Session: 03-09-03: Design of Engineering Materials

Paper Number: 100127

100127 - Broadband Acoustic Lens Design Using Gradient-Based Optimization and Adjusting Radii and Positions of Scatterers 

Metamaterials are architectured materials that can manipulate the energy flow with capabilities exceeding those possible in conventional materials and have applications such as super-focusing, imaging, sensing, cloaking, beamforming, splitting, steering, localization, wavefront manipulation, sound diffusion and absorption. Metamaterials yield optimal solutions using either the forward design or the inverse design. Current forward design techniques rely mostly on tuning parameters by trial and error. When using such methods, the low efficiency and limited exploration of the design variations tend to omit the optimal solution. Using the inverse design approaches, one can start from the opposite end and optimize certain objective functions describing the desired functionality. The progress in inverse design has led to the discovery of metastructures with exceptional performances. Among various optimization methods, the gradient-based optimization (GBO) method became a popular approach to the inverse design metastructures containing a vast number of degrees of freedom.

In this work, we present a GBO method for the design of an acoustic lens. This design is based on an optimization process using the semi-analytical optimization approach by adjusting the radii and position of each scatterer in the non-uniform planar configuration of scatterers of various radii. This idea differs from earlier inverse designs that use topology optimization, shape optimization, and generic algorithms. We derive a formula for the gradients of the absolute pressure at the focal point with respect to positions and radii of a set of cylindrical scatterers. The derived analytic form of gradients enhances modeling capability when combined with optimization and parallel computing. The GBO algorithm maximizes the sound amplification at the focal point by evaluating pressure derivative with respect to the cylinder positions and radii, and then perturbatively optimizing the position and radius of each cylinder in the lens while taking into account the acoustic multiple scattering between the cylinders. Computations are performed on MATLAB using the fmincon solver with sequential quadratic programming (SQP) algorithms and combined with a MultiStart optimization solver while supplying the gradient of pressure at the focus as well as the gradient of nonlinear constraints. The results of the GBO of the broadband acoustic lens are presented including several performance measures for the frequency dependence and the incidence angle. The real part of computed total pressure fields clearly shows the focusing effect. Numerical examples are given for non-uniform clusters of the cylindrical configuration of rigid cylinders, cylindrical voids and sets of elastic thin shells in the water.

Presenting Author: Vaishnavi Dabhade San Jose State University

Presenting Author Biography: Vaishnavi Dabhade is a Masters student in Mechanical Engineering at San Jose State University. Variational Autoencoders, Metamaterials and acoustic cloaks are her topics of interest.

Authors:

Vaishnavi Dabhade San Jose State University
Dr. Feruza Amirkulova San Jose State University
Dr. Samer Gerges San Jose State University