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Title: Off-body antenna analysis and system level impact for wireless remote health monitoring systems in the 2.4 GHz band
Author: Giddens, Henry
ISNI:       0000 0004 5917 3176
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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Abstract:
Understanding antenna performance is important when designing a communication system. For wearable applications the performance of the body worn antenna should be characterized in terms of the influence of the body. This thesis presents a comprehensive analysis on the performance of wearable antennas in off-body communications systems and their impact on remote health monitoring applications. An electrically-small loop antenna was developed for use in remote health monitoring systems operating in the 2.4 GHz band. By considering the requirements of such systems, the antenna was designed to be small, lightweight and comfortable when worn, whilst operating efficiently on the body and radiating power away from the user. It is shown through two prototype designs how magnetic coupling can be used to feed this type of antenna. When mounted on a 230 x 155 mm textile ground plane and positioned on a tissue-emulating phantom, the antenna had an average transmission efficiency of 75% across the 2.4 GHz band. The performance was also characterized in terms of the ground plane size, and the average transmission efficiency dropped to 39% as the ground plane dimensions were reduced to 22 x 35 mm. The performance of two off-body antennas designed for in indoor remote health monitoring applications are then analysed in terms of their 3D radiation patterns. It is shown how the polarisation and pattern shape of a highly polarised textile patch antenna changes as the user position is tilted. The performance of the wearable antennas in remote health monitoring systems was then quantified in terms of their 3D power distribution, where it is shown that, despite radiating more power in unnecessary directions, the loop antenna radiated more evenly than the patch antenna over the desired sectors. Multiple off-body antenna systems were also considered, and the effects on the radiation patterns of three different combining methods are shown. The equal gain combining method is shown to introduce a significant ripple effect to the radiation pattern of the multi- loop antenna system, highlighting the interference effects that can occur when multiple antennas are incorporated in wearable systems. Finally, the performance of an indoor wearable off-body communications system is analysed through a series of measurements. In order to characterize the system in terms of the limitations imposed by body shadowing and fading, the wearable antennas were mounted on the torso shaped phantom and rotated through 3600 in the azimuth plane, and the received signal strength was recorded across the 2.4 GHz band. At the 0.1 % outage probability, it is concluded that multipath fading effects are the main limiting factor on the performance of the system, but can be accounted for through polarisation diversity in the access point, even for highly linearly polarised antennas. The performance of two antennas is then compared, and although it is shown that the loop antenna outperforms the patch antenna in most scenarios due to its higher efficiency and wider radiation pattern, it is also noted that antennas performed within the predefined system requirements as long as the user remained in the same room as the access point antennas. When multiple antennas were positioned on the front and back of the phantom, the performance at the 0.1 % outage probability was significantly improved, equating to a 15 dB reduction in the minimum required transmit power when a line-of-sight between the user and a polarisation diversity enabled access point is used in conjunction with the electrically-small loop antenna
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.685968  DOI: Not available
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