Quizzes Before Midterm

Question 1

Why is sound almost entirely reflected at a soft tissue:air interface?

Answer 1

The impedance mismatch is too large.

Question 2

In order for refraction to occur, what 2 conditions must be met?

Answer 2

Oblique incidence & different propagation speeds

Question 3

T or F
The propagation speed for medium 1 is 1,250 m/s. the propagation speed of medium 2 is 1,500ms. Reflection will def occur.

Answer 3

False. We don’t know the impedances or the type of incidence to answer the question

Question 4

A sound pulse travels through medium 1 and strikes an interface with another tissue, medium 2 at 35 degrees. The angle of transmission is 40 degrees. From these facts alone what can we say about the speed of sound in medium 1?

Answer 4

The speed of sound in medium 1 is less than. The speed of sound in medium 2.

Question 5

A sound wave strikes a boundary at 90 degrees. The impedances are identical. What % of sound is reflected?

Answer 5

There is n reflection because the impedances must be different for reflection to occur. 0%

Question 6

Synonyms for normal incidence

Answer 6

Normal incidence
Perpendicular incidence
Orthogonal
90 degrees

Question 7

An angle of less than 90 degrees is called an ______ angle

Answer 7

Acute

Question 8

If the intensity reflection coefficient is 40% what is the intensity transmission coefficient ?

Answer 8

ITC= 60%

Question 9

The incident intensity of the beam must equal the _______ intensity plus the ______ transmitted intensity.

Answer 9

Reflected+ transmitted

Question 10

In order for reflection to occur what 2 conditions must be met?

Answer 10

Normal incidence

Different impedances

Question 11

A a soft tissue: air interface, what percent of sound is transmitted?

Answer 11

0%

Question 12

Sound travels through a tissue at Norma incidence and strikes a boundary. The incident intensity is 100 mW/cmsq. If the reflected intensity is 0 mW/cmsq, what can we say about Medium 2?

Answer 12

Impedances are the same so there was no reflection.

Question 13

Sound travels obliquely through a soft-tissue at a 30 degree angle and strikes a boundary. Assuming reflection Occurs, what is the angle of reflection?

Answer 13

Angle of reflection = the incident angle. So 30 degrees = 30 degrees.

Question 14

Increasing the Doppler angle ______ the risk for aliasing?

Answer 14

Decreases

Question 15

Fast Fourier transform is used for Doppler processing because…

Answer 15

It is slow but accurate

Question 16

At what angle is the Doppler shift at a maximum?

Answer 16

0 degrees.

60 degrees is the highest angle you are premitted to use due to error, but that is not what the question asked for.

Question 17

Sound travels through 3cm of fat, 2.5 cm of muscle, and 5 cm of fluid. If the attenuation coefficient (Ac) at 10. Cm is 1.25 dB/cm, what is the frequency of the transducer used?

Answer 17

F = Ac(2)
F = (1.25)(2) = 2.5 MHz