# US 4,400,695 A · Electronic intruder detection system

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- Number: US 4,400,695 A
- Document ID: US4400695A
- Status: Granted
- Kind: A
- Application number: 06/297,807
- Filed: 1981-08-31
- Granted: 1983-08-23
- Earliest claimed: 1977-10-07
- Assignees: The United States of America as represented by the Secretary of the Army
- Inventors: Otto E. Rittenbach; Reinhard G. Olesch
- Web page: https://patentgrep.com/patent/US4400695A

## CPC

- G08B 13/126: {for a housing, e.g. a box, a safe, or a room}
- 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)}
- G01S 15/04: Systems determining presence of a target
- G08B 13/10: by pressure on floors, floor coverings, stair treads, counters, or tills
- Y10S 73/08: Fluid circuits
- G08B: SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

An electronic detection system for detecting intruders employs a transmisn line as a sensing element. In one embodiment the transmission line is a modified surface-wave transmission line, for example, a Goubau line, which is positioned about the perimeter of the area to be protected. An intruder in the field of the line causes an RF reflection back toward the source, which reflection may be detected by Doppler range-gating techniques. In other embodiments of the invention the transmission line is an insulated, twisted wire pair or a deformable transmission line. In some instances, the transmission line may be replaced with an active or passive pressure line.

## Claims

### Claim 1

An intrusion detection system comprising:
first and second fluid-filled cables placed substantially plane parallel at a preselected surveillance location, transducing means at both ends of each cable for converting fluid pressures passively arising within the cables into representative electrical signals;
differential amplifier means connected to said transducing means for generating a signal representative of the difference of fluid pressure in the cables at respective ends of said cables; and
indication means connected to the said differential amplifier means for indicating occurence of an intrusion whenever a threshold level output signal is generated by said differential amplifier means.

### Claim 2 (depends on 1)

An intrusion detection system as in claim 1 further comprising means for finding the distance along the cables at which an intrusion is indicated comprising a correlator means, comprising:
means for multiplying and an adjustable means for delaying by a delay amount, the output of said means for multiplying; and
calibrated scale means on said adjustable means for delaying for indicating location along said cables at which an intrusion is indicated based on the adjusted delay amount.

### Claim 3 (depends on 2)

An intrusion detection system as in claim 2 wherein said means for finding further comprises;
means for integrating over time the output of said means for multiplying; and said indication means displaying the output of said means for integrating.

### Claim 4 (depends on 2)

An intrusion detection system as in claim 2 wherein said means for delaying comprises more than one delay unit.

### Claim 5 (depends on 1)

An intrusion detection system as in claim 1 wheren said transducing means comprises a pair of balanced transducers which generate a differential a.c. signal when said cables are disturbed by an intruder and said differential amplifier means comprises a pair of differential amplifiers connected respectively to each of said balanced transducers.