Wireless Energy Transfer

Brandon Wu
May 26, 2018

Submitted as coursework for PH240, Stanford University, Fall 2017


Fig. 1: Wireless Charging Cellphone. (Source: Wikimedia Commons)

Wireless energy transfer has many benefits versus normal corded electrical power transmission. Wireless charging is perhaps the most applicable way that this can benefit society, providing a tremendous convenience to charging electrical devices such as smartphones to larger objects such as electric cars. A wireless charging cellphone is pictured in Fig. 1. Along with adding convenience, wireless charging also eliminates lots of waste associated with conducting cables. [1] In a society where efficiency is so important, being able to charge wirelessly and when constantly on the move is a huge convenience.

How It Works

Wireless energy transfer can happen in a couple different ways, and people are still inventing new ways to improve the process. Today, this process is often done by using two resonant inductors. One inductor is excited by radio waves, coming from a power source. Once this process begins, the inductor will be able to build up electromagnetic energy. [2] Then, when the similar inductor is brought into range, the energy is exchanged from one inductor to the other. [3] This process occurs faster than the inductors are acquiring and dissipating energy themselves and behave like a single complete circuit, where energy between the two are distributed evenly amongst the two. Energy can be transferred in this fashion up to 1 meter. [3]

Fig. 2: Wireless Charging Car. (Source: Wikimedia Commons)

Moving Forward

Beyond conveniently charging your phones, one very useful application for wireless energy transfer is actually in the medical world. This comes in the form of implanted devices. Implanted devices are very important to the bioengineering world, and ones that require high levels of energy cannot acquire this from batteries in the long term, as the batteries will be drained and need replacement. [4] Being able to wirelessly charge these implants would be a huge convenience. Outside of charging, wireless energy transfer can control certain apparatuses such as a food intake device expanding and shrinking. [5] These devices need to change sizes and this would be an optimal way to control it. The next step in wireless energy transfer is to do it without static coils, enabling this energy transfer to happen while moving. Pictured in Fig. 2 is a wireless charging car, which is where wireless energy transfer while moving can be applied. This has begun to be studied and scientists have been able to observe 100% efficiency in energy transfer with no variability when coils are within 70 cm of each other. [3] This technology will open even more applications to wireless energy transfer.

© Brandon Wu. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] A. A. Eteng et al., "Low-Power Near-Field Magnetic Wireless Energy Transfer Links: A Review of Architectures and Design Approaches," Renew. Sustain. Energy Rev. 77, 486 (2017).

[2] K. Surakitbovorn, "Wireless Power Efficiency," Physics 240, Stanford University, Fall 2016.

[3] G. Lerosey, "Applied Physics: Wireless Power on the Move," Nature 546, 354 (2017).

[4] Y.-H. Li et al., "Wireless Energy Transmission System For Implantable Device," University of Chinese Academy of Sciences, 2017.

[5] P. Forsell, "Food Intake Restriction With Wireless Energy Supply," U.S. Patent 6,454,699, 24 Sep 02.