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vibrate
sound waves cause molecules to ______
medium
sound needs to pass through a ______ (solid, liquid, gas)
longitudinal and transverse
types of sound waves
longitudinal wave
parallel to sound wave, pass through liquids and solids, doesn’t work on bone
transverse wave
perpendicular to sound wave, pass through solids but not liquids
cylindrical
what shape beam does the sound head produce?
3 cm
how deep does 3 MHz go?
5 cm
how deep does 1 MHz go?
more focused
the larger the sound head, the ________ the beam
when beams pass through tissue
when does divergence occur?
the crystal in the sound head
what propagates sound?
reflection, refraction, absorption
three types of scattering
reflection
wave strikes and reverses direction, happens when there is no medium
refraction
wave bends, happens when there is a damaged crystal
absorption
transfer of energy, less energy is transmitted by each layer of skin as it goes deeper and deeper
hot spot
caused by a standing wave
large amount of heat absorption
standing wave - reflected sound waves and new sound waves coming into contact and lead to a _________
move sound head continuously, not too slow
how to avoid hot spots?
16-20 kHz
audible sound frequency
20 kHz
greater than _____ is ultrasound
less
higher frequency » ____ divergence
more
lower frequency » ____ divergence
superficial tissue
when to use a higher frequency?
use medium, keep head directly on skin
how to reduce scattering?
acoustical impedance
determines the amount of energy that will be scattered or absorbed at different boundary levels
deep tissue
when to use a lower frequency?
Note 
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