Since most of the contact conduction type of heart sound sensors don’t take into account the acoustic signal attenuation problem caused by the heart sound signal transmitting to a sensor whose filling materials’ impedance is different to human soft tissue, the signal-to-noise ratio (SNR) of the heart sound sensors is not very well. Human heart is immersed in blood. If the sensor’s core sensitive element can be immersed in fluid, the attenuation of heart sound signal may be decreased greatly. Inspired by the principle of hydroacoustic signal’s detection, this paper proposes the design of heart sound sensor based on the bionic vector hydrophone. Then theoretical analysis and finite element method (FEM) simulation about the sensor have been carried out. Combined sensitivity with resonant frequency, the optimum dimension of the sensor’s structure has been determined. The sensor’s micro-structure has been fabricated by using Micro-Electro-Mechanical System (MEMS) technology and coupling encapsulated by choosing a kind of medical coupling agent as the filling material. Finally, the performance of the proposed sensor is tested. The fact is that the proposed sensor can work well with either healthy people or patients with heart disease. The obtained data clearly show that: the SNR of the proposed heart sound sensor is superior to 3200-type of 3M Littmann 8.2 dB.
In this paper, an electronic stethoscope is designed based on a bionic Micro-Electro-Mechanical System (MEMS) sound-sensitive sensor. Inspired by the strong sound reflection effect of the water-air interface, a double-sided diaphragm MEMS electronic stethoscope (DMES) encapsulated by a novel double-sided diaphragm packaging is proposed. The double-sided diaphragm packaging's superiority is verified by comparing a single diaphragm MEMS electronic stethoscope (SMES) with DMES. The frequency of the clinical heart sound signal is mostly in the range of 20-600 Hz. Finite simulation results show that for the same incident sound source, the sound pressure level inside double-sided diaphragm packaging is 4dB higher than that of single diaphragm packaging in this frequency band. Furthermore, the actual auscultation test results show that the signal-to-noise ratio (SNR) of DMES reaches 41.3dB, which is 2.2dB higher than SMES. Besides, comparing the heart sound signals collected by DMES and a commercial electronic stethoscope (Model 3200, 3M Littmann, USA), the high consistency of the two signals' characteristic parameters in the time domain and frequency domain proves the feasibility of DMES. Finally, DMES has the advantages of low cost, and its SNR is 10.2db higher than that of the 3M electronic stethoscope. All these show that DMES has a broad prospect in the popularization of basic medical treatment.
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