Simple Equation-Based Rectifier Model and Its Application to Efficient Energy Harvesting From Amplitude Modulation Broadcasting Radio Waves

Starting from the theoretical equations and ideal characteristics of a diode, a simple equation-based rectifier model has been developed through some approximations. It comprises basic arithmetic operations without complicated time-integral or trigonometric functions. The proposed model illustrated that an appropriate ratio between the output current and the saturation current of a diode according to the output voltage is quite important for the efficient operation of the rectifier. As an application example, energy harvesting (EH) from amplitude modulation (AM) broadcasting radio waves was demonstrated with an optimally designed EH prototype using the developed model. The prototype comprises a high-Q ferrite rod antenna and a single-series rectifier with a Schottky diode, selected based on the developed model. The ferrite rod antenna is operated under parallel-resonance conditions by adding a tuning capacitor. The very high equivalent resistance of the ferrite rod antenna under LC resonance is suitable for efficiently connecting to the rectifier, which inherently has high input impedance. Impedance matching is realized by tap selection of the ferrite rod antenna and output load tuning of the rectifier. The prototype was evaluated in an electromagnetic anechoic chamber and in the field. Power levels of 3.87 and $1.25~\mu $ W were harvested at locations 2.31 and 6.35 km away from an AM radio station transmitting 500 kW of radio waves at 774 kHz, respectively.