Basic Transducers - Chapter 8 Flashcards
what is a transducer? give 3 examples
any device that converts one form of energy into another. electric motor (elec to kinetic), light bulb (elec to heat/light), speaker (elec to acoustic)
what is the piezoelectric effect?
a property of certain materials to create a voltage when pressure is applied or when the material is mechanically deformed
what is the reverse piezoelectric effect?
when certain materials deform or change shape when a voltage is applied to them
what are two categories piezoelectric materials fall under? what are some examples of each?
synthetic (man-made) - lead zirconate titanate (PZT), barium titanate, lead titanate, lead metaniobate. AKA ferroelectric material. Or Natural - quartz, tourmaline
what piezoelectric materials are found in a transducer?
PZT, ceramic, active element, crystal
what is curie temp/point?
when PZT is heated above this temperature (app 360 C or 680 F) its piezoelectric properties are destroyed. AKA the PZT is depolarized.
how do you prevent a transducer from being depolarized?
never heat sterilize or autoclave transducers
what is sterilization?
the complete destruction of all living microorganisms by means of exposure to heat, chemical agents, or radiation
what to avoid when sterilizing transducers?
should never be sterilized using dry heat, moist heat, or chemicals
what does disinfection mean?
refers to the application of a chemical agent to reduce or eliminate infectious organisms on an object
what kind of instruments require high-level disinfection? what does this entail?
endocavitary probes; HLD is the destruction/removal of all microorg except bacterial spores. electrical safety testing should be performed bw each use.
In regard to infection control which are the most critical objects?
those that intend to penetrate skin or mucous membranes - requiring a sterile covering
what to avoid when disinfecting?
alcohol
what are the 5 major components of a basic imaging transducer?
wire, case, backing material, matching layer, crystal
what is the active element in a transducer? how thick is this element?
the piezoelectric crystal, aka ceramic, PZT, or crystal. it is 1/2 wavelength thick
what is the purpose of the case in a transducer?
protects the internal components from damage and insulates the patient from electrical shock.
what is the purpose of the wire in a transducer?
active element in a transducer requires electrical connection so voltage from the system can excite the crystal, thereby producing sound during transmission.
(similar to reception)
what is the reason that the matching layer works?
impedance differences result in reflection at boundaries.
what is the matching layers’ role in the transducer? (regarding transmission bw diff boundaries)
matching layer has an impedance bw those of the skin and the active element to increase transmission bw the active element and the skin. Gel’s impedance is bw the matching layer and the skin the further increase sound transmission.
how thick is the matching layer?
1/4 wavelength thick
give order of impedances from greatest to least
PZT > matching layer > gel > skin
what can multiple matching layers be used for? how does impedance work through the multiple layers?
further increase the percentage of sound traveling into and out of the body. impedance of each layer decreases going from PZT crystal to the face of the probe
why is a damping element/ backing material used?
short pulses create more accurate images so this material is bonded to the active element to reduce its “ringing”
what is the backing material usually made of?
epoxy resin impregnated w metal powder
what are 6 characteristics of imaging transducers?
- damping is effective (backing material)
- short pulse length & duration
- low sensitivity *
- wide bandwidth (broadband) *
- low Q
- decreased output power
what would be a reason for a transducer not to include backing material?
continuous wave transducers - do not create images so damping material is not required.
what is a bandwidth?
range of frequencies bw the highest and lowest frequency emitted from the transducer
why is a bandwidth created by the transducer?
an imaging transducer does not emit a sound beam with only a single pure frequency. The pulse is more like a short sound that contains a range of frequencies below and above the main frequ
what is bandwidth measured in?
Hertz
what does the process of damping do?
increases the range of frequencies present in any pulse, also making it shorter
what are some synonyms for main frequency that is emitted by the transducer?
center, resonant, primary, natural frequency
what is quality factor?
a unitless number related to extent of damping
Low-Q?
damping and wide bandwidth = imaging (pulsed transducers)
High-Q?
no damping and narrow bandwidth - CW and therapeutic transducers
what determines the frequency in continuous wave transducers?
sound frequency = electrical frequency
what determines the main or center frequency of sound from a pulse transducer? where do these characteristics come from?
determined by the crystal
1. thickness
2. propagation speed of the piezoelectric material
what is the typical propagation speed of the PZT?
4-6 mm/us
what does a thin crystal and fast PZT mean for the frequency?
higher frequency; faster active elements = higher frequ sound; thinner active elements = higher frequ sound
what does a thick crystal and slow PZT mean?
lower frequency
when a PZT crystal is half as thick how does this affect frequency?
frequency is twice as high
