CN216388742U

CN216388742U - Acoustic insulation panel and assembly comprising an acoustic insulation panel

Info

Publication number: CN216388742U
Application number: CN201990001261.1U
Authority: CN
Inventors: 克莱芒·拉加里格; 达米安·勒科克
Original assignee: Matt Acoustics
Current assignee: Matt Acoustics
Priority date: 2018-12-21
Filing date: 2019-12-23
Publication date: 2022-04-26
Anticipated expiration: 2029-12-23
Also published as: KR20210001934U; ES1275530U; ES1275530Y; DE212019000455U1; FR3090981B1; WO2020128103A1; FR3090981A1

Abstract

The utility model relates to an acoustic insulating panel (10) and to an assembly comprising such a panel, comprising a layer (10a) having a first face (10c) and a second face (10d), said layer (10a) being formed from a material having a Young's modulus between 1kPa and 100MPa and a density of 5kg/m³And 1000kg/m³And comprising a plurality of diffusers (10f) interposed between a first face (10c) and a second face (10d), the diffusers (10f) having a Young's modulus greater than that of the material of the layer in which the diffusers (10f) are arranged parallel to the first faceThe directions of the face (10c) and of the second face (10d) form a periodic array of cells positioned side by side, wherein each cell (10e) comprises at least one diffuser (10f), the panel further comprising sealing means (16) designed to prevent the entry of air from outside the panel into said layer (10 a).

Description

Acoustic insulation panel and assembly comprising an acoustic insulation panel

Technical Field

The present invention relates to an acoustic insulation panel and an assembly comprising an acoustic insulation panel, which make it possible to limit the transmission of sound waves between the two faces of said panel.

Background

Among the known acoustic attenuation solutions, therefore, there are single-wall panels whose principle of isolation is described by the law of mass which states that the greater the mass and thickness of the wall, the better the isolation. These walls are often combined with absorptive acoustic materials, such as porous materials, which make it possible to shorten the reverberation time in the transmission chamber. By shortening the reverberation time, the sound level in the transmitting chamber and thus the sound level in the receiving chamber can be slightly reduced. In recent years, there are many acoustic products of this type on the market, in particular machine housings or elements for separating work tables in factories.

At present, the materials used for acoustic absorption are mostly materials with a porous matrix, such as the so-called cellular materials (polyurethane foams, etc.) or the so-called fibrous materials (glass wool, palm fibers, etc.). The incorporation of these materials in the acoustic panel is readily accomplished. In addition, the panel thus obtained is light in weight and has good performance for acoustic attenuation of most frequencies of the audible spectrum.

However, these materials do not attenuate very low frequency sounds very well, that is, for thin panels of thickness on the order of 2cm to 5cm, sounds of frequency on the order of 50Hz to 500Hz, which for example correspond to the noise emitted by an idling engine. This is especially true for frequencies where the corresponding wavelength is greater than four times the material thickness.

All single wall panels show the same behavior and the same insulating curve. The scale of the curve depends only on the density and thickness of the sheet. Therefore, there is a problem that an extremely heavy and thick wall is required in order to have strong insulation. Thus, heavy objects (usually bituminous materials) are added in the walls or even in the porous material. However, such porous materials are very ineffective unless they can be made to a thickness of several tens of centimeters.

For transport purposes and in the building field, this cannot be envisaged, since the real purpose is to make the structure light and as thin as possible.

