Helmholtz Resonator With Movable Pellet For Broadband Absorption
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Solution Overview
Problem
Current passive noise reduction solutions, such as Helmholtz resonators, face limitations in absorption performance, flexibility in frequency adaptation, and resistance to external constraints, particularly in high-stress environments like aircraft engines, where active solutions are complex, costly, and not feasible.
Innovation Solution
A passive sound absorber design incorporating a cavity with a movable pellet suspended by mechanical connections, obstructing the neck in a non-sealed manner, tuned to resonate at a specific frequency range, combined with optional electromagnetic systems for adaptive impedance control, to enhance absorption efficiency and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Helmholtz resonator is used for noise reduction, then absorption at a specific resonant frequency is achieved, but the absorption bandwidth is narrow and frequency adaptation is limited
Solution Approach 1:
The patent introduces a movable pellet that can change position within the cavity, transforming the static Helmholtz resonator into a dynamic system. By moving the pellet to different positions, the effective cavity volume changes, allowing continuous adjustment of the resonant frequency. This enables the system to adapt to different frequency requirements while maintaining precise tuning capability at each position.
Solution Approach 2:
The invention changes the key parameter of cavity volume dynamically by moving the pellet. As the pellet position changes, the volume of the resonating cavity is adjusted, which directly modifies the resonant frequency according to the Helmholtz resonator formula. This parameter change approach allows broad frequency coverage while maintaining precise control over the absorption frequency.
2Device complexity
If passive Helmholtz resonators are used in high-stress environments like aircraft engines, then simplicity and cost-effectiveness are maintained, but absorption performance is insufficient and resistance to external constraints is poor
Solution Approach 1:
The movable pellet introduces dynamic adaptability to the passive system, allowing it to respond to varying acoustic conditions and external constraints in real-time. This enhances the reliability of the passive resonator in high-stress environments by enabling adjustment to maintain optimal performance under different operating conditions.
Solution Approach 2:
The system can automatically adjust the pellet position in response to acoustic pressure variations, enabling self-regulation of the resonant frequency without external control systems. This maintains the simplicity of the passive approach while improving reliability through adaptive behavior.
3Measurement precision
If the absorption frequency is tuned to a specific high frequency, then narrowband absorption is achieved, but lower frequency coverage and broader bandwidth are lost
Solution Approach 1:
The movable pellet enables continuous adjustment of the effective cavity volume, allowing the system to sweep through a broad frequency range from high to low frequencies. At any given moment, the system maintains precise absorption at the tuned frequency, while the ability to reposition the pellet provides extensive frequency coverage.
Solution Approach 2:
The system can periodically adjust the pellet position to cover different frequency bands, achieving both precise narrowband absorption at each position and broad frequency coverage through the sequence of positions. This periodic repositioning allows the system to address multiple frequency requirements over time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves improved absorption performance, shifts absorption frequencies to lower ranges, and allows for broader frequency coverage, while maintaining cost-effectiveness and simplicity, suitable for harsh environments where traditional solutions fail.
Implementation Method 1
at least one movable element, or pellet, suspended or held by suspensions in a position obstructing said neck in a non-sealed manner
Implementation Method 2
a cavity open towards the outside on the side where the sound wave is incident by a neck passing through the front wall to form a Helmholtz resonator for a first frequency
Implementation Method 3
the relative stiffness of the suspensions and of the pad is determined so that the assembly formed by the pad and the suspension arms vibrates according to a 'piston' type resonance mode at a second frequency
Data Source
Figure 1~3
Figure 4~8
Figure 9
AI summary
The invention relates to a passive sound absorber (3, 4, 6, 7, 8) comprising a closed cavity (30, 80) opening to the outside via an inlet direction (D3) via a collar passing through the front wall in order to form a Helmholtz resonator for a first frequency. According to the invention, said absorber further comprises at least one moving element, or membrane (32, 42, 62, 72a, 72b), suspended or held by suspensions (33, 43, 6140) in a position obstructing said collar in a non-sealed manner. The relative stiffness of the suspensions and of the membrane is determined such that the assembly resonates in a vibration following a "piston" movement at a second frequency different from the first frequency, producing an absorption for said second frequency or range of frequencies. A hybrid version comprises a coil (324) that is controlled to adjust the acoustic impedance of the absorber. The invention proposes an acoustic wall comprising a plurality of such absorbers produced by a repetitive structure opening through perforations, each receiving such a membrane, as well as a method for designing and producing such an absorber or wall.