The present disclosure generally relates to acoustic metamaterials and, more particularly, to acoustic absorption metamaterials that are porous to ambient fluid.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it may be described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present technology.
Acoustic metamaterials having elastic acoustic properties that differ from those of their constituent materials are known. Such metamaterials have arrays of periodic structures, typically on a scale smaller than the target wavelength. Such metamaterials are typically solid surfaces that are impermeable to ambient fluid (e.g. air). Such metamaterials also frequently have narrow ranges of effective absorption frequency.
Accordingly, it would be desirable to provide an improved acoustic material having sparse (spaced apart) unit cells that allow fluid to flow freely between the unit cells, and that have very broad frequency absorption range.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
In various aspects, the present teachings provide an acoustic absorber. The acoustic absorber includes a periodic array of laterally spaced-apart, two-sided Helmholtz resonators. The periodic array further includes a plurality of unit cells spaced apart by a lateral midpoint-to-midpoint distance P, each unit cell having a maximum lateral dimension W, wherein P is greater than W. Each unit cell includes first and second Helmholtz resonators. The first Helmholtz resonator includes a first chamber portion bounded by at least one first boundary wall defining a first chamber volume and having a longitudinal neck placing the second chamber portion in fluid communication with the ambient environment. The second Helmholtz resonator includes a second chamber portion bounded by at least one second boundary wall defining a second chamber volume and having a lateral neck forming an opening on a second side of the at least one second boundary wall and placing the second chamber portion in fluid communication with the ambient environment. The first side of the at least one first boundary wall and the second side of the at least one second boundary wall are substantially perpendicular to each other, and the second chamber volume is equal to the first chamber volume.
In other aspects, the present teachings provide a layered broadband sparse acoustic absorber. The acoustic absorber includes a periodic array of laterally spaced-apart, two-sided Helmholtz resonators. The periodic array further includes a plurality of unit cells spaced apart by a lateral midpoint-to-midpoint distance P, each unit cell having a maximum lateral dimension W, wherein P is greater than W. Each unit cell includes first and second Helmholtz resonators. The first Helmholtz resonator includes a first chamber portion bounded by at least one first boundary wall defining a first chamber volume and having a longitudinal neck placing the first chamber portion in fluid communication with the ambient environment. The second Helmholtz resonator includes a second chamber portion bounded by at least one second boundary wall defining a second chamber volume and having a lateral neck forming an opening on a second side of the at least one second boundary wall and placing the second chamber portion in fluid communication with the ambient environment. The first side of the at least one first boundary wall and the second side of the at least one second boundary wall are substantially perpendicular to each other, and the second chamber volume is equal to the first chamber volume. The layered broadband sparse acoustic absorber further includes a second plurality of unit cells, layered relative to the first plurality, and having third and fourth Helmholtz resonators. The third Helmholtz resonator includes a third chamber portion bounded by at least one third boundary wall defining a third chamber volume and having a second longitudinal neck placing the third chamber portion in fluid communication with the ambient environment. The fourth Helmholtz resonator includes a fourth chamber portion bounded by at least one fourth boundary wall defining a fourth chamber volume and having a lateral neck forming an opening on a fourth side of the at least one fourth boundary wall and placing the fourth chamber portion in fluid communication with the ambient environment. The third side of the at least one third boundary wall and the fourth side of the at least one fourth boundary wall are substantially perpendicular to each other, and the third chamber volume is equal to the fourth chamber volume.
In still other aspects, the present teachings provide a sound suppression system for a sound emitting device. The system includes a sound emitting device, such as an internal combustion engine. The system further includes a periodic array of laterally spaced-apart, two-sided Helmholtz resonators. The periodic array further includes a plurality of unit cells spaced apart by a lateral midpoint-to-midpoint distance P, each unit cell having a maximum lateral dimension W, wherein P is greater than W. Each unit cell includes first and second Helmholtz resonators. The first Helmholtz resonator includes a first chamber portion bounded by at least one first boundary wall defining a first chamber volume and having a longitudinal neck placing the second chamber portion in fluid communication with the ambient environment. The second Helmholtz resonator includes a second chamber portion bounded by at least one second boundary wall defining a second chamber volume and having a lateral neck forming an opening on a second side of the at least one second boundary wall and placing the second chamber portion in fluid communication with the ambient environment. The first side of the at least one first boundary wall and the second side of the at least one second boundary wall are substantially perpendicular to each other, and the second chamber volume is equal to the first chamber volume.
