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72 Cards in this Set

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  • Back
A general term for transducers
they convertone form of energy into another
What is the Piezoelectric effect
when a mechanicl force is applied to certain materials they create a voltage and vice versa
Piezoelectric is also called
ferroelectric
Ultrasound transducer transfer __________ energy into the body and recieve___________ energyfrom the body
sound
sound
Transducers convert electrical energy into sound energy by way of a
Piezoelectric element
Give the breakdown of the Piezoelectric effect
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
Piezolectric Elements are also called the
Active Element
What are the elements made of
Man made and natural materials
What materials are transducers usually made of
Lead zirconate titanate (PZT) or barium titanate
Piezoelectric elements are heated to what point
The Curie point which is 365
Never do what to a transducer
Sterilize it
What is the main component of an ultrasound transducer with piezoelectric properties
Crystal
What are some of the natural materials
Quart, Rochelle, Tourmaline and Salts
Transducer crystals lose their piezoelectric properties when they are heated
above the Curie point
What happens to the material
it becomes depolarized
Name another material that is not naturally piezoelectric
Ceramics
What must be done to ceramics to make them become piezoelectric
placed in a strong magnetic field while being heated at a hgh temperature
Which element is bonded to the back of the active element
Damping element
What does the damping element do
Reduces ringing
By reducing the ringing you
Shorten pulse duration and SPL, improving the overall image
What happens to transducer crystals when they are heated above the Curie point
They become depolarized
Name the transducer components
Wire, Acoustic insulator,Electrical shield, Damping element, Active element, Matching layer
What is bandwidth
range of frequencies within a pulse
Damping material does what to bandwidth
increases it.
Damping material does what to the Q Factor
Decreases it.
Damping material does what to the transducers sensitivity to reflected echoes
Decreases it
bandwidth and Q factor are (inversly or directly) related
Inversly - wide bandwidth = low Q factor
What is Damping material analogous to
putting your hand on a bell fter you rint it to stop the vibrations
What material sits in front of the active element
Matching layer
What does the matching layer do
It reduces reflections at the transducer tissue interface
Matching layer is also called
Impedance matching layer
What wavelength of the US beam is the matching layer
1/4
The matching layer helps to send more
US energy into the body rather than reflecting it b/c of the impedance difference at the skin
What else also helps to reduce impedance difference at the transducer skin interface
Gel
Impedance Range from highest to lowest: Gel, skin, PZT, matching layer
PZT
Matching layer
Gel
Skin
Composite piezoelectic elements are closer to that of
Soft tissue
What component is connected to the transducer element that sends and receives electrical voltages
The wire
What does an electrical voltage do to the crystal (remember the crystal is aka piezoelectric element)
Causes it to vibrate creating a mechanical energy.
The plastic or metal housing surrounding all of the transducers components is
Case and Insulation
What does Case and Insulation prevent
Electrical noise from altering the transducers perfomance
What natural frequency called
Resonant frequency
Resonant frequency is
The operating frequency of the transducer
Transducer frequency depends on
The thickness of the crystal and the speed of sound in the crystal
What happens to frequency in the following:
Higher speed =
Lower speed =
Thinner crystal =
Thicker crystal =
Higher frequency
Lower frequency
Higher freqency
Lower frequency
Where is the resonant frequency located in relation to bandwidth
Center of the bandwidth
Advantage of wide bandwidth
Fewer cycles per pulse give longer lstening time
Can receive a wider range of frequencies
Disadvantage of wider bandwidth
Decreased sensitivity
What calculates the Q Factor
Resonant frequency divided by bandwidth
Shorter pulses have
Fewer cycles
wider or broader bandwidth
lower Q
more listening time
Near Zone is aka
Fresnel Zone
Near zone is located
b/t the transducer and focus
Near zone is determined by
The size and operating frequency of the element
More variation in beam intensity happens in which zone
Near Zone
If the frequency increases what happens to the near zone
it increases as well
What is the space b/t the near zone and focus called
Focal length or near zone length
A larger crystal diameter does what to the focal length
makes it longer
Higher frequencies do what to the focal length
longer
Far Zone aka
Fraunhofer
Focus is aka
Focal Depth
A large crystal diameter does what to focal depth
makes it go farther or deeper

A smaller crystal = more shallow focal depth
Beam width depends on three things
Aperture (size of source)
Frequency
Distance from the transducer
What is beam diameter to transducer diameter in the near zone, focus and far zone
equal
half
equal
Frequency and Diameter are directly _______________ to near zone length
proportional
One near zone length starts from _____________ to the _________
Near zone
Focus
Two near zone lengths start from __________ to the _______
Near zone
Far zone
Frequency and Diameter are __________ proportional to divergence
inversely - smaller frequency or diameter = more divergence
What is diffraction
Diffraction occurs when sound waves are produces by a small sound source, they diverge or spread as sound propagates
Huygen's Principle
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.
Another definition of Huygens principle
many points on the crystal combine to act as a large sound source rather than a small one
What are the Beam Characteristics
Beam Freqquency
Focal Depth
Beam divergence
What are the crystal properties of beam frequency, Focal depth and Beam divergence
Crystal thickness and propagation speed of crystal

Crystal diameter and crystal frequency

Crystal diameter and crystal frquency
What are the four ways to focus
Lens = external focusing
Curved Crystal = internal foc.
Mirror
Electronic = Phased Array