Wearable antenna sensor based on bandwidth-enhanced metasurface for elderly fall assistance detection

Abstract

With the aggravation of aging, sudden falls have become one of the important causes of death. This article presents a metasurface-based wearable antenna sensor for fall assistance detection of the elderly. The dimension of the wearable metasurface antenna sensor (WMAS) is (50 × 50) mm2, and it works in the C-band-based wireless body area network. Both the metasurface and the slot antenna are printed on the flexible felt substrate, achieving wearability and comfort. The theoretical principle of realizing circular polarization is explained by analyzing the metasurface unit and the metasurface unit array using characteristic mode theory. By loading the metasurface onto the slot antenna, the operating bandwidth is increased by 189 %, and polarization conversion is achieved. As the applied pressure increases, the coupling degree of the metasurface and the slot antenna increases, and the bandwidth and the number of resonance points of the WMAS will increase accordingly. Based on this characteristic, by setting benchmarks for the bandwidth and the number of resonance points, it can be determined whether the elderly have fallen or not. The measured sensitivity of WMAS operating bandwidth and axial ratio bandwidth is 165 MHz/mm and 320 MHz/mm, respectively. By constructing a human tissue model to measure the radiation degree of WMAS to the human body, the results show that the specific absorption rate values are in line with international standards. Experimental results show that the proposed WMAS with broadband, circular polarization, and high sensibility is a promising candidate for assisted fall detection in the elderly.