Ch.8 Transducers Flashcards by Stefani Romero

What is a transducer?

is any device that converts one form of energy into another

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What two functions does the transducer perform?

Transmission
Reception

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Transmission

electrical energy from the system is converted into sound

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Reception

the reflected sound pulse is converted into electricity

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Transducer Converts frm-to
ultrasound transmit
ultrasound receive
car engine

from To
electrical acoustic
acoustic electrical
chemical motion

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Transducer Converts frm-to
Electric motion
Light bulb
Muscle

From To
electrical motion
electrical light & heat
chemical motion

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what is the Piezoelectric effect?

describes the property of certian materials to create a voltage when they are mechanically deformed or when pressure is applied to them.

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What is the reverse piezoelectric effect?

a process when piezoelectric materials change shape when a voltage is applied to them

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What are piezoelectric materials?

materials which convert sound into electricity (and vice versa)
Also called:
piezoelectric
ferroelectric

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What is the most commonly used piezoelectric material used in transducers ?

lead zirconate titanate (PZT)

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What is the most commonly used piezoelectric material used in nature?

quartz and tourmaline

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PZT synonyms 3

ceramic
active element
crystal

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What are the seven components of a basic transducer?

Case
Electrical shield
Acoustic insulator
PZT or active element
Wire
Matching layer
Backing material (damping material)

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Case

the cylindrical tube, constructed of metal or plastic, that protects the internal components of the transducer from damage. The case also insulates the patient from electrical shock

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Electrical shield

A thin metallic barrier lining the inside of the case. The shield prevents spurious electrical signals in the air, unrelated to diagnostic information, from entering the transducer.

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Electrical shield prevents

electrical noise from contaminating the clinically important electrical signals used to create diagnostic images.

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Acoustic insulator

A thin barrier of cork or robber that isolates or “uncouples” the internal components of the transducer from the case.

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Acoustic insulator prevents

vibrations in the case from inducing an electrical voltage in the PZT of the transducer

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PZT or active element

Piezoelectric crystal shaped like a coin.

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The characteristics of the sound beam emitted by the transducer are related to ________ of the ______ _______.
PZT is one-half ________ _____.

dimensions of the active element

wave length thick

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Wire

provides an electrical connection between the PZT and the ultrasound system.

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The active element requires electrical contact (wire) so that during transmission, the voltage from the ultrasound system can cause the crystal to ______ and produce an ______ ______.

vibrate
ultrasonic wave

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During reception, the crystal’s vibration produces a _______ that must return to the system for processing into a _____.

voltage
image

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Matching layer

Positioned in front of the PZT at the face of the transducer. It is one-quarter wavelength thick.

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What are the two functions of the matching layer?

1) Increases the efficiency of sound energy transfer btw the active element and the body. 2) Protects the active element

Backing Material Crystal damping enhances what?

(damping element) Bonded to the back of the active element, it reduces the "ringing" of the PZT. -Axial Resolution

When an electrical spike excites the PZT, the backing material restricts the _ _ _ of ______.

the PZT deformation The emitted sound pulse is dampened; thus it is short in duration and length

Transducer layers A-P? back to front?

case Electrical shield Acoustic insulator Wire Backing material PZT Matching layer Acoustic insulator Electrical shield

How thick is the matching layer? Active element?

1/4 wavelength thick 1/2 wavelength thick

The matching layer and gel _____ the efficiency of sound transfer between the transducer's _ _ _ and ____.

increases PZT skin

Label in decreasing order of impedance: PZT Matching layer Skin Gel

PZT > matching layer > gel > skin

The impedance of the PZT is about _ _ ____ greater than the impedance of ____.

20 times skin

The matching layer is designed with an impedance that is ______ that of the _____ _______ and the _____.

between active element skin

The impedance of gel is _______ that of the ______ and _______.

between matching layer biologic media

What is the function of the gel?

it further increases the percentage of sound transmitted into out of the body. described as coupling the transducer to the patient

What are the two characteristics of the damping material?

high degree of sound absorption acoustic impedance similar to PZT

What are the consequences related to the use of a backing material?

decreased sensitivity wide bandwidth low quality factor

Backing material not only _____ active element vibration during _______-, but also during _______ .

reduces transmission reception

Why is decreased sensitivity by the backing material undesireable?

the transducers are less responsive to the tiny reflected sound waves returning from reflectors in the body.

