January 15, 2009 The promise of wireless electricity has been around for over 100 years. Nikola Tesla spent much of his productive life experimenting with wireless power, the familiar Tesla coils is actually a resonant wireless power transmitter, and the dream of wireless power was also his undoing when his Wardenclyffe project was terminated in 1904. Over the following decades very little research has been conducted with the prominent exception of Bill Brown who’s experiments in microwave wireless power transmission culminated in a successful demonstration in 1975 by transmitting 30kw over 1 mile at 82.5% efficiency at the Goldstone Deep Space Communication Complex.

Wireless power research was dormant again unit 2007 when an MIT scientist demonstrated wireless powering of a 60W light bulb with 40% efficiency at a 2m (7ft) distance using two 60cm-diameter coils. In 2008 Intel reproduced the MIT group's experiment by wirelessly powering a light bulb with 75% efficiency at a shorter distance.

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At this year's Consumer Electronics Show in Las Vegas half a dozen companies are demonstrating wireless power products that will be on sale as early as April this year to recharge your laptop, iPhone or power tools. Some of those products promise to render extension cords, cigarette lighter plugs, 8 plug powerboards and multiple chargers a thing of the past.

There are several different wireless electricity technologies on offer:

1. Inductive Coupling

They look like a mouse pad and can send power through the air, over a distance of up to a few inches. A powered coil inside that pad creates a magnetic field, which much like a conventional transformer, induces current to flow through a small secondary coil that's attached to a portable device. A company called Powermat is showcasing a pad which can charge up to 6 different enabled electronic devices. Powermat's inductive technology pairs an ultra-thin mat (5 models to choose from) with a variety of receivers, which connect to your favorite electronic devices. Future applications could be embedded directly into tabletops or other surfaces. The system even allows for the wireless transmission of data - audio & video - allowing users to sync their iPods or transmit video to their TVs at very efficient transfer rates. Another company Fulton Innovation who are exhibiting at the show, with their partners - Texas Instruments, Energizer, Leggett & Platt and Bosch Power Tools - will feature over a dozen new applications and products that will demonstrate wireless power in the home, office, garage, and beyond. Their eCoupled technology eliminates the need for power cords by creating an electromagnetic conduit combined with an intelligent control system that constantly monitors the power flow to insure optimal efficiency and safety. ECoupled uses a wireless powering technique called "close proximity coupling," which uses circuit boards and coils to communicate and transmit energy using magnetic fields. The technology is efficient but only works at close ranges. Typically, the coils must be bigger than the distance the energy needs to travel. What it lacks in distance, it makes up in intelligence. In conjunction with the Wireless Power Consortium, Fulton, a subsidiary of Amway, has developed a standard that can send digital messages back and forth using the same magnetic field used to power devices. These messages are used to distinguish devices that can and can't be charged wirelessly, and to relay information like power requirements or how much battery is left in a device.

One of Fulton partners Bosch has designed wireless chargers into battery power tool carry cases while Leggett & Platt have designed a center console for vehicles that can inductively charge flash lights and cell phones. The charging surfaces come in three power levels: low is for devices less than 5 watts, medium can handle 100 watt charging, and high power charging surfaces can produce kilowatts. These charging surfaces are harmless to touch, and a Leggett and Platt representative assured us there were no dangerous radiation levels.

Texas Instruments announced last November that it would manufacture a chip-set that will reduce the manufacturing cost of integrating eCoupled wireless power into consumer electronic devices. Devices now in the pipeline at companies such as Bosch, Energizer, and others will look just like their conventional ancestors. Companies such as Philips Electronics, Olympus, and Logitech will create a standard for products, from flashlights to drills to cell phones to TV remotes, by the end of this year.

Wipower demonstrate 5 light bulbs powered using inductive coupling with 74% efficiency which they say compares favorably to the median efficiency of 58% found in many corded power supplies today, (a PC power supply typically is 70-75% efficiency). The WiPower Surface is designed like a tablet on top of which devices can be placed for charging. The Surface is typically a standalone unit but, later versions are expected to be integrated into desks and other furnishings. On the other side, the receiver is retrofitted to, or integrated with, the device intended to be charged. When devices with a receiver are placed in any position or orientation atop a transmitter, they will charge as if it were connected to a conventional power supply. Their technology and products are based on a modified coreless inductive technology architecture.

2. Radio-frequency

PowerCast offer a wireless electricity technology based on what's known as radio frequency, or RF. This can transmit power across distances of up to 85 feet. A transmitter plugs into the wall, and a dime-size receiver (the real innovation, costing about $5 to make) can be embedded into any low-voltage device. The Powercast demonstration transmits 3 Watts at 900Mhz through a patch antenna that is received by several LED equipped rectenna, which is a simple dipole antenna with a Schottky diode at the feedpoint that converts radio waves into direct current. Powercast and its first major partner, electronics giant Philips, are set to launch their first device powered by electricity broadcast through the air.

3. Laser

PowerBeam showcases wireless lamps and picture frames. Located in Sunnyvale, Calif., the company uses yet another wireless-powering approach. Its technology beams optical energy into photovoltaic cells using laser diodes. Although the company says it can maintain a constant energy flow across long distances, the difficultly of targeting a laser means that it's not ideal for charging moving devices. Their laser can currently generate about 1.5 watts of power to solar cell 10 metres away. This would be enough to power an electronic speaker or small LED (light-emitting diode) lights, but not enough to operate a laptop, which requires an estimated 30 to 50 watts. However, the company claims that the technology could comfortably be scaled up.

4. Conductive Pad

Boulder, Colorado based WildCharge is demonstrating a mat that uses a conductive powering technique. This is more efficient than inductive powering but requires direct contact between the devices and the charging pad. Though most of the mats or pads on display are intended to power only a handful of devices at a time, WildCharge says the product design is certified for up to 150 watts - enough to power 30 laptops.

5. Magnetically Coupled Resonance

Another wireless power technology is on display in a private suite high in the Venetian hotel tower. Magnetically Coupled Resonance was demonstrated in 2007 when an MIT scientist demonstrated wireless powering of a 60W light bulb with 40% efficiency at a 2m (7ft) and has been dubbed WiTricity. As proof that it works, an LCD TV is powered by a coil hidden behind an oil painting located 5 feet away. Another demonstration involves walking in the direction of another coil with an iPod Touch in your hand, it starts to charge when it gets within two meters.

The technique can power an entire room, assuming the room is filled with enabled devices. Though WiTricity uses two coils, just like the eCoupled system, it differs in that the coils don't have to be close to each other to transfer energy. Instead, they depend on so-called magnetic resonance. WiTricity doesn't depend on line-of-sight. A powered coil in your basement could power the rest of the house, wirelessly.

These wireless electricity products represent an entirely new product sector and although it’s very early days and the varied technologies have yet to find their most appropriate niche (here's hoping a long drawn out battle over mobile phone wireless charging standards is avoided) the industry certainly has enormous potential. For example, the Mitsubishi MiEV Sport shown at the 2007 Tokyo motor show presented the idea of wireless battery charging for Electric Vehicles via a microwave system where the receiving antenna was located on the rear bumper next to the license plate. Inductive coupling would also work well in this application so perhaps we might see a network of induction coils buried in roads and parking spaces (much like traffic lights have induction coils buried in the road surface as vehicle sensors) . As with some of the above systems that can communicate, much like a toll tag, this could facilitate intelligent opportunity recharging of EVs without any input required from the driver.

Paul Evans

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