METHOD AND MEANS FOR SENSING STRAIN WITH A PIEZOELECTRIC STRAIN SENSING ELEMENT

• US 3,750,127 A
• Filed: 10/28/1971
• Issued: 07/31/1973
• Est. Priority Date: 10/28/1971
• Status: Expired due to Term

• Current Assignee: Joseph G. Hirsch, Weston D. Ayers
• Original Assignee: Joseph G. Hirsch, Weston D. Ayers
• Inventors: Ayers, Weston D., Hirsch, Joseph G.
• Primary Examiner(s): Trafton, David L.
• Application Number:
  US05/193,419
• Time in Patent Office: 642 Days
• Field of Search: 340/421,227C,258R,261 310/8.5 174/11R,11PM,113R 73/88.5R
• US Class Current: 340/665
• CPC Class Codes: G01K 1/024 for remote indication
• CPC Class Codes: G01L 1/16 using properties of piezoelectric devices
• CPC Class Codes: G08B 13/02 Mechanical actuation
• CPC Class Codes: H10N 30/60 having a coaxial cable structure
• CPC Class Codes: Y10S 310/80 Piezoelectric polymers, e.g. PVDF
• CPC Class Codes: Y10S 73/04 Piezoelectric

Abstract

A piezoelectric strain sensing element is used in strain gage, in intrusion detector, or in thermal gradient detector systems to provide an electrical charge or signal proportional in amplitude and polarity to the strain transmitted to the sensing element.

Claims

1. Strain sensing apparatus comprising:

a first conductor having a prescribed length;

a second conductor having a prescribed length compatible with said first conductor substantially surrounding said first conductor in spaced relationship therewith;

a layer of strain sensing piezoelectric material disposed intermediate and firmly engaging said conductors and extending therebetween so as to be capable of generating an electrical charge when subjected to strain;

said electrical charge proportional in amplitude and polarity to the amount of strain transmitted to said strain sensing piezoelectric material;

said strain sensing material comprising a material selected from the group consisting of polyethylene, polytetrafluoroethylene, polyvinyl chloride, polyvinyl fluoride, polyvinylidine fluoride, polyethylene terephthalate and polypropylene; and

electronic means responsive to said electrical charge connected to said conductors for indicating the occurrence of strain.

2. The strain sensing apparatus defined in claim 1, wherein said first and second conductors and said strain sensing material are disposed in coaxial relationship.

3. The strain sensing apparatus defined in claim 1, additionally including an insulating jacket having a prescribed length substantially surrounding said second conductor.

4. The strain sensing apparatus defined in claim 3, additionally including a protective layer disposed intermediate and extending between said insulating jacket and said second conductor.

5. The strain sensing apparatus defined in claim 3, additionally including a third conductor having a prescribed length compatible with said second conductor substantially surrounding said second conductor in spaced relationship therewith, an additional layer of strain sensing piezoelectric material disposed intermediate said second and third conductors and extending therebetween, said third conductor and said additional layer of strain sensing piezoelectric material disposed intermediate said second conductor and said insulating jacket.

6. The strain sensing apparatus defined in claim 1, wherein said electronic means comprises amplifier means connected to said first conductor for amplifying said electric charge and strain indicating means connected to said amplifier means for indicating the occurrence of strain.

7. A strain sensing apparatus comprising:

a first conductor having a prescribed length;

a second conductor having a prescribed length compatible with said first conductor substantially surrounding said first conductor in spaced relationship therewith;

strain sensing piezoelectric material disposed intermediate and firmly engaging said conductors and extending therebetween so as to be capable of generating an electrical charge when subjected to strain;

said electrical charge proportional in amplitude and polarity to the amount of strain transmitted to said strain sensing piezoelectric material;

an insulating jacket having a prescribed length substantially surrounding said second conductor; and

electronic means responsive to said electrical charge connected to said conductors for indicating the occurrence of strain.

8. The strain sensing apparatus defined in claim 7, additionally including a protective layer disposed intermediate and extending between said insulating jacket and said second conductor.

9. In combination with an alarm system, a strain sensing piezoelectric device comprising:

a first conductor having a prescribed length;

a second conductor having a prescribed length compatible with said first conductor substantially surrounding said first conductor in spaced relationship therewith; and

strain sensing piezoelectric material disposed intermediate and firmly engaging said conductors and extending therebetween so as to be capable of generating an electrical charge when subjected to strain;

said electrical charge proportional in amplitude and polarity to the amount of strain transmitted to said strain sensing piezoelectric material.

10. The alarm system defined in claim 9, wherein said device additionally includes an insulating jacket having a prescribed length substantially surrounding said second conductor.

11. The alarm system defined in claim 10, wherein said device additionally includes a protective layer disposed intermediate and extending between said insulating jacket and said second conductor.

12. A piezoelectric device comprising:

a piezoelectric sensing element responsive to strain;

said piezoelectric sensing element comprising a first conductor having a prescribed length, a second conductor having a prescribed length compatible with said first ocnductor substantially surrounding said first conductor in spaced relationship therewith, a layer of strain sensing piezoelectric material disposed intermediate and firmly engaging said conductors and extending therebetween to a prescribed length compatible with said conductors so as to be capable of generating an electrical charge when subjected to strain;

said electrical charge porportional in amplitude and polarity to the amount of strain transmitted to said strain sensing piezoelectric material;

said strain sensing material comprising material selected from the group consisting of polyethylene, polytetrafluoroethylene, polyvinyl chloride, polyvinyl fluoride, polyvinylidine fluoride, polyethylene terephthalate and polypropylene; and

at least one conductor section electrically connected to said piezoelectric sensing element, said conductor section being non-responsive to strain.