Sound We Don’t Hear Pt.1

Question 1

Frequency

Answer 1

number of cycles in a wave in 1 sec

Question 2

Rarefactions

Answer 2

Low pressure and low density

Question 3

Compressions

Answer 3

High pressure and high density

Question 4

Longitudinal wave

Answer 4

compressional wave with back and forth particle motion that is parallel to the direction of wave travel

Question 5

Acoustic variables

Answer 5

Pressure
Density
Particle motion

Question 6

Frequency units

Answer 6

Hz
kHz
MHz

Question 7

Infrasound

Answer 7

Less than 20 Hz
Too low for human hearing

Question 8

Ultrasound

Answer 8

20,000Hz or higher

Question 9

Human hearing

Answer 9

20-20,000Hz

Question 10

Period (T)

Answer 10

Time it takes for one cycle to occur

Question 11

Duty factor

Answer 11

percentage of time that pulsed ultrasound is on

Question 12

The relationship between period and frequency

Answer 12

Period decreases and frequency increases

Question 13

Wavelength (cycle length)

Answer 13

the length of space one cycle takes up from front to back

Question 14

Propagation speed (c)

Answer 14

The speed a wave moves through a medium

Question 15

What does wavelength depend on?

Answer 15

It depends on frequency and propagation speed.

Question 16

Detailed resolution improves with…

Answer 16

Increasing frequency because the wavelength decreases

Question 17

Propagation speed is determined by…

Answer 17

Stiffness of the medium

Question 18

Stiffness

Answer 18

Resistance of a material to compression

Question 19

Propagation speeds are highest in..

Answer 19

Solids

Question 20

Propagation speed is lowest in..

Answer 20

Gases

Question 21

Harmonics

Answer 21

Frequencies that are even and odd multiples of the fundamental frequency.

Continuous wave

Nonlinear propagation

Question 22

Nonlinear propagation

Answer 22

Higher pressure portions of the wave travel faster than lower pressure portions

Question 23

Average longitudinal propagation speed in soft tissues

Answer 23

1540 m/s

Question 24

Fundamental frequency

Answer 24

Original frequency

Question 25

Continuous wave

Answer 25

Cycles repeat indefinitely

Question 26

Pulsed ultrasound

Answer 26

Pulses separated by gaps in time

Question 27

Pulses

Answer 27

a few cycles that travel together, separated by gaps in time

Question 28

2 components of pulsed US

Answer 28

Transmit time (send,on) Receive time (listening, off)

Question 29

Pulse Repetition Frequency (PRF)

Answer 29

number of pulses that occur in 1 sec

Question 30

Pulse Repetition Period (PRP)

Answer 30

the time from the beginning of one pulse to the beginning of the next Includes pulse duration and listening time

Question 31

The PRP ____ while PRF increases. Why?

Answer 31

decreases. When more pulses occur in a second, the time between them decreases.

Question 32

Pulse duration

Answer 32

the time it takes for one pulse to occur 

Question 33

How does the number of cycles and frequency affect pulse duration?

Answer 33

Pulse duration decreases when number of cycles in a pulse is decreased or if the frequency is increased (reducing T)

Question 34

Which pulse durations improve image quality?

Answer 34

Shorter

Question 35

What affects the duty factor?

Answer 35

Longer pulses increase DF because the sound is on more of the time.

Question 36

What increases DF? Why?

Answer 36

Higher PRFs because there is less listening time between pulses

Question 37

What happens when DF increases?

Answer 37

Pulse duration increases

Question 38

What happens when PRF increases?

Answer 38

PRP decreases and DF increases

Question 39

What happens when wavelength decreases?

Answer 39

Frequency increases

Question 40

What happens when frequency is increased?

Answer 40

Period is decreased, reducing pulse duration

Question 41

Spatial pulse length

Answer 41

the length of a pulse from front to back

Question 42

What increases spatial pulse length?

Answer 42

wavelength and the number of cycles in a pulse

Question 43

With SPL what improves resolution?

Answer 43

Shorter pulse lengths

Question 44

Bandwith

Answer 44

a range of frequencies

Question 45

Which bandwidth has a large range of frequencies?

Answer 45

Broad

Question 46

Which pulses have a broad bandwidth?

Answer 46

Short pulses

Question 47

Fractional bandwidth

Answer 47

bandwidth divided by operational frequency

Question 48

Wavelength is the length of ____ over which one cycle occurs.

Answer 48

space

Question 49

The ___ and ___ of a medium determine propagation speed.

Answer 49

density, stiffness

Question 50

Propagation speed increases if ____ is increased.

Answer 50

stiffness

Question 51

Classifications of matter in order of increasing sound propagation speed

Answer 51

gas, liquid, solid

Question 52

Wavelength in soft tissues ___ while frequency increases.

Answer 52

decreases

Question 53

Propagation speed in bone is ____ that in soft tissues.

Answer 53

higher than

Question 54

Sound travels faster in ____.

Answer 54

solids

Question 55

Solids have higher propagation speeds than liquids because they have greater _____.

Answer 55

stiffness

Question 56

Sound travels most slowly in _____.

Answer 56

gases

Question 57

Sound is a ______ _______ wave.

Answer 57

mechanical longitudinal