Also known are double-walled panels comprising two sheets between which a sheet of air or porous material is disposed. The acoustic isolation of this type of panel is at the breathing frequency (breathing frequency) f_respAnd a critical frequency f_cExhibits two local minima. These minima are problematic because they reflect the weakness in acoustic isolation. The critical frequency lies in the high frequency (a few kHz) and corresponds to the coincidence of the vibration wavelength of the wall with the acoustic wavelength reflected by the strong transmission of acoustic energy. The breathing frequency is in itself in a very low frequency (between 50Hz and 500 Hz) and is associated with mass-air-mass resonance (mass-air-mass resonance) of the wall: the sheets oscillate in anti-phase under the stiffness of the compressible acoustic medium in the cavity. In addition to these two frequencies, the double wall has interesting behavior from an acoustic point of view, since among these frequencies the isolation slope is +18dB/Oct (decibel/octave) and then +12 dB/Oct. Thus, at medium and high frequencies (between 500Hz and 4000 Hz), the isolation performance is significant. It is important to note that such systems have not only acoustic but also vibrational behavior. In fact, on the source side, the acoustic waves reach the first sheet, which will be mechanically stressed and deformed (there are acoustic waves in the solid, also called vibrations), and will then radiate the acoustic waves in the air cavity. The acoustic waves in the cavity will then excite the second sheet, which will vibrate and radiate in the receiving part, which is desired to be isolated from the source. Typically, a porous material is added to the cavity toThe acoustic mode in the cavity is attenuated without affecting the vibration of the sheet. Furthermore, from a weight and thickness point of view, the sheets are optimized to have the lowest possible breathing frequency (typically below 100Hz) and the highest possible critical frequency (between 2500Hz and 5000 Hz). It will be appreciated that single or double wall panels encounter similar difficulties with respect to the volume and weight of the panel in order to produce acceptable acoustic insulation.

Thus, a double-walled panel makes it possible to obtain significant acoustic insulation at medium and high frequencies, but still exhibits low acoustic insulation at low frequencies, in particular due to the breathing frequency. As with single-walled panels, this solution consists in increasing the weight of the outer walls or their thickness, which is obviously problematic.

In order to solve the problem of acoustic isolation, i.e. the problem of reducing the noise transmission of the sound source, and to overcome the difficulties of the above-mentioned techniques, the possibility of using a photonic crystal (sonic crystal) technique is currently being studied. This technique consists in arranging the acoustic diffusers at predetermined intervals with respect to each other so as to block the frequency range of the acoustic waves emitted by the source, the wavelength of which is proportional to the periodicity (pitch) of the diffusers.

In order to work effectively, these phononic crystals require a plurality of rows of diffusers, which can create very thick barriers, between 50cm and 2m thick, which limits them to outdoor applications such as, in particular, for noise-resistant barriers, for example for acoustic isolation of railway lines or motor vehicle lanes, in particular on both sides of highways. In one known application, the diffuser consists of a resonator surrounded by a porous material to increase the effective frequency range (see also

Et al, "Noise characterization of a sonic crystalline silicon designed used a triangular lattice encoding to the standards EN1793 (-1; -2; -3)" (according to standard EN1793 (-1; -2; -3) Noise certification for phononic crystal acoustic shielding using a trigonal lattice design), EuroNoise, 2015). Furthermore, it will be noted that the diffuser is expensive and complex to implement. In factEach diffuser is made up of three elements, i.e. a metal tube coated internally with rock wool, the whole tube being covered with a micro-perforated aluminium tube. In fact, such assembly is complicated and microperforated tubes are difficult to obtain without existing commercial proposals. Therefore, installing anti-noise walls at distances exceeding one meter would be very expensive and not guarantee effectiveness, since technical solutions of this type are still under development.

It is also known from document US2011/0100746 to use rubber strips perforated by holes and filled with fluid (air or water). This material serves to join two media and prevent vibration from being transmitted from one medium to the other. Which is optimized to handle compression waves propagating along the direction of the hole stack. The frequency range of the processing is too high to be applied to the low frequency isolation problem. This is particularly relevant in relation to the choice of materials and their mechanical properties, which prevent extended applications to lower frequencies.

Finally, document FR3010225 discloses a material having an absorbent unit comprising a porous layer and an acoustic resonator arranged between the two faces of the porous layer. When they are used in acoustic isolation applications, only the resonance of the resonator is active and allows improved isolation in a very low frequency range. This may be useful for dealing with double-walled breathing frequencies, but does not add isolation over a wide frequency band. The size of the resonator for handling low frequencies may also be critical and may quickly reach several centimeters in diameter and several meters in length. In transportation applications, this is problematic.

The object of the present invention is, inter alia, to provide a simple, effective and economical solution to these problems.

SUMMERY OF THE UTILITY MODEL

To this end, an acoustic insulation panel is proposed, comprising a layer having a first face and a second face and comprising a plurality of diffusers interposed between the first face and the second face, the diffusers being arranged in the layer so as to form a periodic array of cells positioned side by side in a direction parallel to the first face and to the second face, wherein each cell comprises at least one diffuser, the panel further comprising sealing means able to prevent the ingress of air into the layer from outside the panel.

