Patent ID: 7075304

Claim:
A pulse inductive metal detector comprising: an electronic switch for switching a power source on and off; a coil coupled with the electronic switch that can be charged with current from the power source in a transmitter mode such that when the electronic switch is abruptly switched open the coil emits a magnetic field that induces eddy currents in a metal target, and once the transmitter magnetic field has decayed enough, the electronic switch can be closed and the coil can be operated in a receiver mode to detect a magnetic field resulting from eddy currents in the metal target; and a variable resistor coupled across the coil for varying the resistance across the coil to optimize the pulse inductive metal detector sensitivity to the metal target, wherein the variable resistor comprises: a FET transistor having a source-drain path coupled across the coil, and a gate; a digital-to-analog converter (DAC) having an output coupled with the gate of the FET; and a computer, coupled to an input of the DAC, for controlling the DAC, wherein the computer sends a control signal to the DAC to control a gate voltage of the FET and thereby control the resistance of the source-drain path of the FET.