A Flexible 2.45-GHz Power Harvesting Wristband With Net System Output From −24.3 dBm of RF Power

• Published in: IEEE transactions on microwave theory and techniques Vol. 66; no. 1; pp. 380 - 395
• Main Authors: Adami, Salah-Eddine, Proynov, Plamen, Hilton, Geoffrey S., Guang Yang, Chunhong Zhang, Dibin Zhu, Yi Li, Beeby, Steve P., Craddock, Ian J., Stark, Bernard H.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-01-2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antennas; Boost converter; Broadband; Efficiency; Energy harvesting; fabric antenna; fabric-to-PCB connector; Fabrics; Impedance matching; Insertion loss; Internet of Things; Materials selection; Microstrip; Microstrip antennas; Microstrip transmission lines; Permittivity; Power management; Radio frequency; rectenna array; rectenna impedance matching; Rectennas; RF energy harvesting; RF power transfer; smart fabric; Substrates; T-resonator method; textile antenna; two-line method
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2017.2700299

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.