Physics Chapter 8 & 9 Flashcards
If you have 2 types of crystals made of the same material, the thicker crystal will do what?
Thicker active elements create pulses with lower frequency, longer wavelength cycles
What are the characteristics of non-imaging transducers?
- creates continuous waves or pulses with long duration and length
- no backing material
- increased sensitivity
- narrow band width
- higher Q-factor
- cannot create an image
If PZT is heated to the curie point, what happens to it?
The crystals piezoelectric properties are destroyed
Reverse Piezoelectric Effect
The process of piezoelectric materials changing shape when a voltage is applied to them
PZT is also known as _____?
Active element, crystal, or ceramic
What is the active element that reduces the ringing of the PZT?
- backing material
- dampening element
How is the Q-factor calculated?
Quality factor = main frequency / band width
What type of crystal will have a lower frequency?
A thicker PZT crystal
What is the impedance difference between the crystal, skin, matching layer, and gel?
PZT > matching layer > gel > skin
What type of resolution does the dampening material improve?
Axial resolution
The frequency of sound emitted is equal to to the frequency of the electrical signal in what type of transducer?
Continuous wave transducers (non-imaging)
How many rayls are in an active element transducer?
2 Mrayls
What is the impedance level of PZT, matching layer, gel, and skin?
PZT = 2 Mrayls
Matching layer = 1.6 Mrayls
Gel = 1 Mrayls
Skin = 0.8 Mrayls
*values on p121 question 1. don’t know if these are really the values or not. know she mentioned something about it
Cylinderical tube constructed of metal or plastic that protects the internal components of the transducer from damage
Case
What insulates the patient from electrical shock?
Case
A thin metallic barrier lining the inside of the case that helps prevent electrical noise from contaminating the clinically important electric signals used to create diagnostic images
Electrical shield
A thin barrier of cork or rubber that isolates the internal components of the transducer from the case
Acoustic insulator
What prevents vibrations in the case from inducing an electrical voltage in the PZT of the transducer?
Acoustic insulator
What size wave length is PZT?
1/2 wave length thick
In a simple probe, the characteristics of the sound beam emitted by the transducer are related to the dimensions of _____?
Active element
In a simple probe, the characteristics of the sound beam emitted by the transducer are related to the dimensions of _____?
Active element
Provides an electrical connection between the PZT and the ultrasound system
Wire
What lies in front of the PZT at the face of the transducer?
Matching layer
Helps increase the efficiency of sound energy transfer between the active element and the body and protects the active element
Matching layer
What size wave length is the matching layer?
1/4 wave length thick
Bonded to the back of the active element, it reduces the ringing of the PZT
Backing material or dampening element
What is commonly made of epoxy resin impregnated with tungsten filaments
Backing material or dampening element
What would create a beam with a deeper focus?
- a larger diameter of PZT
- a higher frequency
What would create a beam with a shallower focus?
- a smaller diameter of PZT
- a lower frequency
A probe with a smaller diameter and a lower frequency will diverge more or less?
More
What probe creates a beam with the least divergence?
A larger diameter and higher frequency
The frequency of a transducer does not change. If the diameter of the new piezoelectric crystal increases, what happens to the wavelength?
no change
At the transducer, the beam diameter is greater than, equals, or less than the transducer diameter?
equals
At the focus, the beam diameter is 1/2, 1/4, or the same as the transducer diameter?
1/2
At 2 near zone lengths, the beam diameter is..
equal to the transducer diameter
Deeper than 2 near zone lengths, the beam diameter is
wider than transducer diameter
The frequency of a transducer does not change. If the diameter of the new PZT crystal increases, what happens to the near zone length?
Increases
The frequency of a transducer does not change. If the diameter of the new PZT crystal increases, what happens to the beam diameter in the far zone?
Decreases
What characteristics of the active element determine the frequency of sound created by a pulsed wave transducer?
- speed of sound in the PZT
- thickness of the PZT
What determines the depth of the focus?
the characteristics of the active element
fixed focus transducer:
- transducer diamter
- frequency of sound
