Patent Publication Number: US-11021870-B1

Title: Sound blocking enclosures with antiresonant membranes

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/785,909, filed on Mar. 14, 2013, which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present invention relates to sound blocking enclosures and more particularly to sound blocking enclosures with antiresonant membranes. 
     BACKGROUND 
     Noise has long been regarded as a harmful form of environmental pollution mainly due to its high penetrating power. Typically the performance of a noise shielding enclosure to control noise is governed by the sound transmission loss of the barriers along with level of acoustic energy dissipation (absorption) incorporated into the enclosure. For the enclosure walls, the current noise shielding solutions are directly tied to the mass of the barrier. In general, noise transmission for walls is governed by the mass density law, which states that the acoustic transmission T through a wall is inversely proportional to the product of wall thickness l, the mass density ρ, and the sound frequency f. Hence doubling the wall thickness will only add (20 log 2=) 6 dB of additional sound transmission loss (STL), and increasing STL from 20 to 40 dB at 100 Hz would require a wall that is eight times the normal thickness. IKn enclosure design the efficacy is determined by the insertion loss which is the amount of acoustic attenuation with the enclosure in place as compared to without the enclosure. In general the maximum insertion loss is limited to the STL of the enclosure walls. 
     Referring to  FIG. 1 , an enclosure  100  is shown around a pump and/or motor  110 . The enclosure  100  comprises walls to contain acoustic energy along with foam or fibrous material  120  to provide acoustic absorption for trapped acoustic energy from the motor  110 . The foam material  120  is positioned to cover the internal walls of the enclosure  100  and provides an absorption coefficient of between 0.1 and 10. The performance of this enclosure limited by the sound transmission loss of the enclosure walls which is tied to the mass per unit area of the panels for conventional treatments. 
     The prior art discloses different approaches to achieving at least partial sound transmission losses. For example, U.S. Pat. No. 7,510,052 discloses a sound absorption honeycomb based on modified Helmholtz resonance effect. This type of solution can provide effect absorption but does not increase the sound transmission as required in enclosure application. U.S. Application 20080099609 discloses a tunable acoustic absorption system for an aircraft cabin that is tuned by selecting different materials. The invention specifically calls out a barium titanate loaded membrane that provides mass law sound transmission behavior. Therefore, the structures disclosed in U.S. Application 20080099609 are heavy and bulky. U.S. Pat. No. 7,263,028 discloses embedding a plurality of particles with various characteristic acoustic impedances in a sandwich with other light weight panels to enhance the sound isolation. Although it could be lighter or thinner than traditional solid soundproofing panels, it operates over a relatively narrow frequency range and doesn not provide a significant improvement over the mass law due to the influence of the matrix vibrations. U.S. Pat. No. 7,249,653 discloses acoustic attenuation materials that comprise an outer layer of a stiff material which sandwiches other elastic soft panels with an integrated mass located on the soft panels. By using the mechanical resonance, the panel passively absorbs the incident sound wave to attenuate noise. This invention has a wire mesh barrier that does not effective decouple adjacent cells leading to poor performance in the case of a close fitting enclosure. U.S. Pat. Nos. 4,149,612 and 4,325,461 disclose silators. A silator is an evacuated lentiform (double convex lens shape) with a convex cap of sheet metal. These silators comprise a compliant plate with an enclosed volume wherein the pressure is lower than atmospheric pressure to constitute a vibrating system for reducing noise. To control the operating frequency, the pressure enclosed in the volume coupled with the structural configuration determines the blocking noise frequency. The operating frequency dependence on the pressure in the enclosed volume makes the operating frequency dependent on environment changes such as temperature. U.S. Pat. No. 5,851,626 discloses a vehicle acoustic damping and decoupling system. This invention includes a bubble pack which may be filled with various damping liquids and air to enable the acoustic damping. It is a passive damping system dependent on the environment. Finally, U.S. Pat. No. 7,395,898 discloses an antiresonant cellular panel array based on flexible rubbery membranes stretched across a rigid frame. However, the materials disclosed in U.S. Pat. No. 7,395,898 limit the bandwidth to about 200 Hz and a single attenuation frequency and require completely rigid frames which are impractical to achieve for many applications. 
     Embodiments disclosed in the present disclosure overcome the limitations of the prior art and provide improved insertion loss. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  depicts an enclosure as known in the art. 
         FIG. 2  depicts an embodiment according to the present disclosure. 
         FIG. 3 a    depicts another embodiment according to the present disclosure. 
         FIG. 3 b    depicts an embodiment of a membrane as known in the art. 
         FIG. 4 a    depicts an embodiment of a wall according to the present disclosure. 
