundle to excite said
temperature sensitive element; and
1ight responsive detection means located proximate said second
group of optical fibers at said one end of said bundle, said light
emitted from said temperature sensitive element passing through
said second bundle to said light responsive detection means..].
.[.3. The temperature probe according to claim 2 wherein said
temperature sensitive element is a phosphorescent material..].
.[.4. The temperature probe according to claim 3 wherein said
phosphorescent material is zinc sulfide activated with camdium..].
.[.5. The temperature probe according to claim 3 wherein said
phosphorescent material is calcium sulfide activated with Europium
and tin..]. .[.6. The temperature probe according to claim 2
wherein said temperature sensitive element is a phosphorescent
material encapsulated in an optically opaque element..]. .[.7. The
temperature probe according to claim 2 wherein said temperature
sensitive element is a phosphorescent material having a luminescent
decay time which is temperature dependent..]. .[.8. A temperature
probe adapted to be implanted in a material whose temperature is to
be measured, said temperature probe comprising:
an optical fiber bundle having at least one optical fiber;
a temperature sensitive element having temperature sensitive
luminescent properties and having the property of emitting
radiation at a different frequency than that it absorbs, said
temperature sensitive element being located at one end of said
bundle and being adapted to be implanted in such material whose
temperature is to be measured;
1ight source located proximate the other end of said bundle, said
light source having a given frequency spectrum;
means proximate said other end for separating the light passed from
said source toward said temperature sensitive element from that
being emitted from said temperature sensitive element; and
1ight responsive detection means located proximate said other end
of said bundle, said light responsive detection means including
means for detecting the light emitted from said light sensitive
element as a function of the change in temperature of said
temperature response element..]. .[.9. The temperature probe
according to claim 8 wherein said temperature sensitive element is
a phosphorescent material..]. .[.10. The temperature probe
according to claim 9 wherein said phosphorescent material is zinc
sulfide activated with camdium..]. .[.11. The temperature probe
according to claim 9 wherein said phosphorescent material is
calcium sulfide activated with Europium and tin..]. .[.12. The
temperature probe according to claim 8 wherein said temperature
sensitive element is a phosphorescent material encapsulated in an
optically opaque element..]. .[.13. The temperature probe according
to claim 8 wherein said temperature sensitive element is a
phosphorescent material having a luminescent response which is
temperature dependent, said luminescent response being a function
of temperature..]. .[.14. The temperature probe according to claim
8 wherein said separating means includes a beam splitter and an
excitation frequency filter associated with said source and a
luminescent response filter associated with said light responsive
detection means..]. .[.15. A temperature probe adapted to be
implanted in a material whose temperature is to be measured, said
temperature probe comprising:
an optical bundle having at least one optical fiber;
a temperature sensitive element having temperature sensitive
luminescent properties, said temperature sensitive element being
radioactive and being located at one end of said bundle and being
adapted to be implanted in such material whose temperature is to be
measured;
a radioactive source located proximate said temperature sensitive
element for exciting said temperature sensitive element; and
1ight responsive detection means located proximate the other end of
said bundle for detecting the emission response of said temperature
sensitive element as a function of its temperature..]. .[.16. The
temperature probe according to claim 15 wherein said temperature
sensitive element is a phosphorescent material..]. .[.17. The
temperature probe according to claim 16 wherein said phosphorescent
material is zinc sulfide activated with camdium..]. .[.18. The
temperature probe according to claim 16 wherein said phosphorescent
material is calcium sulfide activated with Europium and tin..].
.[.19. The temperature probe according to claim 16 wherein said
temperature sensitive element is a phosphorescent material
encapsulated in an optically opaque element..]. .[.20. A
temperature probe adapted to be implanted in a material whose
temperature is to be measured, said temperature probe
comprising:
an optical bundle having at least one optical fiber;
a temperature sensitive element having radioactive and luminescent
temperature sensitive properties, said temperature sensitive
element being located at one end of said bundle and being adapted
to be implanted in such material whose temperature is to be
measured;
1ight responsive detection means located proximate the other end of
said bundle for detecting the emission response of said temperature
sensitive element as a function of its temperature..]. .[.21. The
temperature probe according to claim 20 wherein said temperature
sensitive element is a radioactivated phosphorescent material..].
