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The Ideal Angle Beam Probes for DGS Evaluation

The Ideal Angle Beam Probes for DGS Evaluation. Wolf Kleinert , York Oberdoerfer, Gerhard Splitt, GE Sensing & Inspection Technologies GmbH, Huerth, Germany. The Discussion About the Near Field Length of Angle Beam Probes With Rectangular Transducers Is Quite Old.

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The Ideal Angle Beam Probes for DGS Evaluation

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  1. The Ideal Angle Beam Probes for DGS Evaluation Wolf Kleinert, York Oberdoerfer, Gerhard Splitt,GE Sensing & Inspection Technologies GmbH, Huerth, Germany

  2. The Discussion About the Near Field Length of Angle Beam Probes With Rectangular Transducers Is Quite Old. Source: http://www.ndt.net/forum/thread.php?forenID=1&rootID=8596#

  3. The DGS Method Was Developed for Straight Beam Probes With Circular Flat Transducers Normalized DGS Diagram Gain [dB] Distance s/N

  4. Existing Tools at the Time of the Developmentof the DGS Method

  5. Sound Pressure on the Acoustic Axis of a Circular Transducer by Continuous Sound (Algebraic Solution)

  6. Sound Pressure on the Acoustic Axis of a Circular Transducer by Continuous Sound (Algebraic Solution) The sine has maxima for z under the following condition: With this for the last maximum on the acoustic axis follows: D: Transducer diameter N: Near field length l: Wave length

  7. Conversion of the Near Field Length From a Rectangular Transducer to an Equivalent Circular TransducerState of the Art The near field length of a rectangular transducer is calculated by: • With: • a: half of the longer side • b: half of the shorter side • h: correction value (refer to the table) • l: wave length in the test material For a 8 times 9 mm2 rectangular transducer follows: N = 15,4 mm Refer to: J. und H. Krautkrämer, Werkstoffprüfung mit Ultraschall, 5. Editon, page 82

  8. Sound Pressure on the Acoustic Axisby Continuous Sound Circular transducer (algebraic) Rectangular transducer (numeric) 9 times 8 mm2, N = 14.8 mm Sound Pressure p(z) Sound Pressure p(z) Distance z [mm] Distance z [mm] Good match between the calculation of the near field length according to the state of the art with the numeric solution.

  9. Comparison Between the Rectangular Transducerand the Equivalent Circular Transducer Rectangular transducer 9 times 8 mm2 Circular transducer Depth [mm] Depth [mm] Depth [mm] Depth [mm] Depth [mm] Depth [mm]

  10. Recent Measurements With Angle Beam Probes Show Significant Deviation Evaluation using the equivalent circular transducer

  11. Problem to Be Solved Sound field contour in 2 dB steps How does the transducer look like? Depth z [mm] Distance x [mm] f = 4 MHz, c = 3 255 m/s, D = 12,2 mm

  12. Just Two Preconditions Are Used. At the end of the near field the difference between the central beam and a perimeter beam equals half the wave length. Fermat-Principle: The fastest path from a point A in a first medium to a point B in a second medium follows Snell‘s Law. Not only valid in the 2D plane but as well in the 3D space.

  13. Constructing an Angle Beam Probe WithPredefined Angle of Refraction b and Pre-defined Delay Line vw M W W‘ M‘ Transferring the sound path for each angle g from a given straight beam probe to the angle beam probe to be modeled. (Not only in the 2D plane, but as well in the 3D space)

  14. Result (Probe Similar to the MWB 60-4) Cross Section Transducer Shape Longitudinal Section Longitudinal Section after coordinate transformation

  15. Current Technology OVER Sizing NEW Technology PRECISE Sizing True DGS Technology Drives Accuracy DGS software in our instruments will support both probes

  16. Curved Coupling Surfaces For concave test surfaces the Standard EN 583-2 requests matching of the delay line of the probe to the surface of the test piece in all cases unless the diameter is large enough to ensure good coupling. (The following figure is taken from the European Standard EN 583-2) For convex surfaces matching is required when: In these cases the EN 583-2 does not allow the use of the DGS method. The model described above can nevertheless be easily expanded to curved coupling surfaces to ensure even in these cases the validity of the DGS method.

  17. Positive Phasing Angles The delay laws can be calculated directly when positive phasing angles are used , by comparing the position and orientation of the original transducer with those of the virtual transducer. The delay laws follow then from the distances between the transducer elements of the original and the virtual transducer:

  18. Necessary Additional MatchingUsing Negative Phasing Angles

  19. Phased Array Angle Beam ProbeMWB 56-4 trueDGS, 45° Phasing

  20. Phased Array Angle Beam ProbeMWB 56-4 trueDGS, 60° Phasing

  21. Phased Array Angle Beam ProbeMWB 56-4 trueDGS, 70° Phasing

  22. Sound path to the near field end Sound path [mm] Phasing angle in steel [°] Summary of the Evaluation Single Element Phased Array All measurements were done manually Significantly improved DGS accuracy can be achieved with this new trueDGS technology without any „Focus Pocus“, if the angle beam probe is designed according to the trueDGS technology: „Focus Physics“

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