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Re: why TOFD cursor is parabola?

Posted by: John , E-mail: jiangyunxi@leepipe.com, on November 29, 2006 at 03:04 :

In Reply to: Re: why TOFD cursor is parabola? posted by : Ed Ginzel    , E-mail: eginzel@mri.on.ca, on November 28, 2006 at 13:28 :

Some guys use two phase array probe as TOFD,would you like tell me that is there any differene between typical TOFD?
Thank you for your reply.

----------- Start Original Message -----------
: YunXi:
: Typically TOFD uses a relatively small diameter element. The pressure boundary of such a probe can be approximated by a cone. Now imagine passing such a cone past a small point diffractor in its path. The point will first be detected far away as the edge of the cone detects the flaw. As the probe is moved along its straight scan path the flaw gets closer until the flaw is directly across from the probe. As the probe continues its scan movement past the flaw the process reverses and the flaw gets further away. The effect is like taking a slice through the cone. If you were to cut a cone at some point parallel to the central axis the remaining cross section is the definition of a parabola!
: The actual shape of the beam boudary is defeined by a Bessel function but the effect is effectively the same as a cone.
: The same effect can be seen on the shape of small targets in pulse-echo but the process is called backscatter instead of TOFD (forward scatter).
: Ed
:
: : I want to know why TOFD cursor is parabola?and what decide the parameter of the curve?is there any equation?Thanks a lot
------------ End Original Message ------------

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Follow Ups:

• Re: why TOFD cursor is parabola? Ed Ginzel 15:37 Nov-29-2006 (4)
  • Re: why TOFD cursor is parabola? John 04:03 Nov-30-2006 (3)
    • Re: why TOFD cursor is parabola? Nigel 09:00 Nov-30-2006 (2)
      • Re: why TOFD cursor is parabola? Ed Ginzel 17:28 Nov-30-2006 (0)

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----------- Start Original Message ----------- : Some guys use two phase array probe as TOFD,would you like tell me that is there any differene between typical TOFD? : Thank you for your reply. : : : YunXi: : : Typically TOFD uses a relatively small diameter element. The pressure boundary of such a probe can be approximated by a cone. Now imagine passing such a cone past a small point diffractor in its path. The point will first be detected far away as the edge of the cone detects the flaw. As the probe is moved along its straight scan path the flaw gets closer until the flaw is directly across from the probe. As the probe continues its scan movement past the flaw the process reverses and the flaw gets further away. The effect is like taking a slice through the cone. If you were to cut a cone at some point parallel to the central axis the remaining cross section is the definition of a parabola! : : The actual shape of the beam boudary is defeined by a Bessel function but the effect is effectively the same as a cone. : : The same effect can be seen on the shape of small targets in pulse-echo but the process is called backscatter instead of TOFD (forward scatter). : : Ed : : : : : I want to know why TOFD cursor is parabola?and what decide the parameter of the curve?is there any equation?Thanks a lot ------------ End Original Message ------------

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