Analysis of the Influence of Surface Roughness on Measurement of Ultrasonic Nonlinearity Parameter Using Contact-Type Transducer
Round 1
Reviewer 1 Report
The paper presents an analysis of the influence of surface roughness on measurement of ultrasonic nonlinearity parameter using contact-type transducer. According to the reviewer’s opinion, the paper is well-structured and clear. The topic is interesting and falls within the aim of the journal. In addition, the results are well-presented and could be helpful to further develop the same topic. Therefore, the paper can be accepted for publication in the current form.
Author Response
Thank you for the reviewer’s kind comments.
Reviewer 2 Report
This paper addresses the impact of the surface roughness on the measurement of ultrasonic nonlinearity parameter. It is found that by using the contact through transmission technique below the certain surface roughness value the nonlinearity parameter is not affected by the roughness if proper calibration is used. This is an useful finding for reliable measurements of microstructural changes. In general this manuscript is well and clearly written, though there could be more discussion of the findings. I think it would deserve to be published in Applied Sciences after considering the following points.
The results tell us that the small roughness does not affect much the nonlinearity parameter estimation but the nonlinearity parameter is not zero for the studied materials. What is the reason for intrinsic nonlinearity, why nonlinearity parameter is not zero?
What is the reason for having two setups for Figure 1b)? Can be the wave physics different if the wave interacts with the roughness on different sides?
There should be a figure/information where the transducer was placed on the specimen and which is the thickness direction (40mm?).
Currently, it difficult to understand the calibration procedure. Some reference are not easily accessible and could not help the majority of the readers. How is the equation (3) derived? The energy loss compensation has been obtained from pulse echo measurement – the pulse traveling two thickness distances, later applied on through-transmission measurement with one thickness distance. What is the role of measured voltage and current?
In calibration test pulse echo waves travel 80 mm. Were there any surface waves excited (propagation distance ~100 mm) to disturb the measurements. They are slower but a long excitation signal was used.
What was the shape and area of the transducer? What were the velocities (any variations with frequency?) and density, their estimation accuracy?
What/if couplant was used? Provide the parameters. Its transmission effect on nonlinearity estimation? In calibration the waves pass two times the contact area of 10 MHz transducer, in through transmission 5 MHz and 10MHz contact area. Different conditions?
What pressure was applied on the transducers? Reference [21] indicates to the possibility of surface deformation which changes the roughness. Did you examine the changes in surface roughness after the test?
What is the meaning of the dashed box in Figure 3b)? Is it a window, some cycles left out?
Describe the trend in Figure 3b,c), increasing roughness decreases the amplitude of waveforms?
The results indicate that the relative nonlinearity parameter increases when maximum roughness is used. I expect opposite trend, higher frequency component should be more sensitive to roughness and loose energy due to scattering? This is somewhat explained in lines 260-276 that the central frequency comes down. To me it is not clear at what frequency the results in figures 5-7 were obtained, at 5/10 or at maximums as shown in figure 8 b)? If you use a fixed frequency then this trend should be opposite?
Why roughness of the reception surface has more influence on the nonlinearity parameter measurement?
Author Response
Comments and Suggestions for Authors
This paper addresses the impact of the surface roughness on the measurement of ultrasonic nonlinearity parameter. It is found that by using the contact through transmission technique below the certain surface roughness value the nonlinearity parameter is not affected by the roughness if proper calibration is used. This is a useful finding for reliable measurements of microstructural changes. In general this manuscript is well and clearly written, though there could be more discussion of the findings. I think it would deserve to be published in Applied Sciences after considering the following points.
- The results tell us that the small roughness does not affect much the nonlinearity parameter estimation but the nonlinearity parameter is not zero for the studied materials. What is the reason for intrinsic nonlinearity, why nonlinearity parameter is not zero?
Answer) The ultrasonic nonlinearity parameter is related second-order nonlinear elastic constant. That is, the nonlinearity parameter is material property, so the nonlinearity parameter is not zero.
- What is the reason for having two setups for Figure 1b)? Can be the wave physics different if the wave interacts with the roughness on different sides?
Answer) There is a big difference between the amplitude of ultrasonic waves incident on the material from the transmitting transducer and the amplitude of the ultrasonic waves incident on the material to the receiving transducer. It is expected that there will be a difference in the interaction with the rough surface depending on the amplitude of the ultrasound, so the experiment was divided into two cases.
- There should be a figure/information where the transducer was placed on the specimen and which is the thickness direction (40mm?).
Answer) As reviewer's comment, we added photo of the experimental setup was added in the revised manuscript.