         FIG. 4 b    depicts another embodiment of a wall according to the present disclosure. 
         FIG. 4 c    depicts another embodiment of a wall according to the present disclosure. 
         FIG. 4 d    depicts another embodiment according to the present disclosure. 
         FIG. 5  depicts another embodiment of a wall according to the present disclosure. 
         FIG. 6  depicts another embodiment of a wall according to the present disclosure. 
         FIG. 7  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. 
     The prior art in architected barriers discussed above does not consider the use of these barriers in enclosures. For enclosures there are different concerns including the proximity of the noise component, the thermal and moisture conditions, the integration of damping, and the multifunction of the enclosure stiffness and other functions with its acoustic performance. As discussed above, the prior art is limited to rubber materials which have potential issues with fluid exposure degradation, sensitivity to thermal fluctuations and flammability and toxicity concerns. Further to reach higher frequency with soft rubber materials, one must use very small cell sizes which leads to large system weight. 
     Contrary to the prior art, in some embodiments, the presently disclosed enclosures may use rigid or semi-rigid polymers as well as metal foils to reach higher frequencies common to small and mid-size components. In some embodiments, the presently disclosed enclosures comprise antiresonant membranes which provide improved bandwidth over previously disclosed concepts and also have the ability to target a primary tone and its multiple harmonic tones that is common in components that emit tonal acoustic emission. 
     Antiresonant membranes are disclosed in more detail in U.S. application Ser. No. 13/645,250, filed on Oct. 4, 2012, which is incorporated herein by reference in its entirety. Antiresonant membranes are disclosed in more detail in U.S. Pat. No. 7,249,653, granted on Jul. 31, 2007, which is incorporated herein by reference in its entirety. 
     Referring to  FIG. 2 , in some embodiments, a component  210  is encased in an enclosure  215  according to the present disclosure. The component  210  is any device that emits noise. For example, the component  210  is a pump or a motor. The enclosure  215  comprises side walls  220  and  230 , top and bottom walls  225  and  235  and a rear wall  240 . Front wall (the wall that is opposite the rear wall  240 ) of the enclosure  215  is not shown for ease of reference. 
     In some embodiments, the enclosure  215  may be configured to perform one or more of the following functions: mounting of the component  210 , thermal mitigation, physical protection of the component  210 , and acoustic performance. The design of the acoustic function may be dependent on other system constraints for example sufficient cooling or packaging size. 
     In some embodiments, at least one the walls  220 ,  225 ,  230 ,  235 ,  240  comprises an array of antiresonant membranes with acoustic reflection properties (or purely of antiresonant array materials). In some embodiments, at least one of the walls  220 ,  225 ,  230 ,  235 ,  240  comprises traditional enclosure materials (such as, for example, sheet metal). 
     Referring to  FIG. 3 a   , in some embodiments, the wall  230  comprises an outer panel  310  and an inner barrier layer  315 . The outer panel  310  forms the outer surface of the wall  230  and the inner barrier layer  315  forms the inner surface of the wall  230 . In some embodiment, the outer panel  310  is made out of, for example, sheet metal. 
     In some embodiments, the barrier layer  315  is an array of resonators  320  (shown in  FIGS. 3 a  and 3 b   ) in the form of membranes  325 . In some embodiments, the membranes  325  are defined by a grid structure  330  that specifies the length and width of the resonators  320  and provides a backing which counters any tension within the membranes  325 . 
     In some embodiments, the membranes  325  comprise a ring  335  and a mass  340  (as shown in  FIGS. 3 a - b   ) which can be used to create two separate reflection frequency bands (i.e. antiresonances). In some embodiments, the membranes  325  comprise the mass  340  without the ring  335 . It is to be understood that the membranes  325  may comprise other central mass configurations. In one embodiment, the ring  335  and/or the mass  340  are disposed between the membrane  325  and the outer panel  310  (as shown in  FIG. 4 a   ). In another embodiment, the ring  335  and/or the mass  340  are disposed on the surface of the membrane  325  facing away from the outer panel  310  (as shown in  FIG. 5 ). In some embodiments, the membrane  325  comprises a hinge structure  345  as shown in  FIG. 3 b   . Different membrane structures are disclosed in more detail in U.S. application Ser. No. 13/645,250, filed on Oct. 4, 2012, which is incorporated herein by reference in its entirety. 
     Different embodiments of the wall  230  are disclosed below with reference to  FIGS. 4 a - c    and  5 - 6 . Referring to  FIG. 4 a   , in some embodiments, the wall  230  of the enclosure  215  (marked by dotted line) defines a cavity  410  formed by of the barrier layer  315  and the panel  310 . The cavity  410  is configured to allow the resonators  320  to function by allowing the membranes  325  to deflect towards and away from the panel  310 . 
