Patent ID: 7474102
Filing Date: 2009-01-06
Classification: G01V

Abstract:
1. An electronic metal detector comprising transmit electronics comprising switching electronics arranged and adapted to generate a transmit signal, the transmit electronics comprising at least two power sources, a first power source and a second power source, the transmit electronics being connected to a transmit coil arranged and adapted to transmit an alternating magnetic field, wherein the switching electronics are adapted and arranged to switch a first voltage of the first power source to the transmit coil for at least a first period and also a third period, the switching electronics being adapted and arranged to switch a second voltage of the second power source to the transmit coil for at least a second period, the switching electronics being adapted and arranged to switch approximately zero volts to the transmit coil for at least a fourth period, the second voltage being opposite in polarity to the first voltage, and an absolute magnitude of the first voltage being at least ten times an absolute magnitude of the second voltage, the first voltage, second voltage, first period, second period, third period and fourth period being selected so that a transmit coil current increases in a second polarity sense during the second period and changes sign during the second period, and the transmit coil current increases in an opposite polarity sense to the second polarity sense during the first period and also the third period, receive electronics is adapted and arranged to receive and process a receive magnetic field during at least some of the second period and fourth period to produce an indicator output, the indicator output at least indicating the presence of at least some metal targets under the influence of the said alternating magnetic field and indicating at least a characteristic of the said metal targets.