Wireless energy transfer
LIFE WITHOUT CORDS
By: Will Griffith
Reviewed By: Erik Biesenthal
Have you ever thought to yourself, "There are too many cords here," or wished you could put an electronic item somewhere else in a room but couldn't because of how far away the plug for you power cord was? That problem could end in the near future. Some scientists have found an efficient way of transmitting power wirelessly. Though there are a few obstacles to overcome, the idea of wireless power seems like a very distinct possibility in the near future.The man given the most credit for the idea of transferring energy wirelessly is Nikola Tesla. Tesla advanced the science of electricity and energy transfer. He invented such things as the transformer, currently the backbone of modern energy transfer. He made other useful inventions such as circuit breakers and condensers; he also came up with an idea for a wireless telegraph, which paved the way for modern radio (Nikola Tesla Museum).Additionally, Tesla played a big part in creating the modern power system. He had a bitter rivalry with Thomas Edison who supported Direct Current (DC) rather than Alternating Current (AC). Edison used DC for his power plants while Tesla tried to convince him to use AC. AC is more dangerous, but it has the ability, through transformers, to be sent much further with little energy loss. The key problem with using DC is that it does not work well over long distances. It is hard to produce the high voltages needed from a power plant in order to easily transport the electricity over distance. If the electricity is transported at low voltages, the current must be increased to compensate for the low voltage. This is not very efficient as seen in Ohm's law.
V= I*R
This equation shows the voltage drop over a given resistance. With the current higher, the voltage lost due to a certain resistance is increased. Since everything has resistance, even with the best wiring, the longer the electricity travels the more of it will be lost. A solution to this is the transformer. A transformer sets up two coils of wires. The first is small and is attached to the power plant. When a current is passed through it, a magnetic field is formed. The second coil is in close proximity to the first and is affected by the field. The second coil has many more wrappings of wire around it. The amount of times a wire is wrapped around a coil determines the effect the magnetic field will have on it. The next equation demonstrates that the voltage changes in relationship to the number of times the coil is wrapped changes. In the equation, "s" stands for secondary and "p" for primary.
This equation illustrates that the ratio of the secondary voltage over the primary voltage is equal to the ratio of the number of turns around the secondary coil over the number of turns in the primary coil. Also, as the voltage is stepped up, the current is stepped down, as expressed in the following equation.
This creates an ideal situation in which the voltage is high and the current is low, thereby allowing the power plant to send the electricity over large distances without losing much along the way. Once at its destination, the electricity is stepped back down to a safer voltage (Liebrand 2007). This concept is the basis of power transfer today. Transformers were just one of Tesla's revolutionary ideas, but he had much grander ones than that. Between 1900 and 1902, Tesla received multiple patents for his ideas of wireless energy transfer. He had planned to have a "world-wireless-system" where everyone would receive power without cables. Eventually, he planned to use a very large power plant and magnetic fields to transfer power to the entire world. It is on these ideas that new wireless energy transfer is based. Tesla was unable to make headway on this project because his financial backers pulled out (Grebb 2005). Since he was not able to bring his idea of wireless energy to fruition, he turned his sights to other areas of research. With his efforts thwarted, Tesla spent his later years expanding other areas of engineering. He invented different turbines, pumps, and other water transfer systems that were unique because they did not have paddles in them. Some of these designs are still in use today (Nikola Tesla Museum). But now, about a century later, Tesla's idea for wireless energy transfer may be resurrected; someday a true "world-wireless-system" might actually be created. Transferring energy wirelessly has its complications but is fundamentally simple. The one previous method that scientists have been aware of is using electromagnetic waves. Electromagnetic waves come in many forms such as light and radio waves. These are generally harmless, but there are others such as radiation or microwaves that can be quite harmful. The kind of waves that would be used for energy transfer would be more like those of radiation than ones of radio or light. This is dangerous though because these waves affect most organic and inorganic elements. The design requires the source of power and the object to be in direct line of sight. If something gets between them, the object would stop receiving power, but also whatever got in the way would be affected by the wave. In the case of living beings, this could be very dangerous (Derbyshire 2007). Recently, an idea occurred to some researchers at Massachusetts Institute of Technology (MIT): Rather than using electromagnetic waves, they could use magnetic fields similar to a transformer, but, rather than raising the voltage, the power could be transferred and the receiver could take the voltage as it is or even possible reduce it. This cannot be an