ultra sound test
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Sound Generation
Hammers (Wheel tapers)
Magnetostrictive
Lasers Piezo-electric
magnetostrictive
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Piezo-Electric Effect
When exposed to an alternating current acrystal expands and contracts
Converting electrical energy into mechanical
- + + - - +
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Piezo-Electric Materials
QUARTZ Resistant to wear
Insoluble in water
Resists ageing
Inefficient converter ofenergy
Needs a relatively high
voltage
Very rarely used nowadays
LITHIUM SULPHATE Efficient receiver
Low electrical
impedance
Operates on lowvoltage
Water soluble
Low mechanical
strength Useable only up to 30CUsed mainly in medical
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Polarized Crystals
Powders heated to
high temperatures
Pressed into shape Cooled in very
strong electrical
fields
Examples
Barium titanate (Ba Ti O3)
Lead metaniobate(Pb Nb O6)
Lead zirconate titanate
(Pb Ti O3 or Pb Zr O3)
Most of the probes for conventional usage use
PZT : Lead Zirconate Titanate
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Probes
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Probes The most important part of the
probe is the crystal The crystal are cut to a
particular way and thickness to
give the intended properties
Most of the conventional crystal
are Xcutto produce
Compression wave
Z
X
X X
Y
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Probes
The frequency of the probe depends on
the THICKNESSof the crystal
Formula for frequency:
Ff = V / 2tWhere Ff = the Fundamental frequency
V = the velocity in the crystal
t = the thickness of the crystal
Fundamental frequency is the frequency of the material ( crystal )where at that frequency the material will vibrate.
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Probes
The Thinnerthe crystal the Higherthe frequency
Which of the followings has the Thinnest crystal ?
1 MHz Compression probe
5 MHz Compression probe
10 MHz Shear probe
25 MHz Shear probe
25 MHz ShearProbe
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Probe Design
Compression Probe
Normal probe
0
Damping
Transducer
Electricalconnectors
Housing
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Probe Design
Shear Probe
Angle probe
DampingTransducer
Perspex wedge
Backing
medium
Probe
Shoe
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Probe Design
Twin Crystal
Advantages
Can be focused
Measure thin plate
Near surface
resolution
Disadvantages
Difficult to use on
curved surfaces Sizing small defects
Signal amplitude /
focal spot length
Transmitter Receiver
Focusing
lens
Separator /
Insulator
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Sound Intensity
Comparing the intensity of 2 signals
1
0
1
0
P
P
I
I
Electrical power proportional to the
square of the voltage produced
2
1
2
0
1
0
)(
)(
V
V
P
P
2
1
2
0
1
0
)(
)(
V
V
I
IHence
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Sound Intensity
2
1
2
0
1
0
)()(
VV
II Will lead to large ratios
21
2
0
10..1
0
10.. )(
)(
V
VLog
I
ILog Therefore
dBV
VLog
I
ILog
1
0
10..
1
0
10.. 20
BELS
V
VLog
I
ILog
1
0
10..
1
0
10.. 2
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1
0
10..20
H
HLogdB
2 signals at 20% and 40% FSH.
What is the difference between them in dBs?
2..2020
4020
1010.. LogLogdB
3010.020dB
dBdB 6
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1
0
10..20
H
HLogdB
2 signals at 10% and 100% FSH.
What is the difference between them in dBs?
10..2010
10020
1010.. LogLogdB
120dB
dBdB 20
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Amplitude ratios in decibels
2 : 1 = 6bB
4 : 1 = 12dB
5 : 1 = 14dB 10 : 1 = 20dB
100 : 1 = 40dB
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Automated Inspections
Pulse Echo
Through Transmission
Transmission with Reflection
Contact scanning
Gap scanning
Immersion testing
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Gap Scanning
Probe held a fixed
distance above the
surface (1 or 2mm)
Couplant is fed intothe gap
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Immersion Testing
Component is placed in a water filled
tank
Item is scanned with a probe at a fixed
distance above the surface
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Immersion Testing
Water
path
distance
Water path distance
Front surface Back surface
Defect