Innovative 3-D Printing Processing Techniques for Flexible and Wearable Planar Rectennas

This work demonstrates the use of a low-cost, lossy, flexible substrate processed by novel 3-D printing techniques which significantly mitigate its intrinsic losses, thus providing performance comparable to those of traditional substrates. These processing techniques are applied to both microstrip and coplanar waveguide structures; they are first derived theoretically, starting from the electromagnetic theory of modes propagation, then numerically validated by full-wave analysis, and finally experimentally verified. The design of a miniaturized 868 MHz rectenna, adopting a coplanar-fed patch antenna based on the proposed fabrication approach, is presented. By means of nonlinear/electromagnetic co-design, the antenna is directly matched to the rectifier. A 30-dB power range starting from -20 dBm is considered. Direct matching allows to get rid of a dedicated matching network and its associated losses, resulting in a slight efficiency increase and a significant reduction of the overall dimensions. Finally, the 3-Dprinted prototype is presented: the overall rectenna performance proves that design freedom enabled by 3-D printing paves the way to the use of low-cost flexible dielectric materials, even with poor electromagnetic properties, to realize wearable battery-free wireless nodes.