A Novel Surface LC Wireless Passive Temperature Sensor Applied in Ultra-High Temperature Measurement

In this paper, we demonstrate a passive wireless surface temperature sensor, based on a high-temperature cofired ceramic process and a thick-film technology, which is functional up to 1400 °C. In addition, we propose a temperature measurement technique that makes use of the absolute amplitude of the S 11 parameter. The sensor comprises an inductor (created from platinum) deposited on a ceramic substrate (99% alumina), making it cheap and easy to fabricate using a screen-printing technology, due to its simple structure. The use of temperature resistant materials, and a completely passive structure, means that this sensor is robust to harsh environments. The device operates using the principle of LC resonance, illustrated in this paper with a lumped circuit model. The dielectric constant of the substrate increases with increasing temperature, leading to a monotonic variation in the resonant frequency of the sensor, which is retrieved wirelessly via a readout antenna. We set the test distance between the sensor and the antenna to 10 mm and observed a repeatable response between 26 °C and 1400 °C. S 11 amplitude and resonant frequency are used to reflect the change temperature, respectively. And we found that it is more accurate to test the temperature by resonant frequency after comparing the experimental results. The average sensitivity of temperature test by resonance frequency is obtained, which is 14.3 kHz/°C.