Chapter 9: Sound Beams

What is the overall shape of a sound beam?

Hourglass shape

What determines the depth of the beam focus?

The diameter and frequency of the transducer (the bigger the crystal is at the start the longer it will take to narrow therefore the deeper the focus point)

The degree to which the sound beam spreads is determined by:

Frequency and diameter of the crystal

At it’s starting point, the beam is the same length as the aperture. The beam starts to get narrower until it reaches the narrowest point known as the _________, then it will _______ (spread apart)

focus; diverge

Define aperture

The piezoelectric area of a transducer from which a sound beam is transmitted. More simply, the size of the “opening” on the transducer that the sound comes out of.

What is the aperture in a single element transducer?

the diameter of the crystal

What is the aperture of a phased array transducer?

the width of the group of elements/crystals that fire together to make one beam

The region from the transducer to the focus is called?

The Near Zone

What marks the end of the near zone?

The focus point

Fresnel zone is another name for?

Near zone: the region from the transducer to the focus point

The length/distance from the transducer to the focus point is called the:

Near zone length

What is the relationship between NZL and frequency of transducer?

directly related

What is the relationship between NZL and diameter of the crystal?

directly

The region surrounding the focus point is the ____________. explain the relevance of 1/2

Focal zone. Half of the focal zone is in the Near zone and half is in the far feild

The location where the beam is the narrowest

The focus

The width of the beam at the focus is _______ of the width of the beam as it leaves the transducer

1/2

Fraunhofer zone (AKA _________) is the region from the _____ to one length of the near zone

far zone; focus point

One near zone length past the focus, the width of the sound beam is:

back to the same width as the initial transducer; further than this point the beam diverges/widens wider than the original active element

How are transducer frequency and crystal diameter related to divergence?

Inversely.

• A smaller crystal will give more divergence

• Larger crystal diameter → less divergence

states that each point of the face of the transducer is the source of a small “wavelet”. Wavelets interfere with each other (either combine to form one big wave → addition; or combine to form one smaller wave/cancel each other out → subtraction).

Huygens Principle of interference

the bending of a sound to avoid obstacles and holes. A deviation of sound that is not due to reflection, refraction or scattering.

Diffraction