What is Wireless Charging, and How Does It Operate?

What is Wireless Charging: Power transmission via a magnetic field between a transmitter and a receiver has been possible since the late 19th century when electricity pioneer Nikola Tesla demonstrated magnetic resonant coupling.

But, for about a century, it was a technology with few useful applications beyond a select number of electric toothbrush models.

There are now a half-dozen different wireless charging technologies on the market; this attempt to eliminate the need for wires in a variety of settings, from mobile devices to home appliances to automobiles.

With the potential for more mobility and developments that could allow tiny internet-of-things (IoT) devices to acquire power many feet away from a charger, wireless charging is gaining traction in the healthcare, automotive, and manufacturing sectors.

Most current wireless solutions rely on an electromagnetic field created by a gap between two copper coils, which significantly reduces the charging distance. Apple’s iPhone 8 and iPhone X include this type of charging technology.

The science behind wireless power

The research manager at IHS Markit David Green has identified three main categories of wireless charging. Charging bowls or through-surface type chargers use radiative electromagnetic resonant charging to transmit a charge a few centimeters, and uncoupled radio frequency (RF) wireless charging enables a trickle charging capability at distances of many feet. Charging pads use tightly-coupled electromagnetic inductive or non-radiative charging.

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The physical concept at work in both tightly coupled inductive charging and loosely coupled resonant charging is the induction of a current in a closed loop of wire by a time-varying magnetic field.

By oscillating a magnetic field, a magnetic loop antenna (copper coil) can induce a current in a reception antenna or antennas. The induced current in the receivers will grow if the right amount of capacitance is applied to make the loops resonate at the same frequency. This is magnetic resonance, also known as resonant inductive charging, and it allows for more efficient power transmission over longer distances. Power transmission range is also affected by coil size. The larger the coil or the greater the number of coils, the farther a charge can travel.

The copper coils used in wireless smartphone charging pads, for example, are only a few inches in diameter, so the range over which they can transmit electricity efficiently is quite short.

Yet, greater wireless energy transmission occurs when coils are sized appropriately. WiTricity, a startup spun off MIT research a decade ago, is at the forefront of this strategy. It offers patent licensing for applications ranging from vehicles and wind turbines to robotics that make use of loosely linked resonant technologies.

Although MIT physics professor Marin Soljai demonstrated in 2007 that electricity could be sent over a distance of two meters, the efficiency of the transmission was just 40%, meaning that 60% of the power was lost in translation. Later that year, Soljaic founded WiTricity to market the technology, and it has seen significant improvements in power transfer efficiency ever since.

With copper coils larger than 25 centimeters in diameter at the receivers, WiTricity’s car charging system is able to efficiently transfer electricity over distances as short as 25 centimeters. According to WiTricity’s chief technology officer, resonance allows for the transmission of high power (up to 11kW) and excellent efficiency (more than 92% end-to-end). Capacitors are included in WiTricity’s conducting loop to increase the amount of potential energy harvested and stored in a battery.

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A wireless power transfer system for automatic guided vehicles based on WiTricity’s technology has been shipped by Japanese robotics firm Daihen Corp. since last year (AGVs). Automated racking and storage vehicles (AGVs) using Daihen’s D-Broad wireless charging system can easily pull up to a charging station, replenish their juice, and continue their warehouse responsibilities.

Despite the vast possibilities of remote charging, charging pads have been the public’s primary introduction to wireless power.

Green stated that “charging pads have been shipping in volume since 2015; charging bowls/through-surface type is really just launching this year; and charging across a room is probably still at least a year away from commercial high-volume reality,” despite the fact that the new Energous products show this method working over a very short range, e.g., a couple of centimeters.

In 2016, about 200 million devices with wireless charging capabilities were launched, the vast majority of which used an inductive (charging pad) design.

Apple, which has lagged behind other handset makers for years, eventually took a position in September by adopting the WPC’s Qi standard, which is also used by Samsung and other Android smartphone makers and has been for at least two years.

Tightly linked or inductive charging, which requires users to set a smartphone in a precise location on a pad in order for it to charge, debuted as the first class of mobile device wireless chargers about six years ago.

According to Benjamin Freas, chief analyst at Navigant Research, “in my perspective, lining it up exactly to charge doesn’t save you a lot of effort from just plugging it in.”

Freas noted that while early adopters and technologists embraced inductive charging, many others did not.

The Nokia 920, released in September 2012, pioneered Qi-based wireless charging in a commercially accessible smartphone.

Standardization conflict in wireless charging

The Alliance for Wireless Power (A4WP), the Power Matters Alliance (PMA), and the Wireless Power Consortium were three rival wireless charging standards bodies for inductive and resonance charging specifications for several years (WPC). The latter boasts 296 members, including Apple, Google, Verizon, and many other major IT companies.

The Qi (pronounced “chee”) standard, developed by the Wireless Power Consortium, is the most widely used for wireless charging since it allows for inductive or pad-style charging and short-distance (1.5cm or less) electromagnetic resonant inductive charging. Apple has embraced the Qi standard for charging its devices.

Wireless charging technology developed by the PMA and its Powermat inductive charging protocol was successfully tested in public places like cafes and airports. In 2014, for instance, Starbucks started providing customers with wireless charging mats.

Due to incompatible standards, mobile device compatibility has remained patchy, with most phones requiring a special cover to allow for wireless charging.

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The AirFuel Alliance was formed in 2015 by the merger of the A4WP and the PMA, and it now counts 110 companies as members, such as Dell, Duracell, Samsung, and Qualcomm.

