MOTION DETECTOR AND INTRUDER ALARM SYSTEM

• US 3,736,584 A
• Filed: 08/13/1971
• Issued: 05/29/1973
• Est. Priority Date: 08/13/1971
• Status: Expired due to Term

• Current Assignee: Kenneth R. Hackett, Ralph W. Goble
• Original Assignee: Kenneth R. Hackett, Ralph W. Goble
• Inventors: Hackett, Kenneth R., Goble, Ralph W.
• Primary Examiner(s): Trafton, David L.
• Application Number:
  US05/171,420
• Time in Patent Office: 655 Days
• Field of Search: 340/258A,1R,3D,258A,258B 343/5PD,7.7
• US Class Current: 367/94
• CPC Class Codes: G01S 15/523 for presence detection burglar, theft or intruder alarms G08B13/00, e.g. G08B13/16
• CPC Class Codes: G08B 13/1627 using Doppler shift detection circuits

Abstract

Sound is generated at a reference frequency within a selected area to be protected and a plurality of sound sensing transducers are positioned to individually sense echo signals carrying Doppler beat frequencies produced by the movement of an object, hence an intruder, within the protected area. Amplifiers substantially isolated from electrical interference are connected to each transducer to amplify each sensed signal and the amplified signals are summed and processed to detect the Doppler beat frequency and generate an alarm actuating signal to indicate the presence of an intruder.

Claims

1. An intruder alarm system, comprising:

sound producing means for generating sound waves of a predetermined reference frequency, said sound producing means being positioned to generate said sound waves within a selected area to be protected whereby said sound waves are reflected from objects within said area to produce, when reflected from stationary objects, reference echo signals at said reference frequency and when reflected from moving objects frequency shifted echo signals, said frequency shifted echo signals being caused by the doppler frequency shift of sound waves from a moving object and combined with said reference echo signals to produce a beat frequency signal having a frequency equal to the difference between the frequencies of said reference echo signals and said frequency shifted echo signals;

a plurality of sound sensing transducers positioned to sense said reference and frequency shifted echo signals reflected from objects within said area, said transducers being operable to generate a plurality of electrical outputs corresponding to said sensed echo signals;

a plurality of amplifiers corresponding in number to said transducers, each of said amplifiers being connected with one of said transducers and being operable to amplify the electrical output of the one of said transducers, to which it is connected, whereby a plurality of amplified electrical signals are generated which correspond to said sensed echo signals;

summing means connected to said amplifiers for summing said amplified signals whereby to generate a summed output; and

signal processing means connected to said summing means for detecting the beat frequency signal portion of said summed output, said signal processing means being responsive to said detected beat frequency signal to generate an alarm actuating signal which indicates the presence of a moving object, hence an intruder, within said area.

2. The invention recited in claim 1, including an alarm means connected to said signal processing means, said alarm means being selectively actuated by the alarm actuating signal generated by said signal processing means.

3. The invention recited in claim 1, wherein said signal processing means includes:

integrator and amplifier means for integrating said detected beat frequency signal and generating an amplified integrator output signal as a function of time; and

means for generating said alarm actuating signal whenever said integrator output signal exceeds a predetermined level.

4. The invention recited in claim 3, wherein said integrator and amplifier means has an optimum range of frequency response whereby to integrate and amplify only the portion of said detected beat frequency signal characteristic of intruders while attenuating portions of said detected beat frequency signal characteristic of ambient noise and darting insects.

5. The invention recited in claim 3, wherein:

said integrator and amplifier means has a substantially flat frequency response from zero to about 50 hertz and is operable to attenuate electrical signals above 50 hertz; and

said means for generating said alarm actuating signal is a relay means; and

including;

an alarm connected to said relay means, said alarm being selectively actuated by said alarm actuating signal generated by said relay means.

6. The invention recited in claim 1, wherein said sound producing means includes:

a plurality of sound producing transducers positioned to generate said sound waves within said area, each of said sound producing transducers having a natural resonant frequency equal to said reference frequency;

driving oscillator means connected for driving one of said sound producing transducers; and

driving circuit means connected between said oscillator means and the other ones of said souNd producing transducers for being driven by said oscillator means to drive said other sound producing transducers, said driving circuit means being operable to substantially attenuate all frequencies but the reference frequency component whereby to conserve power.

