A Metasurface-based Flexible Triple Bandpass Filter in ISM and IoT bands towards Wearable Applications

In this paper, a single layered, flexible metasurface (MS)-based slot type triple bandpass filter has been proposed for the ISM and IoT bands. The unit cell of the proposed MS structure consists of three slots designed on a flexible jeans substrate viz., one rectangular ring, one inverted U-shaped slot and a circular slot at its centre. The proposed MS exhibits three distinct transmission bands at $2.4 \mathrm{GHz}, 5.28 \mathrm{GHz}$ and 5.82 GHz. In addition, two stop bands are also realized at 3.77 GHz and 5.67 GHz making the structure suitable for wearable antenna applications. The performance of the structure is analyzed under incident angle variation to find that the structure is angularly stable up to 45°. The electric field distributions have been studied at the frequencies of operation to find the roles of the various slots used in the MS design. The first and the last transmission bands have potential applications in the ISM domain while the middle one makes the transmission feasible for IoT applications. The low profile combined with the compact design make the MS structure useful for wearable spatial filter.