WiTricity – The Dawn of Wireless Power
Within grasp: A world without (charging) wires
by Jane Porter
Cars,
medical devices, industrial machines, and oh yes, your phone—the tech industry
is hard at work developing ways to cut the cord. Standing in its way: physics
and a nasty war over standards.
Last June, Toyota revealed plans to release a plug-in electric Prius in 2016 that needed no plug at all to recharge, thanks to wireless technology from a U.S. company called WiTricity. The next day, Intel INTC 0.80% announced plans to release a completely wire-free personal computer by 2016—no power cord or monitor cable necessary. Nine days later, Starbucks SBUX 0.26% announced that it would begin installing Duracell Powermat wireless charging pads in tables and counters in its stores across the United States.
It’s not just the month of June that was charged with wireless power headlines. Wireless charging technology is poised to break through in the next few years, dramatically changing our relationship with our mobile, but still power-tethered, electronic devices. Thoratec, a healthcare company, is working with WiTricity on a wireless way to charge heart pumps and other medical equipment. Lockheed Martin, the aerospace and defense giant, is working on a laser-based system to recharge drones in mid-flight. The list goes on.
The wireless power market is expected to explode from a $216 million in 2013 to $8.5 billion in 2018 globally, according to IHS Technology, a market research firm. Why, then, are most of us still wrestling with a pile of cords at home?
“The reality is that the overall wireless charging market for consumer electronics is in the very early stages,” says Kamil Grajski, vice president of engineering at Qualcomm QCOM 0.12% and the founding president of the Alliance for Wireless Power, or A4WP for short, one of three groups working on the development of wireless charging technologies.
Induction, the technology behind wireless charging, isn’t new—it’s been around for well over a hundred years. Here’s how it works: an induction coil creates an electromagnetic field (on a charging dock of some kind) that comes in contact with another induction coil (attached to the device to be charged), transferring electricity to it. It’s the same process used to juice up your electric toothbrush in its charging stand, Grajski says.
But induction technology has limitations that have limited its mainstream appeal. It only allows for a single device to be charged per coil, making it clunky and relatively inefficient in today’s multi-device world, and it requires precise placement of the device to be charged so that the coils are aligned in order to initiate and sustain the charging process.
Proponents of inductive technology like Ran Poliakine, chief executive of Powermat, believe the key to increasing adoption of wireless charging lies not in figuring out the fastest or most efficient connection, but in making the technology available to people where they need it most. “The issue we are trying to address is how do we keep consumers charged throughout the day,” he says. “The barrier to entry was relevancy. Where do we put the charging spots?” He added: “The place you mostly need this service is outside your home and your office.”
He has a point. Placing charging stations in Starbucks locations is one way to do that, saving customers from the inevitable outlet search that comes with a drawn-out session at the café. Placement in airports and hotels, also in the works at Powermat, are two more ways. (One thing people may not know about Powermat’s charging stations: when used in conjunction with a cloud-based management system the company provides, a retailer can monitor who is at which station and for how long. Which means Starbucks could either give you the boot for squatting for six hours or beam you a coupon for a free refill to keep you there.)
Another reason for the technology’s slow adoption? A good old-fashioned standards war between industry groups. The Power Matters Alliance, or PMA, backs one type of induction standard and counts Duracell, Procter & Gamble, Qualcomm, and WiTricity as members. The Wireless Power Consortium, or WPC, backs an induction standard called Qi (pronounced chee) and counts Hitachi, IKEA and Verizon as members. Some companies, such as Microsoft and Samsung, are members of both groups.
The two standards use what is essentially the same technology but apply it with different specifications, creating problems for the companies that must embed the technology in their products. According to John Perzow, vice president of market development for WPC, 63 phones on the market today support the Qi standard, including those from Nokia, Google, and Sony. Meanwhile, Google Nexus and LG phones, among others, will have Powermat compatibility built into them.
To up the ante, Powermat has plans to give away free “charging rings,” similar to those made by the Finnish firm PowerKiss it acquired last year, to Starbucks customers to encourage them to use in-store chargers. (It plans to sell them at retail for less than $10.) Meanwhile, the PMA struck a deal with A4WP in February to support its Rezence standard, which uses another kind of wireless charging technology called magnetic resonance.
Both industry groups look to magnetic resonance technology as the likely second-generation standard for wireless charging, thanks to its ability to transfer larger quantities of energy and therefore support larger devices such as kitchen appliances. (The WPC says it is working on its own version of the tech.) The wireless PC that Intel demonstrated at Computex last month—you can see it in a video here—uses the Rezence standard.
Magnetic resonance technology relies on resonant magnetic coupling, which creates a magnetic field around each coil that transfers power without having to align coils precisely. It can charge a device across small distances (about two inches) rather than requiring near-direct contact—a table can be retrofit with a charging pad attached underneath it instead of embedded in its surface.