Transducers with damping material are less able to convert low-level ____ ______ into meaningful _____ _____.

sound reflections electrical signals

Resonant Frequency

a long pure tone of sound that vibrates freely for a long time at a single frequency

The PZT is restricted from vibrating freely by the ____ ____ , and the pulse emitted by an imaging probe is a _____ duration sound "_____" rather than a steady ____ ____.

backing material short click long tone

Bandwidth

is the range of frequencies in the pulse. It is the difference between the highest and lowest frequencies

Imaging probes produce pulses that are identifies as ___ _______ or (_______). Continuous wave doppler, do not use ______ ______ and produce ______ _____ pulses.

wide bandwidth (Broadband) backing material narrow bandwidth pulses

Long duration events are _____ bandwidth, whereas short duration events are ____ bandwidth.

narrow wide

Quality factor

is a unitless number that is inversely related to bandwidth. Q-factor is the main frequency divided by the bandwidth.

Q-Factor formula

Q-factor = main frequency / bandwidth

Wide bandwidth probes have a ___ Q-factor. Narrow bandwidth probes have a ___ Q-factor

low high

What is the relationship between Q-factor and pulse length?

directly related

A short, damped pulse has a ____ Q-factor. A longer, undamped pulse has a ______ Q-factor.

low higher

What are the 6 characteristics of imaging transducers?

1) Pulses with short duration and length 2) Uses backing material to limit ringing 3) Reduced sensitivity 4) Wide bandwidth or broadband 5) Lower Q-factor 6) Improved axial resolution

What are the 6 characteristics of non-imaging transducers?

1) Creates continuos wave or pulses with long duration and length 2) No backing material 3) Increased sensitivity 4) Narrow bandwidth 5) Higher Q-factor 6) NO images created

How is PZT created?

polarization (created by exposing the material to a strong electrical field while being heated to a substantial temprature)

What is the Curie temperature?

the temperature at which PZT is polarized

What is the importance of the curie temperature?

if the polarized PZT is heated above the Curie temperature the crystal's piezoelectric properties are destroyed. (called depolarization)

Depolarization

the loss of piezoelectric properties (depolarized)

Which method is used to clean transducers?

transducers should be disinfected with Cidex or other cold germicides.

What determines the frequency of sound produced by a transducer?

differs depending on whether the transducer produces continuous wave sound or pulses

Continuous wave produces

a continuous electrical signal that constantly excites or drives the active element in the transducer.

The frequency of sound emitted by a continuous wave probe is equal to the?

frequency of the electrical signal

Electrical frequency = _______

Acoustic frequency

Pulse wave creates

a short duration electrical spike that travels thru the wire and strikes the PZT crystal in the transducer

The frequency of sound created by the active element of a pulsed wave transducer depends upon the characteristics of what?

the active element in the transducer

What 2 characteristics of the active element determine the frequency of sound created by a pulsed wave transducer?

1) Speed of sound in the PZT 2) Thickness of the PZT

How does the speed of sound in PZT affect frequency?

the speed of sound in PZT and the frequency of sound are directly related

What is the range of speed of sound in most piezoelectric materials?

from 4 to 6 mm/us (4 times greater than the speed of sound in soft tissue)

How does the thickness of the PZT crystal affect frequency?

PZT thickness and frequency are inversely related

The thickness of the PZT crystal in a pulsed wave transducer is equal to ?

1/2 of the wavelength of sound in the PZT

What are the two characteristics of high frequency pulsed wave imaging transducers?

1) Thinner PZT crystals 2) PZT with higher speeds

What are the two characteristics of low frequency pulsed wave imaging transducers?

1) Thicker PZT crystals 2) PZT with lower speeds

What is the formula for frequency (MHz) ?

(MHz) = sound's speed in PZT (mm/us) / 2 x thickness (mm)