click below
click below
Normal Size Small Size show me how
Physics Module 2
Vocabulary
Term | Definition |
---|---|
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 | |
apodization | |
subdicing | |
side lobes | |
grating lobes | |
density | |
stiffness | |
bulk modulus | |
temperature | |
decibels | |
pulse | |
pulse duration | |
pulse repetition frequency | |
pulse repetition period | |
duty factor | |
range equation | |
13 microsecond rule | |
pulsed wave | |
acoustic line | |
display line | |
frame | |
frame time | |
frame rate | |
scanned modality | |
non-scanned modality | |
temporal resolution |