Duracell Powermat, through its membership in the AirFuel Alliance, claims to have more than 1,500 charging locations in the United States. Another 1,000 locations across Europe’s airports, hotels, and cafes are available through Powermat’s relationship with PowerKiss. Wireless charging is now available at some McDonald’s locations, as revealed by AirFuel. Freas suggests this as a means by which wireless charging can gain popularity.

AirFuel is devoted to electromagnetic resonance and radio frequency.

AirFuel prioritized two charging technologies—magnetic resonant and radio frequency—to provide freedom of movement while charging mobile devices.

“There have been many signs from the market that resonant and RF solutions are optimal. Both technologies have important benefits that contribute to the creation of market value and customer pleasure, such as more flexibility in terms of installation and usability “Sharen Santoski, a representative for AirFuel, noted this. And we think resonant is the greatest tech to facilitate rapid public infrastructure rollout.

According to Santoski, this has led to the widespread installation of resonant-based wireless charging stations in public places including cafes, restaurants, and airports. Similarly to China, “Taiwan is investing substantially,” Santos said.

A partnership between AirFuel and the Taoyuan Airport Metro to install Resonant charging in the metro’s trains and stations was recently announced. Now a new collection of Resonant-enabled furniture has been developed by Order Furniture.

People are more likely to utilize it and purchase a charging pad for their house if it’s available in public places like restaurants and coffee shops, according to Freas.

Freas said that most of these endeavors remained in the pilot stage and that consumers and businesses were less likely to prefer tightly linked charging than loosely coupled resonant charging. The reason is, with loosely coupled charging, you can just set your phone, tablet, or laptop down on a desk and it will start charging.

Powering cars using WiTricity and wireless chargers

WiTricity, situated in Watertown, Massachusetts, licenses technology created at the Massachusetts Institute of Technology, and in July, Dell debuted a Latitude laptop with WiTricity’s resonant wireless charging built-in (MIT). With a Latitude laptop, the Dell wireless charger’s maximum charging output of 30W is equivalent to being hooked into a wall outlet.

Yet, WiTricity’s primary market is the automotive sector. According to WiTricity CEO Alex Gruzen, the company is anticipating announcements from multiple electric car manufacturers on wireless charging for their vehicles. WiTricity is a member of the AirFuel Alliance.

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Power can be transferred from a charging pad to an object up to around nine inches away, thanks to the company’s electromagnetic resonant technology. Just parking an electric vehicle on a huge charging pad would be sufficient to recharge its battery.

This year, Mercedes-Benz will begin selling the S550e plug-in hybrid sedan, which is compatible with WiTricity’s technology and can be charged by just parking on a pad.

According to Kesler, electromagnetic resonant charging is ideal for use with electric vehicles. Because the wireless charging pad provides electricity more efficiently than a cable, and because the car doesn’t require a charging cable. (Kesler estimated that the efficiency of wired charging systems, which utilize electronics to convert AC to DC and manage the flow of power, dropped to around 86%.)

From the electrical outlet to the battery, Kesler claims that 93% efficiency is possible with their wireless charging system.

Long-distance, wireless power transfer

Apple’s acquisition of PowerByProxi last month startled some in the industry because it was a New Zealand firm working on loosely-coupled resonant charging technology based on the Qi protocol.

Fady Mishriki, an entrepreneur, started PowerbyProxi in 2007 as a university spin-off. PowerByProxi has demonstrated charging bowls and boxes that can simultaneously charge a number of electronic gadgets.

The Aukland, New Zealand, firm initially specialized in the sale of large-scale equipment to the building, telecom, military, and farming sectors. A wireless wind turbine control system is one example.

In addition to being embedded directly into devices, PowerByProxi, a member of the WPC’s Steering Committee, has shrunk its technology and inserted it inside AA rechargeable batteries. The wireless components only add roughly 10% in height to the standard AA battery.

Apple might employ PowerByProxi’s technology to charge more than just iPhones wirelessly in the future. This could include TV remote controls, computer accessories, and more.

While wireless charging pads for mobile devices have received the most attention, the technology is finding its way into everything from warehouse robots to tiny IoT gadgets that previously required wires or replaceable batteries.

Wireless charging has been shown to work at distances of over 15 feet by both Ossia and Energous. Ossia’s charger can transmit roughly two watts up to a few feet, but the power rapidly decreases after that. However, Ossia CEO Mario Obeidat claims that even at 30 feet, the amount of power that can be communicated is “significant,” pointing to trickle-powering gadgets to keep them charged.

Others inquire

How is wireless charging carried out?

A specialized wireless charging pad uses electromagnetic induction, also known as “inductive coupling,” to transfer energy to your device instead of plugging it into a charging cable. Any phones that allow wireless charging can still be charged with a cable; it does not take the place of cable charging.

What does wireless charging mean in plain English?

What Exactly Is Wireless Charging? The method of electrically charging battery-powered devices like laptops, cellphones, and electric cars without the need for a cable connection is known as wireless charging, sometimes known as wireless power transfer (WPT).

What distinguishes wireless charging from rapid charging?

Without a doubt, Qi wireless chargers are slower than conventional chargers. In our testing, the fastest chargers recharged a totally discharged iPhone XR to only 50% battery capacity in an hour, which is about half as quickly as a cable charger. Nonetheless, any wireless charger can provide a full night’s charge for any phone.

Can a wireless charger be used to charge a regular phone?

Can any phone use a wireless charger? You can use any wireless charger with your smartphone as long as they support the same wireless charging standard (like Qi). It’s not necessary for both to be produced by the same company; for instance, you may use an iPhone and a Samsung wireless charger.

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