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

This article presents 16and 81-element broadband rectenna arrays screen printed on a cotton tee-shirt for harvesting 4-130-μW/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 λ
₀
/6 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 P
_dc
= 32 μW for incident power densities of 4 μW/cm
²
, with a dc load of Rdc = 2 kQ. At higher incident power density levels of 100 μW/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.