WiTricity

History

The term WiTricity was used for a project that took place at MIT, led by Marin Soljačić in 2006. The MIT researchers successfully demonstrated the ability to power a 60 watt light bulb wirelessly, using two 5-turn copper coils of 60 cm (24 in) diameter, that were 2 m (7 ft) away, at roughly 45% efficiency. The coils were designed to resonate together at 9.9 MHz (wavelength ≈ 30 m) and were oriented along the same axis. One was connected inductively to a power source, and the other one to a bulb. The setup powered the bulb on, even when the direct line of sight was blocked using a wooden panel. Researchers were able to power a 60 watt light bulb at roughly 90% efficiency at a distance of 3 feet. The research project was spun off into a private company, also called WiTricity.

The emerging technology was demonstrated in July 2009 by CEO Eric Giler at the TED Global Conference held in Oxford. There he refers to the original idea, first applied by the physicist Nikola Tesla between his coils, and shows a WiTricity power unit powering a television as well as three different cell phones, the initial problem that inspired Soljacic to get involved with the project.

Automobile manufacturer Toyota made an investment in WiTricity in April 2011.

In September 2012, the company announced it would make a $1000 demonstration kit available to interested parties, to promote development of commercial applications.

Technology

WiTricity is based on weakly coupled electromagnetic resonant objects to transfer energy wirelessly. This differs from other methods like simple induction, microwaves, or air ionization. The system consists of transmitters and receivers that contain magnetic loop antennas critically tuned to the same frequency.

Because WiTricity devices operate in the electromagnetic near field, receiving devices must be no more than about a quarter wavelength from the transmitter. In the system demonstrated in the 2007 paper, this was only a few meters at the frequency chosen. In their first paper, the group also simulated GHz dielectric resonators. WiTricity devices are coupled almost entirely with magnetic fields (the electric fields are largely confined within capacitors inside the devices), which they argue makes them safer than resonant energy transfer using electric fields (most famously in Tesla coils, whose high electric fields can generate lightning), since most materials couple weakly to magnetic fields.

Unlike the far field wireless power transmission systems based on traveling electro-magnetic waves, WiTricity employs near field resonant inductive coupling through magnetic fields similar to those found in transformers, except that the primary coil and secondary winding are physically separated, and tuned to resonate to increase their magnetic coupling. These tuned magnetic fields generated by the primary coil can be arranged to interact vigorously with matched secondary windings in distant equipment but far more weakly with any surrounding objects or materials such as radio signals or biological tissue.

In particular, WiTricity is based on using resonance to achieve a high power-transmission efficiency. Aristeidis Karalis, referring to the team's experimental demonstration, says that "the usual non-resonant magnetic induction would be almost 1 million times less efficient in this particular system". The researchers suggest that exposure levels are below the threshold for FCC safety regulations, and the radiated-power levels comply with FCC radio interference regulations.

Researchers attribute the delay in developing wireless-power technology to limitations of well-known physical laws and a simple lack of need. Only recently have modern consumers obtained a high number of portable electronic devices that use batteries and plug-in chargers.

Radiation levels

The company's FAQ [1] claims it uses a "...non-radiative mode of energy transfer, relying instead on the magnetic near field. Magnetic fields interact very weakly with biological organisms—people and animals—and are scientifically regarded to be safe." No actual studies or reports are claimed of the specific technology, power levels and use in home environments, although it does claim that, "WiTricity products are being designed to comply with applicable safety standards and regulations."