Metal detector utilizing asynchronous demodulation

A metal detector for detecting a metal target under ground, comprising:

• a transmitter switching circuit configured to switch a voltage of a transmitter signal consisting of a series of multi-period rectangular waves;
• a transmitter coil configured to emit the transmitter signal received from the transmitter switching circuit;
• a receiver coil induced by receiving a magnetic field and configured for generating a receiving signal of the magnetic field received;
• a receiver amplifier circuit for amplifying the receiving signal received from the receiver coil to obtain an amplified receiving signal;
• an AD converter for converting the amplified receiving signal and a transmitter current from analog to digital, wherein the AD converter is connected to the receiver amplifier circuit for receiving the amplified receiving signal and to a transmitter voltage adjusting circuit for receiving the transmitter current generating the transmitter signal, and the AD converter is connected to the transmitter voltage adjusting circuit to receive a transmitter signal current;
• a control unit connected to the AD converter for receiving the transmitter current and the receiving signal converted to digital, wherein the control unit comprises a demodulation unit configured for obtaining amplitude and phase values by processing the transmitter current and the receiving signal using asynchronous demodulation process, a correction unit configured for correcting phase differences in the transmitter current and a receiver voltage due to asynchronous demodulation, and a signal processing unit for operating a user interface based on a phase corrected receiving signal.