Transducers and Sound Beams

Question 1

How are time of flight and depth related?

Answer 1

Directly
depth (mm) = (1.54 mm/us x go return time us)/2

Question 2

What is the 13 microseconds rule?

Answer 2

states that for every 13 us of go return time, the object that creates the reflection is 1 cm deeper in the body

Question 3

How are PRP and depth related?

Answer 3

Directly

PRP (us) = imaging depth (cm) x 13 us/cm

Question 4

What is a transducer?

Answer 4

Any device that turns one form of energy into another

Question 5

What is the piezoelectric effect?

Answer 5

Describes the property of materials to create a voltage when pressure is applied or when they are mechanically deformed

Question 6

What is another term for piezoelectric materials?

Answer 6

Ferroelectric

Question 7

What happens to the ultrasound transducer during transmission?

Answer 7

the transducer converts electrical energy from the system into sound

Question 8

What happens to the ultrasound transducer during reception?

Answer 8

the transducer converts the reflected sound pulse into electricity

Question 9

What is PZT?

Answer 9

Lead zirconate titanate

Question 10

What are the synonyms for PZT?

Answer 10

Ceramic
Active element
Crystal

Question 11

What is the Curie Temperature?

Answer 11

the temperature at which PZT is polarized

Question 12

What happens when PZT reaches the Curie point?

Answer 12

If it goes higher than the Curie point, the crystal’s piezoelectric properties are destroyed, called depolarization.

Question 13

Should you heat sterilize or autoclave a transducer?

Answer 13

No, you should not sterilize a transducer with heat.

Question 14

What is sterilization?

Answer 14

Destroying all microorganisms by exposing them to extreme heat, chemical agents, or radiation

Question 15

What is disinfection?

Answer 15

Applying a chemical agent to an object to reduce or eliminate infectious organisms

Question 16

What is the purpose of the case?

Answer 16

protects the internal components of the transducer and insulates the patient from electrical shock

Question 17

Is it safe to use a transducer if the case is cracked?

Answer 17

No

Question 18

How are the active element and wavelength related?

Answer 18

Active element is 1/2 wavelength thick

Question 19

What is the purpose of the matching layer?

Answer 19

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

Question 20

How thick is the matching layer?

Answer 20

1/4 wavelength thick

Question 21

What is the purpose of the backing material?

Answer 21

to reduce the “ringing” of the PZT

Question 22

How does backing material affect pulse duration?

Answer 22

It produces short pulses and makes pulse duration shorter

Question 23

How does backing material affect transducer sensitivity?

Answer 23

It decreases the sensitivity - because it makes the transducer less able to convert low-level sound reflections into electrical signals

Question 24

What are the three consequences of using a backing material?

Answer 24

Decreased sensitivity
Wide bandwidth
Low quality factor

Question 25

Do continuous or pulsed wave transducers need backing material?

Answer 25

Pulsed wave

Question 26

What is bandwidth?

Answer 26

The range of frequencies in a pulse and the difference between the highest and lowest frequencies

Question 27

Do long or short pulses have a wider bandwidth?

Answer 27

Short duration pulses have a wider bandwidth

Question 28

What are the synonyms for the main frequency produced by a transducer?

Answer 28

Center Resonant Primary Natural frequency

Question 29

Does a short or long pulse have a higher quality factor?

Answer 29

A longer pulse has a higher q-factor

Question 30

For a CW transducer how are frequency of voltage and the sound frequency related?

Answer 30

The frequency of the voltage is equal to the sound frequency. Electrical frequency = acoustic frequency

Question 31

What two characteristics of the active element determine transducer frequency?

Answer 31

The speed of sound in PZT and thickness of PZT

Question 32

How are speed of sound in PZT and frequency related?

Answer 32

Speed of sound in PZT and frequency are directly related. | When sound in PZT is faster, frequency is higher, and when sound in PZT is slower, frequency is lower.

Question 33

How are crystal thickness and frequency related?

Answer 33

Crystal thickness and frequency are inversely related. | Thinner PZT crystals produce higher frequency waves, and thicker crystals produce lower frequency waves.

Question 34

What is the focus or focal point?

Answer 34

The point at which the sound beam is the narrowest

Question 35

What is the focal depth?

Answer 35

The distance from the transducer to the focus

Question 36

What are synonyms for focal depth?

Answer 36

Focal length | Near zone length

Question 37

What is the near zone?

Answer 37

The region from the transducer to the focus

Question 38

What are synonyms for near zone?

Answer 38

Near field | Fresnel zone

Question 39

What is the far zone?

Answer 39

The region that starts at the focus and extends deeper

Question 40

What are synonyms for far zone?

Answer 40

Far field | Fraunhofer zone

Question 41

What is the focal zone?

Answer 41

The region around the focus that is relatively narrow

Question 42

``` For an unfocused CW transducer, what is the beam diameter at: transducer end of near zone 2 near zone lengths deeper than 2 near zone lengths ```

Answer 42

Transducer - beam dia = transducer dia End of near zone - beam dia = 1/2 transducer dia 2 near zone lengths - beam dia = transducer dia Deeper than 2 near zone lengths - beam diameter > transducer dia

Question 43

What factors determine sound beam divergence in the far zone?

Answer 43

Transducer diameter | Frequency of sound

Question 44

Do smaller or larger diameter crystals create beams that diverge more in the far field?

Answer 44

Smaller crystals produce beams that diverge more in the far field

Question 45

Do higher or lower frequency beams spread out more in the far field?

Answer 45

Lower frequency beams

Question 46

What is a Huygen's Wavelet?

Answer 46

A V-shaped wave created when the source is about the size of the sound’s wavelength.

Question 47

What is Huygen's Principle?

Answer 47

The inconsistency between large and small sound sources and their beams. It states that a large active element can be thought of as millions of tiny sound sources.