An adaptive buck-boost resonant regulating rectifier (B2R3) with an integrated on-chip coil and low-loss H-Tree power/signal distribution is presented for efficient and robust wireless power transfer (WPT) over a wide range of input and load conditions. The B2R3 integrated on a 9 mm2 chip powers integrated neural interfacing circuits as a load, with a TX-load power conversion efficiency of 2.64 % at 10 mm distance, resulting in a WPT system efficiency FoM of 102.