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How does the "wireless charger" achieve air-to-air charging?

When charging is mentioned in life, your first reaction is whether to use a charger and a charging cable. In recent years, a variety of "wireless chargers" have been on the market, which can be used for "over-the-air" charging. What principles and technologies are used?

As early as 1899, physicist Nikola Tesla had already begun the exploration of wireless power transmission. He built a wireless power transmission tower in New York and conceived a wireless power transmission method: using the earth as the inner conductor and the earth’s ionosphere as the outer conductor, amplifying the transmitter in a radial electromagnetic wave oscillation mode to establish between the earth and the ionosphere with a low frequency resonance of about 8 Hz, the surface electromagnetic waves surrounding the earth are used to transmit energy.

Although this idea was not realized at the time, it was a bold exploration of wireless charging by scientists a hundred years ago. Nowadays, people continue to research and experiment on this basis, and successfully developed wireless charging technology, and the initial scientific concept is gradually landing.

Wireless charging is a technology that uses non-physical contact to achieve power transmission. There are currently three common wireless transmission technologies for electric energy, namely electromagnetic induction, electromagnetic resonance, and radio wave. Among them, electromagnetic induction is a widely used method, which not only has high charging efficiency, but also low cost.

The working principle of electromagnetic induction wireless charging technology is: install the transmitting coil on the wireless charging base, and install the receiving coil on the back of the mobile phone. When the mobile phone is charged close to the charging base, the transmitting coil will generate an alternating magnetic field due to the alternating current. The change of the magnetic field will cause an induced current in the receiving coil to transfer energy from the transmitting end to the receiving end, and finally complete the charging process.

The charging efficiency of electromagnetic induction wireless charging method is as high as 80%. The disadvantage is that it can only be charged in a short distance, and the charging equipment needs to be close together. In order to solve this problem, scientists began a new attempt.

In 2007, a research team in the United States successfully used electromagnetic resonance technology to light up a 60 watt light bulb about 2 meters away from the power source. The power transmission efficiency reached 40%, which started the development of electromagnetic resonance wireless charging technology.

The principle of electromagnetic resonance wireless charging technology is the same as the principle of sound resonance: an energy transmitting device and an energy receiving device are adjusted to the same frequency, and the energy of each other can be exchanged during resonance.In this way, the coil in one device can transmit electrical energy to the coil in another device over a long distance to complete the charging.

Electromagnetic resonance wireless charging technology breaks the limitation of electromagnetic induction short-distance transmission, extending the charging distance to a maximum of 3 to 4 meters, and it also gets rid of the limitation that the receiving device must use metal materials when charging.

In order to further increase the distance of wireless transmission of electric energy, researchers have developed radio wave charging technology. The principle is: a microwave transmitting device and a microwave receiving device complete wireless power transmission. The transmitting device can be installed in the wall plug, and the receiving device can be installed on any low-voltage product.

After the microwave transmitting device transmits the radio frequency signal, the receiving device can capture the radio wave energy bounced from the wall, and obtain a stable direct current after wave detection and high frequency rectification, which can be used by the load.

Compared with traditional charging methods, wireless charging technology breaks the limitations of time and space to a certain extent, and brings many conveniences to our lives. I believe that with the further development of wireless charging technology and related products, there will be a broader future application prospects.