Research On Humidity Sensor And Performance Based On QCM

In modern society,environmental humidity detection is not only closely related to human production and social activities,but also has important influences on industrial production,agricultural planting,meteorology,environmental protection,aerospace,national defense and other fields.With the development of the times and the advancement of technology,the market's performance requirements for humidity sensors are becoming higher and higher.In recent years,capacitive and resistive humidity sensors have been the most widely used.But they all have some shortcomings.The capacitive humidity sensor has low measurement accuracy,poor corrosion resistance,and it is difficult to measure in a high humidity environment,while the resistance type humidity sensor has poor linearity and product interchangeability,and it's sensitivity in low humidity environment is insufficient.Therefore,it is of great significance to develop a humidity sensor with high sensitivity,fast response,small wet hysteresis,good linearity and low cost.This paper studies the humidity sensor based on Quartz Crystal Microbalance(QCM),which has the advantages of high sensitivity,good stability,good linearity,small size,wide working range and simple structure.The QCM humidity sensor uses a humidity sensitive film on the surface of the quartz crystal resonator electrode as a sensitive component.The quartz crystal resonator acts as a transducer element,converting the quality change of the electrode surface into a change of the corresponding electrical signal(frequency)output from the oscillation circuit,thereby realizing the measurement of humidity.The structure,physical properties,frequency temperature characteristics,piezoelectric effect,measurement principle,energy trapping theory and mass sensitivity of quartz crystal resonator are analyzed.The coating amount of humidity sensitive film is obtained according to Sauerbery equation,and it's influence to the performance of QCM humidity sensor is analyzed.And the formula for calculating the equivalent circuit parameters of quartz crystal resonator is derived.The formula has certain guiding significance for the improvement of QCM humidity sensor;after theoretical research,the suitable QCM sensor for detecting environmental humidity is selected,and ordinary oscillation circuit is adopted as the method of quartz crystal resonator signal acquisition.FPGA is chosed to design software and hardware,then it is used to measure the output frequency of the oscillation circuit;the QCM humidity sensor detection platform is built to analyze the sensitivity,linearity,repeatability,short-term stability,wet hysteresis and response/recovery time of the QCM humidity sensor.The experimental results show that the detection range of the humidity sensor is 15.1%RH-97.3%RH,with good linearity and repeatability,the sensitivity is 22.4Hz/%RH,the stability frequency amplitude within 25Hz,the wet hysteresis is 3%RH,the response time within 29s,the recovery time within 11s,the QCM humidity sensor met the expected requirements.