Ch. 8 Transducers Flashcards
Define transducer
Any device that converts one form of energy into another.
Ultrasound transducers two functions:
Transmission and reception
Transmission
Electrical energy from the system is converted into sound.
Reception
The reflected sound pulse is converted into electricity.
Piezoelectric effect defined
Describes the property of certain materials to create a voltage when they are mechanically deformed or when pressure is applied to them.
Reverse piezoelectric effect
When a voltage is applied to piezoelectric materials change shape.
Piezoelectric or ferroelectric materials
Convert sound into electricity (and vice versa).
Piezoelectric materials found in nature
Quartz and tourmaline
Piezoelectric materials commonly used in clinical transducers
Lead zirconate titanate or PZT, are synthetic or man-made.
Synonyms for PZT
Ceramic, active element, or crystal.
The thickness of the matching layer
One-quarter of the wavelength of sound.
The thickness of the active element
One=half of the wavelength of sound.
Backing material
Plays an essential role in optimizing the pulses created by imaging transducers.
The three consequences of using backing material are:
- Decreased sensitivity
- Wide bandwidth
- Low quality factor
The characteristics of damping material include:
High degree of sound absorption.
Acoustic impedance similar to PZT.
Bandwidth
The range of frequencies in the pulse. It is the difference between the highest and lowest frequencies.
Imaging probes produce pulses that are identified as
Wide bandwidth or broadband
As a general rule, long duration events are ____ bandwidth, whereas short duration events are ___ bandwidth (broadband).
Narrow, wide.
Average transducer thickness
0.2 1 mm
Quality factor defined
A unitless number that is inversely related to bandwidth.
What probes have a low Q-factor?
Wide bandwidth probes
Which probes have a high Q-factor?
Narrow bandwidth probes.
Because imaging probes use backing material and have a wide bandwidth they are referred to as ____.
Low-Q.
Transducers used in therapeutic ultrasound and have continuous wave doppler do not contain backing material. They have a narrow bandwidth and ____.
High- Q
PZT is created by
Exposing the material to a strong electrical field while being heated to a substantial temperature. Polarization.
The temperature at which PZT is polarized is called
Curie temperature or curie point.
How can piezoelectric properties be destroyed?
Exposure to high temperature.
Depolarization
The loss of piezoelectric properties when crystals are heated above the curie temperature.
