Estimation of stray coupling capacitances in biopotential measurements

Abstract

Biopotential measurements are very sensitive to electromagnetic interference (EMI) from power-lines. Interference conditions are mainly imposed by electric-field coupling, whose effects can be described by coupling capacitances. The main of them are the patient-to-ground and the patient-to-power-line capacitances, usually denoted as C(B) and C(P), respectively. A technique to estimate these elements and experimental data obtained in different environmental conditions are presented. It was found that C(B) ranges from hundreds of pF to nF, and C(P) from hundredths of pF to few pF. The presented technique also lets it know the small amplifier-to-ground and amplifier-to-power-line capacitances. The knowledge of all these capacitances allows estimating the EMI conditions that biopotential amplifiers can be subject to, thus, resulting useful data for specifying their design requirements and constraints in real working conditions.

Variation-Aware System Design Simulation Methodology for Capacitive BCC Transceivers

“…In a later work, body-to-ground capacitance was experimentally measured between 136 pF to 273 pF for sitting and standing positions touching different objects [52]. The highest value for body-to-ground capacitance was found to be 3932 pF when metallic object was being touched in the standing position [52]. This shows that body-to-ground capacitance is effected when body is touching grounded objects.…”

“…the value of body-to-ground capacitance was measured between 110 pF to 3.9 nF at different locations for different situations in [51]. In a later work, body-to-ground capacitance was experimentally measured between 136 pF to 273 pF for sitting and standing positions touching different objects [52]. The highest value for body-to-ground capacitance was found to be 3932 pF when metallic object was being touched in the standing position [52].…”

“…This shows that body-to-ground capacitance is effected when body is touching grounded objects. Common mode voltage of front end amplifier is also affected by body-to-ground capacitance and other stray impedance as measured in [52]. The value of body-to-ground capacitance has been estimated by using finite element method in [30] for capacitive body coupled communication but the maximum estimated value is 4.2 pF.…”

A fast method to estimate body capacitance to ground at mid frequencies

“…It is also an intervening factor in the assessment of human body impedance for risk analysis in case of electric contacts [3] or electromagnetic radiation [4] and in electrostatic discharge studies [5], and has strong influence in power-line interference in biopotential measurements [6][7][8]. Finally, changes due to body capacitance are the sensing principle of capacitive tactile, proximity [9] and seat occupancy sensors [10].…”

“…Body capacitance to ground can be measured by using a grounded oscilloscope and a passive 10:1 voltage divider probe [6,7], or a variable resistor, an amplifier and a voltmeter with grounded reference terminal [8], that estimate the power line (50/60 Hz) current through the body. These methods, however, heavily depend on the strength of existing power line fields and on the resistance of the contact with the body, hence on contact pressure.…”