Ultrasound Transducers, Beams & Resolution

Front 1

A general term for transducers

Back 1

they convertone form of energy into another

Front 2

What is the Piezoelectric effect

Back 2

when a mechanicl force is applied to certain materials they create a voltage and vice versa

Front 3

Piezoelectric is also called

Back 3

ferroelectric

Front 4

Ultrasound transducer transfer __________ energy into the body and recieve___________ energyfrom the body

Back 4

sound
sound

Front 5

Transducers convert electrical energy into sound energy by way of a

Back 5

Piezoelectric element

Front 6

Give the breakdown of the Piezoelectric effect

Back 6

US machine sends an electric voltage to Piezoelectric element causing it to vibrate

Vibration sends sound energy into the body

Echoes return from structures in the body which vibrates the piezoelectric element causing it to generate an electrical signal

This signal gets sent back to the US maching which makes an image

Front 7

Piezolectric Elements are also called the

Back 7

Active Element

Front 8

What are the elements made of

Back 8

Man made and natural materials

Front 9

What materials are transducers usually made of

Back 9

Lead zirconate titanate (PZT) or barium titanate

Front 10

Piezoelectric elements are heated to what point

Back 10

The Curie point which is 365

Front 11

Never do what to a transducer

Back 11

Sterilize it

Front 12

What is the main component of an ultrasound transducer with piezoelectric properties

Back 12

Crystal

Front 13

What are some of the natural materials

Back 13

Quart, Rochelle, Tourmaline and Salts

Front 14

Transducer crystals lose their piezoelectric properties when they are heated

Back 14

above the Curie point

Front 15

What happens to the material

Back 15

it becomes depolarized

Front 16

Name another material that is not naturally piezoelectric

Back 16

Ceramics

Front 17

What must be done to ceramics to make them become piezoelectric

Back 17

placed in a strong magnetic field while being heated at a hgh temperature

Front 18

Which element is bonded to the back of the active element

Back 18

Damping element

Front 19

What does the damping element do

Back 19

Reduces ringing

Front 20

By reducing the ringing you

Back 20

Shorten pulse duration and SPL, improving the overall image

Front 21

What happens to transducer crystals when they are heated above the Curie point

Back 21

They become depolarized

Front 22

Name the transducer components

Back 22

Wire, Acoustic insulator,Electrical shield, Damping element, Active element, Matching layer

Front 23

What is bandwidth

Back 23

range of frequencies within a pulse

Front 24

Damping material does what to bandwidth

Back 24

increases it.

Front 25

Damping material does what to the Q Factor

Back 25

Decreases it.

Front 26

Damping material does what to the transducers sensitivity to reflected echoes

Back 26

Decreases it

Front 27

bandwidth and Q factor are (inversly or directly) related

Back 27

Inversly - wide bandwidth = low Q factor

Front 28

What is Damping material analogous to

Back 28

putting your hand on a bell fter you rint it to stop the vibrations

Front 29

What material sits in front of the active element

Back 29

Matching layer

Front 30

What does the matching layer do

Back 30

It reduces reflections at the transducer tissue interface

Front 31

Matching layer is also called

Back 31

Impedance matching layer

Front 32

What wavelength of the US beam is the matching layer

Back 32

1/4

Front 33

The matching layer helps to send more

Back 33

US energy into the body rather than reflecting it b/c of the impedance difference at the skin

Front 34

What else also helps to reduce impedance difference at the transducer skin interface

Back 34

Gel

Front 35

Impedance Range from highest to lowest: Gel, skin, PZT, matching layer

Back 35

PZT
Matching layer
Gel
Skin

Front 36

Composite piezoelectic elements are closer to that of

Back 36

Soft tissue

Front 37

What component is connected to the transducer element that sends and receives electrical voltages

Back 37

The wire

Front 38

What does an electrical voltage do to the crystal (remember the crystal is aka piezoelectric element)

Back 38

Causes it to vibrate creating a mechanical energy.

Front 39

The plastic or metal housing surrounding all of the transducers components is

Back 39

Case and Insulation

Front 40

What does Case and Insulation prevent

Back 40

Electrical noise from altering the transducers perfomance

Front 41

What natural frequency called

Back 41

Resonant frequency

Front 42

Resonant frequency is

Back 42

The operating frequency of the transducer

Front 43

Transducer frequency depends on

Back 43

The thickness of the crystal and the speed of sound in the crystal

Front 44

What happens to frequency in the following:
Higher speed =
Lower speed =
Thinner crystal =
Thicker crystal =

Back 44

Higher frequency
Lower frequency
Higher freqency
Lower frequency

Front 45

Where is the resonant frequency located in relation to bandwidth

Back 45

Center of the bandwidth

Front 46

Advantage of wide bandwidth

Back 46

Fewer cycles per pulse give longer lstening time
Can receive a wider range of frequencies

Front 47

Disadvantage of wider bandwidth

Back 47

Decreased sensitivity

Front 48

What calculates the Q Factor

Back 48

Resonant frequency divided by bandwidth

Front 49

Shorter pulses have

Back 49

Fewer cycles
wider or broader bandwidth
lower Q
more listening time

Front 50

Near Zone is aka

Back 50

Fresnel Zone

Front 51

Near zone is located

Back 51

b/t the transducer and focus

Front 52

Near zone is determined by

Back 52

The size and operating frequency of the element

Front 53

More variation in beam intensity happens in which zone

Back 53

Near Zone

Front 54

If the frequency increases what happens to the near zone

Back 54

it increases as well

Front 55

What is the space b/t the near zone and focus called

Back 55

Focal length or near zone length

Front 56

A larger crystal diameter does what to the focal length

Back 56

makes it longer

Front 57

Higher frequencies do what to the focal length

Back 57

longer

Front 58

Far Zone aka

Back 58

Fraunhofer

Front 59

Focus is aka

Back 59

Focal Depth

Front 60

A large crystal diameter does what to focal depth

Back 60

makes it go farther or deeper

A smaller crystal = more shallow focal depth

Front 61

Beam width depends on three things

Back 61

Aperture (size of source)
Frequency
Distance from the transducer

Front 62

What is beam diameter to transducer diameter in the near zone, focus and far zone

Back 62

equal
half
equal

Front 63

Frequency and Diameter are directly _______________ to near zone length

Back 63

proportional

Front 64

One near zone length starts from _____________ to the _________

Back 64

Near zone
Focus

Front 65

Two near zone lengths start from __________ to the _______

Back 65

Near zone
Far zone

Front 66

Frequency and Diameter are __________ proportional to divergence

Back 66

inversely - smaller frequency or diameter = more divergence

Front 67

What is diffraction

Back 67

Diffraction occurs when sound waves are produces by a small sound source, they diverge or spread as sound propagates

Front 68

Huygen's Principle

Back 68

tiney wavelets combine to produce a sound beam with most of the energy transmitted along a main central beam having the shape of an hourglass.

Front 69

Another definition of Huygens principle

Back 69

many points on the crystal combine to act as a large sound source rather than a small one

Front 70

What are the Beam Characteristics

Back 70

Beam Freqquency
Focal Depth
Beam divergence

Front 71

What are the crystal properties of beam frequency, Focal depth and Beam divergence

Back 71

Crystal thickness and propagation speed of crystal

Crystal diameter and crystal frequency

Crystal diameter and crystal frquency

Front 72

What are the four ways to focus

Back 72

Lens = external focusing
Curved Crystal = internal foc.
Mirror
Electronic = Phased Array