A compact wearable antenna with a novel miniaturized EBG structure at 2.4 GHz for medical application is presented in this letter. The design demonstrates a robust, compact and low-profile solution to meet the requirements of wearable applications. The EBG structure reduces the back radiation and the impact of frequency detuning due to the high losses of human body. In addition, the structure improves the front-to-back ratio (FBR) by 15.5 dB. The proposed compact antenna with dimensions of 46 × 46 × 2.4 mm 3 yields an impedance bandwidth of 27% (2.17-2.83 GHz), with a gain enhancement of 7.8 dBi and more than 95 % reduction in the SAR. Therefore, the antenna is a promising candidate for integration into wearable devices applied in various domains, specifically biomedical technology.

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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 compact and robust fabric antenna incorporated with metamaterials (MTM) at 2.4 GHz is introduced for wearable devices application where the MTM behaves as EBG/AMC. The benefit of introducing MTM in a wearable antenna is to diminish the influence of frequency detuning and reduces the backward radiation specifically when loaded on the human body. The overall size of the presented antenna incorporated with MTM is 60 × 60 × 2.4 mm3. Furthermore, the integrated design has the capability of controlling Specific absorption rate (SAR) and improved the bandwidth, front‐to‐back ratio (FBR), and gain up to 14.5%, 13.7dB, and 7.5dBi, respectively. The operations under different bending diameters on real and modelled human body are studied. Compared with conventional antennas, MTM‐inspired antennas reduce the SAR to safe levels of more than 90%. The presented integrated design can be a good candidate for incorporation into a variety of flexible systems for medical application.

Device-to-device (D2D) communication is one of the most promising technologies in wireless cellular networks that can be employed to improve spectral and energy efficiency, increase data rates, and reduce links latency. This paper investigates fifth generation and beyond (5GB) networks, the basics of D2D communication, applications, and classification. Herein, D2D in in-band (IBD) and out-band (OBD) modes are discussed. This paper also presents the integration of D2D communication with other prominent technologies and demonstrates the importance of integration with possible solutions in improving network performance. We further investigate the challenges of D2D communication, opportunities, and future research directions of D2D in 5GB networks. In addition, D2D communication in 6G network challenges and open research areas are introduced.INDEX TERMS 5G, 5GB, 6G, D2D communication, millimeter wave (mm-Wave), visible light communication (VLC), ultra-dense network (UDN), and unmanned aerial vehicle (UAV).

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