Magnetic anomaly detector
First Claim
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1. A magnetic anomaly detector, comprising:
- a magnetic field detector for generating analog signals in response to an incident magnetic field;
a sample-and-hold device coupled to said magnetic field detector for generating time-quantized analog signals from said analog signals;
a discrete-time differentiator coupled to said sample-and-hold device, for differentiating said time-quantized analog signals to thereby generate differentiated signals;
a low-pass filter coupled to said differentiator, for rejecting spectral frequencies above a given value and for passing spectral frequencies below said given value, to thereby generate filtered signals;
a Fourier transform device coupled to said low-pass filter for receiving said filtered signals, and for transforming said filtered signals into a frequency-amplitude spectrum;
a reference spectrum source for generating at least one frequency spectrum representing the presence of a magnetic anomaly;
an error detector coupled to said Fourier transform device and to said reference spectrum source, for generating an error signal representative of differences between said reference spectrum and the frequency-amplitude spectrum; and
an alarm coupled to said error detector for responding to identification of one of a match and no match between said reference spectrum and the frequency-amplitude spectrum.
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Abstract
A magnetic anomaly detector includes a magnetically active device which produces analog signals in response to magnetic fields. The analog signals are time quantized and then discrete-time differentiated. The differentiated signals are applied to a low-pass filter. The filtered signals are Fourier transformed into an amplitude-frequency spectrum. An error detector compares at least one reference amplitude-frequency spectrum with the reference spectrum to identify the presence or absence of a magnetic anomaly. The resulting error is displayed on a monitor or operates an alarm.
60 Citations
20 Claims
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1. A magnetic anomaly detector, comprising:
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a magnetic field detector for generating analog signals in response to an incident magnetic field; a sample-and-hold device coupled to said magnetic field detector for generating time-quantized analog signals from said analog signals; a discrete-time differentiator coupled to said sample-and-hold device, for differentiating said time-quantized analog signals to thereby generate differentiated signals; a low-pass filter coupled to said differentiator, for rejecting spectral frequencies above a given value and for passing spectral frequencies below said given value, to thereby generate filtered signals; a Fourier transform device coupled to said low-pass filter for receiving said filtered signals, and for transforming said filtered signals into a frequency-amplitude spectrum; a reference spectrum source for generating at least one frequency spectrum representing the presence of a magnetic anomaly; an error detector coupled to said Fourier transform device and to said reference spectrum source, for generating an error signal representative of differences between said reference spectrum and the frequency-amplitude spectrum; and an alarm coupled to said error detector for responding to identification of one of a match and no match between said reference spectrum and the frequency-amplitude spectrum. - View Dependent Claims (2, 3)
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4. A magnetic anomaly detector, comprising:
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a photoresponsive solid-state crystalline device with lattice imperfections, in which lattice imperfections electrons resonate at a given wavelength; a source of timed sequential pairs of light pulses at said given wavelength, said source being directed toward said device, wherein the first of said pulses raises the energy state of said electrons over a ground state, thereby creating first and second distinct quantum spin state populations, and said second of said pulses of each pair of pulses occurs at a time such that the energy state of said electrons is reduced to said ground state, and wherein the reduction of said energy state generates photons which exit said device, the number of said photons exiting said device being related to a magnitude of a magnetic field through said device; a photon detector for responding to said photons and for generating an electrical signal in response to said photons; a sample-and-hold device coupled to said photon detector for generating time-quantized electrical signals; a differentiator coupled to said sample-and-hold device for differentiating said time-quantized electrical signals to produce differentiated signals; a low-pass filter coupled to said differentiator for low-pass-filtering said differentiated signals to produce reduced-noise signals; an amplitude-time-to-spectrum converter coupled to said low-pass filter, for converting said reduced-noise signals to an amplitude-frequency spectrum; a library of reference amplitude-frequency spectra, each representing an amplitude-frequency spectrum of a magnetic anomaly; and a comparator for comparing said amplitude-frequency spectrum with at least one reference amplitude-frequency spectrum to determine the presence or absence of said magnetic anomaly. - View Dependent Claims (5, 6, 7, 8)
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9. A method for detecting a magnetic anomaly, comprising:
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sensing a magnetic field using a single-axis sensor; applying a signal output from the single-axis sensor to a sampling device to produce a time sequence of signals; applying the sequence of signals to a differentiator to obtain discrete time rate of change scalar signals; filtering the output from the differentiator to reduce high-frequency noise contamination of the time rate of change scalar signals; transforming the low-pass filtered signals using a Fourier transform to convert the low-pass filtered signals to the instantaneous frequency domain; applying the Fourier transformed signals a non-inverting input port of an error detector; applying a plurality of reference signals to an inverting input port of the error detector; wherein the plurality of reference signals represent a respective plurality of magnetic anomalies; comparing the transformed signals with the plurality of reference signals to produce a plurality of signals, each of the plurality of signals representing a similarity of the associated reference signals to the transformed signals; identifying that reference signals of said plurality of reference signals which most closely match the transformed signals; and displaying the magnetic anomaly associated with the matching reference signals. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification