Study And Design Of Magnetogastrogram Measurement System Based On GMI Sensor

Surface gastric electromagnetic signal is an important basis for the study of gastrointestinal dynamics. The current clinical application of gastric electrical detection system and analysis method, still remain in the level of that in the twentieth Century 80s to 90s, Surface electrode method can only collects the gastric slow wave which is the characterization of gastric contraction rhythm. But it can to collect the gastric electrical fast signal which is the characterization of the contraction strength of stomach. Because of the filtering effect of the fat layer on the gastric electric signal. And because the permeability of the fat layer is approximate to 1, it can be measured by the gastric magnetic signal to acquire the feature of gastric electrical fast wave. To solve this problem, this paper puts forward a method of using the sensor base on the giant magneto impedance effect (GMI) to measure the gastric magnetic signal.To study the mechanism of gastric electromagnetic signals, the parameters of gastric electromagnetic detection system are determined. Discussing the feasibility of the giant magneto impedance effect applied to the gastric electromagnetic signal detection field, through theoretical analysis and experiments, according to density and direction of the magnetic field lines of the stomach on the surface of humans’body, it is put forward that the principle of placing the giant magneto impedance sensor for detecting gastric electromagnetic signals.In the signal data acquisition process, aiming at the low amplitude, low frequency and the low signal to noise ratio, gastric magnetic signal acquisition circuit have been designed. In order to avoid the background noise saturating the amplifier, the amplifier circuit of three amplification mode have been designed. The circuit is also provided with the band-pass filtering function, which can carry out preliminary filtering. Circuit simulation can improve the feasibility of the designed circuit. At the same time, in order to achieve the portable measuring, the bluetooth data transmission circuit have been designed. The wireless data is transmitted between the acquisition circuit and PC. In the PC software design, integrated the powerful real-time display function of Lab VIEW, and powerful data processing function of MATLAB, using Lab VIEW and MATLAB nested programming environment, realizes the PC bluetooth data acquisition and processing of signal denoising.In the analysis and processing of giant magneto signal, the AR power spectrum has been introduced to instead of the traditional power spectrum analysis method. Through the experiments verified that this method can obtain higher resolution in time domain and frequency domain resolution. Considering the nonlinear and nonstationary of the gastric electromagnetic signal, and the interference of cardiac magnetic, intestinal magnetic, baseline drift, muscle electromagnetic, the wavelet analysis and chaos theory combining denoising algorithm is put forward for gastric magnetic signal. In other words, inputing the signal after the wavelet filtering to the chaotic system to denoising again, Duffing intermittent chaotic system have been selected. Through the experiment, it proves the feasibility of the algorithm, extracting the gastric magnetic signal with high SNR.