Patent Publication Number: US-2020291645-A1

Title: Acoustic panel

Description:
FIELD 
     The present disclosure relates generally to structural noise suppression systems and, more particularly, to acoustic panels used to suppress noise in aircraft gas turbine engine systems. 
     BACKGROUND 
     Acoustic panels may be used for noise suppression in aerospace applications and other fields. The panels typically comprise two skin surfaces that sandwich between them at least one layer of a core material or structure. The two skins and the core structure may be bonded together or cured or otherwise formed together, but mechanical fastening is also used in some applications. The core structure ties the skins together structurally and can form a very rigid, efficient and lightweight structure for noise suppression useful in aerospace applications. The panels may be given acoustic properties by perforating one skin (typically an air washed side of the panel) with specifically sized holes. This enables the cells of the core structure to act like individual Helmholtz resonators that attenuate a certain tone or tones, at specific frequencies or wavelengths, of noise generated by an engine. Further, additional layers of core structure, separated by additional skins, sheets or septa, may be used to attenuate multiple tonal frequencies. In many applications, the acoustic sandwich panel serves a structural role in addition to an acoustic role, but in some applications the structural function may be secondary to the acoustics. In aerospace applications, nacelles that house turbofan gas turbine engines may use acoustic panels to form the inner barrel of the inlet, the inner fixed structure of a thrust reverser, the translating sleeve of a translating sleeve type thrust reverser or portions of an exhaust system. 
     SUMMARY 
     An acoustic panel is disclosed. In various embodiments, the acoustic panel includes a first layer; a cell having a first cell end connected to the first layer and a second cell end spaced a cell length from the first cell end, the cell having a first wall extending between the first cell end and the second cell end; and a septum having a central portion positioned within the cell and a first tab extending from the central portion, the first tab defining a first surface positioned against the first wall and a first distal end positioned adjacent the first layer. 
     In various embodiments, the cell includes a second wall extending between the first cell end and the second cell end and the septum includes a second tab extending from the central portion. In various embodiments, the second tab includes a second surface positioned against the second wall. In various embodiments, the second tab includes a second distal end positioned adjacent the first layer. In various embodiments, the first distal end of the first tab and the second distal end of the second tab are secured to the first layer by an adhesive. In various embodiments, the first tab is secured to the first wall by a first weld and the second tab is secured to the second wall by a second weld. In various embodiments, the septum comprises a mesh and, in various embodiments, the mesh comprises stainless steel. 
     In various embodiments, the first tab defines a first proximal end connected to the central portion and a first tab length extending from the first proximal end to the first distal end. In various embodiments, the first tab length is between about twenty-five percent and about seventy-five percent of the cell length. In various embodiments, the cell defines a cell cross-sectional shape in a form of a polygon. In various embodiments, the polygon is one of a triangle, a square and a hexagon. 
     In various embodiments, the cell includes a second wall extending between the first cell end and the second cell end and the septum includes a second tab extending from the central portion. In various embodiments, the second tab defines a second proximal end connected to the central portion, a second distal end positioned adjacent the first layer, and a second tab length extending from the second proximal end to the second distal end, the second tab length equal to the first tab length. In various embodiments, the first distal end of the first tab and the second distal end of the second tab are secured to the first layer by an adhesive. In various embodiments, the first tab is secured to the first wall by a first weld and the second tab is secured to the second wall by a second weld. 
     A septum for an acoustic panel is disclosed. In various embodiments, the septum includes a central portion configured for positioning within a cell; a first tab extending from the central portion, the first tab defining a first surface configured for positioning against a first wall of the cell and a first distal end configured for positioning adjacent a first layer of the acoustic panel; and a second tab extending from the central portion, the second tab defining a second surface configured for positioning against a second wall of the cell and a second distal end configured for positioning adjacent the first layer of the acoustic panel. In various embodiments, the cell defines a cell cross-sectional shape in a form of one of a triangle, a square and a hexagon. 
     A method of fabricating an acoustic panel is disclosed. In various embodiments, the method includes the steps of providing a core structure having a cell, the cell having a first cell end and a second cell end spaced from the first cell end; inserting a septum into the cell, the septum having a central portion configured for positioning within the cell, a first tab extending from the central portion, and a second tab extending from the central portion; positioning the first tab against a first wall of the cell and a first distal end of the first tab adjacent the first cell end of the cell; positioning the second tab against a second wall of the cell and a second distal end of the second tab adjacent the first cell end of the cell; and adhering one of a back-skin and a perforated layer to the first distal end of the first tab, the second distal end of the second tab, the first wall proximate the first cell end of the cell and the second wall proximate the first cell end of the cell. In various embodiments, the method further includes the step of welding the first tab to the first wall and the second tab to the second wall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the following detailed description and claims in connection with the following drawings. While the drawings illustrate various embodiments employing the principles described herein, the drawings do not limit the scope of the claims. 
         FIG. 1  is a partial sectional view of an acoustic structure located near a noise source, in accordance with various embodiments; 
         FIG. 2  is a perspective view, partially cutaway, of a dual degree of freedom (DDOF) acoustic structure, in accordance with various embodiments; 
         FIG. 3  is a perspective view, partially cutaway, of a single degree of freedom (SDOF) acoustic structure, in accordance with various embodiments; 
         FIGS. 4A, 4B, 4C and 4D  illustrate an acoustic panel and details of a septum configured for mounting within a cell of the acoustic panel, in accordance with various embodiments; 
         FIGS. 5A, 5B, 5C and 5D  illustrate various processes for fabricating an acoustic panel, in accordance with various embodiments; and 
         FIG. 6  illustrates method of fabricating an acoustic panel, in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of various embodiments herein makes reference to the accompanying drawings, which show various embodiments by way of illustration. While these various embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it should be understood that other embodiments may be realized and that changes may be made without departing from the scope of the disclosure. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected, or the like may include permanent, removable, temporary, partial, full or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. It should also be understood that unless specifically stated otherwise, references to “a,” “an” or “the” may include one or more than one and that reference to an item in the singular may also include the item in the plural. Further, all ranges may include upper and lower values and all ranges and ratio limits disclosed herein may be combined. 
     Referring to  FIG. 1 , a partial sectional view of a noise suppression system  100  is illustrated. The noise suppression system  100  includes an acoustic panel  102  configured for positioning proximate a noise source  104 . The acoustic panel  102  includes an outer layer  106 , an inner layer  108  and a core structure  110  sandwiched therebetween. In various embodiments, the outer layer  106  is a solid layer and the inner layer  108  is a perforated layer. The core structure  110  typically includes a plurality of cells  112  extending between the outer layer  106  and the inner layer  108 . Each of the plurality of cells  112  of the core structure  110  forms a hollow cavity that acts as a Helmholtz resonator to attenuate noise. Accordingly, noise generated by the noise source  104  enters the core structure  110  through the inner layer  108  and is attenuated. The noise source  104  may be, for example, a gas turbine engine for an aircraft and the acoustic panel  102  may be a portion of a nacelle that surrounds the engine or an inlet to the engine. Although the acoustic panel  102 , as illustrated, is positioned radially outward of the noise source  104  and extends a circumferential arc length from one end to the other, the acoustic panel  102  is not limited to the arc length shown. For example, the acoustic panel  102  may form a cylindrical shape that surrounds the noise source  104 . The acoustic panel  102  illustrated in  FIG. 1  shares certain characteristics of a single degree of freedom (SDOF) structure. The basic configuration of a SDOF structure comprises the inner layer  108 , also referred to as a perforated layer  114 , the outer layer  106 , also referred to as a back-skin  116 , and the core structure  110  sandwiched therebetween, where the core structure  110  comprises the plurality of cells  112  extending between the inner layer  108  and the outer layer  106 . However, as described more fully below, in various embodiments, the acoustic panel  102  may include a septum  120  disposed within each of the plurality of cells  112 , which provides the acoustic panel  102  with certain characteristics of a dual (or double) degree of freedom (DDOF) structure. 
     Referring now to  FIG. 2 , a partially cutaway perspective view of a noise suppression system  200  is illustrated. In contrast to the noise suppression system  100  described above with reference to  FIG. 1 , exhibiting a SDOF-like structure, the noise suppression system  200  exhibits a dual (or double) degree of freedom (DDOF) structure. The noise suppression system  200  includes an acoustic panel  202  having an outer layer  206  (also referred to as a back-skin  216 ) and an inner layer  208  (also referred to as a perforated layer  214 ). In various embodiments, the inner layer  208  is perforated and the outer layer  206  is solid. Between the inner layer  208  and the outer layer  206  is a middle layer  218  (also referred to as a septum  220 ) In various embodiments, the middle layer  218  is solid, while in other embodiments, the middle layer  218  is porous or perforated. Disposed between the inner layer  208  and the middle layer  218  is a first core structure  222 . Disposed between the middle layer  218  and the outer layer  206  is a second core structure  224 . Similar to the core structure  110  described above, cross-sections of the first core structure  222  and the second core structure  224  may exhibit various structural shapes, such as, for example, square or hexagonal or, in general, n-polygonal (where n is the number of sides of the polygon). In various embodiments, the first core structure  222  and the second core structure  224  both have a honeycomb structure. In various embodiments, the cross-sections of the first core structure  222  and the second core structure  224  comprise tessellated hexagons, as illustrated in  FIG. 2 . In various embodiments, the cross-sections of the first core structure  222  and the second core structure  224  comprise quadrilateral or square tessellations or combinations thereof, including other polygonal or circular shapes. 
     Referring now to  FIG. 3 , a partially cutaway perspective view of a noise suppression system  300  is illustrated. The noise suppression system  300  is a DDOF system, exhibiting features from both a SDOF system (e.g., a noise suppression system similar to the noise suppression system  100  described above, but without the septum  120  disposed within each of the plurality of cells  112 ) and a DDOF system (e.g., the noise suppression system  200  described above). Whereas the noise suppression system  200  described above with reference to  FIG. 2  includes the first core structure  222  and the second core structure  224  separated by the middle layer  218 , the noise suppression system  300  illustrated in  FIG. 3  includes a core structure  310  similar to the core structure  110  described above with reference to  FIG. 1  (e.g., the noise suppression system  100 , including the septum  120  disposed within each of the plurality of cells  112 ). The core structure  310  includes a plurality of cells  312 . Each of the plurality of cells  312  is separated into two cells by a septum  320  disposed between the ends of each cell (e.g., the septum  320  may be disposed midway between the axial ends defining the cell, between an outer layer  306  and an inner layer  308 ). Accordingly, in various embodiments, the noise suppression system  300  may exhibit the noise suppression characteristics of a DDOF system, but with the smaller size and simpler construction of a SDOF system. 
     Referring still to  FIG. 3 , the noise suppression system  300  includes an acoustic panel  302  having the outer layer  306  (also referred to as a back-skin  316 ), the inner layer  308  (also referred to as a perforated layer  314 ) and the core structure  310 . The septum  320  disposed within each of the plurality of cells  312  may exhibit the same cross sectional shape as does the corresponding cell and serves to divide each cell into an inner cell  322  proximate the inner layer  308  and an outer cell  324  proximate the outer layer  306 . In various embodiments, each septum  320  may be held in place by an adhesive, a weld or by friction. The adhesive, for example, adheres one or more portions of the septum to one or more walls of each cell, while the weld may be a spot weld or tack weld between one or more of the surfaces of the septum and the one or more walls of each cell. When secured in place, the septum  320  substantially seals the inner cell  322  apart from the outer cell  324  around a periphery of the septum  320 . 
     In various embodiments, the outer layer  306  may be formed from any suitable material, including, for example, metals, such as titanium or aluminum, plastics, such as phenolics, and composites, such as fiber reinforced composites. The inner layer  308  may be formed of similar materials. In various embodiments, the inner layer  308  and the outer layer  306  are formed of the same material, while in other embodiments, the inner layer  308  and the outer layer  306  are formed of different materials. In various embodiments, the outer layer  306  is impervious to airflow and the inner layer  308  is perforated. The size, number and spacing of perforations may depend on the acoustic requirements. For example, in various embodiments, the perforations are between about 0.030 inches (≈0.76 mm) and about 0.100 inches (≈2.54 mm) in diameter. In various embodiments, the perforations provide about 15% to about 35% open area and may be arranged in a uniform pattern across the inner layer  308 . 
