Chapter 3: describing sound waves Flashcards
Define Parameters
describe features of a sound wave.
what the seven paramets are used for?
they are values used to characterize a sound wave
list the seven parameters
PERIOD
FREQUENCY
INTENSITY
POWER
AMPLITUDE
WAVELENGTH
PROPAGATION SPEED
PETER
FELL
IN
PRACTICE
AFTER
WAVING
(AT) SALLY
PERIOD
FREQUENCY
INTENSITY
POWER
AMPLITUDE
WAVELENGTH
SPEED
source
the transducer and the ultrasound system
medium
soft tissue
period
Define
the time it takes a wave to vibrate a single cycle.
the time from the start of one cycle to the start of the next.
period
Units for period
time (seconds,microseconds
what is period determined by?
the sound source only
is period adjustable?
no
What are the seven acoustic parameters?
Frequency
period,
wavelength,
propagation of speed,
intensity,
amplitude
and power.
Frequency
the number of events that occur in a specific duration of time
in diagnostic ultrasound, the frequency of a wave is described as
the number of cycles that occur in one second
Unit for frequency
per seconds, 1/second, hertz, Hz
Hertz is another way to say
per second
Is frequency adjustable?
no
what is frequency determined by?
the sound source only
frequency for infrasound
less than 20 Hz
frequency for ultrasound
greater than 20 kHz or 20,000 Hz
frequency for audible
Between 20Hz and 20 kHz
frequency for diagnostic ultrasound
1MHz to 20MHz
Why is frequency important?
It affects the penetration and image quality
What is the relationship between period and frequency?
Period and frequency are inversely related to each other
As frequency increases, period____
decreases
As frequency decreases, period____
increases
Period and Frequency have a special relationship called….
Reciprocal
Formula for period and frequency
period x frequency =1
A wave takes up 1/8 of a second to vibrate up and down. What is the period and the frequency?
Period = 1/8
Frequency = 8
1/8x8=1`
The higher the frequency
the lower the period
which of the following waves is infrasonic?
4 Mhz
400 kHz
28 Hz
2 Hz
2 Hz
less than 20Hz cannot be heard
which wave is ultrasonic?
400 mHz
4 MHz
28 Hz
2 Hz
4 MHz
greater than 20kHz cannot be heard
indetify all which are audiable
4 MHz
400 kHz
28 Hz
2 Hz
4 MHz, 400kHz,2 Hz are all audiable
which of the following has the longest period
2MHz
4,000 Hz
6 Hz
1 kHz
6Hz
which has the highest frequency
8 s
80 µseconds
8 Ms
8000 ks
8 µseconds
The three bigness parameters
IPA
intensity
power
amplitude
Three parameters used to describe the size, magnitude, or strength of a sound wave
the three bigness parameters, Intensity, power, amplitude
define amplitude
The difference between the maximum value and the average value of an acoustic variable
which parameter defines the “bigness” of a wave
amplitude
Units for amplitude
decibels (dB) any units associated with acoustic variables
-pressure; pascals (pa)
-density; grams/cubic cm
-particle motion; units of distance
what is amplitude determined by?
sound source
is amplitude adjustable?
Yes!
what is the difference between amplitude and peak-to-peak amplitude
amplitude is measured by the MIDDLE or UNDISTURBED, value to the maximum value
Peak-to-peak amplitude
the difference between maximum and minimum values of an acoustic variable,
(twice the value of amplitude)
Power
the rate of energy transferor rate at which work is performed
power is like what other parameter? in what sense?
power is like amplitude. they both describe the “bigness” of a wave
units for power
Watts or (W)
is power adjustable?
Yes!
what is power determined by?
They are determined by the sound source`
how are power and amplitude related?
both amplitude and power describe the size or magnitude of a wave.
when power increases….. amplitude
increases
Power is proportional to the waves amplitude squared
power ∝ amplitude^2
what relationship does power and amplitude have
the are directly proportional
what happens to power if amp^2 is increased by a factor of 3
power is increased by a power of 9
what happens to power if amp^2 is decreased by a factor of 2
power is decreased by a power of 4
Intensity
The concentration of energy in a sound beam
units for Intensity
W/cm^2
what is intensity determined by?
Source
Is intensity adjustable?
Yes!
intensity relates
to how the power in a wave is spread or is distributed in a space, therefore making it dependent on power and area
Intensity is proportional to
power
Intensity (W/cm^2)=
power (w)/ area (cm^2)
intensity is proportional to
amplitude ^2
what happens to intensity if a waves power is doubled?
Intensity is also doubled
what three parameters tend to be directly related
intensity, power, and amplitude
what happens to intensity when a waves amplitude^2 is doubled
the intensity increases four times its original value.
Wavelength
The distance or length of one complete cycle
unit for wavelength
length (mm,meters,inches,feet…)
what is wavelength determined by?
source and the medium
true or false? is wavelength the only parameter determined by both source and the medium
true
is wavelength adjustable?
no
λ = c/f
wavelength (mm) = propagation speed (µs)/frequency (MHz
What is the difference between period and wavelength
-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?
wavelength and frequency are INVERSELY related. As f increases w decreases.
the lower the frequency … (wl)
the longer the wavelength
If a waves frequency is twice that of another
wavelength will be half as much
what is the wavelength of 1MHz in soft tissue?
1.54 mm
to find the wavelength in soft tissue
divide 1.54 mm by the frequency in MHz
why is wavelength important in diagnostic imaging?
shorter wavelengths are created by high frequency; resulting in higher quality images with greater detail
Propagation Speed
the rate at which sound travels through a medium
what is the unit for speed?
m/s or mm/s
what is speed determined by?
the medium ONLY
is speed adjustable?
no
what is the speed of sound in soft tissue?
1,540 m/s or1.54 mm/s or 1.54 km/s
list the speed of sound in biologic tissue
-lung
-fat
SOFT TISSUE
-liver
-blood
-muscle
-tendon
-bone
order of sound traveling
fastest to slowest
solids>liquids>gases
formula for speed
speed (m/s)= frequency (Hz) X wavelength (m)
two characteristics that affect speed
-stiffness (bulk modulus) :how squishy something is
-density; object weight/mass
what relationship do stiffness and speed have
direct relationship
the opposite of stiffness
elasticity and compressability
what relationship do density and speed have?
they are inversely related
