Patent Publication Number: US-11024278-B1

Title: Acoustic absorber

Description:
FIELD 
     The present invention relates to an absorber. More particularly, the present invention relates to an acoustic absorber. 
     BACKGROUND 
     As known in the art, porous sound absorber materials are commonly placed inside walls to reduce sound transmission or they are placed against solid walls to reduce in-room reflections. They are lightweight, inexpensive, flexible, wide-band, and they dissipate sound as opposed to absorbing it, which reduces the likelihood of exciting various sound radiating vibration modes of host structures. However, they have to cover a significant enough fraction of a wavelength to be effective. While this is not an issue with higher frequencies that have short wavelengths, significant thickness is required for lower frequencies, making them impractical and ineffective as described below with reference to  FIG. 1 . 
     As known in the art, acoustic waves are typically described by a combination of pressure and fluid particle velocity fields. Porous type absorbers known in the art act on fluid velocity by converting kinetic energy into heat through viscous dissipation. Referring to  FIG. 1 , fluid particle velocity represented by dotted line  20  of an acoustic wave is relatively zero adjacent to rigid boundaries like a wall  5  and it increases as the distance from the wall  5  increases until it reaches peak amplitude at a distance of about one quarter wavelength (λ/4). Thus, a thin porous sound absorber  10 , confined to the near-zero velocity region adjacent to the wall  5 , is very ineffective because of low fluid velocity in the absorber material. If the thickness of the absorber  10  is increased to extend towards the quarter wavelength peak, where fluid velocities are higher, the sound absorption would increase accordingly. A practical consequence of this phenomenon is that sound dissipation at lower frequencies requires substantial thickness of absorber material, which takes up space and adds weight and cost. For example, at 40 Hz, the wavelength of sound is about 28 feet, so that would require a porous absorber layer to be about 3-4 feet thick to be somewhat effective. 
     Embodiments presently disclosed address the deficiencies in the known art. 
     SUMMARY OF THE INVENTION 
     According to some embodiments, an acoustic absorber is presently disclosed. The acoustic absorber comprising a plurality of adjacent passages defined by walls configured to generate alternating high and low pressure zones as an acoustic energy travels though the acoustic absorber. 
     According to some embodiments, an acoustic absorber is presently disclosed. The acoustic absorber comprising a plurality of conically shaped through holes configured to generate alternating high and low pressure zones as an acoustic wave travels though the acoustic absorber. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  depicts fluid particle velocity away from a rigid wall as known in the art. 
         FIG. 2 a    depicts an embodiment according to the present disclosure. 
         FIG. 2 b    depicts perspective view of the embodiment shown in  FIG. 2   a.    
         FIG. 3 a    depicts an embodiment according to the present disclosure. 
         FIG. 3 b    depicts another embodiment according to the present disclosure. 
         FIG. 4 a    depicts high pressure at a narrow end of a converging nozzles according to the present disclosure. 
         FIG. 4 b    depicts high fluid particle velocity jets at the exit of converging nozzles according to the present disclosure. 
         FIG. 5  depicts simulation results for embodiments presently disclosed. 
         FIG. 6 a    depicts another embodiment according to the present disclosure. 
         FIG. 6 b    depicts another embodiment according to the present disclosure. 
         FIG. 7  depicts measurement results for one or more embodiments presently disclosed. 
         FIG. 8  depicts another embodiment according to the present disclosure. 
         FIG. 9  depicts dimensional parameters of an embodiment according to the present disclosure. 
         FIG. 10 a - c    depict simulation results for embodiments presently disclosed. 
         FIG. 11 a - b    depict simulation results for embodiments presently disclosed. 
         FIG. 12  depicts another embodiment according to the present disclosure. 
         FIG. 13  depicts another embodiment according to the present disclosure. 
         FIG. 14  depicts another embodiment according to the present disclosure. 
         FIG. 15 a - b    depict another embodiment according to the present disclosure. 
         FIG. 16 a    depicts another embodiment according to the present disclosure. 
         FIG. 16 b    depicts another embodiment according to the present disclosure. 
         FIG. 17  depicts another embodiment according to the present disclosure. 
         FIG. 18  depicts another embodiment according to the present disclosure. 
