Design And Realization Of Acquisition Device For Milli-volt Bioelectric Signals

Surface EMG is widely used in the diagnosis of neuromuscular function diagnosis,assessment of the degree of muscle fatigue and disease diagnosis. In modern times, the study of artificial limb is extensive, and the control of the artificial limb is mainly derived by the surface EMG. Therefore, it has an important significance to develop a convenient, practical and cost-effective EMG acquisition circuit. Surface EMG is neuromuscular electrical signal,which is recorded from the skin surface by the electrodes, and it is a kind of weak and unstable signal.The design and realization of the surface EMG signal acquisition device is introduced in the paper. The amplifying circuit, which is designed by the amplifier AD620, magnify primary the original EMG signal in the design. The amplifying circuit adopts AD620 to magnify primary the original EMG signal in the design. In the design of acquisition circuit, in order to reduce the influence of the interference signal, the high-pass filter circuit, the low-pass filter circuit, and the frequency notch filter circuit are designed. Firstly, the simulation software Multisim is used to make sure the correctness of the circuit in principle.Then using discrete components to build circuits, and producing relevant PCB diagrams to test by Altium Designer. The Real-time EMG signal is collected finally.In the test experiment, EMG can be collected through physical movement and using weak DC to stimulate median nerve. In the article, it uses the time domain and frequency domain Methods to study and analyze the collected EMG. We analyze on the time-frequency of fist EMG when move the limb, it accords with the general features of EMG signal. In electrical stimulation experiments, As can be seen from the time-domain waveform, when stimulate at the rising edge of the square-wave voltage, the upward EMG pulse waveform is obtained at the starting point, when stimulate at the falling edge of the square-wave voltage,the downward EMG pulse waveform is obtained at the starting point, therefore the EMG signal is verified to be the result of the electric field gradient effect. In the spectrum analysis,the FFT in Matlab is used to analysis the EMG signal frequency spectrum. When the limb motions, fist signal frequency ranges between 0Hz and 500 Hz is the more concentrated, and when the frequency ranges between 50 Hz and 200 Hz, the amplitude is higher. In electrical stimulation experiments, it can be draw that as the stimulus voltage increases, the different frequencies of nerve EMG amplitude also increased. Stimulation under the different voltages,the main frequency of nerve electrical signal is 67.5676 Hz, in the band-pass filter range 0Hz and 500 Hz, the amplitude of EMG signal increases gradually from DC to main frequency, the amplitude nerve electrical signal decreases gradually from main frequency to 500 Hz.