Introduction to Ultrasonic:
- The word ultrasonic combines the Latin roots ultra, meaning ‘beyond’ and sonic, or sound.
- The sound waves having frequencies above the audible range i.e. above 20000Hz are called ultrasonic waves.
- Generally these waves are called as high frequency waves.
- The field of ultrasonics have applications for imaging, detection and navigation.
- The broad sectors of society that regularly apply ultrasonic technology are the medical community, industry, the military and private citizens.
Properties of ultrasonic waves:
They have a high energy content.
Just like ordinary sound waves, ultrasonic waves get reflected, refracted and absorbed.
They can be transmitted over large distance with no appreciable loss of energy.
If an arrangement is made to form stationary waves of ultrasonics in a liquid, it serves as a diffraction grating. It is called an acoustic grating.
They produce intense heating effect when passed through a substance.
In ultrasonic testing, high-frequency sound waves are transmitted into a material to detect imperfections or to locate changes in material properties.
The most commonly used ultrasonic testing technique is pulse echo, whereby sound is introduced into a test object and reflections (echoes) from internal imperfections or the part’s geometrical surfaces are returned to a receiver.
Below is an example of shear wave weld inspection. Notice the indication extending to the upper limits of the screen.
This indication is produced by sound reflected from a defect within the weld.
PRINCIPLES OF ULTRASONIC GENERATIION:
- Ultrasonic waves are introduced into a material where they travel in a straight line and at a constant speed until they encounter a surface.
- At surface interfaces some of the wave energy is reflected and some is transmitted.
- The amount of reflected or transmitted energy can be detected and provides information about the size of the reflector.