Electricity With No Strings Attached

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Over the past century, electricity has evolved from being a luxury affordable to a few, to an indispensable fuel to our everyday lives. The rapid advancements in technology have only been possible through the parallel development of electrical and electronic devices. So pervasive is electricity's influence, so entrenched its universal utility, the invention and evolution of virtually every conceivable modern device may not have been possible without electricity.

From communications to transportation, design to manufacturing, electricity has become essential to modern life.

Ironically, little has changed as far as how electricity gets transmitted. Despite all the seemingly magical gizmos and nick-nacks of modern life —cellular phones, PDAs, laptops, etc—what remains anachronistically stuck in the age of Tesla and Edison is the actual means by which we transmit this vital energy. Metal Wire.

In terms of power transmission, it seems the world has stood still for over a century. While power generating technologies have grown tremendously since the advent of electricity, power distribution is an area that has remained virtually stagnant since the first utility company strung its first supply line to a home to light a bulb. This fact is an indication of the daunting challenges we face in the pursuit of wireless power transmission.

But things are beginning to change—and rapidly. In just the past few years, several teams of researchers have made significant strides in transmitting electrical power wirelessly. Finally, the advancement of electricity is beginning to catch up with the sophistication of the machines it powers. It would not be an exaggeration to state that we are finally on the threshold of a truly end-to-end wireless world.

A walk through parts of any city in the world would provide views of skies crisscrossed with power lines; casting a look further would reveal endless miles of cables astride spindly pylons disappearing over the horizon. The money invested in developing the U.S. power infrastructure is estimated at over 1 trillion dollars [1]. Professor of Power Engineering, Robert Castro, quotes “about $1.5M to $2M a mile for overhead 500kV transmission, and 500kV transformers at $2.5M each phase.” As one can assess from these staggering numbers, depending upon these existing technologies in order to supply power to an ever-expanding customer base could be very cost-prohibitive, and perhaps ultimately even impractical and ecologically insensitive. Obviously, this is a glaring obstacle to growth.

With recent developments in wireless power transmission, however, we may finally be able to solve this problem. New means of providing power are crucial in order to accommodate emerging technologies and swelling populations worldwide. Understanding how this new technology works, and how it can substantially influence the course of human life on this planet could be invaluable­—especially to students pursuing various branches of engineering and technology.

Figure 1 Power lines of San Francisco [2]

The Concept of Wireless Electricity

Wireless electricity has been a “futuristic” concept for a very long time. The famous nineteenth century inventor, Nikola Tesla, grappled for much of his life with the challenges of transmitting electricity over very long distances. It was Tesla who first conceived and proposed the idea of wireless transmission of power. It has been claimed Tesla came close to perfecting a “power transmitter” in the course of his Wardenclyffe Tower experiment, but due to inadequate funding from sponsors his dream was never realized [3]. Following Tesla’s death much of his work was lost, but photographs such as the recognizable tower on Rhode Island have kept Tesla’s exciting ideas alive. Recently, some of Tesla’s ideas were resuscitated through the research of Marin Soljacic of MIT. In 2007 Soljacic and his MIT team became the first to transmit electricity wirelessly over a distance of several meters using magnetic induction and resonance [4]. The MIT team continues to work to improve their wireless systems and has evolved into a company named Witricity (an acronym coined from Wireless Electricity). Other companies have since followed suit by further developing and adding momentum to this new technology.

While the essential concept of wireless electricity is relatively easy to grasp, the details behind Soljacic’s method, and the many challenges he overcame, are rather more complex.  Soljacic’s unique approach is based on a marriage of electromagnetism and resonance. It is important to understand how these laws work and interact in order to comprehend Soljacic’s ingenious invention.

It begins with an understanding of how magnetic fields are generated. One can generate a magnetic field by simply propelling an electron using an EMF. The field thus produced “curls” around the trajectory of the electron in a clockwise direction. Any conductor that carries an electric current also generates a magnetic field around the electrons’ path.  The converse of this concept also holds true: applying a magnetic field around a conductor induces a current within that conductor.

Figure 2 Magnetic fields curling around a wire [5]

The generation (and effects) of magnetism can be amplified by wrapping multiple current-carrying coils in parallel. One can generate a current through this electromagnet by passing a magnetic field through the center of the loops. The principal involved is known as magnetic induction [5][6]. Using such a technique, one can employ power coupling, where the magnetic field generated by one coil induces a current through a second coil. This is the basic principle by which transformers operate. By controlling the number of windings, the current and voltage of each separate system can be manipulated as seen in Figure 3.

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Figure 3 Depiction of a transformer. Current fed from the primary winding induces a magnetic field through the transformer core. This field in turn induces a current through the secondary winding. As seen, the Magnetic flux must remain constant throughout the core. Therefore, changing the number of windings in the secondary coil changes the new current. 

