Study On Optical Fiber Temperature Sensors For Human Body Temperature Monitoring

The accurate and fast measurements of temperature were needed inclinical medicine and animal experiments. Especially in tumor hyperthermia, thereal-time and accurate measurement of tumor temperature requires the appliedtemperature sensor can realize multi-point measurement and eliminate thedisturbance of electromagnetic radiation. The optical fiber sensor can be well appliedin human body temperature measurement due to the advantage of electromagneticanti-jamming quality.In order to overcome the shortcomings of the current medical temperaturesensors, several kinds of fiber optic temperature sensor used for the human bodytemperature measurement were proposed and demonstrated according to the sensortheory of fiber Bragg grating （FBG） and long period fiber grating （LPFG）.1、Prepare medical FBG temperature sensor and study on the characteristics ofmedical FBG temperature sensorUtilizing ordinary quartz fiber and Cladding Mode Suppression（CMS）fiber as raw materials, two kinds of Fiber Bragg gratings（FBGs） werefabricated via phase mask methods. And the temperature and bendingcharacteristic of the as-made FBGs were studied. The results showed thatboth of the as-prepared temperature sensors have similar temperaturesensitivity,11.5pm/℃for ordinary FBG and10.6pm/℃for CMSFBG. Thelinear correlation coefficients were greater than0.99. However, the CMSFBG was less insensitive to the curvature than the ordinary FBG. Therefore,CMS FBG was more suitable for human body temperature measurement.2、Study on the temperature-sensitive packaging of medical FBGAccording to the basic principles of the temperature-sensitive packing, severalkinds of material which had larger coefficient of thermal expansion and stabletemperature change were chosen for FBG encapsulation. First, we used epoxy resinto encapsulate the FBG in Teflon pipe. Although temperature sensitivity wassignificantly improved, which was about12times higher than naked FBG temperature sensor, its linearity was inferior to naked FBG sensor. In order to keepthe linearity of the temperature sensor, we let the FBG keep a free state in thecapillary tube, and only fix the two endpoints. The substrate materials we used werecapillary glass tube, steel tube and Teflon tube. The temperature sensitivities were8.7pm/℃,38pm/℃and23.4pm/℃respectively, and all of the three packed FBGsensors have a good linearity. The structure of double tube without glue was used.The temperature sensitivity was18.9pm/℃, and the linearity was better than otherencapsulation methods applied. The temperature sensitivity of packed FBGtemperature sensor not only relates to thermal expansion coefficient but also tothermal conductivity.3、Prepare LPFG temperature sensor and study on the characteristics of LPFGtemperature sensorLPFG were fabricated via high frequency CO₂laser. And the temperatureand bending characteristics of as-made LPFG were studied. The temperaturesensitivity was75pm/℃,7.5times higher than naked FBG. The amplitude oftransmission peak was sensitive to bend curvature, while insensitive to temperature.In order to make it more suitable for application in engineering, an alcohol filledencapsulation method was proposed. After encapsulation, two obvious resonancepeaks appeared. The wavelength of peak1exhibited blue shift when the temperaturerising, while the wavelength of peak2showed red shift. The temperature sensitivityof peak1was56.9pm/℃. The temperature sensitivity of peak2was531.2pm/℃,7times higher than naked LPFG and53times higher than naked FBG.4、Test the characteristics of packed fiber temperature sensor in themicrowave and supersonic wave environmentPacked fiber temperature sensors were put into microwave environmentand supersonic wave environment. Then the temperature characteristics ofpacked fiber temperature sensors were tested. The results showed that packedfiber temperature sensors were microwave and supersonic wave immune, theoriginal temperature sensitivity were still retained, the linearity and thestability of temperature measurement were very good.The fiber grating temperature sensors which were proposed in this paper havegood temperature resolution of0.02℃, andhave the advantage of microwave, supersonic wave and electromagnetic immune. The fiber grating temperaturesensors can be widely used in medical applications, in particular, magnetic heattreatment and nuclear magnetic resonance.