2 Ch 8: Transducers

Question 1

Define ‘transducer’.

Answer 1

Any device that converts one form of energy into another.

Question 2

During ___, electrical energy from the system is converted into sound.

Answer 2

transmission

Question 3

During ___, the reflected sound pulse is converted into electricity.

Answer 3

reception

Question 4

This is the property of certain materials to create a voltage when they are mechanically deformed or when pressure is appiled to them.

Answer 4

The piezoelectric effect

Question 5

This is the process of piezoelectric materials that change shape when a voltage is applied to them.

Answer 5

reverse piezoelectric effect

Question 6

Materials which covert sound into electricity (and vice versa) are called…

Answer 6

piezoelectric or ferroelectric

Question 7

The piezoelectric material commonly used in clinical transducers that are synthetic are…

Answer 7

lead zirconte titanate or PZT

Question 8

PZT is also known as…

Answer 8

ceramic, active element, or crystal.

Question 9

This cylindrical tube, constructed of metal or plastic, protects the internal components of the transducer from damage.

Answer 9

case

Question 10

This insulates the patient from electrical shock.

Answer 10

case

Question 11

This thin metallic barrier lines the inside of the case.

Answer 11

electrical shield

Question 12

This prevents spurious electrical signals in the air, unrelated to diagnostic information, from entering the transducer.

Answer 12

electrical shield

Question 13

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

Answer 13

electrical shield

Question 14

This is a thin barrier of cork or rubber that isolates or ‘uncouples’ the internal components of the transducer from the case.

Answer 14

acoustic insulator

Question 15

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

Answer 15

acoustic insulator

Question 16

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

Answer 16

wire

Question 17

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.

Answer 17

PZT or active element

Question 18

This produces a voltage that must return to the system for processing into an image.

Answer 18

PZT or active element

Question 19

This is postioned in front of the PZT at the face of the transducer.

Answer 19

matching layer

Question 20

This increases the efficiency of sound energy transfer between the active element and the body.

Answer 20

matching layer

Question 21

This protects the active element.

Answer 21

matching layer

Question 22

How thick is the active element/PZT?

Answer 22

one-half wavelength

Question 23

How thick is the matching layer?

Answer 23

one-quarter wavelength

Question 24

This is bonded to the back of the active element.

Answer 24

backing material or damping element

Question 25

This reduces the 'ringing' of the PZT.

Answer 25

backing material or damping element

Question 26

This is commonly made of epoxy resin impregnated with tungsten filaments.

Answer 26

backing material or damping element

Question 27

When an electrical spike excites the PZT, this restricts the extent of PZT deformation.

Answer 27

backing material or damping element

Question 28

T/F? Crystal damping enhances axial resolution.

Answer 28

true

Question 29

The matching layer and gel ___ the efficiency of sound transfer betwen the ___ and the skin.

Answer 29

increase, transducer's PZT

Question 30

T/F? Damping material has a low degree of sound absorption.

Answer 30

false, a HIGH degree

Question 31

T/F? Damping material has an acoustic impedance similar to PZT.

Answer 31

true

Question 32

The three consequences of using backing material are...

Answer 32

1. decreased sensitivity 2. wide bandwidth 3. low quality factor

Question 33

During reception, tranducers with ___ are less able to convert low-level sound reflections into meaningful electrical signals.

Answer 33

damping material

Question 34

This is the range of frequencies in the pulse.

Answer 34

bandwidth

Question 35

Long duration events are ___ bandwidth, and short duration events are ___ bandwidth.

Answer 35

narrow, wide (broadband)

Question 36

This is a unitless number that is inversely related to bandwidth.

Answer 36

quality factor

Question 37

Main frequency divided by bandwidth equals...

Answer 37

quality factor.

Question 38

Because imaging probes used backing material and have a wide bandwidth, they are often referred to as...

Answer 38

low-Q.

Question 39

Transducers used in therapeutic u/s and continuous wave Doppler do not contain...

Answer 39

backing material.

Question 40

Transducers used in therapeutic u/s and continuous wave Doppler have...

Answer 40

narrow bandwidth and high-Q.

Question 41

A 3 MHz transducer with a bandwidth of 4 MHz has a Q factor of...

Answer 41

3/4 or .75.

Question 42

Q factor and pulse length are ___ related.

Answer 42

directly. The shorter the pulse, the lower the Q factor.

Question 43

This is the process of exposing material to a strong electrical field while being heated to a substantial temperature.

Answer 43

polarization

Question 44

The temperature at which PZT is polarized is called...

Answer 44

the Curie point or the Curie temperature.

Question 45

The loss of piezoelectric properties is called...

Answer 45

depolarization.

Question 46

This is the destruction of all microorganisms by exposure to extreme heat, chemical agents, or radiation.

Answer 46

sterilization

Question 47

This is the application of a chemical agent to reduce or eliminate infectious organisms on an object.

Answer 47

disinfection

Question 48

What determines the frequency of sound produced by a transducer?

Answer 48

Depends on whether it produces a continuous wave or a pulse.

Question 49

The frequency of sound emitted by a ___ probe is equal to the frequency of the electrical signal.

Answer 49

continuous wave

Question 50

What is the frequency of sound from continuous wave transducer when the transmitter creates a 6 MHz electrical signal?

Answer 50

6 MHz, electrical frequency = acoustic frequency

Question 51

The frequency of sound created by a ___ probe depends upon the characteristics of the active element in the transducer.

Answer 51

pulsed wave

Question 52

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

Answer 52

1. the speed of sound in the PZT | 2. the thickness of the PZT

Question 53

The speed of sound in the PZT and the frequency of sound are ___ related.

Answer 53

directly. The faster the speed of sound in the PZT, the higher the frequency of sound.

Question 54

The pped of sound in most piezoelectric material ranges from...

Answer 54

4 to 6 mm/microseconds (about 4 times greater than the speed of sound in soft tissue).

Question 55

The PZT thickness and frequency are ___ related.

Answer 55

inversely. The thinner the PZT, the higher the frequency pulses.

Question 56

The thickness of PZT crystals in diagnostic imaging transducers range from...

Answer 56

0.2 to 1 mm.

Question 57

PZT sound speed (mm/microseconds) divided by twice the PZT thickness (mm) equals...

Answer 57

frequency (MHz).

Question 58

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

Answer 58

one-half of the wavelength of sound in the PZT.