Infrared intrusion sensor

• US 5,465,080 A
• Filed: 09/07/1994
• Issued: 11/07/1995
• Est. Priority Date: 03/09/1992
• Status: Expired due to Fees

• Current Assignee: Commonwealth of Australia
• Original Assignee: Commonwealth of Australia
• Inventors: Watson, Rodney J., Liddiard, Kevin C., Rice, Brian W.
• Primary Examiner(s): SWANN III, GLEN R
• Application Number:
  US08/295,857
• Time in Patent Office: 426 Days
• Field of Search: 340/567, 250/340, 250/395
• US Class Current: 340/567
• CPC Class Codes: G08B 13/19 using infrared-radiation detection systems G08B13/194 takes precedence
• CPC Class Codes: G08B 13/193 using focusing means
• CPC Class Codes: Y10S 250/01 Passive intrusion detectors

Abstract

An infrared intrusion sensor includes an array of infrared detectors, infrared collection optics, a focal plane scanning device having a dither adapted to repetitively scan the infrared radiation across the detector array, signal process devices, and local or remote displays. The sensor incorporates heterodyne detection techniques with a local oscillator signal derived from the scanning frequency of the focal plane scanning device. The sensor has a low false alarm rate and enhanced detection range. A method of processing the signals includes analog to digital conversion, integration of the digital signals to produce a background signal, phase sensitive detection of the digital signal producing a target signal, and comparison of the background and target signals producing a difference signal. The difference signal is integrated to produce a background noise signal and processed to become a threshold signal which is finally compared to the difference signal to produce an alarm signal.

Claims

1. An infrared intrusion sensor comprising:

a detector, including an infrared detector array, adapted to provide a signal indicative of infrared radiation impinging upon the detector;

infrared collection optics adapted to collect and direct infrared radiation to the detector array;

dither means adapted to repetitively scan the infrared radiation across the detector array;

signal processing means adapted to analyse the detector signal and produce output alarm signals; and

output display means adapted to display the output alarm signals;

said detector being a heterodyne detector with a local oscillator signal being the scanning frequency of the dither means.

2. The infrared intrusion sensor of claim 1 wherein the infrared detector array comprises a focal plane array of metal film bolometer detectors.

3. The infrared intrusion sensor of claim 1 wherein the optics comprise an infrared transmitting entrance window and Cassegrain-style objective telescope formed by a primary mirror and a secondary mirror wherein the secondary mirror is mounted on the dither means.

4. The infrared intrusion sensor of claim 1 wherein the optics comprise an infrared transmitting entrance window having a hard carbon coating on an outer surface adapted to provide protection against scratching or other damage and an anti-reflection coating on an inner surface and a Cassegrain-style objective telescope.

5. The infrared intrusion sensor of claim 1 wherein the optics comprise an infrared transmitting entrance window, Cassegrain-style objective telescope and a correction lens between the Gassegrain-style telescope and the infrared detector array.

6. The infrared intrusion sensor of claim 1 wherein the dither means is a focal plane scanning device having a mirror pivoted to nod driven by at least one of a pair of piezoceramic drive elements arranged generally parallel to the plane of the mirror.

7. The infrared intrusion sensor of claim 1 wherein the signal processing means is comprised of:

an analogue-to-digital converter adapted to convert analogue signals received from the detector to digital signals;

memory means adapted to provide storage of information; and

a digital signal processing module adapted to process the digital signals to produce output alarm signals.

8. The infrared intrusion sensor of claim 1 wherein the signal processing means is comprised of:

an analogue-to-digital converter adapted to convert analogue signals received from the detector to digital signals;

memory means adapted to provide storage of information; and

a digital signal processing module adapted to process digital signals from the analogue-to-digital converter and produce output alarm signals wherein the output alarm signals are one or more of;

Target detection

Target direction of movement;

Near/far field indication;

Sensor identification;

Detection probability.

9. An infrared intrusion sensor comprising:

a detector, including an infrared detector array, adapted to provide a signal indicative of infrared radiation impinging upon the detector;

infrared collection optics adapted to collect and direct infrared radiation to the detector array;

dither means adapted to repetitively scan the infrared radiation across the detector array;

signal processing means adapted to analyse the detector signal and produce output alarm signals; and

output display means adapted to display the output alarm signals;

wherein the signal processing means is comprised of;

an analogue-to-digital converter adapted to convert analogue signals received from the detector to digital signals;

memory means adapted to provide storage of information; and

a digital signal processing module adapted to process the digital signals to produce output alarm signals;

said digital signal processing module consisting of a processor means and a program memory means and being adapted to perform digital signal processing comprising the steps of;

integration over time to produce a background signal;

phase sensitive detection to produce a target signal;

comparison between the target signal and the background signal to produce a difference signal;

a second integration over time to produce a background noise signal;

processing of the background noise signal to produce a threshold signal; and

comparison of the difference signal with the threshold signal to produce an alarm signal.

10. The infrared intrusion sensor of claim 9 wherein the target signal is derived from the detector signal by phase sensitive detection at the scanning frequency of the dither means.

11. The infrared intrusion sensor of claim 9 wherein processing of the background noise signal to produce a threshold signal consists of multiplying the background noise signal by an alarm threshold factor.

12. A method of signal processing of signals within an infrared intrusion sensor comprising the steps of:

generating analogue signals indicative of infrared radiation impinging on an infrared detector array;

converting the analogue signals to digital signals;

integrating the digital signals over time to produce a background signal;

producing a target signal by phase sensitive detection of the digital signal;

comparing the target signal and the background signal to produce a difference signal;

integrating the difference signal over time to produce a background noise signal;

processing of the background noise signal to produce a threshold signal; and

comparing of the difference signal with the threshold signal to produce an alarm signal.

13. A wide area surveillance apparatus comprising:

a plurality of infrared intrusion sensors each sensor comprising;

a detector, including an infrared detector array, adapted to provide a signal indicative of infrared radiation impinging upon the detector;

infrared collection optics adapted to collect and direct infrared radiation to the detector array;

dither means adapted to repetitively scan the infrared radiation across the detector array;

signal processing means adapted to analyse the detector signal and produce output alarm signals;

said detector being a heterodyne detector with a local oscillator signal being the scanning frequency of the dither means;

network control means adapted to receive output alarm signals from each sensor; and

network display means adapted to display the output alarm signals.

14. The apparatus of claim 13 wilerein the network control means includes communication means in the form of a radio frequency link between each sensor and the network control means.

15. The apparatus of claim 13 wherein the network control means comprises a computer and a network controller adapted to interface between the plurality of infrared intrusion sensors and the computer.