Constant current metal detector with driven transmit coil

A method for detecting a metallic target in a soil using a metal detector, the method comprising:

• a) generating a repeating transmit signal cycle, the repeating transmit signal cycle including a first receive period and a first non zero transmit coil reactive voltage period, the first non zero transmit coil reactive period being different from the first receive period and does not overlap with the first receive period, wherein an absolute average voltage value across a transmit coil during the first non zero transmit coil reactive voltage period is higher than an absolute average voltage value across the transmit coil during the first receive period;
• b) receiving the repeating transmit signal cycle in the transmit coil having an inductance, the transmit coil connected to transmit electronics to generate a transmitted magnetic field;
• c) receiving a received magnetic field in a receive coil during the first receive period and providing a received signal induced by the received magnetic field;
• d) sensing a current in the transmit coil during the first receive period;
• e) determining a modulation of the inductance of the transmit coil;
• f) maintaining the current during the first receive period to be constant, with zero reactive voltage, and of a fixed value from cycle to cycle, and a voltage applied across the transmit coil during the first receive period to be constant, wherein the step of maintaining is arranged and configured such that the fixed value of the current during the first receive period from cycle to cycle is not affected by the modulation of the inductance of the transmit coil;
• and
• g) processing the received signal during the first 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,