A Self-Powered Microwave Sensor Using Perfect Metamaterial Absorbers for Liquid Characterization

This article introduces a self-powered microwave sensing platform designed for precise liquid characterization, specifically targeting methanol concentrations in water. The system leverages a power harvester based on a high-efficiency perfect metamaterial absorber (PMA), which captures ambient electromagnetic (EM) energy and converts it to direct current (dc) through an integrated two-stage rectifier to sustain an active split-ring resonator (SRR) sensor. With an absorption efficiency exceeding 98%, the PMA harvester utilizes transmission-line metamaterials optimized with lumped inductors and series capacitors, providing robust performance across diverse incident angles and polarizations. The sensor operates at 2.4 GHz and demonstrates high sensitivity to methanol concentrations ranging from 0% to 100% in water, achieving this with a compact and symmetric design that ensures stability under variable conditions. The proposed self-sustaining system presents a low-cost, energy-efficient solution ideal for remote, continuous operation, paving the way for applications in the food, beverage, and chemical industries, where detecting low chemical concentrations is critical. This work advances self-powered microwave sensing technologies, offering new opportunities for reliable, high-resolution material characterization.