EP4083996A1 - Schallschutzwand mit einem plattenförmigen akustischen metamaterial - Google Patents

Schallschutzwand mit einem plattenförmigen akustischen metamaterial Download PDF

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Publication number
EP4083996A1
EP4083996A1 EP21171395.3A EP21171395A EP4083996A1 EP 4083996 A1 EP4083996 A1 EP 4083996A1 EP 21171395 A EP21171395 A EP 21171395A EP 4083996 A1 EP4083996 A1 EP 4083996A1
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EP
European Patent Office
Prior art keywords
strip
mass
shaped
soundproofing wall
baseplate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP21171395.3A
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English (en)
French (fr)
Inventor
Felix Dr.-Ing. Langfeldt
Wolfgang Proft. Dr.-Ing. Gleine
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hochschule fuer Angewandte Wissenschaften Hamburg
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Hochschule fuer Angewandte Wissenschaften Hamburg
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hochschule fuer Angewandte Wissenschaften Hamburg filed Critical Hochschule fuer Angewandte Wissenschaften Hamburg
Priority to EP21171395.3A priority Critical patent/EP4083996A1/de
Priority to PCT/EP2022/061446 priority patent/WO2022229371A1/en
Publication of EP4083996A1 publication Critical patent/EP4083996A1/de
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/162—Selection of materials

