Lesson 14 Flashcards
What are the 4 different componets to a transducer?
- Lens
- Matching layer
- Single crystal element
- Backing material
- damping
What are elements?
Crystals
What happens to beam profiles in transducers?
They go in and out at the same time
- no pulses
What is happening to beam width in pulse waves?
They are changing
- naturally shortens and widens again
Where is the natural focus on a pulse wave beam profile?
At the smallest point
Where is the near zone?
Between the focus point and the transducer
- minimun beam width
Where is the far zone?
From the focus point and onwards
What are 2 other names for the near zone?
- Fresnel zone
2. Near field
What happens to the beam width when increasing distance from the transducer in the near field?
It decreases
Beam convergence
Light rays comes together (converges) after reflection and refraction at a single point known as the focus
What are 2 other names for far zone?
- Fraunhofer zone
2. Far field
What happens to the bandwidth with increasing distance from the transducer in the far-field?
It increases
Beam divergence
When beams of light move away from each other after passing the focus point and going into the far field
Aperture
For a single disk transducer, this is the element size or width of group of elements
- opening
- top by the transducer
What does beam width change with?
Depth
What does beam width affect? (2)
- Resolution of signal at that depth
2. Intensity of the sound beam at that depth
What happens to the resolution with a more narrow beam width?
It gets better
When is intensity the strongest?
At a smaller focus point
What is considered to be uniform?
Power
- equal at any point along the beam
What is the formula for beam width (Wb) at the focus?
1/2 the aperture size
NZL
Near zone length
What is NZL determined by? (2)
- Size of the element
- aperture - Operating frequency
What happens to NZL if aperture increases?
It increases
What happens to NZL if frequency increases?
It increases
Is there a far zone length?
No
What happens to NZL if aperture goes up?
It goes up by 2
- aperture^2 proportional to NZL
What is the near zone length the same length is?
The focal length
What is a footprint?
Width of the probe
What do you need to do if you want a high frequency disk transducer to look at superficial structures?
Adjust the focus because intensity is highest at the focus and the resolution will be better
Do we want a large footprint or a small one when looking at smaller structures?
Smaller footprints because your NZL will be shorter and your focus will be higher
What kind of footprints do higher frequency transducers have?
Smaller footprints
Why do we adjust the focus?
Because the resolution is best when the focus is smallest
Smallest beam width (2)
- Strongest intensity
- will pick up more signals - Better resolution with smaller beam width
Where is focusing only accomplished?
In the near zone
What happens to the focus when the curve increases?
You get a closer focus
- mechanical focusing
