The Ideal Angle Beam Probes for DGS Evaluation Wolf Kleinert , York Oberdoerfer, Gerhard Splitt, GE Sensing & Inspection Technologies GmbH, Huerth, Germany
Dec 16, 2015
The Ideal Angle Beam Probes for DGS Evaluation
Wolf Kleinert, York Oberdoerfer, Gerhard Splitt,GE Sensing & Inspection Technologies GmbH,
Huerth, Germany
2
April 18, 2023
Wolf Kleinert
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
April 18, 2023
Wolf Kleinert
The DGS Method Was Developed for Straight Beam Probes With Circular Flat Transducers
Normalized DGS Diagram
Distance s/N
Gai
n [
dB
]
5
April 18, 2023
Wolf Kleinert
Sound Pressure on the Acoustic Axis of a Circular Transducer by Continuous Sound (Algebraic Solution)
6
April 18, 2023
Wolf Kleinert
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 diameterN: Near field length: Wave length
7
April 18, 2023
Wolf Kleinert
Conversion of the Near Field Length From a Rectangular Transducer to an Equivalent Circular Transducer
State of the Art
The near field length of a rectangular transducer is calculated by:
Ratiob/a
h
1,0 1,370,9 1,250,8 1,150,7 1,090,6 1,040,5 1,010,4 1,000,3 0,990,2 0,990,1 0,99
Refer to: J. und H. Krautkrämer, Werkstoffprüfung mit Ultraschall, 5. Editon, page 82
For a 8 times 9 mm2 rectangular transducer follows:N = 15,4 mm
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
8
April 18, 2023
Wolf Kleinert
Sound Pressure on the Acoustic Axisby Continuous Sound
Good match between the calculation of the near field length accordingto the state of the art with the numeric solution.
Circular transducer (algebraic) Rectangular transducer (numeric)9 times 8 mm2, N = 14.8 mm
So
un
d P
ress
ure
p(z
)
So
un
d P
ress
ure
p(z
)
Distance z [mm] Distance z [mm]
9
April 18, 2023
Wolf Kleinert
Comparison Between the Rectangular Transducerand the Equivalent Circular Transducer
Rectangular transducer 9 times 8 mm2 Circular transducer
Dep
th [
mm
]
Dep
th [
mm
]
Dep
th [
mm
]
Dep
th [
mm
]
Dep
th [
mm
]D
epth
[m
m]
10
April 18, 2023
Wolf Kleinert
Recent Measurements With Angle Beam Probes Show Significant Deviation
Evaluation using the equivalent circular transducer
11
April 18, 2023
Wolf Kleinert
Problem to Be Solved
f = 4 MHz, c = 3 255 m/s, D = 12,2 mm
How does thetransducer look like?
Sound field contour in 2 dB steps
Distance x [mm]
Dep
th z
[m
m]
12
April 18, 2023
Wolf Kleinert
Just Two Preconditions Are Used.
At the end of the near field the difference betweenthe central beam and a perimeter beam equalshalf the wave length.
Fermat-Principle:The fastest path from a point A in a firstmedium to a point B in a second mediumfollows Snell‘s Law.
Not only valid in the 2D plane but as wellin the 3D space.
13
April 18, 2023
Wolf Kleinert
Constructing an Angle Beam Probe WithPredefined Angle of Refraction and Pre-defined Delay Line vw
Transferring the sound path for each angle g from a given straight beamprobe to the angle beam probe to be modeled.(Not only in the 2D plane, but as well in the 3D space)
M W
M‘W‘
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April 18, 2023
Wolf Kleinert
Result (Probe Similar to the MWB 60-4)Transducer Shape Cross Section
Longitudinal Section Longitudinal Section after coordinate transformation
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April 18, 2023
Wolf Kleinert
True DGS Technology Drives Accuracy
DGS software in our instruments will support both probes
Current Technology
OVER Sizing
NEW Technology
PRECISE Sizing
16
April 18, 2023
Wolf Kleinert
Curved Coupling SurfacesFor concave test surfaces the Standard EN 583-2 requests matching of the delay line ofthe probe to the surface of the test piece in all cases unless the diameter is large enoughto 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 modeldescribed above can nevertheless be easily expanded to curved coupling surfaces toensure even in these cases the validity of the DGS method.
17
April 18, 2023
Wolf Kleinert
Positive Phasing Angles
The delay laws can be calculated directly when positive phasing angles are used , by comparingthe 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 theoriginal and the virtual transducer:
22
April 18, 2023
Wolf Kleinert
Summary of the Evaluation
Significantly improved DGS accuracy can be achieved with this new trueDGS technologywithout any „Focus Pocus“, if the angle beam probe is designed according to thetrueDGS technology: „Focus Physics“
Phasing angle in steel [°]
Sound path to the near field end
So
un
d p
ath
[m
m]
Single Element Phased Array
Probe FBH [mm] ERS [mm] [%]
MWB 45-2 tD 3 0,10 3,3%MWB 60-2 tD 3 0,14 4,7%MWB 70-2 tD 3 0,10 3,3%MWB 45-4 tD 3 0,17 5,7%MWB 60-4 tD 3 0,16 5,3%MWB 70-4 tD 3 0,16 5,3%
All measurementswere done manually