Physics Exam #1 Flashcards
what is wavelength? what’s parameters? what’s wavelength equation?
wavelength = propagation velocity / frequency
it is a distance so it is in mm
*or any other distance related unit
what is period? what’s parameters? what’s equation for period?
period equals 1 over the frequency
5 Hz = 1/5Hz = 1 / 5 = .2 seconds
what is frequency? what’s parameters?
it is a rate so needs a _______per________.
ex. cycles per second.
cycles per second is a Hertz, or Hz. Hz is the unit in US.
how does wavelength, period, and frequency affect the wave?
what’s difference between rarefactions and compressions?
what determines propagation speed of sound in the medium?
what’s propagation velocity for soft tissue
how do the properties of the medium affect the speed of sound: density, stiffness, compressibility, bulk modulus…
define density
define stiffness
define compressibility
define bulk modulus
explain: what is propagation through a medium and what determines the speed?
speed of sound order of various media
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Air, Lung, Fat, Water, Liver, Blood, Kidneys, Muscle, Skull
what is attenuation
attenuation is
defined as a decrease in wave
amplitude (or intensity) due to
the mechanical interaction with
the medium
represents a transfer
of energy through absorption and
scattering represented by
reflection and refraction.
what is attenuation coefficient for soft tissue
the degree of sound beam attenuation in
a tissue is usually given in decibels per
centimeter (dB/cm)
Soft Tissue Attenuation Rate:
0.5dB/cm/MHz
attenuation coefficient is one half of the frequency (0.5)
Attenuation coefficient is the amount of attenuation per
centimeter per MHz
Attenuation coefficient is the # of decibels
of attenuation that occurs when sound
travels one centimeter.
what affect does increasing the frequency of a sound wave have on attenuation?
Attenuation coefficient is the # of decibels
of attenuation that occurs when sound
travels one centimeter.
For each centimeter that sound travels more
energy is lost from high frequency sound than
from low frequency sound.
Its units are dB/cm
what is the biggest factor in attenuation?
absorption
the foundation for US is
reflection
high frequency =
high attenuation
low frequency =
low attenuation
The angle that a sound wave
approaches the boundary
between two different types of
mediums helps determine
whether __________, ___________, or _________ will occur.
transmission, reflection, or refraction
what is the angle of incidence?
The angle at which a
sound wave approaches a boundary
what is the angle of transmission?
The angle at which it continues on
past the boundary
what is the angle of reflection?
The angle at which the sound wave
reflects back to the transducer (after
striking the boundary)
“normal incidence” of an angle is exactly equal to how many degrees
90 degrees
The angle at which the
wave strikes the
boundary determines
the behavior (of the pulse)
Oblique incidence
occurs when
the incident sound beam strikes
the boundary at any angle other
than 90º
If reflection occurs the incident
angle equals the
reflected angle, WHATEVER IS NOT TRANSMITTED MUST BE REFLECTED
The strongest echoes are produced when the
angles of incidence approach the angle of reflection.
define acoustic impedance
property of tissues that influences the strength or amplitude of reflected echoes in a quantity
Z=ρc
ACOUSTIC IMPEDANCE
The acoustic impedance of a
material is equal to the product of
the medium’s density and its
speed of sound
(Acoustic impedance is a measure of the ease or difficulty with which
a sound wave propagates through a particular medium)
the unit for acoustic impedance is called
1 Rayl = kg/m²sec
2 media have identical impedances…
NO or LITTLE reflection
2 media have substantially different impedances…
LARGE reflection
explain acoustic impedance in a paragraph
Lets take 100 (we will call this our “incident”
marbles) marbles throw them at a paper wall,
while the marbles are rolling through the air
there is no reflection. Air is homogenous
therefore there is no change in impedance,
no reflection
Now we will throw them at a hard paper wall
hard enough that 20 of the marbles come
back toward us (Our reflected marbles) and
80 go through the paper. (Our transmitted
marbles) This represents a difference (a
mismatch) in impedance relative to the air
incident Intensity is (marble idea approach here)
the sound waves
intensity immediately
before it strikes a
boundary
Reflected Intensity (marble idea approach here)
is the
intensity of the portion of
the incident sound beam
that after striking a
boundary returns back
where it came from.
transmitted intensity (marble idea approach here)
is the intensity of the
portion of the incident
beam that after
striking a boundary
continues forward in
the same direction that
it was traveling
acoustic impedance media from smallest to highest
air
lung
fat
water
liver
blood
kidney
muscle
skull bone
air
lung
fat
water
liver
blood
kidney
muscle
skull bone
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