Thermal measuring and testing – Temperature measurement – Nonelectrical – nonmagnetic – or nonmechanical temperature...
Patent
1995-05-24
1998-07-14
Gutierrez, Diego F. F.
Thermal measuring and testing
Temperature measurement
Nonelectrical, nonmagnetic, or nonmechanical temperature...
2524081, 252962, 128736, G01K 1100, A61B 500
Patent
active
057793654
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a temperature sensor for medical applications.
BACKGROUND OF THE INVENTION
For use in a microwave hyperthermia therapy against cancers, various thermometers have been used employing an optical fiber for measuring the temperature at local portions of a body. Optical thermometers have been used for the reasons that correct measurement is obtained without interference from electromagnetic waves and no electric shock is given to the living body. It is desired to use the optical thermometer not only for the hyperthermia apparatus but also for extracorporeal blood circulation instruments such as an artificial heart-lung device or an artificial dialysis device, as well as for probing the blood during cardiac catheterization, since it is capable of reducing the danger of electric shock.
At present, there have been proposed optical thermometers employing optical fibers in four principal systems.
A first system is a sensor using a semiconductor as a transducer. That is, the semiconductor usually exhibits an energy gap that varies depending upon a change in the temperature and, hence, exhibits an optical absorption and an accompanying light transmission spectrum that changes thereto. Therefore, there has been proposed an optical fiber sensor by utilizing such properties (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 62-85832). For example, InGaAs and GaAs may be used as semiconductors. FIG. 9(A) shows an example of the constitution of a temperature sensor using such a semiconductor. A sensor 11 composed of the above semiconductor is fixedly provided to an end of optical fiber 10 on the side closer to a body that is to be measured, and a suitable reflector plate 12 is brought into contact with the sensor. Light having a suitable wavelength is permitted to be incident (L.sub.IN) on the other end of the optical fiber: the incident light is reflected by the reflector plate 12 via the semiconductor sensor 11 and returns back to the incident end passing through the semiconductor sensor 11 again. The intensity of light at this moment is measured to determined the temperature of the body that is being measured. FIG. 9(B) shows a relationship between the wavelength of light in the semiconductor and the transmittance factor for a semiconductor sensor having a thickness of 250 .mu.m, from which it will be understood that the transmittance changes depending upon the temperature. (Curve "A" illustrating the relationship at 53.degree. C., and curve "B" illustrating the relationship at 40.degree. C.) By utilizing these characteristics, therefore, it is possible to fabricate a temperature sensor which works depending upon light. However, this method lacks precision for a change in the temperature and has not been put into practical use in medical applications.
A second method is a sensor utilizing a change in the refractive index of a cladding material. According to this system, there is provided a temperature sensor in which, as shown in FIG. 10(A), a cladding 13 is removed from the end of the optical fiber 10, and a cavity 15 containing glycerine 14 therein, is formed at this portion (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 59-160729). The refractive index of the glycerine 14 changes depending upon the temperature and, hence, the angle of reflection of light changes on the interface between the core 16 and the cladding 13. As a result, the intensity of light returning (i.e., reflected by the reflector plate 12) from the end of the fiber changes. Measuring the quantity of light that has returned makes it possible to measure the temperature.
That is, as shown in FIG. 10(B), the DC voltage that is converted through the sensor from the quantity of returned light undergoes a change depending upon a change in the temperature. Therefore, measurement of the DC voltage makes it possible to measure the temperature of the material being measured. In the sensor of this type, however, the end of the probe has insufficient strength. M
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English Abstract of Japan (JP) 53043539, published 21 Nov. 1978.
Gutierrez Diego F. F.
Minnesota Mining and Manufacturing Company
Ubel F. Andrew
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