초록

This invention is for a pulse induction metal detector which uses combinations of the signal detected during non-transmission of the magnetic field to eliminate those contributions to the signal due to the remanent magnetization of ferrites and asynchronous magnetic fields within the target volume.

대표청구항 ▼

A conducting metal detection apparatus comprising: transmission means including a transmit coil for transmitting a discontinuous pulse voltage waveform in order to transmit a magnetic field to a target volume, the discontinuous pulse voltage waveform providing periods of non-transmission of the magn

A conducting metal detection apparatus comprising: transmission means including a transmit coil for transmitting a discontinuous pulse voltage waveform in order to transmit a magnetic field to a target volume, the discontinuous pulse voltage waveform providing periods of non-transmission of the magnetic field; a detector coil for producing a detected signal by detecting changes in magnetic fields; measurement means for measuring the detected signal during at least a first and second pre-determined period which is separate from that period which has significant signal resulting from decay of ground eddy currents, the measuring occurring during the periods of non-transmission of the magnetic field, the measurement means producing at least a first and a second measurement respectively; and processing means for processing at least two of the measurements to provide an output signal derived by substantially removing that component of the detected signal due to electrically non-conducting ferrite within the target volume from the said detected signal by forming a combination of the at least two measurements, said combination being dependent upon the first time derivative of the magnetic field due to the electrically non-conducting ferrite during the periods of non-transmission, wherein the first time derivative of the magnetic field is dependent upon the duration and temporal evolution of the transmitted magnetic field, the output signal thus being useful to indicate the presence of a metallic object within the target volume.