WiTricity’s technology is more than…
Traditional Magnetic Induction
At first glance, WiTricity’s technology for power transfer appears to be traditional magnetic induction, such as is used in power transformers, where conductive coils transmit power to each other wirelessly, over very short distances. In a transformer, an electric current running in a sending coil (or “primary winding”) induces another current in a receiving coil (or “secondary winding”). The two coils must be very close together, and may even overlap, but the coils do not make direct electrical contact with each other. However, the efficiency of the power exchange in traditional magnetic induction systems drops by orders of magnitude when the distance between the coils becomes larger than their sizes. In addition to electric transformers, other devices based on traditional magnetic induction include rechargeable electric toothbrushes, and inductive “charging pads” which require that the object being charged be placed directly on top of, or very close to, the base or pad supplying the power.
The power exchange efficiency of some induction systems is improved by utilizing resonant circuits. These so-called resonantly enhanced induction techniques are used in certain medical implants and high-frequency RFIDs for example. However, to the best of our knowledge, WiTricity’s founding technical team was the first to discover that by specially designing the magnetic resonators, one could achieve strong coupling and highly efficient energy exchange over distances much larger than the size of the resonator coils, distances very large compared to traditional schemes.
WiTricity’s technology is different than…
Radiative Power Transfer
A microwave oven utilizes microwave radiation to cook food.
The June 5, 1975 NASA JPL Goldstone Demonstration of directed radiative microwave power transmission successfully transferred 34kw of electrical power over a distance of 1.5km. View movie
Artist rendering of European Space Agency Aeolus Satellite with laser beam pointing at the Earth's atmosphere. Aeolus will use laser Doppler radar to better understand weather phenomena. Credits: ESA/AOES Medialab
WiTricity’s technology for power transfer is non-radiative and relies on near-field magnetic coupling. Many other techniques for wireless power transfer rely on radiative techniques, either broadcasted or narrow beam (directed radiation) transmission of radio, or light waves.
Broadcasted radiation of radio frequency energy is commonly used for wireless information transfer because information can be transmitted over a wide area to multiple users. The power received by each radio or wireless receiver is miniscule, and must be amplified in a receiving unit using an external power supply. Because the vast majority of radiated power is wasted into free space, radio transmission is considered to be an inefficient means of power transfer. Note that while more energy can be supplied to the receiver by “cranking up the power” of the transmitters in these systems, such high power levels may pose a safety hazard and may interfere with other radio frequency devices.
“Directed radiation”, using highly directional antennas, is another means of using radio transmission to beam energy from a source to a receiver. However, directed radiation—in particular microwave radiation—may interact strongly with living organisms and certain metallic objects. Such energy transfer methods may pose safety hazards to people or objects that obstruct the line-of-sight between the transmitter and receiver. These limitations make directed radio transmission impractical for delivering substantial levels of wireless power in a typical consumer, commercial, or industrial application. In fact, defense researchers are exploring the use of directed energy systems to deliver lethal doses of power to targets in space and on the battlefield.
In addition to radio waves, visible and invisible light waves can also be used to transfer energy. The sun is an excellent radiative source of light energy, and industry and academia are working hard to develop photovoltaic technologies to convert sunlight to electrical energy. A laser beam is a form of directed light radiation, in which visible or invisible light waves may be formed into a collimated beam, delivering energy in a targeted way. However, as in the case of directed radio waves, safe and efficient transmission of laser power requires a clear line of sight between the transmitter and receiver.
As mentioned at the beginning of this section, WiTricity’s technology is based on non-radiative energy transfer. It does not require a clear line of sight between the power sources and capture devices and it is safe for use in typical home, hospital, office, or industrial environments.
WiTricity’s technology is different than…
Magnetic Resonance Imaging(MRI)
MRI machines use “magnetic resonance imaging” to produce diagnostic images of soft tissue.
Many people assume that WiTricity’s “Resonant Magnetic Coupling” must be similar to magnetic resonance imaging (MRI) technology, however, the technologies are similar in name only. MRI is, as its name suggests, a technology for using magnetism as a basis for diagnostic imaging of soft tissue in the human body. It utilizes a strong DC magnet to orient the magnetic fields of atoms within tissues, and radio frequency fields to manipulate those atoms in a selective way, so that tissues and structures can be imaged clearly. The “resonance” referred to in “MRI” refers to the resonance of atomic structures. MRI is not considered to be a method for wireless power transfer.
WiTricity’s technology is different than…
Tesla’s Vision of a Wireless World
In the late 1800’s and early 1900’s, at the dawn of the electrification of the modern world, some scientists and engineers believed that using wires to transfer electricity from every place it was generated to every place that it could be used would be too expensive to be practical. Nikola Tesla, one of the most well known of these scientists, had a vision for a wireless world in which wireless electric power and communications would reach around the world, delivering information and power to ships at sea, factories, and every home on the planet. Tesla contributed significantly to our understanding of electricity and electrical systems and is credited with inventing three-phase AC power systems, induction motors, fluorescent lamps, radio transmission, and various modes of wireless electric power transfer. WiTricity technology for power transfer is different than the technologies proposed by Tesla, but his work is referenced and acknowledged in the scientific articles published by WiTricity’s founding technical team.
Nikola Tesla’s Wardenclyffe tower built on Long Island, NY in 1904. This tower was intended to implement Tesla’s vision of transmitting power and information around the world. The tower was destroyed in 1917.
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