Further areas of applicability and various methods of enhancing the disclosed technology will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The present teachings will become more fully understood from the detailed description and the accompanying drawings, wherein:
It should be noted that the figures set forth herein are intended to exemplify the general characteristics of the methods, algorithms, and devices among those of the present technology, for the purpose of the description of certain aspects. These figures may not precisely reflect the characteristics of any given aspect, and are not necessarily intended to define or limit specific embodiments within the scope of this technology. Further, certain aspects may incorporate features from a combination of figures.
The present technology provides an asymmetric, unidirectional noise attenuation structure, and various devices built from the structure. The structure has a sparse periodic structure, with open space between adjacent unit cells, allowing fluid to flow freely through the structure. The unique design of the structure enables it to exhibit very broadband acoustic absorption, that is tunable to a desired frequency range.
The broadband sparse absorber is based on a unit cell having an inverted, asymmetric pair of Helmholtz resonators. Arrays of such unit cells can be stacked in high frequency and low frequency layers, enhancing the frequency range of high efficiency absorption. The broadband sparse absorption structures have unique applicability in any application that benefits from sound dampening, while allowing air or other fluid to pass freely through. In an example, the broadband sparse absorber can surround a vehicle engine, rendering the engine substantially silent while allowing air or liquid coolant to pass through to the engine.
In the example of
With particular reference to
With reference to
With continued reference to
In some implementations, the unit cells 110 of the broadband sparse acoustic absorber 100 can be positioned periodically on a porous substrate, through which ambient fluid 170 can pass with little constraint. Such a porous substrate could be a mesh or screen, such as an air screen of the type used in a window, a sheet of material having periodic apertures or perforations, or any other suitable substrate.
Referring now more particularly to
The first Helmholtz resonator 130A has a longitudinal neck 122A that provides an opening, parallel to a longitudinal axis of the resonator 130A (e.g. the y-axis of
where f is the resonance frequency of the Helmholtz resonator; c is the speed of sound in the ambient fluid; A is the cross-sectional area of the neck; Vis the chamber volume; and L is the neck length.
While the unit cell 110 of
It will further be understood that each chamber 132A, 132B defines a volume, corresponding to the volume of ambient fluid 170 that can be held in the chamber 132A, 132B, exclusive of the neck 122A, 122B. The volume of the first and second Helmholtz resonators 130A, 130B will generally be the same. Thus, and with renewed reference to Equation 1, the first and second Helmholtz resonators 130A, 130B will generally be the same.
The at least one enclosure wall and the end wall 120 will typically be formed of a solid, sound reflecting material. In general, the material or materials of which the at least one enclosure wall and the end wall 120 are formed will have acoustic impedance higher than that of ambient fluid 170. Such materials can include a thermoplastic resin, such as polyurethane, a ceramic, or any other suitable material.
With continued reference to
In some implementations, two or more broadband sparse acoustic absorber 100 arrays can be layered to create a stacked broadband sparse acoustic absorber 200 and increase breadth of absorption.
While the sound emitting device 310 is shown abstractly and generically as a square in the stylized view of
In instances in which the one or more broadband sparse acoustic absorbers 100 include one or more one-dimensional arrays of the type discussed above in reference to
The preceding description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical “or.” It should be understood that the various steps within a method may be executed in different order without altering the principles of the present disclosure. Disclosure of ranges includes disclosure of all ranges and subdivided ranges within the entire range.
The headings (such as “Background” and “Summary”) and sub-headings used herein are intended only for general organization of topics within the present disclosure, and are not intended to limit the disclosure of the technology or any aspect thereof. The recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features, or other embodiments incorporating different combinations of the stated features.
As used herein, the terms “comprise” and “include” and their variants are intended to be non-limiting, such that recitation of items in succession or a list is not to the exclusion of other like items that may also be useful in the devices and methods of this technology. Similarly, the terms “can” and “may” and their variants are intended to be non-limiting, such that recitation that an embodiment can or may comprise certain elements or features does not exclude other embodiments of the present technology that do not contain those elements or features.
The broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the specification and the following claims. Reference herein to one aspect, or various aspects means that a particular feature, structure, or characteristic described in connection with an embodiment or particular system is included in at least one embodiment or aspect. The appearances of the phrase “in one aspect” (or variations thereof) are not necessarily referring to the same aspect or embodiment. It should be also understood that the various method steps discussed herein do not have to be carried out in the same order as depicted, and not each method step is required in each aspect or embodiment.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations should not be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
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Number | Date | Country | |
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20200202831 A1 | Jun 2020 | US |