Definitions

  • the invention relates to a soundproofing wall for isolating a first room on one side of the soundproofing wall from a sound source on the other side of the soundproofing wall.
  • soundproofing walls find application in various fields, for example to isolate an interior of a vehicle, a vessel or an aircraft from an external sound source, to encapsulate a noise generating machine from its surroundings, within buildings, etc.
  • the efficiency of a soundproofing wall can be characterised in terms of the sound transmission loss (STL) which describes the loss of intensity of an incident acoustic wave having passed the soundproofing wall.
  • STL sound transmission loss
  • the sound transmission loss is determined by the mass-law for frequencies below the coincidence frequency, leading to the well-known problem that efficient soundproofing of low frequencies requires walls having a large mass.
  • MAM membrane-type acoustic metamaterials
  • a solution to this problem is to use a plate instead of a membrane as the base material to which the masses are attached.
  • PAM plate-type acoustic metamaterials
  • the spring stiffness is generated by the bending stiffness of a baseplate and a pretension is not required.
  • PAM plate-type acoustic metamaterials
  • Several different designs of PAM have been investigated, for example PAM with a frame and no masses in the unit cells, PAM with added masses or double-layer PAM with air cavities and orifices.
  • One particular PAM design which has particularly promising properties for applications with strong weight limitations, consists of a baseplate with a periodic array of rigid masses attached to the baseplate and no frame structure at all.
  • the soundproofing wall is for isolating a first room on one side of the soundproofing wall from a sound source on the other side of the soundproofing wall and comprises a plate-type acoustic metamaterial with a baseplate and a plurality of masses arranged on the baseplate, wherein at least one of the masses is strip-shaped.
  • plate-type acoustic metamaterial means that, in contrast to a membrane-type acoustic metamaterial, the vibroacoustic properties of the metamaterial (of the combination of the baseplate and the masses) do not rely on a membrane that must be held under tension, but rather on the elastic properties of the "unsupported" baseplate itself. No tensioning of the baseplate is required.
  • the soundproofing wall therefore does not require a frame or any other support structure that provides a pretension of the baseplate. However, the soundproofing wall may nevertheless comprise a frame or support structure to which the baseplate is fastened, in order to maintain the plate-type acoustic metamaterial in place.
  • the soundproofing wall may comprise any number of further structural or acoustic elements in layered or any other suitable form, such as one or more layers of a sound absorbing material, acoustic metamaterials, structural wall elements such as bricks, structural steel work, concrete wall elements, wood, sheet metal, fibre-reinforced plastics, and so on.
  • the soundproofing wall by means of the plate-type acoustic metamaterial provides improved sound insulation.
  • At least one of the masses of the plate-type acoustic metamaterial is strip-shaped.
  • a plurality of the masses, a majority of the masses or all of the masses may be strip-shaped.
  • the at least one strip-shaped mass covers an elongated section of the baseplate and imparts additional stiffness to the metamaterial, and thereby alters the possible vibrational motion of the metamaterial, it was found that a comparable frequency response can be achieved, in particular including resonances and anti-resonances similar to a plate-type acoustic metamaterial with point-like masses. For this reason, using at least one strip-shaped mass is an economically viable alternative to a larger number of point-shaped masses.
  • the baseplate has a stiffness. It is this stiffness that leads to the vibroacoustic properties of the metamaterial.
  • the stiffness can be selected and adapted in relation to the at least one strip-shaped mass such that a desired frequency response of the plate-type acoustic metamaterial is achieved. It is noted that for an efficient sound transmission loss in a low-frequency range, such as for example 20 Hz to 100 Hz, the stiffness of the baseplate may be relatively low. This is true in particular when a lightweight overall structure is desired, including relatively lightweight masses.
  • the stiffness of the baseplate may be tailored by selecting a material for the baseplate (or a combination of materials) having a certain Young's modulus, and/or by selecting a suitable thickness of the baseplate.
  • the baseplate may comprise a thin layer of an impermeable material, e.g. a polymeric foil, and an adjacent, preferably thicker layer of another material, for example an absorber material such as a glass or mineral wool, the adjacent layer imparting stiffness and/or elasticity to the thin layer.
  • an impermeable material e.g. a polymeric foil
  • an adjacent, preferably thicker layer of another material for example an absorber material such as a glass or mineral wool
  • the at least one strip-shaped mass has a length and a width, wherein the length is at least three times the width.
  • the length to width-ratio of the at least one strip-shaped mass may be larger, such as at least 5, at least 10, or at least 20.
  • Another parameter to quantify the length of the at least one strip-shaped mass is the ratio of the length to a distance between the strip-shaped mass and an adjacent mass. This ratio may be at least 5, at least 10 or at least 20.
  • the at least one strip-shaped mass has a length extending in a length-direction, wherein the length of the at least one strip-shaped mass extends over at least 50% of a dimension of the baseplate measured in the length-direction.
  • the length of the at least one strip-shaped mass may extend over at least 80% of said dimension, or over the entirety of said dimension.
  • the ratio ⁇ between a surface mass density of the at least one strip-shaped mass to a surface mass density of the baseplate is 3.5 or more.
  • the ratio ⁇ may also be 5.0 or more, or 10 or more.
  • the ratio between a bending stiffness D M of the at least one strip-shaped mass to a bending stiffness D b of the baseplate is in a range of about 50 to about 500.
  • the bending stiffness may be increased as desired by using stiffer materials for and/or larger heights/thicknesses of the masses/the baseplate.
  • the at least one strip-shaped mass When the at least one strip-shaped mass has a high bending stiffness, it will move as a rigid body, and the vibroacoustic properties of the metamaterial will be dominated by the deformability of the baseplate. This may be assumed as long as the bending stiffness of the at least one strip-shaped mass is about 1,000 times larger than the bending stiffness of the baseplate.
  • the first anti-resonance of the plate-type acoustic metamaterial shifts towards lower frequencies.
  • an additional anti-resonance appears at a frequency below the first anti-resonance, which leads to a broadening of the frequency range with high sound transmission loss, and/or to a second peak in sound transmission loss at a lower frequency. Both effects can be beneficial when aiming for an efficient soundproofing for a specific noise problem.