- Currently, it difficult to understand the calibration procedure. Some references are not easily accessible and could not help the majority of the readers. How is the equation (3) derived? The energy loss compensation has been obtained from pulse echo measurement – the pulse traveling two thickness distances, later applied on through-transmission measurement with one thickness distance. What is the role of measured voltage and current?
Answer) The piezoelectric method consists of two steps; nonlinear measurement and calibration as shown in Fig. A. In the nonlinear measurement shown in Fig. A(a), the monochromatic electrical power,, is converted into monochromatic acoustic power, , at the transmitting transducer. As the acoustic power propagates through the material, harmonic components are generated. Then, the acoustic power with the harmonic frequency component,, is converted to electrical power, , at the receiving transducer. This mechanism at the receiving transducer can be expressed using the transfer function, , as follows:
This mechanism was explained in the references [1, 2]. Therefore, in this paper, a detailed description was skipped.
[1] G. E. Dace, R. B. Thompson, L. J. H. Brasche, D. K. Rehbein, and O. Buck, "Nonlinear acoustics, a technique to determine microstructural changes in material," Review of Progress in Quantitative Nondestructive Evaluation, vol. 10B, pp. 1685-1692, 1991.
[2] G. E. Dace, R. B. Thompson, and O. Buck, "Measurement of the acoustic harmonic generation for materials characterization using contact transducers," Review of Progress in Quantitative Nondestructive Evaluation, vol. 11, pp. 2069-2076, 1992.
- In calibration test pulse echo waves travel 80 mm. Were there any surface waves excited (propagation distance ~100 mm) to disturb the measurements. They are slower but a long excitation signal was used.
Answer) In the calibration measurement, only longitudinal wave was received, and surface wave was not received. Since the size of the specimen was 100 mm × 40 mm × 200 mm, the longitudinal ultrasonic wav transmitted from the center of the specimen was faster than the surface wave, so the surface wave was not received.
- What was the shape and area of the transducer? What were the velocities (any variations with frequency?) and density, their estimation accuracy?
Answer) In the experiments, a 0.25-inch circular transducer was used. The ultrasonic velocity and density were repeatedly measured 3 times, and the deviation within 0.1%.
Revision of Manuscript) In the revised manuscript, some comment about the transducer size was added as following in section 3.2;
Original: The calibration was carried out for the 10 MHz PZT transducer used as a receiver in the nonlinear measurement.
A 5 MHz PZT transducer was used as the transmitter, and a 10 MHz PZT transducer was used as the receiver, to sensitively receive the second-order harmonic frequency component.
Revised: Calibration was carried out for the 0.25-in 10-MHz PZT transducer used as the receiver during the nonlinear measurements.
A 0.25-in 5-MHz PZT transducer was used as the transmitter and a 10-MHz PZT transducer was used as the receiver to sensitively receive the second-order harmonic frequency components.
- What/if couplant was used? Provide the parameters. Its transmission effect on nonlinearity estimation? In calibration the waves pass two times the contact area of 10 MHz transducer, in through transmission 5 MHz and 10MHz contact area. Different conditions?
Answer) In all ultrasonic experiments, the couplant was applied between the material and the transducer.
The calibration process was conducted to obtain a calibration function H(w) that converts the current signal measured in a nonlinear experiment into a displacement signal. Therefore, the experimental condition of calibration and through transmission does not need to be the same.
Revision of Manuscript) In the revised manuscript, some comment was added as following in section 3.2;
Original: The piezo-electric method was carried out to measure the absolute ultrasonic nonlinearity parameter [13], which was proceeded in two procedures: calibration and nonlinear measurement. This The calibration was conducted using the pulse-echo method as shown in Figure 2(a) to obtain the calibration function which converts the electrical output signal of the receiving transducer into displacement amplitude [12,13].
Figure 2(b) shows the calibration function obtained from the calibration, which increases slightly as the surface roughness increases by scattering of the propagating ultrasonic wave.
Revised: The piezoelectric method were carried out at room temperature to measure the absolute ultrasonic nonlinearity parameter [13], which involved two steps: calibration and nonlinear measurement. The calibration process converts a measured electrical current into acoustic displacement. Calibration was conducted using the pulse-echo method, as shown in Figure 2(a), to obtain the calibration function that converts the electrical output signal of the receiving transducer into the displacement amplitude [12,13].
Figure 2(b) shows the calibration function , which converts a measured electrical current into the acoustic displacement, obtained from the calibration, which increases slightly as the surface roughness increases by scattering of the propagating ultrasonic wave.
- What pressure was applied on the transducers? Reference [21] indicates to the possibility of surface deformation which changes the roughness. Did you examine the changes in surface roughness after the test?
