Flexible hybrid solar/EM energy harvester for autonomous sensors

A flexible electromagnetic (EM) / solar energy harvester is proposed that finds application in low power energy autonomous wireless sensor networks and RFID-enabled sensors. A low cost, compact and conformal harvester is implemented on a flexible polyester (PET) substrate combining a rectenna for EM harvesting and a flexible amorphous silicon solar cell for solar energy harvesting. A compact design is achieved by placing the solar cell on top of the radiating element. A coplanar UWB monopole antenna is designed and a rectifying network is optimized using harmonic balance in order to maximize the rectenna efficiency for low power electromagnetic signals in the GSM-850 and GSM-1900 frequency bands. The solar cell is integrated on the surface of the UWB antenna and electromagnetic simulation is used to optimize its location and the required DC interconnects in order to minimize the performance degradation of the antenna. Measured results of the performance of the hybrid energy harvester are presented showing good agreement with simulation.