Doubly Negative Acoustic Metamaterials with Air-Coupled Diaphragms

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In recent years, Acoustic Metamaterials (AMM) have become an emerging tool to create materials with exotic properties that are not found in natural materials. A central idea in this research project is the realization of doubly negative mass density and bulk modulus (a.k.a. negative index material), which is the key to designing many AMM devices with novel functionalities. Such material's refractive index for an electromagnetic wave has a negative value over some frequency range. This research supports fundamental advances on the creation of a new type of AMM with double negativity, whose unit cell consists of diaphragms directly coupled by an air cavity. With this simple yet innovative configuration, the unit cell can be easily scaled to form 1D, 2D, and 3D AMM, paving the ways for transforming many applications ranging from super-resolution imaging, cloaking, to perfect absorbers. The outcome from the this research will be integrated into new course that will serve as a catalyst to motivate students, particularly minority and women, to pursue advanced degrees and careers in science and engineering.This research project supports fundamental research on a new type of AMM with double negativity. The research will investigate characteristics of such materials using a comprehensive approach including analytical, numerical, and experimental methods. The overall objective of the awarded research program is to achieve a fundamental understanding of the AMM with air-coupled diaphragms, develop fiber optic sensors for in situ pressure and displacement measurements, and use the gained understanding and the developed new tools to create AMM with double negativity. With a simple configuration of air-coupled diaphragms, the unit cells can be scaled to form 1D, 2D, and 3D AMM that has the potential to transform many applications requiring double negativity (e.g. sub-wavelength imaging and transformation acoustics) and complex geometry (e.g. acoustic metasurface). Newly developed fiber optic sensors will be used for mapping the pressure and displacement fields inside and outside the AMM. The work also complements theoretical and numerical studies with the well-thought out experiments that use high-performance fiber optic probes to map the acoustic wave. This work provides a new paradigm to the study of wave manipulation by AMM and has wide spread applications in fields such as imaging, cloaking, and several others.