Ch. 8 Physics: Transducers

Question 1

What are devices that converts one form of energy into another?

Answer 1

Transducers

Question 2

What are the two functions of the transducers?

Answer 2

Transmitting sound
Receiving sound

Question 3

When electrical energy converts to sound it is called

Answer 3

Transmitting

Question 4

When reflected sound pulse is converted into electricity it is called

Answer 4

Receiving

Question 5

What describes the property of certain materials to create a voltage when they are mechanically deformed or when pressure is applied?

Answer 5

Piezoelectric effect

Question 6

What is it called when the piezoelectric materials changes shape when voltage is applied?

Answer 6

Reverse piezoelectric affect

Question 7

What is piezoelectric matiera?

Answer 7

Quartz or tourmaline
Lead zirconate titanate or PZT

Question 8

The cylindrical tube that protects the internal components and insulates the patient from electrical shock.

Answer 8

Case

Question 9

A metallic barrier lining the inside of the case, preventing extraneous electrical signals in the air from entering the transducer and causing noise.

Answer 9

Electrical sheild

Question 10

A thin barrier of cork or rubber that isolates the internal components of the transducer from the case, preventing vibrations from the case interfering with the electrical voltage.

Answer 10

Acoustic insulator

Question 11

In a simple probe, it is shaped like a coin. The characteristics of the sound beam are related to the dimensions of the active element. The PZT is ½ wavelength thick.

Answer 11

PZT or active element

Question 12

Provides an electrical connection between the PZT and the system since the voltage is needed in order to vibrate and produce a wave.

Answer 12

Wire

Question 13

Increases the efficiency of sound transfer between the element and tissue, while protecting the element. The matching layer is ¼ wavelength thick.

Answer 13

Matching layer

Question 14

Bonded to the active element, it reduces the “ringing” of the PZT which reduces the spatial pulse length and improving axial resolution.

Answer 14

Backing material or damping element

Question 15

This layer is designed to have an impedance between the skin and the element, increasing the sound transmitted

Answer 15

Matching layer

Question 16

What layer reduces the acoustic impedance mismatch between the crystal and the patient?

Answer 16

Matching layer

Question 17

What happens with no matching layer?

Answer 17

80% of the sound beam would be reflected before entering the body.

Question 18

Allows the crystal to ring, but dramatically reduces the vibration.

Answer 18

Backing material

Question 19

What shortens the pulse and ring by absorbing some of the vibration?

Answer 19

Backing material

Question 20

What is the disadvantages of the backing material?

Answer 20

Decreased sensitivity

Wide bandwidth

Low quality factor

Question 21

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

Answer 21

Bandwidth

Question 22

What kind of bandwidth is for (CW) continuous wave frequencies; longer durations

Answer 22

Narrow bandwidth

Question 23

What kind of bandwidth is for imaging probes; shorter durations?

Answer 23

Wide bandwidth

Question 24

What is a unitless number that is inversely related to bandwidth?

Answer 24

Quality factor “Q-Factor”

Question 25

What are the two different transducers?

Answer 25

imaging and non-imaging transducers

Question 26

What determines the natural resonance frequency of the PZT?

Answer 26

Crystal thickness

Question 27

What is the normal propagation speed for PZT?

Answer 27

4-6mm/ microsec

Question 28

When sound is fast, the frequency is

Answer 28

high

Question 29

when sound is slow, the frequency is

Answer 29

low

Question 30

Can sound in PZT be changed?

Answer 30

No

Question 31

True or False:
Two PZT crystals are made from identical material.
The thickness of the crystal will make a CW transducer have a lower frequency.

Answer 31

FALSE.
CW active elements are not determined by thickness, only by the electrical frequency

Question 32

True or False:
A CW transducer frequency has an electrical excitation of 3MHz, so the operating frequency will be 3MHz.

Answer 32

True

Question 33

Which of the following matching layer impedances would be acceptable if the active element is 1,600,000 Rayls and the skin is 1,300,000 Rayls?

1,700,000 Rayls

1,200,000 Rayls

1,300,000 Rayls

1,500,000 Rayls

Answer 33

1,500,000 Rayls – since it is in between

Question 34

A pulsed wave transducer is operating at a frequency of 6MHz. The lowest frequency is 1MHz and the highest is 9MHz. What is the bandwidth?

What is the resonant frequency of the same transducer?

Answer 34

8MHz – since 9 – 1 = 8

6MHz – resonant = operating

Question 35

List skin, PZT, gel, and matching layer in decreasing order of impedance:

Answer 35

PZT, matching layer, gel, skin

Question 36

The PZT thickness is _______ the wavelength.

Answer 36

half

Question 37

Which component is ¼ wavelength thick?

Answer 37

Matching layer

Question 38

What is the Q-factor of a transducer with a 4MHz bandwidth that is operating at 3Mhz?

Answer 38

¾ or .75
Quality factor = main frequency / bandwidth

Question 39

What is the quality factor of a transducer with frequencies between 2MHz and 6MHz operating at 4MHz?

Answer 39

1

6-2 = 4MHz bandwidth, Q = 4 / 4 = 1

Question 40

Will the pulse of a shorter, dampened pulse have a lower or higher quality factor?

Answer 40

Lower