Questions - ATTEMPT ALL QUESTIONS

Question 1 - It was recently discovered that gold bars (density 19.32 g/cm3) have been adulterated with a cheaper metal of similar density such as Tungsten (density 19.25 g/cm3). It has been proposed that ultrasonic probes can be used to detect the presence of a different metal in the gold.

Estimate the relative sizes of the reflected longitudinal beams that would be received by an ultrasonic probe i.e. the relative size of the beam reflected off the tungsten layer and the beam reflected off the back wall -- State any assumptions made. Please note that Tungsten has a Young's modulus is 411 GN/m2, and a poisson's ratio is 0.284 and Gold has longitudinal wave velocity of 3240 m/s.

A standard gold bar which has a standard thickness of 8.3 mm, has 6 mm of tungsten inserted in the middle. If we use an ultrasonic probe to measure the thickness using longitudinal waves, what thickness would be found? -- State any assumptions made

Using all the above information, find the values of a and b in the following line equation that relates the measured thickness, d, with the thickness of tungsten, dt: dt = a(b -d)

Question 2 - A circular probe with a diameter of 12mm uses a 2 MHz longitudinal wave in steel. Calculate the height of the pulse that is reflected from a circular reflector with a diameter of 0.5 mm at a depth of 25 mm, assuming that the velocity in steel is 5.96mm/μs, and the attenuation coefficient is 0.03 nepers/mm.

If a block of steel, 50 mm thick is tested using the same frequency, the required amplification of the back wall echo is found to be 37.6 dB. Now a block of unknown material, 50mm thick, is tested using the same probes and couplant and the required amplification of the back wall echo is found to be 72.4dB. What is the attenuation coefficient of the unknown material?

Briefly describe in your own words what an electromagnetic acoustic transducer is and how it works. List 2 of its advantages and 2 disadvantages compared to conventional ultrasonic probes.

Question 3 - A 12mm diameter transducer at 2MHz is used to detect a disc-shaped reflector at a depth of 20mm. The amplitude of the echo is -36.3dB. If we assume the velocity in the block is 5.96 mm/μs, use the normalized DGS diagram to estimate the area of the reflector. Please note that you can the value of the attenuation coefficient from Q2.

Attachment:- Assignment Files.rar