By Brian Dodson
Hatem Zeine, the CEO of Ossia Incorporated and inventor of the Cota wireless charging system, demonstrated charging of his smartphone during a presentation at Tech Crunch Disrupt 2013 (Photo: Ossia, Inc.)
In 2008, Gartner Research released a report in which it identified the number one IT grand challenge as "Never having to manually recharge devices." Physicist Hatem Zeine has invented what he believes to be the answer to this challenge. The Cota wireless power transmission system uses intelligently steered phased array antennas to focus a beam of microwaves on a receiver module – and only on that module. The inherently safe technology can deliver electrical power up to 30 feet from a central transmitter without any line-of-sight requirement and without interfering with other devices. The system is projected to hit the market in 2015.
Cota uses a single microwave transmitter, operating in the 2.4 or 5.8 GHz industrial, scientific, and medical (ISM) bands that are also used by Wi-Fi routers. Unlike most wireless charging systems we've seen that require the close proximity between the transmitter and the device being charged, the Ossis transmitter will provide effective charging to distances of about 30 feet (9 m). This means that a single unit would suffice for most households and offices. The microwave power from the transmitter is directed onto charging receivers that convert the received power into a form that can be used to charge device batteries, or even to directly run portable devices.
The charger is housed in an 18" cube while the receiver resides on a chip and uses a chip antenna for operation. The commercial version of the receiver will be small enough to fit inside a phone or even a AAA battery according to Zeine. The amount of electrical power that will initially be made available by a single receiver is expected to around 1 W (about a third the power transmitted via a USB socket), which is sufficient for charging multiple portable devices. However, the use of unmodulated RF power to transfer power does not seem to fall under any specific FCC regulation in the US. As Cota is not being used for telecommunication, the power which could be made available will be controlled by the general ISM regulations, which allow much larger power than the maximum one watt of a Wi-Fi router. Worldwide, of course, the limits will depend on local regulations.
The Cota system works by a clever combination of phased-array steering antennas on the transmitter and locator beacons on the receivers. In a room without obstacles, the RF radiation from the locator beacon (pulsed at 100 times/sec) travels directly from the receiver to the walls of the room. A portion of that radiation will strike the transmitter unit, whose electrically-steerable phased-array antennas (20,000 individually controlled antennas are being planned for the first commercial system) will not only detect the radiation, but also the direction from which it is arriving. This is similar in principle to the Lytro camera, which records the complete light field of a scene, rather than just the intensity of light at a particular surface.
The transmitter then uses this information to fabricate a beam of microwave power that is focused only onto the receiver. This is accomplished by using a physical property of RF fields called time-reversal symmetry. If you reverse the beacon wave detected by the transmitter, it will follow the same path back to the receiver as it took on its way to the transmitter. As seen above, this means that the transmitter does not waste power heating the walls of the room, but rather makes nearly all of its output available at the charging receiver. Because of the rapid pulsing rate of the locator beacon, the transmitter is easily able to track the motion of the charging receiver (it is, after all, charging a portable device) as it moves around the room, and into adjoining rooms. The Cota system will charge your smartphone in your pocket as you wander around your house.
What happens if a person is standing in the room between the charging receiver and the Cota transmitter? An attempt to generate a direct microwave beam between the transmitter and the receiver would result in very little power transmission to the receiver, and quite a bit of microwave exposure for the person – not a good or safe situation. Fortunately, the property of time reversal symmetry saves the day.
As shown above, the locator beacon signal from the charging receiver again bounces around the room, but the portions that hit the person are absorbed and do not reach the Cota transmitter. (The power level of the beacon signal is too small to cause any biological damage, even with long exposures.) What does reach the transmitter's antennas are reflections of the beacon signal from the walls.
When the time-reversed microwave transmission is generated, the radiation reverses course, bouncing off the walls in just the right manner to once again focus on the charging receiver, while missing the person in the room. (The person is subjected to a very small microwave exposure from diffuse scattering at the walls, but again this is at a very safe level.) Extensions of the same principle work for rooms containing multiple obstacles as well as multiple charging receivers (see photo gallery for examples). Owing to the way the Cota system harnesses the time-reversal symmetry of electromagnetic radiation, it is extremely flexible and intrinsically safe in use.
Ossia plans to license the technology to consumer electronics OEMs and ODMs for integration into consumer electronics products and the system could also be retrofitted to existing devices via an add-on dongle arrangement.
The potential of the Cota system for recharging and directly powering portable devices seems nearly unlimited. If these systems become a common feature of our everyday environment, in stores, offices, restaurants, cars, trains, and planes, the reliability and convenience of our portable connectivity will leap far beyond the current state of affairs. At a price point expected to be not terribly in excess of that of a Wi-Fi router, this could well be a dream that comes true.
Zeine demonstrates and discusses the prototype system in the video below.
Source: Ossia, Inc.
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