Broadband mechanoresponsive liquid metal sensors

Abstract

Stretchable electronics have the fundamental advantage of matching the complex geometries of the human body, providing opportunities for real-time biomechanical sensing. We report a method for high-frequency AC-enhanced resistive sensing that leverages deformable liquid metals to improve low-power detection of mechanical stimuli in wearable electronics. The fundamental mechanism of this enhancement is geometrical modulation of the skin effect, which induces current crowding at the surface of a liquid metal trace. In combination with DC sensing, this method quantitatively pinpoints mechanical modes of deformation such as stretching in-plane and compression out-of-plane that are traditionally impossible to distinguish. Here we explore this method by finite element simulations then employ it in a glove to detect hand gestures and tactile forces as well as a respiratory sensor to measure breathing. Moreover, this AC sensor uses lower power (100X) than DC sensors, enabling a new generation of energy-efficient wearables for haptics and biomedical sensing.

3D Woven Liquid Metals for High-Frequency Stretchable Circuits

“…As the signal frequency increases, these phenomena concentrate current density near the conductors' outer surface, increasing ohmic losses. [11,[32][33][34] The skin effect occurs due to the formation of circulating eddy currents, which null current density at the center and produce a current density that decreases exponentially as a function of depth with a characteristic length scale, δ, the skin depth. This skin depth (δ) is characteristic of a conductor with a given resistivity ( ) and permeability ( ), de ned mathematically as:…”

“…However, this magnetic energy storage is counterbalanced by losses originating in the series resistance of the windings while subjected to direct current (DC) and alternating current (AC). For instance, when subjected to high-frequency excitation using alternating current (AC), inductors incur extra resistive losses in addition to their inherent DC resistance (R dc ) [11][12][13] . Figure 1b shows an electrical model of an inductor that accounts for interwinding capacitance and the frequency-dependent AC resistance (R ac ).…”

Twin‐Wire Sensor Networks

“…As another example, we have also demonstrated a twin-wire network of 29 photoresistors. The proposed strategies can provide crucial advantages for high-density 4-wire interfacing of arrays of resistive or impedance sensors, independently on materials (conventional or nano-cracked metals, [2,[30][31][32] liquid metals, [33] etc. ), signal to be measured (temperature, strain, blood flow, light, etc.…”

Electrochemically-driven actuators: from materials to mechanisms and from performance to applications

“…[355][356][357][358] These properties have expanded their applications in fields like flexible sensors, wearable electronic devices, biomedicine, exoskeleton systems, and soft robotics. [359][360][361][362] LMs have demonstrated remarkable deformability and mobility in both aqueous and non-aqueous environments, 363 making them promising for soft actuators. Several LM-based soft actuation methods, including electrochemical actuation, are being developed for pumps, soft robots, and motors.…”