In 2009, the first wireless charging mobile phone went on the market; in 2011, mobile phones deviating from 5V1A wired slow charging also began to appear. Subsequently, every year there will be new technologies trying to hit a new height of mobile phone charging experience. On January 29, 2021, charging became a hot topic again. Because Xiaomi and Motorola announced the “Space Charge” on the same day. They can enable the mobile phone to achieve “true” wireless charging at a distance of 1 meter or more from the charger.
Mi Air Charging Demo
However, the two parties did not disclose the mass production time of the air charger, which drew everyone’s appetite. “Where can I buy it” has become one of the biggest questions. To know the answer, we still have to start with the technical principles and development status of wireless charging.
01 Wireless charging: the usage methods are divided into three categories, and the principles are divided into two categories
Although “air charging” sounds very “black technology”, it is actually a type of wireless charging. From the perspective 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 principle of realization, there are two types of wireless charging. Electromagnetic induction and electromagnetic resonance wireless charging with the same principle are collectively referred to as “electromagnetic coupling wireless charging”, and radiofrequency wireless charging with independent principles is a separate category.
Schematic diagram of electromagnetic coupling wireless charging
At present, the mobile phones and earphones that support wireless charging on the market basically use electromagnetic induction wireless charging. These devices will use the wireless magnetic circuit of the magnetic field instead of wired wires to realize the transmission of electricity. When charging, both the charger and the device to be charged must have coils, and the coils of the two must be aligned and can work normally at a very close distance (touch).
A mobile phone being charged by electromagnetic induction wireless charging
Electromagnetic resonance wireless charging also requires a coil, but this technology has a longer working distance (up to 25 cm). Electromagnetic resonance wireless charging is more popular with large devices, such as automobiles and industrial robots.
Electromagnetic resonance wireless charging
Radiofrequency wireless charging directly transmits wireless signals through the built-in antenna of the charger. After the wireless signal is received by the antenna of the charging device, the wireless signal is converted into electricity to realize charging. Radiofrequency wireless charging has the longest working distance, which can reach several meters.
Motorola’s air charging demonstration
Radiofrequency transmission itself is nothing new. Wireless products such as Bluetooth, Wi-Fi, and walkie-talkies all work based on radiofrequency. Radiofrequency wireless charging only converts wireless signals into electricity. The real difficulty lies in improving conversion efficiency.
02Electromagnetic resonance replaces electromagnetic induction?
Electromagnetic induction wireless charging has become quite popular, and most high-end mobile phones support this wireless charging method, and 50W-level fast wireless charging has appeared in 4000 yuan mobile phones. Mobile phones that can be used as chargers for low-power wireless charging of other devices are no longer rare.
However, the need to align the coils, the distance is too close, and the number of charging devices at the same time is three shortcomings that limit the development of electromagnetic induction wireless charging. Apple once tried to solve this problem with AirPower, which was filled with multiple coils, but abandoned the product because it could not control the heat.
In fact, in terms of technical characteristics, electromagnetic resonance wireless charging has a better chance to solve the problems of charging location and the number of charging devices at the same time, because the technology has lower requirements for location and distance. Some companies have made “charging baskets” in which multiple devices in the basket can be charged at the same time without touching the charger. Although the charging distance is not as good as “air charging”, electromagnetic resonance wireless charging is more convenient than electromagnetic induction wireless charging.
“Charging basket” for charging multiple devices
Turning our attention to the field of electric vehicles, electromagnetic resonance wireless charging has been able to meet the daily use of electric vehicles. WiTricity’s electromagnetic resonance charging base can achieve 90% to 93% end-to-end charging efficiency within a distance of 10 to 25 cm, and the charging power reaches more than 11kW. At present, the power of wired charging piles is as small as 7kW, and the power is more than 200kW. As a wireless charging method, 11kW power is still possible.
In addition, the electromagnetic resonance wireless charging base can be charged through asphalt, cement, ice and snow. In other words, the parking lot will not have a charging base that hinders driving and protrudes from the ground. Some manufacturers are even trying to lay wireless charging boards (similar to trams) under the road or mid-air to realize charging while walking.
Witricity charging board
Globally, there are two models on the market that use electromagnetic resonance wireless charging, namely BMW and McLaren. China has also released the “National Standard for Wireless Charging of Electric Vehicles” based on WiTricity’s electromagnetic resonance technology in May 2020.
Whether in the field of electronic products or electric vehicles, compared to electromagnetic induction wireless charging, electromagnetic resonance wireless charging can better solve the pain points of current consumers.
03Space charging products have been on the market for almost 2 years
The application of radiofrequency wireless charging is very rare, but there are many companies wading this technology. Not only Xiaomi and Motorola, but companies such as Ossia, Energous, and Humavox have also demonstrated working RF wireless charging products. For example, the Ossia Cota system shown by Ossia in 2017 can charge up to 32 devices within a range of 9 meters at the same time, and it has also passed the FCC certification in the United States.
Energous is involved in more fields. The company is trying to push radio frequency wireless charging into the home, automobile, office, medical and military fields. Its WattUp wireless charging system supports a charging distance of up to 4.5 meters. In August 2019, hearing aids using WattUp wireless charging technology have been launched.
Hearing aids supporting radio frequency wireless charging
04Accelerate the transition to air charging
In principle, the electromagnetic induction technology used in wireless charging of mobile phones is relative “backward”. But the reason why it is widely used by manufacturers is because of the low threshold. However, this low threshold sacrifices the user experience, which is why wireless charging of mobile phones is not very popular outside of technology enthusiasts, and most users do not mind using wired charging at all. After mature, low-cost electromagnetic resonance and radio frequency wireless chargers appear, wireless charging can truly realize the convenience that everyone imagines is much higher than plug-in charging.
However, judging from the products of these companies focusing on “space charging” technology in the industry, and the confidence of Xiaomi and Motorola in new technologies, space charging may no longer require a long transition. If this is the case, then in the field of consumer electronics (the prospects for electric vehicles are still very good), electromagnetic resonance wireless charging should not have the opportunity to replace electromagnetic induction wireless charging, because everyone is likely to directly transition from the existing electromagnetic induction wireless charging to Charge in the