Activated Cavity Acoustic Panels for Low-Frequency Noise Control
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Solution Overview
Problem
Current noise control technologies in aircraft face challenges in providing both broadband transmission loss through cabin walls and improved absorption in the cabin interior, especially at lower frequencies, due to weight and volume constraints, and lack a single solution that effectively addresses both issues.
Innovation Solution
The integration of active components with passive cavity absorbers, utilizing a combination of a microphone, accelerometer, and actuator within shallow cavities, forms a hybrid system that extends frequency range and reduces noise transmission and absorption, using a flow resistive screen and lightweight actuators to achieve simultaneous insertion loss and absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional passive cavity absorbers are used to achieve sound absorption, then absorption performance is improved at specific frequencies, but the system cannot provide broadband transmission loss and the cavity depth required for low frequency absorption creates excessive volume and weight
Solution Approach 1:
The patent merges passive cavity absorbers with active control components (actuators and sensors) into a hybrid system. The actuator is integrated within the cavity structure, combining the passive acoustic absorption function with active noise control capability. This allows the same structure to provide both broadband transmission loss through the cabin wall and improved absorption in the cabin interior without requiring separate systems.
Solution Approach 2:
The patent transforms the static passive cavity into a dynamic system by adding actuators that can actively adjust the acoustic properties. The actuator responds to sensor feedback to dynamically control the sound pressure within the cavity, extending the absorption frequency range to much lower frequencies without increasing cavity depth. This dynamic adjustment allows the system to adapt to different noise conditions and frequency ranges.
2Object-affected harmful factors
If thicker materials are used to absorb lower frequencies, then absorption performance at low frequencies is improved, but weight and volume constraints are violated
Solution Approach 1:
The patent replaces the traditional mechanical approach of using thick passive absorptive materials with an active control system. Instead of relying on the physical depth and mass of absorptive material to achieve low frequency absorption, the system uses actuators to actively generate counter-phase sound waves that cancel low frequency noise. This substitution of active control for passive mechanical absorption dramatically reduces the weight and volume requirements while maintaining or improving absorption performance.
3Object-affected harmful factors
If multiple devices are used together to achieve broadband noise control, then noise control performance is improved, but control interaction increases and system complexity increases
Solution Approach 1:
The patent divides the noise control system into multiple independent cavity units, each equipped with its own actuator and sensor. Each cavity operates as a relatively independent control element with local feedback, reducing control interaction when multiple devices are used together. This segmented architecture allows parallel operation of multiple units to achieve broadband noise control while maintaining manageable system complexity through modular design and localized control.
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
This hybrid system enhances noise control by extending the frequency range of absorption to lower frequencies, reducing noise transmission and absorption, while minimizing system complexity and maintenance costs, and providing robust noise reduction without significant weight penalties.
Implementation Method 1
A control system receives inputs from the microphone and accelerometer and provides an output that drives the actuator, so that an acoustic output of the actuator provides simultaneous insertion loss and absorption
Implementation Method 2
Sound absorption by materials is typically limited by their size; thicker materials are required to absorb lower frequencies. A classic sound absorber is a cavity faced by an absorbent screen. When the depth of the cavity is one quarter of the wavelength of incident sound, a pressure null occurs inside the screen, reducing the local sound field and forcing the incident sound wave to expend energy by an increased acoustic particle velocity through the resistance of the screen
Implementation Method 3
At the front of each cavity is a microphone that measures the sound pressure near the flow resistive screen
Implementation Method 4
an accelerometer that measures the acceleration of the cavity in the direction normal to the flow resistive screen
Data Source
AI summary
A method and apparatus for providing simultaneous enhancement of transmission loss and absorption coefficient using activated cavities is presented. A layer of material is provided, and a backing plate having a plurality of cavities on the top surface of said backing plate, is disposed adjacent a top surface of said layer of material. A screen is disposed along the top surface of said cavities on said backing plate and at least one cavity includes an actuator disposed within the cavity and a control system receiving a signal from the microphone and receiving a signal from the accelerometer and providing a drive signal to the actuator to provide an acoustic output to provide simultaneous insertion loss and absorption which serves to minimize a linear combination of the signal from the microphone and the signal from the accelerometer.