     In some embodiments, the wall  230  comprises an absorber material  420  disposed within the cavity  410  to at least partially dissipate trapped acoustic energy. In some embodiments, the barrier layer  315  does not absorb energy, but rather reflects energy. In this embodiment, the absorber material  420  may be used to absorb and/or reduce energy not reflected by the barrier layer  315 . The absorber material  420  is incorporated in a way which does not interfere with the operation of the resonators  320 . In some embodiments, standoffs (not shown) or other means may be used to control position of the absorber material  420 . In some embodiments, the absorber material  420  is foam, fiber mat, foam of fibrous blanket or a porous material. In some embodiment, a Helmholtz absorber (not shown) which is a tuned helmholtz cavity, combined with a porous absorber which creates a strong absorption effect over a relatively narrow band may be used together with the wall  230 . 
     In some embodiments, an absorber material  460  is disposed on the mass  340  (as shown in  FIG. 4 d   ) to at least partially dissipate trapped acoustic energy. 
     In some embodiments, the barrier layer  315  spans the entire wall distance by coupling to the panel  310  only at the edges as shown in  FIG. 4 a   . In some embodiments, one or more damping posts  440  (shown in  FIG. 4 b   ) are used to provide additional support for the barrier layer  315 . In some embodiments, the damping posts  440  are rigid mounts that are part of the barrier layer  315  and/or part of the panel  310 . In some embodiments, the damping posts  440  are used for walls  230  about 12 feet high or larger. In some embodiments, the damping posts  440  are soft supports such as rubber or viscoelastic materials for providing marginal coupling to the barrier layer  315  and/or the panel  310 . Using a viscoelastic material for the damping posts  440  may damp vibrations in the barrier layer  315 , yielding better acoustic performance since unwanted vibrations can degrade the effectiveness of the barrier layer  315 . 
     Referring to  FIG. 4 c   , in some embodiments, the wall  230  comprises one or more heat sync elements  450  to aid in heat transport through the wall  230 . In some embodiments, the damping posts  440  are configured to transport the heat from the heat sink elements  450  disposed in the inside of the enclosure  215  to the outside of the enclosure  215 . In some embodiments, fans (not shown) or other means (not shown) for introducing convective heat transfer to the outer surface of the enclosure  215  may be used to remove heat from the inside of the enclosure  215  while still maintaining an acoustically isolating solution. This solution can be used with all of the enclosure embodiments presently disclosed. 
     In some embodiments, heat from the inside of the enclosure  215  is removed by making the barrier layer  315  and/or the membranes  325  from good thermal conducting materials such as, for example, metals, aluminum, copper and/or their alloys. 
     Referring to  FIG. 5 , in some embodiments, the wall  230  of the enclosure  215  (marked by dotted line) defines a plurality of cavities  510  formed by of the barrier layer  315  and the panel  310 . In some embodiments, the cavities  510  are configured to allow the resonators  320  to function by allowing the membranes  325  to deflect into and out of the cavities  510 . In one embodiment, an absorber material (not shown) is disposed within one or more cavities  510  to help dissipate any transmitted acoustic energy. In one embodiment, the absorber material disposed within the cavities  510  is porous. 
     Referring to  FIG. 6 , in some embodiments, the wall  230  of the enclosure  215  (not shown) comprises two barrier layers  610  and  615  coupled together to form a cavity  620 . In this embodiment, the grid structure  330  acts as a core layer giving bending stiffness to the overall wall  230 . Using two barrier layers  610  and  615  as shown in  FIG. 6  provides a number of performance benefits such as, for example, raised frequency panel vibration modes, enhanced acoustic isolation at a single frequency or the ability to target two distinct frequencies that can be matched to the operation of the component to be isolated. 
     In some embodiments, the enclosure  215  presently disclosed is used as an isolator box that would be placed over the component  110  and rigidly mounted to the floor or wall of another component. 
       FIG. 7  shows a proof of concept embodiment of this invention. The  5  sided enclosure  700  can be placed over a noise source to provide acoustic isolation. It uses the sandwich layer construction shown in  FIG. 6  with an average area density of 70 oz/yd 2 . Simple labs tests demonstrated that this prototype solution provided a 20 dB transmission loss near the antiresonant frequency of 500 Hz. This is approximately 10 dB greater than the mass law prediction for a limp isotropic barrier at this frequency showing a significant weight savings over traditional designs. 
     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 . . . .”