     
    
    
     In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of every implementation nor relative dimensions of the depicted elements, and are not drawn to scale. 
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth to clearly describe various specific embodiments disclosed herein. One skilled in the art, however, will understand that the presently claimed invention may be practiced without all of the specific details discussed below. In other instances, well known features have not been described so as not to obscure the invention. 
     According to some embodiments, structures presently disclosed are configured to be embedded inside traditional porous type sound absorbers—such as open pore foam, mineral wool, and/or glass fibers—in order to enhance their absorption performance, enabling thin acoustic absorption treatments particularly in the low frequency. In some embodiments, absorption enhancement is obtained by accelerating acoustic “fluid particles”, since porous absorbers damp acoustic waves by acting on their “fluid particle” velocity through viscous dissipation. According to some embodiments, structures presently disclosed induce fluid movement within a porous absorber, i.e. wave motion, both in the longitudinal and transverse directions, thereby enhancing absorption over a wide bandwidth of frequencies. In some embodiments, structures presently disclosed produce pressure gradients that induce fluid movement where normally fluid particle velocity is about zero or very low, such as near sound-reflecting rigid surfaces and during the low fluid velocity phase of acoustic waves. 
     According to some embodiments, structures presently disclosed comprise arrays of alternating converging and diverging nozzles arranged in a plane. In some embodiments, nozzle structures presently disclosed create acoustic pressure gradients, which in turn generate transverse (in-plane) and normal (out-of-plane) fluid particle motion upon which porous absorbers act to dissipate acoustic energy. According to some embodiments, structures presently disclosed create pressure oscillations to induce and enhance fluid particle oscillations. 
     According to some embodiments, presently disclosed structures improve the performance of porous acoustic absorbers by inducing and increasing fluid movement within them, especially when the noise frequency is very low or when presently disclosed structures are placed in regions where fluid velocity is normally very low or about zero without their presence, such as near reflecting walls and corners. 
     According to some embodiments, structures presently disclosed are embedded inside porous absorbers, allowing more sound to be dissipated with a given thickness of absorber, or conversely, the same level of dissipation can be achieved with a much thinner layer, thereby minimizing space wasted to sound insulation. 
     According to some embodiments, porous absorbers enhanced by structures presently disclosed remain effective when placed against sound-reflecting solid walls. According to some embodiments, structure presently disclosed create fluid particle motion near a solid wall where fluid velocity is about zero, permitting the use of thinner absorber layers, thereby minimizing wasted space in rooms and cabins. 
     According to some embodiments, structures presently disclosed provide sound dissipation enhancement that is effective over a wide spectrum of frequencies. According to some embodiments, structures presently disclosed are stacked inside a bare absorber for increased performance. According to some embodiments, structures presently disclosed are fabricated with flexible materials to preserve surface conforming ability of porous absorbers. 
     According to some embodiments, structures presently disclosed may be used on wheel wells, inside doors, dashboards, and floor pans, under hoods, between fuselage panels, etc. According to some embodiments, structures presently disclosed may be used to form and/or be part of containment encasements placed over noisy equipment such as compressors, pumps, and/or transformers. 
     According to some embodiments, structures presently disclosed accelerate the fluid particle of acoustic waves to enhance dissipation by porous absorber materials. 
     According to some embodiments, structures presently disclosed are configured to increase significantly local fluid velocity, and therefore they enhance dissipation accordingly. As a consequence, thinner absorber layers can be used, or a given thickness of absorber can provide more sound dissipation. 
       FIG. 2 a    depicts a front view and  FIG. 2 b    depicts a perspective view of an array  200  of structures  210  according to some embodiments presently disclosed. In some embodiments, the structures  210  comprise strips  220  arranged on a plane to form two-dimensional converging and diverging nozzles, with the strips  220  forming the nozzle walls secured to each other by thin rods or strips perpendicular to the plane (as shown in  FIGS. 6 a - b   ). According to some embodiments, the strips  220  are planar. According to some embodiments, two adjacent structure  210  share a common strip  220 . According to some embodiments, two adjacent nozzles share a common strip  220 . 
