Applications of ultrasonics in engineering and medicine
1. Detection of flaws in metals
2. Ultrasonic drilling
3. Ultrasonic welding and soldering
4. Ultrasonic cutting and machining
5. Ultrasonic cleaning
6. Ultrasonic sonography
7. Ultrasonic blood flow meter
8. Ultrasonic local heat generation (ultrasonic hypothermia)
9. Dental cleaning
10. Lithotripsy
11. Ultrasound elastography
12. Transesophageal Echocardiography (TEE)
SB Non Destructive Technique to Detect Flaws in Metals
Ultrasonic (UT) inspection is a non-destructive method in which beams of high-frequency
sound waves are introduced into materials for the detection of surface and subsurface flaws in
the material.
There are two methods for US NDT for detecting flaws in metals:
(a) Pulse echo inspection
(b) Through Transmission
Pulse echo inspection
1. Ultrasonic pulse-echo devices are built with a transducer that produces a wide-band
pulse.
2. The pulse travels through the sample/material until it meets with either discontinuity
within the material (such as flaws or defects) or when it reaches a new medium.
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3. The wave is then reflected (echo) to the transducer.
4. The two-way transit time measured is divided by two to account for the down-and-
back travel path and multiplied by the velocity of sound in the test material.
5. The result is expressed as,
𝑑 = 𝑣 × 𝑡/2
Where “d” is the distance from the surface to the discontinuity in the test piece, “v” is the
velocity of sound waves in the material, and “t” is the measured round-trip transit time.
The diagram below shows how a basic pulse echo NDT is executed,
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Figure: Pulse echo inspection
SB • Sometimes in pulse echo mode two transducers are used but both are on same side. One
transmits the US waves and other catches back the reflected wave. This kind of
arrangement where separate sending and receiving transducers are incorporated are
widely known as pitch-catch pulse echo inspection.
Figure: Pitch catch pulse echo inspection
Through Transmission method
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1. An examination technique where the material is characterized based on the intensity of
mechanical energy of the ultrasonic pulse after it has passed through the object/material
of interest.
2. It uses two aligned transducers placed on either side of the object. One transducer acts
as transmitter and the other as receiver.
3. When a signal encounters defect, it attenuates and receiver receives an attenuated signal
indicating the presence of flaw.
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Figure: Through transmission inspection method
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The principal advantages of UT inspection are
(1) Superior penetrating power for detection of deep flaws
(2) High sensitivity permitting the detection of extremely small flaws
(3) Accuracy in determining size and position of flaws
(4) Portability
Ultrasound testing involves image reconstruction from the reflected sound waves
from various parts of the sample under test. There are three most common
methods of scan that one can implement to test the given material:
1. A scan
2. B scan
3. C scan
A Scan:
1. A scan is the amplitude scan wherein the ultrasound probe is held at a stable
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position on the test material.
2. Echoes from the samples are displayed as amplitude v/s time/depth on an
oscilloscope.
3. Echoes from flaws are lower in amplitude and can be easily differentiated
from the echos of flawless regions.
4. It consists of time-gated reflections.
5. A scan is used to find the flaws' location and the material's thickness. In
medicine, A scan is primarily used to assess ocular biometry.
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Figure: A scan in which the transducer’s position remains stable during
SB the scan and intensity peaks distinguishes flawless regions from flawed
regions.
B scan
1. B scan is a brightness scan where the transducer is moved linearly along
the sample and a plot of brightness v/s position is generated.
2. It gives information on the linear extent of the flaw/defect.
3. Bright region along the length of the defect represents length of the
defect.
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Figure: B scan experimental setup and output profile as viewed on
oscilloscope
C scan
1. C scan combines A and B scan to create a depth profile of the defect. With
A scan one can detect the defect's present at what distance and with B scan
one can know the extent of the defect.
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2. With C scan one can construct a 2D plot of linear and diametrical
(longitudinal) profile of the defect.
3. As the probe moves along the sample it collects multiple amplitude scans
and combine it with brightness profile to reconstruct the image of defect.
SB Figure: C scan representation of experimental setup and output image as
viewed on the display unit.
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