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　　Think what you dare not think - Talking about wireless charging technology

　　We all know that wireless energy seems like a novel concept that sounds great, but it’s hard to imagine it being commercialized anytime soon.

　　As the name suggests, "wireless charging" uses a special device to convert power from a power socket into rechargeable radio waves, thereby directly charging electronic devices without throwing away wires.

　　Wireless charging generally transfers energy through magnetic fields, and most of the objects around humans and humans are non-magnetic. Another benefit of wireless charging is power saving. The efficiency of wireless charging equipment is around 70%, which is the same as wired charging equipment. However, it has an automatic shutdown function when fully charged to avoid unnecessary energy consumption. Moreover, this performance acceptance rate is constantly improving and will soon reach 98%.

　　Wireless charging equipment is much "smarter" than ordinary chargers. For different electronic products, the power interface can automatically correspond. When charging is needed, the transmitter and receiving chips will automatically start working at the same time. When fully charged, both parties will automatically shut down. It can also automatically identify different devices and energy needs and perform "personalized work". This is intelligence.

　　1Wireless charging technology

　　In fact, as early as 1890, physicist and electrical engineer Nikola Tesla had already conducted wireless power transmission experiments (Figure 1). He proposed and realized alternating current generation. The SI unit of magnetic induction is also named after him. The wireless power transmission method conceived by Tesla uses the earth as the inner conductor and the earth's ionosphere as the outer conductor. By amplifying the transmitter in the radial electromagnetic wave oscillation mode, a low-frequency resonance of about 8Hz is established between the earth and the ionosphere. Uses surface electromagnetic waves that surround the Earth to transmit energy. However, due to lack of financial resources, Tesla's bold idea was not realized. Although future generations have completely confirmed the feasibility of this solution in theory, the world has not yet achieved unity, and it is impossible to broadcast and obtain energy for free around the world. Therefore, a great scientific idea was stillborn.

　　Tesla conducts wireless power transmission experiment

　　In fact, there are electromagnetic waves everywhere around us, from low-frequency waves to cosmic rays, and they all carry more or less energy. In the opinion of many physicists, all people have to do may be to find suitable ways to receive and utilize this energy. Although Tesla's idea is unlikely to become a reality, wireless power transmission is of great significance to the development and utilization of new energy and solving the problem of future energy shortages. Therefore, many countries have not given up research in this area. In 1968, American engineer Peter Glaser proposed the concept of Space Solar Power (SSP). The idea was to establish a solar power generation base in the outer space of the earth and transmit electrical energy back to the earth through microwaves (Figure 2). And the microwave is converted into electrical energy through the rectenna. In 1979, NASA and the U.S. Department of Energy jointly proposed a solar energy plan to establish the "SPS Solar Satellite Reference System." The European Union built a 100,000-kilowatt experimental microwave power transmission device on Reunion Island in Africa, which delivered electricity to local villages in 2003. Ambitious Japan plans to build an experimental space solar power station SPS2000 in 2020 and enter large-scale operation in 2050.

　　In fact, wireless charging technology is not out of reach for ordinary people like us. I believe someone must have used an electric toothbrush of a certain brand (Figure 3). As long as the toothbrush is inserted into the 220V charging stand, non-contact wireless charging can be achieved, which is very convenient to use. This kind of wireless charging uses the principle of electromagnetic induction to solve the problem of electricity safety in humid environments.

　　There are three basic methods of wireless power transmission: electromagnetic induction, radio frequency and microwave. These three technologies are suitable for short-range, medium-short-range and long-range power transmission respectively. But each wireless charging method has some shortcomings, which limits its development. For example, the energy transmitted by electromagnetic induction is small and the transmission range is small. This is why electric toothbrushes must be placed on the charging stand to charge, and the toothbrush cannot be placed arbitrarily. Therefore, the current research direction of various companies is to improve and perfect these technologies, so as to ultimately achieve commercialization.

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