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Re: Smallest detectable flaw size, especially for low frequency test (f= 0.5 MHz) and in general.

Posted by: Bill Grandia , E-mail: wgrandia@aol.com, on September 08, 1996 at 00:32:42:

In Reply to: Smallest detectable flaw size, especially for low frequency test (f= 0.5 MHz) and in general. posted by : R.Died on September 06, 1996 at 23:31:52:

: For an applied frequency of 0.5 MHz what will be the smallest flaw
: that air coupled ultrasound could find?

: Furthermore I want to enter into a general discussion about smallest detectable flaw sizes.
: Is there a certain relation between flaw size and frequency?

: - lambda/flaw dia ratio?

: - Is this relation linear?

Yes, we estimate the minimal detectable flaw size to be in the order of the size of the wavelength.
The focal spot diameter in air for a 25mm diameter element with a focal distance of 35 mm is 1.2 mm (-3dB points) at 400 kHz, with a focal depth of 25 mm (-3dB). In through-transmission with the focal spots coinciding with each surface, the lateral resolution therefore is about 1.2 mm.

:
: Preconditions: ideal reflection (shape and impedance).

:
: Rolf Diederichs

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Follow Ups:

• Re: Smallest detectable flaw size, especially for low frequency test (f= 0.5 MHz) and in general. Robert A. Day 23:37:40 9/11/96 (size: 4645) (5)
  • Re: Smallest detectable flaw size, especially for low frequency test (f= 0.5 MHz) and in general. Bill Grandia 23:47:01 9/14/96 (size: 9685) (0)
  • Re: Smallest detectable flaw size, especially for low frequency test (f= 0.5 MHz) and in general. Rolf D. 10:24:22 9/12/96 (size: 1138) (2)
    • Re: Smallest detectable flaw size, especially for low frequency test (f= 0.5 MHz) and in general. Yosi Bar-Cohen 09:40:40 9/19/96 (size: 1880) (0)
    • Re: Smallest detectable flaw size, especially for low frequency test (f= 0.5 MHz) and in general. Bill Grandia 00:01:18 9/15/96 (size: 10660) (0)
  • Re: Smallest detectable flaw size, especially for low frequency test (f= 0.5 MHz) and in general. W. Grandia 02:17:45 9/12/96 (size: 5424) (0)

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Comments:
: : For an applied frequency of 0.5 MHz what will be the smallest flaw : : that air coupled ultrasound could find? : : Furthermore I want to enter into a general discussion about smallest detectable flaw sizes. : : Is there a certain relation between flaw size and frequency? : : - lambda/flaw dia ratio? : : - Is this relation linear? : Yes, we estimate the minimal detectable flaw size to be in the order of the size of the wavelength. : The focal spot diameter in air for a 25mm diameter element with a focal distance of 35 mm is 1.2 mm (-3dB points) at 400 kHz, with a focal depth of 25 mm (-3dB). In through-transmission with the focal spots coinciding with each surface, the lateral resolution therefore is about 1.2 mm. : : : : Preconditions: ideal reflection (shape and impedance). : : : : Rolf Diederichs

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