Design And Optimization Of Electronic Stethoscope Based On MEMS Acoustic Sensor

The number of deaths from cardiovascular diseases has increased year by year and has become a major public health problem globally.Electronic stethoscopes have many advantages in the field of early cardiovascular diagnosis and are being widely used in the medical field.If the heart sound signal collected by the electronic stethoscope is applied to telemedicine and artificial intelligence diagnosis,it needs to have enough accurate and abundant data.However,limited by the sensors used,different electronic stethoscopes have their problems.This thesis proposes to apply MEMS acoustic sensors to auscultation and optimizes the sensor microstructure for auscultation applications so that the sensitivity and bandwidth of the sensor system can meet the needs of auscultation;in order to maximize the advantages of MEMS acoustic sensors,the overall packaging structure is designed to maximize the acoustic-electric conversion efficiency of the MEMS acoustic sensor.First of all,this thesis analyzes the beam stress and resonance frequency of the original sensor microstructure theoretically,determines the optimization direction of the sensor microstructure,and designs an“umbrella”high-sensitivity sensing microstructure.On the basis of meeting the bandwidth requirements of auscultation,this sensitivity achieves an increase of 4.75 times.Secondly,based on the study of the influence of the viscosity of the packaging liquid on the resonance frequency of the sensing system,deionized water is determined as the optimal sound transmission medium.Based on the sound transmission theory,the influence of the material and thickness of the sound-transmitting diaphragm on the sound transmission efficiency is analyzed,and a PET film with a thickness of 0.02mm is designed as the sensor encapsulation sound-transmitting diaphragm.In addition,a two-dimensional finite element model of acoustic wave transmission in different media was established,which confirmed that the sound pressure level in the single-film package under the action of the sound field was higher than that in the double-film package.Finally,the influence of the shape of the package shell on the sensing performance was analyzed through three-dimensional simulation,and the optimal package shell shape was determined.Based on the above theoretical simulation research,this thesis encapsulates the"umbrella"sensing microstructure and pre-processing circuit to make a MEMS electronic stethoscope prototype,and conducts clinical heart sound auscultation test together with the commercial product 3M 3200 electronic stethoscope.Studies have shown that the heart sounds collected by the two electronic stethoscopes show a high degree of consistency in the time domain and frequency domain.In addition,the signal-to-noise ratio(SNR)and sensitivity of the MEMS electronic stethoscope proposed in this thesis have also been preliminarily measured and calibrated.Its vibration sensitivity is about 0.572 vs~2/m.It has superior performance and has important engineering application prospects.