5 WIRELESS CHARGING 無線充電 Explained 大解構 By Daria Zaitseva Wireless technology is the new black. Latest technological advances helped us ditch the hassle of cables and enjoy seamless use of devices with wireless charging pads and stands. Have you ever wondered how these chargers work? The answer is much simpler than you might think! Wireless charging, also called inductive charging, is based on some physical principles of electromagnetism and electromagnetic induction. The first principle to know is Ampere’s law, which implies that an electric current in a conductor generates a magnetic field with a strength proportional to the current. If we pass a current through a solenoid (a helical coil), the solenoid becomes an electromagnet with the north and south poles at either of its ends depending on the current direction. This is the transmitter coil installed in the charging pad. When the transmitter is plugged in, a current runs through the coil and turns it to an electromagnet. An alternating current (a.c.) with the direction of electron flow reverses regularly can be supplied, so that we get an electromagnet with the two poles switching constantly, creating a changing magnetic field. Then here comes the second principle: Faraday’s law of electromagnetic induction. Discovered by Michael Faraday in 1831, this law states that a changing magnetic field can induce a voltage called an electromotive force (e.m.f.), which can drive a current to flow through a conductor. Let’s say we take advantage of this principle and install a receiver coil into the device we want to charge. The coil picks up the changing magnetic field and develop an e.m.f. across it, eventually inducing a current to flow through the device. Voilà, the current is now transmitted wirelessly. As smartphones and watches can only be charged by direct current (d.c.), there is an electrical device called a rectifier to convert the induced a.c. into d.c. by restricting the electron flow to only one direction. Many people may not know: W i r e l e s s charging could be much more than a convenient accessory for your phone.
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