RF-Harvesting Tightly Coupled Rectenna Array Tee-Shirt With Greater Than Octave Bandwidth

• Published in: IEEE transactions on microwave theory and techniques Vol. 68; no. 9; pp. 3908 - 3919
• Main Authors: Antonio Estrada, Jose, Kwiatkowski, Eric, Lopez-Yela, Ana, Borgonos-Garcia, Monica, Segovia-Vargas, Daniel, Barton, Taylor, Popovic, Zoya
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.09.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antenna arrays; Antenna measurements; Bandwidths; Broadband; Broadband antennas; Cotton; Density measurement; Energy harvesting; Impedance; Pattern analysis; Power measurement; rectenna; Rectennas; Schottky; Schottky diodes; screen printed; Simulation; tee-shirt; Torso; wearable
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2020.2988688

This article presents 16- and 81-element broadband rectenna arrays screen printed on a cotton tee-shirt for harvesting 4-130-<inline-formula> <tex-math notation="LaTeX">{\mu }\text{W} </tex-math></inline-formula>/cm 2 power densities between 2 and 5 GHz. A packaged SMS7630-079LF Schottky diode is connected with silver paint and soldered to each element of the array. The diode impedance over frequency as a function of dc load and input power is analyzed using source-pull harmonic-balance simulations. The antenna is a quasi-self-complementary tightly coupled bow-tie array with a period of about <inline-formula> <tex-math notation="LaTeX">{\lambda _{0}/6} </tex-math></inline-formula> at the highest frequency. The impedance at the element ports of the array and the array radiation pattern are analyzed with source-pull diode complex impedance port terminations. Full-wave simulations are performed with the cotton fabric on top of specific tissue layer stack-up for a human torso, as well as for a body phantom. Measurements using a water-filled phantom show up to <inline-formula> <tex-math notation="LaTeX">{P_{\mathrm{ dc}}=32}\,\,{\mu }\text{W} </tex-math></inline-formula> for incident power densities of 4 <inline-formula> <tex-math notation="LaTeX">{\mu }\text{W} </tex-math></inline-formula>/cm 2 , with a dc load of <inline-formula> <tex-math notation="LaTeX">{R_{\mathrm{ dc}}=2}\,\,\text{k}{\Omega } </tex-math></inline-formula>. At higher incident power density levels of 100 <inline-formula> <tex-math notation="LaTeX">{\mu }\text{W} </tex-math></inline-formula>/cm 2 , up to 32% efficiency is measured. Measured rectified voltage and efficiency for the wearable tee-shirt are in good agreement with phantom measurements for the 81-element array. In addition, the effects of body curvature, air layer between tee-shirt and skin, and washing of the fabric are quantified in either simulation or measurements.