Patent ID: 6686742
Filing Date: 2004-02-03
Classification: G01V

Abstract:
A metal detector apparatus comprising:a transmit coil adapted to transmit a magnetic field, the transmit coil being energized by electrical current flowing therethrough, transmit timing control circuitry that includes timing for a first semiconductor switch, and receive signal circuitry and receive signal processing circuitry; a transmit coil damping network including at least one resistor connected in series with the said first semiconductor switch across the transmit coil, whereas the timing control circuitry generates a timing sequence selected so that for a period of time no transmit field is generated and at least during part of the energization of the coil the first semiconductor switch is controlled to be off and is turned on before the cessation of the transmit field whereby said resistor damps a back e.m.f. across said coil when said first semiconductor switch is on.