REVIEW chap 9 sound beams

The frequency of a transducer does not change. If the diameter of the new PZT crystal increases, what happens to the near zone length?

Increases

The frequency of a transducer does not change. If the diameter of the new PZT crystal increases, what happens to the beam diameter in the far zone?

Decreases

• bigger crystal → less divergence → smaller diameter in far zone

The frequency of a transducer does not change. If the diameter of the new PZT crystal increases, what happens to the wavelength?

No change

• wavelength depends on frequency & propagation speed

The frequency of a transducer does not change. If the diameter of the new PZT crystal increases, what happens to the beam diameter in the near zone?

Increases

• near zone = transducer size

• larger crystal = starts out wider

At what location is the sound beam diameter three times greater than the transducer diameter?

A. At the end of the near zone

B. At a depth equal to four focal lengths

C. At the end of the far zone

D. At the triple-diameter depth

B. The only region where the beam diameter exceeds the transducer diameter is at depths exceeding two focal lengths.

• >2 focal lengths → beam larger than transducer

• 4 focal length → 3x transducer diameter

What is the shape of a sound beam created by a tiny piece of PZT?

A. . Hourglass shaped

B. V shaped

C. Round

D. Shaped like a tube

B. A small piece of PZT creates a sound beam that is V-shaped. This wave is also called a diffraction pattern or Hyugens’ wavelet

• tiny = V = diffraction

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

A. Bernoulli’s Principle

B. Sheffield’s Law

C. Ohm’s law

D. Huygens’ Principle

D. Huygens’ Principle

Which of the following locations is the deepest?

A. End of the Fresnel zone

B. End of the focal zone

C. End of the Fraunhofer zone

D. End of the near zone

C. The end of the Fraunhofer zone identifies the deepest part of a sound beam.

• fraunhofer = far zone

Which of the following locations is the most shallow?

A. Beginning of far zone

B. Beginning of focal zone

C. Focal depth

D. Beginning of fraunhofer zone

B. Of these choices, the beginning of the focal zone is the most shallow

• beginning of focal zone is closest to the transducer