The Sound Beam (4)

Question 1

Near (Fresnel) Zone

Answer 1

Zone at the start of the sound beam.

• Point sources from the crystal face, that effect when sound is generated
• cause amplitude errors
• sound intensity fluctuates
• signal amplitudes (height) in this zone can’t be trusted

Question 2

Far (Fraunhofer) Zone

Answer 2

Sound pressure builds making the sound wave uniform

- sound spreads into a cone shape, growing as sound moves further

Question 3

Beam Spread or Beam Divergence

Answer 3

Into the far zone sound spreads into a cone shape, growing as it gets further into the test specimen.
- can be used for sizing

Question 4

Where is the maximum sound intensity of a sound beam?

Answer 4

Start of the far field/end of near field.

Question 5

Define Plane Wave

Answer 5

sound pressure builds and the wave front becomes uniform.

Question 6

What is a Constructive or Destructive Interface?

Answer 6

Sound waves from the crystal face cross over each other causing amplitude errors

Question 7

What does a Distance Amplitude Correction Curve (DAC) do?

Answer 7

Uses the cone shape of the far field sound waves to size a test specimen.

Question 8

How can we alter Beam Spread?

Answer 8

Changing the diameter and/or the frequency of the transducer.

Question 9

What happens to the Beam Spread in a narrow test specimen?

Answer 9

Causes the sound to hit the sides of the specimen, thus producing mode conversion.

Question 10

Where is Sound Intensity, strongest on a sound beam?

Answer 10

The centerline is 100% and gets weaker towards the edges of the sound beam.

Question 11

How can we “maximize” a discontinuities signal?

Answer 11

Maximizing the signal of a discontinuity by moving the transducer so the sound beams centerline is directly over the discontinuity.
- Making the amplitude maximal