Sound absorption device with vibroacoustic metamaterials and noise barrier comprising at least one such soundproofing device

Abstract

The invention relates to a sound absorption device (1) for reducing sound transmission, comprising an arrangement of mechanical resonators (2), which each contain at least one vibrating mass (3) and a spring element (4), wherein the mechanical resonators (2) are coordinated to each have at least one natural frequency in a relevant frequency range, wherein the arrangement of mechanical resonators (2) is configured such that it generates at least one stop band for wave propagation in the relevant frequency range. In addition, a noise barrier is described, which comprises at least one sound absorption device (1).

Description

[0001] Soundproofing device with vibroacoustic metamaterials and noise barrier comprising at least one of these soundproofing devices

[0002] Soundproofing device with vibroacoustic metamaterials

[0003] The invention relates to a soundproofing device based on vibroacoustic metamaterials, as well as a noise barrier containing the same.

[0004] Noise protection is relevant in many areas of everyday life when it comes to protecting people and the environment from the negative impacts of elevated noise levels. Noise protection is therefore particularly relevant in road traffic, where noise is primarily generated by rolling and drive noise, as well as aerodynamic noise from vehicles. This noise is loudest in the frequency range from 500 Hz to 1000 Hz. To protect people and animals from road noise, in addition to options for reducing noise emissions from roads and vehicles, so-called noise barriers are used to dampen the propagation of sound. However, noise protection is also relevant in other areas, for example on construction sites, in industry, in open-plan offices, or in the construction industry in general.Soundproofing devices, insulating elements such as facades, partition walls, windows and doors or other components that act in a similar way to noise barriers are also used in these areas.

[0005] Conventional noise barriers reduce sound transmission by increasing the mass per unit area, i.e., by increasing the wall thickness or by using high-density materials. Particularly low transmission values ​​are therefore achieved with concrete noise barriers, for example. Sound transmission can also be reduced by improving the absorption properties of the noise barrier. Absorbent materials such as mineral wool, which is used in cassette-type noise barriers, as well as the integration of earth embankments or vegetation into the noise barrier, serve this purpose. Other options for improving absorption properties include the use of porous materials, membranes, or Helmholtz resonators. However, the resulting noise barriers always have the disadvantage of being large and requiring a high material investment.In addition, they usually have to be massive and expansive, which means they have a negative impact on the landscape.

[0006] Another option for dampening sound propagation that has not yet found widespread application in noise control is the use of vibroacoustic metamaterials. Metamaterials are artificial, usually periodic, structures designed to achieve special conductive, insulating, damping, or amplifying properties. This approach can be used, for example, to create structures that form stop bands. Stop bands are frequency ranges in which wave propagation is greatly attenuated. In vibroacoustic metamaterials, these concepts are applied to control and manipulate the propagation of elastic and acoustic waves. In this context, the properties of solids, such as density, bulk modulus, and elastic modulus, are relevant.A simple example of such a metamaterial is a structure made of materials with periodically changing refractive indices, realized in the acoustic domain, for example, by jumps or inhomogeneities in the elastic parameters of a structure. Bragg scattering occurs in such a structure: At the transitions of the refractive indices, the sound waves are reflected in a frequency-dependent manner. In certain frequency ranges, which depend on the lattice structure of the inhomogeneities, destructive interference occurs, creating a stop band. Another possibility for generating stop bands using vibroacoustic metamaterials is periodic arrangements of resonant structures, so-called local resonators. Due to the interactions of the local resonators with their environment, the resulting structure behaves as if it had a negative effective mass, so that wave propagation in this range is severely impeded.To create a pronounced stopband, the individual resonators must all be tuned to the same frequency. Deviations in the periodicity and frequency tuning of the resonators result in a wider, but less pronounced, stopband. Through clever design of vibroacoustic metamaterials, these effects can be exploited to create structures with particularly low sound transmission.

[0007] The object of this patent application is therefore to propose a soundproofing device that, compared to conventional noise protection devices, offers improved reduction of sound transmission with a lower surface-related mass. This allows mass and material savings to be achieved in the construction of noise barriers and allows for the creation of improved, partially transparent noise barriers.

[0008] This object is achieved by a soundproofing device according to independent claim 1.

[0009] Such a soundproofing device comprises an arrangement of mechanical resonators, each containing at least one vibrating mass and one spring element, wherein the mechanical resonators are tuned to each have at least one natural frequency in a relevant frequency range, wherein the arrangement of mechanical resonators is configured to generate at least one stop band for wave propagation in the relevant frequency range.

[0010] The soundproofing device comprises an array of mechanical resonators. This array of mechanical resonators forms a vibroacoustic metamaterial. The array can be two-dimensional, i.e., in a plane, or three-dimensional in space. In particular, multiple two-dimensional arrays can be stacked on top of or next to each other. The individual resonators each consist of at least one vibrating mass and one spring element. The vibrating mass can have any shape and size and be made of different materials. The mass of the vibrating mass is an important factor in tuning the frequency of the resonator. The spring element has elastic properties. The spring element can be formed integrally with the vibrating mass. It can also be a single elastic element, such as a leaf spring or coil spring. The spring element can have any shape and size.In particular, the shape and dimensions of the spring element are important factors in tuning the frequency of the resonator. The spring element can be made of the same material as the vibrating mass, or it can be an elastomer, for example. It should be noted that the vibrating mass and the spring element are not necessarily clearly distinguishable from each other. The vibrating mass and spring element can be formed as one piece, and the vibrating mass can also deform during vibration. The vibrating mass, the spring element, and a certain area surrounding the resonator form a unit cell of the resonator. The arrangement of mechanical resonators consists of a spatial repetition of these unit cells.

