Ultracompact RF Rectifier Circuit for Implantable Devices

Abstract

This study proposes an innovative design approach for an ultra-compact RF rectifier, emphasizing high power conversion efficiency (PCE). The rectifier design employs a dual-branch cell configuration, labeled as Section-1 (S1) and Section-2 (S2), to enhance its performance characteristics. To support biomedical implant applications, these branches are incorporated with a meandered line network, designated as (ML1 and ML2). A radial stub is employed in the S1 structure, while series inductors are additionally connected to S1 and S2 to achieve improved performance characteristics. To improve power delivery performance, the proposed rectifier is specifically optimized for enhanced transfer efficiency within the frequency range of 1.28 GHz to 1.52 GHz. This makes it highly suitable for integration into wireless power transfer systems (WPTs) designed for biomedical implants. Both the simulated (experimental) results confirmed a maximum RF-to-DC PCE of 78.80% (77.7%), achieved at an input power <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_in</i> level of 4 dBm. Moreover, the proposed design achieves an RF-to-DC conversion efficiency greater than 25% at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_in</i> level of -20 dBm, thereby demonstrating its suitability for efficient operation under low-power conditions. The rectifier is fabricated on an RT/Duroid substrate, resulting in a compact footprint measuring 7.8 mm by 9.3 mm. A single-series diode (SSrd) configuration is employed to achieve the desired rectification performance. To ensure a wide impedance bandwidth, a sequential matching technique is applied, effectively optimizing the device’s performance throughout the specified frequency spectrum. This work demonstrates the effectiveness of the proposed rectifier in enabling WPT for biomedical implant applications, with particular emphasis on scenarios that demand efficient harvesting of ambient energy.