Motivation

Civil infrastructure is aging in many industrialized countries around the world. Autonomous monitoring of existing civil and industrial structures is of growing interest, as it has the potential to reduce cost for maintenance and repairs drastically, replace tedious, time-consuming and error-prone manual inspections, and allows to detect damage long before the human eye can. Especially in large structures, wireless sensor networks are preferable, as the deployment of cable-bound solutions is very costly. However, communicating with wireless sensors is challenging in many environments, as conventional communication techniques rely on electromagnetic waves, which cannot penetrate metal boundaries, e.g. if sensors are embedded within the structure. Furthermore, powering such devices with batteries requires regular battery replacements, which are costly when sensor nodes are in hard-to-reach places. Wireless power transfer is therefore an attractive solution to power sensor nodes in closed metal containers, such as pressure tanks or pipelines.

Goals and Contributions

Our ongoing research in this project aims to enable battery-free wireless sensor nodes shielded by metal. We, therefore, leverage piezoelectric backscatter communication, in which a sensor node can transmit data by reflecting an existing carrier in the metal with near-zero energy consumption, thereby achieving power consumption as low as several hundreds of microwatts during transmission. At the same time, we investigate acoustic power transfer through metals, supplying the sensor nodes over distances of several meters. To achieve these goals, we adopt recent advances in fields such as radio frequency (RF) energy harvesting and RFID and apply them to acoustic waves. However, the through-metal channel poses special challenges that must be overcome. This includes strong frequency dependency and multipath propagation of signals within the metal structure. In our research, we emphasize the practicability of our approaches. Hence, our work not only encompasses theoretical modeling and simulation, but we also build hardware prototypes from commercially available components and validate our results in practice.