Enclosure for leak detector

1. A leak detection sensor for attachment to a fire hydrant, the leak detection structure comprising:

a housing that is fixed to the fire hydrant, the fire hydrant defining an internal surface that defines a hydrant cavity, the housing being in fluid communication with the hydrant cavity, the housing having internal surfaces defining a housing cavity internal to the housing; and

a leak detection subassembly, the leak detection subassembly including:

at least one piezoelectric vibration sensor mounted with a fastener to an internal surface of the housing within the housing cavity, the at least one piezoelectric vibration sensor including a base and a piezoelectric layer deposited onto the base, the piezoelectric layer composed of piezoelectric crystals, the at least one piezoelectric vibration sensor arranged to receive a vibration from the housing via the fastener;

at least one circuit arranged within the housing cavity and in electrical communication with the at least one piezoelectric sensor;

an antenna in electrical communication with the at least one circuit;

and wherein the housing is rigid.

2. The leak detection structure of claim 1 , wherein the housing is a housing assembly including a primary housing and a mating housing connected to the primary housing.

3. The leak detection structure of claim 2 , wherein the housing cavity is open on one side of the primary housing, and wherein the mating housing is connected to the primary housing on the open side of the housing cavity such that the mating housing substantially seals the interior of the primary housing from the exterior of the primary housing.

4. The leak detection structure of claim 1 , wherein each at least one circuit is encased in potting and wherein each piezoelectric vibration sensor is not encased in potting.

5. The leak detection structure of claim 1 , further comprising at least one battery.

6. The leak detection structure of claim 5 , wherein the housing is a housing assembly including a primary housing and a mating housing connected to the primary housing, wherein the at least one battery is arranged in a mating cavity of the mating housing, and wherein the at least one battery is encased in potting.

7. The leak detection structure of claim 6 , wherein the at least one battery is removably connected to the at least one circuit.

8. The leak detection structure of claim 1 , wherein the antenna protrudes from the housing.

9. The leak detection structure of claim 8 , wherein an antenna cable connects the antenna to the at least one circuit.

10. The leak detection structure of claim 8 , wherein the housing defines an internal surface and an external surface, the internal surface and external surface defining a bore extending from the internal surface to the external surface, an intersection between the bore and the external surface defining a housing outlet; and the antenna protrudes out from the housing through the housing outlet.

11. The leak detection structure of claim 1 , wherein the housing includes threading for attachment to the threading of the fire hydrant.

12. The leak detection structure of claim 1 , wherein the at least one piezoelectric vibration sensor is coated with a sensor damping material that dampens frequencies outside of a desired frequency range within which leak detection is expected.

13. The leak detection structure of claim 1 , wherein the at least one piezoelectric vibration sensor includes:

a conduction layer deposited above the piezoelectric layer, the conduction layer composed of conductive material.

14. The leak detection structure of claim 1 , wherein the base and the piezoelectric layer of the at least one piezoelectric vibration sensor are a first base and a first piezoelectric layer, wherein the at least one piezoelectric vibration sensor includes:

a second base joined to the first base through an adhesive layer;

a second piezoelectric layer deposited onto the second base opposite the adhesive layer, the second piezoelectric layer composed of piezoelectric crystals; and

a conduction layer deposited above each piezoelectric layer, the conduction layer composed of conductive material.

15. A leak detection structure permanently attached to a fire hydrant, the leak detection structure comprising:

a nozzle cap fixed to the fire hydrant, the nozzle cap having internal surfaces defining a cavity internal to the nozzle cap, the nozzle cap defining an internal surface and an external surface, the internal surface and the external surface defining a nozzle cap bore extending from the internal surface to the external surface, an intersection between the nozzle cap bore and the external surface defining a nozzle cap outlet;

a housing secured to the nozzle cap within the cavity of the nozzle cap, the housing having internal surfaces defining a cavity internal to the housing,

at least one piezoelectric vibration sensor mounted with a fastener to an internal surface of the housing, the at least one piezoelectric vibration sensor including a base and a piezoelectric layer deposited onto the base, the piezoelectric layer composed of piezoelectric crystals, the at least one piezoelectric vibration sensor arranged to receive a vibration from the nozzle cap via the fastener;

at least one circuit arranged in the cavity and in electrical communication with the at least one piezoelectric vibration sensor; and

an antenna in electrical communication with the at least one circuit, the antenna protruding out from the fire hydrant through the nozzle cap outlet.

16. The leak detection structure of claim 15 , wherein at least one battery is removably connected to the at least one circuit.

17. A leak detection structure for attachment to a fire hydrant, the leak detection structure comprising:

a housing assembly including a rigid primary housing and a rigid mating housing connected to the primary housing, the primary housing fixed to the fire hydrant, the primary housing defining a cavity that is open on one side of the primary housing, wherein the mating housing substantially seals the cavity;

a leak detection subassembly, the leak detection subassembly including

at least one piezoelectric vibration sensor mounted with a fastener to an internal surface of the housing within the cavity, the at least one piezoelectric vibration sensor including a base and a piezoelectric layer deposited onto the base, the piezoelectric layer composed of piezoelectric crystals, the at least one piezoelectric vibration sensor arranged to receive a vibration from the housing via the fastener,

at least one circuit arranged within the cavity and in electrical communication with the at least one piezoelectric vibration sensor, and

an antenna in electrical communication with the at least one circuit; and

an antenna enclosure fixed to the fire hydrant, the antenna arranged within the antenna enclosure.

18. The leak detection structure of claim 17 , wherein at least one battery is removably connected to the at least one circuit.

19. The leak detection structure of claim 17 , wherein:

the antenna enclosure defines an internal surface and an external surface, the internal surface and external surface defining a bore extending from the internal surface to the external surface, an intersection between the bore and the external surface defining an antenna enclosure outlet; and

the antenna protrudes out from the antenna enclosure through the antenna enclosure outlet.