Wireless charging is a method of charging batteries without cables or adapters by using electromagnetic fields. There are three main types of wireless charging: resonant charging, inductive charging, and radio charging. Resonant charging uses coils tuned to the same frequency to transfer power over larger distances and is used for electric cars and robots. Inductive charging creates an electromagnetic field to induce current in a receiving coil and is used for phones, MP3 players, and electric toothbrushes. Radio charging propagates radio waves to power devices like watches and hearing aids. The basic design consists of a transmitter that sends power signals, antennas to mediate between transmitter and receiver, and a receiver to rectify alternating current into direct current to charge a battery.