Preparation And Characteristics Of Wireless Passive Temperature And Humidity Sensors

Recently,temperature and humidity sensors are very important.They have an important role and huge demand in many industries such as agriculture,industry,medical industry,and bioengineering.However,with the development of science and technology,traditional sensors are unable to meet the detection demands in harsh environments.The aging of batteries and wires also makes traditional sensors rely on manual maintenance and replacement.Therefore,research on wireless passive temperature and humidity sensors can meet the demands under these special conditions.Without a power supply,these sensors can reduce their sizes,save cost,and theoretically their lives are close to infinity.Based on the principle of LC resonant circuit and a reasonable process,LC resonant wireless passive Temperature and humidity sensors are developed.Firstly,the principle of the LC resonant circuit is introduced in this article.The inductive coil coupling method is used to achieve wireless and passive testing of the sensors.After considering the influence of the inductive capacitance on the sensor performance,the variable dielectric constant type capacitive sensor type is chosen.After studying the sensitive mechanism of temperature and humidity sensors,the sensor models were determined according to their respective needs.The temperature adopts the upper and lower plate capacitance structure,and the humidity uses the interdigitated electrode structure.The appropriate substrate material and electrode material are selected for these sensors.A variety of structural sizes and parameters of single-parameter sensors have been determined.Temperature sensors have been designed with capacitors in series with circular inductance coils and square inductance coils;humidity sensors with interdigital electrode series weakly coupled inductance coils and common inductance coils are designed.Through MATLAB simulation calculation of the designed sensors' structure under the conditions of 0-100? and0-100%RH,the optimal structures are selected,and the responses of these single parameter sensors are obtained.The screen printing process was used to prepare these sensors.Through the reasonable construction of the temperature and humidity test platform,the performance of the LC resonant wireless passive temperature sensor and humidity sensor aremeasured respectively.When the temperature changes from 15? to 85?,the resonance frequency of the LC resonant wireless passive temperature sensor is reduced by65.53 MHz.When the humidity changes from 11.3% RH to 97.3% RH,the resonance frequency of the LC resonant wireless passive humidity sensor is reduced by 31.6MHz.The test result showed the feasibility of the single-parameter sensors,and the sensitive structural of the integrated LC resonant wireless passive temperature and humidity sensor are designed,and finally the integrated LC resonant wireless passive temperature and humidity sensor is prepared.The performance of the temperature and humidity compound sensor was carried out in a compound environment test.Test results showed that the sensor's resonant frequency changes when temperature and humidity change.The sensitivity of the temperature sensing unit is-0.2725 MHz /?,and the sensitivity of humidity sensing unit is-0.426MHz/%RH.The test results also prove that the wireless passive sensor can meet the wireless passive detection of temperature and humidity.