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Application of Ultrasound

Thursday, December 16, 2010

Ultrasound has many applications in our lifes. Below are some of the applications.

Ultrasound has a broad range of applications in medicine, where it is referred to as medical ultrasound.
It is widely used in obstetrics to follow the development of the fetus during pregnancy, in cardiology
where images can display the dynamics of blood flow and the motion of tissue structures (referred to as
real-time imaging), and for locating tumors and cysts. 3-D imaging, surgical applications, imaging from
within arteries (intravascular ultrasound), and contrast imaging are among the newer developments.

Ultrasonic leak detector
Ultrasonic leak detector

In industry, ultrasound is utilized for examining critical structures, such as pipes and aircraft fuselages, for cracks and fatigue. Manufactured parts can likewise be examined for voids, flaws, inclusions, debonding, etc. Such defects can exist immediately after manufacturing, or were formed due to stresses, corrosion, etc. Ultrasound has also widespread use in process control. The applications are collectively called Non- Destructive Testing (NDT) or Non-Destructive Evaluation (NDE). In addition, acoustic microscopy refers
to microscopic examinations of internal structures that cannot be studied with a light microscope, such as an integrated circuit or biological tissue.

Ultrasound is likewise an important tool for locating structures in the ocean, such as wrecks, mines, submarines, or schools of fish; the term SONAR (SOund Navigation And Ranging) is applied to these applications.

Range Measurements, Air
Ultrasound range measurements are used in cameras, in robotics, for determining dimensions of rooms, etc. Measurement frequencies are typically around 50 kHz to 60 kHz. The measurement concept is pulse-echo, but with burst excitation rather than pulse excitation. Special electronic circuitry and a thin low-acoustic-impedance air transducer is most commonly used. Rugged solid or composite piezoelectric-based transducers, however, can also be used, sometimes up to about 500 kHz.
Thickness Measurement for Testing, Process Control, Etc.
Measurement of thickness is a widely used application of ultrasound. The measurements can be done with direct coupling between the transducer and the object of interest, or — if good surface contact is difficult to establish — with a liquid or another coupling agent between the transducer and the object. Ultrasound measurements of thickness have applications in process control, quality control, measuring build-up of ice on an aircraft wing, detecting wall thickness in pipes, as well as medical applications. The instrumentation involves a broadband transducer, pulser-receiver, and display or, alternatively, echo detecting circuitry and numerical display.

Ultrasonic Flow Sensor
Doppler Flow Measurements
The flow velocity of a liquid or a moving surface can be determined through Doppler measurements, provided that the liquid or the surface scatters ultrasound back in the direction of the transducer, and that the angle between the flow direction and the ultrasound beam is known. Further details are given in the section about Doppler processing. CW and PW Doppler instruments are commercially available, with CW instrumentation being by far the least expensive.

Upstream/Downstream Volume Flow Measurements
When flow velocity is measured in a pipe with access to one or both sides, an ultrasound transmission technique can be used in which transducers are placed on the same or opposite sides of the pipe, with one transducer placed further upstream than the other transducer. From the measured difference in travel time between the upstream direction and the downstream direction, and knowledge about the pipe geometry, the volume flow can be determined. Special clamp-on transducers and instrumentation are available. An overview of flow applications in NDE is given in.

Elastic Properties of Solids
Since bulk sound speed varies with the elastic stiffness of the object, sound speed measurements can be used to estimate elastic properties of solids under different load conditions and during solidification processes. Such measurements can also be used for measurement of product uniformity and for quality assurance. The measurements can be performed on bulk specimens or on thin rods, using either pulse-echo or transmission instrumentation. Alternatively, measurements of the material’s own resonance frequencies can be performed for which commercial instruments, such as the Grindo-sonics, are available.

Porosity, Grain Size Estimation

Measurement of ultrasound attenuation can reveal several materials parameters. By observing the attenuation in metals as a function of frequency, the grain size and grain size distribution can be estimated. Attenuation has been used for estimating porosity in composites. In medical ultrasound, attenuation is widely used for tissue characterization, that is, for differentiating between normal and pathological tissues. Pulse-echo instrumentation interfaced with a digitizer and a computer for data analysis is required.

Acoustic Microscopy
The measurement approaches utilized in acoustic microscopy are similar to other ultrasound techniques, in that A-scan, B-scan, and C-scan formats are used. It is in the applications and the frequency ranges where acoustic microscopy differs from conventional pulse-echo techniques. Although acoustic microscopes have been made with transducer frequencies up to 1 GHz, the typical frequency range is 20 MHz to 100 MHz, giving spatial resolutions in the range from 100 µm to 25 µm. Acoustic microscopy is used for component failure analysis, electronic component packaging, and internal delaminations and disbonds in materials, and several types of acoustic microscopes are commercially available.

Ultrasonic Reference Books:

Ultrasonics: Data, Equations and Their Practical Uses
Ultrasonics: Data, Equations and Their Prac...
Physical Principles of Medical Ultrasonics
Physical Principles of Medical Ultrasonics
Fundamentals and Applications of Ultrasonic Waves (Pure and Applied Physics)
Fundamentals and Applications of Ultrasonic...


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