Truncated half-sine methods for metal detectors

A metal detector comprising:

• (a) one or more transmit coils for producing a cyclic transmitted magnetic field in response to a cyclic transmit current, wherein each transmit current cycle is comprised of one or more transmit current pulses, wherein one or more transmit current pulses exhibit approximately a half-sine waveform during turn-on which sinusoidally rises to a peak current, and which at or past the peak current is truncated by substantially shutting off the coil current, and which is followed by a turn-off time in which the applied transmit current is substantially zero;
• (b) transmit circuitry for generating the transmit current pulses applied to the one or more transmit coils comprising one or more switching networks for switching the one or more coils to appropriate drive circuitry comprised of a unipolar or bipolar power supply voltage and one or more series-connected resonant capacitors for the purpose of producing a substantially half-sine response during the turn-on time;
• (c) one or more receive coils for receiving a response signal created from the transmitted magnetic field and its effect on a surrounding matrix and conductive targets;
• (d) receive circuitry comprising a plurality of receive channels each comprised of sampling circuitry and processing circuitry, wherein a receive channel samples a received flyback response created by the truncation of the transmit current and herein called the flyback sample, and wherein a receive channel samples a received half-sine response after the beginning of the transmit half-sine current turn-on point and herein called the R sample, and wherein the flyback sample is used to determine the presence of a conductive target and the R sample is used to determine probable target type.

A metal detector method comprising:

• providing one or more transmit coils for producing a cyclic transmitted magnetic field in response to a cyclic transmit current, each transmit current cycle providing one or more transmit current pulses, wherein the one or more transmit current pulses exhibit approximately a half-sine waveform during turn-on which waveform sinusoidally rises to a peak current, and which at or past the peak current is truncated by substantially shutting off the coil current, and which is followed by a turn-off time in which the applied transmit current is substantially zero,
• providing transmit circuitry for generating the transmit current pulses applied to the one or more transmit coils, providing one or more switching networks for switching the one or more coils to drive circuitry, providing the drive circuitry with a unipolar or bipolar power supply voltage and one or more series-connected resonant capacitors, and producing a substantially half-sine response during turn-on time,
• providing one or more receive coils for receiving a response signal created from the transmitted magnetic field and its effect on a surrounding matrix and conductive targets,
• providing receive circuitry having a plurality of receive channels of sampling circuitry and processing circuitry, wherein one receive channel samples a received flyback response created by the truncation of the transmit current which is a flyback sample, and wherein another receive channel samples a received half-sine response after the peak of the transmit half-sine current but before the truncation point which is a ground sample, and combining the flyback sample and the ground sample and adjusting either or both samples are adjusted such that the combined response due to a ground matrix is substantially minimized.

A metal detector method comprising:

• providing one or more transmit coils for producing a cyclic transmitted magnetic field in response to a cyclic transmit current, each transmit current cycle providing one or more transmit current pulses, wherein the one or more transmit current pulses exhibit approximately a half-sine waveform during turn-on which waveform sinusoidally rises to a peak current, and which at or past the peak current is truncated by substantially shutting off the coil current, and which is followed by a turn-off time in which the applied transmit current is substantially zero,
• providing transmit circuitry for generating the transmit current pulses applied to the one or more transmit coils, providing one or more switching networks for switching the one or more coils to drive circuitry, providing the drive circuitry with a unipolar or bipolar power supply voltage and one or more series-connected resonant capacitors, and producing a substantially half-sine response during turn-on time,
• providing one or more receive coils for receiving a response signal created from the transmitted magnetic field and its effect on a surrounding matrix and conductive targets,
• providing receive circuitry having a plurality of receive channels of sampling circuitry and processing circuitry, wherein one receive channel samples a received flyback response created by the truncation of the transmit current called the flyback sample, and another receive channel samples a received half-sine response after the beginning of the transmit half-sine current turn-on point called the R sample, and using the flyback sample to determine the presence of a conductive target and using the R sample to determine probable target type.