Patent Description:
Current technologies in noise insulation use passive noise control approaches such as sound absorbers, dampers, or blockers. These components are usually either too large or too heavy, making the approaches either inefficient for noise control or ineffective for low frequency noise control. Active noise control provides another noise control option. However, active noise control requires wiring and power, which can make active noise control complex, costly, and/or difficult to implement for noise control in applications where large surface areas are present, such as in motor vehicles, boats, or an aircraft (e.g., "acreage noise control").

<CIT>, in accordance with its abstract, states a recyclable sound insulating material for a vehicle. A raw fabric mat M is formed when a fiber material prepared by mixing together a long-fiber recyclable PET and cotton with shape maintaining characteristic and impregnated with a phenol resin. A sound absorbing base material is formed by thermocompression molding the raw fiber mat M that is suitable for an engine room.

<CIT>, in accordance with its abstract, states a transportation vehicle part including: a patch member constructed of a plate-like metal patch panel, and a vibration attenuating resin layer provided along a surface of the patch panel; and a metal base plate closely adhered with the vibration attenuating resin layer of the patch member and affixed with the patch member. The patch panel is produced via a rolling step. An acute angle between a longitudinal direction and a rolling direction of the patch panel is <NUM> to <NUM> degrees.

<CIT>, in accordance with its abstract, states an acoustic barrier structure including a support structure that defines a plurality of cells, a weight attached to the support structure, and at least one resonant membrane covering one of the plurality of cells. The at least one resonant membrane can comprise at least one weight.

<CIT>, in accordance with its abstract, states a membrane containing a first weight disposed at a center portion of the membrane, and a first hinge structure disposed away from the center portion of the membrane.

<CIT>, in accordance with its abstract, states a light viscoelastic damping structure having a plurality of damping strips widely separated on the surface of a lightweight panel. The strips may be arranged parallel or at right angles to each other. Each damping strip includes a viscoelastic damping layer, a first honeycomb structure having opposing face sheets and attached to one surface of the damping layer, and a second honeycomb structure having face sheets on opposing sides thereof attached to the damping layer and to the panel.

<CIT>, in accordance with its abstract, states an acoustic attenuation panel including a resistive skin having acoustic holes, a solid skin and an acoustic structure. The acoustic structure includes a sound-absorbing material and is arranged between the resistive skin and the solid skin. In particular, the solid skin is structural and forms a transverse spacer between the solid skin and the resistive skin.

Noise-insulating panels are provided herein. The noise-insulating panel is an anti-resonant panel as defined in claim <NUM>, and comprising a base panel having a base panel core material and two base panel face sheets, wherein each of the two base panel face sheets is adjacent to an opposite side of the base panel core material. The anti-resonant panel further includes at least one stiffener-member positioned along the base panel in a defined area of the base panel, where the defined area is less than a full area of the base panel. The stiffener-member includes a stiffener-member core material and two stiffener-member face sheets. Each of the two stiffener-member face sheets is adjacent to an opposite side of the stiffener-member core material, and the stiffener-member is configured to provide anti-resonant performance to the base panel. The anti-resonant panel further includes a perimeter-type stiffener-member disposed along one or more edges of the at least one stiffener-member. The stiffener-member may be configured to provide anti-resonant performance to the base panel by adding stiffness to the defined area of the base panel at a low mass density. The stiffener-member may be disposed on one of the two base panel face sheets. The stiffener-member may be disposed between the two base panel face sheets and adjacent to the base panel core material. In some embodiments, the stiffener-member may be disposed along less than <NUM>% of a total surface area of the base panel and a mass of the stiffener-member is about <NUM>% or less of a total mass of the anti-resonant panel.

In some embodiments, the anti-resonant panel may include two or more stiffener-members each positioned along the base panel in respective defined areas of the base panel.

The stiffener-member core material may comprise polyethylene terephthalate (PET) foam, aramid honeycomb construction, or combinations thereof. The stiffener-member face sheets may comprise carbon fiber, fiberglass, or combinations thereof.

In some embodiments, the anti-resonant panel may reduce noise propagation through the anti-resonant panel at frequencies between about <NUM> to about <NUM>.

In some embodiments, the stiffener-member may include an interior wall defining a hollowed portion in the stiffener-member. In some embodiments, the anti-resonant panel may include at least one inertial member, the inertial member configured to provide a mass increase over the defined area of the sandwich-type panel. The inertial member may have a mass density of about <NUM> times a mass density of the stiffener-member. The inertial member may comprise solid aluminum, rubber, tungsten, ceramic, or a combination thereof.

In some embodiments, the anti-resonant panel may include a reinforcing member. The reinforcing member may be disposed along a perimeter of the defined area of the base panel and define an acoustic boundary for the defined area of the base panel. In some embodiments, the anti-resonant panel may include a grounding member. The grounding member may be configured to anchor the anti-resonant panel to a structure and define an acoustic boundary for the defined area of the base panel.

A method of making an anti-resonant panel is defined according to claim <NUM>. The method includes: providing a base panel, where the base panel includes a base panel core material and two base panel face sheets. Each of the two base panel face sheets are adjacent to an opposite side of the base panel core material. The method further comprises: adding at least one stiffener-member disposed along the base panel in a defined area of the base panel. The stiffener-member includes a stiffener-member core material and two stiffener-member face sheets. Each of the two stiffener-member face sheets are adjacent to an opposite side of the stiffener-member core material. The stiffener-member is configured to provide anti-resonant performance to the base panel. The method further comprises: adding a perimeter-type stiffener-member disposed along one or more edges of the at least one stiffener-member.

In some embodiments, attaching the stiffener-member to the base panel may include composite layup, hot-pressing, vacuum-forming, vacuum bagging, vacuum assisted resin transfer molding (VARTM), or a combination thereof. In some embodiments, attaching the stiffener-member to the base panel may include incorporating at least one of a screw, adhesive, adhesive film, rivet, or a combination thereof to attach the stiffener-member to the base panel. In some embodiments, the method may further include removing an interior portion of the stiffener-member creating a hollowed portion in the stiffener-member prior to attaching at least one stiffener-member to the base panel.

Other examples provided herein may also relate to non-claimed methods of forming a stiffener-member. For instance, the method may include forming a stiffener-member configured to provide anti-resonant performance to a base panel by attaching the stiffener-member to a defined area of the base panel. The method may include disposing two stiffener-member face sheets over the stiffener-member core material and then attaching the stiffener-member face sheets and core material to a base panel in a defined area of the base panel.

In some embodiments, a system may be provided that includes a structure (e.g., a fuselage skin) defining an exterior section and an interior section and may form an enclosed cabin. The structure may be adjacent to an anti-resonant panel and may work in conjunction with the anti-resonant panel to provide improved noise-insulation. In some embodiments, the anti-resonant panel may be used in an aircraft, the aircraft being the system including the anti-resonant panel.

Having described certain example embodiments of the present disclosure in general terms above, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale:.

In general, embodiments of the present disclosure provided herein include methods and systems for providing noise insulation, particularly noise control for low frequencies. More specifically, noise insulation is provided by using an anti-resonance approach. Some embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the disclosures are shown. Indeed, these disclosures may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements, the scope being defined by the appended claims.

As used herein, "anti-resonant performance" refers to the sound transmission loss resulting from reduction of structural net vibratory displacement. In certain embodiments described herein, this reduction of structural net vibratory displacement is generally obtained by reflecting the impacting sound waves off of the component. Such reflection may be obtained with the disclosed materials. For example, the addition of a stiffener-member as described herein to a base panel as described herein may provide anti-resonant performance to the panel making the panel an anti-resonant panel.

The term "mass density" refers to the amount of matter per volume.

The term "hollowed portion" refers to a hole or vacancy of material in a defined area of the respective component such that the hollowed portion lacks the material otherwise continuous in the component. The hollowed portion may be created by removing an interior portion of the component and be defined by an inner wall of the component. As used herein, "defined area" is generally in reference to anti-resonant units or portions of the anti-resonant panel. That is, the anti-resonant panel may be divided into defined areas or portions. Stiffener-members may cover all or part of the defined areas. Additional components such as inertial members may be added to the defined areas and reinforcing members and/or grounding members may be added to defined areas, particularly along the perimeter forming the defined areas.

