Acoustic Pressure Monopole, Velocity Monopole, and Hybrid Monopole

TL;DR

This paper identifies two types of acoustic monopoles, pressure and velocity, and introduces a hybrid device combining both, which could enhance absorption in subwavelength acoustic applications.

Contribution

The study reveals the existence of pressure and velocity monopoles and demonstrates a hybrid monopole device with unique symmetry-breaking properties.

Findings

Pressure monopoles exhibit monopolar symmetry in the pressure field at resonance.

Velocity monopoles exhibit monopolar symmetry in the velocity field at resonance.

Hybrid monopoles show two resonances with broken symmetry, potentially increasing absorption.

Abstract

We show that there are two types of acoustic monopoles, namely the pressure monopoles (PMs) and the velocity monopoles (VMs). Under one wave incidence, only the pressure field near a PM at resonance possesses monopolar symmetry, while for a VM at resonance only the velocity field possesses monopolar symmetry. It is the dipolar response function of the monopoles that dictates whether they are PMs or VMs. A hybrid monopolar device with neither velocity nor pressure field symmetry is also demonstrated by combining a VM and a PM, which exhibits two monopole resonances with neither PM nor VM symmetry. The breaking of symmetry could lead to higher absorption of the subwavelength scale devices.