EchoTube: Robust Touch Sensing along Flexible Tubes using Waveguided Ultrasound

While pressing can enable a wide variety of interesting applications, most press sensing techniques operate only at close distances and rely on fragile electronics. We present EchoTube, a robust, modular, simple, and inexpensive system for sensing low-resolution press events at a distance. EchoTube works by emitting ultrasonic pulses inside a flexible tube which acts as a waveguide and detecting reflections caused by deformations in the tube. EchoTube is deployable in a wide variety of situations: the flexibility of the tubes allows them to be wrapped around and affixed to irregular objects. Because the electronic elements are located at one end of the tube, EchoTube is robust, able to withstand crushing, impacts, water, and other adverse conditions. In this paper, we detail the design, implementation, and theory behind EchoTube; characterize its performance under different configurations; and present a variety of exemplar applications that illustrate its potential.