The panel according to the utility model is a vibro-acoustic metamaterial and is therefore composed of a solid elastic matrix and of a diffusely rigid inclusion, i.e. a vibration diffuser (instead of an acoustic resonator) positioned within the matrix. The present invention may be applied to a single wall, or to the interior of a double wall, rather than the traditional porous materials described previously. The benefit is the ability to handle low frequencies for thin thicknesses, and relatively low added weight where conventional materials require large thicknesses and significant added weight.

Sonication within the material proceeds differently than in the prior art. The proposed panel construction makes it possible to have a low propagation velocity of the vibration wave in the layer/matrix, more particularly when the young's modulus is sufficiently low and in particular between 1kPa and 100 MPa. The low propagation speed of the mechanical waves in the layers of the panel implies short wavelengths and therefore small diffusive inclusions are required, so that a panel with a small thickness compared to the prior art is obtained. By successfully converting the low frequency sound waves (long wavelengths) into vibration waves (short wavelengths) in the material, they can thus be blocked at the diffuser, preventing them from passing through the panel, i.e. in the direction through the first and second faces. Furthermore, the density of the layer may be in the range of 5kg/m³And 1000kg/m³In the meantime.

Thus, due to the intention of mounting the panel on a support such as a sheet, the support may be used as an attachment support on a wall or any other wall to be acoustically isolated, which will increase the acoustic isolation of the sheet with a thin super-thickness (overthickness). The super-thick portion may be disposed on the side of the sound emitting source or on the opposite side. However, it will be more effective if it is placed on the source side, because it is easier to attenuate the sound waves before they reach the supporting sheet, rather than trying to dampen the vibrations of the sheet that have already come into play. In fact, for the purpose of fixing to said support, it is possible to provide the face intended to be fixed to the support with an adhesive film.

In order to obtain a vibrating acoustic panel that is effective in the audible acoustic range (20Hz to 20kHz) and in particular in the frequency range between 50Hz and 4000Hz, it is therefore necessary to combine three elements: a matrix or flexible material with a low young's modulus, a periodic array of cells, each cell comprising at least one diffuser and ensuring that airborne sound waves are indeed converted into elastic waves in the material. Without one of them, the technique does not work at the industrial frequencies of interest (between 50Hz and 4000 Hz). The elements are the same here.

The addition of the air seal allows all of the acoustic energy to be transmitted to the panel mechanically.

The applicant of the present application therefore proposes a panel which avoids the use of traditional absorbent materials, in particular porous and ultra-porous materials, which are known to be effective in terms of acoustic absorption (very little reflection), but very poor in terms of isolation (waves easily pass through the material). When the material is porous, the addition of a gas-tight membrane on the surface of the layer removes the absorption properties of the porous material, but makes it possible to excite only the skeleton. In this way, very little acoustic energy is transmitted through the air contained in the pores of the material. This is a fundamental difference with respect to other existing acoustic superporous materials, especially those in patent US9818393B2, in which the porous material is considered to be the equivalent fluid in which acoustic energy propagates and dissipates, and the vibration of the skeleton is low. In other words, most of the acoustic energy propagates in the pores, that is, in the skeleton of the pores.

The young's modulus of the diffuser may be greater than the young's modulus of the material of the layer, and is preferably very significantly greater, that is to say at least ten times greater.

According to another feature, the layer is a porous matrix, such as for example polyurethane foam, foam with shape memory, polyester fibres and polyethylene foam. The porosity of the porous matrix may be between 0.5 and 0.99. In particular, the porosity may be between 0.7 and 0.99. The increase in porosity makes it possible to provide flexibility to the matrix of the material, thus increasing the attenuation of very low frequencies. The substrate may have open or closed cells.

When using a porous matrix with open pores, the sealing means may for example comprise an air barrier film covering the first side of the layer. The thickness of the film may be at least equal to 0.05 mm. This minimum thickness makes it possible to ensure a solid state of the film. The thickness of the air barrier film may be less than 0.5 mm. Indeed, beyond this thickness, the film becomes too heavy and becomes sheet-like.

