With wireless charging technology, Xiaomi has completely revolutionized mobile phone charging!

The next era of mobile phone charging is here.

#Xiaomi launches its first self-developed wireless charging technology#

At 10:30 this morning, Xiaomi released a charging method from the future: wireless charging, named MI Air Charge. This time, the power of Xiaomi's wireless charging has reached 5W, and it has been implemented on an engineering machine based on Xiaomi 11.

Considering the intensity of daily use of mobile phones, 5W seamless charging can actually meet the needs of the public. In addition, Xiaomi's wireless charging can already realize functions such as multi-device charging, mobile charging, and charging while playing. Xiao Lei believes that as of now, Xiaomi's wireless charging solution is the most technically feasible solution.

Why is Xiao Lei so confident? This has to start with the development of wireless charging.

An attempt at wireless charging

The wireless charging we use today is based on electromagnetic induction technology. Let’s review our high school knowledge here: electricity generates magnetism, magnetism generates electricity, and the changing magnetic field generates an electric field.

The coil in the wireless charger will continuously change the current in the charger and generate a changing magnetic field when your phone is in contact with it. Due to the principle of electromagnetic induction, the coil inside your phone will convert the magnetic field into an electric field and charge the phone.

Image credit: Belkin

However, this charging mode also has great limitations, namely, the transmission distance is short and the coil needs to be aligned so that the phone can sense it correctly.

In fact, people have been exploring solutions for long-distance charging of mobile phones. To date, there are two feasible wireless charging modes, one is called magnetic field resonance and the other is called laser charging.

Let’s talk about magnetic field resonance first. In 2007, MIT proposed their idea: to apply the principle of sound resonance to electromagnetic waves. Just use two coils of “the same frequency” and radiate electromagnetic waves of a specific frequency at one end, which can induce resonance at the other end and generate electricity.

As a new generation of wireless charging technology, magnetic field resonance can achieve a transmission distance of several meters, and the transmittable power has also increased from watts to kilowatts.

Magnetic field resonance is also what the electrical master Nikola Tesla was interested in. More than a century ago, Tesla was able to light up a lamp from a distance.

Tesla's manuscript

Why has there been no progress in magnetic field resonance, which is such a mature technology?

Although magnetic field resonance realizes wireless charging, its shortcomings are also obvious: if you want to charge from several meters away, magnetic field resonance requires a strong magnetic field as a basis, and strong magnetic fields may cause health risks and do not comply with national safety regulations.

Therefore, the current magnetic field resonance wireless charging technology is generally used in the "wireless charging table" in restaurants: a small table top is embedded in the table, and the wireless charger is under the table, which can perform magnetic field resonance charging across the table. Domestic companies such as Zhejiang Wei'e Technology and Shanghai Chushan Technology are already conducting research and development.

Charging table on the table

Compared with magnetic resonance that requires a strong magnetic field, laser charging is obviously much more advanced. As we all know, laser is a beam of light that is emitted straight out, which happens to be its advantage: compared with the "radiation" of the magnetic field, laser has high energy density, strong directionality, and is easier to achieve in terms of safety.

Scientifically, the feasibility of laser charging has long been proven. In 2010, LazerMotive used lasers to provide energy for drones to fly continuously in the air for 12 hours. In 2017, the University of Washington successfully achieved laser charging of mobile phones.

Mobile phone manufacturers are also obviously more interested in laser charging: On April Fool's Day, April 1, 2020, OPPO released a concept video of wireless charging called "FreeVooc". Although it was just a spoof, the response of VOOC chief engineer Zhang Jialiang was intriguing.

In a video on April 25, Zhang Jialiang directly stated that wireless charging is technically feasible, but the problem is that the cost is too high and it is difficult to commercialize it.

Coincidentally, in September last year, Huawei also exposed its laser charging solution to the media. Huawei said that after two or three generations of mobile phones, Huawei will be able to achieve mass production of laser charging.