[0011] Each individual resonator has at least one first relevant resonant frequency. When excited at a resonant frequency, the amplitude of the resonator's oscillation is maximized. The resonant frequency of a resonator is determined by the properties of the entire unit cell. In addition to the mass of the oscillating mass and the spring element, and the elastic properties of the spring element, the geometry, mass, and elasticity of the surrounding structures also play a role. The frequency of the resonators can therefore be tuned by varying these properties. The unit cells should be dimensioned on the order of half a wavelength of the first relevant frequency, or smaller.

[0012] All mechanical resonators of the metamaterial are tuned to the same, or at least approximately the same, resonant frequency. This creates a stopband around this frequency, which significantly attenuates wave propagation within the metamaterial. By tuning the resonant frequency of the mechanical resonators, a stopband can be created that reduces the transmission and reflection of sound waves in the soundproofing device and in associated components. If the resonators have multiple resonant frequencies in the relevant frequency range, multiple stopbands can be created around them. These multiple stopbands can separately reduce vibrations in different frequency ranges or overlap to form a large stopband.

[0013] The arrangement of mechanical resonators can be periodic. A periodic structure results from the spatial repetition of the unit cells of the mechanical resonators.

[0014] The distance between the mechanical resonators in the array of mechanical resonators may be less than half a wavelength of the first relevant frequency to ensure advantageous behavior of the array.

[0015] The periodic arrangement of the mechanical resonators with spacings of less than or equal to half a wavelength can also result in at least one additional stop band being formed in the noise protection device, which is created by Bragg scattering at the arrangement. In this way, an additional stop band can be utilized around another frequency. Further stop bands can also be created by designing the mechanical resonators so that they have multiple resonant frequencies. Furthermore, the arrangement of the mechanical resonators can be selected so that additional resonant frequencies are created for the arrangement, either by using resonators with different relevant frequencies in the arrangement or by creating additional stop bands due to the shape of the arrangement.

[0016] If the individual mechanical resonators are tuned slightly differently, the stopband can be broadened around the first resonance frequency. However, this also results in a loss of sharpness, and the reduction of vibrations in this frequency range is less pronounced. However, these effects can be desirable. Furthermore, slightly different frequency tunings of the resonators can be useful to adapt the resonators to their position in the array of local resonators, for example, if additional forces are expected to act on certain areas of the array.

[0017] In addition to the oscillating mass and spring element, the resonators can also include a damping element. This could, for example, be a viscoelastic material incorporated into the unit cell. Damping can influence the shape of the stopband. Additional damping of the resonator broadens the stopband, which can be a desirable effect.

[0018] The mechanical resonators can be designed so that their frequency tuning cannot be altered by external influences. External influences include, for example, weather or external mechanical influences. For this purpose, the mechanical resonators can have an encapsulated form or housing, or be arranged so that they are protected from wind, weather, or the accumulation of dirt. This is particularly important when using the soundproofing device in outdoor areas, such as road traffic, where they are exposed to weather and temperature fluctuations as well as dirt from the road and air, yet reliable function over a long service life is desired.

[0019] There are various forms of mechanical resonators that can be arranged in a soundproofing device. These can be selected depending on the intended application, the location of the soundproofing device, and in particular the planned size of the entire arrangement of mechanical resonators. Different forms of resonators, which nevertheless have the same or at least similar frequency tuning, can also be combined in one arrangement, for example, to meet mechanical or aesthetic requirements. In addition, resonators can be designed to influence sound reflection. The mechanical resonators described here enable stop bands in frequency ranges between 50 Hz and 5000 Hz, in particular in the range between 1000 Hz and 1500 Hz.

[0020] The mechanical resonators can, for example, be designed as cup resonators. In a cup resonator, a cup-shaped, elastic membrane forms the spring element, and an oscillating mass is arranged inside this cup. If such an arrangement is applied to a surface, it can be completely sealed off from the outside, thus providing protection from external influences. Furthermore, such a cup resonator is easy to manufacture and dimensioned for the relevant frequency range. A cup can be understood as dome-shaped, cylindrical, or truncated cone-shaped. The cup does not necessarily have to have a circular or even round basic shape, although this can be useful for frequency tuning. The cup has one open side and one closed side.The closed side can be flattened or rounded and decorated with concentric waves to reduce stiffness or similar features. On the open side, the wall of the cup forms a collar, allowing the resonator to be easily attached to a surface, for example, by gluing or screwing.

[0021] In a cup resonator, the cup can be designed as a spring element integrally with the vibrating mass. Die-casting or injection-molding processes are suitable for manufacturing such a cup resonator. Materials such as steel, zinc, aluminum, or other metals and plastics can be used. Zinc is particularly suitable due to its low modulus of elasticity compared to steel and only slightly lower density, making it ideal for use as the elastic membrane of the resonator. Zinc also acts as a corrosion inhibitor, thus providing additional weather resistance. A one-piece cup resonator offers the advantages of a small number of parts and simple assembly, while being relatively easy to mass-produce.

[0022] Instead, the cup and vibrating mass can be designed as separate parts, with the mass being secured within the cup. The cup can be made from formed sheet metal, for example. It can also be injection-molded from plastic. However, a material with a significantly higher density, such as steel or lead, can be chosen to produce the mass, providing more options for frequency tuning. The mass is arranged within the cup and firmly connected to it, for example by screwing or gluing. If the cup is injection-molded, the mass element can be overmolded and thus connected to the cup during this manufacturing step. Since plastic cups can also be manufactured in combination, this cup resonator can also be easily manufactured in large-scale series.

