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1. EP2660579 - Ultrasonic sensor system and method

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Claims

1. An ultrasonic sensor (110) for detecting a source of airborne ultrasound within a detection frequency range, which ultrasonic sensor (110) is characterised by an undamped piezoelectric crystal (114) held in a material which permits substantially uninhibited deformation of said piezoelectric crystal (114) 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 (114) when subjected to vibrations outside said detection frequency range.
  2. An ultrasonic sensor (110) as claimed in claim 1, wherein said piezoelectric crystal (114) 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.
  3. An ultrasonic sensor (110) as claimed in claim 1 or 2, wherein said material comprises a foam.
  4. An ultrasonic sensor (110) as claimed in claim 1, 2 or 3, wherein said material surrounds and is in contact with substantially all of the surface of said piezoelectric crystal (114), except for a sensing face and an area on a face opposite said sensing face to which an electrode is attached.
  5. An ultrasonic sensor (110) as claimed in any of claims 1 to 4, wherein said piezoelectric crystal (114) 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.
  6. An ultrasonic sensor (110) as claimed in any of claims 1 to 5, wherein said piezoelectric crystal (114) has a length such that a resonance point of said piezoelectric crystal (114) lies outside said detection frequency range.
  7. An ultrasonic sensor (110) as claimed in any of claims 1 to 6, further comprising a Faraday cage (128, 130) for insulating said piezoelectric crystal (114) from electromagnetic noise.
  8. An ultrasonic sensor (110) as claimed in claim 7, wherein said Faraday cage (128, 130) is surrounded by a damping material for damping external vibration of said sensor.
  9. A detector comprising an ultrasonic sensor (110) as claimed in any of claims 1 to 8.