Resonance is a property of oscillating systems with which we commonly interact. Essentially, the amplitude of an oscillating system increases when the applied frequency of an external source—e.g., a human voice or musical instrument—begins to resonate in sympathy with the natural frequency of the object at which it is directed. A clear example of this principle at work can be shown with a wine glass. The diameter of the glass determines the wavelength of the glass’s natural frequency. When one sings in close proximity to the glass with a steady, sustained note, the energy of the emitted sound waves ricochet within the glass, thereby inducing sympathetic mechanical vibrations in the physical structure of the glass. These vibrations, however, are only amplified if/when the frequency of the sung notes matches the natural frequency of the glass. If the vocal pitch and volume can be sustained, the resulting stresses induced can actually shatter the glass [5][7].

In the case of Soljacic’s model as depicted in Figure 4, resonance amplifies the effects of power coupling in much the same way as with sound and the glass. Rather than employing sound waves, however, oscillating magnetic fields generated by an AC current are made to pass through a coil. A second coil with a shared natural frequency serves as the receiver. The identical natural frequencies of the coils allow for the efficient transfer of power between the units. This method of power transmission has some advantages. For example, because the system relies on a magnetic field, a current could still be generated even if a physical barrier were to separate the two sets of coils. Given the system’s demonstrable success in a laboratory, it would seem that a viable solution for the century-old challenge of wireless power transmission has finally arrived [5].

Figure 4 the first prototype produced by the MIT team

What Wireless Electricity Can Accomplish

All home appliances require either batteries, or at the very least direct wiring, in order to function. Batteries, however, come at an economical and environmental price. Billions of dollars are spent annually in the research, development and production of disposable batteries. Batteries are composed of various environmentally toxic substances such as mercury, lead, and lithium. As such, their safe disposal requires expensive and tedious methods. It is estimated that some 180,000 tons of batteries are deposited in landfills annually[8]. As Eric Giler, leader of the Witricity team, explains, "There is something like 40 billion disposable batteries built every year for power that, generally speaking, is used within a few inches or feet of where there is very inexpensive power"[9]. 40 billion batteries! This not only assumes a large percentage of improperly disposed batteries, which could be hugely detrimental to the environment, but also represents a colossal loss of investment in a temporary power source that will inevitably be discarded. Since a majority of battery-powered appliances are generally located in close proximity to mains supplies anyway, batteries are a costly and impractical answer to the problem they are primarily intended to address: portability.

Giler demonstrated the capabilities of the wireless electric device during the 2008 TED expo at Cambridge University. He showed that the technology could be incorporated into certain mobile devices so they could be charged wirelessly. Such a fundamental application alone would free billions of devices of the need for batteries.

This exciting new technology also holds much potential for use on a macro scale. Current power distribution networks around the world rely on a vast number of ancillary structures and systems. Our power plants (nuclear, hydroelectric, solar), while reasonably efficient, require transformers to step up the voltage, transmission lines to conduct the electricity, and additional step-down transformers to provide usable electricity to be routed for commercial use. Additionally, there are numerous redundant safety and backup systems to guarantee uninterrupted service. And continuous monitoring and maintenance are required to keep these elaborate systems working and in check. All of this demands massive investments in materials and manpower, and translates into exorbitant operating costs. With further developments in wireless technology, such inefficient systems would be quickly rendered archaic and forced to go the way of the buggy whip. At the same TED event, Giler proceeded to demonstrate the transmitter’s potential by using it to fully power a television. As he later explained in an interview with BBC, "Imagine you get one of these things [television] and you want to hang it on the wall. Think about it, you don't want those ugly cords hanging down." It is this unprecedented ability to replace unsightly cords with invisible electromagnetic power—today, inside homes; tomorrow, outside of them—that distinguishes wireless power transmission as a revolutionary new technology whose time has truly come.

Safety concerns and Limitations

The magnetic induced resonator is a relatively safe device due to its reliance on magnetic fields, as opposed to electromagnetic radiation. Prior to this discovery, there existed another wireless power transmission technology that employed high frequency microwaves. The transmitted microwaves were absorbed by nano-antennas (nantennas), which resonated to the microwave frequency, and this resonant energy was in turn converted into electricity for practical use [10]. However, the resulting microwave radiation posed a serious health hazard, causing these systems to be deemed unfit for commercial use. Magnetic fields, on the other hand are known to be harmless. In order to demonstrate to his audience the system’s innocuous nature, Giler walked through the flux field. Similarly, MRI machines rely on the use of magnetic fields to display three-dimensional models of the human anatomy. Individuals are sometimes placed in MRI machines for hours at a time with no long-term side affects. Indeed, magnets are actually used by many modern medical practitioners for healing the human body [11]. And if ultimate proof of the safety of the technology were needed, one only needs consider the fact we humans are immersed in a perpetual terrestrial magnetic field since birth. Therefore it would not be unreasonable to deduce that even long-term exposure to these induced magnetic fields would present no known health issues.

The most pressing concern, it appears, is one related to the technology’s commercial ramifications: how would such a system of distributed energy be metered?  The possibilities are interesting indeed.  In fact, it has been claimed by several historians that this was the very reason why Tesla was eventually deprived of all funding for his project. The problem today, as then, remains unchanged: How would end users be billed for their consumption? In our current system, meters mounted on homes and commercial buildings measure usage, and consumers are billed accordingly. However, in the case of wirelessly supplied electricity, measuring usage would present serious—albeit perhaps not insurmountable—challenges, and require novel solutions. And then there are the philosophical implications. Tesla’s suggestion that electricity should be freely accessible by all inhabitants of the planet isn’t one that went down well with the power companies of the time, and is unlikely to be any more palatable today (albeit in an egalitarian world such an idea would make a degree of sense).

