Session: 16-01-01: Poster Session: NSF-Funded Research (Grad & Undergrad)

Paper Number: 99605

99605 - Suppression of Higher Acoustic Harmonics by Application of Solid-Solid Periodic Layered Structure 

Over the last decades, the nondestructive evaluation (NDE) using ultrasound, ranging from 1 MHz to 5 MHz, has been widely used in various industrial fields as the most powerful way to evaluate structural changes in materials and accumulated damage or degradation in the material properties for the early-stage detection of structural failure. The linear mechanical properties and defects in the structure can be determined by measuring acoustic parameters, such as sound speed, attenuation, transmission, and reflection coefficients. The existing defects can alter the amplitude and phase of the propagating signal as it passes through structures. Although NDE is sensitive to gross defects or cracks, it is less sensitive to material degradation, fatigue, or microcracks because the scale is much less than the wavelength. Recently, the nonlinear ultrasonics (NLU) nondestructive evaluation [HH1] method was introduced to overcome these limitations. Unlike the existing linear NDE, NLU is sensitive to the microscopic discontinuities or imperfections that correlate to the second harmonic generation (SHG).

However, there is a critical setback due to the technique being affected by not only the sample’s nonlinearity but also the measuring device’s nonlinearity. To remedy this problem, various solutions have been proposed. Among them, Mostavi et al. proposed a superlattice, a phononic crystal consisting of solid and fluid layers, for immersion NLU to cut out the nonlinearity generated in water and instrument. This superlattice significantly reduced the amplitude of the second harmonic by the bandgap, allowing the fundamental frequency to be transmitted to samples of interest. Smith et al. developed metal additively manufactured (AM) three-dimensional phononic crystals to the extraneous nonlinearities. They showed AM phononic filters could block the second harmonic. However, these studies are difficult to be used in some NDE field because of portability and size.

Adding to this problem, this study focuses on developing a metamaterial band filter by blocking the inherent device’s nonlinearity. To filter out nonlinearities induced by the instrument, we propose that one-dimensional acoustic metamaterial, called superlattices (SLs). The SL ultrasonic filter is designed with the bandgap of the SL, thus preventing wave propagation for a certain frequency range, i.e., the second hormonic. The SL is made of periodic layers of solid-solid, alternating copper and Sn-Pb solder layers, which is advantageous in portability and size.

The metamaterial in this study has the pass and stop band for a fundamental frequency of 5 MHz and a frequency of 10 MHz of secondary harmonics, respectively. The reason we choose 5 MHz as fundamental frequency is because the second harmonic nonlinearity in this frequency can detect very small micro-scale damage. With Rytov’s equation[HH2] , well-known in the one-dimensional band structures in periodic layers field, we determined the thickness of each layer. We then conducted Finite Element Analysis for this model in COMSOL program to calculate the band structure.

To validate feasibility of the SL ultrasonic filter, the experiments using acoustic waves were conducted with aluminum specimen, sample of interest, and SL filter, respectively. A function-generator generates 3 pulses sine signal, and the frequency range is from 2.5 MHz to 20MHz.  As a result, in the case of the SL, there is a band gap around 10 MHz, which means the SL can filter out the second harmonic. Compared to data of aluminum experiment, it shows that the intensity of the SL’s second harmonic is much smaller than the intensity of the aluminum’s second harmonic.

In summary, by filtering out the device’s inherent nonlinearity with the SL ultrasonic filter, one can detect the microcrack, fatigue and material degradation in materials of interest, which is portable and useful in various engineering fields.

 

Presenting Author: Jinho Kang University of North Texas

Presenting Author Biography: Jinho Kang is a graduate student of Mechanical System and Design Engineering at the University of North Texas (Denton, TX). He obtained his bachelor’s degree in Automation Mechanical System Design Engineering from Seoul National University of Science and technology in Korea. His research focuses on an Acoustic Phononic Crystal in engineering field.

Authors:

Jinho Kang University of North Texas
Heo Hyeonu Graduate Program in Acoustics, The Pennsylvania State University
Taeyoul Choi Department of Mechanical Engineering, University of North Texas
Arkadii Krokhin Department of Physics, University of North Texas
Hyunjo Jeong Department of Mechanical Engineering, Wonkwang University