  • the at least one strip-shaped mass consists of a material having a higher mass density and/or a higher stiffness than a material of the baseplate. Both measures help to obtain a desired ratio ⁇ of surface mass densities and/or a desired ratio D M / D b of bending stiffnesses in a compact/thin package.
  • a plurality of the masses are strip-shaped and arranged in a regular pattern.
  • the regular pattern may include a simple repetition of strip-shaped masses arranged in parallel, but may also be more complex, as will be shown in some of the embodiments.
  • the regular pattern may include a geometric structure such as a square, a rectangle, or a spiral.
  • Each geometric structure may be formed by one or by several strip-shaped masses.
  • Each geometric structure may comprise additional/internal structures or patterns.
  • a width of the at least one strip-shaped mass forming the spiral may increase from a centre of the spiral towards an outer area of the spiral.
  • a plurality of geometric structures, each formed by one or more strip-shaped masses, may be arranged on the baseplate in a regular pattern. It was found that regular patterns from strip-shaped masses make it easy to predict and tailor the vibroacoustic characteristics of the plate-type acoustic metamaterial as desired and in a consistent manner for the entire soundproofing wall.
  • the plate-type acoustic metamaterial comprises a plurality of unit cells each including at least one of the strip-shaped masses and an adjacent, strip-shaped baseplate region in which none of the masses is present.
  • Unit cells arranged in a regular pattern also help to achieve predictable, consistent vibroacoustic characteristics.
  • the baseplate has a thickness h b and a longitudinal wave velocity c b and two of the strip-shaped masses are arranged in a distance /, wherein the materials used for the strip-shaped masses and the baseplate and their dimensions are selected such that the ratio between h b times c b and l 2 is 30 per second or more.
  • this reads as follows: h b c b l 2 ⁇ 30 1 s
  • E b Young's modulus
  • ⁇ b specific density
  • the lowest anti-resonance of the plate-type acoustic metamaterial is expected to fall in a frequency range suitable for many noise problems.
  • most practical noise problems will benefit from selecting the ratio between h b times c b and l 2 at or below 15,000 per second, at or below 7,500 per second or even at or below 1,500 per second.
  • each of the unit cells includes at least two of the strip-shaped masses. This makes it possible do design the plate-type acoustic metamaterial such it comprises one or more peaks in sound transmission loss at different, selected frequencies.
  • the at least two strip-shaped masses have different surface mass densities. This may be achieved by using different dimensions and/or materials having different mass densities for the at least two strip-shaped masses. This offers additional options for selecting suitable frequency responses of the soundproofing wall.
  • the plate-type acoustic metamaterial has a surface mass density of 5 kg/m 2 or less. While a common, solid soundproofing wall with this surface mass density will have relatively low performance in the low frequency range, as predicted by the mass-law, the inventive soundproofing wall can perform much better.
  • the inventive soundproofing wall has an overall weight low enough to be suitable for weight-sensitive applications, such as, for example, for soundproofing of an aircraft passenger cabin.
  • the inventive soundproofing wall may be integrated in a cabin wall of an aircraft.
  • the at least one strip-shaped mass is attached to the baseplate.
  • the at least one strip-shaped mass may be adhered or welded to the baseplate. Manufacturing the plate-type acoustic metamaterial in this way can be done with proven techniques and offers great flexibility with regard to the selection of materials.
  • the at least one strip-shaped mass may consist of a single layer or of more than one layer, such as, for example two, three or more layers. These layers may consist of different materials and/or may have different structures so that they have different viscosities, stiffnesses, densities and/or thicknesses.
  • the at least one strip-shaped mass may comprise a bottom layer of an adhesive, arranged between the baseplate and at least one upper layer.
  • the at least one strip-shaped mass comprises a first mass layer, a second mass layer and an elastic layer arranged between the first mass layer and the second mass layer.
  • the at least one strip-shaped mass itself forms a system of two elastically coupled masses that can vibrate on its own. This allows for additional anti-resonances of the plate-type acoustic metamaterial, which may be helpful for obtaining a broad frequency range of high transmission loss.
  • the elastic layer may extend over the entire length and/or over the entire width of the first and second mass layers, or it may cover selected connection regions or connection points thereof only, for example arranged in a certain pattern, such as in strips running in the crosswise or lengthwise direction of the first and second mass layers.
  • connection regions or points may be distributed over a length direction of the mass layers such that longitudinal sections of the mass layers arranged between neighbouring connection regions remain unconnected. This allows for additional bending vibration modes of the first mass layer and/or the second mass layer and related, additional anti-resonances.
  • the first mass layer may be connected to the baseplate by any suitable means, such as an adhesive layer.
  • the first mass layer can also be formed integrally with the baseplate and from the same material as the baseplate, for example when a thickened strip of the baseplate forms the first mass layer. It is understood that the concept may be extended by adding one, two or more additional pairs of an elastic layer and a mass layer.
  • the elastic layer comprises a pressurised gas.
  • variations of the distance between the two mass layers translate into pressure changes within the elastic layer.
  • Suitable examples of such elastic layers include various foamed materials as well as larger gas volumes encapsulated in a container, such as a hose or closed profile.
  • Elastic layers comprising a pressurised gas are relatively lightweight, cost efficient and can provide a desired degree of elasticity with low damping.
  • a material of the first mass layer and a material of the second mass layer are selected such that these layers are pulled towards one another by a magnetic force.
  • one of these layers may comprise a ferromagnetic material and the other one may comprise a permanent magnet.
  • the pulling force may be helpful for holding the two mass layers and the elastic layer together.
  • the various layers may be interconnected by any other means as well, such as by additional adhesive layers.
  • the magnetic force leads to a desired level of compression of the elastic layer.
  • the baseplate and the at least one strip-shaped mass are integrally formed from the same material.
