Selectively tuned acoustic asymmetry in a three-dimensional-printed Willis scatterer

This work lies at the intersection between Willis media, tunable acoustic metamaterials, and multi-material three-dimensional printing. A four-microphone, two-termination impedance tube was used to measure the acoustic response of a subwavelength scatterer composed of two resonant plates. The resonance frequency of one plate was controlled via resistive heating, which introduced a geometric asymmetry, observed dynamically through reflection coefficients that differed depending on the incident wave direction. For the acoustically small scatterer, coupled polarizabilities meaningfully captured the tuned asymmetry and characterized the observed Willis coupling. Model-data comparison shows good agreement between the measured and modeled results.