Transducer Quiz text version

Transducer Online Workshop - Quiz

by the panel of experts Interactive version in Java

1. Question:
1-3 Composite Transducers provide a higher acoustic Impedance than PZT Transducers.
a) true
b) false

Answer:
false is correct.
The acoustic impedance is lower than for PZT. Composite provides 6.5 Mrayl, on the contrary 29.3 Mrayl for Piezoceramic PZT P5.

2. Question:
What polymer is the most effective transducing material?.

Answer:
PVF2

3. Question:
Polymer transducers work effectively as:
a) transmitters b) receivers c)or both?

Answer:
Mostly as receivers because of their low noise and inherent damping.

4. Question:
Can piezoelectric transducers be used to perform test at single digit Kelvin Temperatures (0 deg. C = 273 degree K)

Answer:
Yes they can be used. However, their various coefficients decrease significantly and can be compensated by use of a higher drive voltage.

5. Question:
While using an ultrasonic through-transmission method, a near surface flaw , such as a void in Carbon-Carbon material is better detected.
a) when the wet squirter method is used
b) when a non-contact air-coupled method is used

Answer:
b) is correct.
Explication: Carbon-Carbon material is very porous. When water is absorbed, especially near the surface of the part, the water fills the void and the through transmitted signal is no longer attenuated and therefore, the wet method fails to detect the void.This is not the case with air-coupled ultrasonic through transmission, because the void now causes a major reflection loss and therefore detects the presence of the flaw.

6. Question:
Which transducer has the smaller focal spot size:
a) A 1 inch diameter, 1 MHz test frequency, focal length 1.5 inches in water
b) A 1 inch diameter, 400 kHz test frequency, focal length 1.5 inches in air

Answer:
b) is correct
Explication: The wavelength at 1 MHz in water, having a sound velocity of 1500 m/sec, is 1.5 millimeter. The wavelength in air, having a sound velocity of 340 m/sec at 400 kHz, is 0.85 millimeter. The focal spot diameter dx is directly proportional to the wavelength l for equal element diameter D and focal distance zi. The Rayleigh Criterion yields the defenition for -4 dB points as: (dx=l zi /D) .

7. Question:
Air cannot be used as an ultrasonic couplant.
a) True
b) False

Answer:
b) is correct.
Explication: Physically, air has to be considered an ultrasonic couplant, since it does transmit ultrasound, in contrast to the vacuum, where absolutely no sound propagation occurs. However, special transducers and instrumentation have to be used in order to compensate for the high reflection losses between transducer and test part.

8. Question:
Polymer probes are compared to conventional ceramic probes are:
a) more noisy
b) less noisy

Answer:
b) is correct.
The internal damping in the polymer foil is much better and the excitation of radial modes is considerably lower than in ceramic probes.

9. Question:
Ultrasonic NDT at elevated temperatures is
a) only possible when the probe is cooled down to less than 60 °C with water or air b) not possible c) possible with special probes up to 800 °C surface temperature

Answer:
c) is correct.

10. Question:
Piezocomposite transducers are preferably used for

a) Normal beam probes in direct contact with steel
b) Immersion or delay line probes

Answer:
b) is correct.
Due to the low acoustic impedance of piezocomposite material (<10 Mrayls) it is better matched to water (1.5 Mrayls) or plastic delay lines of single or dual beam probes (2 to 4 Mrayls) and wedges of angle beam probes than to steel (45 Mrayls).

11. Question:
Variable steering can be obtained with:
a)mechanical rocking/rotating transducers
b)electronic phased linear array
c)electronic phased annular array
d)electronic phased bi-dimensional array

Answer:
a),b)and d) are correct c)is wrong
Electronic phased annular array is dedicated to variable focusing versus depth along the central axis of the transducer and permits an increase of the depth of field.

12. Question:
Aspherical focusing is used to:
a)provide a sharp focus by compensating aberration effects when transmitting or receiving through refractive interfaces
b)create asymmetrical beam in the inspection of oriented flaws.

Answer:
a) is correct
asymmetrical beam can be obtained with special active apertures providing more lateral resolution in one direction compared to an other.

13. Question:
The performances of array transducers are:
a)limited in bandwidth and temporal response due to coupling effects inside the array structure.
b)comparable to single element transducers for bandwidth and temporal response

Answer:
a)is not more true
b)is correct if the right technology is employed.
For instance, piezocomposite technology can provide excellent decoupling of parasitic modes and many applications have now been developped which demonstrates the great interest of array transducers in many applications requiring flexibility and/or fast scanning.