As used herein, "acoustic boundary" refers to a limit, generally imposed by a physical component, creating a defined acoustic transmission path where sound travels differently (with regards to speed, path, transmission efficiency etc.) compared to the adjoining space. As used herein, various components may be incorporated into the anti-resonant panels to create acoustic boundaries allowing for more control of noise propagation when contacting the panel. The acoustic boundaries may be in line with the perimeter of the defined area.

Provided herein are systems, devices, panels, and methods for providing noise control, in particular by reflecting and/or blocking noise. Noise insulation, according to the claimed subject matter, is provided by noise insulating panels that include stiffener-members that impart anti-resonance to the panel, which are then referred to as anti-resonant panels. The resulting anti-resonant panels may reduce the external acoustic energy passing through the panel, thereby providing improved noise insulation. The anti-resonant panels include a base panel and stiffener-members distributed along the base panel. The anti-resonant panel may enable anti-resonance frequencies with locally out-of-phase vibration modes to passively neutralize the sound radiation through the panel and into any enclosed structure. In conventional enclosed structures, such as aircraft cabins, cars, boats, etc., the complex geometry, large dimension, and existing attached components, such as windows, may impose significant challenges in structural vibration management for noise control. However, the anti-resonant design of the base panels combined with the stiffener-members may allow for acreage noise control for such enclosed structures. The lightweight nature and high bending stiffness of the anti-resonant panels may provide anti-resonant based noise control or anti-resonant performance. The anti-resonant panels may achieve high sound transmission loss over a wide frequency range, particularly in the low frequency regime of hundreds to a thousand Hertz (Hz), outperforming conventional added-mass and damping approaches in the same frequency range. Benefitting from existing components, such as attached windows or nearby frames, inertial members may be incorporated into the anti-resonant panels to further tune the anti-resonant design.

The anti-resonant panels may also improve double-leaf noise insulation by interacting with nearby structures, such as the fuselage skin of an aircraft. The anti-resonant panels may provide a lightweight, compact, practical, and economic solution to providing targeted noise control to structures, such as aircraft cabins and other enclosed structures where noise control is of concern. The anti-resonant panels may be particularly beneficial for areas where contoured panels are needed, as such were previously difficult to control acoustically. The anti-resonant panels, with the distinct stiffener-members distributed along the base panels in defined areas, may be able to conform to the desired shape while still achieving the anti-resonant performance of the anti-resonant panels. In some embodiments, the anti-resonant panels may provide lightweight noise blocking barriers for structures such as aircraft cabins and improve upon existing panels (e.g., trim panels of boats, vehicles, or aircraft) particularly those of large dimension (e.g., acreage noise control) with conformal as well as asymmetric geometry and may work with other components of the structure, such as cabin windows, to control noise propagation.

The anti-resonant panels may replace simple to complex panels. As compared to existing noise-insulating panels, the anti-resonant panels may have reduced manufacturing costs with simpler manufacturing techniques, enable stiffness control, and generally provide a panel with reduced mass compared to existing noise-insulating panels. In particular, previous technologies use passive noise control approaches such as sound absorbers, dampers, or blockers. These components are usually either too large or too heavy, especially for low frequency noise control. Active noise control may provide another noise control option. However, active noise control typically requires wiring and power requirements making the option complex, costly, and hard to implement for acreage noise control applications.

Indeed, there has been a long-felt need for lightweight acoustic attenuation, particularly inside enclosed cabins (e.g., cabins in cars, aircraft, boats, trains, etc.). State of the art noise control used for vehicular trim panel routinely involves recycled noise control mechanisms, such as Helmholtz-style absorption, constrained layer damping, mass-loading, fibrous-type batting for acoustic absorption, or combinations thereof. Generally speaking, noise above <NUM> may be dealt with using these approaches. However, there exists a need for lightweight noise control in the lower-frequency range, e.g., below <NUM>.

Trim panels used in vehicles requiring lightweight design typically include a sandwich-type design, which enables a relatively durable boundary wall that forms the interior walls of the enclosed cabin, yet offers a relatively lightweight solution. Such panels and any panel that is lightweight, relatively stiff, and relatively large in area makes for a sound radiator. These trim panels also make up much of the interior surface of the vehicle, which make the trim panels a prime influence on the acoustic properties inside the vehicle. These trim panels can produce global vibratory modes that dominate the noise frequency range, especially below <NUM>, and have been difficult to mitigate without mass loading the trim panels, which, if implemented, results in a significant mass penalty and corresponding decreased fuel efficiency.

Provided herein is a passive noise control technology with advantages of lightweight, compactness, high noise reduction, and environmental robustness. The anti-resonant panels provide a conformal sound insulating panel with high noise reduction that may provide a lightweight noise control solution for high quality travelling experience. For instance, the anti-resonant panels can be used as trim panels in an aircraft cabin, as partitions, bulkhead, sidewalls, and floors for various airplane models, to reduce noise propagation into and between chambers. In addition, the anti-resonant panels may be used as, for example, housings or partitions, in various commercial products that contain noisy components (e.g., motors, pumps, compressors, transmissions, transformers, ducts, etc.) including appliances, grinders, blenders, microwave ovens, sump pumps, etc. The anti-resonant panels may be suitable for a variety of applications, such as any application where noise control is desired, without deviating from the intent of the present disclosure.

The anti-resonant panels may employ a sound-reflection mechanism, using anti-resonance to reflect a tuned bandwidth of sound energy from the panel. The disclosed mechanism may involve a slight mass penalty as compared to unmodified panels, although the mass penalty involved may be significantly less than what would otherwise be used to create similar transmission loss performance based on mass law predictions. The anti-resonant panels' transmission loss performance may extend beyond the panel's predicted mass-law sound-attenuation limit within the low frequency range of interest by modifying the global panel vibratory modes. In some embodiments, other components, such as one or more inertial members, grounding members, and reinforcing members may be added to modify the global panel vibratory modes.

The anti-resonant panel may be particularly effective in the low frequency range (e.g., about <NUM> to about <NUM>) without adding a significant amount of mass. The anti-resonant bandwidth may be tailored to meet a target range of problem noise frequencies associated with the unmodified base panel as disclosed herein. Furthermore, current engineered trim panel designs are inherently complex in shape, as architectural designs and features are desired in most passenger aircraft and vehicles. Such complexity can make the implementation of an anti-resonant design difficult. Provided herein are panels with anti-resonant performance using a diverse range of panel materials, shapes, sizes, and orientations to enhance the versatility of the panels for use in various applications. The noise control mechanism may have an added benefit of being relatively unaffected by temperature, humidity, and pressure changes, which further makes the panels suitable for vehicles that routinely experience fluctuations in environmental conditions, such as aircraft, trains, and automobiles.

The anti-resonant panels may improve upon existing tunable sandwich-structured acoustic barriers by implementing anti-resonance control, particularly for geometrically complex panels with asymmetric geometry and of a large dimension. Further, the anti-resonant panels may enhance double-pane soundproofing in terms of wide bandwidth and noise reduction by interacting with nearby panels.

In some embodiments, pre-qualified materials may be used for the anti-resonant panels to create a noise control or acoustic blocking structure over an acreage area for noise management.

Having described example embodiments at a high level, the design of the various configurations performing various example operations is provided below.

Provided herein are anti-resonant panels with anti-resonance sound blocking performance to provide noise insulation. In some embodiments, the technology may be passive in nature, not relying on electronics or actuation for the sound blocking performance. The anti-resonant panels may include sandwich-type base panels, which are lightweight and stiff; can be manufactured in various sizes, thickness, and materials, such as pre-qualified aviation materials; and can be mounted in various ways. The anti-resonant panels also include a stiffener-member with the base panel. Without intending to be bound by theory, the stiffener-member provides localized stiffness to specific areas ("defined areas") of the base panel resulting in anti-resonant performance of the resulting panel.