     According to some embodiments, the array  200  of the strips  220  is disposed on a surface of a porous absorber materials (not shown). According to some embodiments, the array  200  of the strips  220  is disposed within an absorber material  300  as shown in  FIG. 3 a   . According to some embodiments, the absorber material  300  is porous. According to some embodiments, the absorber material  300  absorbs acoustic energy. According to some embodiments, the absorber material  300  is an acoustic energy absorber material. According to some embodiment, the array  200  of the strips  220  are disposed adjacent to a wall  5  as shown in  FIG. 3 a   . According to some embodiments, the wall  5  comprises non-absorbent material. 
     Referring to  FIG. 3 a   , according to some embodiments, the array  200  presently disclosed increases fluid movement in the low velocity region. As an acoustic wave (represented by lines  230 ) propagates through the array  200 , pressure and velocity magnitude drop across diverging nozzles as shown by reference number  235  and they increase across converging nozzles as shown by reference number  240 . According to some embodiments, the majority of the incident energy is captured by the converging nozzle formed by strips  220  to produce a high velocity jet at the exit, creating a large amount of dissipation. The diverging nozzles formed by the strips  220  on the other hand, produce a low pressure zone at the exit, which results in alternating high and low pressure zones at the exits of the converging and diverging nozzles, respectively, resulting in transverse fluid particle flow from the high pressure zones to the low pressure ones (as shown by reference number  245 ), as predicted by the acoustics momentum equation ∇p=iωρ{right arrow over (ν)}. Thus, the jets at the exit of the converging nozzles include both forward and transverse components, leading to further dissipation efficiency. Furthermore, since fluid particles are rushing back and forth throughout each wave period, this fluid flow mechanism is duplicated on the other side of the array  200  during the second half of the wave cycle. 
     Webster&#39;s equation describes approximately an acoustic wave propagating through a variable cross-section duct: 
                     ∂   2     ⁢   p       ∂     x   2         +       [         A   ′     ⁡     (   x   )         A   ⁡     (   x   )         ]     ⁢       ∂   p       ∂   x           =       1     c   2       ⁢         ∂   2     ⁢   p       ∂     t   2                 
where A(x) is the cross section area as a function of axial distance x and c is the speed of sound. Webster&#39;s equation is discussed in more details by Allan D. Pierce in “Acoustics: An Introduction to its Physical Principles and Applications”, which is incorporated herein in its entirety.
 
     According to some embodiments, nozzles formed by strips  220  as presently disclosed comprise dimensions that are smaller than acoustic wavelengths therefore reflections at the ends of the nozzles can be neglected. 
     Referring to  FIG. 3 a   , according to some embodiments, the first strip  220  comprises a first end  250  and a second end  251 , the second strip  220  comprises a first end  260  and a second end  261 , the third strip  220  comprises a first end  270  and a second end  271 . According to some embodiments, a first distance between the first end  250  and the first end  260  is less than a second distance between the second end  251  and the second end  261 . According to some embodiments, a third distance between the first end  260  and the first end  270  is greater than a fourth distance between the second end  261  and the second end  271 . 
     Referring to  FIG. 3 a   , according to some embodiments, the strips  220  are disposed within the absorber material  300 . According to some embodiments, the absorber material  300  surrounds the strips  220 . 
     Referring to  FIG. 3 b   , a first absorber material  301  is disposed between the wall  5  and the strips  220 . According to some embodiments, the first absorber material  301  is porous. According to some embodiments, the first absorber material  301  is positioned to absorb at least a portion of the acoustic wave (represented by lines  230 ) that comes out of the strips  220 . According to some embodiments, the first absorber material  301  is positioned to absorb at least a portion of the energy that comes out of the strips  220 . According to some embodiments, the first absorber material  301  absorbs acoustic energy. According to some embodiments, the first absorber material  301  is a first acoustic energy absorber material. 
     Referring to  FIG. 3 b   , a second absorber material  302  is disposed between the strips  220 . According to some embodiments, the second absorber material  302  is porous. According to some embodiments, the second absorber material  302  is positioned to absorb at least a portion of the acoustic wave (represented by lines  230 ) that is between the strips  220 . According to some embodiments, the second absorber material  302  is positioned to absorb at least a portion of the energy that is between the strips  220 . According to some embodiments, the second absorber material  302  absorbs acoustic energy. According to some embodiments, the second absorber material  302  is a second acoustic energy absorber material. 
