WEHs

Wireless energy harvesting (WEH) refers to the capture and conversion of ambient electromagnetic energy into usable electrical power for electronic devices and systems. The concept emerged in the early 1960s as research into rectifying antennas (rectennas) for satellite communications progressed, but practical implementation only became widespread after the rapid miniaturization of circuits in the 1990s. Modern WEHs operate on various frequency bands, ranging from low‑frequency powerline carriers (50–60 Hz) to the microwave bands (2.45 GHz, 5.8 GHz) used by Wi‑Fi and RFID.

Typical WEH architectures consist of an antenna or sensor array, a rectifying element, and a storage or load‑management stage. The antenna captures incident radio-frequency (RF) energy; diodes or other nonlinear devices rectify the signal into direct current; a microcontroller or low‑power analog controller manages energy distribution to the load or to a rechargeable battery. Recent advances include metamaterial‑enhanced antennas that increase the effective capture area and superconducting diodes that reduce conversion losses.

Applications of WEHs span consumer electronics, medical implants, and the Internet‑of‑Things (IoT). In the consumer sector, wearable gadgets have been powered nonstop by ambient Wi‑Fi signals, reducing battery reliance. In medical implants, low‑power sensors are targeted by RF ports embedded in hospital equipment, delivering energy without surgical recharging. The IoT community uses WEHs to power edge cameras and environmental sensors, allowing maintenance‑free deployments in inaccessible locations. Military and space programs also explore WEHs for covert power delivery to reconnaissance devices.

The primary challenges remain efficiency and regulatory limits. Ambient RF power is typically low, often an order of magnitude lower than the power consumption of even simple microcontrollers. Regulations enforce strict limits on the radiated power density, constraining the amount of energy available for harvesting. Future research concentrates on signal‑processing algorithms that identify energy peaks, advanced rectifiers that operate efficiently at microampere scales, and cooperative network architectures where multiple devices share harvested power. Overall, wireless energy harvesting is advancing from an academic exercise into a viable supplementary power source for low‑power systems.