I believe that friends who pay attention to the mobile phone circle will find such a phenomenon, in the past two years, at the new product launches of major mobile phone manufacturers, everyone seems to no longer mention wireless charging. That's right, when the arms race for wired fast charging is in full swing, the highest power from 80W to 120W and then to 240W, the technological progress of wireless charging seems to have stagnated.
In fact, the matter stemmed from a draft interim regulation issued by the Ministry of Industry and Information Technology in February 2021, which clarified that the rated transmission power requirement for all mobile and portable wireless charging equipment produced, imported, sold and used in China from January 1, 2022 is less than 50W.
Just recently, the Ministry of Industry and Information Technology issued the Interim Regulations on the Radio Management of Wireless Charging (Power Transmission) Equipment (hereinafter referred to as the "Interim Provisions"), which will come into force on September 1, 2024. According to the Interim Provisions, the operating frequency range of mobile and portable wireless charging equipment is 100-148.5kHz, 6765-6795kHz, 13553-13567kHz frequency bands, and the rated transmission power does not exceed 80W. Therefore, this also means that the wireless charging power of mobile phones limited to 50W is about to be lifted.
At present, the highest wireless charging power that has been commercialized in the mobile phone industry is the 67W brought by the Xiaomi 11 Pro and Xiaomi 11 ProUltra released in the spring of 2021. But in the laboratory environment, as early as October 2020, Moji's Xiaomi 10 Pro successfully achieved 80W wireless charging power, making its 4000mAh battery fully charged in only 19 minutes. Subsequently, in May 2021, through the magic modification of the Xiaomi 11 Pro, Xiaomi also achieved 120W wireless second charging under laboratory conditions. However, due to the requirements of the Interim Provisions on Radio Management of Wireless Charging (Power Transmission) Equipment (Draft for Comments), these technologies did not finally be commercialized.
As for why to manage the wireless charging power of mobile phones, it is actually because the wireless charging of mobile phones may affect the wireless radio frequency in the air. The industry's most widely used wireless charging scheme is usually a relatively simple circuit design and low-cost electromagnetic induction type, the principle of which is that the transmitting end, that is, the charging plate alternating current, and then generate a magnetic field through the coil, causing the surrounding magnetic field to change, and then generate an induced electromotive force on the nearby coil, thereby generating current at the receiving end.
In short, wireless charging is a technology that uses the principle of electromagnetic wave induction or other related AC induction technology to send and receive the induced AC signal with corresponding equipment at the sending and receiving ends. Because wireless charging equipment is a non-radio equipment that radiates radio waves, and radio waves have two important characteristics, one is limited frequency band resources, and the other is easy to produce interference when the frequency bands are similar, such as WiFi equipment supports 5GHz because the 2.4GHz band is too noisy.
Electromagnetic interference between devices that can radiate radio waves not only reduces the user experience, but also causes some uncertain dangers, such as Apple's iPhone 12 and MagSafe radio charger, which have been experimentally shown to affect pacemaker work. In addition, high-power wireless charging is also dangerous. According to physics-related knowledge, the energy of electromagnetic waves will gradually decay with the increase of distance, and it is inevitable to increase the frequency of electromagnetic waves to increase the charging power, and the energy of electromagnetic waves is proportional to its frequency, that is, the higher the frequency, the greater the energy, when the frequency of electromagnetic waves is added to more than 1GHz, it will directly heat the water molecules, which is also the principle of microwave ovens.
The reason why the draft proposed by the Ministry of Industry and Information Technology in February 2021 stipulated 50W was speculated by the industry at that time because the highest wireless charging power on the market at that time was the 50W of Huawei Mate 40 Pro and Xiaomi Mi 11, so it was most likely a reference to the high-power wireless charging technology of existing models. After all, it is easy for emerging things to enter a state of disorderly barbaric growth, and as the market grows, the management of subsequent standards becomes more difficult, and it is very difficult for the relevant interim regulations to delineate a specification that is both reasonable and easy to implement, so it is also the most economical way to limit the frequency band use and maximum power that are commercially available in accordance with the original radio management regulations.
It is worth mentioning that except for the relaxation of the wireless charging power of portable wireless charging equipment from 50W to 80W, the current "Interim Provisions" and the original draft for comments have hardly changed. In fact, the biggest impact of the "Interim Regulations" of the Ministry of Industry and Information Technology is actually to almost "death" for far-field wireless charging technology. A few years ago, Xiaomi, Moto, vivo and other manufacturers have pre-developed far-field wireless charging technology, and this kind of "air charging technology" uses large-scale array antennas to achieve beamforming, and then combined with the narrow beam brought by the 26.5-300GHz millimeter wave, the emission energy is focused in a small range.
Unfortunately, the electromagnetic radiation problem of this technology can not be ignored, if the electromagnetic induction wireless charging that has been popularized is an "induction cooker", then the air charging is a "microwave oven". The limit of radiation power density in the millimeter wave frequency band is higher, the highest value is 2W per square meter, even if the power of air charging is only 10W, the power density focused on the small size range of mobile phones has long exceeded the standard by several orders of magnitude. This is why the Interim Regulations limit the operating frequency range of portable wireless charging equipment to a maximum of 13GHz.
In the case that many people do not trust base stations with better electromagnetic shielding and lower control of electromagnetic radiation leakage, and owners complain that base station radiation may affect health, more risky air charging is likely to face more severe challenges once commercialized. So now the situation is already very clear, when wireless charging has a level of 80W, basically can be charged 50% in 15 minutes, fully charged in less than 40 minutes, the user experience is already comparable to the wired fast charging of mid-range models.
Therefore, in the future, many mobile phone manufacturers will re-talk about 80W wireless charging when releasing new machines.