Location-Dependent Performance of Large-Area Piezoresistive Tactile Sensors Based on Electrical Impedance Tomography

The technique of electrical impedance tomography (EIT) has been recognized as a promising method to design tactile sensors with continuous sensing capability over a large area. The mechanism of electrical impedance tomography allows reconstructing tactile information within the sensing area based on measurements made only at the boundary. However, spatial performance of EIT-based tactile sensors has demonstrated location dependency, which severely affects correct interpretation of tactile stimuli. Here, we analyzed the effect of hyperparameter on the spatial performance, in terms of amplitude, size, position error, and shape deformation in the reconstructed images. To obtain uniform sensitivity throughout the entire sensing area, we developed an intensity scaling method to correct reconstructed amplitudes based on simulation studies. A diagonal scaling matrix was developed for a symmetric circular sensing area, and the scaling value were constructed according to the radial positions of the finite elements. The correction method was further evaluated on a compliant EIT-based touch sensor made of polymer filled composites with underlying paddings. We found that the developed method effectively produced a more uniform sensitivity distribution, and improved spatial profiles of shape deformation. The findings shown here help better interpret the strength information of tactile stimuli located at different positions of large area EIT-based sensors.