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This paper explores antenna's polarization for Radio-Frequency Identification (RFID) based non-contact human activity detection. For the first time, a cross circular polarization configuration between reader antenna and tag antenna is proposed to increase the sensing range and spatial sensitivity. Compared to conventional RFID configurations-linearly polarized (LP) tag and circularly polarized (CP) reader, a cross CP configuration can improve the signal-to-noise ratio (SNR) which leads to 230% increase in the detection area over traditional approach in our experiment. As the result of the improvement of spatial sensitivity, the proposed approach can detect subtle and small body movements at almost 4.5m from the reader, such as head movements or even respiration, which enables a low-cost, easy-to-use, non-contact and non-intrusive monitoring of the elderly and disabled peoples in places like hospitals and assisted living homes.

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This work presents a novel tile based approach to constructing, in a modular fashion, massively scalable MIMO and phased arrays for 5G/B5G millimeter-wave smart skins and large-area reconfigurable intelligent surfaces for Smart Cities and IoT applications. A proof-of-concept 29 GHz 32 elements phased array utilizing $$2 \times 2$$ 2 × 2 “8-element subarray” tiles was fabricated and measured and demonstrates $$+/-$$ + / - 30beamsteering capability. The unique benefits of the proposed tile approach utilizes the fact that tiles of identical sizes can be manufactured in large quantities rather than have arrays of multiple sizes serve various user capacity coverage areas. It has to be stressed that the proof-of-concept flexible $$2 \times 2$$ 2 × 2 tile array features no performance degradation when it is wrapped around a 3.5 cm radius curvature. This topology can be easily scaled up to massively large arrays by simply adding more tiles and extending the feeding network on the mounting tiling layer. The tiles are assembled onto a single flexible substrate which interconnects the RF, DC and digital traces, allowing for the easy realization of on-demand very large antenna arrays on virtually any practical conformal platform for frequencies up to sub-THz frequency range.