Energy-Harvesting Fabric Antenna

In this chapter the exploitation of novel fabrics, in place of standard substrates and metallizations, in the realization of radio-frequency energy harvesting systems, commonly referred as rectennas, rectifying antennas, for Body Area Network applications is deeply discussed. 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 prototypes 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, the dispersive/nonlinear behavior of the entire rectenna. In this way the actual available power at the rectifier input port are accurately taken into account. The procedure is deeply described in this chapter through the step-wise 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 in 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.