The anti-resonant panels may have the capability to block low frequency sound and may use preexisting composite materials that may already be fully qualified for use in vehicles, such as aircraft. The mechanical properties of the anti-resonant panels may provide improved sound blocking performance for noise insulation. The anti-resonant panels may be used in any application where lightweight, strong paneling is desired, such as fuel-efficient vehicles and the like.

<FIG> illustrates exemplary shapes for stiffener-members <NUM>. <FIG> illustrates additional exemplary shapes for stiffener-members <NUM>. The stiffener-members <NUM> may include hollowed portions <NUM>, such as shown in <FIG>, such that the stiffness and surface density of the final design of the stiffener-member <NUM> are altered, ultimately altering the stiffness-to-mass ratio of the stiffener-member <NUM>. The stiffener-member <NUM> may include an interior wall <NUM> defining a hollowed portion <NUM> in the stiffener-member <NUM>. The hollowed portions <NUM> may cut vertically through the stiffener-member <NUM> (e.g., through each of the stiffener-member core material <NUM> and stiffener-member face sheets <NUM>, <NUM> of the stiffener-member <NUM> (shown in <FIG>)). Such hollowing of the stiffener-members <NUM> may reduce the mass of the stiffener members <NUM> without significantly reducing the stiffness of the stiffener members <NUM>. That is, the stiffener members <NUM> are still stiff enough to manipulate the dynamics of the anti-resonant panels <NUM> while not adding significant mass to the anti-resonant panels <NUM>. Variations on this manipulation of the stiffener-members <NUM> may be used to obtain the desired anti-resonant performance.

<FIG> provide various exemplary configurations of stiffener-members <NUM> on base panels <NUM>. To provide the anti-resonance effect, one or more stiffener-members <NUM> can be used with the base panel <NUM>. The stiffener-members <NUM> control the global vibratory modes and enable the anti-resonant design. Stiffener-members <NUM> can encompass any shape, number, orientation, or location as needed to enable anti-resonant performance of the resulting anti-resonant panels <NUM>. For example, in some embodiments, the stiffener-members <NUM> may be about <NUM>% to about <NUM>% of the total mass of the anti-resonant panel <NUM>, such as about <NUM>% to about <NUM>% of the total mass of the anti-resonant panel <NUM>, such as about <NUM>% or less of the total mass of the anti-resonant panel <NUM>.

The stiffener-members <NUM> may cover less than <NUM>% of the total surface area of the anti-resonant panel <NUM> (e.g., less than <NUM>% of the total surface area of the side of the anti-resonant panel <NUM> on which the stiffener-member(s) <NUM> are placed), such as less than <NUM>% of the total surface area of the anti-resonant panel <NUM> (e.g., less than <NUM>% of the total surface area of the side of the anti-resonant panel <NUM> on which the stiffener-member(s) <NUM> are placed), such as less than <NUM>% of the total surface area of the anti-resonant panel <NUM> (e.g., less than <NUM>% of the total surface area of the side of the anti-resonant panel <NUM> on which the stiffener-member(s) <NUM> are placed), such as less than <NUM>% of the total surface area of the anti-resonant panel <NUM> (e.g., less than <NUM>% of the total surface area of the side of the anti-resonant panel <NUM> on which the stiffener-member(s) <NUM> are placed), such as less than <NUM>% of the total surface area of the anti-resonant panel <NUM> (e.g., less than <NUM>% of the total surface area of the side of the anti-resonant panel <NUM> on which the stiffener-member(s) <NUM> are placed). In some embodiments, the stiffener-member <NUM> may be disposed along less than <NUM>% of a total surface area of the base panel <NUM> and a mass of the stiffener-member <NUM> may be about <NUM>% or less of a total mass of the anti-resonant panel <NUM>. With such low coverage of the total surface area of the base panel <NUM> (e.g., less than <NUM>% of the total surface area of the anti-resonant panel <NUM>) and low mass addition to the total mass of the anti-resonant panel <NUM> (e.g., less than <NUM>% of the total mass of the anti-resonant panel <NUM>), the stiffener-member <NUM> is able to increase the stiffness of the base panel <NUM> without significantly impacting the mass of the base panel <NUM> and provide control of the anti-resonant performance due to the discrete nature of the stiffener-members <NUM>. The density and thickness of the stiffener-members <NUM> may vary based on the desired anti-resonant performance. The stiffener-members <NUM> will generally have a low mass density and high stiffness.

The various configurations presented in <FIG> are a few examples of configurations that may alter the stiffness and mass-density properties of the resulting anti-resonant panel <NUM>. The stiffener-members <NUM> of the present disclosure are not limited to those shown in <FIG> and may include a variety of materials in a variety of configurations without deviating from the intent and scope of the present disclosure. For instance, the stiffener-members <NUM> can be a combination of the following materials and/or other materials and designs that provide the desired lightweight but stiff combination and impart an acoustic boundary <NUM> to the base panel <NUM>. For instance, the stiffener-member face sheets <NUM>, <NUM> may be lightweight, strong material such as carbon fiber, fiberglass, or combinations thereof. The stiffener-member core material <NUM> may comprise foam (e.g., polyethylene terephthalate (PET) foam), be of a honeycomb construction (e.g., aramid honeycomb construction), otherwise have a porous structure, or combinations thereof. In some embodiments, the stiffener-member core material <NUM> may comprise PET foam, aramid honeycomb construction, or combinations thereof.

The stiffener-member face sheets <NUM>, <NUM> may comprise carbon-fiber, fiberglass, combinations thereof, or other similar materials. In some embodiments, the stiffener-member face sheets <NUM>, <NUM> may comprise carbon fiber, fiberglass, a fiber composite, or combinations thereof. Metal (e.g., aluminum) struts, trusses, or porous structures may be used to impart stiffness while not significantly increasing mass. Two different stiffener-member core materials <NUM> are shown in <FIG>. As the stiffener-members <NUM> are discrete, concentrated areas along the base panel <NUM>, the materials may have a higher modulus than materials that would typically be used for construction of a base panel <NUM>. In addition, materials that may be of a flammability concern in large areas, may be used in the stiffener-members <NUM> as such are generally smaller, more concentrated, discrete areas along the base panel <NUM> rather than the full length/width of the base panel <NUM>.

As shown in <FIG>, multiple stiffener-member face sheets <NUM> and/or <NUM> may be used to form the stiffener-member <NUM> and/or multiple stiffener-member core materials <NUM> may be used to form the stiffener-member <NUM>. In some embodiments, multiple stiffener-members <NUM> may be disposed on a base panel <NUM>. For instance, the anti-resonant panel <NUM> of <FIG> includes a first stiffener-member 108a and a second stiffener-member 108b, each in respective defined areas 110a, 110b on the base panel <NUM>. The first and second stiffener-members 108a, 108b are shown in <FIG> as having the same compositions, however, the compositions of the first and second stiffener-members 108a, 108b may be the same or different and more than two stiffener-members <NUM> may be incorporated on/into the base panel <NUM>. Variations on the number and combination of these materials may be used to achieve the desired anti-resonant performance.

In some embodiments, the anti-resonant panels <NUM> may include stiffener-members <NUM> disposed on one of the two base panel face sheets <NUM>, <NUM>. In some embodiments, the anti-resonant panels <NUM> may include stiffener-members <NUM> disposed between the two base panel face sheets <NUM>, <NUM> and adjacent to the base panel core material <NUM>. <FIG> illustrate stiffener-members <NUM> applied to the base panel face sheets <NUM>, <NUM> while <FIG> illustrate stiffener-members <NUM> applied to the interior of the base panel <NUM> and covered by the base panel face sheets <NUM>, <NUM>. In particular, in <FIG>, the stiffener-members <NUM> replace a portion of the base panel core material <NUM>. As shown in <FIG>, a first stiffener-member face sheet <NUM> may be applied externally to the base panel face sheet <NUM> using an adhesive (attachment mechanism <NUM>). Such placement of the stiffener-member face sheet <NUM> may further increase the bending stiffness of the defined area <NUM> in which the stiffener-member <NUM> is disposed.

