Helmholtz Resonator Array for Fan Noise Absorption Without Airflow Loss

The patent employs porous foam material filling the chambers of the Helmholtz resonators. This porous structure allows fluid to pass through while the foam's acoustic properties provide sound absorption. The porous nature of the material enables simultaneous achievement of acoustic absorption and fluid flow permeability, resolving the contradiction between blocking sound and allowing fluid passage.

The Helmholtz resonator structure acts as an intermediary between the acoustic field and the fluid flow. The resonators are tuned to specific frequencies to absorb acoustic energy while their open-necked design and sparse arrangement allow undisturbed fluid flow through the array. The resonators mediate between the conflicting requirements of sound absorption and fluid flow by providing a frequency-selective acoustic impedance without creating a physical barrier to fluid motion.

The acoustic absorption function is segmented into multiple Helmholtz resonators, each tuned to different frequency ranges. By arranging resonators with varying chamber volumes and neck dimensions, the system achieves broadband acoustic absorption across low, mid, and high frequencies. This segmentation approach allows fluid flow to pass freely while each resonator segment handles specific frequency bands, resolving the contradiction between fluid flow and broadband absorption.

The patent varies key parameters of the Helmholtz resonators including chamber volume, neck area, and neck length to tune the resonant frequencies. By systematically changing these parameters across the array of resonators, broadband acoustic absorption is achieved. The parameter variations enable different resonators to target different frequency ranges while maintaining fluid flow capability, thus resolving the frequency range limitation of conventional absorbers.

The Helmholtz resonator unit cell is designed as a universal module that simultaneously provides acoustic absorption and fluid flow capability. Each unit cell functions as a multi-functional element: the chambers and necks provide acoustic resonance for sound absorption, while the open structure and porous filling maintain fluid flow permeability. This universal module approach reduces overall system complexity by consolidating multiple functions into a single standardized unit that can be repeatedly deployed.

The porous foam material is nested within the chambers of the Helmholtz resonators, creating a hierarchical structure. The foam is embedded inside the resonator chambers, filling the volume while leaving the neck openings clear for fluid flow. This nesting arrangement maximizes acoustic absorption within the available volume without adding external complexity, as the absorbing material is integrated within the existing resonator geometry rather than adding separate components.