[0023] In another form of mechanical resonator that can be used for a soundproofing device, the spring element is made of an elastomer. In the simplest form, for example, a vibrating mass can be connected to a surface by means of an elastomer body and thus mounted so that it can vibrate. Another form of such a resonator is the vibrating mounting of a mass element between two elastomers, encapsulated by a housing. This allows the vibrating mass to be stably mounted so that it can vibrate in one direction. A housing also protects the resonator from the elements. Instead of an elastomer, a compression spring, a fiber cushion, a metal cushion, or a metal foam can also be used.Although this type of resonator has a larger number of components, they are simple and readily available, allowing for good frequency tuning due to the wide range of possible variations. Individually housed in housings, the resonators can be easily applied to a surface. Furthermore, an array of such mechanical resonators results in a particularly good ratio between the free area and the area required for the resonators. This can be advantageous because, in combination with transparent materials, it enables the construction of transparent and semi-transparent noise barriers.

[0024] A sheet metal strip can also serve as the spring element of a mechanical resonator. This can also act as an oscillating mass or be provided with an additional oscillating mass attached to it. In the simplest case, this arrangement acts as a leaf spring with an oscillating mass at one end or in its center. However, a longer sheet metal strip can also be folded or provided with support elements so that it has several springy areas to which individual masses are attached, for example, glued, screwed, or welded. In this way, a large-area arrangement of resonators can be easily realized and applied as a composite to a surface. This creates a large amount of free space between the sheet metal strips.

[0025] Another form of a mechanical resonator comprises a surface from which a one-piece resonator has been machined, so that sections of the surface defined by recesses are capable of vibrating. The soundproofing device can be manufactured from a sheet of metal from which an entire array of resonators is machined using laser or waterjet cutting or punching. The individual resonator consists of a region of the surface defined by recesses. A first section or several first sections of this region, acting as a spring element, connect a second section, acting as an oscillating mass, to the remaining surrounding surface. This arrangement of resonators can be easily produced over large areas. Individual regions can also be provided with additional weights.Since this form of resonator is susceptible to dirt accumulating in the recesses, but also has an extremely flat design, it is particularly suitable for use inside multi-layer components.

[0026] In another form of resonator, a steel cable acts as a spring element, and the vibrating mass is suspended from it. Steel or lead balls, for example, can be used as vibrating masses. The steel cable is stretched between two support elements. The pretension and the mass allow the frequency to be tuned. A steel cable already possesses damping due to its inherent friction. The steel cable can also be supported by several support elements, so that a single steel cable can act as a spring element for several resonators, making it easy to create a large-area arrangement of local resonators. This design of mechanical resonators also results in a good free-area ratio.

[0027] A mechanical resonator can also be realized by embedding a vibrating mass in absorption material. The absorption material, such as mineral wool, thus acts as a spring element. The vibrating masses can be steel or lead spheres arranged at specific distances from one another in the matrix of the absorption material. In this way, a soundproofing device can be integrated into the common cassette construction of noise barriers. In particular, this form of mechanical resonator can be easily combined with other forms of mechanical resonators that are mounted on the surface of a cassette.

[0028] The mechanical resonators of the soundproofing device can each additionally include an energy conversion element so that the vibrations of the resonators can be used to generate energy.

[0029] The mechanical resonators can also include elements for adjusting their natural frequency. This can be achieved by varying the spring stiffness of the spring elements. For example, the preload of the spring elements can be adjusted. This allows for active or passive adjustment depending on external requirements, such as the current traffic situation. The use of actuators that actively apply forces to the noise protection device and thus influence or promote the formation of the stop band is also conceivable. Such actuators could improve the performance of the noise protection device, particularly the width and depth of the stop band.

[0030] One possible application of the described sound insulation device is in noise barriers. The described sound insulation device can be combined with all common types of noise barriers. In concrete noise barriers, the mechanical resonators can be cast into the concrete or applied to external surfaces. In cassette-type noise barriers, the resonators can be mounted in the cassettes or on their surfaces, or integrated directly into surfaces and fill materials. Mechanical resonator arrays can also be applied to noise barriers made of wood, glass, or plastic composites, or arranged in their cavities. Complete noise barrier enclosures and tunnel walls can also be equipped with a sound insulation device.Such noise barriers are primarily used in road traffic, but the use of the described soundproofing device is not limited to this. Other applications include airports, seaports, and railway lines.

[0031] The soundproofing device can be arranged at least partially on the outside of a noise barrier. When arranged on a side facing away from the sound source, this primarily results in a reduction in sound transmission; when arranged on a side facing the sound source, sound reflection can also be reduced. Mechanical cup-shaped resonators, simple resonators with springs or elastomers housed in housings, and sheet metal strips with applied vibrating masses are particularly suitable for applying the soundproofing device to the outside of the noise barrier.

[0032] If the noise barrier has a sandwich structure, such as a cassette-type noise barrier in which the noise barrier consists of several layers of material, the soundproofing device can be arranged in one of the inner layers or form this layer. Mechanical resonators made of sheet metal strips with applied mass, resonators machined from a surface, and resonators formed by mass spheres embedded in absorption material are particularly suitable for this arrangement of the soundproofing device. The noise barrier can also comprise one or more cavities as the inner layer in which the soundproofing device can be arranged. In this way, the mechanical resonators of the soundproofing device can oscillate freely, but are still protected from external influences.Resonators in the form of steel cables with masses suspended from them are particularly suitable for this type of noise barrier.

