types of waves.pptx

7/27/2019 TYPES OF WAVES.pptx

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VISHNU G

12MMF0027


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INTRODUCTION

Ultrasound is an oscillating sound pressure wave with a frequency greater than the

upper limit of the human hearing range.

Ultrasound is thus not separated from 'normal' (audible) sound based on differences

in physical properties, only the fact that humans cannot hear it.

Although this limit varies from person to person, it is approximately 20 kilohertz

(20,000 hertz)

Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz.


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Approximate frequency ranges corresponding to ultrasound, with rough guide of some

applications

The four fundamental modes of ultrasonic wave propagation are:

1. Longitudinal or compression waves

2. Shear or transverse waves3. Surface or Rayleigh waves

4. Plate or Lamb waves


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LONGITUDINAL WAVES

Longitudinal waves are similar to audible sound waves in that they are alsocompressional in nature.

The alternate expansion and contraction of a piezoelectric crystal generates

longitudinal waves. Only longitudinal waves can travel through a liquid.

In this case the particles are oscillating parallel to the direction of energypropagation

This form of energy propagation and particle oscillation is referred to as acompression or longitudinal wave form.


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Particle motion & wave propagation with longitudinal waves


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SHEAR WAVES With shear waves, particle vibration is transverse (at a right angle) to the

direction of wave propagation.

Passing the ultrasonic beam through the material at an angle generates shearwaves.

The following figure illustrates the shear wave relationship between thedirection of particle vibration and direction of wave propagation.

Figure : Particle motion and wave propagation with shear waves.


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RAYLEIGH WAVES

Surface waves travel with little attenuation in the direction of wavepropagation. However, their energy decreases rapidly as the wave penetrates

below the surface of the material.

Figure: Particle motion and wave propagation with surface waves


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LAMB WAVES

When ultrasonic energy is introduced into relatively thin plates, it ispropagated by Lamb waves.

Lamb waves have multiple or varying wave velocities.

Lamb wave velocity is dependent on the thickness of the material andfrequency.

With Lamb waves, a number of modes of particle vibration are possible, butthe two most common modes of vibrational motion are symmetrical andasymmetrical as shown in Figure.


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Figure : Particle motion and wave propagation with Lamb waves.


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THANK YOU..

types of waves.pptx

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