RF wireless charging is a type of uncoupled wireless charging in which an antenna embedded in an electronic device can pick up low level radio frequency waves from external sources and convert the waves’ energy to direct current (DC) voltage. The voltage the antenna harvests over the air is then used to power an electronic device or recharge its batteries. RF wire-free charging is well-suited for powering sensors and other electronic devices that run on very small batteries or use very little direct power.
The concept of wireless power transmission was originally proposed by Nikola Tesla, a Serbian-American electrical engineer and inventor who lived at the turn of the last century. In addition to developing and promoting alternating current (AC), Tesla envisioned a world in which towers scattered across the globe used electromagnetism to transmit electricity and information wirelessly.
Until recently, efforts to make Tesla’s vision a reality have been limited to approaches that use tightly-coupled induction or loosely-coupled resonance to transfer energy. Induction and resonance, which harness the power of magnetic fields, require the transmitter and receiver to be in direct or close contact, respectively. Smartphone charging pads and tablet charging stands are examples of commercial uses for this type of wireless charging.
In contrast, RF wireless charging harnesses the power of waves in the radio spectrum to transfer energy and creates a charging zone that’s very similar to a Wi-Fi hot spot. Tesla coils are no longer needed, which makes it possible to embed RF wireless charging in much smaller form factors than is possible with induction charging.
As of this writing, two companies have been certified by the United States Federal Communication Commission (FCC) to commercialize RF wireless charging. Powercast has been approved for a long-range wireless charging using the 915-MHz Industrial, Scientific, and Medical (ISM) equipment band to broadcast RF energy to all compatible devices in range. Energous Corp has been approved for a transmitter that can wirelessly charge devices without contact if they are within a three foot range.