Metal detector

A metal detector for detecting a target, that is a desirable metal object, within a medium, the metal detector comprising:

• a transmitter configured to transmit a signal into the medium;
• a receiver configured to receive a response signal from the medium, the response signal including a secondary medium response signal from the medium and includes a secondary target response signal from the target;
• a preamplifier configured to amplify the response signal to produce an amplified signal;
• compensation circuitry configured to perform transmit coil transfer function compensation on the amplified signal to produce a compensated signal;
• a first notch module configured to remove a resistive component of the secondary medium response signal from the compensated signal to produce a first notch module output signal;
• a low pass filter configured to perform low pass filtering on the first notch module output signal to produce a filtered signal;
• a first signal vector resistive component demodulator configured to produce a first vector resistive component output signal from the filtered signal;
• a first vector reactive component demodulator configured to produce a first vector reactive component output signal from the filtered signal;
• an analog-to-digital converter configured to digitize the first vector resistive component output signal and the first vector reactive component output signal to produce first digital signals;
• a digital signal processor configured to process the first digital signals;
• a second notch module configured to remove a resistive component of the secondary target response signal from the first notch module output signal to produce a second notch module output signal;
• a second signal vector resistive component demodulator configured to produce a second vector resistive component output signal from the second notch module output signal;
• and
• a second vector reactive component demodulator configured to produce a second vector reactive component output signal from the second notch module output signal;
• wherein the analog-to-digital converter is configured to digitize the second vector resistive component output signal and the second vector reactive component output signal to produce second digital signals.

A method for detecting a target, that is a desirable metal object within a medium, the method comprising:

• transmitting, by a transmitter comprising a transmit coil, an excitation signal into the medium;
• receiving a response signal from the medium, the response signal comprising a secondary medium response signal from the medium and a secondary target response signal from the target;
• amplifying the response signal to produce an amplified signal;
• performing, by a compensation circuitry, transmit coil transfer function compensation on the amplified signal to produce a compensated signal comprising the secondary medium response signal from the medium and the secondary target response signal from the target, wherein the secondary medium response signal from the medium comprises a resistive component and a magnetic component, and wherein the secondary target response signal from the target comprises a resistive component and a magnetic component;
• and
• removing the resistive component of the secondary medium response signal from the compensated signal by a notch module to produce a notch module output signal, wherein removing the resistive component of the secondary medium response signal from the compensated signal by the notch module comprises:
• receiving, by a medium resistive component transfer function compensation circuit, the compensated signal;
• reducing, by the medium resistive component transfer function compensation circuit, the resistive component of the secondary medium response signal in the compensated signal to a decaying remnant of the resistive component of the secondary medium response signal in an output signal of the medium resistive component transfer function compensation circuit,
• receiving, by a gate, the output signal of the medium resistive component transfer function compensation circuit;
• and
• producing, by the gate, the notch module output signal, wherein a timing generator generates a control signal aligned with the excitation signal's rising edge and falling edge transients to open and close the gate to remove the remnant of the resistive component of the secondary medium response signal from the notch module output signal.

A method for detecting a target, that is a desirable metal object, within a medium, the method comprising:

• transmitting a signal into the medium;
• receiving a response signal from the medium, the response signal comprising a secondary medium response signal from the medium and a secondary target response signal from the target;
• amplifying the response signal to produce an amplified signal;
• performing, by compensation circuitry, transmit coil transfer function compensation on the amplified signal to produce a compensated signal;
• removing a resistive component of the secondary medium response signal from the compensated signal by a first notch module to produce a first notch module output signal;
• producing, by a first signal vector resistive component demodulator, a first vector resistive component output signal from the first notch module output signal;
• producing, by a first vector reactive component demodulator, a first vector reactive component output signal from the first notch module output signal;
• digitizing the first vector resistive component output signal and the first vector reactive component output signal to produce digital signals;
• processing the digital signals by a digital signal processor;
• removing a resistive component of the secondary target response signal from the first notch module output signal by a second notch module;
• producing a second vector resistive component output signal from output of the second notch module;
• and
• producing a second vector reactive component output signal from the output of the second notch module.