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Physics Module 2


transducer any device which converts one form of energy into another
piezoelectricity the property of certain materials to generate a voltage (electrical energy) when they are mechanically deformed
quartz Most commonly occurring natural piezoelectric material
PZT the most commonly used man-made ceramic piezoelectric material in constructing ultrasound transducers, highly efficient, stable and can vibrate at high frequencies
poling process by which a strong electric field is applied across the piezoelectric material
Curie Pont the temperature above which the piezoelectric material loses its poling (spontaneous polarization) and piezoelectric properties, 300 degrees C
electrode wires apply voltage to the crystal during transmission and detect electrical charges during reception
backing material bonded to the crystal to limit its ringing
matching layer material attached to the front face of the crystal, protects the crystal and helps with ultrasound energy transmission across the transducer/skin interface
lens used to focus the ultrasound beam
frequency cycles/second
transducer bandwidth range of frequencies above and below the main operating frequency
quality factor unitless number which represents the ability of a transducer to emit a clean (exact) frequency
sensitivity the ability of an ultrasonic system to detect reflectors (or defects) at a given depth in a test material
near field the region located between the transducer face and the point of minimum beam width (natural focus); aka Fresnel zone
far field the region deeper than the natural focus where beam divergence occurs; aka Fraunhoffer zone
natural focus area of minimum beam width
near zone length distance from transducer face to point of minimum beam width
diffraction limited the inability to focus deeper than the focal point
constructive interference occurs when the waves are in phase
destructive interference occurs when the waves are out of phase
Huygen's principle every point on a wave front is a source of wavelets, which spread forward at the same speed
axial resolution (x) SPL/2, the ability to resolve two structures that are parallel to the beam’s main axis
lateral resolution (y) beam width, the ability to resolve two structures that are perpendicular to the beam’s main axis
elevation resolution (z) slice thickness
spatial pulse length number of cycles in a pulse x wavelength
damping shortens the pulse (decreases SPL), widens the bandwidth and improves axial resolution
focusing reducing the beam width to improve image resolution
acoustic lens placed in front of a flat crystal to focus the beam
acoustic mirror concave in shape, is placed behind the flat crystal to focus and direct the ultrasound beam
curved crystal Focusing of the ultrasound beam by using a concave crystal, least common
electronic focusing delaying the central wavelets of the ultrasound beam to create a focus; aka phasing
fixed focus type of focus that cannot be changed, built into the transducer
internal focus type of focus that happens to the crystal (phasing, curved element)
external focus type of focus that happens outside of the crystal or element (lens, mirror)
weak focus produces a long narrow focal zone over a useful range in depth
medium focus produces a narrow focal zone over a limited range in depth
strong focus produces a very narrow focal zone over a small area
mechanical beam steering produced by mounting one (or more) crystal on a motor
electronic beam steering produced by phasing
sequencing groups of elements are activated in a sequence over time to scan across the imaging plane
continuous wave probe
mechanical transducer
linear array
curved array
annular array
multidimensional array
phased array
multi-zone focusing
dynamic receive focusing
side lobes
grating lobes
bulk modulus
pulse duration
pulse repetition frequency
pulse repetition period
duty factor
range equation
13 microsecond rule
pulsed wave
acoustic line
display line
frame time
frame rate
scanned modality
non-scanned modality
temporal resolution
Created by: ginaliane