Cavity mode cancellation by using the perfect absorption of a discrete distribution of Helmholtz resonators
* Presenting author
Perfect absorption is receiving an increasing interest in the field of acoustics due to the possibility to absorb waves in deep-subwavelength scale. In practice, acoustic absorbing systems, porous materials or locally resonant materials, are open lossy resonators, presenting leakage of energy due to the aperture and inherent losses given by dissipative mechanisms. Perfect absorption is produced when there is a balance between the leakage and losses in the system, condition known as critical coupling. Helmholtz resonators have interesting properties for sound absorption. Their simple geometry allows the tuning of the viscothermal losses. Furthermore, they can be used to control the dispersion properties of the host medium, producing regions of frequency with slow sound. In this work, we mix these properties to cancel the reflection of a backing cavity. Resonators embedded in a waveguide in which plane waves are propagated compose the system. The last resonator is backed by the air cavity ended by a rigid wall. Slits are created between the upper part of the tube and the resonators to achieve slow sound propagation and shift down the resonance frequency. Optimization algorithms are applied to the design parameters to get maximized and broadband sound absorption.