Lesson 13 Flashcards
What happens to bandwidth when impedance decreases?
Increases
- also increasing sensitivity and resolution
What do we get when we lower impedance?
Less reflection
- more pulses go through solid tissues
What is damping material also known as?
Backing material
What does the damping material include? (2)
- Metal powder
- tungsten - Plastic/epoxy resin
Where is the damping material?
On the back of the element
What does the damping material do? (2)
- Reduces ringing
- Reduces cycles per pulse
- faster decay time
What 3 thing do you need for the best resolution?
- Decreased PD
- Decreased SPL
- Increased bandwidth
Why do we use gel in ultrasound?
It gets ride of the air bubbles that have a low impedance
Why might we use damping material?
To decrease sensitivity
- have the ability to detect weaker echoes
What is an example of no damping material?
Continuous wave
- better sensitivity
- worse resolution
What is the case made from?
Usually the same material as the damping material
What does the case do? (2)
- Prevents moisture
2. Protects some of the internal structures
Where does the case absorb most of the energy?
From the sides of the crystals
What percentage of the matching layer is IRC?
80%
Matching layer
1-3 layers are used to reduce the large differences in impedances
- 20x in tissue
What is the thickness of each mathching layer?
1/4 of the wavelength
What is the reason we use a matching layer?
Same as why we use gel
- to decrease impedance
What does a transducer convert?
One form of energy to another
What shortens and improves resolution? (2)
- Composites
2. Damping material
What do matching layers and coupling media facilitate?
The passage of ultrasound across the transducer skin boundary
What are single element transducers in the form of?
Discs
What of the transducer element changes when voltage is applied to its face?
Its thickness
What is the resonance frequency of an element determined by?
Its thickness
What do the thinnest elements have?
The largest frequencies
What kind of impedance does the matching layer have?
Intermediate impedance
Composites
Mixtures of a piezoelectric ceramic and a nonpiezoelectric polymer
