Abstract
A low profile, bi-state switchable, and flexible active AMC (AAMC) reflector metasurface is presented for wearable antenna integration to improve radiation performance with low specific absorption rate (SAR). The unit cell structure contains concentric rectangular rings with 2-varactor diodes. The unit cell is designed on a flexible PDMS substrate with dimensions 20 × 20 × 1 mm3. Controlled DC bias is applied to both varactor diodes. In state-1, that is, on state, the AMC surface resonates at 3.5, 5.8, and 8.1 GHz frequency, and in state-2, that is, off state, it resonates at 3.5, 5.8, and 7.5 GHz frequencies with zero degrees reflection phase. The proposed AAMC reflector performance is analyzed by integrating a 3 × 3 AAMC surface with the quad-band wearable textile antenna designed to resonate at 3.5, 5.8, 7.5, and 8.1 GHz frequencies. By controlling operating voltages of the integrated AAMC, the antenna radiation performance is improved in bi-state by adapting to reflection pattern switching. In On-state, the peak gain (dBi), FBR (dB) of integrated antenna improved to 7.36, 9.05, 8.9, 7.53 and 9.25, 11.9, 19.7, 16.70; In Off-state, the values are improved to 7.8, 8.98, 8.33, 7.92 and 12.24, 11.37, 14.6, 16.85, respectively. The proposed AAMC with antenna integration is fabricated, and its measured results are well satisfying. The low SAR values are obtained under a 2 mm gap (<0.924 W/kg) and direct contact (<1.5 W/kg) as well. The enhanced radiation performance characteristics with the bi-state switchable feature make it preferable for wearable antenna integration to meet current WBAN demands.
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