Session: 01-02-02: Acoustic Metamaterials

Paper Number: 139426

139426 - Enhancing Acoustic Response of Metamaterials With the Introduction of Polyurethane Foam Layer 

Acoustic metamaterials are an emerging field of artificially fabricated materials in the world of acoustics with a purpose to direct, control and manipulate sound waves in a medium to achieve certain specific goals. This is possible due to the exotic properties that metamaterials possess not usually found in natural materials. A type of acoustic metamaterial that is being investigated recently is Multiresonant Layered Acoustic Metamaterial (MLAM) which gives a solution for broadband low-frequency noise attenuation. The MLAM is based on the concept of coupled resonances mechanisms and provides enhanced sound attenuation capabilities by using a double peak sound transmission loss. The structure of MLAM is comprised of three materials: polyamide, silicone rubber, and steel that are layered onto one another to make the layered structure. One disadvantage with the current MLAM is its weight, as steel is significantly heavier than the rest of the layers. The idea is therefore to replace steel with a polyurethane foam layer without any loss or, if possible, even increase MLAM’s sound absorption capabilities. A new MLAM structure is fabricated by replacing the steel layers with polyurethane foam of the same thickness with the goal of significantly reducing the weight and enhancing the sound absorption coefficient. In parallel, a single polyurethane foam layer of identical thickness as that of MLAM was also fabricated. These three categories of structures were tested in an impedance tube equipment developed in-house. Acoustic signals obtained from the impedance tube were analyzed to calculate sound transmission loss (STL), sound reflection coefficient, sound transmission coefficient, and sound absorption coefficients at various frequencies. The MLAM structure with steel layer was considered as control in the present investigation. The tests have revealed that MLAM with steel resonating layers has the highest reflection coefficients, lowest transmission coefficient, and highest STL values over most of the frequency domain. Whereas the solid polyurethane sheet has the lowest reflection coefficient (excluding the values in the 950 Hz – 1050Hz frequency domain), highest transmission coefficient and the lowest STL values. The MLAM with polyurethane foam layers has the lowest reflection coefficients over the 950Hz - 1050Hz frequency range and has similar transmission coefficients and STL values compared with the MLAM with steel resonating layers. Additionally, it was observed that at the frequency range, e.g., 950 – 1100 Hz, MLAM with foam layer had the highest absorption coefficient of 0.67 (peak value). The next highest absorption peak (e.g., 0.474) was observed with a single foam layer which was not a MLAM structure. This peak occurred at a frequency of 1100 Hz but still was within the given range mentioned earlier. MLAM structure with still layer showed the lowest absorption coefficient (e.g., 0.141) @ 1050 Hz. Considering the peak values of absorption co-efficients, it is evident that the improvement with modified MLAM (i.e., with embedded foam layer) is 375% compared to control samples. Such enhancement in absorption coefficient is quite remarkable. Even a single layer of polyurethane foam shows an improvement of 236% in absorption coefficient. The reason for such improvement with both structures is the presence of foam layer. Polyurethane foam has hollows inside the foam which steel does not have. These hollows increase air resistance resulting in the attenuation of airborne sound waves. However, the performance of the three categories beyond the mentioned frequency range is different in different sequences. Details of fabrication, experimental setup, data reduction, and analysis of results will be presented.

Presenting Author: Trey Brauch Florida Atlantic University

Presenting Author Biography: Hello, my name is Trey Brauch and I am a PhD student at Florida Atlantic University. I have my Bachelor of Science and Master of Science degrees in Ocean Engineering at Florida Atlantic University as well. I have completed numerous research opportunities including being a NREIP intern in the summer of 2021. I performed research on how a 2D fish swim profile changes with the radial expansion of contracting muscles by producing MATLAB
animations and presented my findings. These animations were useful in building a bioinspired soft robotic propulsor that is actuated by linearly contractile, soft artificial muscles that closely resemble the internal structural features of large pelagic fishes.

Authors:

Hassan Mahfuz Florida Atlantic University
Trey Brauch Florida Atlantic University
Pierre-Philippe Beaujean Florida Atlantic University