A Multibeam and Surface Plasmonic Clothing With RF Energy-Localized Harvester for Powering Battery-Free Wireless Sensor

Abstract

A wearable radio-frequency (RF) energy-localized harvester with multiple antennas and spoof surface plasmon (SSP) structure for multibeam radiation is presented to power the Bluetooth sensor module. The harvester contains four separate antennas connected by SSP waveguides, while the loop is applied to excite the structure to generate multibeam radiation and improve energy harvesting. The radiative waves will be harvested and converted into surface waves on the SSP waveguides, then, confined in a localized area of the structure through the evanescent field interactions between the current of SSP and the loop in a contactless way. More importantly, it is free of RF connectors and soldering works on the interface between the energy harvester and clothing. In addition, the wearable energy harvester is entirely made of flexible materials, such as conductive fabrics, polyimide, and nylon fabrics in a compact and low-profile structure. The loop can easily be integrated with the rectify circuit and power management unit (PMU) to provide direct-current (dc) power for different kinds of wireless sensor modules. In this design, the harvested power can support a battery-free Bluetooth temperature and humidity sensor with a power density of 2.75 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The complete system-level demonstration of RF energy harvesting shows the potential to power small electronic devices for wearable applications.