EIT for tactile sensing:considerations regarding the injection-measurement pattern

Abstract

Bipolar current injection and voltage measurement (I–M) patterns are frequently used in electrical impedance tomography (EIT) for tactile sensing. In this work, the total set of 36 unique combinations for 16-electrode systems is investigated using simulations. Performance is evaluated on a circular sensor as a function of hyperparameter and target position with respect to critical performance measures for tactile sensing; these include not only peak amplitude and resolution, but also susceptibility to noise and, importantly, the uniformity of performance over the sensor area. The determination of which pattern to employ can therefore be based on the needs of the particular application. The relative performance of the I–M patterns is determined at small hyperparameters by electrode placement symmetry, but at large hyperparameters by sensitivity at the center of the sensor. Patterns with high spatial symmetry should be avoided; these include electrode pairs on opposite sides of the sensor. Patterns with electrodes in adjacent positions, which have been the norm for tactile sensing, should also not generally be used. If performance on all metrics across a wide range of hyperparameters is needed, then placing both the injection and measurement electrodes 3 spaces apart (the 3–3 pattern) can be a good strategy for the Gauss-Newton 1-step algorithm with the Laplacian prior. The use of 13 electrodes instead of 16 is also examined. The absence of symmetry provides greater flexibility in the choice of I–M pattern, and the loss in performance may be small; furthermore, the reduction in data collection time may be advantageous. Beyond avoiding the worst I–M patterns, the most important measure to take is decreasing noise on the signal to permit the use of a smaller hyperparameter; this is of greater importance than selecting from among the remaining I–M patterns.