Ch 8: Transducers Flashcards
Define ‘transducer’.
Any device that converts one form of energy into another.
During ___, electrical energy from the system is converted into sound.
transmission
During ___, the reflected sound pulse is converted into electricity.
reception
This is the property of certain materials to create a voltage when they are mechanically deformed or when pressure is appiled to them.
The piezoelectric effect
This is the process of piezoelectric materials that change shape when a voltage is applied to them.
reverse piezoelectric effect
Materials which covert sound into electricity (and vice versa) are called…
piezoelectric or ferroelectric
The piezoelectric material commonly used in clinical transducers that are synthetic are…
lead zirconte titanate or PZT
PZT is also known as…
ceramic, active element, or crystal.
This cylindrical tube, constructed of metal or plastic, protects the internal components of the transducer from damage.
case
This insulates the patient from electrical shock.
case
This thin metallic barrier lines the inside of the case.
electrical shield
This prevents spurious electrical signals in the air, unrelated to diagnostic information, from entering the transducer.
electrical shield
This helps prevent electrical noise from contaminating the clinically important electrical signals used to create diagnostic images.
electrical shield
This is a thin barrier of cork or rubber that isolates or ‘uncouples’ the internal components of the transducer from the case.
acoustic insulator
This prevents vibrations in the case from inducing an electrical voltage in the PZT of the transducer.
acoustic insulator
This provides an electrical connection between the PZT and the ultrasound system.
wire
This requires an electrical contact so that during transmission the voltage from the u/s system can cause it to vibrate and produce an ultrasonic wave.
PZT or active element
This produces a voltage that must return to the system for processing into an image.
PZT or active element
This is postioned in front of the PZT at the face of the transducer.
matching layer
This increases the efficiency of sound energy transfer between the active element and the body.
matching layer
This protects the active element.
matching layer
How thick is the active element/PZT?
one-half wavelength
How thick is the matching layer?
one-quarter wavelength
This is bonded to the back of the active element.
backing material or damping element
This reduces the ‘ringing’ of the PZT.
backing material or damping element
This is commonly made of epoxy resin impregnated with tungsten filaments.
backing material or damping element
When an electrical spike excites the PZT, this restricts the extent of PZT deformation.
backing material or damping element
T/F? Crystal damping enhances axial resolution.
true
The matching layer and gel ___ the efficiency of sound transfer betwen the ___ and the skin.
increase, transducer’s PZT
T/F? Damping material has a low degree of sound absorption.
false, a HIGH degree
T/F? Damping material has an acoustic impedance similar to PZT.
true
The three consequences of using backing material are…
- decreased sensitivity
- wide bandwidth
- low quality factor
During reception, tranducers with ___ are less able to convert low-level sound reflections into meaningful electrical signals.
damping material
This is the range of frequencies in the pulse.
bandwidth
Long duration events are ___ bandwidth, and short duration events are ___ bandwidth.
narrow, wide (broadband)
This is a unitless number that is inversely related to bandwidth.
quality factor
Main frequency divided by bandwidth equals…
quality factor.
Because imaging probes used backing material and have a wide bandwidth, they are often referred to as…
low-Q.
Transducers used in therapeutic u/s and continuous wave Doppler do not contain…
backing material.
Transducers used in therapeutic u/s and continuous wave Doppler have…
narrow bandwidth and high-Q.
A 3 MHz transducer with a bandwidth of 4 MHz has a Q factor of…
3/4 or .75.
Q factor and pulse length are ___ related.
directly. The shorter the pulse, the lower the Q factor.
This is the process of exposing material to a strong electrical field while being heated to a substantial temperature.
polarization
The temperature at which PZT is polarized is called…
the Curie point or the Curie temperature.
The loss of piezoelectric properties is called…
depolarization.
This is the destruction of all microorganisms by exposure to extreme heat, chemical agents, or radiation.
sterilization
This is the application of a chemical agent to reduce or eliminate infectious organisms on an object.
disinfection
What determines the frequency of sound produced by a transducer?
Depends on whether it produces a continuous wave or a pulse.
The frequency of sound emitted by a ___ probe is equal to the frequency of the electrical signal.
continuous wave
What is the frequency of sound from continuous wave transducer when the transmitter creates a 6 MHz electrical signal?
6 MHz, electrical frequency = acoustic frequency
The frequency of sound created by a ___ probe depends upon the characteristics of the active element in the transducer.
pulsed wave
What characteristics of the active element determine the frequency of sound created by a pulsed wave transducer?
- the speed of sound in the PZT
2. the thickness of the PZT
The speed of sound in the PZT and the frequency of sound are ___ related.
directly. The faster the speed of sound in the PZT, the higher the frequency of sound.
The pped of sound in most piezoelectric material ranges from…
4 to 6 mm/microseconds (about 4 times greater than the speed of sound in soft tissue).
The PZT thickness and frequency are ___ related.
inversely. The thinner the PZT, the higher the frequency pulses.
The thickness of PZT crystals in diagnostic imaging transducers range from…
0.2 to 1 mm.
PZT sound speed (mm/microseconds) divided by twice the PZT thickness (mm) equals…
frequency (MHz).
The thickness of the PZT crystal in a pulsed wave transducer is equal to…
one-half of the wavelength of sound in the PZT.
