Abstract
This paper presents a flexible 2.45-GHz wireless power harvesting wristband that generates a net dc output from a −24.3-dBm RF input. This is the lowest reported system sensitivity for systems comprising a rectenna and impedance-matching power management. A complete system has been implemented comprising: a fabric antenna, a rectifier on rigid substrate, a contactless electrical connection between rigid and flexible subsystems, and power electronics impedance matching. Various fabric and flexible materials are electrically characterized at 2.45 GHz using the two-line and the T-resonator methods. Selected materials are used to design an all-textile antenna, which demonstrates a radiation efficiency above 62% on a phantom irrespective of location, and a stable radiation pattern. The rectifier, designed on a rigid substrate, shows a best-in-class efficiency of 33.6% at −20 dBm. A reliable, efficient, and wideband contactless connection between the fabric antenna and the rectifier is created using broadside-coupled microstrip lines, with an insertion loss below 1 dB from 1.8 to over 10 GHz. A self-powered boost converter with a quiescent current of 150 nA matches the rectenna output with a matching efficiency above 95%. The maximum end-to-end efficiency is 28.7% at −7 dBm. The wristband harvester demonstrates net positive energy harvesting from −24.3 dBm, a 7.3-dB improvement on the state of the art.
Highlights
F LEXIBLE RF electronics has many applications in onbody and off-body communications for: healthcare [1], RFID body-centric sensing [2], wearables [3], protectiveManuscript received November 28, 2016; revised March 6, 2017 and April 13, 2017; accepted April 16, 2017
This paper reports, for the first time, a flexible and wearable end-to-end RF-harvesting system, that is designed to operate over a range exceeding 2 m at Wi-Fi transmit power levels (100-mW EIRP)
The flexible fabric antenna is coupled to the rigid rectifier and boost converter, using broadside-coupled microstrip lines
Summary
F LEXIBLE RF electronics has many applications in onbody and off-body communications for: healthcare [1], RFID body-centric sensing [2], wearables [3], protective. This paper reports, for the first time, a flexible and wearable end-to-end RF-harvesting system, that is designed to operate over a range exceeding 2 m at Wi-Fi transmit power levels (100-mW EIRP). The flexible fabric antenna is coupled to the rigid rectifier and boost converter, using broadside-coupled microstrip lines. This system is optimized to operate at a power of −20 dBm in the center of the 2.4-GHz ISM band. This paper presents advances in various areas: antenna, rectifier, interconnection design, and power management. It validates the approach through both simulation and measurement of individual components and through experimental results from a complete system implementation.
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