Ultrasmall-button-shaped Rectifier Module Tied with Conductive-yarn Antenna for Wearable Accessories Powered by Microwaves

This paper describes a gamma match method for light-emitting diode (LED) textile accessories with a conductive-yarn antenna. A textile rectenna structure that has an ultrasmall-button-shaped rectifier module tied with a conductive-yarn antenna makes it possible to perform gamma match simply by moving the module on the antenna element. Since the movement of the module with gamma matching section causes the feeding point on the antenna element to vary, the impedance of the antenna is changed and we can perform impedance matching. To verify the effectiveness of our textile rectenna structure, we fabricate a button-shaped rectifier module 4.5 mm in diameter including an LED and a 6-cm-long bundled conductive-yarn antenna consisting 0.5-mm-thick single yarns. For 2.45-GHz wireless power transmission with an average transmitted power of 1 W, the experimental results show that the LED on the rectifier module blinks while dissipating power of 1.23 mW at a distance of 50 cm from the wireless transmitter. We also fabricated a friendship bracelet and a pair of embroidered socks equipped with our rectenna as LED textile accessories. We show that the LED blinks at a distance of 30 cm from the wireless transmitter when people wear these accessories.