14. Question:
Schlieren measurements of acoustic fields are based on:
a) Change of color with pressure
b) Doppler interaction of light with particle displacement
c) Pressure changing the index of refraction
d) Optical wave changing phase

Answer:
a) is incorrect. Although the wavenumber k is shifted by K (2pi/lambda) of sound, the effect is too small compared to the bandwidth of the light.
b) is incorrect. The light and the sound must propagate in orthogonal directions.
c) is correct.
d) is also correct, changes in the index of refraction cause delay or speed up of the light wave, resulting in phase modulation after interacting with the acoustic beam.

15. Question:
If an acoustic beam propagates along the Z axis, the resulting image has brightness that corresponds to:
a) Intensity in the X-Z plane
b) The integral of phase retardation along the light path squared.
c) The integral of intensity along the light path.
d) The intensity everywhere

Answer:
The correct answer is b).
The change in index of refraction is proportional to the pressure, and this effect is integrated along the light path. The camera sees the intensity of light (square of amplitude), hence the squared term.

16. Question:
For a 3-D map of the acoustic field one needs images:
a) From three views (XZ, YZ and XY)
b) From two views (XZ and YZ) only.
c) From many views that include the Z axis.
d) From any direction perpendicular to the Z axis
e) Depends on the beam geometry.

Answer:
a) is incorrect: the XY view is not possible because the light beam must be perpendicular to the acoustic beam
b) is partially true: only if a beam has separable geometry, i.e. I(x,y)=Io f(x,z)*g(y,z) then it is possible to reconstruct the beam for all space. c) is correct for any arbitrary acoustic beam, the process of reconstruction is standard tomographic reconstruction.
d) is correct only for beams that have cylindrical symmetry. The reconstruction is known as the Abel transform.
e) is true, as seen in answers b), c) and d).

17. Question:
Which wave modes can be generated by the Multifunction UT-Phased Array Probe?
a) shear waves.
b) longitudinal waves.
c) lamb waves.
d) a and b.

Answer: d) is correct. Shear waves and longitudional waves can be generated.

18. Question:
Which features are essential for the Multifunction UT-Phased Array Probe?
a) large dimensions, high sensitive, waterproofed connectors, high signal to noise ratio.
b) small dimensions, high sensitive, large bandwidth, high signal to noise ratio.
c) small dimensions, thin plastic housing, low signal to noise ratio, large bandwidth.
d) none of them.

Answer: correct is b)

19. Question:
What are the main advantages for the use of the Multifunction UT-Phased Array Probe?
a) small probe arrangements
b) reduced scantimes
c) substitution of several standard UT-probes
d) all off the above

Answer: correct is d)

20. Question:
What transducer would I pick to test the bonding of 1 mm Al to 100 micrometer thick Delrin plastic. The bondline is expected to be 1 micrometer or less.
a) 5 MHz PZT-4 so as to penetrate the Delrin.
b) 15 MHz lead metaniobate flat.
c) 40 MHz lead metaniobate focused.
d) 40 MHz PVDF focused.

Answer: c) or d) are both correct.

21. Question:
You need to detect small intergrannular stress corrosion in an austinetic allow in or near a weld. Experience dictates the use of low frequency, horizontally polarized shear waves, or focused beams. What transducer to you select?
a) Use standard 2.25 MHz 45 shear wave probe.
b) Use standard 1 MHz 45 shear wave probe.
c) Use a horizontally polarized 45 shear wave probe.
d Use a focused 45 shear wave probe with aspherical focus.
e) Use more than one of the above methods.

Answer: Best answer is d)

22. Question:
You want to do flaw detection in plastic pipe and the material is very lossy with high attenuation even at 2 MHz. The piping is 10 mm OD and 5 mm ID and you must inspect at a high rate. What sort of transducers would you choose?
a) 1 MHz flat
b) 2 MHz flat
c) 5 MHz flat
d) 1 MHz cylindrical focus
e) 1 MHz spherical focus

Answer: d is best answer.

Authors of this Quiz where the panel of experts of the first online Workshop about transducers.

Gerhard Splitt
Institution:
Krautkraemer - Germany Yoseph Bar-Cohen
Institution:
NASA-JPL - USA Robert A. Day
Institution:
Second Sound - USA Werner Rathgeb
Institution:
Siemens - Germany Willem (Bill) A.Grandia
Institution:
QMI - USA Gérard Fleury
Institution:
IMASONIC - France Klaus Matthies
Institution:
BAM Berlin - NDT Department 8 - Germany