ordinary magnetic field though; if it were, it would affect everything in the room. It would not be a pretty sight if a person was to walk into the kitchen and have all the metal bowls and silverware attached to the walls. This is where the ingenious MIT idea fits in. The researchers created coils that oscillate at a specific frequency with the AC. This creates a magnetic field that only affects objects oscillating at that frequency. Thus, most organic and non-organic elements are not affected at all, and the power not absorbed is returned to the circuit. The addition of frequency to the design enhances this technology greatly also because it increases efficiency. If circuits that did not oscillate at certain frequencies were used it would be about one thousand times less efficient (Hadley 2007). Most likely these coils would be placed in the walls of a building. This would allow for the most coverage inside and thereby maximizing efficiently. Wireless energy transfer has been proposed before but so far the research has not yielded practical results. One conceived concept was to convert electricity to electromagnetic waves, as previously mentioned, but in this case, the waves would be beamed from space to the earth. The United States government was investigating the idea, but at some point, it decided that electromagnetic waves could be even more useful as a weapon. Such use is now being evaluated as a possible non-lethal weapon. Similar to the concept of lasers in science fiction, these waves could be set to immobilize, or they could kill (Grebb 2005). Having this kind of technology in homes or offices would have many advantages. One of the best results would be that cell phones, laptops, or other portable devices could stay charged as long as they are in the home or office. This possibility inspired the research at MIT. Marin Soljacic, an assistant professor of physics at MIT, was once awakened by his cell phone at 3 a.m. The phone’s battery was dying, and the warning signal began beeping. He was irritated and wondered why no one had invented a way to have his phone continuously charging while in his house. He started thinking up a solution to this problem, and with some help from his colleagues, it seems that he has succeeded (Castelvecchi 2007). Another advantage is the freedom of space. With wireless power, it would be possible to arrange a room with little concern for placing electronics. Often, in room arrangement, large electronics are the first items placed, but they are limited to a set range away from a power outlet. Also, these items are often placed alongside the wall so that the cords don't get in the way or trip people. If the power cords were removed, this would eliminate that problem and allow for more pleasing arrangement opportunities. Unfortunately, this aspect of the technology has limitations. One is that it does not work over long distances (Castelvecchi 2007). In a regular house or apartment, most rooms are small enough that all electronics would be within range of the power source. Large dining halls or other large rooms could be a bit more complicated if an electronic item were to be placed at the center of the room. In the experiments done at MIT, the researchers discovered that at the approximate distance of six feet the power efficiency was 40% for their coils (Foire 2007). Due to the drop in efficiency over range it could be a problem to have certain objects too far from the wall. If an object is not close enough it might not be able to draw the amount of power it needs to run.
Efficiency vs. Distance
Figure 1: This shows the drop in efficiency over distance (Kurs 2007).
Another advantage to the energy transfer system is that it could power multiple devices at once. No longer would a person have to deal with power strips or extension cords. The TV, cell phone, and laptop all could be powered at the same time (Thompson 2008). The complication to this system will be getting the electronic companies to create the same receivers for their products. The circuits must be on the same frequency for this to work. At the same time, different frequencies could be used for different types of machines. The appliances such as the dishwasher, the washer and dryer, and the refrigerator could all be on the same frequency while other objects could be on a different one. This would help alleviate another potential problem, needing more power than is available. In a normal circuit, the overload would blow the breaker, but what has not been discussed is how this situation will be handled by the new technology. If there wasn't a breaker the circuit could draw too much power and break, or it could cause other problems like fire. Having different frequencies would help this issue immensely. Some issues still need to be addressed before this technology is adopted. Probably the biggest is safety. Magnetic waves appear to not have much affect on organic life, but there have not been extensive tests on how long-term exposure could affect it. The researchers at MIT are not too concerned. As of now, it appears that this technology is still following the standards set by the Institute of Electrical and Electronics Engineering (IEEE) (Kurs 2007). Still, it will take many more tests to prove that human beings are unharmed by this technology. Also, the safety of other electronics needs to be considered. With magnetic fields going everywhere, it could disrupt other electronic devices. This could cause interference with the electrical flow of simple things like the TV or radio, but it could potentially cause disaster by affecting devices like pacemakers. Either way, much more research needs to be done