Describing Sound Waves Flashcards
describes features of a sound wave
parameters
seven parameters that describe sound waves
period frequency amplitude power intensity wavelength speed
time it takes for a wave to vibrate a single cycle
time from start of one cycle to the start of the next cycle
period
number of particular events that occur in a specific duration of time
frequency
source of a sound wave
ultrasound system and transducer
tissue through which sound is traveling
medium
Period Units? Typical values? Determined by? Adjustable?
units of time
0.06 - 0.05 microseconds
sound source only
no
Frequency Units? Typical values? Determined by? Adjustable?
units per second, Hz, hertz
2 - 15 megahertz
sound source
no
frequency of infrasound
less than 20 Hz
frequency of audible sound
between 20 Hz and 20 kHz
frequency of ultrasound
greater than 20 kHz
What is the relationship between period and frequency?
inversely related
reciprocals
the 3 bigness parameters
intensity
power
amplitude
Amplitude Units? Typical values? Determined by? Adjustable?
units of pressure (pascals), density (g/cm3), or distance (cm, in)
1 - 3 MPa
sound source
yes
measured from the baseline to the maximum or minimum value
difference between max value and undisturbed value of an acoustic variable
amplitude
difference between max and minimum values of an acoustic variable
2x the amplitude
peak-to-peak amplitude
Power Units? Typical values? Determined by? Adjustable?
watts
4 to 90 milliwatts
source
yes
how are amplitude and power related
power is proportional to amplitude squared
Intensity Units? Typical values? Determined by? Adjustable?
W/cm2
0.01 - 300 W/cm2
sound source
yes
how do we calculate intensity (w/cm2)
power (w) / area (cm2)
How is intensity related to power?
directly related
how is intensity related to amplitude?
intensity is directly related to amplitude squared
Wavelength Units? Typical values? Determined by? Adjustable?
units of length
0.1 - 0.8 mm
source and medium
no
What are the similarities / differences between wavelength and period?
they both describe a single cycle in a sound wave
period refers to the time it takes to complete a single cycle
wavelength refers to the length or distance of a single cycle
What is the relationship between wavelength and frequency?
inverse
Formula used to find the wavelength of a sound wave in soft tissue.
wavelength = 1.54 / frequency
Why is wavelength important in diagnostic ultrasound?
shorter wavelengths are greater by high frequencies (high quality image)
sonographers should try to use high frequency transducers for this reason
Speed Units? Typical values? Determined by? Adjustable?
mm/us or any distance/time
500 to 4000 m/s
medium
no
speed in soft tissue
1.54 mm/us
1540 m/s
1.54 km/s
speed of sound formula
speed = frequency x wavelength
2 characteristics that determine the speed of sound in a medium
stiffness
density
ability of an object to resist compression
stiffness
relative weight of a material
density
How does stiffness affect speed?
directly related
How does density affect speed?
inversely related
another term for stiffness
bulk modulus
2 words that describe the opposite of stiff
elasticity
compressibility
rate of energy transfer or the rate at which work is performed
power
concentration of energy in a sound beam
intensity
distance or length of one complete cycle
wavelength