When being applied to the interior of the base panel <NUM>, the stiffener-member <NUM> may include stiffener-member core material <NUM> and one or more stiffener-member face sheets <NUM>, <NUM> or simply stiffener-member core material <NUM> without one or more stiffener-member face sheets <NUM>, <NUM>. Stiffener-member face sheets <NUM>, <NUM> may be applied to the interior of the base panel <NUM> (e.g., under one or more base panel face sheets <NUM>, <NUM> (shown in <FIG>)) and/or applied to the exterior of the base panel <NUM> (e.g., over one or more base panel face sheets <NUM>, <NUM>).

The stiffener-members <NUM> may be designed to provide the desired degree of anti-resonant performance by including the stiffener-members <NUM> in specific regions (e.g., defined areas <NUM>) of base panels <NUM> and with specific constructions. That is, the materials, size, shape, and configuration of materials for the stiffener-members <NUM> may be modified to achieve the desired anti-resonance behavior. In some embodiments, the anti-resonant panel <NUM> may include two or more stiffener-members <NUM> (e.g., first and second stiffener-members 108a and 108b as shown in <FIG>) each positioned along the base panel <NUM> in respective defined areas <NUM> (e.g., first and second defined areas 110a and 110b as shown in <FIG>) of the base panel <NUM>.

Without intending to be limited by theory, the stiffener-member <NUM> may provide an efficient acoustic boundary on the base panel <NUM> thereby enabling alteration of the global vibratory modes of the anti-resonant panel <NUM> (that is, the vibratory modes of the whole base panel <NUM> such as the first and second principal modes and the anti-resonant mode in between). According to the claimed subject matter, the stiffener-member <NUM> has a sandwich-type construction (e.g., comprising two stiffener-member face sheets <NUM>, <NUM> surrounding a stiffener-member core material <NUM> on opposite sides of the core material <NUM>), which may enable lightweight but high bending stiffness resulting in a sandwich-type stiffener member <NUM>. Various other stiffener-member <NUM> configurations with high stiffness-to-mass ratio are discussed herein. The high stiffness-to-mass ratio may allow for anti-resonant performance while also allowing for high fuel efficiency when applied to vehicles. In some embodiments, the anti-resonant panel <NUM> may be configured to reduce noise propagation through the anti-resonant panel <NUM> at frequencies between about <NUM> to about <NUM>. For instance, the anti-resonant panel <NUM> may include a stiffener-member <NUM> (e.g., stiffener-member <NUM> in <FIG>, <FIG>, <FIG>, and <FIG>) on a base panel <NUM> (e.g., base panel <NUM> in <FIG>, <FIG>, <FIG>) that may reduce noise propagation through the anti-resonant panel <NUM> at low frequencies (e.g., about <NUM> to about <NUM>), which are typically difficult to reduce or control with base panels alone.

According to the claimed subject matter, one or more stiffener-members <NUM> are added to one or more base panels <NUM>, in particular to one or more base panel face sheets <NUM>, <NUM> to alter the stiffness-to-mass ratio of the base panel <NUM>. The anti-resonant panels <NUM> include a base panel <NUM> comprising a base panel core material <NUM> and two base panel face sheets <NUM>, <NUM>, each of the two base panel face sheets <NUM>, <NUM> adjacent to an opposite side of the base panel core material <NUM>; and at least one stiffener-member <NUM> positioned along the base panel <NUM> in a defined area <NUM> of the base panel <NUM>, the defined area <NUM> being less than a full area <NUM> of the base panel <NUM>; wherein the stiffener-member <NUM> comprises a stiffener-member core material <NUM> and two stiffener-member face sheets <NUM>, <NUM>, each of the two stiffener-member face sheets <NUM>, <NUM> adjacent to an opposite side of the stiffener-member core material <NUM>, and wherein the stiffener-member <NUM> is configured to provide anti-resonant performance to the base panel <NUM>. The stiffener-member <NUM> may be configured to provide anti-resonant performance to the base panel <NUM> by adding stiffness to the defined area <NUM> of the base panel <NUM> at a low mass density.

For instance, as shown in <FIG>, <FIG>, <FIG>, the stiffener-member <NUM> may provide stiffness by being constructed as a sandwich-type stiffener-member comprising at least one stiffener-member face sheet <NUM>, <NUM> and a stiffener-member core material <NUM> and being prepared with materials described herein. In some embodiments, the stiffener-member <NUM> may add stiffness at a low mass density by including a hollowed portion <NUM> as shown in <FIG> and/or be disposed on the base panel as shown in <FIG> or <FIG>. The one or more stiffener-members <NUM> are disposed on the exterior surface of the one or more base panel face sheets <NUM>, <NUM>. In some embodiments, one or more stiffener-members <NUM> may be added to the interior base panel core material <NUM> and then surrounded by the base panel face sheets <NUM>, <NUM>. The one or more stiffener-members <NUM> may be applied to the base panel core material <NUM> and/or used in place of the base panel core material <NUM> in defined areas <NUM> of the base panel <NUM>. One or more stiffener-members <NUM> may be added to defined areas <NUM> of the base panel <NUM> to alter the stiffness-to-mass ratio of the base panel <NUM> at specific points along the base panel <NUM>. Various stiffener-member face sheets <NUM>, <NUM>, adhesive films or adhesive materials (collectively referred to as "attachment mechanisms" <NUM>), and stiffener-member core materials <NUM> can be used to form the stiffener-members <NUM> and achieve the desired stiffness and specific mass properties of the final stiffener-member <NUM> and the resulting anti-resonant panel <NUM>.

The configurations described in <FIG> and <FIG> are examples of embodiments that can effectively be used as stiffener-members <NUM> for anti-resonant performance. Combinations of these examples as well as other configurations of the stiffener-members <NUM> may be used in conjunction with the base panels <NUM> to provide anti-resonant panels <NUM> with the improved anti-resonant performance.

According to the claimed subject matter, as shown in <FIG>, stiffener-members <NUM> includes a perimeter-type stiffener-member <NUM> that is lightweight and further increases the stiffness of the anti-resonant panel <NUM>. The anti-resonant panel <NUM> includes a perimeter-type stiffener-member <NUM> disposed along one or more edges <NUM> of the stiffener-member <NUM>. For instance, in some embodiments, perimeter-type stiffener-members <NUM> may be included to reinforce a stiffener-member <NUM>, such as a sandwich-type stiffener-member <NUM> (see e.g., <FIG>), or, in non-claimed examples, may be used alone as the stiffener-member <NUM>. The perimeter-type stiffener member <NUM> is particularly effective in performance when disposed along the perimeter of a sandwich-type stiffener-member <NUM> to further improve the anti-resonant performance of the anti-resonant panel <NUM>. For instance, <FIG> shows a lightweight perimeter-type stiffener member <NUM> enhancing the sandwich-type stiffener-member <NUM>, which then engages to a sandwich-type base panel <NUM>.

As shown in <FIG>, the perimeter-type stiffener member <NUM> may be have a Z-shaped cross-section (e.g., two parallel horizontal portions are connected by a vertical portion, the two parallel horizontal portions independently connected to the vertical portion at opposite ends of the horizontal portions, forming a Z-shaped cross section) and extend along one or more sides or edges <NUM> of the sandwich-type stiffener-member <NUM>. For instance, in the embodiment illustrated in <FIG>, the perimeter-type stiffener member <NUM> traces the perimeter of the sandwich-type stiffener-member <NUM> along three edges <NUM> of the sandwich-type stiffener-member <NUM>. However, the perimeter-type stiffener member <NUM> may trace one, two, or all edges <NUM> of a sandwich-type stiffener-member <NUM>. The stiffness of the anti-resonant panel <NUM> is particularly increased when the perimeter-type stiffener member <NUM> connects three or more edges <NUM> enclosing a perimeter as shown in <FIG>. The perimeter-type stiffener member <NUM> may have a cross-section that is I-shaped (e.g., two parallel horizontal portions are connected by a vertical portion, the two parallel horizontal portions centered on top and on the bottom of the vertical portion, forming an I-shaped cross-section), L-shaped (e.g., a single horizontal portion is attached on the bottom of a single vertical portion forming an L-shaped cross-section), Z-shaped, T-shape (e.g., a single horizontal portion is attached on top of a single vertical portion forming a T-shaped cross section), etc. or may have any other suitable configuration to provide a lightweight stiffener member <NUM> to the sandwich-type base panel <NUM>.

