Efficiency measurement of the flexible on‐body antenna at varying levels of stretch in a reverberation chamber

Abstract

Flexible antennas have the potential to transform wearable and fabric‐based wireless sensing technologies. The antenna discussed in this study is part of a sensing system that uses the back‐scattered power level as the decision metric. For a good wireless sensor, it is necessary to offer a feasible read range and maintain good distinctions in the back‐scattered power levels between the different states (i.e. level of stretch) of the antenna. Moreover, effects due to human body proximity should be minimised. For these reasons, the radiation efficiency is a crucial parameter to investigate. This study presents the radiation efficiency measurement of the proposed flexible knitted ‘Bellyband’ antenna at two different levels of stretch in a reverberation chamber. This work validates the reverberation chamber measurements through comparison with simulations and anechoic chamber measurements at 900 MHz. Moreover, this work demonstrates how the approach can be used to quantify bellyband antenna efficiency in the vicinity of a human body. Finally, the efficiency results were used to predict the read range of Bellyband radio frequency identification technology.

UHF RFID Channel Emulation Testbed for Wireless IoT Systems

“…During inhalation, the expanding abdomen stretches the flexible antenna structure, leading to higher radiation efficiency. The investigation of the on-body radiation efficiency [2] shows that the radiation efficiency increases by 3 dB as the antenna is fully stretched. The external reader antenna tracks the change in RSSI as the antenna goes through cycles of relaxation and stretch.…”

“…Passive RFID tags are largely used in logistics and supply chain visibility, asset tracking, transportation, access control, library systems, etc. Omnidirectional dipole antennas show poor performance in the vicinity of the human body [2]. Nevertheless, modern passive tags have very low wake-up power that offers the capability of designing on-body tags for biomedical sensing applications [3].…”

Passive UHF RFID-Based Knitted Wearable Compression Sensor

“…The read range of the system is drastically reduced as a result. For example, our previous work, the Bellyband antenna [3] has on-body read range 0.6 m [4]. Additionally, the weaker signal from the antenna to the reader incurs the detrimental effects of noise.…”

The Effect of Human Tissue on Field Strength Measurements In Vivo Using a Resonant UHF Cavity‐Backed Slot Antenna

“…Over the past decade, wearable antennas have attracted significant attention due to the wide range of potential applications in several fields (e.g., medical, sports, and military). In these applications, the antenna operates in close proximity or directly attached to the human body, which introduces a specific requirement for a compact wearable antenna design [Arif et al, 2019;Tajin et al, 2019]. This requirement includes small, lightweight, robust, easy to manufacture, and ideally conformal to the body surface, yet they must maintain high performance in terms of reliability and efficiency [Agneessens et al, 2015].…”