C5: Huygen's Principle and Wave interference Flashcards
what is a sine wave
a symmetrical wave that describes the movement of something over time
how is an US wave created?
its created by many individual waves that come from their own source and combine to form a wavefront
what are the point sources of individual wavelets called
huygens sources
what is the name for the waves that are emitted from the huygen sources
huygen wavelets
what does the rate of divergence of a huygen wavelet depend on
the size of the source
define divergence
the spreading of the sound beam as it travels
how are the rate of divergence and the size of the source related
smaller source = larger divergence
inversely
define diffraction
diffraction occurs after a beam with planar wavefronts pass through a small aperture (see picture)
what is huygens principle
each point source creates its own sound wave or beam… these multiple wavelets from different sources join together to form a wavefront
when is it important to consider huygens principle
when designing probes… specifically for resolution and sensitivity
what is interference, when does it occur
it occurs when 2 or more waves interact…
it is the adding of the motion of one wave to another
2 types of interference
constructive
destructive
what 2 wave parameters does interference effect
uniformity and amplification
describe constructive interference
the interference of 2 wave that are in-phase… results in an increase in amplitude and intensity
describe destructive interference
the interference of 2 wave that are out of-phase… results in a decrease in amplitude and intensity, or the waves may cancel each other out
what is a beat frequency
occurs when 2 waves are neither completely in phase, nor completely out of phase
how are beat frequency and doppler related
beat frequency is what allows us to detect US doppler signals
can changes in intensity effect the sensitivity of the beam
yes
which phenomenon is responsible for giving the US beam its natural shape and natural area of focus
interference
what are standing waves
occur when 2 waves propagate in the same medium but in opposite directions… when you add these 2 waves together, you will have some points where the amplitude in zero and others where the amplitude is doubled
what are the points of minimum fluctuation called in standing waves
do they have high or low pressure
nodes
they have low pressure
what are the points of maximum fluctuation called in standing waves
do they have high or low pressure
anti-nodes
they have high pressure
what colour will the areas of nodes and anti-nodes be
nodes : black (low intensity)
anti-nodes: bright (high intensity)
how do you limit divergence
fire a groups of elements to create a larger wavefront… larger = less divergence