Magnetic resonance also allows more than one device to be charged at the same time. The Rezence standard uses the Bluetooth connection already present in many mobile electronics to detect the presence of a compatible charger. The technology is not yet on the market, but Grajski anticipates products using Rezence could be seen in stores as soon as this year. “Some of the barriers are just getting the right players in industry to adopt the technology and make it available at a reasonable price,” he says.
Still, two inches is two inches. What about beaming power across a room? That’s where WiTricity comes in. Born out of the Massachusetts Institute of Technology in 2007, the company continues to develop what Kaynam Hedayat, vice president of product management and marketing, calls “highly resonant wireless power transfer” technology.
Imagine an opera singer who can break glass with her voice—that’s how the technology works, Hedayat says. “Objects have a certain frequency by which they start vibrating,” he says. Tune a receiver and a device to the same frequency and they begin communicating with each other. “The energy is only transferred to devices that are tuned to that frequency,” he says. This allows electricity to transfer over distances of up to four feet. “With that, a lot of possibilities open up,” he adds.
Such as charging vehicles or medical equipment wirelessly. “Wires in hospitals are a big issue because you have to sterilize every device,” Hedayat says.
Or use in military applications, where robots in the field can be recharged while in position. Wireless charging tech could also help soldiers cut down on the nearly 40 pounds of battery that many soldiers carry on their backs, Hedayat says. And charging sensors on submarines would enable battery charging in deep-sea conditions, where it’s unsafe to run wires.
For now, the wireless charging standards war rages on, and the technology remains a novelty at best. But it can’t go on forever. Just as Wi-Fi became the standard protocol for wireless data exchange between computers, so shall one wireless charging standard emerge as the winner. Only then will we see what wireless charging is capable of.
“In four or five years, there will be one standard for wirelessly charging devices,” Hedayat says. ” You will forget about different adapters and connecters. You will find a hotspot and it’s just going to work.”
Things that Go Beep in the Night
Eureka! Coupled Resonators
To achieve wireless power transfer in a way that is both practical and safe, one needs to use a physical phenomenon that enables the power source and the device (in this case, the mobile phone) to exchange energy strongly, while interacting only weakly with living beings and other environmental objects, like furniture and walls. The phenomenon of coupled resonators precisely fits this description. Two resonant objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with extraneous off-resonant objects.
A child on a swing is a good example of a resonant system. A swing exhibits a type of mechanical resonance, so only when the child pumps her legs at the natural frequency of the swing is she able to impart substantial energy into the motion of the swing. Another example involves acoustic resonances: imagine a room with 100 identical wine glasses, but each filled with wine up to a different level, so that each resonates at a different frequency (that is, they each emit a different tone or note when tapped, by a utensil, for example). If an opera singer enters that room and sings a very loud single note, the glass having the corresponding resonant frequency can accumulate enough energy to shatter, while the other glasses are unaffected.
Strong Coupling
Coupled resonators are said to operate in a strongly coupled regime if their energy transfer rate is substantially higher than the rate at which they lose energy due to factors such as material absorption and radiation. In the strongly coupled regime, energy transfer can be very efficient. These considerations are universal, applying to all kinds of resonances (e.g., acoustic, mechanical, electromagnetic, etc.). Soljačić and his colleagues at MIT (Karalis and Joannopoulos) set out to explore and develop the physical theory of how to enable strongly coupled magnetic resonators to transfer power over distances to enable the kind of wireless device charging that Soljačić first imagined. Their theoretical results were published first in 2006, and again in 2008 in the Annals of Physics.
Once the physical theories were developed, Soljačić and his team (Kurs, Karalis, Moffatt, Joannopoulos, Fisher) set out to validate them experimentally. The theory was developed to cover a broad range of coupled resonator systems, but the experimental work focused on proving that magnetically coupled resonators could exchange energy in the manner predicted by the theory and required for the wireless charging of devices, such as mobile phones. The team explored a system of two electro-magnetic resonators coupled through their magnetic fields. They were able to identify the strongly coupled regime in this system, and showed that strong coupling could be achieved over distances that greatly exceeded the size of the resonant objects themselves. The team had proven that in this strongly coupled regime, efficient wireless power transfer could be enabled. Their successful experiment was published in the journal, Science, in 2007.
WiTricity Technology is Born
The experimental design consisted of two copper coils, each a self-resonant system. One of the coils, connected to an AC power supply, was the resonant source. The other coil, the resonant capture device, was connected to a 60 watt light bulb. The power source and capture device were suspended in mid-air with nylon thread, at distances that ranged from a few centimeters to over 2.5 meters (8.2 ft). Not only was the light bulb illuminated, but the theoretical predictions of high efficiency over distance were proven experimentally. By placing various objects between the source and capture device, the team demonstrated how the magnetic near field can transfer power through certain materials and around metallic obstacles.
