Electromechanical Coupling Analysis And Design Of High Sensitivity Micro-mass Sensor Based On Impedance Change

Piezoelectric micro-mass sensor can identify the object by measuring the dynamic response before and after loading mass.With the elegance of extremely high sensitivity and resolution,such sensors have been widely used in microbial measurement,particle detection,environmental and food pollution monitoring and other fields.Ordinarily,the frequency shift or impedance variation is mainly measured through sweeping the exciting frequency by utilizing impedance analyzer or complex frequency capture circuit.However,such measuring process is really time-consuming and it is difficult to be used for real-time monitoring.So,in order to simplify the measurement process and to reduce the measurement cost,the impedance measuring method operating at fixed frequency has been proposed.However,to the best knowledge of the authors,the detecting mechanism has not been theoretically investigated.In this paper,according to the BVD equivalent circuit model,the electromechanical coupling model of piezoelectric micro-mass sensor is established,and also,the expression for describing the impedance based sensitivity is deduced.And piezoelectric cantilever sensor with the total length of 26.0mm is manufactured and corresponding impedance sensitivity(537.5? / mg)is 58.4 times as great as that of the frequency shift method(9.2HZ / mg)with the same dimension.The experimental results adequately verify the correctness of the equivalent circuit model,and thus providing a theoretical basis for the engineering application of high sensitivity micro-mass sensor.The specific work includes:(1)The electromechanical coupling model of piezoelectric micro-mass sensor is established as well as the corresponding sensitivity expression based on impedance change.In order to avoid the time-consuming problem induced by frequency sweeping,a dynamic analysis model of piezoelectric cantilever beam sensor working at specific excitation frequency is established.By solving the equivalent circuit equation of the piezoelectric cantilever beam sensor,the equivalent impedance change before and after loading mass is calculated,and the impedance sensitivity description model is deduced.To further improve the impedance based sensitivity,the influence of excitation frequency and structural parameter on output impedance sensitivity is studied,and the method of selecting excitation frequency is presented.The results show that the impedance output sensitivity is closely related to the response of the cantilever beam,and the impedance measurement sensitivity increases with the increase of the structural parameters(such as length),and the selection of the excitation frequency directly affects the sensitivity.(2)Electromechanical design method for piezoelectric mass sensor.The sensitivity analysis model of piezoelectric sensor with additional external circuit capacitance and inductance is established.The influence of additional series capacitance,inductance and shunt capacitance and inductance on sensor sensitivity is analyzed.The results show that the measurement range and the sensitivity value of the resonant micro-mass sensor can be improved by designing the additional measuring circuit reasonably to meet the application requirements of different environments.