Wireless Charging

TIRED OF WIRES?

MARTIN B. QU

Imagine a world where you can charge your phone remotely, imagine if you could charge everything remotely, not only phones but also TVs, stereos, and even electric cars? Nowadays, scientists have already developed such technology to

charge cell phones

wirelessly, as shown

in Figure 1. Scientists

are working further

to charge electronics

over a greater

distance, and are Source: gigmag Figure 1: An in-production wireless charging mat expected to announce the first in-vehicle charging system this year [i]. But do you know what the concept of wireless charging actually started over a hundred years ago?

Wireless Charging Isn’t A New Concept

Early In 19th century, scientists had already discovered the phenomenon of electromagnetic conversion theory. They knew that electricity could be transformed into an electromagnetic wave, which propagating through the almost any mediums, such as water and air. Although in the 19th century, no one had ever think of the idea

Page 1 of 7 Wireless Charging to transfer electricity wirelessly, this characteristic of electricity has later become the fundamental theory for wireless power transfer [ ii ]. Nowadays, many applications that perform the function of wireless charging are based on this phenomenon.

In the 19th century, physicist and engineer Nikola

Tesla conducted a remote wireless energy transfer experiment [iii], also known as the Wardenclyffe Tower Project.

As shown in Figure 2, this most ambitious attempt was used to demonstrate the concept of Source: sftesla.org global wireless energy transfer Figure 2: Wardenclyffe Tower, also known as the Tesla Tower. The tower was designed by Nikola and aimed at transferring energy Tesla and used to demonstrate wireless power transmission. across the Atlantic Ocean. However, after exhausted all of Tesla’s financial resources, this 29-meter-high tower eventually failed.

After the Wardenclyffe Tower Project, scientists tried several other attempts, include laser and directed energy conversion mechanism. However, those attempts all require continuous visual lines, which would have a negative impact on the power facilities around residence. It has not been until very recently that scientists brought out Tesla’s experiment again and put it into practice.

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How Does It Work?

Wireless charging can be completed in several ways. One of the most common ways to transfer energy wirelessly is through a process called resonant inductive coupling, or also called electrodynamic induction. The resonant inductive coupling consists of two processes – induction and resonation. First, to understand induction, it is helpful to know more about some characteristics of electricity. When an electric current flows through an electric wire, it creates a magnetic field around it. In the meanwhile, if another wire is close to the first wire, an electric current will be generated in the second wire. This process is called induction.

But how can electricity transfer over greater distance? In physics, when the natural frequency of one object resonates with another, this other object will oscillate [iv]. Think of this example as an explanation: if we put several cups inside a room, and fill up each cup with wines to different levels, the cups will produce different amplitude. If we hit those cups with a spoon, they will produce different sounds, because they have different frequencies of vibration. Meanwhile, if a singer enters a room, and starts singing with a very high voice, if the voice resonates with one of the cups’ frequency, the cup is possible to explode – a process called resonation. The same concept applies to electricity [v]. In induction, when a coil shaped electric wire picks up the electricity, the electricity eventually dies away over cycles. However, if a second coil is placed near the first coil and oscillates at the same frequency, the second coil will be able to theoretically pick up all of the energy.

This theory upholds if a third and a fourth coil is added, hence transfer electricity over greater distance.

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One of the most well known early-age

application of the resonant inductive coupling is

the Tesla Coil, as shown in figure 3. The coil

transfers high voltage, low current electric

energy through air [vi]. However, the efficiency

of transmit energy using a Tesla Coil is low; the

Tesla Coil can also deliver considerable risk, due

to the high frequency current [vii]. Due to all

these disadvantages, Tesla Coil didn’t gain much

popularity despite in the entertainment

industry. Even today, Tesla Coils can still be

wiki found in many science museums, for education Figure 3: Tesla Coil. An electrical resonant transmitter developed by Nikola Tesla in 1891. and entertainment purposes.

Recent Developments and Applications

It is not until very recently that wireless charging brought attention again. On

June 7, 2007, an MIT research team published their findings in the U.S. "Science" magazine. The research team was able to “seize” electromagnetic energy in air and transferred into electric energy in a safe manner and increasing efficiency. Such technology allows them to light up a light bulb at two-meter distance. They used a copper coil as the object for electromagnetic resonance. One coil is attached to the electric sender, and another coil is attached to the electric receiver. By transmitting the energy into a resonating wave, the electricity will be able to wirelessly transmit.

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After several attempts, this “wireless power” technology could transfer energy wirelessly with 40% efficiency [viii].

