On‐Chip Ultra Small 900‐MHz Wireless Powering Transfer for Smart Biomedical Devices

A compact rectenna operating at 900 MHz for wireless powered implantable devices is presented. With the bending technique of the antenna arms, the proposed rectenna volume was effectively miniaturized to only 3.13 mm 3 , establishing the smallest reported structure to date compared with literature at a similar band frequency. A monolithic integration scheme was employed, yielding a compact footprint of 250 μm × 850 μm. To achieve accurate impedance optimisation for maximum power transfer, the electrical characteristics of the incorporated elements were comprehensively characterized over a wide range of operating frequencies and input power levels. The proposed design methodology demonstrates a matching‐less rectenna integration circuitry, which aided in further reduction in the ultimate volume. Four samples have been explored, and 2 × 15 mm 2 design shows a superior low power reflection of 0.1%, which resulted in a high output voltage and power conversion efficiency of 0.84% and 7.92% at a load resistance of 14 kΩ, respectively. The maximum experimental power transmitted efficiency (PTE) of 0.0013% was obtained for the 5‐mm 2 design, corresponding to a 0.2‐V output voltage at 20‐dBm transmitted power. With a 2 × 15 mm 2 design, the rectenna delivers high PTE of 0.0504%, demonstrating competitive performance together with a significant reduction in the implementation complexity for self‐powered implanted devices.