     The core structure  310  may be formed of any suitable material including, for example, metals, such as titanium, aluminum and alloys thereof, or ceramics and composite materials. In various embodiments, the core structure  310  is a honeycomb structure comprising tessellated polygons, such as, for example, squares or hexagons. In various embodiments, for example, including the embodiment illustrated in  FIG. 3 , the core structure  310  may exhibit hexagons spaced in a regular pattern. In other embodiments, the hexagons are irregular. The cross sectional shape of the core structure  310  may also exhibit other shapes, including, for example, parallelograms, rectangles, squares or general n-polygons. Further, in various embodiments, the cross-sectional shape of the core structure  310  may include more than one different shape, such as, for example, a combination of triangles and squares. 
     Each septum  320  may be formed of any suitable material. Such materials are typically provided as relatively thin sheets that are perforated, porous or an open mesh fabric designed to provide noise attenuation. Each septum  320 , for example, may be formed of a perforated or porous sheet of metal, ceramic or thermoplastic. In various embodiments, each septum  320  is formed of an open mesh fabric woven from monofilament fibers. The fibers may comprise glass, carbon, ceramic or polymers. By way of example, the fibers comprise monofilament polymer fibers made from one or more of polyamide, polyester, polyethylene chlorotrifluoroethylene (ECTFE), ethylene tetrafluoroethylene (ETFE), polytetrafluoroethyloene (PTFE), polyphenylene sulfide (PPS), polyfluoroethylene propylene (FEP), polyether ether ketone (PEEK), polyamide 9 (Nylon, 9 PA6) and polyamide 12 (Nylon 12, PA12). 
     As mentioned above, the septum  320  may be formed from a woven cloth or mesh. Suitable materials for the woven cloth or mesh include stainless steel, aluminum and titanium or mixtures thereof. The woven cloth or mesh may also be made of non-metallic materials, such as those described above. A stainless steel woven material is strong, light weight and has desirable sound attenuation characteristics. As also mentioned above, the septum  320  may be bonded to the core structure  310  using an adhesive. Exemplary adhesives include low solvent solution sprayable adhesives, adhesive films, epoxies, acrylics, phenolics, cyanoacrylates, bismaleimides, polyamine-imides and polyimides. 
     Referring now to  FIGS. 4A-4D , a noise suppression system  400  and various of its component parts are illustrated. Similar to the noise suppression system  300  described above with reference to  FIG. 3 , the noise suppression system  400  includes an acoustic panel  402  having an outer layer  406  (also referred to as a back-skin  416 ), an inner layer  408  (also referred to as a perforated layer  414 ) and a core structure  410 , comprising a plurality of cells  412  illustrated having square cross-sectional shapes. A septum  420  is disposed within each of the plurality of cells  412  and may exhibit the same cross sectional shape as does the corresponding cell. Referring briefly to  FIG. 4D , the septum  420  divides each of the plurality of cells  412  into an inner cell  422  proximate the inner layer  408  and an outer cell  424  proximate the outer layer  406 . In various embodiments, each septum  420  may be held in place by an adhesive, a weld or by friction. An adhesive  430 , for example, adheres one or more tabs  432  of the septum  420  to one or more walls  434  of each cell, while a weld  436 , which may, for example, be a spot weld or a tack weld, secures the one or more tabs  432  of the septum  420  to the one or more walls  434  of each cell. The adhesive  430  may also act to adhere each of the one or more tabs  432 , the one or more walls  434  and the inner layer  408  together. 
     In various embodiments, each cell of the plurality of cells  412  defines a first cell end  440  configured for connection to a first layer  442  (e.g., to the inner layer  408 ) and a second cell end  444  configured for connection to a second layer  446  (e.g., to the outer layer  406 ). The first cell end  440  and the second cell end  444  define a cell length  448 . The septum  420  includes a central portion  450  that is positioned within the cell at a location along the cell length  448 , the location generally falling within a range of from about twenty-five percent (25%) to about seventy-five percent (75%) of the cell length  448  from the first cell end  440 . In various embodiments, the septum  420  includes a first tab  452  extending from the central portion  450 , the first tab  452  defining a first surface  454  configured for positioning against a first wall  456  of the cell and a first distal end  458  configured for positioning adjacent the first layer  442 . 
