Volumetric intrusion alarm using both Doppler and net-change signal processing

• US 3,922,660 A
• Filed: 12/12/1974
• Issued: 11/25/1975
• Est. Priority Date: 12/12/1974
• Status: Expired due to Term

• Current Assignee: ADT Security Services Incorporated (Apollo Global Management, Inc.)
• Original Assignee: Aaron A. Galvin
• Inventors: Galvin, Aaron A.
• Primary Examiner(s): Swann, III, Glen R.
• Application Number:
  US05/532,063
• Time in Patent Office: 348 Days
• Field of Search: 340/258A,258B 343/7.7
• US Class Current: 340/522
• CPC Class Codes: G01S 13/56 for presence detection presence detection using near field arrangements G01V3/00, e.g. G01V3/08, G01V3/12; burglar, theft or intruder alarms with electrical actuation G08B13/22 - G08B13/26

Abstract

Signals returned from a zone under surveillance are precessed in two channels. One channel gives an output on detection of a Doppler signal greater than a predetermined threshold. The other channel gives an output in response to changes in the phase and/or amplitude of the returned signal (with reference to the transmitted signal) indicative of a net change in the position of objects in the zone greater than a predetermined threshold. An alarm is given only if outputs are present from both channels simultaneously.

Claims

1. An intrusion alarm system for detecting a target in ghe presence of interfering phenomena, said system comprising:

means for transmitting signals into a zone under surveillance;

means for receiving signals returned from the surveillance zone;

positional characteristic sensing means including;

means operative in response to said received signals for providing a signal representing change in positional characteristics of objects in the zone;

means establishing a reference threshold in accordance with the static positional characteristics of the zone and stationary objects therein;

means for comparing said positional reference threshold with said positional signal to provide a change of position indication signal upon exceedance of said positional reference signal by said positional signal;

Doppler characteristic sensing means including;

means operative in response to said received signals for providing a signal representing the Doppler characteristics of objects in the zone;

means establishing a reference threshold in accordance with the Doppler characteristics of the zone and objects therein;

means for comparing said Doppler reference threshold with said Doppler signal to provide a motion indication signal upon exceedance of said Doppler reference threshold by said Doppler signal; and

means for producing an alarm only upon the simultaneous occurrence of said motion indication signal and said change of position indication signal.

2. An intrusion alarm system according to claim 1 wherein said signal receiving means comprises:

a receiving transducer operative to receive energy returned from the surveillance zone to provide an output signal;

a mixer operative to receive said receiving transducer output signal and to mix said transducer signal with a local oscillator signal for producing an output signal; and

a bandpass filter operative to pass both a spectrum of frequencies representing positional characteristics and a spectrum of frequencies containing the Doppler characteristics of objects within the surveillance zone.

3. An intrusion alarm system according to claim 2 wherein said receiving means further includes a limiting amplifier receiving said bandpass filter signal output for suppressing signal excursions above predetermined reference levels.

4. An intrusion alarm system acCording to claim 1 wherein:

said positional characteristic sensing means includes an integrator for providing a time averaged output to said positional reference threshold establishing means; and

wherein said positional reference threshold establishing means includes means establishing a bipolar reference threshold in accordance with the static amplitude and/or phase characteristics of objects under surveillance, such that said change of position indication signal is produced as said time averaged signal exceeds either bipolar reference threshold.

5. An intrusion alarm system according to claim 1 wherein:

said Doppler characteristic sensing means includes a detector for providing an output signal representative of the Doppler content of the received signal and an integrator for providing a time averaged output of said Doppler output signal; and

wherein said Doppler reference threshold establishing means includes means establishing a unipolar reference threshold in accordance with the Doppler characteristics of the zone under surveillance, such that said motion indication signal is produced as said time averaged signal exceeds said unipolar threshold.

6. An intrusion alarm system for monitoring a surveillance zone comprising:

a signal source;

a transmitting transducer deriving signals from said signal source;

a receiving transducer for receiving signals introduced into the surveillance zone by said transmitting transducer;

a signal mixer for receiving the signals from said receiving transducer and combining said signals with local oscillator signals from said signal source;

a bandpass filter for passing a predetermined spectrum of the signals produced by said mixer;

a limiting amplifier for limiting said bandpass filter output signals to prevent signal excursions above a predetermined reference level, said limiting amplifier producing output signals for a first channel and a second channel;

said first channel including a Doppler detector, a first integrator for integrating the output of said Doppler detector, and a unipolar threshold circuit, said first channel for producing a motion indication signal in response to signals from said first integrator exceeding a predetermined threshold level;

said second channel including a second integrator and a bipolar threshold circuit, said second channel for producing a change in position indication signal in response to said signals from said second integrator exceeding either one of said predetermined bipolar threshold levels and a gate circuit for producing an alarm signal only upon simultaneous occurrence of the motion indication signal and of the change in position indication signal.

7. A method for detecting an intruder in a zone under surveillance comprising the steps of:

transmitting signals into the surveillance zone;

receiving signals from the surveillance zone, said signals containing Doppler information indicative of motion within the zone and non-Doppler information indicative of the position of objects within the zone;

processing said signals to derive therefrom a position signal independent of motion in the zone to establish when a net change of position among the objects in the zone exceeds a predetermined threshold value;

processing said signals to derive therefrom a motion signal independent of said position information to establish when motion in the zone exceeds a predetermined value; and

indicating the presence of a target in the zone only upon the occurrence of both said motion and position signals.