Signal Conditioning provided by Sensitive Elements of Electric Bioimpedance Sensors

Abstract

Dry polarizable electric bioimpedance sensors for ECG (electrocardiogram) monitoring requires the use of signal conditioning electronic circuits that take over alternating ΔU voltages with a frequency of 40 kHz and peak-to-peak amplitude in the range of 10-50 mV. The sensitive elements of these sensors are made of sensitive materials like as conductive polymer polypyrrole or hybrid nanocomposite with 10 and 20% Ag incorporated in the polypyrrole polymer. The useful signal is picked up in differential mode by an instrumentation amplifier. The gain of the instrumentation amplifier is set to A = 100 by connecting a single external resistor, RG. The problem of eliminating the mass loops and obtaining a common mode signal is solved by using an amplifier with galvanic isolation, with the amplification factor A = 1, supplied with double differential voltage. To reject any parasitic signals that may accompany the useful signal, an electronic bandpass filtering module is used. Electrical measurements were performed which showed the accuracy of the signal amplified by the electronic instrumentation amplifier module used in the "differential mode" connection.