Experimental evidence of Willis coupling in a one-dimensional effective material element

Area of Science:

• Acoustics
• Materials Science
• Electromagnetism

Background:

• Acoustic metamaterials aim to create subwavelength systems with unique properties.
• Willis coupling, analogous to electromagnetic bianisotropy, links stress-strain and momentum-velocity relations.
• This coupling is absent in conventional materials and crucial for understanding complex acoustic responses.

Purpose of the Study:

• To experimentally and theoretically demonstrate the requirement of Willis properties for physically meaningful effective material properties.
• To present an experimental procedure for extracting effective material properties from asymmetric one-dimensional acoustic elements.

Main Methods:

• Theoretical modeling of acoustic metamaterials with asymmetric elements.
• Experimental fabrication and characterization of one-dimensional acoustic elements.
• Development and application of a novel experimental procedure for property extraction.

Main Results:

• Experimental and theoretical validation that Willis properties are essential for local effective material properties.
• Successful extraction of effective material properties from a one-dimensional isolated element.
• High agreement between measured and theoretically predicted material properties.

Conclusions:

• Willis coupling is a fundamental property arising from local behavior in asymmetric acoustic metamaterials.
• The developed experimental method accurately quantifies effective material properties.
• This work enhances the understanding of physical mechanisms behind Willis coupling in acoustic metamaterials.