In some embodiments, the materials for the stiffener-members <NUM> may be pre-qualified materials already suited for the aerospace or automotive industry. In some embodiments, the same materials that make up the base panel <NUM> may be used for the stiffener-members <NUM>, though differing in configuration, size, and thickness to achieve the desired anti-resonant performance.

The anti-resonant performance of the anti-resonant panels <NUM> can be further improved by maximizing the bonding rigidity of the stiffener-member <NUM> to the base panel <NUM>. The engagement of the stiffener-member <NUM> to the base panel <NUM> may be as complete as possible, especially along the perimeter or edges <NUM> of the stiffener-member <NUM>. <FIG> provide exemplary methods of adjoining stiffener-members <NUM> to base panels <NUM>. <FIG> provides a high-stiffness, highly-conformal stiffener-member <NUM> formed in a mold to fit the shape of the base panel <NUM>. As used herein, "conformal" refers to the shaping of the item to closely fit adjacent components. For instance, with regards to the conformal stiffener-member <NUM>, the surface of the stiffener-member <NUM> (e.g., one of the stiffener-member face sheets <NUM>, <NUM>) is immediately adjacent to the base panel <NUM> and follows the curvature of the base panel <NUM>. The stiffener-member <NUM> geometry is traced and cut away to form the stiffener-member <NUM> for the anti-resonant panel <NUM>.

Particularly beneficial for complex stiffener-members <NUM>, the stiffener-member <NUM> may be pre-fabricated as stiffener-member panel stock <NUM> in a mold. From this stiffener-member panel stock <NUM>, a specific area predetermined to produce the desired anti-resonant performance is cut out (stiffener-member cut-out <NUM>) and superimposed as the stiffener-member <NUM> to an existing base panel <NUM>. This method is especially practical if specific defined areas <NUM> requiring the stiffener-members <NUM> are complex or highly contoured, as shown in <FIG>. This treatment allows for high bonding engagement of the stiffener-member <NUM> to the base panel <NUM>, which can increase the effective stiffness of the resulting anti-resonant panel <NUM>.

The stiffener-member <NUM> may be joined to the base panel <NUM> by other methods. <FIG> shows an exemplary process of forming the stiffener-member <NUM> on the base panel <NUM>. In particular, <FIG> illustrates an exemplary method of stiffener-member <NUM> formation by a layup process, in which the constituents (in this embodiment, the stiffener-member face sheets <NUM>, <NUM>, the attachment mechanisms <NUM>, and the stiffener-member core material <NUM>) that make up the stiffener-member <NUM> are flat, but flexible, allowing the constituents to take on the surface contours of the base panel <NUM> (including the base panel face sheets <NUM>, <NUM> and base panel core material <NUM>) during the layup process. The stiffener-member <NUM> and base panel <NUM> are then bonded together to form the anti-resonant panel <NUM>. An autoclave may be used to achieve higher bonding pressures once the setup has been established, or sandbags may be applied over the attachment to aid in bonding. The method shown in <FIG> may be more cost effective and efficient than other methods.

<FIG> illustrates another exemplary method of adjoining stiffener-members <NUM> to base panels <NUM>. In particular, in the embodiment illustrated in <FIG>, a stiffener-member <NUM> may be prepared, for example, by cutting out the stiffener-member <NUM> from stiffener-member panel stock <NUM> (see e.g., <FIG>), building up the stiffener-member with pre-cut constituents of the stiffener-member (see e.g., <FIG>), the like, or combinations thereof. The stiffener-member <NUM> includes a stiffener-member core material <NUM> and stiffener-member face sheets <NUM>, <NUM>. A portion of the base panel core material <NUM> may be removed to allow for the insertion of the stiffener-member <NUM>. Base panel face sheets <NUM>, <NUM> may then be applied to the base panel core material <NUM> and stiffener-member <NUM> forming the anti-resonant panel <NUM>. In such embodiment, the stiffener-member <NUM> is incorporated into the base panel <NUM> thereby imparting the stiffer properties of the stiffener-member <NUM> to the base panel <NUM> and providing a resulting anti-resonant panel <NUM> with a flush or regular surface. In some embodiments, the stiffener-member <NUM> may be incorporated into the base panel <NUM> by adhering the stiffener-member <NUM> to the base panel core material <NUM> and then applying base panel face sheets <NUM>, <NUM> over both the stiffener-member <NUM> and the base panel core material <NUM> without cutting out a portion of the base panel core material <NUM>. Variations on these methods may be used without deviating from the intent of the present disclosure and other methods can be used to achieve similar results based on available supplies or capital.

Once a design for the stiffener-member <NUM> is designated, the stiffener-member <NUM> can be attached to the base panel <NUM> by several means, with some examples shown in <FIG>. In particular, <FIG> provide exemplary processes for attaching a stiffener-member <NUM> to a base panel <NUM>. In <FIG>, the stiffener-member <NUM> is pre-fabricated and attached by way of mechanical fasteners (e.g., attachment mechanism <NUM>) to the base panel <NUM>. <FIG> also shows a cross-section of the resulting anti-resonant panel <NUM>. In <FIG>, the stiffener-member <NUM> is pre-fabricated and attached by way of adhesive film (e.g., attachment mechanism <NUM>) and an auto-clave layup to the base panel <NUM>. <FIG> also shows a cross-section of the resulting anti-resonant panel <NUM> illustrating the direct attachment of the stiffener-member <NUM> to the base panel <NUM>. Variations in bonding techniques can be used, such as hot press, vacuum bagging, sand-bagging, the like, and combinations thereof and various materials can be used such as screws, adhesive, adhesive film, rivet, and combinations thereof. For instance, in one embodiment, a rigid foam-forming adhesive may be used to ensure gaps are securely filled and adhered between the two interfaces (e.g., between the stiffener-member <NUM> (e.g., one or more stiffener-member face sheets) and the base panel <NUM>). Various methods in attaching the components may be used without deviating from the intent and scope of the present disclosure. For instance, in some embodiments, it may be desirable to combine one or more fabrication and adhesion techniques from <FIG> and <FIG>.

<FIG> are exemplary base panels <NUM>, particularly sandwich-type base panels <NUM>, which may be used for the anti-resonant panels <NUM> as described herein. Each of the base panels <NUM> depicted in <FIG> include base panel face sheets <NUM>, <NUM> and base panel core material <NUM> making the panels sandwich-type base panels <NUM>. While the embodiments illustrated in <FIG> use the same base panel face sheets <NUM>, <NUM> for either side of the base panel core material <NUM>, the base panel face sheets <NUM>, <NUM> may vary within an anti-resonant panel <NUM> (that is, different types (i.e., materials) of base panel face sheets <NUM>, <NUM> may be used on opposite sides of the base panel core material <NUM> and/or along the same side of the base panel core material <NUM>). In addition, while the embodiments illustrated in <FIG> use the same base panel core material <NUM> for the length and width of the base panel <NUM>, the base panel core material <NUM> may vary within an anti-resonant panel <NUM>.

