Research On Sapphire Fiber Black Body Cavity High Temperature Sensor

High-temperature environment is very common in the industrial production, military, aerospace such as steel melting, crystal growth, rocket plume, cannon. Usually, high temperature is measured by thermocouple, infrared radiation or other traditional methods. It's not easy for the thermocouple to conduct a long-term and continuous measurement for its unstable physical and chemical properties of materials under high temperature. The non-contact type infrared radiance thermometer although has a higher gauge limit, the emissivity of heat source must be known and it's susceptible to the interference of background radiation. Besides, the measured result is only the surface brightness instead of the true inside one. Optical fiber sensing technology is one of the hotspots in recent years, figured as resistance to the electromagnetic interference, fire-proof, fast response and so on. The high temperature sapphire fiber-based temperature sensing technology, avoiding the influence of the effective emissivity of the object, as well as stray light from space influence or environmental change, is capable of high temperature applications in harsh environments, and with the outstanding advantages of fiber optical sensor, suitable for long-term stability of temperature detection.This paper describes the design and specific fabrication of the high-temperature sensor based on sapphire fiber blackbody cavity. The sensor is based on the basic theory of blackbody radiation, using the chamber in the end of the sapphire fiber formed by sputter-coated film as the temperature sensing media, and as a direct contact with the high temperature heat source, complies the sensing of high temperature. In this paper, finite-element analysis is adopted by ANSYS to optimize the parameters of the cavity structure. The fabrication involves sputtering of the cavity, coupling of the fibers, and packaging of the probe. The methods and processes are easy to achieve with low cost and good feasibility in the laboratory.The high-temperature experiments are taken for the sensor and spectral distribution of the sensor output signal is obtained, which is close to the standard blackbody. The relationship between the output and the measured temperature is tested, increasing exponentially with temperature's increase. It can be conformed that there is a good linear relationship between the sensor output and the temperature, and the sensor has the characteristics of good high-temperature sensing.