Acoustic-structural interaction is the key to understand a wide range of engineering problems such as membrane-based dynamic pressure sensors, hearing devices for sound source localization, and acoustic absorbers for noise reduction. Despite tremendous developments in the last decades, there is still a fundamental size limitation in these areas. In the case of dynamic pressure sensors, sensitivity usually suffers for miniature sensors; the available acoustic directional cues proportionally decrease with size, which adversely affects the localization performance; thick panels are required to achieve superior sound attenuation, particularly for low-frequency sound. It is the motivation of this dissertation research to address the abovementioned size limitation that involves acoustic-structural interaction. The overall goal of this dissertation work is to achieve an enhanced understanding of the acoustic-structural interaction between diaphragms and air cavity and to apply this understanding to develop high-performance miniature acoustic sensors and noise reduction metamaterials. First, a finite element method (FEM) model and large-scale device are developed to understand how the interaction between the diaphragm and its backing air cavity affects the equivalent mass, stiffness, and damping of air-backed diaphragms. The numerical and experimental study shows that the complex interaction cannot be captured by the commonly used lump model. Then, air-backed graphene diaphragms are used to develop fiber optic sensors with sub-millimeters footprint and high sensitivity. Two different configurations are designed to enhance the sensor sensitivity limited by the backing air cavity. One is to increase the mechanical sensitivity by using a larger backing volume, the other is to increase the optical sensitivity by using silver-graphene composite diaphragm. Next, acoustic metamaterials with air-coupled diaphragms as unit cells are developed to achieve perfect acoustic absorption with thickness much smaller than the sound wavelength, which cannot be realized using natural materials. Finally, an expanded configuration of two diaphragms coupled by an air-filled tunnel is experimentally developed to mimic the hearing system of small vertebrates. The goal is to amplify the small directional cues available to the small animals so that a high angular resolution can be achieved. This dissertation provides a quantitative and mechanistic explanation for the interaction between the diaphragms and the sealed air cavity. It offers several frameworks for the development of miniature pressures, directional sensors, and thin sound absorbers. / Mechanical Engineering

The work presented in this dissertation was aimed at understanding biology's application of soft materials to enhance sensing abilities and initiate innovative bio-inspired material-based approaches for flow (fluidic and air) sensors and photo-thermal sensors. A key aim is to help strengthen this niche of functional materials science referred to, here, as bio-inspired materials in sensing roles. The work aspires to traverse the boundaries of the subject in order to provide a strong foundation for future scientific explorations of the subject. The studies presented here, include studies of flow sensing in fish and implementing a bio-mimetic approach to microfabricated flow sensors. The work also includes studies of material based signal filtering in spiders, as well as, bio-inspired photo-thermal transduction mechanisms. The capabilities of the methodology are demonstrated with successful engineering studies.