Design and Performance Analysis of Ultra-Miniaturized Flexible Wearable Antennas Using Metamaterial Substrates for Continuous IoT-Enabled Biosignal Monitoring in WBAN Environments

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 multiobjective optimization minimizes 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 characterized 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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