The technical principle and development status of wireless charging

In 2009, the first wireless charging mobile phone went on sale; In 2011, phones without the 5V1A's wired slow charging also began to appear.

Then, every year, new technologies attempt to push the charging experience to new heights.

On January 29, 2021, charging became a hot topic again. This is because Xiaomi and MOTOROLA announced "air separation charging" on the same day.

They all allow "true" wireless charging at a distance of one meter or more from the charger.

However, the two sides did not reveal when the air separator charger mass production, tantalizing everyone. "Where can I buy it?" became one of the biggest questions. To find out, we still have to start with the technical principles and development status of wireless charging.

Wireless charging: There are three main ways to use it,

The principles fall into two broad categories

While "air separation charging" may sound very "dark tech," it's actually a type of wireless charging. In terms of usage, there are three broad categories of wireless charging: electromagnetic induction wireless charging, electromagnetic resonance wireless charging and radio frequency (RF) wireless charging.

According to the implementation principle, wireless charging can be divided into two categories. Electromagnetic induction and electromagnetic resonance wireless charging with the same principle are collectively referred to as "electromagnetic coupling wireless charging", while radio frequency wireless charging with independent principle is separately classified as one category.

At present, the mobile phones and earphones that support wireless charging on the market basically use electromagnetic induction wireless charging.

These devices transmit power through wireless magnetic circuits of magnetic fields instead of wired wires. When charging, both the charger and the device being charged must have coils, and the coils of both must be aligned and in very close proximity (touching) to work properly.

A phone that is being charged via electromagnetic induction wireless charging also requires a coil for electromagnetic resonance wireless charging, but this technology works over a longer distance (up to around 25cm). Electromagnetic resonance wireless charging is popular for large devices, such as cars and industrial robots.

Electromagnetic resonance wireless charging Radio frequency wireless charging directly transmits wireless signals through the built-in antenna of the charger. After receiving the wireless signals, the antenna of the charged device will convert the wireless signals into electricity to realize charging. Radio frequency wireless charging can work the longest distance, up to several meters.

MOTOROLA's air isolation charging demonstration of RF transmission itself is nothing new, wireless products such as Bluetooth, Wi-Fi and walkie-talkies all work on RF. Rf wireless charging simply converts wireless signals into electricity. The real challenge is to improve the conversion efficiency.

Electromagnetic resonance instead of electromagnetic induction?
Electromagnetic induction wireless charging has been quite popular, most high-end mobile phones support this wireless charging mode, 50W level of fast wireless charging has appeared in the 4000 yuan mobile phone. Mobile phones that can be used as chargers for low-power wireless charging of other devices are no longer a rarity.

However, the need to align the coils, the proximity, and the small number of charging devices have limited the development of electromagnetic induction wireless charging. Apple tried to solve this problem with AirPower, which had multiple internal coils, but abandoned it because it couldn't control the heat.

In fact, from the technical characteristics of the abandoned AirPower, electromagnetic resonance wireless charging has a better chance to solve the problem of charging location and the number of devices charged at the same time, because the technology has lower requirements for location and distance.

One company has made "charging baskets" in which multiple devices can be charged simultaneously without touching the charger. Although the charging distance is not as good as "air separation charging", the convenience of electromagnetic resonance wireless charging is still stronger than that of electromagnetic induction wireless charging.

The "charging basket" for charging multiple devices has shifted its focus to the field of electric vehicles, and electromagnetic resonance wireless charging has been able to meet the daily use of electric vehicles.

WiTricity's electromagnetic resonance charging base is capable of achieving 90 to 93 percent end-to-end charging efficiency over distances of 10 to 25 cm, with charging power of more than 11kW. At present, the power of wired charging pile is as small as 7kW and as large as more than 200kW. As a wireless charging method, 11kW power is still acceptable.

In addition, the electromagnetic resonance wireless charging base can be charged through asphalt, cement, ice and snow. This means that the parking lot will not have charging bases that protrude from the ground and hinder driving. Some manufacturers are even experimenting with wireless charging panels (like trams) under the road or in the air, allowing them to charge on the go.

There are two commercially available models using electromagnetic resonance wireless charging worldwide, one from BMW and the other from McLaren. In China, the National Standard for Wireless Charging of Electric Vehicles based on WiTricity's electromagnetic resonance technology was released in May 2020.

No matter in the field of electronic products or electric vehicles, compared with electromagnetic induction wireless charging, electromagnetic resonance wireless charging can better solve the pain points of current consumers.

Air separation charging products have been on the market for nearly two years
Rf wireless charging applications are rare, but many companies are dabbling in the technology.

It's not just Xiaomi and MOTOROLA. Companies like Ossia, Energous and humavox have also demonstrated working RF wireless charging products.

For example, Ossia demonstrated in 2017 that its OssiaCota system can simultaneously charge up to 32 devices within a 9-meter range and is FCC-certified.

OssiaCotaEnergous is a broader company that is trying to push RF wireless charging into the home, car, office, medical and military sectors.

Its WattUp wireless charging system supports a range of up to 4.5 meters. Hearing AIDS using WattUp's wireless charging technology went on sale in August 2019.

Accelerate the transition to air isolation charging
In principle, mobile phone wireless charging using electromagnetic induction technology is relatively "backward". But is widely used by manufacturers, or because the threshold is low.

This low threshold, however, comes at the expense of user experience, which is why wireless charging has not gained much popularity outside of tech enthusiasts, most of whom don't mind wired charging at all.

With the advent of mature, low-cost electromagnetic resonance and RF wireless chargers, wireless charging will be able to achieve the much more convenient than plug-in charging.

However, judging by the products of companies in the industry that focus on "fly-charging" technology, and the confidence of Xiaomi and MOTOROLA in the new technology, fly-charging may no longer require a long transition.

If this is the case, then in consumer electronics (where electric cars still have a promising future), electromagnetic resonance wireless charging has no chance of replacing electromagnetic induction wireless charging, because it is likely that people will move directly from the existing electromagnetic induction wireless charging to air isolation charging.

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