Wireless power delivery is one of the key issues for fully implantable microsystems in neural engineering applications, such as microminiaturized neural stimulators and neural recording systems implanted in brain or other neural tissues. Although advances in semiconductor microelectronic technologies enable us to develop a low-power chip-scale neural microsystem, active electronics in the chip still consume challenging amounts of electrical energy for wireless energy harvesting to sense neural signals, processing data, and broadcasting the data to external receivers. In this paper, various wireless power delivery or harvesting schemes, including radio frequency, ultrasound, light, thermal, mechanical, and biochemical energies, have been reviewed, and performance characteristics, as well as pros and cons of the schemes, have been compared. This review aims at providing insightful information for system architects to design implantable neural microsystems with optimal wireless powering schemes.
