Design and development of wearable fluidic antenna with AMC

Abstract

In recent years, most wearable antennas are used for emergency and rescue services, tracking purposes, military applications and monitoring human physiological parameters. Design of antennas for wearable applications is challenging due to their operation in the vicinity of human body which causes interference, thus affecting the overall performance. The main reason is because human body absorbs electromagnetic waves emitted from antennas, which leads to the reduction of antenna efficiency when they are placed near to the body. Besides, their electromagnetic (EM) radiation are possibly harmful to human health in the long term when exposed excessively. The objective of this project is to design, develop and fabricate wearable fluidic antennas with low Specific Absorption Rates (SAR) and good resistance to water and moisture. To reduce the impact of the user on the antenna and provide a safe emission level, Artificial Magnetic Conductor (AMC) is a suitable solution. They are typically designed to filter and reflect possible EM wave propagating at predefined sets of frequencies towards a certain direction. A flexible wearable fluidic antenna embedded in a polydimethylsiloxane (PDMS) structure integrated with a liquid metal AMC plane is presented. The antenna is designed based on the operating principles of a patch antenna with slots and slits to cover its operation in the 2.45 GHz and 5.8 GHz wireless communication bands. The first design, denoted as Antenna Design 1 (AD1) is implemented on a PDMS substrate, its AMC is formed using copper sheet, and its radiator using liquid metal Eutectic Gallium Indium (EGaIn). AD1 achieved a gain of 3.58 dB at 2.45 GHz with a bandwidth of 85 MHz, and 6.08 dB at 5.8 GHz with a bandwidth of 278 MHz. For SAR, all planar and bent conditions of AD1 did not exceed 2 W/kg based on the European regulatory requirement. The second design, denoted as Antenna Design 2 (AD2) was designed to improve the drawbacks of AD1, using PDMS as its substrate and Galinstan as the conducting elements of both the AMC and radiator. The main innovation of this work is the integration of an antenna and AMC plane fully made using liquid metal embedded into PDMS to enable a highly flexible and robust antenna, besides potentially adding tunable feature to the structure in the near future. AD2 showed a bandwidth of 80 MHz and 460 MHz in the lower band and upper band, respectively, with gains of between 5.2 and 4.12 dB. In terms of SAR, all planar and bent conditions for AD2 did not result in SAR exceeding 2 W/kg, indicating its safe use as wearable antenna. Finally, experimental validated has indicated that the fluidic antenna is improved in terms of resistance to water compared to textile antennas.