External parasitic elements on clothing for improved performance of wearable antennas

Abstract

A small (30 mm נ50 mm נ8 mm), waterproof 2.45 GHz wireless sensor with a standard meander line printed monopole has poor radiation characteristics when placed against the human body. A suitably optimized H-shape (step impedance resonator) parasitic element was added next to the antenna of the sensor on outer surface of clothing fabric. The parasitic element was placed on the outside of a fabric armband and was found to increase the total efficiency of the antenna by 13% in simulation results and enhanced the measured gain by 3 dB. The technique ensures that the armband is comfortable, washable, flexible, and operates successfully without wired connectors. The technique was optimized using simulation and experimental measurements with an adhesive aluminum strip. As the wireless sensor is waterproof and there is no access to the port of the antenna in the sensor, a two ray ground reflection model was used to match the received power in the spectrum analyzer using least rms curve fitting.