     In various embodiments, each cell of the plurality of cells  412  includes a second wall  460  extending along the cell length  448  between the first cell end  440  and the second cell end  444  and the septum  420  includes a second tab  462  extending from the central portion  450 . The second tab  462  includes a second surface  464  configured for positioning against the second wall  460  and a second distal end  466  configured for positioning adjacent the first layer  442 . In various embodiments, the first tab  452  is secured to the first wall  456  by a first weld  468  and the second tab  462  is secured to the second wall  460  by a second weld  470 . In various embodiments, the first distal end  458  of the first tab  452  and the second distal end  466  of the second tab  462  are secured to the first wall  456  and to the second wall  460 , respectively, by the adhesive  430 . In various embodiments, the first distal end  458  of the first tab  452  and the second distal end  466  of the second tab  462  are secured to the first wall  456  and to the second wall  460 , respectively, and to the first layer  442 , by the adhesive  430 . In various embodiments, the first wall  456  and the second wall  460  are secured to the second layer  446  proximate the second cell end  444  by the adhesive  430 . 
     Referring more specifically, the  FIGS. 4B, 4C and 4D , in various embodiments, the first tab  452  defines a first proximal end  472  connected to the central portion  450  and a first tab length  474  extending from the first proximal end  472  to the first distal end  458 . Similarly, in various embodiments, the second tab  462  defines a second proximal end  476  connected to the central portion  450  and a second tab length  478  extending from the second proximal end  476  to the second distal end  466 . In various embodiments, the first tab length  474  is between about twenty-five percent (25%) and about seventy-five percent (75%) of the cell length  448 , leading to the first proximal end  472  being positioned between about twenty-five percent (25%) and about seventy-five percent (75%) of the cell length  448 . In various embodiments, the second tab length  478  is between about twenty-five percent (25%) and about seventy-five percent (75%) of the cell length  448 , leading to the second proximal end  476  being positioned between about twenty-five percent (25%) and about seventy-five percent (75%) of the cell length  448 . 
     In various embodiments, the first tab length  474  is equal to the second tab length  478 , leading to the central portion  450  of the septum  420  being substantially perpendicular to the first wall  456  and to the second wall  460 . In various embodiments, the first tab length  474  is not equal to the second tab length  478 , leading to the central portion  450  of the septum  420  being substantially non-perpendicular to the first wall  456  and to the second wall  460 . By selecting the tab lengths of the various tabs and positioning the respective distal ends of the tabs proximate the first end of the corresponding cell, the central portion of the septum may be accurately positioned within the cell at a desired location. Positioning the central portion  450  of the septum  420  at different depths along the cell length  448  facilitates acoustic tuning of the noise suppression system  400 . In various embodiments, for example, positioning the central portion  450  proximate the inner layer  408  (e.g., the perforated layer  414 ) provides for linear acoustic noise suppression while positioning the central portion  450  farther away from the inner layer  408  tends to provide for more DDOF performance. Further, selecting identical geometries for all septa enables the central portions of all septa to be positioned at the same axial location within each cell among a plurality of cells throughout a core structure, facilitating uniformity throughout the resulting acoustic panel. 
     As described further below, in various embodiments, the first tab  452  may be deformed or bent from a sheet of material forming the septum  420  at the first proximal end  472 , such that a substantially right angle is formed between the first tab  452  and the central portion  450 . Similarly, the second tab  462  may be deformed or bent from the sheet of material forming the septum  420  at the second proximal end  476 , such that a substantially right angle is formed between the second tab  462  and the central portion  450 . The deformed septum may then be inserted into the cell and welded or adhered as described above. Note that while the foregoing describes formation of the septum  420  having the first tab  452  and the second tab  462 , the disclosure contemplates any number of tabs being constructed, formed and attached to cell walls in the same manner to provide for septa having various cross sectional shapes, such as, for example, square (e.g., as illustrated in  FIGS. 4B and 4C ), triangular or n-pentagonal. 
     Referring now to  FIGS. 5A, 5B, 5C and 5D , various processes for fabricating an acoustic panel  502  are described. In various embodiments, a septum  520  may be pre-cut (e.g., die cut) from a roll of material  580 . The septum  520  may include a plurality of tabs  582  extending from a central portion  550 . For example, as illustrated in  FIGS. 5A and 5B , the septum  520  may include four tabs, although any number of tabs greater than or equal to one is contemplated. The septum  520 , in pre-cut form, may then be urged through a die  584  having an n-sided aperture  586 , substantially in the shape of the central portion  550  of the septum  520 . Urging the septum  520  in pre-cut form through the n-sided aperture  586  deforms or bends the plurality of tabs  582 , such that the tabs are oriented at approximately right angles with respect to the central portion  550 , although spring-back due to material elasticity may render the angles somewhat greater than right angles upon the septum exiting the die  584 . In various embodiments, a punch  588  may be used to urge the septum  520  in pre-cut form through the die  584 , resulting in the septum  520  taking on a deformed shape structure  590 . The septum  520  having the deformed shape structure may then be inserted into a cell of a core structure  510  to form the acoustic panel  502 . Once the septum  520  is inserted into the core structure  510  (or once a plurality of septa are inserted into the core structure  510 ), one or more of the tabs of the septum  520  may be welded to corresponding cell walls of the core structure. 