The distance across which power can be effectively transmitted is a matter that raises its own set of challenges.  Witricity’s device is currently cable of delivering energy across just a few feet.  But, as with other significant technologies that pepper the annals of human history—aviation, for example—the question of range seems to be one that is scalable. What is very encouraging is that, seeing the vast potential this new technology holds, companies around the world are clamoring to climb aboard the wireless wagon. With adequate funding and human resources, the technology shows tremendous promise to be not only a viable alternative to the conventional power grid, but one that could well relegate virtually all aspects of the wired distribution model to history.

The Future of Wireless Electricity/ Research Projects

Leading-edge companies such as Intel are further developing the technology first pioneered by Soljacic and his MIT team. As with similar breakthroughs of the past, these independent projects will hopefully grow exponentially, making the electromagnetic resonator a technology that is commonplace. Bringing different approaches and visions into play can substantially accelerate its development. As lead researcher of the Intel project, Josh Smith explains, "We're building on [what the MIT researchers] demonstrated in 2007 and extending it in different ways" [12].

Nokia, too, has tailored the concept of resonance to their plans for the future. Interestingly, rather than using magnetic induction, Nokia’s variation uses an antenna capable of resonating with ambient electromagnetic waves. Nokia intends to create a system that absorbs all frequencies between 500MHz to 10GHz and which can generate 50 mW—sufficient to recharge a depleted phone battery [13].

As with any such incipient technology, copyright infringement is another predictable concern. The ability of Witricity’s proprietary ideas to hold legal sway against those of emerging competitors is something that is bound to raise interesting legal arguments. However, this much can be predicted with certainty: as the wireless technology market continues to grow at its galloping pace, the search for wireless power solutions will increase with unbridled fervor.

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Work Cited

[1] "R. Castro, Los Angeles Department of Water and Power." E-mail interview. 30 Jan. 2012.

[2] J. Goldstein."Environmental Impact Photography – Blog Action Day." JMG-Galleries: Travel, Landscape, and Nature Pictures - Photos, Fine Art Prints and Videos by Jim M. Goldstein. 1 Feb. 2012. Web. 01 Feb. 2012. <http://www.jmg-galleries.com/blog/2007/10/15/environmental-impact-photography-blog-action-day/>.

[3] "W. Broad. "A Battle to Preserve Wardenclyffe, Tesla’s Bold Failure." The New York Times. ING, 04 May 2009. Web. 01 Feb. 2012. <http://www.nytimes.com/2009/05/05/science/05tesla.html?pagewanted=all>.

[4] J. Fildes. "BBC NEWS | Technology | Wireless Energy Promise Powers up." BBC News. BBC, 7 June 2007. Web. 01 Feb. 2012. <http://news.bbc.co.uk/2/hi/6725955.stm>.

[5] "WiTricity Corp. — Basics of WiTricity Technology." WiTricity Corp. Home — Wireless Electricity Delivered Over Distance. 22 July 2011. Web. 01 Feb. 2012. <http://www.witricity.com/pages/technology.html>.

[6] "How Wireless Power Induction Works." The Tech-FAQ. 1 Feb. 2012. Web. 01 Feb. 2012. <http://www.tech-faq.com/how-wireless-power-induction-works.html>.

[7] "HowStuffWorks "Resonance"" HowStuffWorks "Science" Discovery, 1 Feb. 2012. Web. 01 Feb. 2012. <http://science.howstuffworks.com/resonance-info.htm>.

[8]Batteries | Product Stewardship | US EPA." US Environmental Protection Agency. 16 Feb. 2010. Web. 01 Feb. 2012. <http://www.epa.gov/epawaste/partnerships/stewardship/products/batteries.htm>.

[9] Fildes, Jonathan. "Wireless Power System Shown off." BBC News. 23 July 2009. Web. 01 Feb. 2012. <http://news.bbc.co.uk/2/hi/8165928.stm>.

[10] R.Kwok. "Flexible Nanoantenna Arrays Capture Abundant Solar Energy." Idaho National Laboratory. Web. 02 Feb. 2012. <https://inlportal.inl.gov/portal/server.pt?open=514>.

[11] "HowStuffWorks "How Strong Are the Magnets in an MRI Machine?"" HowStuffWorks "Learn How Everything Works!" Discovery. Web. 01 Feb. 2012. <http://www.howstuffworks.com/question698.htm>.

[12] K. Greene. "Intel's Wireless Power Play - Technology Review." Technology Review: The Authority on the Future of Technology. MIT, 22 June 2009. Web. 01 Feb. 2012. <http://www.technologyreview.in/energy/22906/>.

[13] D. Rowe. "Wireless Power Harvesting for Cell Phones." Technology Review: The Authority on the Future of Technology. MIT, 9 June 2009. Web. 01 Feb. 2012. <http://www.technologyreview.com/communications/22764/>.