Abstract
<title>Abstract</title> <p>Soft robots, owing to their inherent compliance and safety, are ideal for human–machine interaction and applications in unstructured environments. However, proprioception, which is a prerequisite for intelligent interaction, remains difficult to achieve in soft systems. Conventional metal foil strain gauges, featuring low hysteresis and a high signal-to-noise ratio (SNR), are the standard for surface strain measurement; yet their intrinsically nonstretchable nature precludes their use on deformable bodies. Existing flexible strain sensors have addressed stretchability, but generally suffer from signal hysteresis and low SNR; more critically, the bending, twisting, and compressive deformations that accompany soft-body motion introduce severe crosstalk into the output. Here we present a sliding-electrode de-shorting strain sensor that brings near-metallic sensing quality into a flexible architecture via the de-shorting mechanism. The sensing core consists of an elastomeric cavity filled with ionic liquid and a pair of metallic sliding electrodes inserted deep into the cavity. In the initial state, the metallic electrodes electrically short the ionic liquid in the radial direction, confining the signal generation to a small region between the two electrodes. As the sensor is stretched, the electrodes recede relative to the cavity; the ionic liquid previously in the radial region is progressively released from the shorted state and joins the conduction path, and the impedance magnitude changes accordingly. Since the signal is generated essentially by the geometric redistribution of the ionic conduction path under the control of the rigid sliding electrodes, and not by aspect-ratio changes of a flexible material or by percolation-network evolution, the sensor simultaneously achieves low hysteresis and a high SNR approaching those of metal strain gauges. The sliding de-shorting architecture further shields interference signals generated by bending, twisting, and compression in the shorted region, giving the sensor intrinsic insensitivity to off-axis deformation. The sensor exhibits a hysteresis of 0.23% over 0–30% strain, an SNR of 59 dB at 1% strain, an equivalent input strain noise as low as 11 µε, and a maximum stretchability of 70%. Under 360◦ bending, 360◦ twisting, and 50% compression, the output fluctuation remains below 0.5% of the full-scale signal. We integrated the sensors onto an unactuated elastic silicone pillar and, relying solely on the sensors’ own signals as feedback, reconstructed in real time the approximate three-dimensional configuration of the pillar under coupled bending–twisting deformation. The “liquid–rigid–soft” transition design demonstrated here offers a general route to near-metallic sensing quality in flexible systems.</p>