Transducers Flashcards
Ultrasound transducers
Convert electric energy into ultrasound energy and vice versa
Piezoelectric element
A material/element when deformed by pressure produce a voltage
Reverse piezoelectric
The production of pressure when voltage deforms materials
Piezoelectric elements
Quartz
Synthetic crystals (ceramics)
- PZT
- Barium
How are piezoelectric elements made
Placed in strong magnetic field at high temp. This realigns molecular dipoles. Then cooled
Curie point
The temperature in which the magnetic properties of a solid can be changed
PZT curie point 350
What would happen if you brought the crystal back to the curie point but without the magnetic field ?
It would lose its piezoelectric properties
Transducer assembly
Case Damping Element 3 matching layers Gel
Natural frequency of piezoelectric element formula
Propagation speed of the element divided by 2x thickness (wavelength)
Propagation speed of PZT
4 mm/us
Thickness of element
0.2-1 mm
True or false:
Thinner elements have lower frequencies
False. Thinner elements have higher frequencies. Think of smaller bells
How many cycle US pulse does 1 cycle of alternating voltage create
2-3
Longer alternating voltage 5-30 is what
Doppler technique
What does Fvolt = Fo mean
One transducer can have more that one frequency based on the selected voltage
The transducer is driven at one of 2 or 3 selectable frequencies by voltage pulses with the selected frequency
Frequency must fall within the bandwidth of the transducer
Multi-hertz operation
2 or 3 frequencies in the same element
What does damping do
Good and bad
Good: - Decreases n (thus decreasing PD and SPL) - Image resolution - Bandwidth
Bad:
- Decreases amplitude
- Decreases sensitivity
Image resolution is inversely proportional to depth. If you need to go further, you must decrease:
PRF
If you don’t decrease PRF when going into deeper structures, what can happen?
Range ambiguity/echo misplacement
What are piezocomposites
Other materials added to Decrease z
Increase bandwidth
Increase sensitivity & resolution
Damping material reduces
Cycles per pulse - faster decay time
What are some unwanted things that happens with a damping material
Reduces amplitude - weaker sound out, weaker echo in
Decreases sensitivity (ability to detect weaker echoes)
Continuous wave ultrasound do not have damping material true or false
True Not needed because pulses are not used. Higher efficiency Better sensitivity Worse resolution
The case/housing unit
Absorbs energy from sides of crystal