Research On Temperature-humidity-pressure Wireless Passive Sensor For Internet Of Things Applications

This paper presents a wireless passive multi-parameters(pressure,temperature,humidity)sensor based on the theory of capacitive-inductance resonant(LC)mutual inductance coupling technology,and fabricated with LTCC process,which is aimed to use at different environmental conditions such as intelligent industry,intelligent agriculture and other related fields.Reasonable structural design and process methods was adopted to achieve multi-parameters sensors measurement,with the advantage of miniaturization and high reliability.Firstly,the wireless measurement principle of passive integrated multi-parameters sensor is introduced,and the pressure sensitive mechanism,temperature sensitive mechanism and humidity sensitive mechanism of the sensor are described respectively.The influence of inductance and capacitance on the performance of the sensor were considered according to the relevant design experience,and the practicability of the process,the inductance and capacitance values are determined within a reasonable range.Multi-parameter sensor overall structure is much complex,through a reasonable layout of the capacitive and inductance position,the improvement of the sensitivity of the sensor is achieved.Finally,the comparison of the substrate material,the interdigital electrode material and the moisture-sensitive material was carried out,and the most suitable materials were selected for the design and preparation of the sensor.Then sensor of single parameter sensor and integrated multi-parameter integrated sensor is simulated by HFSS,ADS and other electromagnetic simulation software.The comparison of the two results shows the key points and difficulty of multi-parameter sensor design,and also validates the multi-parameters sensor design,and determined the multi-parameter sensor processing size,which laid a good foundation for the preparation and measurement of sensors in next steps.Then the sensor is thermally and mechanically simulated,the maximum stress and maximum sensitive membrane deformation can be obtained and the whole sensor can achieve the uniform heating.After that,the HTCC ceramic based single parameter passive humidity sensor was prepared first,and then the LTCC process was used to realize the monolithic integrated preparation of three parameters(temperature,humidity and pressure)sensor.Finally,the wireless passive sensor is measurement and analyzed accordingly.In order to verify the feasibility of passive humidity sensor wireless measurement,the humidity sensor is preliminary tested.The experimental results show that the humidity sensor has a good humidity response and provides a good experimental basis for the next wireless passive multi-parameters sensor measurement.Then,the multi-parameters sensor was tested under the temperature and pressure composite environment and temperature and humidity composite environment,respectively.The effects of temperature,humidity and pressure on the wireless passive sensor signal were explained.Experiments show that the temperature parameters not only affect the temperature sensor,but also interfere with humidity and pressure sensor signals.Changes in humidity parameters only affect the humidity sensor changes,the impact of temperature and pressure sensors are negligible;pressure parameters only affect the pressure sensor,the impact of temperature and humidity sensor are negligible too.