Transducers, PZT & Crystals, Op Frequency & Bandwidth, Transducer Construction
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44 Terms
What does a transducer do?
Converts one form of energy into another
What are the two roles of a transducer?
Transmit and receive
What happens during transmission?
Electrical energy is converted into mechanical sound energy
What happens during reception?
Reflected sound is converted into electrical energy
What does PZT stand for?
Lead zirconate titanate
What is another name for PZT?
Active element
What is the piezoelectric effect?
Pressure applied to the material creates a voltage
What is the reverse piezoelectric effect?
Electrical voltage causes the crystal to change shape
What is the purpose of piezoelectric crystals?
Convert electrical energy to sound and sound to electrical energy
What is the Curie point?
Approximately 350–360°C
What happens above the Curie point?
The crystal depolarizes
What is polarization?
Positive and negative charges are aligned in opposite directions
What are dipoles?
Equal and opposite charges separated by a distance
How must dipoles be aligned for artificial crystals to function?
In parallel
How should transducers be cleaned?
Cold cleaned with chemicals
What are the 7 basic transducer components?
Matching layer
What is operating frequency?
The natural or resonant frequency of the crystal
What determines PW transducer operating frequency?
Propagation speed in the element and element thickness
How are element thickness and frequency related?
Inversely related
What happens when the element is thicker?
Lower frequency
What happens when the element is thinner?
Higher frequency
What determines CW acoustic frequency?
The frequency of the electrical signal
What is bandwidth?
The range between the highest and lowest frequency in a pulse
What is transducer bandwidth?
Range of frequencies a transducer can produce
What can a wide-bandwidth transducer do?
Operate at multiple frequencies
What is damping material?
Material attached behind the crystal
What is the purpose of damping material?
Reduces cycles/ringing in each pulse
What does damping do to pulse duration and spatial pulse length?
Reduces both
What does shorter pulse duration improve?
Axial resolution
How many cycles do damped pulses generally have?
2–3 cycles
What else does damping reduce?
Sound amplitude
Where is the matching layer located?
In front of the crystal
What are the two main jobs of the matching layer?
Protects the crystal
What is the thickness of the matching layer?
¼ wavelength
What is the thickness of the element?
½ wavelength
Why is a matching layer needed?
Reduces impedance differences and improves transmission
What does the case do?
Protects the transducer and insulates the patient from electrical shock
What does the electrical shield do?
Prevents electrical noise from distorting the image
What does the acoustic insulator do?
Prevents case movement from affecting the crystal
What does the wire do?
Connects the element to the ultrasound machine
What are invasive transducers?
Transducers used within body cavities
What are examples of invasive transducers?
Transrectal
Why can invasive transducers use higher frequencies?
They are closer to the organs and avoid air interference
What is the aperture?
Piezoelectric area activated to form the transmitted beam