Signal modes for design-oriented analysis of active sEMG spatial filter electrodes

Abstract

In this work, the signal modes necessary for the analysis of amplifiers for double differential and normal double differential electrodes are obtained for the first time. Superficial electromyographic (sEMG) electrodes may have multiple dry contacts with particular geometric arrangements in order to better pick up signals originated in motor units just below the electrode while rejecting other EMG signals. The amplifiers used for these electrodes are thus not differential and in order to evaluate their performance, the commonly used decomposition into common mode and differential mode is not applicable. Hence, a set of orthogonal signal modes were derived considering linear combinations of the input signals of a selection of spatial filter amplifiers. The first signal mode was associated with the desired output and the second to common mode electromagnetic interference, but there are other modes present in the amplifier that account for EMG crosstalk interference. The rejection coefficients associated with these modes were derived and the obtained laws were applied to a comparison of two double differential electrode circuit designs.