.[.22. The temperature probe according to claim 21 wherein said
radioactivated phosphorescent material is zinc sulfide activated
with camdium..]. .[.23. The temperature probe according to claim 21
wherein said phosphorescent material is calcium sulfide activated
with Europium and tin..]. .[.24. The temperature probe according to
claim 20 wherein said temperature sensitive element is a
radioactivated phosphorescent material encapsulated in an optically
opaque
element..]. .Iadd.25. A method of measuring temperature of an
environment, comprising the steps of:
positioning luminescent material in thermal communication with said
environment, said luminescent material being characterized by
emitting, when excited with transient illumination radiation,
luminescent radiation that continues in time beyond termination of
the excitation radiation and with a rate of intensity decay that is
related to the temperature of the luminescent material,
exposing said luminescent material to transient excitation
radiation, thereby causing said luminescent material to luminesce
with a decaying intensity extending beyond the termination of said
excitation radiation, and
detecting the rate of decay of said luminescence, thereby to detect
the temperature of the luminescent material and that of said
environment. .Iaddend. .Iadd.26. A method according to claim 25
wherein said luminescent material is further characterized by
comprising zinc sulfide activated with cadmium. .Iaddend. .Iadd.27.
A method according to claim 25 wherein said luminescent material is
further characterized by comprising
calcium sulfide activated with europium and tin. .Iaddend.
.Iadd.28. The method according to claim 25 wherein the exposing
step comprises exposing said luminescent material to a periodically
recurring illumination intensity variation, thereby to cause said
luminescent material to luminesce with a periodically recurring
intensity variation, and further wherein the step of detecting the
luminescence comprises the steps of detecting the periodic
luminescence intensity variations and comparing the phase of those
variations with the phase of the periodically recurring excitation
intensity variation, whereby the phase difference is related to the
rate of decay of the luminescent material emission and the
temperature of the luminescent material. .Iaddend. .Iadd.29. A
method of measuring temperature of an environment, comprising the
steps of:
positioning luminescent material in thermal communication with said
environment, said luminescent material being characterized by
emitting, when excited with transient illumination radiation,
luminescent radiation that continues in time beyond termination of
the excitation radiation and with a rate of intensity decay that is
related to the temperature of the luminescent material,
exposing said luminescent material to transient excitation
radiation, thereby causing said luminescent material to luminesce
with a decaying intensity extending beyond the termination of said
excitation radiation,
detecting the rate of decay of said luminescence, and
determining from said rate of decay the temperature of the
luminescent material, thereby to determine the temperature of said
environment.
.Iaddend. .Iadd.30. The method according to claim 29 wherein the
exposing step comprises exposing said luminescent material to a
periodically recurring illumination intensity variation, thereby to
cause said luminescent material to luminesce with a periodically
recurring intensity variation, and further wherein the step of
detecting the luminescence comprises the steps of detecting the
periodic luminescence intensity variations and comparing the phase
of those variations with the phase of the periodically recurring
excitation intensity variation, whereby the phase difference is
related to the rate of decay of the luminescent material emission
and the temperature of the luminescent material. .Iaddend.
.Iadd.31. A system for measuring temperature of an environment,
comprising:
a quantity of luminescent material positionable in thermal
communication with said environment, said luminescent material
characterized by emitting, when excited with transient radiation,
luminescent radiation that continues in time beyond the termination
of the excitation radiation and with a rate of decay that is
related to the temperature of the luminescent material,
means for exposing said luminescent material to such transient
excitation radiation, thereby to cause said luminescent material to
luminesce with a decaying intensity extending beyond the
termination of said excitation radiation, and
means receiving the luminescent material luminescence for measuring
the rate of decay of said luminescence pulse, thereby to measure
the
temperature of the luminescent material. .Iaddend. .Iadd.32. The
system according to claim 31 wherein said luminescent material
comprises zinc sulfide activated with cadmium. .Iaddend. .Iadd.33.
The system according to claim 31 wherein said luminescent material
comprises calcium sulfide activated with europium and tin.
