Methods for Detection of Bioimpedance Variations in Resource Constrained Environments

Abstract

Changes in a certain parameter are often a few magnitudes smaller than the base value of the parameter, specifying significant requirements for the dynamic range and noise levels of the measurement system. In case of electrical bioimpedance acquisition, the variations can be 1000 times smaller than the entire measured value. Synchronous or lock-in measurement of these variations is discussed in the current paper, and novel measurement solutions are presented. Proposed methods are simple and robust when compared to other applicable solutions. A common feature shared by all members of the group of the proposed solutions is differentiation. It is achieved by calculating the differences between synchronously acquired consecutive samples, with lock-in integration and analog differentiation. All these methods enable inherent separation of variations from the static component of the signal. The variable component of the bioimpedance can, thus, be acquired using the full available dynamic range of the apparatus for its detection. Additive disturbing signals and omnipresent wideband noise are considered and the method for their reduction is proposed.

Multi-Modal Spectroscopic Assessment of Skin Hydration

“…Depending on the application, improvements to the bipolar topology can be made by employing a four-electrode/tetrapolar configuration, where one pair of electrodes is used to inject the current while the other one carries out the sensing voltage. In the latter, one pair of electrodes injects the current, while another pair measures the voltage, greatly minimising the effects of the electrode–electrolyte interface and enhancing measurement accuracy [ 11 , 12 ].…”

“…The primary source of errors in bipolar bioimpedance systems, including typical corneometers, relates to the electrode–electrolyte double layer introducing a contact impedance that can significantly interfere with the measured value [ 10 ]. As measurements are taken across a range of frequencies (typically up to 1 MHz), the detrimental effect of the contact impedance varies significantly, especially when small electrodes and/or low frequencies are employed [ 11 , 12 ].…”