Spatially Selective Filter Design for High-Resolution EMG Arrays

A new technique for designing EMG spatial filters with optimized spatial selectivity is described. Simulations were used to model an action potential (AP) as a tripole source within the muscle, and to calculate the voltage induced at an array of surface monopolar electrodes. Next, a map of desired spatial filter output voltages was created as a function of the location of an AP beneath the array. Linear least squares was used to solve for the filter weights which optimally matched the desired filter outputs to those resulting from the tripole model. The optimized filters were found to be consistently superior to the conventional normal double differentiating filter. Selectivity was a function of the simulated inter-electrode spacing and the number of electrodes in the array.