Design and performance analysis of body wearable textile patch antenna

Abstract

Owing to small size, patch antenna can be embedded in compact devices useful for measurement of some physical phenomena. One major application of patch antenna is in health care devices for continuous measurement and transmission of different bio-signals of human body. This type of bio-sensors with patch antenna can be embedded in garments for continuous monitoring with increased safety level and comfort of the wearer. Due to the low mass, high flexibility and easy to integrate into garments textile antennas are useful for wireless communications as reported in the literature. In present work, focus has been made to design a body wearable textile antenna working at 2.4 GHz of frequency, suitable for ISM band. Then performance of designed antenna is investigated separately on different textile substrates like wash cotton, curtain cotton, polyester and polycot with different dielectric constant and thickness. Performance parameters like return loss, gain and directivity in all cases are observed,analysed and compared. As wearable antenna have to be worn on body so all antennas are further tested on a flat body surface as well bending condition also. For this a body phantom model having different dielectric layer like muscle, fat and skin having dielectric constant and thickness have been used. Being a lossy medium, human body absorbs the back radiated power towards the body. These back radiations increase the body temperature and increases the specific absorption rate which is undesirable and harmful for user. To address this concern in case of bending antenna, EBG is used to decrease the back radiation and an improved SAR is observed. EBG is acting as a high impedance surface at the designed frequency and blocks the back radiations toward the body and directs maximum radiations in desired direction. By using the EBG material with ground plane SAR value of antenna have been reduced by approximately 98% of its value without EBG.