DIFFERENTIAL PYROELECTRIC SENSOR

• US 3,839,640 A
• Filed: 06/20/1973
• Issued: 10/01/1974
• Est. Priority Date: 06/20/1973
• Status: Expired due to Term

• Current Assignee: John A. Rossin
• Original Assignee: John A. Rossin
• Inventors: Rossin, John A.
• Primary Examiner(s): Lawrence, James W.
• Assistant Examiner(s): Willis, Davis L.
• Application Number:
  US05/371,945
• Time in Patent Office: 468 Days
• Field of Search: 250/338,340,342,349,353 136/213
• US Class Current: 250/353
• CPC Class Codes: G01J 5/34 using capacitors, e.g. pyroelectric capacitors
• CPC Class Codes: G08B 13/191 using pyroelectric sensor means
• CPC Class Codes: H10N 15/10 Thermoelectric devices using thermal change of the dielectric constant, e.g. working above and below the Curie point
• CPC Class Codes: Y10S 250/01 Passive intrusion detectors

Abstract

A low cost mass produced intrusion detection device which responds to a temperature difference between ambient temperature and the body temperature of an intruder who is moving past the sensor. The combination of body temperature and movement will unbalance the differential sensor to thereby trigger an alarm. This sensor utilizes a pyroelectric plastic film as the active element. It is not affected by ambient heat. Only a moving person or object can be detected to sound an alarm.

Claims

1. A pyroelectric differential passive infrared sensor comprising:

a. a pyroelectric plastic film having front and rear sides, b. two front conductive stripes applied to the front side of said film, c. a rear conductive stripe applied to the rear side of said film overlapping in part said front conductive stripes defining thereby two heat sensitive capacitors in series with said two front conductive stripes serving as output leads, d. said two heat sensitive capacitors being connected to said front conductive stripes in parallel electrically but in series physically and with said electrode on the rear of said film floating electrically.

2. The detector of claim 1 comprising in addition a high value resistor joining said first conductive stripes at their output ends.

3. The detector of claim 1 wherein said pyroelectric plastic film is polyvinylidene fluoride.

4. The detector of claim 1 comprising in addition:

a. a field effect transistor having gate, source, and drain leads;

b. circuit means connecting one of said first conductive stripes to the gate lead of said field effect transistor; and

c. circuit means connecting the other of said first conductive stripes to the system ground for said field effect transistor.

5. The detector of claim 4 comprising in addition a diode in the drain lead of said field effect transistor whereby the diode causes the voltage on the source lead to swing only towards the positive supply in event of a line transient.

6. The detector of claim 1 comprising in addition:

a. radiation gathering means disposed effective to direct background radiation to said capacitors substantially equally and to direct radiation from a moving intruder to either but not both of said capacitors.

7. The apparatus of claim 6 wherein said radiation gathering means is a concave mirror.

8. The apparatus of claim 6 comprising in addition a sealed housing containing said detector and said radiation gathering means.

9. The apparatus of claim 6 wherein said sealed housing is provided with a window of polyethylene film through which radiation impinges upon said radiation gathering means.

10. The detector of claim 1 comprising in addition:

a. a field effect transistor, b. a ground wire having one end connected to one of said first conductive stripes and the other end wrapped around said field effect transistor, c. an insulating spacer block disposed between said film and said field effect transistor, and d. circuit means connecting the other of said first conductive stripes to the gate of said field effect transistor.

11. A method for the fabrication of infrared detectors comprising:

a. painting conductive stripes on two sides of pyroelectric film to define at least two capacitors, b. applying a polarizing voltage to said capacitors in parallel, and c. connecting output leads to like polarity electrodes of said capacitors in series.