  • this can be done by machining a plate to remove material to form grooves in the area where no masses shall be present or by recasting the material of a plate.
  • These manufacturing techniques are well-suited for mass production, in particular in endless lengths.
  • Various polymeric materials in particular, have favourable characteristics as to stiffness and weight, well suited for achieving surface mass density and bending stiffness ratios in accordance with the above mentioned, preferred ranges.
  • Figure 1 shows a soundproofing wall consisting of a baseplate 10 and a plurality of strip-shaped masses 12, together forming a plate-type acoustic metamaterial.
  • the baseplate 10 has a height h b , a mass density ⁇ b , a Young's modulus E b , and a Poisson's ratio v b . These quantities essentially determine the bending stiffness D b of the baseplate 10.
  • the strip-shaped masses 12 have a length extending along a y-axis, and a width b along an x-axis.
  • the strip-shaped masses have a height h M and a mass density ⁇ M . They are arranged in parallel. Between each two strip-shaped masses 12, there is a spacing l .
  • the soundproofing wall is designed for isolating a first room on one side of the soundproofing wall from a sound source on the other side of the soundproofing wall.
  • FIG. 2 the soundproofing wall of Fig. 1 is shown in cross-section.
  • An incident acoustic wave 14 is illustrated coming from the bottom of the figure, i.e. from a sound source on that side of the soundproofing wall.
  • the figure illustrates a transversal displacement w ( x , y ) along the z-direction of the masses 12 and the baseplate 10 due to the incident acoustic wave 14. It can be seen that a deformation of the baseplate 10 is larger than a deformation of the strip-shaped masses, which have a larger bending stiffness than the baseplate 10.
  • Figure 3 shows a diagram illustrating the sound transmission loss TL measured in dB for a frequency range from 100 Hz to 1,000 Hz for a soundproofing wall as shown in Figs. 1 and 2 as compared to a mass-equivalent homogeneous plate.
  • the sound transmission loss of the inventive soundproofing wall calculated in a mathematical model is depicted as a solid line. It shows a broad peak at about 250 Hz. The calculation is compared to a measurement with a sample having an overall size of 1 m x 1.2 m, depicted by the small circles.
  • the strip-shaped masses 12 were made from strips of polyvinyl-chloride foam (PVC-F) with a height h M of 5 mm and a width b of 50 mm, arranged in distances l of 20 mm, leading to a unit cell width a of 70 mm.
  • PVC-F had a mass density ⁇ M of 460 kg/m 3 .
  • the total surface mass density of the plate-type acoustic metamaterial is 1.8 kg/m 2 .
  • the sound transmission loss of the soundproofing wall is much larger (about 20 dB) in the relevant frequency range.
  • Fig. 4 illustrates the influence of the ratio D M / D b of the bending stiffnesses of the strip-shaped masses to the bending stiffness of the baseplate on the frequency response.
  • the sound transmission loss shows only one prominent peak shifting to lower frequencies with decreasing ratio.
  • the curve shows an additional second peak at a lower frequency.
  • Figures 5 to 10 show various examples of how the strip-shaped masses may be arranged. Only the masses 12 themselves are shown in a schematic top view. In the four examples of Fig. 5 , the strip-shaped masses are arranged in parallel rows, but have different lengths.
  • Figure 6 illustrates that the strip-shaped masses 12 may have widths and spacings that vary over their length.
  • Figure 7 includes a regular pattern of nested squares, each formed by one strip-shaped mass 12. In the middle of each set of nested squares, the arrangement includes one smaller square-mass 16, i.e. an additional mass that is not strip-shaped.
  • Fig. 9 shows four examples of arrangements of strip-shaped masses 12.
  • a single strip-shaped mass 12 forms a spiral, wherein a width of the strip-shaped mass 12 is increasing from the centre towards an outer region of the spiral.
  • the second example shows a spiral formed by a plurality of strip-shaped masses 12.
  • the third example shows a spiral formed by a plurality of strip-shaped masses 12 as well, wherein these are interconnected to each other by narrower sections 18.
  • the fourth example, to the right of the figure shows a plurality of straight, strip-shaped masses 12 arranged in a rectangular pattern.
  • Figure 10 shows another regular pattern of strip-shaped masses 12 of a more complex arrangement, including a plurality of straight strip-shaped masses 12 of different lengths as well as a plurality of strip-shaped masses 12 forming spirals and nested squares.
  • Figure 11 shows another soundproofing wall in cross section, with unit cells of a width a including two strip-shaped masses 12 each.
  • the dimensions of the strip-shaped masses 12 are identical, but their spacing varies.
  • Figure 12 shows yet another soundproofing wall in cross section, with unit cells of a width a including two strip-shaped masses 12 each.
  • the dimensions of the strip-shaped masses 12 vary, wherein one of the two strip-shaped masses 12 has a larger width than the other one, while both have the same height.
  • Figure 13 shows yet another soundproofing wall in cross section, with unit cells of a width a including two strip-shaped masses 12 each.
  • the dimensions of the strip-shaped masses 12 vary, wherein one of the two strip-shaped masses 12 has a larger height than the other one, while both have the same width.
  • Figure 14 shows a unit cell of yet another soundproofing wall, partly in cross section.
  • the unit cell includes only one strip-shaped masse 12, which consists of four layers. These include a first mass layer 22 fastened on the baseplate 10 by means of an adhesive layer 20, a second mass layer 26 and an elastic layer 24 arranged between the first mass layer 22 and the second mass layer 26.
  • the first mass layer 22 comprises a ferromagnetic material
  • the second mass layer 26 is a permanent magnet.
  • the elastic layer 24 comprises a pressurised gas, in particular a foamed material. It may be attached to both mass layers 22, 26 by additional adhesive layers (not shown). The magnetic force between the mass layers 22, 26 leads to a certain level of compression of the elastic layer 24.
  • Figure 15 illustrates the "working principle" of the layered strip-shaped mass 12 of Fig. 14 .
  • the elastic layer 24 acts like a spring connecting the mass layers 22, 26.
  • the adhesive layer 20 has elastic properties as well, leading to an elastic coupling between the baseplate 10 and the system of the two elastically coupled mass layers 22, 26.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Building Environments (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)
EP21171395.3A 2021-04-30 2021-04-30 Schallschutzwand mit einem plattenförmigen akustischen metamaterial Withdrawn EP4083996A1 (de)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP21171395.3A EP4083996A1 (de) 2021-04-30 2021-04-30 Schallschutzwand mit einem plattenförmigen akustischen metamaterial
PCT/EP2022/061446 WO2022229371A1 (en) 2021-04-30 2022-04-29 A soundproofing wall comprising a plate-type acoustic metamaterial