In a particular embodiment, the membrane may take the form of a membrane having tension on a first side of a layer comprising (i.e. housing) the acoustic diffuser.

The sealing means may have a thickness of at least 50000N.m^-4S air passing resistance. Below this value, the air resistance is too low and leaks are created, which do not provide good acoustic isolation.

The layer may be a non-porous substrate, for example a rubber based non-porous substrate. In this case, the layer need not have a hermetic film as described above if the sealing of the non-porous substrate is sufficient. Obviously, it should be understood that the layer housing the diffuser may have a two-material structure, that is to say one or more underlying layers. When the underlying layer for first receiving the acoustic wave is not airtight (e.g., an underlying layer with a porous matrix), then an air barrier film as previously described must be added. The term lower layer herein means a layer of a given thickness of material containing the diffuser, and the term "lower" does not mean a relative arrangement.

In a given embodiment, said diffuser is a straight cylinder, the generatrix of which is substantially parallel to said first and second faces of the layer of material containing the diffuser. The first and second faces may be flat. All diffusers may be identical. They may have a hollow, solid or internal structure with internal reinforcing walls.

The diffuser may extend the entire length of the panel and not have any openings throughout its dimension extending from the first end to the opposite second end.

The young's modulus of the diffuser may be at least ten times the young's modulus of the layer. This value makes it possible to ensure a sufficiently large rigid contrast between the intrinsic structure of the layer and the diffuser, so as to produce a Bragg stop band.

Diffusers made of metals such as aluminum, steel or copper may be used. The diffuser may also be made of a polymeric material of the PVC, polypropylene, PET, PETG, acetate, polycarbonate type. Other materials such as paper, rolled paperboard, kraft paper (kraft paper), or phenolic paper are also suitable.

According to a feature of the utility model, when the spacing α between the elements is equal to the thickness of the panel, the spacing can then be defined as

Wherein f is₀Represents the center frequency of the target frequency range (or frequency range of interest), and V_TRepresenting the velocity of the shear wave in the material. Each cell may include one or more diffusers, a given diffuser of a cell being spaced from a corresponding diffuser in an adjacent cell by a value a. The panel thus has the particular feature of comprising cells of square cross-section. When a source emits an acoustic wave in air, the mechanical wave propagates in two directions: longitudinal waves (compressional waves) and transverse waves (shear waves). In the panel, the shear wave is the slowest. Although it is theoretically necessary to make an accurate dimensioning of the diffuser for optimum isolation, the applicant of the present application notes that a significant effect can be obtained when the period is equal to half the previously indicated shear wavelength.

In yet another embodiment according to the utility model, the layer of material may comprise at least one region having a thickness with a positive young's modulus gradient oriented from the first face towards the second face. Thus, the gradient may extend from the first side to the second side or even only over a portion of the layer. Thus, various combinations are possible. The term "positive gradient" denotes an increase in young's modulus.

The utility model also relates to an assembly comprising a panel, the second face of which is pressed onto the face of the support sheet.

The young's modulus of the support sheet is preferably greater than the young's modulus of the layer.

The young's modulus of the support sheet may be at least ten times the young's modulus of the layer.

The following combinations prove particularly effective for absorbing sound waves in the audible range: a layer having a porous matrix with a diffuser, said layer having a first face covered with an air barrier film and a second face pressed against a support sheet, wherein the young's modulus of the diffuser and the young's modulus of the support sheet are substantially greater than the young's modulus of the layer.

It should be noted that the young's modulus of the diffuser and the young's modulus of the support sheet may be substantially the same.

Drawings

Figure 1 shows a cross-sectional view of a first embodiment of a panel according to the utility model;

FIG. 2 is a graph of the trend of vibration transmission in dB as a function of frequency and at multiple angles of incidence on the panel of FIG. 1;

FIG. 3 is a graph showing transmission loss (in dB) as a function of frequency (logarithmic scale) for the panel of FIG. 1 and a reference panel;

FIG. 4 shows a cross-sectional view of a second embodiment of a panel according to the utility model;

FIG. 5 is a graph of the trend of vibration transmission in dB as a function of frequency and at multiple angles of incidence on the panel of FIG. 4;

FIG. 6 is a graph showing transmission loss (in dB) as a function of frequency (logarithmic scale) for the panel of FIG. 4 and a reference panel;

FIG. 7 illustrates a plurality of diffusers for use with a panel according to the present invention;

fig. 8 shows another possible embodiment of a panel according to the utility model.