<FIG> is a flat sandwich-type base panel <NUM> with carbon-fiber base panel face sheets <NUM>, <NUM> surrounding an aramid honeycomb base panel core material <NUM>. <FIG> is a contoured sandwich-type base panel <NUM> of the same materials used in <FIG> with a thicker base panel core material <NUM> and contoured shape (base panel face sheets <NUM>, <NUM> and base panel core material <NUM>). <FIG> is a flat sandwich-type composite base panel <NUM> with fiberglass base panel face sheets <NUM>, <NUM> surrounding an aramid honeycomb base panel core material <NUM> with in-plane contoured cutouts. <FIG> is a sandwich-type base panel <NUM> composed of thin aluminum base panel face sheets <NUM>, <NUM> surrounding a PET foam base panel core material <NUM>. The thickness of the base panel <NUM>, particularly the base panel core material <NUM>, in <FIG> is varied along the base panel <NUM> to create a contoured portion <NUM> of the base panel <NUM>. The contoured base panels <NUM> may include a variety of curvature and angles to provide the desired shape and configuration. For instance, the base panel <NUM> may be contoured in various portions of the base panel <NUM> to specifically fit the desired location in the wall in which the anti-resonant panel <NUM> is to be used and/or to achieve the desired noise-insulating performance of the anti-resonant panel <NUM>.

The base panels <NUM> of the present disclosure are not limited to those shown in <FIG> and may include a variety of materials in a variety of configurations without deviating from the intent and scope of the present disclosure. For instance, the base panels <NUM> in the anti-resonant panels <NUM> can be a combination of these materials and/or other materials and designs that create lightweight and stiff paneling with anti-resonant performance.

As panel size increases, the anti-resonant sound-blocking performance may become vulnerable to the low-frequency range of audible frequencies, e.g., <NUM>-<NUM>, as the effective acoustic boundaries expand. This behavior is usually governed by the creation of undesirable vibro-acoustic modes having characteristic geometric patterns super-positioned on the panel at distinct frequencies. Mitigation of these modes can be addressed by modifying specific locations on the panel, as determined from various tools used in acoustic measurement and modeling, with the use of the stiffener-members <NUM>. Additional components may be added to the anti-resonant panels <NUM> to provide improved performance. For example, inertial members <NUM> (see e.g., <FIG>), reinforcing members <NUM> (see e.g., FIGS. 8A and 8B), grounding members <NUM> (see e.g., <FIG>), and combinations thereof may be added to strategic panel locations to further improve the anti-resonance of the anti-resonant panels <NUM>. These treatments can further tune the anti-resonant performance of the anti-resonant panels <NUM>. In some embodiments, the additional components may provide a wider bandwidth of transmission loss, may shift the bandwidth to higher frequencies, or combinations thereof. As an added benefit, inertial members <NUM> and/or grounding members <NUM> along the defined acoustic boundary <NUM> of the sub-divided anti-resonant panel <NUM> are effective to increase the quality factor (Q) of the anti-resonant performance, increasing the sound-blocking performance even further.

Inertial members <NUM> are generally discrete high-density components added to the anti-resonant panel <NUM> to provide a relatively small amount of mass in a specific portion of the anti-resonant panels <NUM>. The anti-resonant panel <NUM> may include at least one inertial member <NUM>. The inertial member <NUM> is configured to provide a mass increase over the defined area <NUM> of the anti-resonant panel <NUM>. For instance, as shown in <FIG>, one or more inertial members <NUM> may be added to the anti-resonant panel <NUM>. In such an instances, the inertial members <NUM> include material(s) and have a geometry to increase the mass density of the anti-resonant panel <NUM> at the particular location of the inertial member <NUM>. That is, the inertial members <NUM> provide high mass density in a small diameter (e.g., the inertial members <NUM> generally have a smaller diameter than the diameter of the stiffener-members <NUM>, but have a higher mass density than the mass density of the stiffener-members <NUM>). In some embodiments, the inertial members <NUM> may have a mass density of about <NUM>, <NUM>, or more times the mass density of the stiffener-members <NUM> and are generally too small in size to provide stiffness to the anti-resonant panels <NUM> (e.g., the inertial members <NUM> have a smaller diameter than the diameter of the stiffener-members <NUM> and do not provide the stiffness that the stiffener-members <NUM> are able to provide). The inertial member <NUM> may have a mass density of about <NUM> times a mass density of the stiffener-member <NUM>. The mass density may be such that a high increase in mass is provided over a small diameter to effectively increase the mass at that location without significantly increasing the total mass of the anti-resonant panel <NUM>. In comparison, the stiffener-member <NUM> may increase the stiffness of the panel without significantly increasing the mass of the panel.

For instance, the density of the inertial members <NUM> may be about <NUM>/m<NUM> to about <NUM>/m<NUM>, such as about <NUM>/m<NUM> to about <NUM>/m<NUM>. The inertial members <NUM> provide concentrated masses at a particular location that shift local modes out of the target frequency range or suppress the local vibrations (e.g., <FIG>). In some embodiments, there is a diminishing return in transmission loss gained as mass increases with the incorporation of inertial members <NUM>. Thus, the addition of inertial members <NUM> is a balance between the increase in mass and the desired transmission loss in the desired frequency range. The addition of the inertial members <NUM> as point-masses can help maintain anti-resonance with minimal mass penalty. The inertial members <NUM> may include solid aluminum, rubber, tungsten, ceramic, or a combination thereof as such materials provide a relatively high mass density without significantly increasing the mass of the panel.

The inertial members <NUM> provided herein may be of any suitable geometry and material to provide a relatively small amount of mass to help tune the acoustic properties of the anti-resonant panels <NUM>. The inertial members <NUM> may be fastened using attachment mechanisms (e.g., attachment mechanisms <NUM>), such as mechanical fasteners, adhesives, other methods noted herein, the like, or combinations thereof. Although the inertial members <NUM> can embody any shape, the inertial members <NUM> are constrained to being effective as point-masses irrelevant of shape.

<FIG> illustrates the incorporation of exemplary inertial members <NUM> to an anti-resonant panel <NUM>. <FIG> illustrates both inertial members <NUM> and a stiffener-member <NUM> (one stiffener-member face sheet <NUM> and the stiffener-member core material <NUM> are shown) on a sandwich-type base panel <NUM> (including base panel face sheets <NUM>, <NUM> and base panel core material <NUM>) forming an anti-resonant panel <NUM>.

Another treatment to preserve the anti-resonant performance is the use of reinforcing members <NUM> to reinforce regions of the anti-resonant panel <NUM> (see e.g., <FIG>). The anti-resonant panel <NUM> may include a reinforcing member <NUM>. The reinforcing member <NUM> is disposed along a perimeter <NUM> of the defined area <NUM> of the base panel <NUM> and defines an acoustic boundary <NUM> for the defined area <NUM> of the base panel <NUM>. The reinforcing members <NUM> divide the anti-resonant panels <NUM> acoustically by imposing a barrier at the particular location along the anti-resonant panel <NUM>, forming acoustic boundaries <NUM>. The reinforcing members <NUM> can help improve control of the overall acoustic performance of the anti-resonant panel <NUM> with such division. The reinforcing members <NUM> can be placed in any orientation and any number of the reinforcing members <NUM> may be used in positions suitable to improve the anti-resonant performance. The reinforcing members <NUM> may help delineate acoustic boundaries <NUM> of the anti-resonant panel <NUM>, in particular non-planar or contoured anti-resonant panel <NUM>.

<FIG> illustrates cross-sectional profiles of exemplary reinforcing members <NUM> that can be used for the reinforcement of various anti-resonant panels <NUM>. Solid construction-type and sandwich-type reinforcing members <NUM> are shown. The cross-sectional geometry of the reinforcing members <NUM> can embody several types commonly used in the industry (I-shaped, L-shaped, Z-shaped, T-shaped, etc.), as well as newer or more complex cross-sectional geometries that maximize the stiffness-to-mass ratio. The length and size of the reinforcing members <NUM> may be designed to achieve particular anti-resonant performance.

The reinforcing members <NUM> can be made out of any type of material, can be a composite material, have a sandwich-type construction, the like, or combinations thereof suitable to provide a lightweight component with a high bending stiffness (e.g., comparable to the stiffener-member <NUM>). The attachment mechanism <NUM> for the reinforcing members <NUM> can be those used in attaching the stiffener-members <NUM> described earlier, or other mechanisms favorable for constraining vibratory movement with a minimal mass-density penalty over the footprint of the reinforcing member <NUM>. The reinforcing members <NUM> may include various materials, such as pre-approved composite materials, such as those found in the construction of base panels <NUM>. The reinforcing members <NUM> can be configured in perimeter configurations similar to the perimeter-type stiffener-members <NUM> so long as the reinforcing members <NUM> enhance the partition of the anti-resonant panels <NUM> creating acoustic boundaries <NUM> for higher efficiency anti-resonant panels <NUM>. The reinforcing members <NUM> are generally elongate members (length greater than width).

