Design and Manufacturing of Equipment for Investigation of Low Frequency Bioimpedance

Abstract

The purpose of this study was to highlight a method of making equipment for the investigation of low frequency bioimpedance. A constant current with an average value of I = 100 µA is injected into the human body via means of current injection electrodes, and the biological signal is taken from the electrodes of electric potential charged with the biopotentials generated by the human body. The resulting voltage, ΔU is processed by the electronic conditioning system. The mathematical model of the four-electrode system in contact with the skin, and considering a target organ, was simplified to a single equivalent impedance. The capacitive filter low passes down from the differential input of the first instrumentation amplifier together with the isolated capacitive barrier integrated in the precision isolated secondary amplifier and maintains the biological signal taken from the electrodes charged with the undistorted biopotentials generated by the human body. Mass loops are avoided, and any electric shocks or electrostatic discharges are prevented. In addition, for small amplitudes of the biological signal, electromagnetic interferences of below 100 Hz of the power supply network were eliminated by using an active fourth-order Bessel filtering module. The measurements performed for the low frequency of f = 100 Hz on the volunteers showed for the investigated organs that the bioelectrical resistivities vary from 90 Ωcm up to 450 Ωcm, and that these are in agreement with other published and disseminated results for each body zone.

Bio-potential noise of dry printed electrodes: physiology versus the skin-electrode impedance

“…Baseline noise is one of the most critical parameters in electro-physiological measurements, in particular in applications where very low signals (in the μV range) are anticipated. Commonly, noise values are predicted from the electrode-skin impedance which is used to quantify the quality of the interface and to predict contact quality (Grimnes 1983, Huigen et al 2002, Kim et al 2014, Krachunov and Casson 2016, Roy et al 2020, Pi ̂slaru-Dănescu et al 2022, Xie et al 2022. In wet electrodes, the conducting gel reduces the skin-electrode impedance and ensures low baseline noise levels (Li et al 2017).…”