Energy-harvesting fabric antenna

Abstract

The exploitation of novel fabrics, in place of standard substrates and metallizations, in the realization of radio-frequency energy-harvesting systems - commonly referred to as rectennas, rectifying antennas - for body area network applications is deeply discussed in this chapter. The use of these unconventional materials makes the design approach a delicate issue: firstly, the electromagnetic characterization of fabrics is needed; furthermore, the effects of bending of the whole system as well as the proximity to human tissue must be considered in the optimization procedure. The consequences of an approximate approach in the design of wearable rectennas could lead to significant deviations from the final prototype performance. For these reasons, we consider a computer-aided platform, which relies on the combination of full-wave solvers and nonlinear circuit-level tools, through the rigorous application of the electromagnetic theory: this way, the unavoidable electromagnetic couplings between different system sections and the dispersive/nonlinear behavior of the entire rectenna. In this way, the actual available power at the rectifier input port is accurately taken into account. The procedure is deeply described in this chapter through the stepwise analysis of the project of a fully wearable, fully autonomous tri-band rectenna. The experimental characterization of the prototype is used to provide a validation of the design procedure. The two-step procedure consists of the design of the rectenna with a fixed load in radio-frequency (RF) stationary conditions followed by the transient baseband design of the power management unit which acts as a dynamically variable load, depending on the actual incident RF power.