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Select All piezoelectric effect describes a property of certain materials to create an electrical voltage when they are mechanically deformed (when pressure is applied) during transmission when does reverse piezoelectric effect occur? during reception when does the piezoelectric effect occur? reverse piezoelectric effect during transmission voltage to transducer causing the crystals to vibrate and sound energy is created piezoelectric effect during reception reflected sound pulse is received by transducer causing crystal to vibrate and electricity is created quarts, rochelle salts, and tourmaline what are the natural ferroelectric (piezoelectric) materials barium titanate, lead metaniobate, lead titanate, lead zicronate titanate or PZT what are the man made ferroelectric (piezoelectric) materials ceramic, active element or crystal PZT is also called? transducer what converts one form on energy to another? ultrasound transducer what converts electrical energy into sound (acoustic) energy curie point (or curie temperature0 what is the temperature at which PZT is polarized to attain piezoelectric properties called? approx 360 C or 680 F what is the approximate numerical temperature for curie point? depolarized forever what happens if a PZT is heated above curie point? No (they melt) can we heat sterilize or autoclave (pressure heat) transducers? sterilization the complete destruction of all living microorganism by means of exposure to heat, chemical agents or radiation sterile probe cover what is used for proper sterile techinque No should transducers be sterilized using dry or moist heat? disinfection refers to the application of a chemical agent to reduce or eliminate infectious organisms on an object (txdr); killing of bacteria T-spray and Cidex gluterdehyde what cold germicides are used on transducers? PZT, case, wire, matching layer and damping element what are the 5 key elements of a transducer? PZT (active element, crystal) what is 1/2 the pulse's wavelength thick? case what protects the internal components and insulates patient from shock? wire what is needed for transmission and reception; one for each crystal? matching layer portion of the transducer between crystal and skin; decreases reflections at PZT and skin boundary allowing more sound to enter the body matching layer what is 1/4 wavelength thick damping element (backing material) rubber material that is attached to the back side of the active element that limit's the ringing of the PZT damping element (backing material) what is made of epoxy resin impregnated with tungsten? shortens SPL, shortens pulse duration and decreases transducer sensitivity what are damping element characteristics? (3) PZT, matching layer, gel, skin what is the decreasing order of impedances ? radiofrequency shield what reduces noise level and enhances sensitivity to weak signals? radiofrequency shield what is placed around the crystal and backing material to reduce the electromagnetic interference? bandwidth what is the range of the number of frequencies between the highest and lowest frequency emitted from the transducer? bandwidth max freq- min freq = ? natural frequency, primary, resonant and center the main frequency emitted by the transducer is also called what? (4 names) Quality factor (Q factor) unitless number representing the degree of dampening inversely how are dampening and quality factor related? Low "Q" are imaging trandsducers high or low "Q"? Q factor center frequency (MHz) / Bandwidth (MHz) = Q factor the number o fcycles in a pulse of an imaging transducer is aprox the same as what? continuous wave and therapeutic what kinds of transducers do not require damping material? continuous wave and therapeutic transducers imaging transducers have a lower Q factor and a wider bandwidth than what? continuous wave transducer the frequency of the voltage is applied to the crystal by the systems electronics, equals the sound waves frequency for what kind of transducer? pulsed wave transducers what transducer is determined by propagation speed and the thickness of the crystal? 4-6 mm/ nano sec (us) what is the typical sound speed of a pulsed wave transducer directly how is sound speed related to frequency in a pulsed wave transdcuer? thickness of the crystal in pulsed wave transducers, what is half the wave lenght? inversely how are thickness of crystal and frequency related in a pulsed wave transducer? focus (focal point) the location where the sound beam reaches it's minimum diatmeter; also the point of maximum intensity focal depth the distance from the transducer face to the focus focal depth aka focal length or near zone length near zone the region or zone between transducer and focus near zone aka Frensel zone near zone where do sound beams converge? at the end of the near zone where is the sound beams diameter 1/2 half of the transducer aperature? far zone region or zone beyond the near zone far zone aka Fraunhofer zone far zone where do sound beams diverge? focal zone region or zone surrounding the focus where the beam is narrow and the image is relatively good transducer diameter and frequency focal depth is determined by what 2 factors? deeper the bigger the transducer diameter, the ______ the focus deeper the higher the frequency , the _____ the focus inversely how are diameter and frequency related to far zone (divergence)? Huygen's wavelet diffraction described as v- shaped or spherical waves Huygen's principal principle stating that one large PZT is made up of multiple tiny PZT's each producing a diffraction pattern where waves interfere and produce and hour glass shaped beam Longitudinal, axial, range, radial and depth what does LAARD stand for? (axial resolution) resolution the ability to image acurately axial resolution the ability to distinguish two structures that are close to each other front to back (ant to post), parallel or along the beams axis mm, cm, etc. (distance) resolution is measured in units of? low number what kind of numbers do we want to accurately image reflectors that are very close together? smaller short pulses produce _______ numerical values for LAARD resolution change to transducer with a shorter pulse or to a transducer with a higher frequency how do we produce shorter pulses? 2-4 transducers are designed to have ______ cycles per pulse 0.05-0.5mm what are the typical values for LAARD resolution? Lateral resolution measure's detail in an image lateral, angular, transvers, azimuthal what does LATA stand for (lateral resolution) lateral resolution can distinctly identify two structures that are side by side or perpendicular beam diameter (mm) lateral resolution (mm) = ? at focus only where is lateral resolution optimal? it can not accurately differentiate what happens when the beam width is wider than the distance between reflectors? wider US pulses are ____ than they are short conventional and mechanical what are the other names for fixed focus external (lens), internal (curved PZT crystal) and adjustable or electronic focus what are the 3 types of focus Phased array adjustable focusing or multi focusing is called what? adjustable or elctronic what type of focusing has the best LATA resolution? single crystal transducers what type of transducers are always fixed? narrower waist, decreased focal depth and a reduction in size of focal zone focusing results in what? inversely how is focusing related to focal zone? shorter pulses, less divergence in far feild, narrower beams in far feild, high frequency improves image what are the advantages of using high frequency pulsed sound?