.Iaddend. .Iadd.34. The system according to claim 31 wherein said
exposing means includes means for directing toward said luminescent
material excitation radiation having a periodically recurring
intensity variation, thereby to cause said luminescent material to
luminesce with a periodically recurring intensity variation, and
further wherein said measuring means includes means receiving the
periodically recurring luminescent intensity variation and a signal
corresponding to the periodically recurring excitation radiation
for comparing the phase therebetween, said phase difference being
related to the rate of decay of the luminescent material, whereby
this phase difference is related to the temperature of the
luminescent material.
.Iaddend. .Iadd.35. A system for measuring temperature of an
environment, comprising:
a quantity of luminescent material attached to one end of an
optical fiber communication medium, said luminescent material
characterized by emitting, when excited with transient radiation,
luminescent radiation that continues in time beyond the termination
of the excitation radiation and with a rate of decay that is
related to the temperature of the luminescent material,
means positioned at another end of said optical fiber communication
medium for exposing said luminescent material to such transient
excitation radiation, thereby to cause said luminescent material to
luminesce with a decaying intensity extending beyond the
termination of said excitation radiation, and
means positioned at said another end of said optical fiber
communication medium to receive the luminescent material
luminescence for measuring the rate of decay of said luminescence
pulse, thereby to measure the
temperature of the luminescent material. .Iaddend. .Iadd.36. The
system according to claim 35 wherein said luminescent material
comprises zinc sulfide activated with cadmium. .Iaddend. .Iadd.37.
The system according to claim 35 wherein said luminescent material
comprises calcium sulfide activated with europium and tin.
.Iaddend. .Iadd.38. The system according to claim 35 wherein said
exposing means includes means for directing toward said luminescent
material excitation radiation having a periodically recurring
intensity variation, thereby to cause said luminescent material to
luminesce with a periodically recurring intensity variation, and
further wherein said measuring means includes means receiving the
periodically recurring luminescent intensity variation and a signal
corresponding to the periodically recurring excitation radiation
for comparing the phase there between, said phase difference being
related to the rate of decay of the luminescent material, whereby
this phase difference is related to the temperature of the
luminescent material. .Iaddend. .Iadd.39. The method according to
claim 25 wherein the environment whose temperature is being
measured is biological tissue, and further wherein the step of
positioning luminescent material within this environment includes
positioning said material at the end of an optical fiber that is
implanted into said tissue. .Iaddend. .Iadd.40. The method
according to claim 29 wherein the environment whose temperature is
being measured is biological tissue, and further wherein the step
of positioning luminescent material within this environment
includes positioning said material at the end of an optical fiber
that is implanted into said tissue. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The field of temperature measurement includes a variety of
conventional temperature sensing devices which involve metallic
sensors and elements such as thermisters, thermocouples and
thermometers. Calorimetric techniques may also be employed for
temperature measurement. However, each of these conventional
temperature measuring devices is handicapped when used to measure
temperature changes of biological tissue in the presence of an
electromagnetic field. The metallic elements of the conventional
temperature measuring sensors cause interferences and perturbations
and concentrations of the electromagnetic field in which it is
placed which result in erroneous readings and undesirable,
localized hot spots in the biological tissue being measured.
Calorimetric methods require that the tissue be enclosed in a
container while further restricting the temperature measurements
until after the material being sensed in irradiated.
Medical research has been hampered in the past by the absence of a
non-perturbating and interfering temperature sensor. Science has
had to resort to complicated methods and expensive elements which
are used to sense the temperature of the biological tissue while
the same is in an electromagnetic field such as microwave
radiation.
One example of a successful attempt to produce a temperature probe
having non-perturbing elements which may be used to measure the
biologicl tissue while the tissue is subject to an electromagnetic
field is that shown in the patent to Rozzell, et al. U.S. Pat. No.
4,016,761. The Rozzell patent utilizes the reflective properties of
a liquid crystal at the end of a bundle of optical fibers. While
the liquid crystal is non-metallic and does perturb or interfer
with the electromagnetic field, it is subject to various
disadvantages. For instance, the liquid crystals are subject to
chemical instability and must be both kept in an airtight sealed
arrangement as well as constantly recalibrated or substituted for
new liquid crystals as they deteriorate with time. Moreover, liquid
crystals are subject to drift and hysteresis which create problems
in the reliability of the instrument. Generally, the sensitivity of
optical temperature probes based on reflective phenomena is
critically dependent on the physical dimensions and coupling of the
temperature sensitive element to the optic fiber bundle. Thus, the
sensitive tip of the probe requires careful construction placing
limitations on size and durability. The instrument described in the
Rozzell, et al. patent serves a very useful purpose and is
successful in its partial attempts at temperature measurement.