     Referring to  FIG. 5B , following welding of the septum  520  (or septa) to the core structure  510 , the assembly may be exposed to an adhesive. For example, in various embodiments, an adhesive  530  may be introduced into to a container  592 . The assembly of septa positioned within the core structure  510  may then be dipped into the adhesive  530  to secure the distal ends of each septum to the walls of the core structure  510  proximate the first cell ends of each of the cells, as described above with reference to  FIGS. 4B-4D . In various embodiments, the core structure  510  and septa having adhesive placed on the distal ends of the septa and the first cell ends or each of the cells may then be removed from the container  592  and placed against a first (or second) layer to form an adhered structure similar to that illustrated in  FIG. 4D . 
     Referring now to  FIG. 5C , in various embodiments, following welding of the septum  520  (or septa) to the core structure  510 , the assembly may be overlaid with a layer or film of adhesive. The overlaid layer or film of adhesive is then air-blown, forcing the portions of the overlaid layer or film of adhesive in the center of each cell to be forced onto the sides of each of the septa, thereby forming a hat-like adhesive structure  533  that secures the distal ends of each of the septa to the walls of the core structure proximate the first ends of each of the cells. In various embodiments, the core structure  510  and septa having adhesive placed on the distal ends of the septa and the first cell ends or each of the cells may then be placed against a first (or second) layer to form an adhered structure similar to that illustrated in  FIG. 4D . Referring now to  FIG. 5D , in various embodiments, following welding of the septum  520  (or septa) to the core structure  510 , the assembly may then be positioned on a first (or second) layer  508  (e.g., a perforated layer  514 ), which layer comprises an adhesive layer  531  disposed thereon. The adhesive layer  531  secures the distal ends of each of the septa to the walls of the core structure proximate the first ends of each of the cells, together with the first (or second) layer  508 , to form an adhered structure similar to that illustrated in  FIG. 4D . 
     Referring now to  FIG. 6 , a method  600  of fabricating an acoustic panel may be summarized as follows, consistent with the foregoing description. In a first step  602 , a core structure having a cell (or a plurality of cells) is provided, the cell having a first cell end and a second cell end spaced from the first cell end. In a second step  604 , a septum is inserted into the cell, the septum having a central portion configured for positioning within the cell, a first tab extending from the central portion, and a second tab extending from the central portion. In a third step  606 , the first tab is positioned against a first wall of the cell and a first distal end of the first tab is positioned adjacent the first cell end of the cell. Similarly, in a fourth step  608 , the second tab is positioned against a second wall of the cell and a second distal end of the second tab is positioned adjacent the first cell end of the cell. In various embodiments, the third step  606  and the fourth step  608  are combined into a single step, which may include the positioning of any number of tabs against corresponding walls of the cell. In a fifth step  610 , one of a back-skin and a perforated layer is adhered to the first distal end of the first tab, the second distal end of the second tab, the first wall proximate the first cell end of the cell and the second wall proximate the first cell end of the cell. In various embodiments, an additional step, which may occur prior to the adhering step, includes welding the first tab to the first wall and the second tab to the second wall. The various steps may be repeated for each cell within a composite core to fabricate the acoustic core having the structural and positional characteristics described above. 
     Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosure. The scope of the disclosure is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. Different cross-hatching is used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
     Systems, methods and apparatus are provided herein. In the detailed description herein, references to “one embodiment,” “an embodiment,” “various embodiments,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments. 
     Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112(f) unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. 
     Finally, it should be understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although various embodiments have been disclosed and described, one of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. Accordingly, the description is not intended to be exhaustive or to limit the principles described or illustrated herein to any precise form. Many modifications and variations are possible in light of the above teaching.