<FIG> illustrates exemplary reinforcing members <NUM> that are able to further improve the anti-resonance control for the anti-resonant panels <NUM> and boost transmission loss. More specifically, <FIG> illustrates a profile view of a system <NUM> including reinforcing members <NUM> used to horizontally reinforce anti-resonant panels <NUM> employed as an aircraft cabin panel <NUM>. <FIG> illustrates a system <NUM> including vertical sandwich-type reinforcing members <NUM> to reinforce portions of the anti-resonant panels <NUM> employed as an aircraft cabin panel <NUM>. Various configurations of the reinforcing members <NUM> may be used to improve the anti-resonant performance of the anti-resonant panels.

Periodically mounting the anti-resonant panels <NUM> to a structure <NUM>, such as a fuselage skin <NUM> (see e.g., <FIG>) or a window <NUM> (see e.g., <FIG>), may be used to further redefine the acoustic boundaries <NUM>, favoring anti-resonant performance (see e.g., <FIG>).

Referring to <FIG>, grounding members <NUM> can be used to anchor the anti-resonant panels <NUM> to other components of the structure <NUM>, such as a fuselage skin <NUM> or a window <NUM>. The anti-resonant panel <NUM> may include a grounding member <NUM>. The grounding member <NUM> is configured to anchor the anti-resonant panel <NUM> to a structure <NUM>, such as a fuselage skin <NUM> or a window <NUM>, and define an acoustic boundary <NUM> for the defined area <NUM> of the base panel <NUM>. Grounding members <NUM> may take advantage of existing parts of the structure <NUM> (e.g., those that have high mass, such as a fuselage skin <NUM> or a window <NUM>) to provide the anti-resonant panels <NUM> more stable vibratory acoustic boundaries <NUM>. The grounding members <NUM> can help isolate and control vibrations and improve the anti-resonant performance of the anti-resonant panel <NUM>.

In embodiments where the anti-resonant panels <NUM> are used in aircraft (see e.g., aircraft <NUM> in <FIG>), several locations along the fuselage skin <NUM> can be used as anchoring points to attach grounding members <NUM> to the anti-resonant panels <NUM> to further improve anti-resonant performance. Convenient anchoring locations on portions of the fuselage skin <NUM> can be used, such as the windows <NUM>, stringers, circumferential frame portions, or similar points nearby. The selection of anchoring points for attaching grounding members <NUM> to the anti-resonant panels <NUM> can include nearby components as well that are anchored to the fuselage skin <NUM> to reduce the additional mass of fasteners or parts required to achieve effective anchoring performance.

<FIG> illustrates a profile view of an exemplary system <NUM> including the anti-resonant panels <NUM> and the adjacent fuselage skin <NUM> and <FIG> illustrates a back-facing view of an exemplary system <NUM> including of anti-resonant panels <NUM> and the adjacent fuselage skin <NUM>. Exemplary grounding members <NUM> are illustrated. The grounding members <NUM> are attached at specific portions of the anti-resonant panel <NUM> to form suitable acoustic boundaries <NUM> favorable to anti-resonant performance. The grounding members <NUM> can include brackets, anchoring bolts, other fasteners, or combinations thereof that have the capacity to anchor the portion of anti-resonant panel <NUM> on which the grounding members <NUM> are attached and the adjoining fuselage skin <NUM>. Further, damping can be added along the anchoring grounding member <NUM> to reduce induced vibration from the fuselage skin <NUM> to the anti-resonant panel <NUM> at the attachment point or area.

In aircraft (see e.g., aircraft <NUM> in <FIG>), while the aircraft trim panels <NUM> define the side walls of the cabin of the vehicle, the fuselage skin <NUM> located behind the trim panel <NUM> acts as the exterior vehicle body. The gap between these two components (the trim panel <NUM> and the fuselage skin <NUM>) can be acoustically exploited, in which the overall acoustic attenuation can be increased over a wide bandwidth. This architecture may be referred to as a double-pane architecture. The trim panels <NUM> may be replaced with one or more anti-resonant panels <NUM> having a base panel <NUM> and one or more stiffener-members <NUM>. Accordingly, the anti-resonant panel <NUM> act as an interior side wall panel that at least partially defines an enclosed cabin <NUM> of the aircraft <NUM>.

The double-pane acoustic effect generally has two low-frequency resonant modes, as shown for example in <FIG>, then a rapid increase in acoustic attenuation as the frequency increases. If properly accounted for, the anti-resonance of the anti-resonant panel <NUM> and the double-pane effect can work together to extend the overall acoustic transmission loss through the anti-resonant panel <NUM> into the enclosed structure (e.g., enclosed cabin <NUM> of <FIG>). <FIG> illustrate exemplary double-pane effects caused by two structures (e.g., fuselage skin <NUM> and anti-resonant panel <NUM>) resonating in phase with each other (<FIG>) and out of phase with each other (<FIG>).

Referring to <FIG>, in some embodiments, a method <NUM> is provided for making an anti-resonant panel <NUM> having a base panel <NUM> with a base panel core material <NUM> and two base panel face sheets <NUM>, <NUM>. Each of the two base panel face sheets <NUM>, <NUM> are adjacent to an opposite side of the base panel core material <NUM>. The method <NUM> includes attaching at least one stiffener-member <NUM> to a base panel <NUM> (step <NUM>). As described above, the stiffener-member <NUM> is disposed along the base panel <NUM> in a defined area <NUM> of the base panel <NUM>, and the base panel <NUM> includes a base panel core material <NUM> and two base panel face sheets <NUM>, <NUM>. The stiffener-member <NUM> includes a stiffener-member core material <NUM> and two stiffener-member face sheets <NUM>, <NUM>. The stiffener-member <NUM> is configured to provide anti-resonant performance to the base panel <NUM>. In some embodiments, attaching the stiffener-member <NUM> to the base panel <NUM> may include composite layup, hot-pressing, vacuum-forming, vacuum bagging, vacuum assisted resin transfer molding (VARTM), or a combination thereof (step <NUM>). In some embodiments, attaching the stiffener-member <NUM> to the base panel <NUM> may include incorporating at least one of an attachment mechanism <NUM> comprising a screw, adhesive, adhesive film, rivet, or a combination thereof to attach the stiffener-member <NUM> to the base panel <NUM> (step <NUM>).

<FIG> illustrates an exemplary method <NUM> of providing noise insulation to a structure (e.g., a fuselage skin <NUM>) in accordance with some example embodiments described herein. In particular, method <NUM> is illustrated which includes attaching at least one stiffener-member <NUM> to the base panel <NUM> (step <NUM>) (see e.g., <FIG>, <FIG>, <FIG>and <FIG> and the description related to each provided herein). The method <NUM> may also include providing a base panel <NUM> comprising a base panel core material <NUM> and two base panel face sheets <NUM>, <NUM> (step <NUM>) (see e.g., <FIG>). As described above, attaching the stiffener-member <NUM> to the base panel <NUM> may include composite layup, hot-pressing, vacuum-forming, vacuum bagging, VARTM, and combinations thereof (step <NUM>). Attaching the stiffener-member <NUM> to the base panel <NUM> may include incorporating at least one attachment mechanism <NUM> including a screw, adhesive, adhesive film, rivet, or combinations thereof to attach the stiffener-member <NUM> to the base panel <NUM>, as shown in step <NUM>. Various embodiments as disclosed herein may be incorporated into methods of providing noise insulation.

In some embodiments, the method <NUM> may include removing an interior portion <NUM> of the stiffener-member <NUM> creating a hollowed portion <NUM> in the stiffener-member <NUM> prior to attaching at least one stiffener-member <NUM> to the base panel <NUM> (step <NUM>).

