Sound Beams chapter 9

These flashcards cover the key concepts and terms related to the anatomy and properties of sound beams as discussed in the lecture.

Focus

The location where the beam is the narrowest.

NearZone

The region from the transducer to the focus where the beam narrows.

Focal Length

The distance from the transducer to the focus.

Far Zone

The region that starts at the focus and extends deeper, where the beam diverges.

Focal Zone

The area around the focus where the beam is narrow and provides better resolution.

Beam Profile

The shape and diameter of the sound beam as it exits the transducer and travels through the near and far zones.

Fresnel Zone

Another name for the NearZone, where the beam narrows until it reaches the focus.

Fraunhofer Zone

Another name for the Far Zone, characterized by diverging beam properties.

Sound Beam Divergence

The spread of the ultrasound beam in the far field, influenced by transducer diameter and frequency.

Huygen's Principle

States that small sound sources create wavelets that can lead to varying beam shapes due to interference effects.

Beam Diameter at the Transducer

The beam diameter is equal to the transducer diameter at the starting point of the sound beam.

Beam Diameter at the Focus

The beam diameter is exactly one-half the diameter of the transducer (1/2 \times D) at the location of the focus.

Beam Diameter at 2 Near Zone Lengths

At a distance of two near zone lengths from the transducer, the beam diameter returns to being equal to the transducer diameter.

Beam Diameter Deeper than 2 Near Zone Lengths

At depths greater than two near zone lengths, the beam diameter is always greater than the transducer diameter.

Focal Depth Factors

The distance to the focus is determined by two factors: the transducer diameter and the frequency of the sound.

Transducer Diameter and Focal Depth Relationship

Transducer diameter and focal depth are directly related; a larger diameter results in a deeper focus (\text{Diameter} \uparrow, \text{Focal Depth} \uparrow).

Frequency and Focal Depth Relationship

Frequency and focal depth are directly related; higher frequency sound results in a deeper focus (\text{Frequency} \uparrow, \text{Focal Depth} \uparrow).

Transducer Diameter and Divergence Relationship

Transducer diameter and beam divergence are inversely related; smaller diameter transducers produce beams that spread out more in the far zone.

Frequency and Divergence Relationship

Frequency and beam divergence are inversely related; lower frequency sound beams spread out or diverge more in the far zone (\text{Frequency} \downarrow, \text{Divergence} \uparrow).

V-Shaped Waves

Also known as Huygens' wavelets, these are produced by very small sources (about the size of the sound's wavelength) and diverge in a V-shape.

The focus can also be described as

The focal point, the end of the near zone, the beginning of the far zone, or the middle of the focal zone.

What is the beam diameter at the transducer?

Beam diameter equals transducer diameter.

What is the beam diameter at the focus?

Beam diameter is one- half transducer diameter.

What is the beam diameter at 2 near zone lengths?

Beam diameter equals transducer diameter

What is the beam diameter deeper than 2 near zone lengths?

Beam diameter is wide than transducer diameter.

What characteristics of a fixed focus transducer determine the focal depth?

Transducer diameter, frequency of the sound.

How does transducer diameter affect the focal depth?

Transducer diameter and focal depth are directly related.

How does frequency affect focal depth?

Frequency and focal depth are directly related.

How does frequency affect focal depth?

Frequency and focal depth are directly related.

Factors that affect shallow focus?

Smaller diameter PZT

Lower frequency

Factors that affect deep focus?

Larger diameter PZT And higher frequency.

What is beam divergence?

The gradual spread of the ultrasound beam in the far field.

What characteristics of a transducer determine the spread of the beam in the far field?

1. Transducer diameter

2. Frequency of the sound

How does transducer diameter affect beam divergence in the far field?

Smaller diameter crystals create more divergent beams. Larger diameter crystals create less divergent sound beams in the far field.

Factors that affect beam divergence

Less divergence= larger diameter, higher frequency.

More divergence= smaller diameter, lower frequency.

Which of the following explains why a sound beam created by a disc-shaped crystal is hourglass shaped?

Huygens principle.