7. An intruder alarm system, comprising:

a plurality of sound producing transducers designed to generate sound waves of a predetermined reference frequency, said sound producing transducers being positioned to generate said sound waves within a selected area to be protected so that said sound waves generated are reflected from objects within said area to produce when reflected from stationary objects reference echo signals at said reference frequency and when reflected from moving objects frequency shifted echo signals, said frequency shifted echo signals being caused by the doppler frequency shift of sound waves from a moving object and combining with said reference echo signals to produce a beat frequency signal having a frequency equal to the difference between the frequencies of said reference echo signals and said frequency shifted echo signals;

means for driving said sound producing transducers at said reference frequency, said driving means being operable to substantially attenuate all frequencies except said reference frequency so as to conserve power;

a plurality of sound sensing transducers positioned to sense said reference and frequency shifted echo signals reflected from objects within said area, said sound sensing transducers being operable to generate a plurality of electrical outputs corresponding to said sensed echo signals;

a plurality of current generating amplifiers corresponding in number to said sound sensing transducers, each of said amplifiers connected with one of said sound sensing transducers and being operable to generate an amplified electrical current signal corresponding to the electrical output of the one of said sound sensing transducers to which it is connected whereby a plurality of amplified electrical current signals are generated which correspond to said sensed echo signals;

a shielded cable having a pair of signal carrying conductors, the outputs of said amplifiers being connected to said signal carrying conductors so that said amplified current signals are summed on said cable to produce a summed output;

coupling means connected to said cable for receiving and transferring said summed output, said coupling means also being operable to reject common mode signals whereby to eliminate noise equally induced in both of said signal carrying conductors;

signal processing means connected to said coupling means for detecting the beat frequency signal portion of said summed output, said signal processing means being operable to integrate as a function of time said detected beat frequency signal and generate an alarm actuating signal to indicate the presence of a moving object, hence an intruder, within said area; and

an alarm connected to said signal processing means which is selectively actuatable by said alarm actuating signal.

8. In an intruder alarm system wherein sound of a reference frequency is generated in a selected area to be protected and a plurality of sound sensing transducers are positioned to individually sense echo signals carrying doppler beat frequencies produced by the movement of an object within said area so that the echo signals sensed by each sound sensing transducer may be summed to produce in response to the doppler beat frequency an alarm signal, the improvement of individual amplifier means substantially isolated from electrical interference connected to each sound sensing transducer to amplify each sensed echo signal prior to summing all of the sensed echo signals together whereby to improve the signal to noise ratio of the intruder alarm system.

9. An intruder alarm system comprising:

sound producing means for generating sound waves of a predetermined reference frequency, said sound producing means being positioned tO generate said sound waves within a selected area to be protected whereby said sound waves are reflected from objects within said area to produce, when reflected from stationary objects, reference echo signals at said reference frequency and when reflected from moving objects frequency shifted echo signals, said frequency shifted echo signals being caused by the doppler frequency shift of sound waves from a moving object and combined with said reference echo signals to produce a beat frequency signal having a frequency equal to the difference between the frequencies of said reference echo signals and said frequency shifted echo signals;

a plurality of sound sensing transducers positioned to sense said reference and frequency shifted echo signals reflected from objects within said area, said transducers being operable to generate a plurality of electrical outputs corresponding to said sensed echo signals;

a plurality of amplifiers corresponding in number to said transducers, each of said amplifiers being connected with one of said transducers and having first and second output terminals, each of said amplifiers operating as a current generator and being operable to amplify the electrical output of the one of said transducers to which it is connected whereby a plurality of amplified electrical current signals which correspond to said sensed echo signals are generated on said output terminals of said amplifiers;

summing means connected to said amplifiers for summing said amplified current signals, said summing means including a shielded cable and coupling means for coupling said cable electrically to a signal processing means, said cable having first and second signal carrying conductors connected, respectively, to said first and second output terminals of each of said amplifiers, said coupling means terminating said cable in a low impedance whereby said low impedance terminated cable defines a low impedance load for each of said amplifiers across which said amplified current signals are generated and summed together to generate a summed output; and

, signal processing means connected to said coupling means for detecting the beat frequency signal portion of said summed output of said summing means, said signal processing means being responsive to said detected beat frequency signal to generate an alarm actuating signal which indicates the presence of a moving object, hence an intruder, within said area.

