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2023 | Book

Acoustic Invisibility for Elliptic Objects

Theory and Experiments for Underwater Sound


About this book

The book investigates acoustic cloaking for elliptical targets, starting from the development of a systematic approach to deal with such non-axisymmetrical shapes by adopting transformation acoustics in elliptic coordinates, and concluding with numerical and experimental validation of a microstructured cloak in the underwater environment. The book thus comprises all the steps from theory to practice that led to the first experimental validation of acoustic invisibility for non-cylindrical objects, whose results are presented in the last chapter. Indeed, despite Transformation Theory is now an established tool to design material distributions capable to unlock the design of invisibility devices, it is not trivial to apply it for shapes different than the sphere and the cylinder, which are thus the ones mainly addressed in the literature. This book paves the way for exploration of other shapes, demonstrating the effectiveness of a pentamode cloak in reducing the acoustic visibility of an elliptical target, and discussing design choices that can make the implementation of the required microstructure less cumbersome despite the lack of axial symmetry of the problem, from both the numerical and manufacturing point of views.

Table of Contents

Chapter 1. Introduction and State of the Art
This chapter introduces the notion of cloaking and reviews the main ideas that have been developed during the last fifteen years to take this concept from theory to experimental assessment, underlining issues that remain open challenges for future research.
Davide Enrico Quadrelli, Francesco Braghin
Chapter 2. Wave Propagation in Periodic Media
This chapter is devoted to the review of some useful results related to wave propagation both in homogeneous and in periodic media and is intended to recall the fundamental knowledge on which the following of this work builds, other than to set the general notation used.
Davide Enrico Quadrelli, Francesco Braghin
Chapter 3. Transformation Acoustics
The purpose of this chapter is to review the background knowledge on transformation methods that is then used in the following of the book.
Davide Enrico Quadrelli, Francesco Braghin
Chapter 4. Transformation Acoustics in Elliptic Coordinates
In this chapter, a method based on transformation acoustics is introduced to tackle systematically the design of pentamode cloaks aiming at reducing the acoustic scattering of elliptical obstacles.
Davide Enrico Quadrelli, Francesco Braghin
Chapter 5. Design and Experimental Validation of an Elliptic Cloak
In this chapter we use the method introduced in Chap. 4  to design a non-axisymmetric cloak and produce an underwater experimental validation of its functioning.
Davide Enrico Quadrelli, Francesco Braghin
Acoustic Invisibility for Elliptic Objects
Davide Enrico Quadrelli
Francesco Braghin
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