     Referring to  FIG. 3 b   , a third absorber material  303  is disposed between the incoming acoustic wave (represented by lines  230 ) and the strips  220 . According to some embodiments, the third absorber material  303  is porous. According to some embodiments, the third absorber material  303  is positioned to absorb at least a portion of the acoustic wave (represented by lines  230 ) before it enters the strips  220 . According to some embodiments, the third absorber material  303  is positioned to absorb at least a portion of the energy before it enters the strips  220 . According to some embodiments, the third absorber material  303  absorbs acoustic energy. According to some embodiments, the third absorber material  303  is a third acoustic energy absorber material. 
     Various software simulations, including simulation done of Finite Elements software by COMSOL™ Inc, have confirmed the physical mechanisms described in the previous paragraphs.  FIG. 4 a    depicts how pressure rises across converging nozzles formed by strips  220  and how pressure drops across diverging nozzles formed by the strips  220 , whereas  FIG. 4 b    depicts the resulting fluid particle jets. 
     Another set of simulation results depicted in  FIG. 5  show that adding the array  200  to a layer of foam increases its sound absorption. Adding two layers of the array  200  increases absorption even more. 
       FIG. 6 a    depicts a top view and  FIG. 6 b    depicts a perspective view of an array  600  of nozzle structures  610  according to some embodiments presently disclosed. According to some embodiments, the nozzle structures  610  comprise angled walls perpendicular to Y direction, which defines the nozzle structure  610  area change through the thickness. According to some embodiments, the nozzle structure  610  walls perpendicular to X direction are vertical and do not contribute the area change. In some embodiments, the area ratio between the inlets and exits of the nozzle structure  610  is about 9:1 and the thickness is 9 mm with 0.5 mm thick nozzle wall as shown in  FIGS. 6 a - b   . According to some embodiments, the thickness of the structure in the Z-direction is 1-10 of a wavelength. According to some embodiments, the thickness of the structure in the Z-direction is 1/20 to ⅛ of a wavelength. 
       FIG. 7  depicts sound absorption coefficient measurements made for a layer of foam alone; two foam layers with an air gap between them; and two foam layers with the nozzle structure as disclosed presently between them. As supported by result shown in  FIG. 7 , embedding a nozzle structure as disclosed presently improves sound absorption over a wide range of frequencies. 
     According to some embodiments, a unit cell of a nozzle structure  800  according to the present disclosure is shown in  FIG. 8 . According to some embodiments, the unit cell of the nozzle structure  800  comprises a converging nozzle  810  and a diverging nozzle  820 , as shown in  FIG. 8 . In some embodiments the converging nozzle  810  and the diverging nozzle  820  are sub-wavelength. In some embodiments the converging nozzle  810  and the diverging nozzle  820  are near-wavelength. According to some embodiments, the converging nozzle  810  and the diverging nozzle  820  are less than the conventional ¼ wavelength. 
     Referring to  FIG. 8 , the arrows above the structure  800  indicate the incident wave and the arrows below the structure  800  illustrate the fluid jets at the exits of the converging nozzles  810 . The +P symbol indicates pressure peaks at the exits of converging nozzle  810  and −P symbol indicate pressure valleys at the exits of diverging nozzle  820 , to induce lateral fluid particle flow. 
     As can be appreciated by one skilled in the art, the dimensions of the nozzles  810 ,  820  can be optimized for particular applications or to conform to various constraints. Inlet area, exit area, and length are parameters available for design fine-tuning, as shown in  FIG. 9 . 
       FIGS. 10 a - c    depict various simulation results for structures presently disclosed.  FIG. 10 a    depicts simulation results of a single layer structure embedded within a fixed thickness of foam of thickness of about 34 mm according to the present disclosure.  FIG. 10 b    depicts simulation results of a double layer structure embedded within a fixed thickness of foam of thickness of about 34 mm according to the present disclosure.  FIG. 10 c    depicts simulation results of a triple layer structure embedded within a fixed thickness of foam of thickness of about 34 mm according to the present disclosure. Referring to  FIGS. 10 a - c   , for a set of d_exit values, d inlet has been swept over a range of values generating a reflection coefficient curve for each d_exit value. Simulations results in  FIG. 10 a - c    show that the reflection coefficient can be reduced significantly. Simulations results in  FIG. 10 a - c    show that embedding more layer structures improves performance. A target frequency of 1 kHz was used to obtain results shown in  FIGS. 10 a - c   . According to some embodiments, d_exit ranges from 0.008 to 0.4. According to some embodiments, the ratio ranges from 5:1 to 90:1. 
