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72 Cards in this Set
- Front
- Back
A general term for transducers
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they convertone form of energy into another
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What is the Piezoelectric effect
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when a mechanicl force is applied to certain materials they create a voltage and vice versa
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Piezoelectric is also called
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ferroelectric
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Ultrasound transducer transfer __________ energy into the body and recieve___________ energyfrom the body
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sound
sound |
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Transducers convert electrical energy into sound energy by way of a
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Piezoelectric element
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Give the breakdown of the Piezoelectric effect
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US machine sends an electric voltage to Piezoelectric element causing it to vibrate
Vibration sends sound energy into the body Echoes return from structures in the body which vibrates the piezoelectric element causing it to generate an electrical signal This signal gets sent back to the US maching which makes an image |
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Piezolectric Elements are also called the
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Active Element
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What are the elements made of
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Man made and natural materials
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What materials are transducers usually made of
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Lead zirconate titanate (PZT) or barium titanate
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Piezoelectric elements are heated to what point
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The Curie point which is 365
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Never do what to a transducer
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Sterilize it
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What is the main component of an ultrasound transducer with piezoelectric properties
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Crystal
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What are some of the natural materials
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Quart, Rochelle, Tourmaline and Salts
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Transducer crystals lose their piezoelectric properties when they are heated
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above the Curie point
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What happens to the material
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it becomes depolarized
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Name another material that is not naturally piezoelectric
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Ceramics
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What must be done to ceramics to make them become piezoelectric
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placed in a strong magnetic field while being heated at a hgh temperature
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Which element is bonded to the back of the active element
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Damping element
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What does the damping element do
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Reduces ringing
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By reducing the ringing you
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Shorten pulse duration and SPL, improving the overall image
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What happens to transducer crystals when they are heated above the Curie point
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They become depolarized
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Name the transducer components
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Wire, Acoustic insulator,Electrical shield, Damping element, Active element, Matching layer
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What is bandwidth
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range of frequencies within a pulse
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Damping material does what to bandwidth
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increases it.
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Damping material does what to the Q Factor
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Decreases it.
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Damping material does what to the transducers sensitivity to reflected echoes
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Decreases it
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bandwidth and Q factor are (inversly or directly) related
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Inversly - wide bandwidth = low Q factor
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What is Damping material analogous to
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putting your hand on a bell fter you rint it to stop the vibrations
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What material sits in front of the active element
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Matching layer
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What does the matching layer do
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It reduces reflections at the transducer tissue interface
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Matching layer is also called
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Impedance matching layer
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What wavelength of the US beam is the matching layer
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1/4
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The matching layer helps to send more
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US energy into the body rather than reflecting it b/c of the impedance difference at the skin
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What else also helps to reduce impedance difference at the transducer skin interface
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Gel
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Impedance Range from highest to lowest: Gel, skin, PZT, matching layer
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PZT
Matching layer Gel Skin |
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Composite piezoelectic elements are closer to that of
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Soft tissue
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What component is connected to the transducer element that sends and receives electrical voltages
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The wire
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What does an electrical voltage do to the crystal (remember the crystal is aka piezoelectric element)
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Causes it to vibrate creating a mechanical energy.
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The plastic or metal housing surrounding all of the transducers components is
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Case and Insulation
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What does Case and Insulation prevent
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Electrical noise from altering the transducers perfomance
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What natural frequency called
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Resonant frequency
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Resonant frequency is
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The operating frequency of the transducer
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Transducer frequency depends on
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The thickness of the crystal and the speed of sound in the crystal
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What happens to frequency in the following:
Higher speed = Lower speed = Thinner crystal = Thicker crystal = |
Higher frequency
Lower frequency Higher freqency Lower frequency |
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Where is the resonant frequency located in relation to bandwidth
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Center of the bandwidth
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Advantage of wide bandwidth
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Fewer cycles per pulse give longer lstening time
Can receive a wider range of frequencies |
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Disadvantage of wider bandwidth
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Decreased sensitivity
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What calculates the Q Factor
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Resonant frequency divided by bandwidth
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Shorter pulses have
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Fewer cycles
wider or broader bandwidth lower Q more listening time |
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Near Zone is aka
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Fresnel Zone
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Near zone is located
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b/t the transducer and focus
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Near zone is determined by
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The size and operating frequency of the element
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More variation in beam intensity happens in which zone
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Near Zone
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If the frequency increases what happens to the near zone
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it increases as well
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What is the space b/t the near zone and focus called
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Focal length or near zone length
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A larger crystal diameter does what to the focal length
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makes it longer
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Higher frequencies do what to the focal length
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longer
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Far Zone aka
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Fraunhofer
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Focus is aka
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Focal Depth
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A large crystal diameter does what to focal depth
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makes it go farther or deeper
A smaller crystal = more shallow focal depth |
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Beam width depends on three things
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Aperture (size of source)
Frequency Distance from the transducer |
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What is beam diameter to transducer diameter in the near zone, focus and far zone
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equal
half equal |
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Frequency and Diameter are directly _______________ to near zone length
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proportional
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One near zone length starts from _____________ to the _________
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Near zone
Focus |
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Two near zone lengths start from __________ to the _______
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Near zone
Far zone |
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Frequency and Diameter are __________ proportional to divergence
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inversely - smaller frequency or diameter = more divergence
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What is diffraction
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Diffraction occurs when sound waves are produces by a small sound source, they diverge or spread as sound propagates
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Huygen's Principle
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tiney wavelets combine to produce a sound beam with most of the energy transmitted along a main central beam having the shape of an hourglass.
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Another definition of Huygens principle
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many points on the crystal combine to act as a large sound source rather than a small one
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What are the Beam Characteristics
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Beam Freqquency
Focal Depth Beam divergence |
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What are the crystal properties of beam frequency, Focal depth and Beam divergence
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Crystal thickness and propagation speed of crystal
Crystal diameter and crystal frequency Crystal diameter and crystal frquency |
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What are the four ways to focus
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Lens = external focusing
Curved Crystal = internal foc. Mirror Electronic = Phased Array |