Metal detector

Abstract

A metal detector detects when a target that is a desirable metal object is located within a medium. A signal is transmitted into the medium. A response signal is received from the medium. The response signal includes a secondary medium response signal from the medium and includes a secondary target response signal from the target when the target is located within the medium. The response signal is amplified to produce an amplified signal. Compensation circuitry perform transmit coil transfer function compensation on the amplified signal to produce a compensated signal. A notch module removes a resistive component of the secondary medium response signal from the compensated signal.

What is claimed is: 
     
         1 . A metal detector for detecting when a target that is a desirable metal object is located within a medium, comprising:
 a transmitter that transmits a signal into the medium;   a receiver that receives 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 when the target is located within the medium;   a preamplifier that amplifies the response signal to produce an amplified signal;   compensation circuitry that performs transmit coil transfer function compensation on the amplified signal to produce a compensated signal; and   a first notch module that removes a resistive component of the secondary medium response signal from the compensated signal to produce a first notch module output signal, wherein the first notch module includes:
 a medium resistive component transfer function compensation circuit, and 
 a gate, the gate and the medium resistive component transfer function compensation circuit being configured to remove the resistive component of the secondary medium response signal from the compensated signal. 
   
     
     
         2 . The metal detector of  claim 1 , additionally comprising:
 a low pass filter that performs low pass filtering on the first notch module output signal to produce a filtered signal;   a first signal vector resistive component demodulator that produces a vector resistive component output signal from the filtered signal;   a first vector reactive component demodulator that produces a first vector reactive component output signal from the filtered signal;   an analog-to-digital converter that digitizes the first vector resistive component output signal and the first vector reactive component output signal to produce digital signals; and   a digital signal processor that processes the digital signals.   
     
     
         3 . The metal detector of  claim 2  wherein the transmitter includes a transmit coil and the receiver includes a receive coil. 
     
     
         4 . The metal detector of  claim 2  additionally including a timing generator that provides timing signals to a power amplifier for the transmitter, the first notch module, the first signal vector resistive component demodulator and the first vector reactive component demodulator. 
     
     
         5 . A metal detector for detecting when a target that is a desirable metal object is located within a medium, comprising:
 a transmitter that transmits a signal into the medium;   a receiver that receives 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 when the target is located within the medium;   a preamplifer that amplifies the response signal to produce an amplified signal;   compensation circuitry that performs transmit coil transfer function compensation on the amplified signal to produce a compensated signal;   a first notch module that removes 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 that performs low pass filtering on he first notch module output signal to produce a filtered signal;   a first signal vector resistive component demodulator that produces a vector resistive component output signal from the filtered signal;   a first vector reactive component demodulator that produces a first vector reactive component output signal from the filtered signal;   an analog-to-digital converter that digitizes the first vector resistive component output signal and the first reactive component output signal to proudce digital signals;   a digital signal processor that processes the digital signals;   a second notch module that removes a resistive component of the secondary target response signal from the first notch module output signal when the target is located within the medium to produce a second notch module output signal;   a second signal vector resistive component demodulator that produces a vector resistive component output signal from output of the second notch module; and   a second vector reactive component demodulator that produces a second vector reactive component output signal from the second notch module output signal; and   wherein the analog-to-digital converter digitizes the second vector resistive component output signal and the second vector reactive component output signal to produce second digital signals.   
     
     
         6 . The metal detector of  claim 5 , additionally comprising:
 a third notch module that removes a resistive component of the secondary target response signal from the first notch module output signal when the target is located within the medium to produce a third notch module output signal;   a third signal vector resistive component demodulator that produces a third vector resistive component output signal from the third notch module output signal; and   a third vector reactive component demodulator that produces a third vector reactive component output signal from the third notch module output signal;   wherein the analog-to-digital converter digitizes the third vector resistive component output signal and the third vector reactive component output signal to produce third digital signals.   
     
