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9th Sep, 2001
BASIC ULTRASONIC PRINCIPLES
P.J SURYAVAMSHI
NDE-HZW
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A. What is Ultrasound?
Sound generated above the human hearing range
(20 KHz) is called ultrasound.
Although ultrasound behaves in a similar manner
to audible sound, it has a much shorter wavelength.
This means it can be reflected off very small
surfaces such as defects inside material.
The frequency range normally employed in
ultrasonic testing is 100 KHz to 50 MHz.
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BASIC ULTRASONIC PRINCIPLES
B. Velocity of Ultrasound and Wavelength:
Ultrasonic vibrations travel in the form of a wave,
similar to the way light travels. However, unlike
light waves, which can travel in a vacuum,ultrasound requires an elastic medium.
= v/f Where: = Wavelength
v = material sound velocity
f = frequency
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BASIC ULTRASONIC PRINCIPLES
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BASIC ULTRASONIC PRINCIPLES
C. Wave Propagation and Particle Motion:
The most common methods of ultrasonic examinationutilize either longitudinal waves or Shear wave.
Longitudinal Wave : A wave in which the particle
motion is in the same direction as the propagation of
wave.Shear Wave : A wave motion in which the particle
motion is perpendicular to the direction of the
propagation.
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BASIC ULTRASONIC PRINCIPLES
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BASIC ULTRASONIC PRINCIPLES
D. Sound Field
The sound field of a transducer (probe) is divided
into two zones; the near field and the far field.
Near Field: The region directly in front of the
transducer where the echo amplitude goes through aseries of maxima and minima and ends at the last
maximum.
The near field is the natural focus of the transducer.
It is the function of the transducer frequency, element
diameter, and the sound velocity of the test material.
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BASIC ULTRASONIC PRINCIPLES
N
N = D2
/ 4N = Near field Distance
D = Crystal Diameter
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BASIC ULTRASONIC PRINCIPLES
Far Field: The far field is the area beyond nearfield where the sound field pressure gradually
drops to zero.In the far field the sound beam diverges.
N
Sin (/2) = 0.514 / D
/2 = Half Angle beam
Spread.
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DESIGN CHARACTERISTICS OF TRANSDUCER
A. What is an Ultrasonic Transducer?
A transducer is any device that converts one formof energy to another. An ultrasonic transducer
converts electrical energy to mechanical energy,
in the form of sound, and vice versa.
The main components are the active element,
backing, and wear plate.
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DESIGN CHARACTERISTICS OF
TRANSDUCER
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DESIGN CHARACTERISTICS OF
TRANSDUCER
The Active Element:
The active element, which is piezo electric material,converts electrical energy such as an excitation pulse
from a flaw detector into ultrasonic energy.Backing:
The backing is usually a highly attenuative, highdensity material that is used to control the vibration
of the transducer by absorbing the energy radiating
from the back face of the active element.
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DESIGN CHARACTERISTICS OF
TRANSDUCER
Wear Plate:The basic purpose of the transducer wear plate is to
protect the transducer element from the testingenvironment.
In the case of contact transducers, the wear platemust be a durable and corrosion resistant material
in order to withstand the wear caused by use on a
material such as steel.
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TYPES OF TRANSDUCER
Dual Element Transducer:
Dual element transducer utilize separate transmittingand receiving elements, mounted on delay lines that
are usually cut at an angle.
This configuration improves near surface resolution.
Roof Angle
Delay lines
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TYPES OF TRANSDUCER
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TYPES OF TRANSDUCER
Angle Beam Transducer:Angle beam transducer use the principles of
refraction and mode conversion to produce
refracted shear or longitudinal waves in the test
material.Longitudinal Wave
Shear Wave
First Critical Angle = 28 0
Second Critical Angle = 57 0
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TYPES OF TRANSDUCER
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TYPES OF TRANSDUCER
Beam Path
Surface
Distance
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TYPES OF TRANSDUCER
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FOCUSED PROBE Focusing Configuration:
Focusing is accomplished by either the addition
of a lens or by curving the element.
By definition, the focal length of transducer is the
distance from the face of the transducer to thepoint in the sound field where the signal with the
maximum amplitude is located. Because the lastsignal maximum occurs at a distance equivalent
to the near field, focal distance will be always less
than near field length.
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FOCUSED PROBE
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FOCUSED PROBETypes of focusing:
a.Spherically Focused (Spot Focused)b.Cylindrically Focused (Line Focused)
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RTD PROBES
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RTD PROBES
Hazira RTD Probe 700TRL2-Aust.
2(8 X 14)
SA 100,FS - 21
Wave Mode:
700 Longitudinal
Frequency : 2 MHz
Powai RTD Probe 700TRL2-St
2( 18 - R150)SA 250,FS - 18
Wave Mode:
700 Longitudinal
Frequency : 2 MHz
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RTD PROBES
Hazira RTD Probe
Material to be tested:Aust. Steel
Able to detectdiscontinuity in Aust.
Steel & Steel
Crystal Shape:
Rectangular
Line Focused
Powai RTD Probe
Material to be tested:Steel
Able to detectdiscontinuity in Steel
Crystal Shape:
Elliptical
Spot Focused
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RTD PROBES
Hazira RTD Probe Focus Sound Path:
21 mm
Roof Angle: 100
Powai RTD Probe Focus Sound Path:
18 mm
Roof Angle: 250