in this field before it can be declared safe for people or electronics. A further issue to consider is how people will be billed for their power use. This was the reason Tesla's supporters backed out. They were not sure how they could bill their customers if they just produced electricity and distributed it to the public. While power suppliers can set up meters to read how much goes in and out of a house, someone might be able to splice into his neighbor’s supply and take from the power the neighbor is paying for. This concern has not been sufficiently addressed yet, but if it is ever used wildly research will have to be done by the power companies in this area. Other forms of wireless power transfer exist, but they are not as refined. Powercast, a company currently making a product for small devices, like cell phones or portable music devices, that charge them without cords. The device works to power appliances three feet away from the plug. Plugged into the wall, it produces low-power radio waves. Then if a device has a receiver built in, it can convert these waves to DC and charge itself up. Companies would add little to the cost when incorporating the receivers into their products, possibly five dollars extra per unit. Also, in a few years laptops will probably require much less power, and this device could be powerful enough to charge future laptops. This is a step in the right direction, but at present, it still only works on small objects and within a very limited range (Haiken 2007). Some products already use this technology. For example, many people own an electric toothbrush. Some of these devices now charge, but they are not plugged into the charger. They sit in a cradle and, with no direct connection, charge themselves. These devices use the same concept as that of the MIT design; a cradle has one coil that is connected to the power while the second one is in the object needing to be charged. This way the device does not have to be physically plugged in; just its cradle has to be. This technology may have been incorporated into objects like electric toothbrushes in order to house all the electronics and rid the design of water-damaging problems. Another invention like this is a charging pad, a small, thin pad, shaped kind of like a mouse pad, that a person can put electronic items on which charge without being plugged in (Wilson 2007). These examples illustrate the potential that wireless energy transfer holds. Wireless power transfer has a bright future with some obstacles along the way. The most important, as previously stated, is safety. There are some concerns that must be addressed first by doing further research. Also the integration of this technology needs to be considered. Not only how it will be applied in new buildings, but also how older ones can be retrofitted with the new technology. It will also take a lot of backing from companies who would like this technology in their products. These issues still are far outweighed by the advantages of wireless power and so it will be widely used at some point in the near future. Wireless power seems on the verge of coming out of science fiction and into homes and offices. The science has been around for over a century although scientists have just recently realized its potential. Some other products already use this technology on a smaller scale. Now, after a bit more research, the kinks could be hammered out, and no one would have to plug their electronics into the wall ever again.
WORKS CITED
Castelvecchi, Davide. 2006. "Wireless energy could power consumer, industrial electronics: Dead cell phone inspired researcher's innovation." Massachusetts Institute of Technology: News Office, November 14. http://web.mit.edu/newsoffice/2006/wireless.html (accessed February 6, 2008).
Derbyshire, David. 2007. "The end of the plug? Scientist invent wireless device that beams electricity through your home." Daily Mail: 24 hours a day, June 8. http://www.dailymail.co.uk/pages/live/articles/technology/technology.html?in_article_id=460602&in_page_id=1965 (accessed February 6, 2008).
Fildes, Jonathan. 2006. "Physics promises wireless power." BBC NEWS, November 15. http://news.bbc.co.uk/2/hi/technology/6129460.stm (accessed February 6, 2008).
Fiore Kristina. 2007. Reviving Tesla's wireless power initiatives. Electronic Design. September 13. http://electronicdesign.com/Articles/Index.cfm?AD=1&ArticleID=16478
Grebb, Michael. 2005. "Space geeks seek wireless power." Wired, October 20. http://www.wired.com/gadgets/wireless/news/2005/10/69038 (accessed February 6, 2008)
Haiken, Melanie. 2007. "Death of the cell phone charger." Business 2.0 Magazine, March 30.http://money.cnn.com/magazines/business2/business2_archive/2007/04/01/8403349/ (accessed Febuary 6, 2008).
Hadley, Franklin. 2007. "Goodbye wires. . . ." Massachusetts Institute of Technology: News Office, Jun 7. http://web.mit.edu/newsoffice/2007/wireless-0607.html (accessed February 26, 2008).
Kurs, Andre, and others. 2007. Wireless Power Transfer via Strongly Coupled Magnetic Resonances. Science Express vol. 217, no 5834 (July 6). http://www.sciencemag.org/cgi/content/full/317/5834/83
Liebrand, Fred. 2007. Principles of physics. Class lecture. College Place, WA. Winter quarter.
Nikola Tesla Museum. Biography. Nikola Tesla Museum. http://www.tesla-museum.org/meni_en/nt.php?link=tesla/t&opc=sub1 (acceded Febuary 26, 2007)
Thompson, Dalee. 2008. Electricity in the Air. Popular Science, January 23.
Wilson, Tracy V. How wireless power works. Howstuffworks.com, http://electronics.howstuffworks.com/wireless-power.htm (accessed February 6, 2008) (This was submitted for review on January 07, 2010 10:52 PM)