[0033] The noise barrier can also comprise multiple layers on which soundproofing devices are mounted or which are formed by soundproofing devices. Different designs of soundproofing devices can be combined. In particular, soundproofing devices with stop bands in different frequency ranges can be combined to create a noise barrier that reduces sound propagation in multiple areas. In this way, specific soundproofing devices can also be used to reduce sound transmission and reflection at the noise barrier.

[0034] The noise barrier can include recesses, such as windows, in which the soundproofing device is installed. This allows the noise barrier to be designed more openly, allowing sight lines through the noise barrier without sacrificing sound insulation. Arrangements of mechanical resonators with a high free-area ratio, such as steel cables with suspended masses or sheet metal strip resonators, are particularly suitable for this type of noise barrier.

[0035] The noise barrier can also generally be made of a transparent material such as glass or a corresponding plastic. Since the soundproofing device is applied to the noise barrier as an array of mechanical resonators, and this can have a relatively high open-area ratio, the result is at least a partially transparent noise barrier.

[0036] The noise barrier can be retrofitted with a soundproofing device. However, the noise barrier can also be manufactured in such a way that the soundproofing device is permanently integrated into it. This allows for better coordination of the noise barrier's design with the function of the soundproofing device. In particular, some forms of soundproofing device can be formed integrally with the noise barrier.

[0037] Although the function of soundproofing devices has so far been described using a noise barrier as an example, soundproofing devices can also be used for other components intended to spatially and acoustically separate two areas. These include, in particular, windows, doors, drywalls, facades, machine housings, partition walls, and mobile noise barriers.

[0038] The described embodiments of the subject matter of the present application can be used both individually and in combination to achieve additional effects and to provide a soundproofing device provided with an arrangement of mechanical resonators.

[0039] The above-mentioned and further aspects of the invention will become apparent from the detailed description of the embodiments given with the aid of the following drawings, of which:

[0040] Fig. la and lb illustrate the operation of a vibroacoustic metamaterial,

[0041] Fig. 2a, 2b and 2c show various general embodiments of a noise barrier with vibroacoustic metamaterials, Fig. 3a to 3d illustrate various relevant forms of mechanical resonators, Fig. 4a shows two perspective views of a first form of a cup resonator, and

[0042] Fig. 4b shows a cross-section through the cup resonator of Fig. 5a,

[0043] Fig. 5a shows two perspective views of a second form of cup resonator, and

[0044] Fig. 5b shows a cross-section through the cup resonator of Fig. 6a,

[0045] Fig. 6a shows two perspective views of a third form of cup resonator, and

[0046] Fig. 6b shows a cross-section through the cup resonator of Fig. 7a,

[0047] Fig. 7a, 7b and 7c show three different possibilities of damping using the example of a cup resonator,

[0048] Fig. 8a shows a cross-section through a mechanical resonator with a spring as a spring element,

[0049] Fig. 8b shows a cross-section through a mechanical resonator with an elastomer as a spring element,

[0050] Fig. 8c shows a perspective view of a mechanical resonator with a metal foam as a spring element,

[0051] Fig. 9a is a perspective view of a mechanical resonator consisting of a sheet metal strip with attached masses, Fig. 9b is a side view of the mechanical resonator consisting of a sheet metal strip with attached masses, Fig. 10a is a plan view of an arrangement of mechanical resonators machined from a sheet metal, and

[0052] Fig. 10b is a perspective view of the arrangement with an enlargement of a section,

[0053] Fig. 11 shows a schematic representation of mechanical resonators with a steel cable as a spring element,

[0054] Fig. 12a is a perspective view of a noise barrier provided with a soundproofing device, and

[0055] Fig. 12b shows a frontal view of the noise barrier,

[0056] Fig. 13 shows a cross-section through a cassette-type noise barrier with two different sound insulation devices, Fig. 14a shows a schematic representation of a multi-layer noise barrier with a sound insulation device arranged inside,

[0057] Fig. 14b shows a schematic representation of a multi-layer noise barrier with an externally arranged sound insulation device,

[0058] Fig. 14c shows a schematic representation of a single-layer noise barrier with a sound insulation device arranged thereon,

[0059] Fig. 15a and 15 show schematic representations of noise barriers which are partially provided with a sound insulation device,

[0060] Fig. 16a shows a schematic representation of a noise barrier provided with a sound insulation device on two different areas,

[0061] Fig. 16b shows a schematic representation of a noise barrier having a window provided with a noise protection device, Fig. 17a shows a schematic representation of an embodiment of a curved noise barrier provided with a sound protection device, and

[0062] Fig. 17b shows a schematic representation of a noise protection enclosure provided with a sound protection device.

[0063] The claimed subject matter will be explained in more detail below based on the accompanying drawings. Like reference numerals refer to like elements.

[0064] Fig. 1a and 1b abstractly depict the general structure and functionality of vibroacoustic metamaterials.

[0065] Fig. 1 shows a vibroacoustic metamaterial based on resonant structures, so-called local resonators. In this context, these are mechanical resonators 2. Each comprises an oscillating mass 3 and a spring element 4. The arrangement of mechanical resonators 2 is periodic. If the mechanical resonators 2 all have the same frequency tuning, i.e., they all have at least one common natural frequency, then when excited at this frequency, a stop band forms around the arrangement of mechanical resonators 2 and in the medium coupled to them. The propagation of waves in this frequency range, in the acoustic range, i.e., structure-borne and airborne sound, particularly in the range from 50 Hz to 5000 Hz, is thus greatly reduced. In this range, the structure can practically not be excited to vibrate.Since the mechanical resonators 2 can have multiple natural frequencies depending on their design, multiple stop bands can be formed around additional frequencies. These stop bands can cover different frequency ranges or overlap to create an enlarged stop band. Likewise, the individual mechanical resonators 2 can be designed with slightly different frequency tuning. This weakens the vibration reduction in the stop band range, but broadens the stop band. The arrangement shown in Fig. 1a thus represents the most general form of soundproofing device. This soundproofing device 1 is independent of its application and does not have to be applied to a noise barrier 5, but can also be used in other areas. It is initially only defined by the fact that it comprises an arrangement of mechanical resonators that have the same frequency tuning.

