chapter 9

focus (focal point)

location where the bean is narrowest

near zone (fresnel or near field)

region from the transducer to the focus, sound beam converges

focal length (near zone length)

the distance from the transducer to the focus

far zone (fraunhofer)

region that starts at the focus and extends deeper, sound beam diverges

focal zone

region around the focus where the beam is relatively narrow

focal point (focus)

location where the beam reaches its minimum diameter, where beam is the narrowest

at the transducer

beam diameter equals transducer diameter

at the focus

beam diameter is one half the transducer diameter

at two near zone lengths

beam diameter equals transducer diameter

deeper than two zone lenghts

beam diameter is wider than transducer diameter

focal depth ____ change beam profile

does

fixed focus transducers have two factors that determine thefocal length

transducer diameter and frequency of sound

transducer diameter and focal depth are

directly related

frequency and focal depth are

directly related

shallow focus

small diameter, low frequency

deep focus

large diameter, high frequency

higher frequency creates

deeper focus

sound beam divergence

the spread of the ultrasound beam in the far field

two factors combine to determine beam divergence

transducer diameter and frequency of the sound

crystal diameter and beam divergence are

inversely related

less divergence

larger diameter, higher frequency

more divergence

smaller diameter, lower frequency

frequency and beam divergence are

inversely related

huygen's principle

explains the hourglass shape of an imaging transducer's sound beam

the hourglass shape of a sound beam is the result of the

constructive and destructive interferences

frequency of a pulse wave is determined by

thickness and the speed of sound in the element

focal length is determined by

diameter of the element and the frequency

divergence is determined by

diameter of the element and the frequency

what is the shape of a sound beam created by a tiny piece of PZT

v-shaped

which location is the deepest?

end of the fraunhofer zone

which location is the shallowest?

beginning of the focal zone

at what location is the sound beam diameter three times greater than the transducer diameter?

at the depth equal to four focal lengths

The frequency of a transducer does not change. If the diameter of the new piezoelectric crystal increases, what happens to the beam diameter in the near zone?

it increases

the frequency of a transducer does not change. If the diameter of the new piezoelectric crystal increases, what happens to the beam diameter in the far zone?

it decreases

the frequency of a transducer does not change. if the diameter of the new piezoelectric crystal increases, what happens to the wavelength?

no change

the frequency of a transducer does not change. if the diameter of the new piezoelectric crystal increases, what happens tot eh beam diameter in the near zone?

it increases

divergence is mostly pronounced with

small diameter and low frequency probes

divergence is minimally pronounced with

large diameter and high frequency

shorter focal lengths are associated with

small diameter and low frequency

longer focal lengths are associated with

large diameter and high frequency

diameter and near zone length are

directly related

frequency and near zone length are

directly related

wavelength and near zone are

inversely related

at the beginning, the sound beam diameter is

the same as the diameter as the active element

at the end of the near zone, the beam diameter is

half the transducer diameter

what depth is the focus?

the same as the length of the near zone