Huawei's laser charging demonstration

Today, Motorola also released its own laser (possibly infrared) wireless charging to "intercept" Xiaomi. It can be seen that the laser solution actually has basic feasibility.

Then why does Xiao Lei still think that Xiaomi's solution is the most mature so far?

Xiaomi's efforts

Compared with the laser solutions of OPPO, Huawei and Motorola, Xiaomi has set its sights on millimeter waves. In Xiaomi's announcement, they used beamforming technology to send millimeter waves to mobile phones in a directional manner.

Although Xiaomi did not mention more technical details, if millimeter wave is successful, it will have more advantages than traditional laser. The first is safety. Although laser is good, the biggest problem is that the energy is too high. If the laser is irradiated on the hand for a long time, it may cause burns. Millimeter wave is much safer.

Motorola and the University of Washington both adopted a method of cutting off the power when blocking the laser with hands. According to the University of Washington, they are actually worried about laser burning the skin. In Huawei's patent, we can also see a similar description of the "protection system". As long as the hand blocks the reflected laser, the charging will be immediately interrupted.

In addition to safety issues, millimeter waves have lower frequencies and longer wavelengths, so their diffraction properties are much better than lasers. If a laser is blocked by a hand, it may be interrupted, while millimeter waves + beamforming can basically ensure that it can bypass small obstacles, at least in a room.

Xiaomi's foreign body blocking demonstration

Another major reason for the immaturity of lasers is cost. Laser charging has not yet left the scope of line-of-sight communication (LOS). The term line-of-sight communication means that laser charging is point-to-point linear transmission, and as long as the position changes, it must be repositioned.

To solve the positioning problem, laser charging follows the conventional method in the field of LOS communication and has a built-in receiver for positioning. Huawei has implemented this solution through a built-in receiver. According to OPPO's concept video and Weibo user @薛定谔's英短咕咕咕's revelation, they also use a dedicated receiver to achieve repositioning.

Xiaomi's solution is even smarter. Since millimeter waves are used, wouldn't it be enough to use antennas? In Xiaomi's solution, the "charging pile" uses 5 phase interference antennas, and the mobile phone has built-in beacon antennas and receiving antenna arrays. Compared with specific laser receivers, antennas are undoubtedly the strengths of mobile phone manufacturers, and they are also easier to integrate into traditional mobile phone antennas.

At present, Xiaomi's millimeter-wave wireless charging requires minimal modification to the mobile phone. The fact that Xiaomi 11 supports wireless charging also strongly proves the maturity of millimeter-wave antenna technology. Furthermore, the low cost of millimeter-wave wireless charging also makes it possible to become the standard for wireless charging of mobile phones in the future.

The wireless future

In fact, Xiaomi's success did not happen overnight. According to the revelation of Weibo user @颐心, the concept of Xiaomi's wireless charging had already begun in the MIX 3 era (October 2018). In the publicity, Xiaomi also emphasized the word "self-developed". 17 technical patents and miniaturized antenna arrays are enough to show the efforts Xiaomi has made for this.

In the past two years, Xiaomi has made great progress in the field of charging, and this year it has also made large investments in the field of wireless charging (Dior Microelectronics, Nanxin Semiconductor, Nano Semiconductor, etc.). As IoT home appliances mature, Xiaomi is likely to bring wireless charging technology to the field of home appliances, and products such as speakers and desk lamps will become beneficiaries of wireless charging.

Xiaomi is obviously not satisfied with this. According to the revelation of @薛定谔的英短咕咕咕, Xiaomi may use ultra-wideband chip (UWB) technology for wireless charging.

UWB technology demonstrates amazing accuracy in the Apple ecosystem

Xiaomi has previously released the "one-finger connection" technology. The independent linkage and distance measurement between various devices may make the accuracy and controllability of wireless charging even better.

Many manufacturers have their own ideas about the wireless future. Apple has proposed WiFi charging, Samsung has come up with a charging ring... With Xiaomi's stunning move, we will see more surprises in the charging field in 2021. It may even be a ticket through IoT devices.