Fiber optic acoustic transducer intrusion detection system

• US 4,538,140 A
• Filed: 03/31/1982
• Issued: 08/27/1985
• Est. Priority Date: 03/31/1982
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Corporation
• Original Assignee: Gould, Inc. (Transdigm Group Incorporated)
• Inventors: Prestel, David J.
• Primary Examiner(s): Myracle, Jerry W.
• Application Number:
  US06/363,854
• Time in Patent Office: 1,245 Days
• Field of Search: 340/555-556, 340/557, 340/566, 73/655, 73/705, 250/227, 350/96.29
• US Class Current: 340/556
• CPC Class Codes: G08B 13/126 for a housing, e.g. a box, a safe, or a room
• CPC Class Codes: H04B 10/505 using external modulation
• CPC Class Codes: H04B 10/564 Power control

Abstract

An intrusion detection system for sensing mechanical and acoustical vibrations, comprises a light source, a fiber optic acoustic transducer, a light intensity to current converter circuit, a display and an audio monitor. The light source is positioned at a point remote from an area to be protected and is coupled to the fiber optic acoustic transducer by a low loss fiber optic transmission line. Similarly, the light intensity to current converter circuit, the display and the audio monitor are located at a point remote from the area to be protected, and are coupled to the fiber optic acoustic transducer by a low loss fiber optic transmission line. When mechanical or acoustical vibrations impinge on the fiber optic acoustic transducer it modulates the intensity of the light beam generated by the light source, thereby causing the system to generate both a visual and audio indication that an intrusion is taking place. Since the system emits no radiation, (e.g. thermal, electrical, acoustical, electro-magnetic etc.) and can be embedded in walls, floors, etc. it is not readily detectable by an intruder and hence can not be disabled or avoided by the intruder.

Claims

1. An intrusion detection system for sensing mechanical and acoustical vibrations in a room having walls, comprising:

a light source for generating a light beam at a point remote from the room;

first means, operatively connected to said light source, for transmitting the light beam to the room;

second means, coupled to said first means and positioned inside the walls of the room, for modulating the intensity of the light beam in response to mechanical or acoustical vibrations;

third means, coupled to said second means, for conducting the modulated light beam to a position remote from the room;

fourth means, operatively connected to said third means, for converting the modulated light beam to a detection signal;

fifth means, operatively connected to said fourth means, for generating an intrusion display signal in dependence upon the detection signal; and

sixth means, operatively connected to said fourth means, for generating an audio signal in dependence upon the detection signal, the audio signal being a substantial reproduction of the mechanical or acoustical vibrations at all audio frequencies of the mechanical or acoustical vibrations which cause said second means to modulate the intensity of the light beam.

2. An intrusion detection system as set forth in claim 1, wherein said sixth means comprises:

an amplifier, operatively connected to said fourth means, for receiving and amplifying the detection signal; and

a speaker, operatively connected to said amplifier, for outputting the audio signal.

3. An intrusion detection system as set forth in claim 2, wherein said second means comprises a fiber optic acoustic transducer.

4. An intrusion detection system as set forth in claim 3, wherein said fourth means comprises a light intensity to current converter circuit.

5. An intrusion detection system as set forth in claim 4, wherein said fifth means comprises:

a filter and threshold detector circuit, operatively connected to said light intensity to current converter circuit, for receiving the detection signal and for generating an intrusion signal; and

a display, operatively connected to said filter and threshold detector circuit, for generating the intrusion display signal in dependence upon the intrusion signal.

6. An intrusion detection system for sensing mechanical and acoustical vibrations in a room having walls, comprising:

a light source for generating first and second light beams at a point remote from the room;

first means, operatively connected to said light source and positioned in the walls, for modulating the intensity of the first light beam in response to mechanical or acoustical vibrations;

second means, operatively connected to said light source and positioned outside the room, for modulating the intensity of the second light beam in response to mechanical or acoustical vibrations;

third means, coupled to said first and second means, for converting the first and second modulated light beams into first and second detection signals, respectively; and

fourth means, operatively connected to said third means, for comparing the timing of the first and second detection signals to determine whether the mechanical or acoustical vibrations corresponding to the first detection signal, originated inside or outside the room, and for generating an intrusion signal only in response to mechanical or acoustical vibrations generated within the room.

7. An intrusion detection system as set forth in claim 6, further comprising:

fifth means, operatively connected to said third means, for generating an audio signal in dependence upon the first detection signal, the audio signal being a substantial reproduction of the mechanical or acoustical vibrations at all audio frequencies of the mechanical or acoustical vibrations which cause said first means to modulate the intensity of the first light beam.

8. An intrusion detection system as set forth in claim 7, wherein said first and second means each comprise a fiber optic acoustic transducer.

9. An intrusion detection system as set forth in claim 8, wherein said third, fourth and fifth means are located at a point remote from the room, said system further comprising:

a first fiber optic transmission line coupled between said light source and said first means;

a second fiber optic transmission line coupled between said light source and said second means;

a third fiber optic transmission line coupled between said first means and said third means; and

a fourth fiber optic transmission line coupled between said second means and said third means.

10. An intrusion detection system for sensing mechanical and acoustical vibrations generated within an area to be protected, comprising:

a light source for generating first and second light beams at a point remote from the area to be protected;

first means, operatively connected to said light source and positioned within the area to be protected, for modulating the intensity of the first light beam in response to mechanical or acoustical vibrations;

second means, operatively connected to said light source and positioned adjacent the perimeter of the area to be protected, for modulating the intensity of the second light beam in response to mechanical or acoustical vibrations;

third means, coupled to said first and second means, for converting the first and second modulated light beams into first and second detection signals, respectively; and

fourth means, operatively connected to said third means, for comparing the timing of the first and second detection signals to determine whether the mechanical or acoustical vibrations corresponding to the first detection signal, originated inside or outside the area to be protected, and for generating an intrusion display signal only in response to mechanical or acoustical vibrations generated within the area to be protected.