What are the two types of waves?
- Mechanical (physical medium)
- Electromagnetic (vaccum)
What is a transverse wave?
Particle motionis transverse to wave direction.
What is a longitudinal wave?
The direction of the wave is parallel to the direction.
What does “trans” mean?
Across
What does “ducere” mean?
To lead.
What does a transducer do?
It converts one form of energy to another.
What are some examples of “transducers” (Ea→Eb)
- Microphone
- Spekers
- Light Bulbs
- Eyes
- Ears
T/F:
Is an ultrasound transducer bidirectional.
True.
What is the peizoelectric effect?
It converts voltage energy into pressure.
What does “piezo” mean?
Pressure.
What does “electrum” mean/consist of?
Amber, which is Au/Ag conductive mixture.
What are some materials that are peizoelectric?
- Quartz
- PZT
- Pb=Lead
- Zinconate
- Titanate
- Ceramics
- Ceramic admixtures
What is polarization?
It is the separation of (+) and (-) changes.
What are the 5 steps to polarization?
- Apply heat
- Apply magnetic field
- Remove heat
- Remove magnetic field
- Crystalline sets.
How do you find the curie temperature?
(300xCx9/5)
What is the impedance of a transducer?
30 MR
What are the components of a transducer from top to bottom (chord)?
- 1/2 λ matching layer
- PZT
- Backing material
- Tuning coil
- Coaxial cable
- Metal shield
What does the backing material do?
It shortens the ring of the transducer.
(muffles sound tone and duration)
What is used to avoid reflection at the PZT?
Backing material interface.
Why is the backing material used to avoid relfection at the PZT: backing material interface?
Because it has a similar impedance as PZT.
What is the unit for impedance?
Rayls= kg/m2xsec
What is the formula for impedance?
Z=density x speed
Z=p x c
What is the unit for density?
kg/m3
What is the unit for speed?
m/sec
What is the formula for % reflected?
100-% transmission
or
[(Z2-Z1)/(Z2+Z1)]2X100
What does the “¼ λ matching layer” do?
It elminates reflecting waves by constructive and destructive interference.
Waves offset by ½ λ results in what?
Total destructive interference.
¼ λ (out to surface)+¼ λ(back from surface)=½ λ
What is the impedance of soft tissue?
1.7MR
What is the equation for ¼ λ matching layer?
ZML=√ZPZTxZST
What does a big difference in impedances lead to?
Reflection.
What is destructive interference?
When 2 waves come together and cancel eachotherout.
What does into creating a sound wave?
- Start with a piezoelectric transducer
- Apply alternating electric voltage across PZT
- Expand and contract PZT
- Exerts pressure wave (sound) from PZT surface
- Transmitted into tissues→reflected from tissue
- Reflected pressure wave deforms PZT→Voltage
What is the lateral resolution affected by?
Beam width.
What are the 3 parts of the beam width?
Converge→Focus→Diverge
What does a smaller BW signify?
Better lateral resolution
What are the effects of the transducer frequency on beam?
- The higher the frequency, the smaller divergence in the far field.
BUT…THE HIGHER THE FREQUENCY, THE GREATER THE ATTENUATION.
What is the near field also known as?
Near zone length or fresnel zone.
What is the end of the near zone length known as?
Focus
What is the equation for the NZL?
NZL=D2/4 λ
What is the equation for λ?
λ=c/f
What is the farfield also known as?
Fraunhoffer Zone
What is the equation for the Fraunhoffer Zone?
SINØ=1.2c/Df
What happens to frequency if SINØ increases?
Frequency decreases.
What are the 3 resolution planes?
- Lateral resolution
- Axial resolution
- Elevation resolution
What is resolution?
It os the bility to see two objects as seperate.
What is lateral resolution?
It is the ability to distinguish 2 structures that are perpendicular to the direction of the beam.
What does lateral resolution consist of?
L-A-T-A
LATERAL
ANGULAR
TRANSVERSE
AZIMUTHAL
What is lateral resolution associated with?
Beam width.
What does determines beam width?
It varies with depth.
Where can you find the best lateral resolution?
At the focus (narrowest=D/2)
What does axial resolution consist of?
L-A-R-R-D
- Longitudinal
- Axial
- Range/radial
- Depth
Describe axial resolution:
Pulse duration
In axial resolution, what creates a better resolution?
Shorter pulse durations.
What is the formula for axial resolution
PD=Nc*T
T=1/f
If the pulse duration goes up, what happens to the brandwidth?
BDW goes down
The bigger the BDW, the _____ the quality.
Worst.
Which plane is known as the “forgotten” plane?
Elevation plane.
Elevation resolution is similar to what?
Lateral resolution.
Where is the best resolution seen in an elevation plane?
At the focus.
What is a huygen?
It is a basic assembly.
- It is a row of single element transducers
- Individual electrical signals to each transducer
- Grouped together to form an image.
What is huygen’s principle?
It has phase delays to transducer and it allows for beam steering and focusing.