However, the temperature probe described therein does not satisfy
all of the requirements demanded by rigorous biological
research.
The temperature probe of the present invention goes beyond the
apparatus described in the Rozzell patent as well as all optical
probes based on reflectivity and has several advantages for
reliable and efficient measure of temperature within biological
samples in an electromagnetic environment.
SUMMARY OF THE INVENTION
The present invention is addressed to a temperature probe having
non-metallic parts and is suitable for the measurement of
temperature in an electromagnetic field with specific applications
in biological research. The temperature probe is configured having
at least one distinct group of optical fibers for conducting light
between one end thereof and the other. The probe additionally
includes a temperature sensitive element located at one end of the
optical fiber bundle, the temperature element having temperature
dependent luminescent properties which are extremely relible in
sensing the temperature of materials with which the element is in
thermal equilibrium, the temperature sensitive element being
adapted to be implanted in the material whose temperature is to be
measured. The probe of the present invention also includes a source
for exciting the luminescent temperature sensitive element and a
light responsive detection element located at the other end of the
optical fiber bundle from the temperature sensitive element for
detecting the light emitted from the temperature sensing element
which is passed through the optical fibers. The detection element
takes the intensity of the light and/or the frequency and/or
lifetime shift characteristic of the luminescent process and uses
this information to translate it through conventional electronic
systems into a reading of the temperature of the biological tissue.
As alluded to previously, the luminescent material or materials
used within the end of the probe to be implanted can have a light
intensity (quantum efficiency), frequency spectrum and temperature
dependent decay or lifetime, one or all of which may be used for
temperature detection purposes. Additionally, the frequency of the
excitation source which is passed to the luminescent element is not
equal to the frequency of the light which is passed out from the
temperature sensitive element. In this respect the physical process
is not reflective. This difference in frequency may be used as a
means for selectively differentiating the output signal from input
noise, an advantage in recovering necessary information for the
determination of temperature.
The present invention includes a variety of embodiments which have
individual sources of light for excitation of the luminescent
element as well as one embodiment which includes its own
self-contained source (radioactive) for exciting the luminescent
material.
Accordingly, it is a general object and feature of the present
invention to provide a non-metallic temperature probe for measuring
the temperature of a material while the material is in an
electromagnetic field without interfering with the electromagnetic
field or having its response altered by the electromagnetic field
except through thermal interaction.
It is another general object and feature of the present invention
to provide a temperature probe adapted to be implanted in a
material whose temperature is to be measured having a temperature
sensitive element having luminescent and temperature sensitive
properties.
It is yet another object and feature of the present invention to
provide a temperature probe adapted to be implanted in a material
whose temperature is to be measured, the temperature probe
including a temperature sensitive element which is adapted to
utilize a spectral frequency shift between the adsorbed radiation
it receives to excite it and the emitted radiation it passes out in
response to the temperature surrounding it.
It is still another object and feature of the present invention to
provide a non-metallic temperature probe adapted to be implanted in
a material whose temperature is to be measured, the temperature
probe including merely a single group of optical fibers which may
be used both to conduct excitation light toward the temperature
sensitive element as well as to conduct light from the temperature
sensitive element to a light responsive detection element, the
detection element having means for detecting a change in the time
response (luminescent decay or lifetime) of the temperature
sensitive element indicative of a temperature change in the
material in which the probe is implanted. This time response (decay
or lifetime) may be measured directly or via alternate means, e.g.,
phase sensitive detection technique.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features that are considered characteristic of the
invention are set forth with particularity in the appended claims.
