Abstract
Willis coupling, also known as pressure-velocity cross coupling, in acoustic materials has received much attention in the past years. This effect has been found useful in acoustic metasurface designs for wave redirection. We find that Willis coupling in phononic crystals also provides rich physics to manipulate waves. Here, we report the extreme asymmetric lateral sound beaming effect in a two-dimensional phononic crystal composed of Willis scatterers. By matching the second-order Bragg scattering with two leaky guided modes (a quadrupole resonance and a cross-coupling-induced dipole resonance), a normally incident wave is redirected towards the positive and negative directions orthogonal to the incident wave with different amounts of energy. Simulation and experimental results demonstrate the extraordinary asymmetric lateral beaming effect in the Willis medium. The results presented here may find applications in the design of tunable beam splitters and waveguides.
Highlights
Willis materials are composite materials displaying cross coupling between strain and momentum [1]
Various applications have been reported in elastodynamics, such as nonreciprocal transmission in an active Willis material [8], asymmetric absorption and scattering in a passive Willis material [9], and simultaneous control of transmitted and reflected waves using active Willis materials [10]
We report an extraordinary lateral sound beaming effect in a Willis medium
Summary
Willis materials are composite materials displaying cross coupling between strain and momentum [1]. We report an extraordinary lateral sound beaming effect in a Willis medium (phononic crystal composed of Willis scatterers arranged in a square lattice pattern). Due to the cross coupling between pressure and velocity, Willis scatterers can display dipole response under pressure excitation and display monopole response under velocity excitation [12]. Reported lateral sound beaming effects in phononic crystals are based on the quadrupole mode, which is symmetric, in the unit cell [19,20,21]. By using Willis scatterers in the phononic crystal, the pressure excited dipole moment in the unit cell forms an additional antisymmetric mode orthogonal to the incident wave. By matching the antisymmetric and symmetric modes to the second-order Bragg scattering in the Willis medium, the asymmetric lateral beaming effect is possible
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