Thus, Prof. Soljačić’s dream of finding a method to wirelessly connect mobile electric devices to the existing electric grid was realized. WiTricity Corporation was launched in 2007 to carry this technology forward from the MIT laboratories to commercial production.
WiTricity – The Basics
Understanding what WiTricity® technology is — transferring electric energy or power over distance without wires—is quite simple.
Understanding how it works is a bit more involved, but it doesn’t require an engineering degree. We’ll start with the basics of electricity and magnetism, and work our way up to the WiTricity technology.
 |
An
illustration of the earth’s magnetic field
|
Magnetism: A fundamental force of nature, which causes certain types of materials to attract or repel each other. Permanent magnets, like the ones on your refrigerator and the earth’s magnetic field, are examples of objects having constant magnetic fields.
Oscillating magnetic fields vary with time, and can be generated by alternating current (AC) flowing on a wire. The strength, direction, and extent of magnetic fields are often represented and visualized by drawings of the magnetic field lines.
Electromagnetism: A term for the interdependence of time-varying electric and magnetic fields. For example, it turns out that an oscillating magnetic field produces an electric field and an oscillating electric field produces a magnetic field.
 As current, I, flows in a wire, it gives
rise to a magnetic field,B, which wraps around the wire. When the current
reverses direction, the magnetic field reverses its direction. |
 The blue lines represent the magnetic field
created when current flows through a coil. When the current reverses
direction, the magnetic field also reverses its direction. |
Magnetic Induction: A loop or coil of conductive material like copper, carrying an alternating current (AC), is a very efficient structure for generating or capturing a magnetic field. If a conductive loop is connected to an AC power source, it will generate an oscillating magnetic field in the vicinity of the loop. A second conducting loop, brought close enough to the first, may “capture” some portion of that oscillating magnetic field, which in turn, generates or induces an electric current in the second coil. The current generated in the second coil may be used to power devices. This type of electrical power transfer from one loop or coil to another is well known and referred to as magnetic induction. Some common examples of devices based on magnetic induction are electric transformers and electric generators.
 |
An
electric transformer uses magnetic induction to transfer energy from its
primary winding to its secondary winding, without connected to each other. It
is used to “transform” AC current at one voltage to AC current at a different
voltage.
|
Energy/Power Coupling: Energy coupling occurs when an energy source has a means of transferring energy to another object. One simple example is a locomotive pulling a train car—the mechanical coupling between the two enables the locomotive to pull the train, and overcome the forces of friction and inertia that keep the train still—and, the train moves. Magnetic coupling occurs when the magnetic field of one object interacts with a second object and induces an electric current in or on that object. In this way, electric energy can be transferred from a power source to a powered device. In contrast to the example of mechanical coupling given for the train, magnetic coupling does not require any physical contact between the object generating the energy and the object receiving or capturing that energy.
Resonance: Resonance is a property that exists in many different physical systems. It can be thought of as the natural frequency at which energy can most efficiently be added to an oscillating system.
A playground swing is an example of an oscillating system involving potential energy and kinetic energy. The child swings back and forth at a rate that is determined by the length of the swing. The child can make the swing go higher if she properly coordinates her arm and leg action with the motion of the swing. The swing is oscillating at its resonant frequency and the simple movements of the child efficiently transfer energy to the system.
 |
Two
idealized resonant magnetic coils, shown in yellow. The blue and red color
bands illustrate their magnetic fields. The coupling of their respective
magnetic fields is indicated by the connection of the colorbands.
|
Another example of resonance is the way in which a singer can shatter a wine glass by singing a single loud, clear note. In this example, the wine glass is the resonant oscillating system. Sound waves traveling through the air are captured by the glass, and the sound energy is converted to mechanical vibrations of the glass itself. When the singer hits the note that matches the resonant frequency of the glass, the glass absorbs energy, begins vibrating, and can eventually even shatter. The resonant frequency of the glass depends on the size, shape, thickness of the glass, and how much wine is in it.
Resonant Magnetic Coupling: Magnetic coupling occurs when two objects exchange energy through their varying or oscillating magnetic fields. Resonant coupling occurs when the natural frequencies of the two objects are approximately the same.
WiTricity Technology: WiTricity power sources and capture devices are specially designed magnetic resonators that efficiently transfer power over large distances via the magnetic near-field. These proprietary source and device designs and the electronic systems that control them support efficient energy transfer over distances that are many times the size of the sources/devices themselves.
 |
The WiTricity power
source, left, is connected to AC power. The blue lines represent the magnetic
near field induced by the power source. The yellow lines represent the flow
of energy from the source to the WiTicity capture coil, which is shown
powering a light bulb. Note that this diagram also shows how the magnetic
field (blue lines) can wrap around a conductive obstacle between the power
source and the capture device.
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For more information about wireless power see http://nexusilluminati.blogspot.com/search/label/wireless%20electricity
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