Abstract
Previous works have shown that wearable antennas can operate ideally in free space; however, degradation in performance, specifically in terms of frequency shifts and efficiency was observed when an antenna structure was in close proximity to the human body. These issues have been highlighted many times yet, systematic and numerical analysis on how the dielectric characteristics may affect the technical behavior of the antenna has not been discussed in detail. In this paper, a wearable antenna, developed from a new electro-textile material has been designed, and the step-by-step manufacturing process is presented. Through analysis of the frequency detuning effect, the on-body behavior of the antenna is evaluated by focusing on quantifying the changes of its input impedance and near-field distribution caused by the presence of lossy dielectric material. When the antenna is attached to the top of the body fat phantom, there is an increase of 17% in impedance, followed by 19% for the muscle phantom and 20% for the blood phantom. These phenomena correlate with the electric field intensities (V/m) observed closely at the antenna through various layers of mediums (z-axis) and along antenna edges (y-axis), which have shown significant increments of 29.7% in fat, 35.3% in muscle and 36.1% in blood as compared to free space. This scenario has consequently shown that a significant amount of energy is absorbed in the phantoms instead of radiated to the air which has caused a substantial drop in efficiency and gain. Performance verification is also demonstrated by using a fabricated human muscle phantom, with a dielectric constant of 48, loss tangent of 0.29 and conductivity of 1.22 S/m.
Highlights
Wearable antennas are highly in demand to support various wearable technologies due to the advantage of being flexible, lightweight and integrated with garments
Many considerations should be taken into account when designing a wearable antenna such as interconnectivity issues, consistency of performance and comfortability of users [5,6,7,8]
In the future, based on the analysis presented in this paper, optimization works can be done to improve the performance of the antenna in both free space and on-body conditions
Summary
Wearable antennas are highly in demand to support various wearable technologies due to the advantage of being flexible, lightweight and integrated with garments. Antenna is important to support many wireless communication aspects such as for in-body communication, on-body communication and off-body communication [4]. Many considerations should be taken into account when designing a wearable antenna such as interconnectivity issues, consistency of performance and comfortability of users [5,6,7,8]. Due to the importance of these issues in antenna designing, this paper. Materials 2019, 12, 1636; doi:10.3390/ma12101636 www.mdpi.com/journal/materials copper powder [9]. For these structures, antenna substrate is normally represented by nonconductive material such as cotton, polyester or woven, and the integration of copper as the radiating element is done through various techniques such as embroidery, manual sewing, ironing, gluing etc
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