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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 |
Created by:
ginaliane
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