Novel, Soft, Water-Filled Acoustic Waveguides for Simultaneous Tactile Force and Location Sensing

Soft force sensing holds potential to mimic human tactile sensation across an array of applications, including electronic skin, soft robotics, and wearable human–machine interaction. However, most current soft sensors are difficult to fabricate, expensive in materials and design to achieve sufficient sensing performance, sensitive to bending, and/or cannot estimate force and location simultaneously. We, thus, propose an innovative soft acoustic waveguide, which is fully assembled by three simple and cost-effective modular elements: a water-filled hollow silicone tube, piezoelectric ceramic transducer, and resin stopper. The sensing mechanism leverages acoustic echo time of flight changes when different locations are touched and magnitude changes when different forces are applied. Theoretical consideration and simulations were conducted to evaluate the feasibility of force and location sensing using guided waves. Experimental results further demonstrated the feasibility of simultaneous force and location tactile sensing and insensitivity to bending, and maximum mean absolute errors for detecting force and location were 0.21 N and 2.32 mm, respectively. This is the first work to propose a water-filled acoustic soft sensor that is bending insensitive for real-time simultaneous force and location sensing and could enable a new genre of soft water-filled sensors for the growing array of new applications involving wearable soft tactile sensing.