The invention itself, however, both as to its structure and its
operation together with the additional objects and advantages
thereof will best be understood from the following description of
several embodiments of the present invention when read in
conjunction with the accompanying drawings wherein:
FIG. 1 is a schematic representation of one embodiment of the
temperature probe of the present invention having two distinct
groups of optical bundles;
FIG. 2 is a schematic representation of another embodiment of the
temperature probe of the present invention having a single group of
optical bundle associated therewith;
FIG. 3 is another schematic representation of a temperature probe
according to the present invention which utilizes a radioactive and
luminescent material which is self-exciting and which requires no
other external excitation source; and
FIG. 4 is a graphic representation of the temperature response of
one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Looking to FIG. 1 there is shown in schematic form a temperature
probe 10 and the associated mechanisms for operating the same. The
probe 10 consists of a bundle of optical fibers 12 having any
convenient and reasonably desired diameter, length and number. In
the embodiment shown in FIG. 1 the bundle of optical fibers 12 is
separated into two distinct groups having terminals at 14 and 16
and a common terminal at 18. Provided adjacent to the terminus of
the optical bundle 12 at its end 18 is a temperature sensing
element 20 which has luminescent properties. The temperature
sensing element 20 may be a fluorescent material or may be a
phosphorescent material, or suitable combination of materials.
Applicant has found that the temperature sensitive element 20 may
take any number of specific embodiments, however, zinc sulfide
activated with camdium and calcium sulfide activated with Europium
and tin have been found to have suitable temperature sensitive
properties in order to demonstrate the operability of this
invention. The temperature sensitive element 20 is attached to the
end 18 of the optical fiber bundle by a clear epoxy 22 and includes
about its periphery an opaque encapsulation of an opaque epoxy. The
separated ends of the optical fiber bundles 14 and 16 are also
encapsulated in an opaque casing (not shown). Positioned proximate
the one end 14 of the optical bundle is a source of excitation
radiation 24. The source 24 may take any one of a number of
configurations, however, applicant has found that a xenon flash
lamp provides sufficient optical excitation levels for the purposes
of the present invention. The source 24 is controlled, both as to
its triggering and its source of power by a flash trigger and
charge supply circuit 26 through an electrical line 28. The
specific triggering mechanism and charge supply, as well as the
circuitry involved therein, are not unique and are commonly
available with state of the art electronics and will not be further
discussed herein.
Located proximate the other end 16 of the optical bundle is a light
responsive element 30 which is adapted to sense the levels of light
or radiation emitted by the temperature sensitive element 20 and
passed through the optical bundle toward it. The specific
configuration of the light responsive element 30 is one of design.
However, applicant has found that a photo multiplier tube or
photosensitive diode, commonly available, serves well as a detector
of the luminescent radiation passed to it through the optical
bundle 16. The circuitry and electronics necessary for receiving
the signal from the photo multiplier tube 30 is shown as the
detector circuitry 32 and may take any one of a number of
configurations which are commonly available in the electronics art.
A connection 36 between the detector circuitry 32 and the flash
trigger and charge supply circuitry 26 is provided in order to
relate the time and intensity of the source 24 to the radiation
received by the photo multiplier tube 30 for correlating and
analyzing the luminescent light signal received by the detector
with regard to temperature determination. The exact nature of the
information communicated between source and detector will depend on
which characteristic parameter is being measured and the technique
used for measuring this parameter.
The use of a luminescent temperature probe provides various
advantages over conventional systems. For instance, due to its
non-metallic nature and physical process by which it functions it
does not perturb or interfere with the electronmagnetic field or
microwave radiation to which it is subjected during its temperature
measurement function. Additionally, the luminescent material has a
definite temperature dependence and may be formed of a relatively
small size for delicate biological tissue temperature sensing. In
addition to being small, it is easily fabricated and easily
attached to the end 18 of the optical fiber bundle. The luminescent
materials can have a long term physical and chemical stability
without drift or hysteresis associated therewith. As alluded to
previously, the luminescent material may be one of a variety of
materials depending upon the range and resolution necessary in a
given or desired circumstance. Luminescent materials have a
luminescent intensity which is directly related to temperature and
thereby to the temperature of materials in thermo equilibrium with
it. In addition, the luminescent material has a luminescent decay
time or lifetime which is temperture dependent. This decay time or
lifetime is an intrinsic property of the luminescent material.
Consequently, it allows the measurement of an intensive rather than
extensive parameter for the purpose of temperature measurements.
Specifically, the light which is used to excite the temperature
sensitive luminescent element 20 is absorbed by the material.
