Ultra-Compact and High-Efficiency Rectenna for Wireless Sensing Applications in Concrete Structure

This paper presents an ultra-compact and high-efficiency rectenna which can power wireless sensing nodes fully embedded in a reinforced concrete structure. The proposed innovative design is optimized in terms of efficiency and compactness for the targeted application. The rectenna is compact, with a volume of 56 mm × 32 mm × 10 mm, (0.0004·λ^3), and can reach a maximum RF-to-dc conversion efficiency of 70% at 868 MHz for a 10 kΩ load and for an illuminating RF power density of 4 µW/cm². The use of a metallic cavity increases the rectenna performances and limits the negative impact of the concrete material. Thus, the rectenna into the cavity harvest a dc voltage up to 1.15 V when the rectenna is illuminated with a RF power density of 1 µW/cm². Experimental results of the rectenna embedded in a reinforced concrete beam confirm the feasibility of powering a wireless sensor by wireless power transmission.