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EP21171395.3A EP4083996A1 (de) 2021-04-30 2021-04-30 Schallschutzwand mit einem plattenförmigen akustischen metamaterial

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EP4083996A1 true EP4083996A1 (de) 2022-11-02

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20140339014A1 (en) * 2013-05-17 2014-11-20 Purdue Research Foundation Sound barrier systems

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20140339014A1 (en) * 2013-05-17 2014-11-20 Purdue Research Foundation Sound barrier systems

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
LANGFELDT FELIX ET AL: "Optimizing the bandwidth of plate-type acoustic metamaterials", THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, AMERICAN INSTITUTE OF PHYSICS FOR THE ACOUSTICAL SOCIETY OF AMERICA, NEW YORK, NY, US, vol. 148, no. 3, 9 September 2020 (2020-09-09), pages 1304 - 1314, XP012249974, ISSN: 0001-4966, [retrieved on 20200909], DOI: 10.1121/10.0001925 *
LIU YANG ET AL: "Vibroacoustic characteristics and sound attenuation analyses of a duct-membrane system coupled with strip masses", JOURNAL OF VIBRATION AND CONTROL, vol. 25, no. 23-24, 1 December 2019 (2019-12-01), US, pages 2910 - 2920, XP055846768, ISSN: 1077-5463, Retrieved from the Internet <URL:https://journals.sagepub.com/doi/pdf/10.1177/1077546319873459> DOI: 10.1177/1077546319873459 *

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