At about the same time, a British company developed a wireless cell phone charger based on the idea, the same charging device showed at the beginning of this article (Figure 1). The product looks like a plastic mouse pad. It is equipped with an intensive small coil array, which can produce a weak magnetic field. The receiver inside cell phones will “pick-up” energy from the magnetic field and store energy into the battery. Because the energy is in the magnetic field, the mat is able to charge multiple devices at the same time.

Charging technology has already appeared; however, phone manufacturers need a standard so that the charging device provides the right current and voltage.

Therefore in 2008, Wireless Power Consortium developed the QI standard for inductive wireless power transfer. Today, many leading cell phone brands have already joined QI standard, such as HTC, Huawei, LG, Motorola, Nokia, Samsung and

Sony. The QI standard allows future cell phone productions to follow the same standard [ix]. Following the current trend, it is expected that in near future wireless charging hotpots will arise in public areas such as airports or coffee shops.

Look Into the Future

As the wireless charging technology regain its popularity, many applications are developing to benefit our future. Scientists are looking forward into greater steps to bring wireless charging further into life.

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In-Car Charging (Available: second-half, 2013)

With the development of wireless charging technology, Chrysler has already announced the first in-car charging system, available in later this year. The wireless charging device will be able to charge cell phones when they are placed on top of the charging device [x]. Similarly, Toyota has also announced it will be adding similar features in its models later this year.

In-House Charging (Available: 2020)

Based on the research by the MIT group, scientists expect to announce the first wireless charging room in 2020. The idea is that you can walk into a room and ever electronics in the room will be wirelessly powered. However, although the MIT group announced this concept years ago, such technology is still in the development stage. Several difficulties include the charging efficiency as well as the amount of energy transmitted. Currently, the MIT group can only achieve around 45% efficiency with a limited amount of electric energy being transferred. They are hoping that in future years, both the efficiency and energy amount will be increased.xi

Wirelessly Charged Vehicles (Available: 2022)

In July 2009, researchers at Korea Advanced Institute of Science and

Technology developed a system that can charge electric vehicles over a 12cm gap.

They believe that in the future, it is possible to power buses through an underground power line, so that buses will no longer require gasoline.

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Wireless Charging: What Is the Next Step?

A hundred years ago, Nikola Tesla had a dream. He hoped that one day electricity would flow freely into everyone’s home. Today, his dream is still not achieved. Wireless charging can have great benefits to human beings. Not only such technology can free us from wires, but also wireless charging could become a potential solution to the petroleum crisis. With scientists’ endless effort, hopefully

Tesla’s dream eventually comes true.

References

i Paul Whytock. (2013, January 17). The Life Of Qi: In-Car Wireless Charging Steps Up A Gear [Internet]. Available: http://electronicdesign.com/ed-europe/life-qi-car-wireless-charging- steps-gear ii Nicola Tesla, “Experiments with Alternate Currents of Very High Frequency and Their Application to Methods of Artificial Illumination,” in AIEE, Columbia College, N.Y., 20 May 1891 iii Gernsback, Hugo. "Nikola Tesla and His Achievements," in Electrical Experimenter, January 1919, pp. 615 iv Steinmetz, Dr. Charles Proteus, “Lecture II The Electric Field,” in Elementary Lectures on Electric Discharges, Waves, and Impulses, and Other Transients, 2nd ed, McGraw-Hill, Columbus, 1914, ch II, sec. 7 v Steinmetz, Dr. Charles Proteus, “Lecture II The Electric Field,” in Elementary Lectures on Electric Discharges, Waves, and Impulses, and Other Transients, 2nd ed, McGraw-Hill, Columbus, 1914, ch II, sec. 7 vi Nikola Tesla, "Electrical Transformer Or Induction Device". U.S. Patent No. 433,702, August 5, 1890 vii Tilbury, Mitch (2007). The Ultimate Tesla Coil Design and Construction Guide. New York: McGraw-Hill Professional. pp. 1. ISBN 0-07-149737-4. viii EetIndia.co.in. (2010, May 3). MIT lights 60W light bulb by wireless power transmission[Internet]. Available: http://www.eetindia.co.in ix Mattew Broersma. (2010, September 2). Qi Group Announces Wireless Power Prototypes [Internet]. Available: http://www.techweekeurope.co.uk/news/consortium-announces- wireless-power-prototypes-9405 x Huw Evans. (2012, April 09). Chrysler Lunches In-Car Wireles Charging [Internet]. Available: http://www.autoguide.com/auto-news/2012/04/chrysler-launches-in-car- wireless-charging.html. xi Simon Pickstock. (2012, October 9). Whatever Happened to Wireless Charging [Internet]. Available: http://www.techradar.com/news/world-of-tech/whatever-happened-to- wireless-charging-1103106

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