# Physics-Interaction of Sound and Media

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 Author: aprilh4485 ID: 115265 Filename: Physics-Interaction of Sound and Media Updated: 2011-11-09 16:48:34 Tags: Sonography Folders: Description: Interaction of Sound and Media Show Answers:

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1. A reduction in the intensity of a sound beam to one-half of its original value is _____ dB.
-3 dB
2. A reduction in the intensity of a sound beam to one quarter of its original value is _____ dB.
-6 dB
3. -10 dB means that hte intensity is reduced to _____ of its original value.
one-tenth
4. dB is a mathematical representation with a __________ scale.
logarithmic and relative
5. True or False.
We need one intensity to calculate decibels.
False
6. A wave's intensity is 2 mW/cm2. There is a change of of +9 dB. What is the final intensity?
16 mW/cm2
7. Every 3 dB change means that the intensity will _________.
double
8. Every 10 dB change means that the intensity will __________.
increase 10 times
9. If the final intensity of a sound beam is more than the initial intensity, then the gain in dB is __________ (+ or -).
positive
10. If the initial intensity of a sound beam is less than the final intensity, then the gain in dB is __________ (+ or -).
positive
11. Name the three components of attenuation.
reflection, scattering, and absorption
12. As the path length increases, the attenuation of the ultrasound in soft tissue __________.
increases
13. Attenuation in lung tissue is __________ attenuation in soft tissue. {greater than, less than, the same as}
greater than
14. Attenuation in bone is __________ attenuation in soft tissue. {greater than, less than, the same as}
greater than
15. Attenuation in air is __________ attenuation in soft tissue. {greater than, less than, the same as}
greater than
16. What are the units of attenuation?
decibels (dB)
17. True or False.
In a given medium, attenuation is unrelated to speed of sound.
True.
18. What is the relationship between ultrasound frequency and the attenuation coefficient in soft tissue?
in soft tissue, the attenuation coefficient (dB/cm) is approx one-half of the ultrasonic frequency (MHz)
19. What are the units of the half-value layer thickness?
length; centimeters
20. As frequency decreases, depth of penetration __________.
increases
21. As path length increases, the half boundry layer __________.
remains the same
22. Impedance is characteristic of __________.
only the medium
23. As the path length increases, the attenuation coefficient of ultrasound in soft tissue __________. {decreases, increases, reamins the same}
remains the same
24. Acoustic impedance = __________ x __________.
impedance = density x propagation speed
25. Two media A and B have the same densities. The speed of sound in medium A is 10% higher than in medium B. Which medium has the higher acoustic impedance?
Medium A
26. Impedance is important in __________ at boundarys.
reflections
27. Which is better to use while examining a carotid artery, a 7.5 or 3.0 MHz transducer?
7.5 MHz
28. A sound wave with intensity of 50 W/cm2 strikes a boundary and is totally reflected. What is the intensity reflection coefficient?
• 100%
• since the wave is totally reflected
29. A sound wave with intensity of 50 W/cm2 strikes a boundary and it totally reflected. What is the reflected intensity?
50 W/cm2
30. A pulse of ultrasound is propagating in soft tissue, such as liver. The pulse strikes a boundary with a different soft tissue at normal incidence. What portion of the intensity is reflected back toward the transducer? Why?
a very small percentage (less than 1%) is reflected at a boundary between two soft tissues. very little reflection occurs when the impedances have similar, but not identical, values
31. Sound is traveling in a medium and strikes a boundary with normal incidence. If 63% of the wave's intensity is reflected back toward the transducer what percentage is transmitted?
37%
32. Sound is traveling in a medium and orthogonally strikes a boundary with a different medium. Although the media are very different, no reflection is created. How can this be?
the two different media have the same impedance, and when this happens, no reflection will be created
33. Which of the following terms does not belong with the others?
A. orthogonal
B. oblique
C. normal
D. perpendicular
B oblique
34. Sound is traveling from bone to soft tissue. The impedances of the media differ significantly, and 90% of the beam's intensity is reflected. What percentage of the intensity is transmitted?
10% is transmitted
35. Sound that is traveling in Jell-O passes through an interface at 90 degrees and continues to travel in whipped cream. The impedance of Jell-O and whipped cream are nearly identical. What percentage of the intensity is transmitted?
99%
36. A pulse of ultrasound propagates in soft tissue, such as liver. The pulse strikes a soft tissue-soft tissue inerface with oblique incidence. Some of the sound energy is transmitted. To what extent is the transmitted beam refracted?
beam undergoes little to no refraction because the tissues are both soft tissues
37. A sound pulse travels in Medium 1 and strikes an interface with another tissue, Medium 2, at 30 degrees. The angle of transmission is 10 degrees. From these facts alone, what can be said about:
-the speed of sound in Medium 1
-the speed of soudn in Medium 2
-the difference between the speeds of Media 1 and 2?
nothing can be said about the speed of sound in Medium 1 and 2 but the speeds of these two mediums are very differnt because the beam is refracted significantly
38. A sound pulse travels in Medium 1 and strikes an interface with another tissue, Medium 2, at 30 degrees. The angle of transmission is 10
degrees. In which medium does sound travel slowest?
Medium 2, when the angle of transmission is less than the angle of incidence, sound travels slower in the second medium.
39. A sound pulse travels in Medium 1 and strikes an interface with another tissue, Medium 2, at 30 degrees. The angle of transmission is 10
degrees. In which medium is the impedance higher?
cannot be determined, impedances are unrelated to refraction
40. Sound travels in a medium and orthogonally strikes a boundary with a different medium. Although sound waves traveling in the media have vastly different speeds, there is no refraction. How can this be?
it has normal incidence, refraction cannot occur
41. A sound wve strikes a boundary at normal incidence. The impedances of the two media are identical. What percentage of the sound wave is refracted?
0%, refraction cannot occur with normal incidence
42. The impedance of Medium 1 is 8 rayls and the propagation speed is 1,450 m/s. The impedance of Medium 2 is 6 rayls and the propagation speed is 1.854 km/s. A sound beam strikes the boundary between the media and is both partially transmitted and reflected. The angle of the incident beam is 30 degrees. What is the reflection angle?
30, angle of reflection equals the angle of incidence

43. What does the 100 mW/cm2 stand for?
the incident intensity of the sound beam

44. What does the 3.5 dB/cm represent?
the attenuation coefficient of the sound in the media

45. If the media are soft tissue, waht is an estimate of the ultrasound frequency?
about 7 MHz, attenuation coefficient multiplied by 2 approximates frequency
46. What property ha units of rayls? How is it determined?
• Impedance, it is calculated, not measured.
• Impedance = density x speed

47. The incidence between the sound wave and the boundary between Media 1 and Media 2 is normal. What happens at the boundary between Media 1 and 2? Why?
Reflection and transmission occurs. There is normal incidence and different acoustic impedances.
48. The incidence between the sound wave and the boundary between Media 2 and 3 is normal. What happens at the boundary between Media 2 and 3? Why?
Transmission only. The impedances are the same.
49. What type of incidence is there between Media 3 and 4?
Oblique
50. What happens at the boundary between Media 3 and 4? Why?
Reflection may occur. If transmission does occur, the sound beam will refract because there are different propagation speeds and oblique incidence.
51. What processes occur as the ultrasound passes through all media? What are the units of this process?
Attenuation (scattering, absorption, and reflection) Units: dB

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