What is nikola tesla and his Tesla coil?

Tesla's main inventions are Tesla coil, alternating current and alternating current motor, which can be said to be the basic equipment for power operation in our society at present. As for Tesla coil, it is the originator of infinite electricity and a high-frequency step-up transformer, which skillfully uses the principle of LC*** vibration to realize voltage rise and frequency rise. It is a kind of broad-spectrum radio radiation finger, which was expected to become a very large-scale equipment to realize global wireless power transmission, but it failed to be realized for various reasons.