describing sound waves (lecture 4)

exam 2

what are the seven parameters

period, frequency, amplitude, power, intensity, speed and wavelength

the time it takes a wave to vibrate a single cycle

period

what is the units for period

time - s, ms

what is period determined by?

ONLY the sound source. not adjustable by sonographer

what is this graph showing

period

number of particular events that occur in a specific duration of time

frequency

in ultrasound, the number of cycles that occurs in one second

frequency

how is frequency measured

units per second, herts, Hz

what is the frequency range in diagnostic us

2Mz-15Mhz

what is frequency determined by

sound source ONLY

what frequency does human hearing occur

20-20,000 hz

what frequency is called infrasound

<20 Hz

what is frequency is called ultrasound

>20,000 Hz

what is frequency important for?

image resolution and penetration

what is this graph representing

frequency

what is the relationship between period and frequency

inversely related/inversely proportional and reciprocal relationship

as frequency increases what happens to period

it decreases

when you multiply the frequency and period together, what is the result

1

the distance or length of one complete cycle

wavelength

what is the units for wavelength

mm, meters, etc

what is wavelength determined by?

source AND the medium

what type of wavelength produces higher quality images with greater detail?

SHORTER wavelength

what is this formula for

wavelength

what is this graph measuring

wavelength

what is the relationship between the frequency and wavelength

inversely related as long as they are in the same medium

what happens to wavelength as frequency increases

wavelength decreases

in 1 MHz the wavelength is _____

1.54 mm

the distance that a sound wave travels through a medium in 1 second

propogation speed

what is propagation determined by

MEDIUM ONLY

what does sound travel fastest through

solids

what does sound travel slowest through

gases

what is soft tissue prop speed

1,540 m/s

what are the two medium characteristics that affect speed

density and stiffness

what is the relationship between stiffness and prop speed

directly related — stiff medium = high prop speed

how is density and prop speed related

inversely related — more dense materials = slower prop speed

the difference between the maximum value and the average or undisturbed value of an acoustic variable

amplitude

difference between the minimum and average

amplitude

what is amplitudes units

the acoustic variable units

what are the typical values of pressure for amplitude

1 MPa to 3 MPa

what is amplitude initially determined by

the sound source but values decrease as sound propogates through the body

AMPLITUDE IS ADJUSTABLE BY SONOGRAPHER

YES!

what is this graph measuring

amplitude

the difference between maximum and minimum of an acoustic variable

peak-to-peak amplitude

rate of energy transfer

power

what is power measured by

units of watts

POWER IS ADJUSTABLE BY SONOGRAPHER

YES!!

what is power determined by

sound source, but decreases as sound propagates

what is the relationship between power and amplitude

power is equal to the amplitude squared

is the sonographer decreases the amplitude of a wave to 1/3 of its original value, the power is _____________________

decreased to 1/9 of its original value

concentration of energy in a sound beam

intensity

what is intensity equal to

power/cross sectional area

what are the units for intensity

watts/cm²

INTENSITY IS ADJUSTABLE BY SONOGRAPHER?

YES!!!

what is intensity determined by

sound source initially

intensity and power and amplitude

intensity and power are proportional, intensity is proportional to amplitude squared

know it