i am planning to do a small diy wireless power transfer device. The circuit of the transmitter is receiver has just the coil and load arrangement. my query is, (please correct me if am wrong) -->to induce a voltage in the secondary coil, there must be a varying magnetic field right? -->but according to circuit, the transistor doesn't help in changing the polarity, what is the necessity of using the transistor then? am just a hobbyist. thanks much for your reply in advance.