Data Driven Design of 3D Stiffness Gradient Acoustic Metamaterials for Impedance Matching

Metamaterials are artificially engineered materials designed to exhibit properties not commonly found in natural materials. Acoustic metamaterials, a subset of metamaterials, manipulate sound waves in ways that conventional materials cannot. Acoustic waves play a crucial role in various applications, including medical imaging, non-destructive testing, and sonar systems. One of the significant challenges in the application of acoustic waves is impedance matching, which is essential for minimizing reflections and maximizing the transfer of acoustic energy between different media. Our project focuses on designing 3D stiffness gradient acoustic metamaterials for impedance matching, particularly targeting the creation of a metamaterial with acoustic impedance comparable to that of water using metals. This has significant implications for medical ultrasound devices, where we need a material that transitions from softer at the patient interface to stiffer at the transducer interface. We propose a comprehensive framework capable of designing metamaterials with desired acoustic impedance and gradient stiffness. The key steps in our approach include generating initial designs using a periodic covariance function, ensuring that the unit cells are both periodic and random. Furthermore, we integrated manufacturing constraints into the design process, ensuring that the structures are connected and feasible for fabrication. Therefore, we developed an algorithm to ensure that the generated designs are connected and remain connected throughout the optimization process. We developed both single and multi-objective optimization algorithms, including both a genetic algorithm and other machine learning approaches, to achieve the target stiffness and acoustic impedance. Our approach resulted in the design of metal-based metamaterials that exhibit acoustic impedance near that of water. This project demonstrates the feasibility of designing acoustic metamaterials with gradient stiffness and specific impedance properties through advanced optimization techniques. These innovations pave the way for improved materials in various acoustic applications, particularly in ultrasound devices, by providing better impedance matching and thereby improving the efficiency of acoustic energy transfer.