Who haven’t ever imagined that, all electric wires just disappear and we transmit power without wires…?

the image is used for thumbnail purpose, courtesy to pixabay..!

To me, the most annoying part of recharging an electric device is the connecting cables..! It’s kind of like you are shackled to one corner of your room while the universe is spinning at 460 m/s…! 🤕

Well, thinking about Wireless Power Transmission (WPT), the first thing that pops into our minds is probably “Wireless cellphone charging"..! This is an example of WPT by way of inductive coupling [1].

wireless cellphone charging, snap by Shinya Suzuki _{under CC 2.0}

There are few other methods of transmitting power without wires. Let’s dive a little deeper into Wireless Power Transfer (WPT) technology.

The Background

Fig. 1. Tesla Tower.

Man has desired to deliver electrical power without the use of wires from as far back as the late 1800s. Distinguished scientist Nikola Tesla experimented with transmitting power using his magnifying transmitter. Tesla had the eventual goal of establishing a worldwide power distribution system. He developed the “Tesla Coil” aiming to produce radial electromagnetic waves with about 8 Hz frequency transmitted between the earth and its ionosphere which will eventually transmit energy. In 1901, Tesla built the "Wardenclyffe Tower" (also known as "Tesla Tower") with the intention of using it to broadcasting, wireless communication and transmit wireless power [2]. This project was never fully operational as Tesla ran out of funding and had difficulty finding new investors.

The promise of wireless power would be lost for several decades until it was reexamined with the arrival of microwave technology. While working at Raytheon in 1963, William C. Brown demonstrated the first microwave wireless power transmission system [3]. Since then, WPT technology has grown into a commodity that nearly every one of us wants in our home..! There are a lot of promising implementations of WPT that are being developed today. Samsung, Qualcomm, Texas Instruments, Philips, Witricity and many other leading inventors have been experimenting a wide range of WPT implementation. With aspirations of encouraging an eco-friendly planet, I predict that WPT technology will see great advancements over the next decade...!

WPT Fundamentals

This is quite a complex thing to explain in a blog post. Let’s see how deep we can go without flooding the blog with equations and circuit diagrams...! To get a better understanding of how WPT works, we may categories WPT in three general forms of functionality,

• Inductive Coupling
• Magnetic Resonant Coupling
• Electromagnetic Radiation

Inductive Coupling

Fig. 2. Inductive coupling method.

Inductive coupling is the most commonly used type of WPT. It is mostly used in near-field transmission over short distances, and is used to recharge objects as diverse as cell phones and electric toothbrushes. A basic inductively coupled system is illustrated in Fig. 2. This technology is based on a similar principle to the transformers at our local electric distribution stations. WPT through inductive coupling uses weakly coupled coils to form an air gap transformer between a primary transmitter circuit and a secondary receiver circuit [4]. An alternating magnetic field transmits the energy from primary coil to the secondary coil. Modern inductive coupling WPT occurs at a fixed distance to automatically optimize power transfer. There is also an automatic load recognition system and an additional data link between the transmitter and receiver for additional safety. This also allows better self-regulation of the WPT system.

Application of Inductive Coupling

Inductive coupling is used in industrial heaters, induction stove tops, even in medical science. The technology can be used to safely transmit power to some medical implants [5].
While researching this blog post, I also learned about WiTricity. This company has developed an improved commercial product that uses inductive coupling. Strongly coupled magnetic resonance systems are able to achieve approximately 90% power transfer efficiency at distances below 1m [6]. WiTricity was founded by MIT Physicists and they are currently working on developing this technology and additional intellectual property related to WPT [7].

Let’s wrap this up for today before it gets too long and boring..!!

In the next chapter, we will go through the other two WPT methods and look at other innovative applications of WPT including,

• Wireless portable spotlight
• Smart traffic cones
• Remote sensing equipment
• WPT on biomedical science
• Long distance Power and Data transmission using light beams

In a concluding note, I believe Wireless power transfer (WPT) has the potential to make our daily life truly wire-FREE..! Let’s hope for the revolution of WPT in coming decade…!

References

_{[1] B. Choi, J. Nho, H. Cha, T. Ahn, and S. Choi, ‘‘Design and implementation of low-profile contactless battery charger using planar printed circuit board windings as energy transfer device,’’ IEEE Trans. Ind. Electron., vol. 51, no. 1, pp. 140–147. iEEE Xplore, Accessed on 23rd March, 2018.
[2] N. Tesla, ‘‘Apparatus for transmitting electrical energy,’’ U.S. Patent 1 119 732, Dec. 1914. Accessed on 23rd March, 2018.
[3] W. C. Brown, ‘‘The history of power transmission by radio waves,’’ IEEE Trans. Microw. Theory Tech., vol. MTT-32, no. 9, pp. 1230–1242. iEEE Xplore, Accessed on 23rd March, 2018.
[4] J. Casanova, Z. N. Low, and J. Lin, ‘‘A loosely coupled planar wireless power system for multiple receivers,’’ IEEE Trans. Ind. Electron., vol. 56, no. 8, pp. 3060–3068. iEEE Xplore, Accessed on 23rd March, 2018.
[5] J. C. Lin, ‘‘Space solar-power stations, wireless power transmission, biological implications,’’ IEEE Microw. Mag., vol. 3, no. 1, pp. 36–42, Mar. 2002. iEEE Xplore, Accessed on 23rd March, 2018.
[6] D. Schatz, Wireless energy: Safe, efficient, and over distance, WiTricity, IDTechEx Energy Harvesting and Storage. Accessed on 23rd March, 2018.
[7] WiTricity Corporation. Web portal, Accessed on 23rd March, 2018.}

Thanks to @mobbs, @gra and @dexterdev for the support in mentoring this article.

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_{gif credit goes to @rocking-dave}