Design And Applications Of Tissue Coupled Piezoelectric MEMS Acoustic Transducer

Acoustic transducers can be employed as sensors and actuators,applied in detecting or regulating human’s biomedical parameters.Recently,the piezoelectric acoustic transducers based on microelectromechanical system(MEMS)technology have the benefits of small size,low cost,high performance,low power consumption,good integration,and better biocompatibility,showing a great potential in the applications of wearable and implantable biomedical devices in recent years.However,current studies about piezoelectric MEMS acoustic transducers focus on the air coupled and water coupled devices,and there is a lack of research on the tissue coupled devices and their systematic investigation.This thesis focused on the design principle of the tissue coupled piezoelectric MEMS acoustic transducers and analyzed their resonance mode and no-resonance mode.Facing regulating human’s biomedical parameters,this thesis investigated the feasibility of an implantable application which employed resonance piezoelectric MEMS acoustic transducers to realize wireless nerve electrical stimulation.Facing detecting human’s biomedical parameters,this thesis explored the feasibility of an wearable application which used no-resonance piezoelectric MEMS acoustic transducers to measure heart sounds.The detailed research contents and results are as following:(1)This thesis analyzed the resonance mode and no-resonance mode of piezoelectric MEMS acoustic transducers.Based on the Lamb waves and their mode shapes,the low-frequency flexural mode was investigated as it is suitable for tissue coupling.According to the vibration operation,a lumped parameter equivalent circuit model and a finite element analysis mode were built,and another circuit model for the devices with high acoustic radiation impedance was studied,which was suitable for the tissue coupled devices.In addition,the design principle of resonance mode and no-resonance mode was analyzed.(2)Based on the resonance piezoelectric MEMS acoustic transducers,this thesis firstly proposed tissue coupled wireless nerve electrical stimulation.Facing this application,this thesis designed and fabricated transducer arrays,and characterized their electrical and acoustic performances.A matching circuit was designed to improve the efficiency of wireless energy transfer.The system and integration of the wireless neural stimulator were investigated.Finally,a wireless neural stimulator with the size of 5×5.5×2.4 mm~3 was implanted into a rat,realizing the electrical stimulation of its sciatic nerve.(3)Based on the no-resonance piezoelectric MEMS acoustic transducers,this thesis firstly proposed tissue coupled heart sound monitoring.This thesis designed and fabricated a MEMS transducer based on triangular cantilevers.After integrating the designed signal processing circuit and the MEMS transducer,the sensitivities and noise densities of the sensor were analyzed and measured.The MEMS electronic stethoscope was fabricated after packaging,realizing the detection of human heart sounds and higher SNR than the commercial product.