Electrodes for Clinical Measurement of Bio-electric Potentials: Impedance and Spatial Selectivity

Abstract

The rapid increase in use of physiological measuring and myo-electric control equipment has led to renewed interest in certain properties of measuring electrodes. In gait studies and multi-channel myo-electric control applicatons the spatial selectivity of electrodes assumes prime importance. Development of surgically-implanted myotelemetry control systems, and use of single motor units or small segments of muscle as control sites make this topic even more critical. In all measurements, but particularly in myo-electric control, achievement of stable electrode-to-tissue interface impedance is a prerequisite for reliability.

In this paper, the results of a series of surface electrode measurements are presented, indicating the effects of electrode design, skin preparation and choice of electrode paste upon magnitude and variation of electrode-to-tissue impedance. The balance of the paper is devoted to a discussion of spatial selectivity of electrodes. Experimental data concerning crosstalk measurements on multi-channel myo-electric control systems are presented. Electrode design for specific selectivity is discussed, with examples of special-purpose electrodes developed in the research programme of this Institute.