       FIG. 11 a    depicts reflection coefficient computed as a function of frequency for structures simulated in  FIGS. 10 a - c   . The results depicted in  FIG. 11 a    demonstrate significant reduction in the reflection coefficient over a wide frequency range compared to using bare foam only without embedded nozzle structures according to the present disclosure. For the triple nozzle layer design, a peak reflection coefficient reduction factor of four was achieved, as shown in  FIG. 11   b.    
       FIG. 12  depicts an array  1200  of structures  1210  according to some embodiments presently disclosed. In some embodiments, the structures  1210  comprise walls  1220  arranged on a plane to form two-dimensional converging and diverging nozzles, with the walls  1220  forming the nozzle walls secured to each other by, for example, thin rods (not shown) or strips perpendicular to the plane (not shown). According to some embodiments, the walls  1220  may be formed as strips. In some embodiments, the walls  1220  comprise a geometrical shape. In some embodiments, the walls  1220  comprise semi-circular, oval, non-linear shape. According to some embodiments, the nozzles defined by the walls  1220  may have curved, round, or elliptical shapes. In some embodiments, the walls  1220  comprise semi-circular, oval, non-linear cross-shape. According to some embodiments, two adjacent structure  1210  share a common wall  1220 . According to some embodiments, two adjacent nozzles share a common wall  1220 . 
       FIG. 13  depicts an array  1300  of structures  1310  according to some embodiments presently disclosed. In some embodiments, the structures  1310  comprise walls  1320  arranged on a plane to form two-dimensional converging and diverging nozzles, with the walls  1320  forming the nozzle walls secured to each other by, for example, thin rods (not shown) or strips perpendicular to the plane (not shown). In some embodiments, the walls  1320  comprise a non-linear shape. In some embodiments, the cross-section of the walls  1320  comprise shape with one or more curves. In some embodiments, the walls  1320  comprise shapes with two or more curves. 
     As shown in  FIG. 13 , according to some embodiments, the walls  1330 ,  1331  for a first nozzle  1340  curve inward towards a center axis (represented by a dotted line  1350 ) at one end to define a wide opening and curve outward at the opposite end to define a narrow opening of the first nozzle  1340 . According to some embodiments, the walls  1331 ,  1332  for a second nozzle  1342  curve inward towards a center axis (represented by a dotted line  1350 ) at one end to define a wide opening and curve outward at the opposite end to define a narrow opening of the second nozzle  1342 . According to some embodiments, one or more adjacent nozzles are oriented in the opposite direction. According to some embodiments, the narrow opening of the second nozzle  1342  is disposed next to a wide opening of the first nozzle  1340 . According to some embodiments, two adjacent structure  1310  share a common wall  1320 . According to some embodiments, two adjacent nozzles  1340 ,  13425  share a common wall  1331 . 
       FIG. 14  depicts an array  1400  according to the present disclosure that is three-dimensional in nature. According to some embodiment, the array  1400  is configured by intersecting the array  200  shown in  FIGS. 2 a - b    with its 90-degree rotated version. According to some embodiments, a wider rectangular or square opening of a nozzle may be bordered on four sides by smaller rectangular openings of oppositely oriented nozzles. Other shaped openings and configurations may be achieved by intersecting the array  200  with one or more rotated versions that are rotated at different angles, such as 30, 45, or 75 degrees. 
       FIGS. 15 a - b    depict another array  1500  according to the present disclosure. According to some embodiments, the array  1500  comprises one or more passages  1510 ,  1515 . According to some embodiments, the passages  1510  are conical shape. According to some embodiments, openings at the ends of the conical passages  1510  are circular, triangular, square, hexagonal or a combination of these shapes. According to some embodiments, the passages  1510  vary in diameter between larger and smaller along the length of the passage  1510 . 
