Micro-mass Sensor Based On Parametric Bifurcation Of Piezoelectric Actuated Pre-stressed Bistable Structures

The relatively low quality factor for resonant micro mass sensors operating in damping environments has become a critical issue to hinder their practical applications.Different from the traditional linear elastic resonant micro-mass sensor,the parametric bifurcation of the nonlinear structures has been introduced to avoid the damping influence on the sensor performance.And then,the piezoelectric micro-mass sensor incorporating one linear basic elastic beam and pre-stressed bistable structure is proposed,which integrates the functions of both mass weighing and threshold mass switching.Additionally,the dynamic characteristics of nonlinear structure parametric vibration are studied and the influences of the excitation amplitude,frequency and micro-mass adsorption location on the micro-mass sensing threshold and sensitivity are systematically analyzed.The specific work includes:(1)The dynamic characteristic of nonlinear pre-stressed bistable cosine beam is studied,and the influences of the axial displacement,the excitation load and the configuration of cosine beam on the bifurcation frequency are analyzed,thus resulting a amplitude based bifurcation frequency modulating method is proposed,which is really crucial for designing nonlinear micro-mass sensors.(2)A novel piezoelectric nonlinear mass sensor was designed by utilizing the linear and nonlinear pre-stressed bistable structure which shows parametric bifurcation phenomenon.And then,the accurate relationship between the bifurcation frequency shift and the added mass is obtained as well as the sensitivity and the quality factor.With the established design method,a new bifurcation based micro-mass sensor was designed with the dimension of 58.0mm,4.0mm and 0.2mm for the base elastic structure and 22.0mm span for the bistable pre-stressed structure.The corresponding sensitivity and quality factor are 542.0Hz/g and 192,which are 3.31 and 6.91 times of those of the same size resonant micro-mass.Furthermore,the influence of the excitation amplitude and location of the added mass on the bifurcation frequency has been systematically analyzed.(3)A new threshold mass switch was designed by utilizing the snapping characteristic of the pre-compressed bistable beam.While the external mass load reaches the threshold value,the vibration amplitude of the bistable beam varies sharply.Also,the effects of the excitation(voltage amplitude and frequency)and the mass adsorption location on the minimal detectable mass are analyzed.Comparing with the weighing mass sensor with the same dimension size,the minimal detectable mass can reach 0.2mg.(4)The nonlinear micro-mass sensor was fabricated for experimental validation.And the measuring system is established including the piezoelectric excitation system,laser sensor,Labview,and computer.The measured weighing sensitivity and minimal detectable mass can reach 575.0Hz/g and 0.2mg.The nearly consistence between the simulation and experimental results adequately validated the feasibility of the proposed design method for the micro mass sensor.