Wireless Charging: Turning an Age-Old Idea into Reality
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- Introduction
- Basic Physics Terms Defined
- How Magnetic Induction Coupling Works
| Julia Chen
Wireless Charging: Turning an Age-Old Idea into Reality Abstract Wireless charging, or charging devices without plugging them to the wall socket, is a fairly old concept that never gained ground until recently. Using magnetic induction and magnetic resonant coupling, engineers have created a way to make wireless charging a reality. While in its nascent stage, wireless charging has several problems that need to be solved and improvements to be made. Nonetheless, with products already in the market, the wireless charging movement is moving towards the next generation of electronic products, changing the way people interact with their devices. Introduction Have you ever run into a problem with having too many devices and too few outlets to plug them into? As trivial as it seems, this is a growing frustration for consumers in the 21st century. Although a power strip helps alleviate that issue, it also creates another problem: a nest of tangled cords. However, wireless charging—powering devices without cables—can solve all these problems associated with conventional electronics. As advanced as wireless charging sounds, the concept is not new. This idea was first conceived by Nikola Tesla, who was best known for his work in alternating current, the type of electricity that runs through our power sockets [1]. In 1891, Tesla developed a resonant transformer known as the Tesla coil, which could transmit electrical power through air [2]. During one of his experiments in 1899, he sent “100 million volts of electric power wirelessly over a distance of 26 miles to light up a bank of 200 light bulbs and run one electric motor.” Although the numbers were impressive, the Tesla coils were not safe to use commercially because the resulting high voltages damaged other electrical devices [2]. Now more than a hundred years later, wireless power development, specifically in magnetic induction and magnetic resonant coupling, is gaining momentum and holds a promising future. Basic Physics Terms Defined In order to understand the physics behind wireless charging, it is important to first define certain keywords in electricity and magnetism. Electricity is the flow of electrical charge and has two types: direct current (DC) and alternating current (AC) [3]. As shown in Figure 1, DC—obtained from batteries and cells—flows in one direction, while AC—obtained from wall sockets—flows in both directions; AC plays an integral part in wireless charging [4]. 
http://www.allaboutcircuits.com/vol_2/chpt_1/1.html Figure 1: Illustrates DC (left) and AC (right).
Magnetism is a force by which certain materials attract or repel one another; an example of this is a simple refrigerator magnet. Electricity and magnetism are interdependent; a magnetic field produces an electrical field, and vice versa, in a process known as induction [3]. Another important term to define is energy or power coupling. Coupling refers to the exchange of energy between two objects; in the case of magnetic coupling, direct contact is not necessary to successfully transmit energy [3]. This is another key component of wireless charging. How Magnetic Induction Coupling Works Most wireless charging technologies use magnetic induction coupling. Magnetic induction is a type of energy transfer that involves two coils of conductive material [3]. Conductive material like copper carries electrical current. As shown in Figure 2, the transmitter (Tx) coil is embedded in the charging pad, and the receiver (Rx) coil is embedded in the mobile device [3]. An AC source is first connected to the Tx coil, generating an alternating magnetic field around it. The Rx coil picks up some of the magnetic field created by the Tx coil, which induces a current in the Rx coil [3]. In return, the induced current charges the mobile device. 
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