A compression assembly ( 5 ) forms an airborne sound sensor for detecting sound pressure level. The airborne sound sensor includes a piezo electric transducer ( 11 ) compressed against a top element ( 9 ) and a lower element ( 12 ) so as to compress the transducer ( 11 ) across a first face and a distal second sensing face.
1. A compression assembly ( 5 ) for detecting an airborne sound is mounted in a Faraday cage and comprises:
a piezo electric transducer ( 11 ) arranged to convert the airborne sound to an electrical signal, the transducer having a first sensing face ( 21 ) and a distal second sensing face ( 20 );
wherein a nonconductive first element ( 12 ) and a second element ( 26 ) compress the transducer ( 11 ) across the first sensing face ( 21 ) and the distal second sensing face ( 20 ) with a desired pressure maintained by a reaction structure ( 8 , 9 , 10 ) which clamps the second element ( 26 ) to pressing a first portion ( 161 ) of an electrode ( 16 ) against and into electrical contact with the second sensing face ( 20 ) and which clamps the first element ( 12 ) to press a first conductive pathway ( 23 ) into contact with the first sensing face ( 21 ).
2. The assembly according to claim 1 comprising a resilient means ( 15 ) arranged to press against the first element ( 12 ).
3. The assembly according to claim 2 wherein the reaction structure ( 8 , 9 , 10 ) is immovable with respect to the first element ( 12 ) which braces the resilient means ( 15 ).
4. The assembly ( 5 ) according to claim 1 where the reaction structure ( 8 , 9 , 10 ) is fixed to the second element ( 26 ).
5. The assembly ( 5 ) according to claim 1 wherein the reaction structure comprises an end stop ( 13 ) arranged to limit a distance that the transducer ( 11 ) can travel in a direction from the second sensing face ( 20 ) toward the first sensing face ( 21 ) by blocking the first element ( 12 ).
6. The assembly ( 5 ) according to claim 1 wherein the first element ( 12 ) comprises a printed circuit board comprising the first conductive pathway ( 23 ).
7. The assembly ( 5 ) according to claim 1 wherein the second element ( 26 ) has less mass than the transducer ( 11 ).
8. The assembly ( 5 ) according to claim 1 wherein the second element ( 26 ) has a central region comprising a sheet-like portion pressing against the first portion ( 161 ) of the electrode ( 16 ).
9. The assembly ( 5 ) according to claim 8 wherein the reaction structure ( 9 ) comprises a peripheral region, surrounding a hole in the central region having a larger diameter or width than the second sensing face ( 20 ) of the transducer ( 11 ), to which the sheet-like portion ( 26 ) is attached so as to cover the hole ( 27 ) in the central region.
10. The assembly ( 5 ) according to claim 9 wherein the sheet-like portion ( 26 ) is stretched across the hole ( 27 ) in the central region.
11. The assembly ( 5 ) according to claim 9 wherein the peripheral region is in the form of a flat outer ring.
12. The assembly ( 5 ) according to claim 9 in which a cover seal ( 18 ) occupies the hole ( 27 ) in the central region so to cover the sheet-like portion ( 26 ).
13. The assembly ( 5 ) according to claim 12 wherein the cover seal ( 18 ) is a waterproof compound.
14. The assembly ( 5 ) according to claim 1 wherein the first portion of the electrode ( 161 ) is a metal foil sandwiched between the second element ( 26 ) and the second sensing face ( 20 ).
15. An ultrasonic airborne sound sensor for detecting gas leaks, comprising:
the assembly ( 5 ) according to claim 1 ; and
a front cover ( 2 ) supporting a portion of the second element ( 9 ) having a central opening exposing the second element ( 9 ) to the airborne sound;
characterized in that the front cover ( 2 ) is electrically insulated from the Faraday cage by an insulated spacer ( 6 ) made from a non-electrically conductive material.
16. The assembly according to claim 2 wherein the resilient means ( 15 ) is arranged to react against the reaction structure ( 8 , 9 , 10 ).
17. The assembly according to claim 1 wherein the first element ( 12 ) and the second element ( 26 ) are in the form of a panel or membrane.
18. The assembly ( 5 ) according to claim 1 , wherein the first element ( 12 ) comprises a second conductive pathway ( 24 ) in contact with a second portion ( 162 ) of the electrode ( 16 ).
19. The assembly according to claim 1 wherein the reaction structure ( 8 , 9 , 10 ) forms the Faraday cage ( 8 , 9 , 10 ).