Ultrastable Soft Capacitive Tactile Sensor with Impedance-Modulated Signal

Soft capacitive tactile sensors are widely employed in human-machine interfaces and wearable devices due to their high sensitivity, temperature stability, and low energy consumption. However, the electrical connections between soft capacitive tactile sensors and measurement circuits introduce parasitic capacitance and series resistance, which compromise stability. While coaxial cables and shielding layers are typically used to suppress electromagnetic interference, their nonstretchable and multilayer structures hinder the structural flexibility and robustness of soft sensors. To address this challenge, inspired by biological pulse-coded signals, we propose an ultrastable soft capacitive tactile sensor with impedance-modulated signal. The impedance-modulated sensor converts capacitive signals into impedance-modulated signals by constructing a series resonant circuit, achieving ultrastability against the parasitic and stray capacitance as well as series resistance. The mechanism of the impedance-modulated sensor is theoretically and numerically analyzed, and demonstrated by experiments. In addition, we discovered that compressive stress decreases the equivalent series resistance (ESR) of the liquid metal elastomer used as the dielectric in the capacitive sensor, which in turn affects the impedance-modulated signal. The mechanism of the variation in ESR is analyzed through simulations and experiments. Finally, the applications of the impedance-modulated sensor in human-machine interaction interfaces and wearable electronics are demonstrated.