Tham khảo tài liệu 'overview of fiber optic sensors phần 2', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Figure 18. Blackbody radiation curves provide unique signatures for each temperature. Another type of spectrally based temperature sensor is shown in Figure 19 and is based on absorption 22 . In this case a Gallium Arsenide GaAs sensor probe is used in combination with a broadband light source and input output optical fibers. The absorption profile of the probe is temperature dependent and may be used to determine temperature. GaAs Figure 19. Fiber optic sensor based on variable absorption of materials such as GaAs allow the measurement of temperature and pressure. Fluorescent based fiber sensors 23-24 are being widely used for medical applications chemical sensing and can also be used for physical parameter measurements such as temperature viscosity and humidity. There are a number of configurations for these sensors and Figure 20 illustrates two of the most common ones. In the case of the end tip sensor light propagates down the fiber to a probe of fluorescent material. The resultant fluorescent signal is captured by the same fiber and directed back to an output demodulator. The light sources can be pulsed and probes have been made that depend on the time rate of decay of the light pulse. End Tip Fluorescent Material Etched Figure 20. Fluorescent fiber optic sensor probe configurations can be used to support the measurement of physical parameters as well as the presence or absence of chemical species. These probes may be configured to be single ended or multipoint by using side etch techniques and attaching the fluorescent material to the fiber. In the continuous mode parameters such as viscosity water vapor content and degree of cure in carbon fiber reinforced epoxy and thermoplastic composite materials can be monitored. An alternative is to use the evanescent properties of the fiber and etch regions of the cladding away and refill them with fluorescent material. By sending a light pulse down the fiber and looking at the resulting fluorescence a series of .