     As shown in  FIGS. 15 a - b   , according to some embodiments, one or more adjacent passages  1510 ,  1515  are oriented in the opposite direction. According to some embodiments, the narrow opening of the passage  1515  is disposed next to a wide opening of the passage  1510 . 
     According to some embodiments, structures  1610  and  1620  presently disclosed are stacked on top of each other within an absorbing material  1605  without an air gap as shown in  FIG. 16 a   . According to some embodiments, structures  1630  and  1640  presently disclosed are stacked on top of each other and separated by a layer of absorbing material  1635  with one or more air gaps  1650 ,  1660  as shown in  FIG. 16 b   . According to some embodiments, the air gaps are composed of air filled volumes within the nozzles of  FIG. 16 b   . According to some embodiments, structures  1630  are disposed between a layer of absorbing material  1634  and the layer of absorbing material  1635 . According to some embodiments, structures  1640  are disposed between a layer of absorbing material  1636  and the layer of absorbing material  1635 . 
       FIG. 17  depicts an array  1700  of structures  1710  according to some embodiments presently disclosed. In some embodiments, the structures  1710  comprise strips  1720  arranged on a plane to form two-dimensional converging and diverging nozzles, with the strips  1720  forming the nozzle walls secured to each other by, for example, thin rods (not shown) or strips perpendicular to the plane (not shown). In some embodiments, the structures  1710  are not symmetric about their axis as shown in  FIG. 17 . In some embodiments, the structures  1710  are not symmetric about an axis (represented by dashed lines  1750 ,  1760 ) that extends between center points of two ends of an opening as shown in  FIG. 17 . These embodiments may accommodate a design variation that might beneficial when sound impinges on the array  1700  at oblique angles. According to some embodiments, two adjacent structure  1710  share a common strip  1720 . According to some embodiments, two adjacent nozzles share a common strip  1720 . 
       FIG. 18  depicts an array  1800  of structures  1810  according to some embodiments presently disclosed. In some embodiments, the structures  1810  comprise strips  1820  arranged to form converging and diverging nozzles, with the strips  1820  forming the nozzle walls secured to each other by, for example, thin rods (not shown) or strips perpendicular to the plane (not shown). According to some embodiments, the array  1800  is partially or completely formed out of flexible material to be embedded inside conformal blankets  1830  designed for applications on curved surfaces, as shown in  FIG. 18 . According to some embodiments, the array  1800  is formed from rigid materials on a curved surface. 
     It should be clear to one skilled in the art that all design variations of nozzle structure described above can be exploited/mixed together to optimize and fine-tune absorption performance. It is also to be understood that the converging and diverging nozzles presently disclosed need not be in the same plane or of the same size. 
     While several illustrative embodiments of the invention have been shown and described, numerous variations and alternative embodiments will occur to those skilled in the art. Such variations and alternative embodiments are contemplated, and can be made without departing from the scope of the invention as defined in the appended claims. 
     As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. The term “plurality” includes two or more referents unless the content clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains. 
     The foregoing detailed description of exemplary and preferred embodiments is presented for purposes of illustration and disclosure in accordance with the requirements of the law. It is not intended to be exhaustive nor to limit the invention to the precise form(s) described, but only to enable others skilled in the art to understand how the invention may be suited for a particular use or implementation. The possibility of modifications and variations will be apparent to practitioners skilled in the art. No limitation is intended by the description of exemplary embodiments which may have included tolerances, feature dimensions, specific operating conditions, engineering specifications, or the like, and which may vary between implementations or with changes to the state of the art, and no limitation should be implied therefrom. Applicant has made this disclosure with respect to the current state of the art, but also contemplates advancements and that adaptations in the future may take into consideration of those advancements, namely in accordance with the then current state of the art. It is intended that the scope of the invention be defined by the Claims as written and equivalents as applicable. Reference to a claim element in the singular is not intended to mean “one and only one” unless explicitly so stated. Moreover, no element, component, nor method or process step in this disclosure is intended to be dedicated to the public regardless of whether the element, component, or step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. Sec. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for . . . ” and no method or process step herein is to be construed under those provisions unless the step, or steps, are expressly recited using the phrase “step(s) for . . . .”