Wireless power transmission (WPT) is any technology that can transmit electrical power between two places without wires. As we are moving towards a future with small sensors in homes, fields, and factories, this is an area of research that is getting a lot more attention. The alternative to wireless power is to somehow put small batteries in sensors and devices that have to somehow periodically be replaced.

There are half a dozen techniques that can be used to create electric power remotely. Most involve transmitting some form of electromagnetic radiation that is used to excite a remote receiver that converts the energy into electricity. There have been trials using frequencies of all sorts, including microwaves, infrared light, and radio waves.

The most commonly used form of wireless power transmission today is used in wireless pads that can recharge a cellphone or other small devices. This technology uses inductive coupling. This involves passing alternating current through an induction coil. Since any moving electrical current creates a magnetic field, the induction coil creates a magnetic or electromotive field that fluctuates in intensity as the AC current constantly changes. A cellphone pad only works for a short distance because the coils inside the device are small.

There are a few household applications where induction charging works over slightly greater distances, such as automatically charging electric toothbrushes and some hand tools. We’ve been using the technology to recharge implanted medical devices since the 1960s. Induction charging has been implemented on a larger scale. In 1980, scientists in California developed a bus that could be recharged wirelessly. There is currently research in Norway and China to top off the charge in cars and taxi batteries to avoid having to stop to recharge electric vehicles.

There have successful uses of transmitted radiation to create remote electricity over great distances. Radio and microwaves can be beamed great distances to excite a device called a rectenna or rectifying antenna, which converts transmitted frequency into electricity. This has never been able to produce a lot of power, but scientists are looking at the technology again because this could be a way to charge devices like farm sensors in fields.

The private sector is exploring WPT solutions for everyday life. Wi-Charge is using safe infrared light to charge devices within a room. Energous has developed a radio transmitter that can charge devices within a 15-meter radius. Ossia is developing wireless charging devices for cars that will automatically charge cellphones and other consumer devices. We’re not far away from a time when motion detectors, smoke alarms, CO2 sensor,s and other devices can be permanently powered without a need for batteries or hardwiring.

Scientists and manufacturers are also exploring long-distance power transmission. Emrod in New Zealand is exploring bringing power to remote sites through the beaming of radio waves. On an even grander scale, NASA is exploring the possibility of beaming power to earth gathered from giant solar arrays in space.

Remote power was originally envisioned by Nicola Tesla, and perhaps over the next few decades will become an everyday technology that we take for granted. I’m just looking forward to the day when I’m not wakened in the middle of the night by a smoke detector that wants me to know it’s time to change the battery.