Design of two-dimensional grid electrodes considering spatial characteristics of SEMG signal

Surface grid electrode is a noninvasive technique, which can be utilized for topographic analysis of EMG signals. Grid electrode increases the uptake area and provides a better picture of spatial and temporal characteristics of muscle activity. Determination of clinical parameters such as muscle conduction velocity, location of innervation zone, firing pattern, size and location of motor unit, are some of the challenging applications of multi-electrode array. However, an optimum grid electrode requires detail examination regarding the dimension and inter-electrode distance of the array. In this paper a systematic approach is presented for selecting a grid spacing to reduce spatial abasing. The characteristics of isotropic layers of subcutaneous fat and skin tissues are incorporated in a computer muscle model in order to analyze their effects on complete potential profile and grid spacing. The variation of spatial cutoff frequency and corresponding inter electrode distance with depth of muscle fiber inside the muscle are simulated in both time and frequency domain for three different levels of accuracy.