A Skin-Like Hydrogel for Distributed Force Sensing Using an Electrical Impedance Tomography-Based Pseudo-Array Method

Abstract

Hydrogels are compliant biomaterials that can be integrated with robotic systems to act like human skin for sensing and perception during interactions with their environments. The conventional method for fabricating skin-like hydrogel sensors is based on an array-type design which contains numerous discrete sensitive elements to obtain touch locations and force information. Array-based sensors are complex, with tiny communication units that make manufacturing complicated and expensive. Electrical impedance tomography (EIT) is a noninvasive imaging technique that can be easily implemented to create large-area tactile sensors into a "one-piece" structure without any internal wires. However, EIT-based tactile sensors suffer from low spatial resolution and sensitivity in areas far from the electrodes. This paper introduces a pseudo-array method to remedy the effect of location-dependent sensitivity on the spatial sensing of EIT-based hydrogel sensors and improve their performance for practical applications in detecting distributed contact forces without any arrays or internal wires. As a preliminary study, a skin-like hydrogel-based tactile sensor with an area of 400 cm 2 was fabricated using a simple manufacturing process. The entire piece of the tactile sensor is then divided into a 5 × 5 array, which is referred to as a pseudo-array for simulation and experimental calibration. Each "pseudo-array" unit was calibrated to obtain the mapping relationship between the force and the reconstructed conductivity. Subsequently, a quantitative relationship between the touch force and the EIT measurement for the hydrogel-based tactile sensor for continuous sensing was achieved. Finally, the real-time performance of the EIT-based hydrogel sensor demonstrates that the proposed pseudo-array method can realize more accurate force detection with an error of 1.62 N (10.15% of the maximum force) for sensing distributed force over a large area of 400 cm 2 with only 16 boundary electrodes.

In situ Electrical Impedance Tomography for Visualizing Water Transportation in Hygroscopic Aerogels

“…This indicates that the polymer skeleton of an aerogel acts as a high-speed water transport pathway, expediting the sorption kinetics and enhancing water absorption. [9,45] These Figure 5. Verification of the EIT technique for real-time detection of the water uptake process and the hygroscopic mechanisms of LiCl@ECAs.…”

“…Moreover, researchers have verified the feasibility of the mapping relationship between the force and the reconstructed conductivity of the hydrogel (without salt) based on the EIT strategy. [8,9,53] Therefore, composite hygroscopic sorbents with conductivity have the potential to be visualized using the EIT system when there are observable changes in their conductivity, such as during drying and moisture absorption.…”

“…[7,8] By applying small electrical currents to a given sample and recording the response voltages at the sample surface, EIT reconstructs a conductivity map, providing valuable insights into the underlying structures and activities within the sample. [9] This technique has found applications in various fields such as petrochemicals and biomedicine. It is commonly used to estimate the two dimensional distribution of oil, gas, and water in multi-phase flow transportation pipelines.…”

A Jacobian vector correction method for the force calibration of EIT-based tactile sensor

“…The force calibration tests were conducted to calibrate the force sensing capabilities of the EIT-based tactile sensor proposed in this study. We used a XYZ stage equipped with a commercial force gauge (SH-100, NSCING, China) to precisely apply touch force at a specified location [9]. A range of touch forces from 0.0 to 4.0 N were applied, and five time series samples were recorded for each test.…”

“…In a previous study, a pseudo-array method was introduced for force calibration, which virtually divided the surface of a large-area EIT-based sensor into several equal areas for im-age reconstructions and established the mapping relationship between the force and the reconstructed conductivity for each "pseudo-array" unit [9]. This method still entails extensive data collection, resulting in reduced accuracy and universality.…”