Intruder detection system and method
First Claim
1. A method for detecting an intrusion of a secure area by an entity, comprising:
- sequestering at least one optical fiber, having two ends, in an area to be monitored;
amplitude-modulating an optical carrier signal by an original reference signal;
launching said amplitude-modulated optical carrier signal into one end of said optical fiber;
receiving said amplitude-modulated optical carrier signal from the other end of said optical fiber after passage therethrough;
demodulating said received amplitude-modulated optical carrier signal to recover the reference signal;
at preselected timed sampling intervals, measuring the angular phase shift between said original reference signal and the recovered reference signal; and
initiating a desired action when the measured phase shift changes by an amount in excess of a predetermined threshold level between any two sequential sample intervals.
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Accused Products
Abstract
A microbend-sensitive optical fiber is embedded in a thin pliable padding and laid under an area to be protected. An amplitude-modulated optical light beam is launched into one end of the fiber. The light beam is recovered from the other end of the optical fiber. The angular phase shift between the launched light beam and the recovered light beam is continuously measured and sampled at desired sample intervals. A change in the measured phase shift between any two sequential sample intervals is indicative of the presence of an intruding entity. The magnitude of the phase shift is a function of the mass of the entity. The pattern of repetitive phase shift differences as a function of time provides an estimate of the dynamic characteristics of the intruding entity.
59 Citations
19 Claims
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1. A method for detecting an intrusion of a secure area by an entity, comprising:
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sequestering at least one optical fiber, having two ends, in an area to be monitored; amplitude-modulating an optical carrier signal by an original reference signal; launching said amplitude-modulated optical carrier signal into one end of said optical fiber; receiving said amplitude-modulated optical carrier signal from the other end of said optical fiber after passage therethrough; demodulating said received amplitude-modulated optical carrier signal to recover the reference signal; at preselected timed sampling intervals, measuring the angular phase shift between said original reference signal and the recovered reference signal; and initiating a desired action when the measured phase shift changes by an amount in excess of a predetermined threshold level between any two sequential sample intervals. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A smart intruder detection system, comprising:
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an optical fiber, sensitive to microbending, sequestered in an area to be protected; oscillator means for providing an original reference signal; means for amplitude-modulating an optical carrier signal by said original reference signal and for launching the amplitude-modulated optical carrier signal into said optical fiber; means for receiving said amplitude-modulated optical carrier signal from said optical fiber after passage therethrough; means for demodulating the received amplitude-modulated optical carrier signal to recover the reference signal; means for continuously measuring the angular phase shift between said original reference signal and a recovered reference signal; means for sampling the measured phase shift at timed sampling intervals; means for initiating a desired action when the sampled phase shift measurements change by an amount in excess of a predetermined threshold level between any two sequential sample intervals. - View Dependent Claims (8, 9, 10, 11)
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12. A smart system for detecting intrusion of a secure area, comprising:
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an optical fiber disposed over the area; a source for providing a periodic reference signal; means for amplitude modulating an optical carrier signal by said periodic reference signal and for launching the amplitude-modulated optical carrier signal into said optical fiber; means for detecting and demodulating said amplitude-modulated optical carrier signal, after passage through said optical fiber, to recover the reference signal; means for measuring and sampling, at timed intervals, the angular phase shift between the reference signal and the recovered reference signal; and means for initiating a desired activity when the sampled phase shift measurements change significantly between sequential sample intervals by an amount in excess of a predetermined threshold level. - View Dependent Claims (13, 14, 15)
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16. A method for detecting the presence of an intruding entity in a secure area, comprising:
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disposing an optical fiber over the area; amplitude-modulating an optical carrier signal by an original reference signal; launching said amplitude-modulated optical carrier signal into said optical fiber; detecting and demodulating said amplitude-modulated optical carrier signal after passage through said optical fiber to recover the reference signal; measuring the relative angular phase shift difference between the original reference signal and the recovered reference signal; and initiating a desired activity when the measured phase shift difference significantly exceeds a predetermined threshold level. - View Dependent Claims (17, 18, 19)
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Specification