Novel Electronic Tuned Quartz Crystal Sensor And Its Applications

Sensor technology is a high and new technology in the world,and an important part of the Internet of Things(IoT).In the context of deepening the application demonstration of the IoT,as requested in the IoT fascicule of development plan for information and communication industry(2016-2020)issued by the Ministry of Industry and Information Technology(MIIT),digital sensor has become one of the hot research directions of IoT sensor because of its advantages of direct access to digital system and anti-interference ability.The electronic tuned quartz crystal sensor is a resonant digital sensor with a quartz crystal and a detection electrode in series.Based on quartz crystal electronic frequency modulation effect and using the electrode as a sensing unit,the detection electrode parameter variation caused by the measured object can be converted into frequency signal output characterized by high sensitivity,good stability,digital signal output,and many other advantages.Combining theoretical analysis and experimental research,this thesis takes an exhaustive research on the electronic tuned quartz crystal sensor technology,and achieves the detection of displacement,salt solution concentration and humidity based on the electronic tuned quartz crystal sensor technology.The main innovative works in this thesis are summarized as follows:(1)Based on capacitance frequency modulation theory and frequency deviation theory of quartz crystal,a capacitance tuned quartz crystal sensor with inductance sensitization is proposed.The equivalent electrical model of the sensor is established,and the capacitance-frequency response expression of the circuit is derived.Both the numerical simulation results and the actual circuit test results show that the capacitance-frequency response sensitivity of the capacitance tuned quartz crystal sensor can be enhanced by introducing an inductance element.On this basis and combined with a planar capacitance probe,we have designed a highly-sensitive capacitance tuned quartz crystal displacement sensor.The sensitivity of its displacement detection is three times that of the conventional capacitance tuned quartz crystal displacement sensor.This study provides a practical method for improving the response performance of capacitance tuned quartz crystal sensors from the perspective of circuit optimization.(2)The inductance frequency modulation effect of a quartz crystal series inductor circuit is studied.On the basis of establishing the equivalent circuit model,and combining the resonance theory of oscillation circuit,the inductance-frequency response expression of the equivalent circuit is derived.The numerical simulation results of the expression coincide with test results in view of the actual circuit,which demonstrates the rationality of the expression.The theoretical basis of inductively tuned quartz crystal sensor is established.Combining with a plane inductance coil and the eddy current theory,an inductance tuned quartz crystal micro-displacement sensor has been realized.Relevant test results show that this sensor has a high displacement resolution and a good frequency stability.(3)Taking advantage of the inductance-frequency response characteristics of the quartz crystal series inductor circuit,and combining with a planar spiral inductance probe,an inductance tuned quartz crystal salt solution concentration sensor is constructed and proposed.Salt solution concentration information can be directly converted into resonant frequency of the sensor.The experimental results show that the sensor has a linear response to different concentrations of copper sulfate solution,and the response sensitivity can reach 50 Hz/mM.In addition,the sensor is characterized by fast response and recovery performance,and the response and recovery time is both less than one second.This work implements a high performance salt solution concentration sensor with digital frequency output.(4)By utilizing GOQD materials as humidity sensitive film,a highly-sensitive IDE-PQCR humidity sensor with digital frequency output was constructed.The sensor's humidity sensing characteristics,such as response property,hysteresis property and dynamic response and recovery property,are studied.Experimental results show that the proposed GOQD based IDE-PQCR humidity sensor has a high sensitivity which is four times of the GO based IDE-PQCR humidity sensor.Considering the modulation theory of IDE-PQCR circuit and the infiltration mechanism of water molecules in GOQD film,an impedance-frequency modulation mechanism is presented to explain the humidity sensing principle of the proposed sensor.This work provides a new research idea for building highly-sensitive digital humidity sensors.