Acoustic Metamaterials: A Potential for Cabin Noise Control in Automobiles and Armored Vehicles

Abstract

The aim of this paper is to provide an overview of the existing industrial practices used for cabin noise control in various industries such as automotive, marine, aerospace, and defense. However, emphasis is placed on automobiles and armored vehicles. Generally, automobile cabins usually constitute of thin structural panels, where the fundamental frequency typically falls below 200[Formula: see text]Hz. If a specific structural mode couples with a specific acoustic mode of the cabin, booming noise occurs. As such, discomfort may be felt by the occupants. Fundamentally, vibroacoustics problems may be minimized if the acoustic modes and the structural modes are decoupled, which is achieved usually by structural modifications or acoustical treatments. However, if excessively performed, the weight limitation of an automobile design will be exceeded; not to mention the adverse effect of increased weight on several factors such as fuel efficiency, mileage life of tires and acceleration of the vehicle. Moreover, current solutions have several drawbacks in low frequency noise control. In light of this, it is of great interest to explore the feasibility of acoustic metamaterials as an alternative with hope to improve cabin noise.

Low-Frequency Noise Reduction by Earmuffs with Flax Fibre-Reinforced Polypropylene Ear Cups

“…Keeping in mind the intention of this study, these dips are not as critical since conventional acoustical treatments in the vehicle cabins are likely sufficient to complement noise attenuation at such high frequencies [1]. Nonetheless, with such acoustical performance achieved by the composite earmuffs in the low-frequency range, it was of great interest to evaluate their practicality in vehicle cabins.…”

“…Typically, automobile manufacturers apply several passive and/or active acoustical treatments for cabin noise control. However, the maximum acoustical performance of the treatments may not be achieved due to other design considerations [1]. In practice, the simplest approach is to highlight the importance of hearing protection to the soldiers and engineers on the correct procedures in wearing hearing protection devices, earplugs and earmuffs (or ear defenders).…”

“…Additionally, different configurations were considered (woven and nonwoven). The present study aims to understand the feasibility of composite earmuffs for cabin noise control in military vehicles where the crew's exposure to low-frequency noise is still a concern to date [1]. Consequently, the proposed composite earmuffs may be a potential alternative for low-frequency noise control applicable in vehicle cabins, at airports, and at construction sites involving heavy machineries.…”

Homogenized enriched model for blast wave propagation in metaconcrete with viscoelastic compliant layer

“…Note that the proposed metaconcrete microstructure thus far was similar to the standard single resonator reported in earlier works to address sound wave attenuation, albeit with epoxy as the matrix material. 5,6 In general, full-scale numerical characterization [7][8][9] and/or laboratory experiments [10][11][12] are computationally/logistically expensive. Generalized continuum theories are thus developed to facilitate rapid analyses.…”

Low-Frequency Noise Reduction by Earmuffs with Coir and Coir/Carbon Fibre-Reinforced Polypropylene Ear Cups

“…The acoustical performances of the composite earmuffs were evaluated experimentally in a reverberation chamber. Consequently, the proposed earmuffs may find potential applications in noise environments that are predominantly low-frequency-at airports, at construction sites, and in some automobile cabins, for example [30,31]. In Section 2, the specimen details and experimental approach are elaborated.…”