Who says that charging must connect electric wire? As long as the phone contact the charger, charging can be realized! Let's understand the principle of "wireless charge".
Every time I need to charge my mobile phone, computer, or other electrical appliances, I always need to connect a charging line. There are many charging lines, and they are often connected incorrectly, which is very troublesome. Fortunately, more and more electronic products are using the technology of "wireless charge". As long as you put the mobile phone on a small thing like cup wad gracefully, you can easily charge it without wiring. What's the principle behind such a powerful technology? Let's explore the mystery.
1. Interaction between electricity and magnetism
Generally speaking, the principle of "current magnetic effect" and "electromagnetic induction" are used in wireless charge. In 1819, Danish scientist erster observed that if an electric current was applied to a length of wire, a magnetic field would be generated around it, which could deflect the compass. Later generations further found that the magnetic field generated by wrapping the wire into a ring or even a coil will be stronger and more concentrated, which is called "current magnetic effect".
As for electromagnetic induction, it was discovered by Faraday in 1831. Let a magnet or other magnetic field source close to a coil without current, the coil will produce "induced current", which is called "electromagnetic induction". It is worth noting that the condition of electromagnetic induction is that the magnetic field must have "change", for example, the magnet is getting closer and closer (it is OK to keep away from it). If the external magnetic field remains unchanged, there will be no induced current.
In a word, the current magnetic effect is that the current flows around to produce a magnetic field, while the electromagnetic induction is that the changing external magnetic field makes the coil produce an induced current.
2. Use electromagnetic induction to charge
When these two physical phenomena are used at the same time, wireless charge can be carried out. The current wireless charge equipment includes a "charging stand", which is actually the coil. When the charging base is connected to the household plug, the magnetic field around the coil will be generated due to the current magnetic effect. There is also a coil in the electronic products to be charged. When it is close to the charging base, the magnetic field of the charging base will be electromagnetically induced to generate induced current on the coil of the electronic products. When the induced current is led to the battery, the wireless charging between the charging base and electronic products is completed.
You may ask, isn't a magnetic field changing to have electromagnetic induction? However, the distance between the charging base and the charging object remains unchanged, so why is there electromagnetic induction? It turns out that the electricity flowing out of the household socket is "alternating current", that is to say, the direction of the current constantly alternates, one along the current, the other against the current. Because of this, the magnetic field produced by the coil of the charging base is constantly changing direction, which does not remain unchanged and meets the conditions of electromagnetic induction.
Recently, more and more smartphones and tablet computers begin to provide wireless charge function, but unfortunately, when they are charging, as long as they are a little far away from the charging seat, the charge efficiency will be significantly reduced. Even with the latest technology, the charging distance can't exceed 5cm. In fact, most of the mobile devices that can be charged wirelessly at present need to be completely placed on the charging stand. It's still a little different from the wireless charge that can be charged at every place in the imagination. However, as wireless charging technology develops so quickly, long distance wireless charging has come into the market.
3. Use resonance to lengthen charging distance
In order to increase the distance and efficiency of wireless charge, scientists are trying to use the principle of "magnetic resonance" for wireless charge. Some special elements such as capacitors and inductors are added to the circuit, and a "resonant circuit" will be formed after proper connection. It's like a tuning fork, which must be a tuning tool in an instrument store. Tap the tuning fork once, and it can vibrate for a period of time. Similarly, if the resonant circuit is powered on for a short time, the signal will be generated in the circuit for a period of time.
Tuning fork has the interesting physical property of resonance. Each tuning fork has its own voice frequency. When one tuning fork vibrates, if there is another tuning fork with the same voice frequency nearby, it will vibrate even if it is not directly hit. The resonance of tuning fork can be said to achieve the transmission of energy. The resonance circuit can also resonate. Two resonance circuits with the same vibration frequency are put together. When one of them starts to vibrate due to power on, the other circuit will also vibrate along with it. It "automatically" generates current, so the electric energy is transmitted through the air gap. This phenomenon is called "magnetic resonance". It is used for wireless charging. It can make the charging distance reach several meters and improve the efficiency. The only difficulty is that it is not easy to adjust the two circuits to exactly the same frequency and maintain them for a period of time.
In addition to magnetic resonance, some scientists have tried to use the light energy of laser light to charge, or even transmit the electric energy through the radio frequency band similar to that of home WiFi network. I hope these technological breakthroughs will make our charging more convenient in the future!