Design and Performance Analysis of Ultra-Miniaturized Flexible Wearable Antennas Using Metamaterial Substrates for Continuous IoT-Enabled Biosignal Monitoring in WBAN Environments
DOI:
https://doi.org/10.31838/NJAP/07.03.26Keywords:
Flexible wearable antenna, metamaterial substrate, wireless body area network (WBAN), IoT-enabled biosignal monitoring, antenna miniaturization, SAR reduction, on-body propagationAbstract
The key enablers of next-generation wireless body area networks (WBANs) used in incessant health monitoring in Internet of Things (IoT) systems are ultra-miniaturized, flexible wearable antennas. Still, compactness, mechanical flexibility, and stable on-body performance without sacrificing the stringent specific absorption rate (SAR) limits is one of the greatest challenges. In this paper, the design and performance study of a flexible microstrip wearable antenna using a metamaterial-loaded substrate is provided to identify the antenna to be used in WBANs to explore a continuous biosignal monitoring application. The proposed antenna is based on a periodic metasurface-based unit-cell array which is implemented in a thin polyimide substrate to achieve considerable electrical miniaturization and improved bandwidth of impedance. An optimization scheme based on multi-objective optimization minimises the antenna footprint and on-body detuning and maximizes the radiation efficiency and the link reliability in a typical human-body loading and bending scenario. S-parameters, gain, SAR and bending robustness of a phantom made up of a tissue-equivalent is characterised by full-wave electromagnetic simulations and on-body measurements on a tissue-equivalent phantom. It is found that the proposed metamaterial-based design reduces up to 62% in size and 18% in bandwidth over a traditional flexible microstrip reference, and still has a SAR that is well below regulatory requirements at 2.4 GHz ISM. The antenna is also effective in supporting low-power biosignal acquisition nodes with WBAN indoor environments. The introduced methodology offers a logical guideline on how to incorporate metamaterial substrates with flexible wearable antennas on the robust continuous monitoring of health-centric IoT applications.
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