Medical clinical and animal experiments require accurate and rapid measurement of temperature. Especially in tumor hyperthermia, temperature sensors perform multi-point real-time measurement of tissue temperature while eliminating the problem of traditional thermometers being affected by electromagnetic radiation. Compared with the traditional temperature sensor, the optical fiber temperature sensor can be applied to the biomedical field with its good electrical insulation.
Aiming at the shortcomings of the existing medical temperature sensors, this article finds the fiber temperature sensor-FOT-L-BA, imported from Canada by Industrial Mining Network based on the theory of fiber Bragg grating (FBG) and long period fiber grating (LPFG). This fiber optic temperature sensor is ideal for measuring temperature in extreme environments including low temperature, nuclear environment, microwave and high-intensity RF. They are completely immune to EMI and RFI. At the same time, they are small in size, built-in safety devices for hazardous environments, high temperature, corrosion resistance and high accuracy. Finally, its sensing characteristics are studied. The specific work is as follows:
1. Development and characteristics of medical FBG temperature sensors. Phase mask method was used to etch FBG on ordinary quartz fiber and cladding mode suppression (CMS) fiber, and related experimental research on temperature and bending characteristics was performed. It was found through experiments that the two FBGs carved with two fibers had similar temperature sensitivity, which were 11.5pm / ° C and 10.6pm / ° C, respectively, and had good linearity with a correlation coefficient greater than 0.99. The sensitivity of FBG made of CMS fiber to bending curvature is lower than that of FBG made of ordinary fiber, which is more suitable for measuring human temperature.
2. Research on temperature-sensitive packaging and characteristics of medical FBG temperature sensors According to the principle of temperature-sensitive packaging, FBG temperature sensors are packaged with materials that have a large thermal expansion coefficient and stable temperature change properties, which protect the FBG. At the same time, it has higher temperature sensitivity, better repeatability, linearity and stability. Firstly, epoxy resin was used to encapsulate FBG in polytetrafluoroethylene tube. Although the temperature sensitization effect was obvious, about 12 times that of bare FBG, its linearity was not as good as that of bare FBG. In order not to damage the good linearity of the bare FBG, the FBG is in a free state in the capillary tube. Dispensing at both ends of the capillary tube is used to fix the fiber grating. Capillary glass tubes, capillary steel tubes, and polytetrafluoroethylene tubes were used as the base materials, respectively. The temperature sensitivity coefficients were 8.7 pm / ° C, 38 pm / ° C, and 23.4 pm / ° C, respectively. Linear relationship. In order to avoid the influence of the adhesive on the fiber grating, a double-tube glue-free packaging method is proposed. The packaged temperature sensor has better linearity, and the temperature sensitivity coefficient is 18.9pm / ℃. The experimental results show that the sensitivity of the packaged FBG temperature sensor is not only related to the thermal expansion coefficient, but also closely related to the thermal conductivity of the packaging material.
3. Development of LPFG temperature sensor and study of its sensing characteristics. High-frequency CO_2 laser pulses are used to write LPFG in ordinary quartz fiber. The temperature and bending characteristics of LPFG were studied experimentally. Its temperature sensitivity is about 75 pm/℃, which is about 7.5 times of bare FBG, and it has good linearity. Its transmission peak amplitude is not sensitive to temperature, but sensitive to bending curvature. In order to make it more suitable for engineering applications, a packaging method for filling alcohol is proposed. Two significant resonance peaks appear after packaging. The resonance peak at 1508nm blue shifts with increasing temperature, and the temperature sensitivity is 56.9pm / ℃. The resonance peak at 1472nm shifts red with temperature, and the temperature sensitivity is 531.2pm / ℃, which is 7 times that of bare LPFG and 53 times that of bare FBG. Effectively improve the long-period fiber grating temperature sensing characteristics and avoid interference from other external factors.
4. The packaged fiber grating temperature sensor is tested in microwave and ultrasonic environments. The packaged fiber grating temperature sensor is placed in the microwave environment and the ultrasonic environment and tested for temperature characteristics. Experiments show that the packaged fiber Bragg grating temperature sensor is not affected by microwave and ultrasonic waves, still maintains the original temperature sensitivity, and has good linearity and stability. The fiber grating temperature sensor developed by this project has a resolution of 0.02 ° C, and has the advantages of anti-microwave, ultrasonic and electromagnetic interference. It can be widely used in biomedical fields such as magnetic fluid thermal therapy, nuclear magnetic resonance and other fields with electromagnetic field, microwave and ultrasonic interference.