Design Frequency-Dependent Ion Dynamics for Deformable Shear Sensors with Stimuli Decoupling

Abstract

Advancements in wearable technology have expanded its applicability across diverse fields, from healthcare monitoring to artificial prosthetics. Wearable sensors, designed to mimic human tactile sensations and perceive various stimuli, have become increasingly convenient for users. To ensure seamless interaction with the human body, these sensors require deformable materials that remain soft and flexible. Researchers have extensively studied components composed of polymer-metal composites and polymer-ion conductors, which exhibit modulus and stretchability akin to biological tissues. However, due to the nature of sensors that rely on a single electrical signal for stimulus detection, differentiating between multiple stimuli concurrently applied remains a challenge. This thesis explores the development of tactile sensors using frequency-dependent ion dynamics to separate and identify mechanical stimuli. In this work, shear force sensing with pressure decoupling and omnidirectional shear force perception were implemented. First, I designed the ionic conductor for the proper mechanical and electrical properties of the sensor. By adjusting the materials and ratios of component, impedance could be controlled. Electrical characterization was conducted by bode plot and equivalent circuit. Second, I proposed an ionic conductor-based shear force sensor array utilizing electrical double-layer capacitance. Columnar structure was introduced to easily detect the shear force. Ion gels surrounding columnar electrodes enable the detection of shear forces by measuring the increasing capacitance with applied force. The high capacitance than conventional dielectric materials (~nF), facilitates to construct arrays without noise interference. The sensor was applicated to computer mouse for precise control where mouse movement aligns with shear force direction and speed corresponds to shear force magnitude and 3 x 3 sensor array was applied to a robotic hand to monitor shear force distribution when lifting objects. Third, I proposed a sensor capable of distinguishing between pressure and shear forces by leveraging frequency-dependent ion dynamics. Decoupling pressure and shear forces was demonstrated by collecting data at two different frequencies (20Hz and 10kHz). The sensor design incorporated four direction electrodes on a single ion gel, enabling recognition of shear forces in all directions. The research demonstrated the real-time monitoring of pressure, shear forces, and shear force direction during practical motions performed by a robot, such as pouring water, opening bottle caps, or placing books on shelves, indicating its potential for practical applications in daily life.