A Wearable Localized Surface Plasmons Antenna Sensor for Communication and Sweat Sensing

This article presents a novel wearable antenna sensor based on localized surface plasmons (LSPs) for communication and noninvasive sweat monitoring. The sensor is made up of corrugated plasmonic structures based on the conventional printed monopole antenna, which achieves multiband and miniaturization. The physical dimensions of the antenna sensor are $35\times34$ mm, with a thickness of only 0.13 mm. Simulated and measured results demonstrate that the proposed antenna sensor covers triple operating bands, including 2.4 and 5.8 GHz ISM bands, as well as high-frequency ultrawideband ranging from 7.89 to 9.56 GHz. The antenna sensor exhibits a good radiation pattern with a peak gain of 3.02 dBi and a high quality factor ( ${Q}$ ) up to 35. The use of polyimide as a dielectric substrate enables the antenna sensor to achieve flexibility and conformality, maintaining stable operating states even when bent and deformed. The specific absorption rate (SAR) values in three frequency bands are simulated and evaluated to ensure its safety for human health. Moreover, the resonant frequency of antenna sensor significantly shifts with the volume and concentration of sweat, indicating that the proposed sensor is highly sensitive to sweat volume and concentration with a sensitivity of 120 MHz/1 mm and 4.57 MHz/1 mm, respectively. The proposed wearable antenna sensor is a promising candidate for a sweat monitoring system for athletes or patients, allowing for health monitoring at any time and place.