Subsequently, the material 20 is adapted to emit a radiation with a
time dependent intensity which is characteristic of the atomic and
solid state properties of luminescent material and independent of
the intensity of the source used to excite the luminescent
material. Thus the time dependence of the emission intensity rather
than the intensity itself can be used as a thermo parameter. The
time dependence of the emission intensity can be measured directly
as a decay time from a single excitation pulse or as a phase shift
between a modulated excitation source and the resulting modulated
luminescent emission. It should also be noted that the frequency
spectrum of the light emitted by the temperture sensitive element
20 is also temperature dependent and may also be used in order to
determine the temperature proximate the probe.
Another important aspect of luminescence phenomenon (from a
frequency standpoint) is that the emitted radiation is
characteristically different from the adsorbed radiation. For
example, the emission frequency of the radiation from the
temperature sensitive element 20 is different from the adsorption
frequency of the light from source 24. In this regard, luminescence
phenomenon is not a reflectance effect. It is this difference in
the character of the excitation or absorption radiation from the
emission radiation which offers an advantage with regard to
detection techniques used for luminescent studies. Luminescence is
traditionally subscategorized into two processes, i.e.,
fluorescence and phosphorescence. Fluorescence and phosphorescence
are processes in which radiation is emitted by a luminescent
material that has been excited via the absorption of specific types
of radiation. If the quantum states from which the emission
originates and terminates have the same multiplicity, the emission
is called fluoroescence and is characterised by a relatively short
lifetime (10.sup.-2 to 10.sup.-10 sec.). If the states from which
the emission originates and terminates differ in spin
(.DELTA.S.gtoreq.1), the emission is known as phosphorescence and
the lifetime can be relatively long (10.sup.- 3 to 10.sup.+ sec.).
The luminescent emission intensity, lifetime and frequency spectrum
can be temperature dependent and therefore one or more of these
characteristic properties may be used as a thermo-response
parameter. Combined with an optical fiber bundle serving as a light
guide for optical excitation as well as a return guide for
observing the luminescent response, a luminescent material has the
potential for making a relatively small non-electronic non-metallic
temperature probe. Such an optically activated luminescent
temperature probe can be useful in situations where more
conventional type probes (thermisters and thermocouples, etc.) are
handicapped due to electrical perturbation and interference, i.e.,
in an electromagnetic field.
Of the possible techniques available for detecting the luminescent
response phase flurometry appears to be one which shows
attractiveness. This technique uses a modulated excitation source
and detects the phase shift between the modulated excitation source
and the consequently modulated luminescent response. Since the
phase shift is directly related to the luminescent lifetime, which
is temperature dependent, a change in relative phase in the
luminescent signal excitation source can be related through known
procedures to a change in temperature of the luminescent material
located at the probe tip. This type of detection technique will
allow the use of phase sensitive lock-in amplification which offers
a considerable advantage in recovering a weak luminescent emission
signal. The phase detection technique can be independent of
excitation source intensity and offers an additional advantage with
regard to detection electronics and probe interchangeability.
Looking to FIG. 2 there is shown an alternative embodiment of the
present invention, utilizing the temperature dependent parameters
(intensity, lifetime, frequency spectrum) previously described. A
bundle of optical fibers 40 is provided which is presented in a
single group. Provided at one end 42 of the optical bundle is a
temperature sensitive element 44. The temperature sensitive element
44 is attached to the end 42 of the optical bundle 40 by a clear
epoxy 46. The end of the temperature sensitive element 44 is
sheathed or encapsulated in an opaque epoxy material 48 for
excluding any ambient or extraneous light from the temperature
sensitive element 44. The other end 50 of the optical fiber bundle
40 is located outside and away from the electromagnetic field and
has associated with it a source of illumination 52 which may take
any one of a number of configurations as previously discussed. The
source 52 is triggered and supplied with energy by a flash trigger
and charge supply circuit 54 and is connected to the source 52 via
electrical line 56. A beam splitter 48 is provided along the
optical path between the source of illumination 52 and the end of
the optical fiber bundle 50. The beam splitter may take any one of
several configurations including those which not only split the
beam but additionally filter the inherent characteristics of light
such as color, frequency or polarization. Corrugated light wave
guides are only one example of such alternatives. The beam splitter
is employed for separating the incoming excitation radiation from
the outcoming luminescent response radiation from the temperature
sensitive element 44. Located proximate beam splitter 58 is another
light responsive detector element 60 similar to that described
previously which has associated with it its own detector circuitry
62 and is connected to the detector via appropriate electrical line
64. A comparative connection 66 between the flash trigger and
charge supply circuitry 54 and the detector circuitry 62 is
provided if necessary for comparing the intensity and/or phase
differential between the outgoing illumination 68 and the incoming
radiation 70. The beam splitter 58 is available in the current
state of the art in guided wave optics. It should be noted,
however, that the single bundle of optical fibers 40 may be
utilized for both incoming as well as outgoing illumination due to
the frequency differential properties of the luminescent material
44 used at the end of the probe. Moreover, by modulating the source
52 and measuring the consequent modulated luminescent response to
detect a phase shift, which is temperature dependent, a phase
change in the luminescent signal can be related to a temperature
change.
