UNIT 8

The primary function of the piezoelectric element is to:

Convert electrical energy to mechanical (sound) energy

what does the reverse piezoelectric element do?

Convert mechanical (sound) energy to electrical energy

The matching layer is placed between the piezoelectric element and the patient to:

increase impedance mismatch

what is the thickness of the matching layer?

One-quarter wavelength

The backing (damping) material is located:

Behind the crystal

The primary purpose of backing material is to:

Decrease pulse duration

Increasing damping of the transducer will result in:

Shorter spatial pulse length

A heavily damped transducer will have:

Low Q-factor and wide bandwidth

Q-factor is defined as the ratio of:

Frequency to bandwidth

Increasing Q-factor will result in:

Narrower bandwidth

A transducer with a wide bandwidth will have:

Short pulse duration

Which transducer characteristic MOST improves axial resolution?

Wide bandwidth

Which change would widen bandwidth?

Increasing damping

A transducer that rings excessively will have:

Narrow bandwidth

Which component primarily limits “ring-down” of the crystal?

Backing material

The best combination for optimal axial resolution is:

Low Q-factor and wide bandwidth

Transducer sensitivity is BEST defined as the ability to:

Detect weak returning echoes

Polarization of PZT refers to the process of:

exposing material to a strong electrical field while being heated to a substantial temperature

The Curie point is defined as the temperature at which the PZT:

Loses its piezoelectric properties

Exceeding the Curie point of a transducer will result in:

Permanent depolarization of the crystal

what is frequency dependent on in a transducer?

PZT Thickness

Increasing the thickness of the PZT crystal will result in:

Lower frequency

A thin PZT crystal will produce ultrasound with:

High frequency

PZT thickness is approximately equal to:

Half a wavelength

Which component prevents ultrasound energy from radiating out?

Acoustic insulation

Which component prevents electrical noise from interfering with the signal?

Electrical shield

which component protects internal components and patient from shock?

case

Which transducer component is located in front of the PZT crystal?

Matching layer

Which component is located behind the PZT crystal?

Backing material

Which structure is the FIRST component encountered by sound returning from the patient?

Matching layer

Which component of an ultrasound system is made of lead zirconate titanate (PZT)?

Transducer active element

Which component of an ultrasound transducer is made from a slab of epoxy embedded with tungsten particles?

Damping material

Which of the following lists orders the impedance from highest to lowest?

PZT, matching layer, gel, skin

Damping material is secured to piezoelectric material during the fabrication of an ultrasound imaging transducer. Which of the following is not a consequence of this attachment?

Sensitivity increases

Which of the following actions would cause a PZT crystals to lose its special properties?

Exposing it to high temperatures

With pulsed wave ultrasonic imaging, what helps to establish the primary frequency of the acoustic energy discharged by the transducer?

Piezoelectric crystal thickness

An ultrasound pulse is traveling in soft tissue. Which of the following is most important in the determination of the frequency of the sound?

The propagation speed of the transducer active element

Which properties of the piezoelectric crystal of an imaging transducer result in the highest emitted acoustic wave frequency?

Thin, high propagation speed

You are asked to fabricate a pulsed ultrasound transducer with the highest possible frequency. Which piezoelectric crystal would you select?

2 mm thick, 6 cm diameter, 6 mm/us propagation speed

You are asked to fabricate a pulsed ultrasound transducer with the lowest possible frequency. Which piezoelectric crystal would you select?

8 mm thick, 2 cm diameter, 2 mm/us propagation speed