<FIG> is a flow chart for an exemplary method <NUM> of forming an anti-resonant panel <NUM> in accordance with some example embodiments described herein. In particular, method <NUM> includes forming a stiffener-member <NUM> configured to provide anti-resonant performance to a base panel <NUM> by disposing at least one stiffener-member face sheets <NUM> and/or <NUM> over a stiffener-member core material <NUM> (step <NUM>) and attaching the stiffener-member <NUM> to a defined area <NUM> of the base panel <NUM> (step <NUM>). Various embodiments as disclosed herein may be incorporated into methods of providing noise insulation.

Referring again to <FIG>, <FIG>, in some embodiments, a system <NUM> may be provided that includes a structure <NUM> (e.g., fuselage skin <NUM>) and at least one anti-resonant panel <NUM> adjacent the structure (e.g., fuselage skin <NUM>). The structure <NUM> (e.g., fuselage skin <NUM>) defines an exterior section 138a and an interior section 138b and may form an enclosed cabin <NUM>. The structure <NUM> (e.g., fuselage skin <NUM>) is adjacent to the anti-resonant panel <NUM> and may work in conjunction with the anti-resonant panel <NUM> to provide improved noise-insulation (see e.g., grounding members <NUM> discussed with regards to <FIG> and/or double pane effect discussed with regards to <FIG>). In some embodiments, the anti-resonant panel <NUM> is used in an aircraft (e.g., aircraft <NUM>), where the aircraft is the system <NUM> having the anti-resonant panel <NUM>.

<FIG> provides exemplary areas where the anti-resonant panels <NUM> may be used on an aircraft <NUM> and provides an example of anti-resonant panels <NUM> incorporated with the fuselage skin <NUM> of the aircraft <NUM> forming an enclosed cabin <NUM>. The anti-resonant panels <NUM> may be added to the aircraft <NUM> as an addition or substitution where the trim panels <NUM> are located. For instance, the stiffener-members <NUM> may be incorporated onto a base panel <NUM>, which enables broadband sound-blocking performance of the anti-resonant panel <NUM>. <FIG> provides one example of the application of the stiffener-members <NUM>; however, the stiffener-members <NUM> may be added to various locations throughout the enclosed cabin <NUM>. As shown in <FIG>, the incorporation of the stiffener-members <NUM> to the base panels <NUM> provides improved sound blocking as compared to the base panel <NUM> alone. Sound waves <NUM> are reflected off the anti-resonant panels <NUM>. The anti-resonant panels <NUM> thereby provide improved noise blocking for the enclosed cabin <NUM>, particularly at low frequencies.

In some embodiments, noise insulation may be provided to an enclosed cabin <NUM>. Noise insulation may be provided to an enclosed cabin <NUM> by positioning at least one anti-resonant panel <NUM> adjacent to the enclosed cabin <NUM>, the at least one anti-resonant panel <NUM> comprising a base panel <NUM> and at least one stiffener-member <NUM> attached to the base panel <NUM>, wherein the at least one stiffener-member <NUM> provides anti-resonant performance to the base panel <NUM> to reduce noise propagation into the enclosed cabin <NUM>. In some embodiments, positioning at least one anti-resonant panel <NUM> adjacent to the enclosed cabin <NUM> includes positioning the anti-resonant panel <NUM> as previously described adjacent the enclosed cabin <NUM>. In some embodiments, the at least one anti-resonant panel <NUM> may be coupled to the enclosed cabin <NUM>. In some embodiments, the at least one anti-resonant panel <NUM> may be coupled to the enclosed cabin <NUM> using grounding members <NUM>.

An example of effective anti-resonant performance is depicted in <FIG>. In particular, <FIG> illustrates an exemplary prediction using the finite element analysis (FEA) method and experimentally measured results. The performance shown in <FIG> is merely representative and is relative to the noise that may be blocked. The performance shown in <FIG> is not intended to limit the present disclosure. <FIG> shows the insertion loss performance of an anti-resonant panel <NUM> (solid line), along with the matched FEA prediction (depicted as diamonds). The dashed curve is the equivalent mass law prediction using an identical mass density of an isotropic plate. As shown in <FIG>, the anti-resonant panel <NUM> may provide improved noise blocking, particularly at relatively low frequencies, and much higher noise blocking than seen with an equivalent mass density. As shown in <FIG>, in this embodiment, the equivalent mass to achieve the shown loss in noise is about sixteen (<NUM>) times that used in the anti-resonant panel <NUM>. Other degrees of improvement may be possible.

<FIG> illustrates an effect of adding exemplary inertial members <NUM> to an anti-resonant panel <NUM> to enable a wider bandwidth of anti-resonant performance in an exemplary embodiment. As shown in <FIG>, in some embodiments, the addition of the inertial members <NUM> (shown by squares) may provide a wider bandwidth of anti-resonant performance compared to an embodiment without the inertial member <NUM> (shown by triangles). In some embodiments, the addition of the inertial members <NUM> may reduce dips in anti-resonant performance seen in embodiments without the inertial members <NUM>. The inertial members <NUM> generally help tune the acoustic performance of the anti-resonant panel <NUM>, providing a wider bandwidth of anti-resonant performance. The inertial members <NUM> may define a new acoustic boundary <NUM> point, line, or area, and may enable the creation of a better-defined anti-resonant panel <NUM>. The inertial members <NUM> may help move the resonance frequencies away from the target frequency range.

<FIG> illustrates how the anti-resonance and double pane effects may add together to attenuate a very large acoustic frequency band gap. In particular, <FIG> illustrates an exemplary predicted transmission loss performance comparison using the double-pane effect between the untreated trim panels (dashed curve) (including a base panel <NUM> and grounding members <NUM>) and anti-resonant trim panels (triangle marks) (including a base panel <NUM>, grounding members <NUM>, and stiffener-members <NUM>). For instance, as shown in this embodiment, the low-frequency transmission-loss performance may increase, and any dips in the transmission loss may shift to a higher frequency thereby providing improved noise insulation for lower frequencies.

Also provided are the following illustrative, non-claimed examples that are compatible with the claimed subject matter.

The stiffener-member core material may comprise polyethylene terephthalate (PET) foam, aramid honeycomb construction, or combinations thereof.

The stiffener-member face sheets may comprise carbon fiber, fiberglass, a fiber composite, or combinations thereof.

The at least one inertial member may comprise solid aluminum, rubber, tungsten, ceramic, or a combination thereof.

The anti-resonant panel may further comprise a reinforcing member, the reinforcing member disposed along a perimeter of the defined area of the base panel and defining an acoustic boundary for the defined area of the base panel.

The word "exemplary", when used herein, is intended to mean "serving as an example, instance, or illustration". Any implementation described herein as "exemplary" is not necessarily preferred or advantageous over other implementations.

As used in the specification and in the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly indicates otherwise. For example, reference to "a stiffener-member" includes a plurality of such stiffener-members, unless the context clearly indicates otherwise.

As used in the specification and in the appended claims, reference to "on" includes both embodiments in which a component is disposed directly on another component as well as embodiments in which one or more intervening layers or elements are disposed between the components.

Claim 1:
An anti-resonant panel (<NUM>) comprising:
a base panel (<NUM>) comprising a base panel core material (<NUM>) and two base panel face sheets (<NUM>, <NUM>), each of the two base panel face sheets adjacent to an opposite side of the base panel core material; and
at least one stiffener-member (<NUM>) added to the base panel in a defined area (<NUM>) of the base panel, the defined area being less than a full area (<NUM>) of the base panel,
wherein the at least one stiffener-member comprises a stiffener-member core material (<NUM>) and two stiffener-member face sheets (<NUM>, <NUM>), the stiffener-member face sheets are each adjacent to an opposite side of the stiffener-member core material,
characterized in that the anti-resonant panel (<NUM>) further comprises a perimeter-type stiffener-member (<NUM>) disposed along one or more edges (<NUM>) of the at least one stiffener-member (<NUM>).