Enhancing Energy Harvesting for Wearable Sensors: A Circular 8-Element Array with Spatial Diversity

This paper presents a receiving antenna array for self-powered battery-less system utilizing far field RF energy harvesting. The design, simulations, optimizing, fabrication and testing of the proposed array is presented, composed of 8 elements circularly configured for wide angular range and diversity. The design exhibits dual band characteristics operating at ISM 2.45 and 5.8 GHz, which was fabricated on a flexible, wearable EPDM substrate. The simulations and optimization of the design was achieved in a realistic environment, a three-layered homogeneous body model consists of skin, fat and muscle. The simulated results were validated through testing the S parameters and radiation patterns of the fabricated prototype. Both the simulated and measured results show good agreement in terms of S<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> surpassing -20 dB and S<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> less than -20 dB. The 3D gain plots of the array confirm the omnidirectional patterns with maximum gain of 2.9 and 7.1 dBi at 2.45 and 5.8 GHz respectively. This works features significant potential in the fields of smart textile and wearable electronics, offering key benefits such as compactness, spatial diversity and dual band capability.