A wearable passive microwave fluid sensor wirelessly activated

This work proposes a novel wearable passive microwave sensor in the 2.45 GHz ISM band, to detect the presence of aqueous solutions on the skin surface. The sensing sub-system consists of a modified open-end coupled-line microwave filter, with one (or more) open termination replaced by a resonant open-end stub, integrating a microfluidic channel. In this way the filter behavior is strictly related to the microfluidic channel content. The equivalent circuit of the microfluidic channel is derived from EM simulation, to allow accurate and efficient design of the whole sensor system. In order to provide power remotely, a narrowband antenna is seamless connected to the filter input port and the channel content is transduced at the filter output by a low-power detector. The chosen novel topology is suitable for both its frequency selective behavior, which enables high-accuracy fluid discrimination, and its ease implementation in flexible and thin substrates, allowing the realization of a low-cost wearable sensor.