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How wireless charging works

Computerworld | Sep 16, 2019

Wireless charging technology has been around for over 100 years, but it has only recently found mainstream practical use for powering electronic devices like smartphones. Learn how this technology works and what advancements we may see in the future.

Copyright © 2019 IDG Communications, Inc.

How wireless charging works

Wireless charging has been around since the late 19th century, when electricity pioneer Nikola Tesla demonstrated magnetic resonant coupling – the ability to transmit electricity through the air by creating a magnetic field between two circuits, a transmitter and a receiver.

But for about 100 years it was a technology with few practical uses, except, perhaps, for electric toothbrushes.

Today, there are nearly a half dozen wireless charging technologies in use or being piloted, all aimed at cutting cables to everything from smartphones and laptops to kitchen appliances and cars.

Wireless charging is making inroads in the healthcare, automotive and manufacturing industries because it offers the promise of increased mobility and the ability to power tiny internet of things from many feet away. Some day, wearable medical sensors could be charged by router-like devices meters away.

The most popular wireless technologies now in use, however, rely on an electromagnetic field created between two copper coils, which greatly limits the distance between a device and a charging pad to a few millimeters. That's the type of charging Apple introduced with the iPhone 8 in 2017 and what Android smartphones used even earlier.

Broadly speaking, there are three types of wireless charging: tightly-coupled inductive, loosely-coupled resonant and uncoupled charging; the latter sends power through radio frequencies, infrared beams -- even ultrasound. It offers exciting promise, but without mass production, widespread adoption is likely years away.

When wireless charging first gained interest from tech vendors nearly a decade ago, there were three wireless charging standards groups focused on inductive and resonance charging specifications: The Alliance for Wireless Power (A4WP); the Power Matters Alliance (PMA); and the Wireless Power Consortium (WPC). WPC’s members include Apple, Google, Verizon and a veritable who's who of electronics manufacturers. In 2015, the WPC and the PMA merged to form the AirFuel Allliance, which now supports the development of several wireless charging protocols – mainly Qi (pronounced “chee”)”. The A4WP, which began in 2012, supports the Rezence charging protocol; it can transfer power up to five centimeters. Members include Broadcom, Intel, Qualcomm, Samsung Electronics and WiTricity

Today, the market is dominated mostly by charging pads that use both tightly coupled inductive and loosely-coupled resonant charging; they operate on the same principle: a time-varying magnetic field induces a current in a closed loop of wire. The only difference: resonance charging offers more leeway in how you position a device to be charged; with tightly-coupled inductive charging, you’ve got to be spot-on in your placement of a device being charged.

Much of the industry has united around the Qi standard, which enables inductive or pad-style charging and short-distance (1.5cm or less) electromagnetic resonant inductive charging.

Eventually, wireless charging hardware could be as invisible as WiFi is now, enabling mobile devices, IoT sensors and even healthcare wearables to trickle charge throughout the day even as you’re walking through a room. For now, however, the market will be dominated by charging pads.
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