     
         7 . The metal detector of  claim 5 , wherein the second notch module includes:
 a target resistive component transfer function compensation circuit; and   a gate, the gate and the target resistive component transfer function compensation circuit being configured to remove the resistive component of the secondary target response signal from the first notch module output signal.   
     
     
         8 . The metal detector of  claim 5 , additionally comprising:
 a timing generator that provides timing signals to a power amplifier for the transmitter, the first notch module, the first signal vector resistive component demodulator, the first vector reactive component demodulator, the second notch module, the second signal vector resistive component demodulator, the second vector reactive component demodulator.   
     
     
         8 . The metal detector of  claim 5 , additionally comprising:
 a low pass filter that performs low pass filtering on the second notch module output signal to filter the second notch module output signal prior to the second notch module output signal being received by the second signal vector resistive component demodulator and the second vector reactive component demodulator.   
     
     
         10 . The metal detector of  claim 1 , wherein the first notch module includes:
 a regulator that adjusts a medium resistive component transfer function timing constant for the medium resistive component transfer function compensation circuit.   
     
     
         11 . A method for detecting when a target that is a desirable metal object is located within a medium, comprising:
 transmitting a signal into the medium;   receiving 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 when the target is located within the medium;   amplifying the response signal to produce an amplified signal;   using compensation circuitry to perform transmit coil transfer function compensation on the amplified signal to produce a compensated signal; and   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, wherein removing the resistive component of the secondary medium response signal from the compensated signal by the first notch module is performed using a medium resistive component transfer function compensation circuit and a gate, wherein the gate and the medium resistive component transfer function compensation circuit are configured to remove the resistive component of the secondary medium response signal from the compensated signal.   
     
     
         12 . The method of  claim 11 , additionally comprising:
 using a first signal vector resistive component demodulator to produce a first vector resistive component output signal from the first notch module output signal;   using a first vector reactive component demodulator to produce 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; and   using a digital signal processor to process the digital signals.   
     
     
         13 . The method of  claim 12 , additionally comprising:
 performing low pass filtering on the first notch module output signal.   
     
     
         14 . The method of  claim 12 :
 wherein transmitting the signal is performed using a transmit coil; and   wherein receiving the response signal is performed using a receive coil.   
     
     
         15 . The method of  claim 12  additionally comprising:
 using a timing generator to provide timing signals to a power amplifier for transmitting the signal, the first notch module, the first signal vector resistive component demodulator and the first vector reactive component demodulator. 
 
     
     
         16 . The method of  claim 11 , wherein a regulator adjusts a medium resistive component transfer function timing constant for the medium resistive component transfer function compensation circuit. 
     
     
         17 . A method for detecting when a target that is a desirable metal object is located within a medium, comprising:
 transmitting a signal into the medium;   receiving 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 when the target is located within the medium;   amplifying the response signal to produce an amplified signal;   using compensation circuitry to perform 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 ouput signal;   using a first signal vector resistive component demodulator to produce a first vector resistive component output signal from the first notch module output signal;   using a first vector reactive component demodulator to produce 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;   using a digital signal processor to process the digital signals;   removing a resistive component of the secondary target response signal from the first notch module output signal when the target is located within the medium 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.   
     
     
         18 . The method of  claim 17 , additionally comprising:
 removing an additional resistive component of the secondary target response signal from the first notch module output signal when the target is located within the medium by a third notch module;   producing a third vector resistive component output signal from output of the third notch module; and   producing a third vector reactive component output signal from the output of the third notch module.   
     
     
         19 . The method of  claim 17 , wherein removing the resistive component of the secondary target response signal from the first notch module output signal by the second notch module is performed using a target resistive component transfer function compensation circuit and a gate, wherein the gate and the target resistive component transfer function compensation circuit are configured to remove the resistive component of the secondary target response signal from the first notch module output signal. 
     
     
         20 . The method of  claim 17  additionally comprising:
 using a timing generator to provide timing signals to a power amplifier for transmitting the signal, the first notch module, the first signal vector resistive component demodulator, the first vector reactive component demodulator and the second notch module.