[0066] Fig. 1b additionally shows a vibroacoustic metamaterial based on the effect of Bragg scattering. This effect arises from periodically occurring jumps in the phase velocity of waves in a medium, such as those generated by the periodic arrangement of masses 2. The reflection of the waves at these inhomogeneities leads to destructive interference in certain frequency ranges, depending on the spacing of the inhomogeneities, so that a stop band is also generated. The spacing of the inhomogeneities corresponds to half the wavelength of the frequency of the stop band. This effect is of course also present in more complex arrangements, as shown in Fig. 1a. In the context of the present application, however, Bragg scattering plays a rather subordinate role, since the noise protection device always comprises an arrangement of mechanical resonators 2.However, Bragg scattering can be used to form additional stop bands. Figs. 2a, 2b, and 2c show various basic embodiments of a noise barrier 5 with a soundproofing device 1 based on vibroacoustic metamaterials, each schematically shown in perspective and in cross-section. Fig. 2a shows a noise barrier 5 with mechanical resonators 2 applied thereto (shown abstractly). In Fig. 2b, the mechanical resonators 2 are incorporated into the noise barrier 5. In Fig. 2c, the mechanical resonators 2 are integrated into the noise barrier 5 by machining spring elements 4 out of the wall in certain regions, here in the form of a thinning of the wall thickness, and applying vibrating masses 3 to them. However, the masses 3 could also be formed integrally with the noise barrier 5.The mechanical resonators 2 can be connected to the noise barrier 5 by gluing, screwing or other joining methods.

[0067] The following describes various concepts of mechanical resonators that can be used in a noise protection device 1. These can be roughly classified into four different types, which are schematically shown in Fig. 3a to 3d. Fig. 3a shows a columnar resonator in which an oscillating mass 3 is mounted on a discrete spring element 4. This shape is easy to implement and theoretically possible even without an additional mass 3. Coil springs, elastomers, or metal cushions and foams are conceivable as the spring element 3. Fig. 3b shows a bending beam resonator. Here, the majority of the beam is marked as the spring element 4 and is provided with a mass 3 at the tip. However, these do not have to be discrete components; a continuous beam is also conceivable. Therefore, in this configuration, the spring element 4 and the oscillating mass 3 cannot be strictly separated.A cantilever resonator can be easily manufactured using additive manufacturing, laser cutting from plastic, or using sheet metal forming processes. Fig. 3c shows a membrane resonator. In this case, an oscillating mass 3 is applied to a membrane as a spring element 4. The membrane does not have to be flat, but can take on various shapes. However, the membrane must have elastic properties. The oscillating mass 3 can be glued, screwed, or otherwise connected to the membrane, or it can be formed integrally with it. Fig. 3d shows a resonator consisting of an oscillating mass 3 and an elastic medium surrounding it as a spring element 4. In a resonator of this shape, the oscillating masses are essentially embedded in the spring element.

[0068] Membrane resonators such as those shown in Fig. 3c have proven particularly advantageous for use in soundproofing systems. These can be manufactured as cup resonators, in which the membrane is formed into a cup-shaped spring element 4 in which the vibrating mass is arranged. This resonator shape allows the mechanical resonator 2 to be constructed in a sealed manner, thus protecting it from external influences. Embodiments of such cup resonators are shown in Figs. 4a to 6b.

[0069] Fig. 4a and 4b illustrate a cup resonator in which the vibrating mass 3 and the cup are formed as a single piece, forming the spring element 4. Fig. 4a shows two perspective views of the resonator, one obliquely from below and one obliquely from above. Fig. 4b shows a cross-section through the resonator along line AA. Since this cup resonator is formed as a single piece, the mass 3 and the spring element 4 do not need to be connected by additional means. As can be seen, the mass 3 is centered in the cup of the spring element 4. To adjust the resonator's natural frequency, the membrane thickness, the diameter of the cup, and the diameter or mass of the vibrating mass can be varied. The cup resonator can also be provided with concentric waves (not shown) on its outer surface to reduce the stiffness of the spring element 3.Die casting or injection molding processes are suitable for the production of such a cup resonator. Materials that can be used include steel, zinc, aluminum, or other metals and plastics. Zinc is particularly suitable because of its low Young's modulus and only slightly lower density compared to steel, making it ideal for use as the elastic membrane of the resonator. Zinc also acts as corrosion protection, thus providing additional weather resistance. A one-piece cup resonator offers the advantages of a small number of parts and simple assembly with relatively simple large-scale production. The lower collar of the cup resonator allows for easy attachment, for example by gluing or screwing, to a surface such as a noise barrier.

