Subcategory: Physics (not Nanoscience)
Meyer Shinder - University of North Texas
Co-Author(s): J. Kang, T.-Y. Choi, A. Krokhin
The nondestructive testing (NDT) using ultrasound band 1-5 MHz, has been widely used in various industrial fields as the most powerful way to evaluate accumulated damage or degradation in the material properties for the early-stage detection of structural failure. The mechanical properties and structural defects can be determined by measuring acoustic transmission and reflection coefficients. The defects alter the amplitude and phase of the signal propagating through a structure. Although the existing linear NDT is sensitive to gross defects, it fails in detection of material degradation, fatigue, and microcracks. The NDT with nonlinear ultrasound (NLU) method was introduced to overcome these limitations. NLU can detect a microscopic discontinuity or imperfection that may be a source of the second harmonic in the reflected signal. However, there is a critical setback due to the technique being affected by not only the intrinsic sample’s nonlinearity but also by the presence of high harmonics in the scanning signal. To remedy this problem, we focus on creating a metamaterial band filter by blocking the device’s inherent nonlinearity. This material will filter out nonlinearities induced by the instrument, to do this we propose 1D elastic superlattice (SL). The SL acoustic filter is designed with a bandgap in its frequency spectrum that covers the frequency range of second harmonic. The SL is made of periodically alternating Cu and Sn-Pb solder layers. We conducted analytical and numerical calculations to obtain the appropriate thickness of each layer. The metamaterial in this study has the pass band for the fundamental frequency of 5 MHz and the first stop band centered near the frequency of 10 MHz. The reason we choose 5 MHz as fundamental frequency is because the second harmonic at 10 MHz can detect 200um micro-scale damage. To validate feasibility of the SL ultrasonic filter, experiments with aluminum as the reference specimen and with SL filter were conducted. A function-generator generates 3 pulses sine signal, within the frequency range from 2.5 MHz to 20MHz. Spectral analysis of the signal transmitted through the SL filter shows 100 times voltage suppression of the second harmonic as compared to the signal transmitted through the Al specimen. By filtering out the device’s inherent nonlinearity with the SL ultrasonic filter, one can detect microcracks, fatigue and material degradation with much higher accuracy. Future work includes making a more homogeneous SL filter. References: Mostavi A., November 2017, The integration of superlattices and immersion nonlinear ultrasonics to enhance damage detection threshold. Applied Physics Letters. Volume 111, Issue 20 Smith S.J., 2021, Metal additively manufactured phononic materials as ultrasonic filters in nonlinear ultrasound measurements. The Journal of the Acoustical Society of America, Volume 149, Issue 6
Funder Acknowledgement(s): This work was supported by EFRI Grant No. 1741677 from the National Science Foundation.
Faculty Advisor: Arkadii Krokhin and Tae-Youl Choi, email@example.com
Role: I was heavily involved with the fabrication of the metamaterial and testing of the metamaterial. I was also involved with research, continuation, and problem-solving done within this project.