Common-Mode Voltage Reduction in Capacitive Sensing of Biosignal Using Capacitive Grounding and DRL Electrode

Abstract

A capacitive measurement of the biosignals is a very comfortable and unobtrusive way suitable for long-term and wearable monitoring of health conditions. This type of sensing is very susceptible to noise from the surroundings. One of the main noise sources is power-line noise, which acts as a common-mode voltage at the input terminals of the acquisition unit. The origin and methods of noise reduction are described on electric models. Two methods of noise removal are modeled and experimentally verified in the paper. The first method uses a passive capacitive grounding electrode, and the second uses an active capacitive Driven Right Leg (DRL) electrode. The effect of grounding electrode size on noise suppression is experimentally investigated. The increasing electrode area reduces power-line noise: the power of power-line frequency within the measured signal is 70.96 dB, 59.13 dB, and 43.44 dB for a grounding electrode area of 1650 cm2, 3300 cm2, and 4950 cm2, respectively. The capacitive DRL electrode shows better efficiency in common-mode noise rejection than the grounding electrode. When using an electrode area of 1650 cm2, the DRL achieved 46.3 dB better attenuation than the grounding electrode at power-line frequency. In contrast to the grounding electrode, the DRL electrode reduces a capacitive measurement system’s financial costs due to the smaller electrode area made of the costly conductive textile.

Digital Control and Demodulation Algorithm for Compact Open-Loop Fiber-Optic Gyroscope

“…However, this approach requires a larger circuit layout area, which is unsuitable for developing a small-volume open-loop fiber-optic gyroscope. It has been found that most noise results from the gyro’s electric source and ground wire [ 22 ], which is independent of the modulation polarity. According to Equation (12), because J 1 ( ϕ m ) is an odd function, the error can be easily eliminated by flipping the modulation polarity regularly and changing the output polarity simultaneously.…”

Sensors, Circuits, and Systems for Biomedical Applications

“…A number of investigations are currently underway to overcome the issues associated with measuring signals from the human body and existing signal measurement methods. In this Special Issue, four articles focus on this issue [ 5 , 6 , 7 , 8 ]. Ben Atitallah B. et al present a systematic comparison of methods for bioimpedance spectroscopy (BIS) measurement, including the use of a gain phase detector (GPD), IQ demodulation, and fast Fourier transform (FFT), with a focus on magnitude and phase measurement accuracy, signal processing, hardware and software complexity, and power consumption [ 5 ].…”

“…Bednar T. et al explored the use of capacitive bio-signal measurement for long-term and wearable monitoring but highlighted its susceptibility to environmental noise, particularly power-line noise. Their paper describes the origin of noise and proposes two electric models for its reduction: a passive capacitive grounding electrode and an active capacitive driven right leg (DRL) electrode [ 8 ].…”