physics chapter 3

Describes features of a sound wave

parameters

How many parameters are there?

7

what is the source of a sound wave?

ultrasound system and transducer

The time it takes for a wave to vibrate a single cycle, or the time from the start of one cycle to the start of the next cycle.

Period

Units for period:

units of time

what is a period determined by?

Sound source only

Is the period adujustable?

No

Typical values for period:

0.06 to 0.5 microseconds

how else can be 0.06 microseconds be written

6 x 10^ -8 or 0.00000006

The number of cycles occurring per second

frequency

units for frequency:

units per second; 1/second, hertz, or Hz

1 cycle/ second =

1 Hertz (Hz)

1 kHz =

1,000 cycles/second

1,000,000 cycles/second

1 MHz

typical values of frequency:

2MHz to 15 MHz

Frequency of a sound wave is determined by the ______.

sound source only

Is frequency adjustable by the sonographer?

no

Less than 20 Hz

infrasound

between 20 Hz and 20 kHz

audible sound

greater than 20 kHz

ultrasound

what is frequency considered too low for humans to hear

infrasound

what frequency is considered for hearing

audible sound

what frequency is considered too high for humans to hear

ultrasound or ultrasonic

What is the relationship between frequency and period?

inversely related

Why is frequency important in sonography?

it affects penetration and image quality

as frequency increase, period...

decreases

as frequency decrease, period...

increases

If one of these parameters (period/frequency) remain constant then the other...

remains unchanged

period and frequency are..

reciprocals

Period x Frequency = ?

1

(reciprocal relationship)

p= 1/____?

1/f

f=1/_____?

p

what three parameters describes the size, magnitude, or strength of a sound wave:

Amplitude, power, intensity

The maximum or minimum deviation from the average; the maximum variation that occurs

amplitude

What is the unit of amplitude

pressure, density, particle motion

Typical values of amplitude

1MPa-3MPa

what unit is Pa

pascal

Amplitude can also be expressed in...

decibels (dB)

Amplitude is determined by...

initially the sound source

amplitude then _________ as sound propagates through tissue

decreases

Is amplitude adjustable by the sonographer?

yes

Amplitude is measured from the....

middle/ undisturbed value to the maximum value

peak to peak amplitude the difference between...

maximum and minimum values of an acoustic variable

Peak-to-peak amplitude is _____ the value of the amplitude.

twice

the rate at which work is performed, or energy is transferred

power

what is the unit of power?

watts

what is the typical values of power:

0.004 to 0.090 watts

how else can you write 0.004 watts

4mW

how else can you write 0.090 watts

90 mW

what is power deterimined by?

initially the sound source

Power then _________ as sound propagates through tissue

decreases

Is power adjustable by the sonographer?

yes

what is the relationship between power and amplitude?

directly related

when power increases, amplitude...

increases

when power decreases, amplitude....

decreases

power is always proportional to..

amplitude squared

the concentration of energy in a sound beam.

Intensity

what are the units of intensity?

W/cm^2

what are the typical values of intensity?

0.01 to 300 W/cm^2

What is intensity determined by?

initially the sound source

intensity then _____ as sound propagates through tissue

decreases

What is the relationship between amplitude, power, and intensity?

directly related

Amplitude is always..

squared

intensity (W/cm^2) =

power (w) / area (cm^2)

The length of a single cycle; the distance from the beginning of a cycle to the end of that cycle

wavelength

What are the units for wavelength?

any unit of length (mm, meters)

what are the typical values for wavelength?

0.1-0.8 mm

What is wavelength determined by?

Both the source and the medium

Can wavelength be adjusted by the sonographer?

no

What is the difference between period and wavelength?

period is a unit of time, wavelength is a unit of distance

What is the only parameter that is determined by both the source and the medium?

wavelength

What is the relationship between wavelength and frequency?

inversely related

wavelength (λ) =

c / f (c = propagation speed ) (f=frequency)

if the wavelength increase the frequency...

decreases

if the wavelength decreases the frequency...

increases

a frequency of 1 MHz has a wavelength of...

1.54mm

a frequency of 2MHz has a wavelength of...

0.77mm

what is the equations for finding the wavelength in soft tissue?

λ(mm) = 1.54mm/ µs divided by f (MHz)

The rate at which a sound wave travels through a medium

propagation speed

what units are used for propagation speed?

meters per second (m/s)

what are the typical values for propation speed?

550 m/s- 4000 m/s

what determines propagation speed?

medium only

is propagation speed adjustable by the sonographer?

no

What is the only parameter that is determined solely by the medium?

propagation speed.

What is the speed of sound in soft tissue?

1540 m/s

if you have increased stiffness, your speed...

increases

if you have increased density, your speed...

decreases

what material has the slowest speed of sound

air/ gases

what material has the fastest spped of sound

solids

what organ has the slowest speed of sound?

lungs

what part of the body would have the fastest speed of sound

bone

the ability of an object to resist compression

stiffness

how are stiffness and speed related

directly

bulk modulus relates to

stiffness

how are density and speed related

inversley