Answer) we applied 0.45 MPa on the transducer. We checked whether the surface roughness was changed during repeated experiments. The pressure applied to the transducer was very small, so the surface roughness did not change.
- What is the meaning of the dashed box in Figure 3b)? Is it a window, some cycles left out?
Answer) Figure 3(b) shows an example of received signal. In order to measure the magnitude of the fundamental and harmonic components in the frequency spectrum domain, the stable 20 cycle tone-burst signal was processed through fast Fourier transform (FFT) excluding the transient part and ringing part of the ultrasonic received signal. The dashed box represents a section subjected to FFT signal processing.
Revision of Manuscript) In the revised manuscript, some comment about the dashed box in Figure 3(b) was added as following in section 3.2;
Original: The received current signal was processed by FFT to obtain .
Revised: The rectangular-marked tone-burst received current signal was processed via FFT excluding the transient and ringing parts to obtain I_out (ω).
- Describe the trend in Figure 3b,c), increasing roughness decreases the amplitude of waveforms?
Answer) Yes. The Figure 3 (b) and (c) means that increasing roughness decreases the amplitude of waveform.
Revision of Manuscript) In the revised manuscript, some comment about Figure 3 (b) and (c) was added as following in section 3.2;
Revised: As the roughness increased, the amplitude of the received signal in Figure 3(b) and the magnitude of the FFT result in Figure 3(c) decreased.
- The results indicate that the relative nonlinearity parameter increases when maximum roughness is used. I expect opposite trend, higher frequency component should be more sensitive to roughness and loose energy due to scattering? This is somewhat explained in lines 260-276 that the central frequency comes down. To me it is not clear at what frequency the results in figures 5-7 were obtained, at 5/10 or at maximums as shown in figure 8 b)? If you use a fixed frequency then this trend should be opposite?
Answer) As reviewer commented, the energy loss of the high frequency component becomes larger than that of the low frequency component as the surface roughness increases. However, the nonlinearity parameter is determined from the ratio of the second-order harmonic displacement amplitude to the square of the fundamental frequency–displacement amplitude as follows.
That is, the shifting of the resonant frequency of the receiving transducer to a lower value does not indicate a decrease in the relative nonlinearity parameter.
This nonlinearity parameter results were obtained at fixed frequencies (5, 10 MHz)..
- Why roughness of the reception surface has more influence on the nonlinearity parameter measurement?
Answer) This result is considered that the amplitude of the ultrasonic wave, which is smaller in the receiving part than in the transmitting part, was greatly influenced by the surface condition.
Revision of Manuscript) In the revised manuscript, some comment was added as following in section 4.2;
Original: These experimental results indicate that the roughness of the reception surface has more influence on the nonlinearity parameter measurement.
Revised: These experimental results indicate that the roughness of the reception surface has more influence on the nonlinearity parameter measurement. We inferred that the amplitude of the ultrasonic wave, which is smaller in the receiving part than in the transmitting part, was significantly influenced by the surface roughness.
Author Response File: 
Author Response.docx
Reviewer 3 Report
In this study, the authors studied the influence of surface roughness on the measurement of the ultrasonic nonlinearity parameter, they evaluated two specimens, Al6061-T6 and SUS304 materials, both with different surface roughnesses. Obtained results reveal that the surface roughness has a lesser influence on the absolute measurement than the relative measurement, and that the transmission surface is less affected by the reception surface. I think this paper is suitable to be published and please see below some comments of revision:
- The authors used two samples of general-purpose materials: Al6061-T6, which is duraluminium, and SUS304 stainless steel. Therefore, I would expect some comparison of the measured values of nonlinearity parameters and the values that are known/expected for these materials (from other literature or some technical specification).
- Was any couplant (lines 48, 50) material between transducer and the material being tested?
- How does temperature of the material influence this measurement? And if so, what was the temperature of the material during the tests?
- How were the relatively big specimens supported during the measurement? I think a photo of the setup will be suitable.
Author Response
- The authors used two samples of general-purpose materials: Al6061-T6, which is duraluminium, and SUS304 stainless steel. Therefore, I would expect some comparison of the measured values of nonlinearity parameters and the values that are known/expected for these materials (from other literature or some technical specification).
Answer) The LiNbO3 transducer is generally used to measure the absolute nonlinearity parameter, because the LiNbO3 transducer has a small nonlinearity that occurs in the transducer. However, the LiNbO3 transducer is unsuitable for this experimental setup as it is fragile when used under rough surface conditions. Therefore, in this manuscript, the experiments were performed using a PZT transducer; thus, the value of the absolute nonlinearity parameter measured by PZT transducer is larger than the previously known reference value (which was measured with a LiNbO3 transducer) as followed Table.
