Large area motion sensor
First Claim
1. A motion sensor for detecting intruder motion within a protected area and for discriminating against motion outside the protected area, comprising:
- transceiver means including means for transmitting frequency modulated continuous wave signals in a pattern to cover said protected area, said transmitted signals having a selected, repetitive frequency sweep, and means for receiving signals reflected by target scatterers;
means for demodulating said received signals to produce an ensemble of audio tones, each tone representing the range of a target scatterer;
noise filter means for said tones, said filter means discriminating against tones produced by noise and clutter;
range filter means for discriminating against tones received from target scatterers outside a predetermined zone;
means for storing values representing said audio tones for a first frequency sweep of said transmitter;
means for comparing said stored values with corresponding values derived from a second frequency sweep of said transmitter and for producing error signals corresponding to differences between the values corresponding to said first and second frequency sweeps, said differences representing motion of a target scatterer within said protected area; and
alarm means responsive to a predetermined number of error signals.
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Accused Products
Abstract
An intrusion detector operating with electromagnetic sensors to detect intruder motion within large, defined areas is disclosed. The system provides an acceptably low false alarm rate by means of range discrimination whereby moving objects outside the protected area do not affect the system and by improving sensitivity to slow-moving targets even when located very close to the sensor location. The system incorporates a transmitter which is frequency modulated by a triangular or sawtooth wave and a receiver which produces an output signal that varies in accordance with the instantaneous difference between the transmitted and received frequencies. The frequency of this difference signal is the beat frequency, and is proportional to the range of the target. Storage means are provided to permit comparison of successively received signals over a predetermined period of time, and this comparison serves to reveal slowly varying changes in the return signal pattern. Alarm means are provided which respond to significant variations in successive measurements, and when a threshold level of difference is exceeded for a certain number of consecutive sweeps, an alarm is sounded.
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Citations
22 Claims
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1. A motion sensor for detecting intruder motion within a protected area and for discriminating against motion outside the protected area, comprising:
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transceiver means including means for transmitting frequency modulated continuous wave signals in a pattern to cover said protected area, said transmitted signals having a selected, repetitive frequency sweep, and means for receiving signals reflected by target scatterers; means for demodulating said received signals to produce an ensemble of audio tones, each tone representing the range of a target scatterer; noise filter means for said tones, said filter means discriminating against tones produced by noise and clutter; range filter means for discriminating against tones received from target scatterers outside a predetermined zone; means for storing values representing said audio tones for a first frequency sweep of said transmitter; means for comparing said stored values with corresponding values derived from a second frequency sweep of said transmitter and for producing error signals corresponding to differences between the values corresponding to said first and second frequency sweeps, said differences representing motion of a target scatterer within said protected area; and alarm means responsive to a predetermined number of error signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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Specification