A Wearable Flexible Energy-Autonomous Filtenna for Ethanol Detection at 2.45 GHz

Abstract

This work proposes the design and implementation of a wearable rectifying filtenna (filtering antenna) which is activated and powered wirelessly, to detect the presence of ethanol solutions. The system is implemented on a Rogers RT/Duroid 5880 substrate ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{r} =2.2$ </tex-math></inline-formula> and thickness: 0.508 mm), whose flexibility facilitates the system wearability. The fluid detection is performed by a resonant stub embedding a microfluidic channel on its end, which resonates as an open circuit at 2.45 GHz when the channel is filled with the ethanol solution and undergoes a dramatic shift on its input impedance behavior when the channel is filled with water or when it is empty. The system is powered wirelessly by means of a 2.45-GHz narrowband antenna, and the frequency selection is performed by a second-order open-end coupled-line filter whose one end is loaded with the resonant stub. The filtenna RF signal is transduced by a full-wave rectifier exploiting low-threshold voltage diodes, and fluid detection is read out through different values of dc-output voltages, allowing an immediate response. The system is designed and optimized by means of full-wave/nonlinear co-simulations and the realized prototype is measured to confirm a safe detection of the tested solution.