Module2.1

Question 1

When does piezo-electric effect occur?

Answer 1

In some naturally occurring insulating crystals where an ‘electric charge ‘ separation occurs when opposite faces of the crystal experience a compressive (push together) or tensile (pull apart) force.

Question 2

How does the charge separation arise?

Answer 2

As the atomic electrons and the nucleus have slightly displaced centres of their respective charges; electron and protons.

Question 3

What is the unit of stress ?

Answer 3

Same as pressure Pa or N/m^2

Question 4

What is the commonest naturally occurring piezo electric crystal?

Answer 4

Quartz

Question 5

These days ultrasound piezo electric materials are also fabricated from?

Answer 5

Lead zirconium titanate or PZT or LZT

Question 6

what is the inverse piezo electric effect?

Answer 6

The strain that is produced when a voltage V is applied

OR

The production of a dimensional change in the crystal when a voltage is applied

-> this effect is used to produce ultrasound pulses or waves
»»»»»> inverse piezo electric effect produces the pulses

Question 7

What is strain?

Answer 7

The change of shape dud to applied stress

Question 8

What is the piezo electric effect ?

Answer 8

The production of a voltage on the crystal when it is deformed by returning ultrasound pulses or waves

> > > > > > > > > > piezo electric effect proper reads the echo pulses

Question 9

What is anisotropy?

Answer 9

Material property where the crystal properties depend on the direction within the crystal.

Eg) fluids : isotropic
Tissues like muscle and tendons: anisotropic

Question 10

What is CW?

Answer 10

When the ultrasound wave continues as long as the sinusoidal voltage is applied thus continuous wave

Question 11

What happen to CW if frequency changes?

Answer 11

If frequency of the voltage is altered, the CW ultrasound wave just possesses this new frequency

Question 12

What is PRP?

Answer 12

Pulse repetition period, the time delay when each voltage pulse to the LZT crystal occurs after a fixed time interval following the previous pulse / unit is s or ms

Question 13

What is PRF?

Answer 13

Pulse repetition frequency/ unit is Hz or called pulse repetition rate PRR

Question 14

What does it mean by damped/damping?

Answer 14

Mechanical damping is another way of saying the ultrasound pulse energy is attenuated by the ultrasound energy being absorbed by the material through the medium&raquo_space;> sound duration is shortened and exists for only about 2-5periods so only 1-10micro sec depending on the frequency

Electrical damping is by shaping the electric pulse to the transducer.

Question 15

What is a transducer?

Answer 15

A device that transforms one kind of energy( eg. electrical) to another form (eg. Acoustic)

Question 16

What is piezo electric crystal!?

Answer 16

Is an ultrasound transducer and the source of the ultrasound energy

Question 17

What are the ultrasound elements?

Answer 17

Electrodes, two wires, damping block, backing

Question 18

What is the bandwidth when damping is applied?

Answer 18

The frequency interval between the two points on the frequency response curve where the response is 1/2 of that at the resonance frequency

Question 19

How is q factor and damping for ultrasound transducer ?

Answer 19

Low q factor and high damping

Question 20

What is SPL?

Answer 20

Spatial pulse length, the pulse length in space 2~5 ㅅ

Question 21

What is the echo time?

Answer 21

The total time for the round trip

Question 22

What is PW?

Answer 22

Pulse wave

Question 23

When is maximum depth measured?

Answer 23

measure when it returns to the transducer during the next ‘off’ time of the duty cycle (처음꺼 도착전까지는 다음 웨이브 홀드)

Question 24

What is the central ray?

Answer 24

An ultrasound wave emitted by a transducer/ it describes its initial beam direction(ray) from the LZT transducer face./ perpendicular to the transducer faceplate