[0070] Fig. 5a and 5b depict a cup resonator in which the cup is formed from sheet metal as a spring element 4, and the vibrating mass 3 is centered within it and firmly connected to it. Fig. 5a shows two perspective views of the resonator, one obliquely from below and one obliquely from above. Fig. 5b shows a cross-section through the resonator along line BB. Since this cup resonator is constructed in two parts, the mass 3 and the spring element 4 must be connected by additional means. The mass 3 can, for example, be glued to the cup, but can also be welded or screwed. To adjust the resonator's natural frequency, the membrane thickness, the diameter of the cup, and the diameter or mass of the vibrating mass can be varied. The cup resonator can also be provided with concentric waves or other embossings (not shown) on its outer surface to reduce the stiffness of the spring element 3.For the production of such a cup resonator, a metal sheet, for example, is used, which is formed into a cup using a forming process. For the mass, however, a material with a significantly higher density, such as steel or lead, can be chosen, thus providing more possibilities for frequency tuning. Using sheet metal and simple forming processes, this type of resonator is easy to manufacture. The lower collar of the cup resonator allows for easy attachment, for example, by gluing or screwing, to a surface, such as a noise barrier.

[0071] Fig. 6a and 6b also show a cup resonator, the cup as a spring element 4 and the oscillating mass 3 are manufactured as separate parts. In this case, the spring element 4 is realized as a plastic cup in which the mass 3 is fastened. Fig. 6a shows two perspective views of the resonator, both from below and from above. Fig. 6b shows a cross-section through the resonator along the line CC. The plastic cup is manufactured using an injection molding process. The mass 3 is glued to the cup or is overmolded with the plastic during production of the cup and thus permanently connected to it. To adjust the natural frequency of the resonator, the membrane thickness, the diameter of the cup and the diameter or mass of the oscillating mass can be varied.The cup resonator can also be provided with concentric waves or (not shown) on its outer surface to reduce the stiffness of the spring element 3. Various plastics with elastic but durable properties are suitable for the production of such a cup resonator. However, a material with a significantly higher density, such as steel or lead, can be chosen for the mass, thus providing more options for frequency tuning. By using an injection molding process, this form of cup resonator can be manufactured in composites and thus easily produced in large series. The lower collar of the cup resonator allows for easy application, for example by gluing or screwing, to a surface, such as a noise barrier. Similar to the one shown in Fig.The plastic cup resonator shown in Figures 6a and 6b can also be a cup resonator made of a metal foam, in which the membrane of the cup is made of a metal foam.

[0072] Fig. 7a to 7c illustrate various possibilities for damping a mechanical resonator 2 in a soundproofing device 1 using the example of a cup resonator. However, these damping methods can also be applied to other embodiments of mechanical resonators 2. In Fig. 7a, the cavity of the cup is filled with a damping foam 6. In Fig. 7b, a damping element 7 made of an elastomer or silicone is introduced into the resonator. In Fig. 7c, the resonator is damped by being connected to its substrate via elastic adhesives 8. In Fig. 7d, a damping element is applied to the membrane of the resonator. This can be, for example, a layer of bitumen, which additionally seals the resonator and protects it from corrosion. Depending on the shape of the mechanical resonator 2, other forms of damping are also possible.However, these all have the same effect: they influence the shape of the stop band of the noise protection device 1. In particular, the stop band is weakened by the damping (loses depth), but also widens, which can be a desired effect. By using damping elements, the shape of the stop band can be specifically adapted to the respective application. Fig. 8a, 8b and 8c show the different mechanical resonators 2, each of which can be assigned to the type of columnar resonator from Fig. 3a. Fig. 8a and 8b are similar in that they each comprise a housing 9 in which an oscillating mass 3 is arranged between two spring elements 4. In Fig. 8a, the spring element 4 is designed as a helical spring, in Fig. 8b by elastomers. However, metal cushions could also be used instead of elastomers.The arrangement of the oscillating mass 3 between two spring elements 4 ensures uniform preload, which also allows for frequency tuning. In Fig. 8c, the spring element 4 is a metal foam. Metal foams exhibit inherent damping and are easy to process in large series. Furthermore, a metallic oscillating mass 3 can be cast directly onto the metal foam and thus firmly bonded to it. The housing 9 encapsulates the mechanical resonator 2 and protects it from external influences. Since these embodiments of the mechanical resonator 2 use standardized and readily available components, they are easy to manufacture and versatile in their application.

[0073] Fig. 9a and 9b show a resonator or an arrangement of resonators based on a sheet metal strip. A sheet metal strip can be understood as a bending beam resonator as in Fig. 3b. In the embodiment shown in Fig. 9a, however, it also has properties of a membrane resonator as in Fig. 3c. Because the sheet metal strip is folded multiple times, it defines a series of spring elements 4, each provided with an oscillating mass 3. The masses 3 can be glued or screwed to the sheet metal strip. Thus, an arrangement of resonators 2 can be created using a sheet metal strip and applied as a composite. If damping is desired, this can be achieved by elastically bonding the sheet metal strip to the substrate. A further advantage of this embodiment is that in an arrangement of such mechanical resonators 2, a relatively large amount of free space results between the individual sheet metal strips.

