| Heart sounds(HS)refer to the sounds produced by vibrations caused by myocardial contraction,heart valve closure,and blood striking the walls of the ventricles and aorta.Heart sounds is one of the most important signals of human body.Heart sound auscultation is one of the most basic methods of clinical assessment of cardiac function status.When cardiovascular disease has not developed enough to produce clinical and pathological changes,the murmurs and distortions that appear in heart sounds are important diagnostic information.Traditional auscultation methods cannot record heart sounds.Auscultation effect was influenced by subjective factors such as experience,skills and hearing of doctors.At present,many heart sound sensor have the characteristics of large size.During the application,only a single area signal is detected,and researchers cannot study the relationship between different regions.In order to solve the above problems,this thesis designs a new mini heart sound sensor,and analyzes the principle of propagation.The main research contents are as follow.(1)Design a heart sound sensor.In this paper,the volume of the sensor is small,and the sensor has a high spatial resolution.According to the characteristics of human heart sounds and application environment,the author has formulated design standards.The components of the sensor were chosen carefully by the author,and the software of Altium Designer was used to design the sensor circuit.In order to increase the sensitivity of the sensor,the housing of the sensor is designed.To collect human heart sound array signal,the author designed multi-channel acquisition device.(2)Test sensor performance.Firstly,test sensor performance parameters.Secondly,test the accuracy and stability of the sensor.At last,test the difference between sensors.The test results show that the amplitude-frequency response bandwidth of the sensor is 20 Hz ~ 20000 Hz,and SNR is 24 dB.The sensor can work stably for a long time.And there are very few differences between sensors.When multiple sensors are applied to the surface of human body,heart sound array signals can be collected.(3)Research on the relationship between heart sound channels based on linear system.Heart sound signal in different regions are significantly different.In the same intercostal space and adjacent intercostal space,the heart sound signals were collected by multiple mini heart sound sensors simultaneously.This paper uses a linear system to simulate the relationship between different channels.First,preliminary processing of heart sound signals,includes Butterworth de-noising,wavelet de-noising,zero-phase filtering,etc.After heart sound de-noising,normalize the heart sound,and use frequency response method to simulation the relationship of different channels.Fourier Transform the signal,and the author will get the frequency domain function of the signal,then use frequency domain function to get the transfer function of the system.Now,the system has be emulated by the model.Then simulate the output signal through the model,and evaluate the performance of the model.The model is evaluated from two aspects.For the time domain,the model is evaluated by root mean square error.For the frequency domain,the model is evaluated by power spectral density.Evaluation results shows that the root mean square error of the model output signals and the original output signals is 0.0895,and the power spectral density in the frequency domain is relatively close.It can be seen that the linear system could simulate the relationship between different channels to a certain extent.The research is helpful to aid people understand the propagation relationship of heart sound signals.In summary,the heart sound sensor can effectively collect human heart sound array signals,and the linear system may simulate the relationship between different channels. |
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