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1. WO2010007435 - DETECTOR AND METHODS OF DETECTING

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[ EN ]

CLAIMS

1. An ultrasonic detector suitable for mounting in a position for surveying an area for a source of airborne ultrasound, which detector comprises a sensor for detecting an ultrasonic sound signal, characterised by a transducer configured to produce a broadband ultrasonic sound signal for reception by said sensor enabling said ultrasonic detector to perform a self-test.

2. An ultrasonic detector as claimed in claim 1, wherein said transducer is configured to produce said broadband ultrasonic sound signal having a frequency spectrum similar to that produced by a gas leak.

3. An ultrasonic detector as claimed in claim 1 or 2, wherein said transducer comprises a choke through which a gas is passable in use, wherein said choke is shaped to produce said broadband ultrasonic sound signal upon passage of said gas at sufficient pressure therethrough.

4. An ultrasonic detector as claimed in claim 1, 2 or 3, wherein said transducer is mounted inside an external housing of said detector in an area behind said sensor, whereby a sensing face of said sensor is unaffected by said transducer, but correct functioning of said sensor may still be tested by said detector.

5. An ultrasonic detector as claimed in claim 1, 2 or 3, wherein said transducer is mounted so as to produce said broadband ultrasonic sound signal external of said detector, whereby correct functioning of said sensor may be tested.

6. An ultrasonic detector as claimed in any preceding claim, wherein said detector is configured to check the calibration of said sensor using said transducer.

7. An ultrasonic detector as claimed in claim 6, wherein in use said transducer produces a substantially flat frequency spectrum within a frequency sensing range of the detector, whereby calibration of said detector is facilitated.

8. An ultrasonic detector as claimed in any preceding claim, wherein said detector is configured, in use, to process an output signal from said sensor to estimate a direction of said source of said ultrasonic sound signal.

9. An ultrasonic detector as claimed in claim 8, wherein said detector comprises at least two sensors and is configured, in use, to process output signals from each of said at least two sensors to provide said estimate of direction.

10. An ultrasonic detector as claimed in claim 8 or 9, wherein in use said detector is rotatable about an axis whereby said sensor may be rotated whilst said output signal is monitored, and said detector is configured to rotate until said signal is substantially at a maximum, whereby said indication of direction is provided by the rotational position of said detector relative to a reference position.

11. An ultrasonic detector as claimed in any preceding claim, wherein said detector is configured, in use, to monitor a frequency bandwidth for said ultrasonic sound signal, at least a part of which frequency bandwidth is removed or ignored so as to inhibit said detector generating a false alarm in response to an unwanted ultrasonic sound signal.

12. An ultrasonic detector as claimed in claim 11, wherein said detector is configured, in use, to examine said frequency bandwidth for any sound pressure levels above an alarm threshold and to remove or ignore any frequency range that is below a predetermined percentage of said frequency bandwidth, whereby said detector may operate substantially without false alarms being caused by said unwanted ultrasonic sound signal.

13. An ultrasonic detector as claimed in claim 11 or 12, wherein said detector is configured to periodically monitor said bandwidth so that any frequency shift of said unwanted ultrasonic sound signal is detected, whereby a corresponding shift may be made of said part of said frequency band that is removed or ignored.

14. A method of surveying an area for a source of airborne ultrasound, which method comprises the steps of surveying said area using an ultrasonic detector as claimed in any preceding claim and using said transducer to emit a broadband ultrasonic sound signal whereby a self-test of said detector is effected.

15. A method of surveying an area for a source of airborne ultrasound, which method comprises the steps of installing in or adjacent said area one or more ultrasonic detector as claimed in any of claims 1 to 13.

16. An ultrasonic sensor for detecting a source of airborne ultrasound within a detection frequency range, which ultrasonic sensor is characterised by an undamped piezoelectric crystal held in a material which permits substantially uninhibited deformation of said piezoelectric crystal in response to incident ultrasound within said detection frequency range so that a voltage is generated between two faces thereof, but which material inhibits vibration of said piezoelectric crystal when subjected to vibrations outside said detection frequency range.

17. An ultrasonic sensor as claimed in claim 16, wherein said piezoelectric crystal comprises a piezoelectric material and a ratio between a density of said piezoelectric material to a density of said material is between about 1 :50 and 1 :60.

18. An ultrasonic sensor as claimed in claim 16 or 17, wherein said material comprises a foam.

19. An ultrasonic sensor as claimed in claim 16, 17 or 18, wherein said material surrounds and is in contact with substantially all of the surface of said piezoelectric crystal, except for a sensing face and an area on a face opposite said sensing face to which an electrode is attached.

20. An ultrasonic sensor as claimed in any of claims 16 to 19, wherein said piezoelectric crystal comprises a sensing face and a longest dimension of said sensing face is not longer than about twice the shortest wavelength in said detection frequency range.

21. An ultrasonic sensor as claimed in any of claims 16 to 20, wherein said piezoelectric crystal has a length such that a resonance point of said piezoelectric crystal lies outside said detection frequency range.

20. An ultrasonic sensor as claimed in any of claims 16 to 19, further comprising a Faraday cage for insulating said piezoelectric crystal from electromagnetic noise.

- so ¬

il. An ultrasonic sensor as claimed in claim 20, wherein said Faraday cage is surrounded by a damping material for damping external vibration of said sensor.

22. A detector comprising a sensor as claimed in any of claims 16 to 21.