Table. Results of the absolute ultrasonic nonlinearity parameter in Al 6061-T6
|
Measured value (In this manuscript) |
Reference value |
|
10.69 ± 0.01 |
4.5~5.69 [1,2] |
[1] P. Li, W. T. Yost, J. H. Cantrell, and K. Salama, "Dependence of acoustic nonlinearity parameter on second phase precipitates of aluminum alloys," 1985 Ultrasonics Symposium, pp. 1113-1115, 1985.
[2] J. Kim, D.-G. Song, and K.-Y. Jhang, "Absolute measurement and relative measurement of ultrasonic nonlinear parameters," Research in Nondestructive Evaluation, 2016.
In this study, the absolute and relative nonlinearity parameters were measured under the same experimental conditions according to the surface roughness of the material. Then, the experimental results were normalized by the initial value (Ra = 0.5 μm). Thus, we think that this experimental result is sufficient to analyze the influence of the surface roughness on the measurement of ultrasonic nonlinearity parameter without comparing the measured values of nonlinearity parameters with known/expected values for this material.
2. Was any couplant (lines 48, 50) material between transducer and the material being tested?
Answer) In all ultrasonic experiments, the couplant was applied between the material and the transducer.
Revision of Manuscript) In the revised manuscript, some comment about the couplant was added as following in section 3.1;
Original: The calibration was carried out for the 10 MHz PZT transducer used as a receiver in the nonlinear measurement. The pulser-receiver (Panamertrics, PR5072, USA) was used to incident a broadband pulse ultrasonic wave into the specimen. The incident ultrasonic wave propagated through the specimen.
Revised: The calibration was carried out for the 10 MHz PZT transducer used as a receiver in the nonlinear measurement. The couplant was applied between the material and the transducer. The pulser-receiver (Panamertrics, PR5072, USA) was used to incident a broadband pulse ultrasonic wave into the specimen. The incident ultrasonic wave propagated through the specimen.
3. How does temperature of the material influence this measurement? And if so, what was the temperature of the material during the tests?
Answer) The temperature of the material can effect on the measurement results of the ultrasonic nonlinearity parameter. In this study, the experiments were conducted in room temperature. We added comment about the temperature of experimental circumstance.
Revision of Manuscript) In the revised manuscript, some comment about the temperature of experimental circumstance was added as following in section 3.1;
Original: The piezo-electric method was carried out to measure the absolute ultrasonic nonlinearity parameter [13], which was proceeded in two procedures: calibration and nonlinear measurement.
Revised: The piezo-electric method was carried out at room temperature to measure the absolute ultrasonic nonlinearity parameter [13], which was proceeded in two procedures: calibration and nonlinear measurement.
4. How were the relatively big specimens supported during the measurement? I think a photo of the setup will be suitable.
Answer) As reviewer's comment, we added photo of the experimental setup was added in the revised manuscript.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
In general, the answers are acceptable, only a few remarks:
2. You should include this justification also in the article, then the reason for the second setup is understood. line 133 "thrice"?
6. You should give the estimated values also in the paper, as you apply eq 3.
Author Response
In general, the answers are acceptable, only a few remarks: 2. You should include this justification also in the article, then is understood. line 133 "thrice"? Answer) We included the reason for the second setup in the revised manuscript. And the “thrice” means three times. Revision of Manuscript) In the revised manuscript, the reason for the second setup was added as following in section 3.1 Original: Next, the positions of the transmitting and receiving transducers were interchanged to analyze the influence of the reception surface on the measurements.The absolute and relative nonlinearity parameters were measured thrice in both cases. Revised: Next, the positions of the transmitting and receiving transducers were interchanged to analyze the influence of the reception surface on the measurements. There is a difference between the amplitude of the ultrasonic wave incident on the material from the transmitting transducer and the amplitude of the ultrasonic wave incident on the receiving transducer from the material. This difference in amplitude is expected to cause a difference in the interaction with the rough surface, so the experiment was divided into two cases. The absolute and relative nonlinearity parameters were measured thrice in both cases. 6. You should give the estimated values also in the paper, as you apply eq 3. Answer) In the revised manuscript, we added H(ω)values calculated in Equation 3. H(ω) 0.5 μm 1.0 μm 1.5 μm 2.2 μm 2.7 μm 5 MHz 3.69E-08 4.03E-08 4.49E-08 5.34E-08 5.78E-08 10 MHz 1.33E-08 1.61E-08 1.97E-08 2.59E-08 2.84E-08
Author Response File: Author Response.docx
