The recent advancement in the wireless technology has led to the advent of wearable antennas. These antennas are utilized for Wireless Body Area Networks (WBANs) purposes such as healthcare, military sportive activities and identification systems. Compared to conventional antennas, wearable antennas operate in an environment which is in highly near proximity to the curved human body. Therefore, the wearable /flexible antenna performance parameters, including reflection coefficient, bandwidth, directivity, gain, radiation characteristic, Specific Absorption Rate (SAR), and efficiency are anticipated to be influenced by the coupling and absorption by the human body tissues. In addition, an electromagnetic bandgap structure is introduced in the wearable /flexible antenna designs to enable and give a high degree of isolation from the human body which also decreases the SAR dramatically. This paper reviews the stateof-the-art wearable/flexible antennas integrated with the electromagnetic band-gap structure on flexible materials concentrating on single and dual-band designs. Besides, it also highlights the challenges and considerations for an appropriate wearable/flexible antenna. INDEX TERMS Wearable/flexible antennas, EBG, AMC, metamaterials, metasurface, textile/fabric antennas, WBAN applications, ISM, SAR. I. INTRODUCTION Wearable devices are critical in the ICT field for on-body applications and the deployment of the Internet of Things and Wireless Sensor Networks. They must be low-powered, small, and capable of connecting to a hub or gateway device to access the internet or the cloud. The goal of these devices is to enhance the quality of life by improving the functionality of clothing by combining fabrics and electronics. They are continually showing a vision of the future since they are The associate editor coordinating the review of this manuscript and approving it for publication was Chow-Yen-Desmond Sim. going to be an essential part of daily clothing and serve as an intelligent personal assistant [1]-[3]. With the tremendous growth of wearable devices, academics, engineers, and researchers are concentrating on the investigation of ''Wireless Body Area Networks'' (WBAN) that link different electronic devices on the human body. The WBANs have a variety of applications in our daily lives. In the healthcare arena, they are applied to monitor a patient's serious health condition, such as a glucose monitoring system, capsule endoscopy, and blood pressure. Furthermore, they can be utilized in entertainment, military, business, and rescue operations, as well as incorporated into helmets, raincoats, shoes, jackets in emergency and rescue
A compact wearable symmetrical e-slots antenna operated at 2.4 GHz was proposed for Medical Body Area Network applications. The design was printed onto a highly flexible fabric material. The final design topology was achieved by the integration of symmetrical e-slots antenna with an Electromagnetic Band-Gap (EBG) and Defected Ground Structure (DGS). The use of EBG was to isolate the body and antenna from each other whereas the DGS widened the bandwidth. This combination forms a novel and compact structure that broadens bandwidth. This broadened bandwidth makes the structure robust to deformation and loading in the human body. The design achieved a measured impedance bandwidth of 32.08 %, a gain of 6.45 dBi, a Front to Back Ration (FBR) of 15.8 dB, an efficiency of 72.3% and a SAR reduction of more than 90%. Hence, the integration of symmetrical e-slots antenna with EBG and etched DGS is a promising candidate for body-worn devices.
A square-shaped complementary split ring resonator (CSRR) filtering structure for isolation improvement is presented in this paper. The proposed research work investigates the design and development of a simple and compact CSRR structure. In order to verify the performance of the proposed filtering element and to improve the isolation among the closely placed antenna elements, arrays of configured CSRR structures are implemented between two antenna elements. An array of configured CSRR elements has been integrated with the printed antenna on the top and bottom layers. The proposed filtering elements offer an enhancement in isolation by 25 dB as compared to the simple array. The entire configuration has been simulated using the Ansoft HFSS simulator. Finally, the proposed design is fabricated and experimentally validated. In the experiment, coupling suppression of −51 dB at the operating frequency is successfully achieved, resulting in a recovery of the array pattern. The proposed antenna is highly efficient, which is suitable to be utilized for 5G communication.
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