Chapter 3

Question 1

Period (P or T)

Answer 1

the duration of a cycle; one compression and one rarefaction
Units = typically microseconds
Typical value is .5 to .066 µsec
Determined by sound source

Question 2

Frequency (ƒ)

Answer 2

the number of cycles that occur in one second
Units = MHz or million of cycles per second
Typical value is 1 to 15 MHz
determined by the sound source

Question 3

ultrasound

Answer 3

Sound with frequencies > 20kHz (20,000 Hz) cannot be heard by man

Question 4

Audible sound

Answer 4

Sound with frequencies of 20Hz - 20KHz (20,000 Hz)

Question 5

infrasound

Answer 5

Sound with frequencies < 20 Hz cannot be heard by man

Question 6

Amplitude

Answer 6

the difference between the maximum value and the average value of an acoustic variable
Units: Pa (pressure), kg/cm3 (density), mm (particle motion)
determined by the sound source
output power or transmit power knob

Question 7

Power

Answer 7

the rate of energy transfer in the beam
Units = watts
Typical value 4-90 mwatts
determined by the sound source
power output/transmit power knob

Question 8

the change in power is proportional to the change in amplitude squared

Answer 8

power ∝ amplitude2

Question 9

Intensity

Intensity W/cm2 = power (W)/ area (cm2)

Answer 9

The power in the beam divided by the cross sectional area of the beam
Units = W/cm2
Typical values = .01-300 W/cm2
determined by the sound source
power transmit knob

Question 10

Amplitude, power, and intensity are directly related

Answer 10

Intensity ∝ Power
Intensity ∝ Amplitude2

Question 11

Wavelength (λ)

Answer 11

is the length of a single cycle
Units: mm
Typical values: .15-.77 mm
determined by both the sound source and the medium

Question 12

Propagation Speed (PS) (c)

Answer 12

is the distance that a sound wave travels through a medium in 1 second or other unit of time (rate of travel)
Units: mm/µs, m/s
Typical values: In the body the speed of sound ranges from 500 to 4000 m/s
determined by the medium

Question 13

Common PS of biologic tissue

Answer 13

Lung 500 m/s
Fat 1450 m/s
Soft Tissue 1540 m/s
Liver 1560 m/s
Blood 1560 m/s
Muscle 1600 m/s
Tendon 1700 m/s
Bone 3500 m/s

Question 14

Stiffness

Answer 14

is the ability of the material to resist compression
Another word for stiff = bulk modulus
A non-stiff material can also be described as compressible or elastic

Question 15

Density (mass per volume)

Answer 15

describes the relative weight of a material