Design Of 12?13GHz RF Temperature Measurement System Based On Polymer Derived Ceramic Sensor

Polymer Derived Ceramics sensor is a kind of wireless passive sensor which can measure high temperature.The sensor is based on the principle of resonant cavity.When the temperature of the sensor changes,the resonant frequency of the sensor also changes,and each temperature value corresponds to its resonant frequency.According to this characteristic,the RF signal of a frequency band is sent to the sensor,then the reflected signal of the sensor is analyzed,and the resonant frequency is obtained,so that the temperature value can be obtained.The design idea of this paper can be divided into two points: one is how to generate RF signals in a frequency band and transmit RF signals to sensors;the two is how to collect reflected signals from sensors and get the resonance frequency through reflected signals.The 12~13GHz RF temperature measurement system based on Polymer Derived Ceramics sensor is divided into controller module,signal generator module,signal conversion module,signal acquisition module and LabVIEW host module.This system uses FPGA as the controller,control the production of the banner LMX2592 baseband signal source generates RF signals required by frequency doubler,RF signal through the circulator and waveguide antenna wireless transmission to the sensor;sensor by RF excitation will produce a reflection signal,it also receives the reflected signal through the waveguide antenna;reflection signal received by detector after conversion into voltage signal can be collected,and collected by the AD converted into digital signal;the FPGA controller then processed the data collected by AD through filtering and so on,and finally got the resonant frequency.Through heating test of the sensor,the variation of the resonant frequency at 25~350°C is obtained.The measured resonant frequency and the real-time temperature displayed on the heating platform are fitted to the data in LabVIEW software,and the fitting function relation is finally obtained.In the later measurement,the FPGA controller directly transforms the measured resonant frequency into the temperature value in the display module through the fitting function relation between the resonant frequency and temperature.The experiment shows that the resonance frequency of the sensor has decreased by100.9MHz from 25~350°C,that is,the average frequency of every degree of centigrade,theresonance frequency has decreased by 310.46 KHz,and its resolution is 0.0032°C/KHz.Under the condition of constant temperature,the resonant frequency of the sensor will have a jump less than 900 KHz,so the temperature measurement accuracy is about 2.88°C,which meets the design requirements of the temperature measurement system.