Ch. 8-9 Physics Flashcards
Materials that convert electricity into sound and vice versa is called
piezoelectric or ferroelectric
The piezoelectric material we use in ultrasound is man made and is
lead zirconate titanate or PZT
PZT is also know as the
crystal, active element or ceramic
Other piezoelectric materials found in nature are
quartz and tourmaline
The temperature at which PZT is _____ is called the ______ or ______
polarized, curie temperature, curie point
Process of exposing the PZT to a strong electrical field while being heated to the curie temperature
polarization
If PZT is heated above the curie point, it becomes
depolarized
A transducer is any device that converts one form of ____ to another
energy
During _______, electric energy from the system is converted to sound
transmission
During ______, the reflected sound is converted into electricity
reception
Describes the property of certain materials to _____ a voltage when they are mechanically deformed or when pressure is applied to them
the piezoelectric effect, create
The piezoelectric material change shape when a voltage is applied to them
reverse piezoelectric effect
Protects the internal components- insulates the patient from electrical shock
case
thin metallic barrier lining the inside of the case- keeps electrical signal in the air from entering the transducer- prevents electrical noise from contaminating the images
electrical shield
Cork or rubber barrier- prevents the vibrations in the case
acoustic insulator
The piezoelectric crystal itself
PZT/active element
PZT is _____ wavelength thick
1/2
provides electrical connection between the PZT and the US system
wire
Positioned in front of the PZT- at the face of the transducer
matching layer
The matching layer is ____ wavelength thivk
1/4
Increases the efficiency of sound energy transfer between the active element and the body
matching layer
Protects the active element
matching layer
Bonded to the back of the active element
backing material/damping
Reduces the “ringing” of the crytsal
backing material/damping
Damping enhances
axial resolution
Damping also reduces ______ during reception, so _____ sound reflections are not detected- creating _____ sensitivity
vibration, low-level, decreased
_____ and ______ increase the efficiency of sound transfer between the crystal and the skin
matching layer, gel
in DECREASING order of impedance
PZT>matching later>gel>skin
range of frequencies in a pulse. Difference between the highest and lowest frequency
bandwidth
Imaging probes produce pulses that are identified as
wide bandwidth of broadband
Therapeutic and continuous wave doppler probes DO NOT USE _________ and produce ____________ and DO NOT CREATE images
backing material/damping, narrow bandwidth pulses
Is a UNITLESS number that is _______ related to bandwidth
Quality factor (Q-factor), inversely
WIDE bandwidth probes (imaging probes) have a _____ q-factor
low
Therapeutic and CW doppler probes have a _____ bandwidth and a ______ Q-factor
narrow, high
Math for Q-factor
main frequency divided by the bandwidth
Pulses with short duration and length
imaging transducer
Uses backing material to limit ringing
imaging transducer
Reduced sensitivity
imaging transducer
Wide bandwidth/broadband
imaging transducer
Low Q-factor
imaging transducer
Improved axial resolution
imaging transducer
Created continuous wave or pulses with long duration and length
non-imaging transducer
No backing material
non-imaging transducer
Increased sensitivity
non-imaging transducer
Narrow bandwidth
non-imaging transducer
High Q-factor
non-imaging transducer
Cannot create an image
non-imaging transducer
Destruction of all microorganisms by exposure to extreme heat, chemical agents or radiation
sterilization
Application of chemical agent to reduce or eliminate infectious organisms on an object
disinfection
Continuous wave transducers frequency=
frequency of the electrical signal/voltage
With pulsed wave transducers, two characteristics of the active element/crystal combine to determine the frequency of sound:
Speed of sound of the crystal, thickness of the crystal
speed of sound in the crystal and frequency of sound are _____ related
directly
Crystal thickness and frequency are ______ related
inversely
Characteristics of high frequency pulsed wave transducers are
thin crystals with higher speed crystals
Characteristics of low frequency pulsed wave transducers are
thick crystals with lower speed crystals
Location where the US beam is the narrowest
focus/focal point
The width of the sound beam at the focus is _____ the width of the beam as it leaves the transducer
1/2
Region from the transducer to the focus
near zone/near field
Near field/near zone is also called
fresnel zone
The focus is located at the end of the
near zone
Distance from the transducer to the focus
focal length
Starts at the focus and extends deeper
far zone/far field
Far zone/far field also called
fraunhofer zone
In the far zone, the beam
diverges
At the beginning of the far zone, the beam is _____ as wide as it is at the transducer (focus)
1/2
When the beam is _____ near zone lengths from the transducer, the beam is again the same size as the active element- and then the beam diverges more
two
Region around the focus where the beam is relatively narrow
focal zone
______ arising from the focal zone created images that are more accurate then those from other _____
reflection, depths
_____ of the focal zone is in the near field and _____ is in the far field
half, half
How does transducer diameter affect the focal depth
Transducer diameter and focal depth are directly related
So, with two transducers of different diameters, the transducer with the _____ diameter with have a DEEPER focus/DEEPER focal depth
larger
How does frequency affect focal depth
frequency and focal depth are directly related
So, two transducers with the same diameter but different ______ - the _____ frequency will have a deeper focus/deeper focal depth
frequencies, higher
High frequency (which has shallower imaging depth) has a deeper focal depth is considered
clinical dilemma/ bad physics
Low frequency (which allows for a deeper imaging) has a shallower focal depth is considered
clinical dilemma/ bad physics
So, manufacturers make higher frequency transducer with extremely _________ crystals
small diameter
So, manufacturers make lower frequency transducer with _________ crystals
larger diameter
Describes the gradual spread of the US beam in the far field
sound beam divergence
Two factors combine to determine beam divergence which are
transducer diameter and frequency of the sound
How does the transducer diameter affect divergence in the far field
crystal diameter and beam divergence are inversely related
Smaller diameter crystals produce beams thatspread out more in the
far field
Large diameter crystals produce beams with ______ divergence
less
Large diameter crystals improve _____ resolution in the ____ field
lateral, far
How does frequency alter beam divergence in the far field
Frequency and beam divergence are inversely related
Higher frequency transducers diverge ____ in the ____ field
less, far
Lower frequency transducers diverge ____ in the ___ field
more, far
So ____ frequency sound improves ____ resolution in the far field
high, lateral
States that a large active element/crystal may be thought of as millions of tiny distinct sound sources
Huygens’ Principle
Each of these tiny particles is a _____ source and creates a _____ wavelet with a ____-shape
Huygens’, Huygens’, V
The V-shape waves are known as
spherical waves, diffraction patterns or Huygens wavelets
The hourglass shape produced by a large crystal is the result of
interference of the many Huygens’ wavelets.
Some wavelets are _______ (interfere constructively) and some of the wavelets are _______ (destructive interference)
in-phase, out-of-phase
Explains the shape of an imaging transducer’s emitted sound beam based upon in-phase and out-of-phase wavelets interfering with each other
Huygens’ principle