[0074] Another embodiment based on a sheet metal is shown in Fig. 10a and 10b. Here, an arrangement of mechanical resonators 2 is machined from the surface of a sheet metal. Laser or water jet cutting or other machining processes can be used to produce such a resonator arrangement. In this way, soundproofing devices 1 with large-area arrangements of mechanical resonators 2 can be manufactured in just one step. As can be seen in the enlargement in Fig. 10b, recesses in the sheet metal define plate-shaped oscillating masses 3 and spring elements 4 designed as webs, which connect the masses to the remaining surface of the sheet metal. However, oscillating masses 3 and spring elements 4 cannot be defined discretely, since both parts of the arrangement deform when the resonator 2 is excited to oscillate.Frequency tuning is achieved by selecting the shape and dimensions of the oscillating masses 3 and spring elements 4. Due to the relatively low mass of the individual resonators 2, a relatively large surface area is required in this design of a soundproofing device 1, resulting in a low free area ratio. However, this form of resonator can also be made very thin and thus easily integrated into other components, for example in noise barriers 5 with a cassette design. To protect against external influences, this form of soundproofing device 1 should be completely encapsulated. In addition, the entire sheet metal must be mounted over its edges in such a way that the individual mechanical resonators 2 can oscillate. This design has been described here using a sheet metal example. However, it can also be implemented in other surfaces and materials in which two-dimensional resonators can be defined by means of cutouts.

[0075] Fig. 11 shows a further embodiment in which a mechanical resonator 2 can be easily expanded to form an array of resonators 2. The spring element 4 here is a steel cable that is stretched between support elements 9 and from which an oscillating mass 3 is suspended. The steel cable can thus serve as the spring element 4 for several resonator unit cells. The frequency tuning can be adjusted by the masses 3 and the pretension of the steel cable. The steel cable already offers inherent damping due to internal friction. A two-dimensional arrangement of mechanical resonators 2 can be easily achieved by using several steel cables arranged in parallel. This form of soundproofing device also offers a good free-area ratio. Figs. 12a and 12b show an overview of a simple noise barrier 5 equipped with a soundproofing device 1.The mechanical resonators 2, which are distributed over the surface of the noise barrier 5, can be, for example, cup resonators, as in Fig. 4a to Fig. 6b, or column resonators, as in Fig. 8a to 8c. Since the soundproofing device 1 forms a stop band for sound propagation in a relevant area in the noise barrier 5, this reduces sound transmission and can be less solid than conventional noise barriers or have a higher sound transmission reduction. Furthermore, it can be made of glass or another transparent material. Even with the soundproofing device 1 applied, the noise barrier is then at least partially transparent and restricts lines of sight less severely.

[0076] Fig. 13 shows a cross-section through a noise barrier 5 in the cassette design, as is used in many conventional noise barriers. In this embodiment, however, the noise barrier 5 uses a combination of two soundproofing devices 1 that utilize the properties of vibroacoustic metamaterials. On the left side of the noise barrier 5, a soundproofing device 1 is arranged, which uses a sheet metal resonator, as shown in Fig. 10a and b. This is shown in the enlarged cross-section at the bottom left. To allow the mechanical resonators 2 to vibrate freely, the soundproofing device is applied to a support element 9. In addition, the soundproofing device 1 is protected from the weather and external mechanical influences by the cassette 10. On the right side, the noise barrier is provided with a second soundproofing device 1.This consists of a matrix of absorption material as a spring element 4, into which mass spheres 3 are embedded. This embodiment of the soundproofing device 1 utilizes mechanical resonators 2, as shown in Fig. 3d. Since cassette-type noise barriers are generally already provided with corresponding cavities for absorption material, the shape of the soundproofing device can be easily combined with this design of the noise barrier 5. Likewise, a cassette-type noise barrier can of course be realized with only a first soundproofing device, and the second soundproofing device can be replaced with a conventional absorption material.When using two soundproofing devices 1 on opposite sides of the noise barrier 5, these can, for example, be adjusted so that they particularly effectively reduce both the reflection of sound on the side of the noise barrier 5 facing the noise source and the transmission through the noise barrier 5 on the side facing away.

[0077] In the following, some other forms of noise barriers 5 equipped with sound insulation devices 1 will be described.

[0078] Fig. 14a shows a noise barrier 5 in sandwich construction, consisting of two support panels 11, between which a sound insulation device 1 is arranged. Since the sound insulation device 1 increases the sound absorption within the noise barrier due to its stop band, the support panels 11 can be thinner and lighter than the components of conventional noise barriers, or can be made of a material with poor sound absorption, such as glass. Instead, or in addition, the sound insulation device can also be attached to an outer side of a support panel 11, as shown in Fig. 14b. This is particularly useful if the sound insulation device 1 is designed to reduce the transmission or reflection of sound in or from a specific direction. To enable a lightweight construction, a noise barrier 5, as shown in Fig.14c, also consists of a single carrier plate 11, to which a soundproofing device 1 is applied. In particular, the soundproofing device 1 can also be integrated into the carrier plate or manufactured together with it. For such a noise barrier, a soundproofing device such as that shown in Figs. 9a and 9b or 10a and 10b is suitable, for example.

[0079] A noise barrier 5 can also be provided with a soundproofing device 1 only in certain areas. For example, Fig. 15a shows a noise barrier 5 that has a solid lower section and a thinner upper section. However, to improve the absorption properties of the upper section, this section is provided with a soundproofing device. It is also possible, as indicated in Fig. 15b, to provide a section of the noise barrier 5 with a soundproofing device 1 that is tuned to a frequency range in which this section of the noise barrier 5 is not suitable for reducing sound propagation due to its design, wall thickness, or material.

[0080] Fig. 16a shows a noise barrier 5 provided with two sound insulation devices 1 in different areas of the noise barrier 5. The two sound insulation devices 1 can be differently tuned to compensate for differences in wall thickness, design, and material of the area of ​​the noise barrier 5 to which they are applied.

[0081] Fig. 16b shows a noise barrier 5 equipped with a window to break up the otherwise solid form of the wall. To ensure that this window still contributes to reducing sound transmission, it is equipped with a soundproofing device 1. Thus, the soundproofing device 1 can be used to create more aesthetically pleasing noise barriers 5 without compromising their functionality.

