Transducers and Sound Beams Flashcards
How are time of flight and depth related?
Directly depth (mm) = (1.54 mm/us x go return time us)/2
What is the 13 microseconds rule?
states that for every 13 us of go return time, the object that creates the reflection is 1 cm deeper in the body
How are PRP and depth related?
Directly
PRP (us) = imaging depth (cm) x 13 us/cm
What is a transducer?
Any device that turns one form of energy into another
What is the piezoelectric effect?
Describes the property of materials to create a voltage when pressure is applied or when they are mechanically deformed
What is another term for piezoelectric materials?
Ferroelectric
What happens to the ultrasound transducer during transmission?
the transducer converts electrical energy from the system into sound
What happens to the ultrasound transducer during reception?
the transducer converts the reflected sound pulse into electricity
What is PZT?
Lead zirconate titanate
What are the synonyms for PZT?
Ceramic
Active element
Crystal
What is the Curie Temperature?
the temperature at which PZT is polarized
What happens when PZT reaches the Curie point?
If it goes higher than the Curie point, the crystal’s piezoelectric properties are destroyed, called depolarization.
Should you heat sterilize or autoclave a transducer?
No, you should not sterilize a transducer with heat.
What is sterilization?
Destroying all microorganisms by exposing them to extreme heat, chemical agents, or radiation
What is disinfection?
Applying a chemical agent to an object to reduce or eliminate infectious organisms
What is the purpose of the case?
protects the internal components of the transducer and insulates the patient from electrical shock
Is it safe to use a transducer if the case is cracked?
No
How are the active element and wavelength related?
Active element is 1/2 wavelength thick
What is the purpose of the matching layer?
increases efficiency of the transfer of sound energy between the active element and body and protects the active element
How thick is the matching layer?
1/4 wavelength thick
What is the purpose of the backing material?
to reduce the “ringing” of the PZT
How does backing material affect pulse duration?
It produces short pulses and makes pulse duration shorter
How does backing material affect transducer sensitivity?
It decreases the sensitivity - because it makes the transducer less able to convert low-level sound reflections into electrical signals
What are the three consequences of using a backing material?
Decreased sensitivity
Wide bandwidth
Low quality factor
Do continuous or pulsed wave transducers need backing material?
Pulsed wave
What is bandwidth?
The range of frequencies in a pulse and the difference between the highest and lowest frequencies
Do long or short pulses have a wider bandwidth?
Short duration pulses have a wider bandwidth
What are the synonyms for the main frequency produced by a transducer?
Center
Resonant
Primary
Natural frequency
Does a short or long pulse have a higher quality factor?
A longer pulse has a higher q-factor
For a CW transducer how are frequency of voltage and the sound frequency related?
The frequency of the voltage is equal to the sound frequency.
Electrical frequency = acoustic frequency
What two characteristics of the active element determine transducer frequency?
The speed of sound in PZT and thickness of PZT
How are speed of sound in PZT and frequency related?
Speed of sound in PZT and frequency are directly related.
When sound in PZT is faster, frequency is higher, and when sound in PZT is slower, frequency is lower.
How are crystal thickness and frequency related?
Crystal thickness and frequency are inversely related.
Thinner PZT crystals produce higher frequency waves, and thicker crystals produce lower frequency waves.
What is the focus or focal point?
The point at which the sound beam is the narrowest
What is the focal depth?
The distance from the transducer to the focus
What are synonyms for focal depth?
Focal length
Near zone length
What is the near zone?
The region from the transducer to the focus
What are synonyms for near zone?
Near field
Fresnel zone
What is the far zone?
The region that starts at the focus and extends deeper
What are synonyms for far zone?
Far field
Fraunhofer zone
What is the focal zone?
The region around the focus that is relatively narrow
For an unfocused CW transducer, what is the beam diameter at: transducer end of near zone 2 near zone lengths deeper than 2 near zone lengths
Transducer - beam dia = transducer dia
End of near zone - beam dia = 1/2 transducer dia
2 near zone lengths - beam dia = transducer dia
Deeper than 2 near zone lengths - beam diameter > transducer dia
What factors determine sound beam divergence in the far zone?
Transducer diameter
Frequency of sound
Do smaller or larger diameter crystals create beams that diverge more in the far field?
Smaller crystals produce beams that diverge more in the far field
Do higher or lower frequency beams spread out more in the far field?
Lower frequency beams
What is a Huygen’s Wavelet?
A V-shaped wave created when the source is about the size of the sound’s wavelength.
What is Huygen’s Principle?
The inconsistency between large and small sound sources and their beams. It states that a large active element can be thought of as millions of tiny sound sources.
