Constant Current Metal Detector with Driven Transmit Coil

A metal detector used for detecting a metallic target in a soil comprising:

• a) transmit electronics having a plurality of switches for generating a repeating transmit signal cycle, the repeating transmit signal cycle including at least one receive period and at least one non-zero transmit coil reactive voltage period, the at least one non-zero transmit coil reactive voltage period is different from the at least one receive period;
• b) a transmit coil having an inductance connected to the transmit electronics for receiving the repeating transmit signal cycle and generating a transmitted magnetic field;
• c) a receive coil for receiving a received magnetic field during at least one receive period and providing a received signal induced by the received magnetic field;
• d) one or more negative feedback loops for sensing a current in the transmit coil during the at least one receive period to provide a control signal, and based on the control signal, the one or more negative feedback loops control a magnitude of a voltage and/or duration of the at least one non-zero transmit coil reactive voltage period;
• and
• e) receive electronics connected to the receive coil for processing the received signal during at least one receive period to produce an indicator output signal, the indicator output signal including a signal indicative of the presence of a metallic target in the soil;
• wherein when the inductance of the transmit coil is modulated by the soil during an operation of the metal detector, the one or more negative feedback loops change the magnitude of a voltage and/or duration of the at least one non-zero transmit coil reactive voltage period to maintain an average value of the current during at least one receive period in a cycle to be substantially the same value as an average value of the current during at least one receive period in any other cycle.