[0082] The soundproofing device 1 can also be combined with other known noise protection concepts, for example, with the noise barrier 5 shown in Fig. 17a with an angled attachment, which serves to influence the diffraction angle of the sound waves diffracted at the upper edge of the noise barrier 5. Fig. 17b shows a complete noise protection enclosure 12, which is provided with soundproofing devices 1 on its exterior to reduce sound transmission.

[0083] Likewise, corresponding soundproofing devices 1 can also be applied to other components intended to spatially and acoustically separate two areas. For example, such soundproofing devices can be used for passive noise protection in building facades or soundproof windows. Other possible areas of application in construction include drywalls and doors. Soundproofing devices 1 can also be attached to machine housings. Mobile noise barriers equipped with soundproofing devices 1 can be used on construction sites, or corresponding partition walls in open-plan offices or factories. The embodiments shown here are therefore not limiting. In particular, these embodiments can be combined with one another to achieve additional effects.It will be obvious to a person skilled in the art that changes may be made to these embodiments without departing from the basic principles of the subject matter of this patent application, the scope of which is defined in the claims.

Claims

Claims: A soundproofing device (1) for reducing sound transmission, comprising an arrangement of mechanical resonators (2), each containing at least one vibrating mass (3) and a spring element (4), wherein the mechanical resonators (2) are tuned to each have at least one natural frequency in a relevant frequency range, and wherein the arrangement of mechanical resonators (2) is configured to generate at least one stopband for wave propagation in the relevant frequency range. A soundproofing device (1) according to claim 1, characterized in that the arrangement of the mechanical resonators (2) is periodic. A soundproofing device (1) according to claim 1 or 2, characterized in that the distance between the mechanical resonators (2) is less than half a wavelength of the first relevant frequency.A soundproofing device (1) according to one of the preceding claims, characterized in that, due to the periodic arrangement of the mechanical resonators (2), at least one further stop band for elastic wave propagation is formed at at least one further frequency as a result of Bragg scattering. A soundproofing device (1) according to one of the preceding claims, characterized in that the arrangement of mechanical resonators (2) is such that and / or the mechanical resonators (2) are such that several stop bands for wave propagation are generated.

6. Soundproofing device (1) according to one of the preceding claims, characterized in that the individual mechanical resonators (2) have a slightly different frequency tuning, so that the at least one stopband is broadened.

7. Soundproofing device (1) according to one of the preceding claims, characterized in that the mechanical resonators (2) additionally comprise a damping element (6, 7, 8).

8. Soundproofing device (1) according to any of the preceding claims, characterized in that the mechanical resonators (2) are designed in such a way that their frequency tuning cannot be influenced by weather or by external mechanical influence.

9. Soundproofing device (1) according to one of the preceding claims, characterized in that at least one of the mechanical resonators (2) is designed as cup resonators, wherein a cup resonator comprises an elastic membrane as a spring element (4) which forms an externally closed cup, and a mass (3) arranged in this cup.

10. Soundproofing device (1) according to claim 9, characterized in that the cup and mass (3) are made in one piece.

11. Soundproofing device (1) according to claim 9, characterized in that the cup and mass (3) are designed as separate parts and the mass (3) is fixed in the cup.

12. Soundproofing device (1) according to one of the preceding claims, characterized in that at least one of the mechanical resonators (2) is designed with at least one elastomer or metal cushion as a spring element (4).

13. Soundproofing device (1) according to one of the preceding claims, characterized in that at least one of the mechanical resonators (2) is designed with a sheet metal strip as a spring element (4).

14. Soundproofing device (1) according to one of the preceding claims, characterized in that at least one of the mechanical resonators (2) is machined in one piece from a surface and is defined by recesses.

15. Soundproofing device (1) according to one of the preceding claims, characterized in that at least one of the mechanical resonators (2) is designed with a prestressed steel cable as a spring element (4) on which the vibrating masses (3) are suspended.

16. Soundproofing device (1) according to one of the preceding claims, characterized in that at least one of the mechanical resonators (2) is designed with an absorption material as a spring element (4) in which the vibrating masses are embedded.

17. Soundproofing device (1) according to one of the preceding claims, characterized in that the mechanical resonators (2) additionally comprise an energy conversion element.

18. Soundproofing device (1) according to one of the preceding claims, characterized in that the mechanical resonators (2) additionally comprise an element for adjusting the at least one natural frequency.

19. Noise barrier (5) comprising at least one soundproofing device (1) according to one of the preceding claims.

20. Noise barrier (5) according to claim 19, characterized in that the soundproofing device (1) is arranged at least partially on an outside surface of the noise barrier (5).

21. Noise barrier (5) according to claim 19, characterized in that the noise barrier (5) has a sandwich structure made of several layers (11), wherein the soundproofing device (1) is arranged in an inner layer of the sandwich structure.

22. Noise barrier (5) according to claim 19, characterized in that the noise barrier (5) has a sandwich structure of several layers (11), wherein several soundproofing devices (1) are arranged in different layers of the sandwich structure.

23. Noise barrier (5) according to claim 19, characterized in that the soundproofing device (1) is arranged in a recess of the noise barrier (5).

24. Noise barrier (5) according to one of claims 19 to 23, characterized in that the noise barrier (1) consists of a transparent medium.

25. Noise barrier (5) according to one of claims 19 to 23, characterized in that the soundproofing device (1) is manufactured permanently installed with the noise barrier (5).

26. Component for reducing sound propagation between two areas, comprising a soundproofing device (1) according to any one of claims 1 to 17.

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