Looking to FIG. 3, there is shown a third embodiment of the present
invention. The temperature probe 10 of this third embodiment
includes a single bundle of optical fibers 72 having a probe end 74
and a response end 76. Located proximate the probe end 74 is a
temperature sensitive element 78 having both luminescent as well as
radioactive properties. The temperature sensitive element 78 is
attached to the probe end 74 via a clear epoxy 80 and is
encapsulated or sheathed by an opaque epoxy layer 82 for preventing
extraneous and ambient illumination from affecting the temperature
sensitive element 78. Provided proximate the response end 76 of the
optical fiber bundle 72 is a detector 84 of the variety described
above. A detector circuit 86 is attached to the detector 84 via an
appropriate electrical line 88 in much the same manner as
previously described in the first and second embodiments. There is
no external source associated with the temperature probe embodiment
shown in FIG. 3 inasmuch as the radioactive luminescent material
utilized in the temperature sensitive element 78 includes its own
source of excitation radiation. However, the luminescent material
used in the element 78 remains temperature sensitive and will emit
luminescent light intensity and/or frequency spectrum dependent
upon the temperature it is subjected to. The advantages of using a
radioactivated luminescent material as a light source at the
temperature sensitive element 78 is that a single optical fiber
bundle may be used since the light source is the luminescent
material. This eliminates the need for an external light source to
excite the luminescent material and also eliminates the problems
associated with controlling the excitation source intensity. Using
a radioactive luminescent material additionally makes the probe
simple and easy to fabricate thereby resulting in a diminished size
for delicate temperature sensing.
FIG. 4 is indicative of the time response received by the detector
from the temperature sensitive element in the embodiments
previously discussed. The vertical axis for the family of curves
shown in FIG. 4 represents the response in volts per centimeter for
a given excitation pulse at different temperatures. As should be
evident from a review of the graph in FIG. 4, the voltage
representation of the light response for lower temperatures is
greater than that for higher temperatures. In this regard,
Applicant has determined that the tolerance levels or temperature
resolution is in the vicinity of .+-.0.3.degree. C. thereby
providing an accurate measurement of the temperature to which the
probe end is subjected. The configuration of each curve of the
family of curves in FIG. 4 may be utilized in various ways to
determine temperature. For example, the peak response is indicative
of a substantially linear decrease with temperature increase.
Additionally, the area under each curve may be integrated thereby
resulting in an inverse proportional relationship between the area
under one curve and its related temperature. The specific shape of
the curve and/or its decay time (as is indicated by the curve's
tail) may be equally utilized to temperature determination.
In conclusion, it will be seen that there is provided a simple,
efficient, and easily maintained temperature probe adapted for
primary use in a non-ionizing electromagnetic radiation field. The
temperature probe is constructed with non-conductive dialectric
materials and therefore is non-interfering and non-perturbing of
the electomagnetic field. Additionally, based on the physical
phenomena of luminescence, its response will be independent of
electromagnetic fields in the radio and microwave frequency range.
Using various temperature sensitive elements (luminescent materials
of different physical properties), the sensitivity of the
temperature probe may be varied to any one of a number of
temperature ranges to which the operator will subject the
probe.
While certain changes may be made in the above noted apparatus
without departing from the scope of the invention herein involved,
it is intended that all matter contained in the above description
or shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
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