10. The invention recited in claim 9, wherein said coupling means includes means for rejecting common mode signals whereby to eliminate noise equally induced in both signal carrying conductors.

11. The invention recited in claim 10, wherein said means for rejecting common mode signals includes a transformer and said coupling means is operable to amplify the electrical current signals corresponding to said sensed echo signals which are summed on said cable.

12. The invention recited in claim 11, wherein each of said transducers with its associated one of said amplifiers are enclosed in the same metal pickup housing to improve signal to noise ratio by substantially shielding said amplifiers from electrical noise and D.C. power is supplied to said amplifiers over said cable.

13. An intruder alarm system, comprising:

sound producing means for generating sound waves at a predetermined reference frequency, said sound producing means including a plurality of sound producing transducers, driving oscillator means, and driving circuit means, each of said sound producing transducers having a natural resonant frequency equal to said reference frequency, said driving oscillator means connected for driving one of said sound producing transducers, said driving circuit means connected between said oscillator means and the other ones of said sound producing transducers for being driven by said oscillator means to drive said other sound producing transducers, said driving circuit means being operable to substantially attenuate all frequencies but the reference freqUency component to conserve power, said driving circuit means including two sets of transistors which are alternately driven by said oscillator means to drive said other sound producing transducers so as to reduce transistor power dissipation, said plurality of sound producing transducers being positioned to generate said sound waves within a selected area to be protected whereby said sound waves are reflected from objects within said area to produce, when reflected from stationary objects, reference echo signals at said reference frequency and when reflected from moving objects frequency shifted echo signals, said frequency shifted echo signals being caused by the doppler frequency shift of sound waves from a moving object and combined with said reference echo signals to produce a beat frequency signal having a frequency equal to the difference between the frequencies of said reference echo signals and said frequency shifted echo signals;

a plurality of sound sensing transducers positioned to sense said reference and frequency shifted echo signals reflected from objects within said area, said transducers being operable to generate a plurality of electrical outputs corresponding to said sensed echo signals;

a plurality of amplifiers corresponding in number to said transducers, each of said amplifiers being connected with one of said transducers and being operable to amplify the electrical output of the one of said transducers, to which it is connected, whereby a plurality of amplified electrical signals are generated which correspond to said sensed echo signals;

summing means connected to said amplifiers for summing said amplified signals whereby to generate a summed output; and

signal processing means connected to said summing means for detecting the beat frequency signal portion of said summed output, said signal processing means being responsive to said detected beat frequency signal to generate an alarm actuating signal which indicates the presence of a moving object, hence an intruder, within said area.

14. An intruder alarm system, comprising:

sound producing means for generating sound waves of a predetermined reference frequency, said sound producing means being positioned to generate said sound waves within a selected area to be protected whereby said sound waves are reflected from objects within said area to produce, when reflected from stationary objects, reference echo signals at said reference frequency and when reflected from moving objects frequency shifted echo signals, said frequency shifted echo signals being caused by the doppler frequency shift of sound waves from a moving object and combined with said reference echo signals to produce a beat frequency signal having a frequency equal to the difference between the frequencies of said reference echo signals and said frequency shifted echo signals;

a plurality of sound pickup means positioned to sense said reference and frequency shifted echo signals reflected from objects within said area, each of said sound pickup means being positioned remotely from each other and including a sound sensing transducer and an amplifier connected to said transducer, each of said transducers being operable to generate an electrical output corresponding to said sensed echo signals, each of said amplifiers being operable to amplify the electrical output of the one of said transducers to which it is connected whereby a plurality of amplified electrical signals are generated which correspond to said sensed echo signals;

summing means connected to said amplifiers for summing said amplified signals whereby to generate a summed output; and

signal processing means connected to said summing means for detecting the beat frequency signal portion of said summed output, said signal processing means being responsive to said detected beat frequency signal to generate an alarm actuating signal which indicates the presence of a moving object, hence an intruder, within said area.

15. The invention recited In claim 14, including means for shielding each of said sound pickup means from electrical interference and eliminating VHF frequencies from said amplified electrical signals generated by said amplifiers.