Detailed Description

Fig. 1 and 4 show a first embodiment of an assembly 10 comprising a panel 10a according to the utility model and a second embodiment of an assembly 12 comprising a panel 12a, respectively.

In the two different embodiments presented, the

panels

10a, 12a are carried by a supporting sheet 14, in the different examples the sheet 14 is made of wood. The weight of the sheet was 3.5 kg. The use of an absorbent sheet such as wood makes it possible to enhance the noise-reduction index (noise-reduction index), thereby enhancing acoustic insulation.

The

panels

10a, 12a comprise

layers

10b, 12b, the

layers

10b, 12b comprising a

first face

10c, 12c and a

second face

10d, 12d opposite each other. The second faces 10d, 12d are brought into contact with the support sheet 14, for example using an adhesive means such as a bonding film. As shown in fig. 1, the

layers

10a, 12a comprise several units arranged side by side. It should be understood that here these are not

units

10e, 12e that are structurally different from each other. Each

cell

10e, 12e includes a diffuser 10f, 12f1, 12f2, and all

cells

10e, 12e are identical. Thus, with respect to FIG. 1, the diffusers 10f form a row in a direction parallel to the first and second faces. With respect to FIG. 4, the diffusers 12f1 form a first row in a direction parallel to the first and second faces, and the diffusers 12f2 form a second row in a direction parallel to the first and second faces. The second row of diffusers 12f2 is disposed between the first row 12f1 and the second face 12 d.

In fig. 1 and 4, the diffuser is shown in cross-section. The diffusers 10f, 12f1, 12f2 have an elongated form in a direction substantially at right angles to the cross-sectional plane and extend parallel to the first and

second faces

10c, 10d, 12c, 12 d. Here, the diffusers 10f, 12f1, 12f2 are straight cylinders, the generatrices of which are substantially parallel to said first and

second faces

10c, 10d, 12c, 12d of the

layers

10a, 12a of material housing the diffusers 10f, 12f1, 12f 2. Other forms of straight cylinders will be shown in figure 8.

In order to obtain good attenuation of low frequencies of the audible range, the

acoustic insulation panels

10a, 12a are such that the layer housing the diffuser consists of a Young's modulus between 1kPa and 100MPa and a density of 5kg/m³And 1000kg/m³The material in between. Furthermore, the

layers

10a, 12a comprise sealing means capable of preventing the entry of air into said layers from the outside of the panel. These seals are shown in FIG. 1 as being in layers 10a, 12aThe dotted line 16 on the first face. These sealing means 16 may be an integral part of the

layers

10a, 12a when the construction of the layers allows such air sealing, or the sealing means 16 may be formed by an air barrier film covering the first side of the layers when the material does not inherently ensure the air sealing function. Thus, in the latter case, line 16 represents the hermetic membrane. The hermetic thin film may be deposited on the first side of the layer 10 a.

The

panels

10a, 12a are constructed in such a way that they are constructed with: a flexible substrate having a low Young's modulus; a periodic array of

cells

10e, 12e comprising at least one diffuser 10f, 12f1, 12f2 (a single diffuser in FIG. 1, and two diffusers in FIG. 4); and an air seal which makes it possible to ensure the conversion of the airborne sound waves emitted by the source into sound waves in a solid, so that the panel makes it possible to obtain a good attenuation at the industrial frequencies of interest, i.e. at frequencies between 50Hz and 4000 Hz.

Thus, any material having a low young's modulus and effective density may be used. This makes it possible to obtain a low mechanical wave propagation velocity: (<<340 m/s). The associated wavelength is then smaller than in air, which means a small spatial period of the diffuser (a few centimeters) to obtain the effect at low frequencies. Young's modulus of between 1kPa and 100MPa and density of 5kg/m³And 1000kg/m³Preferably between 10kg/m³And 100kg/m³The material in between satisfies this condition.

The material of the

layers

10b, 12b may have a porous matrix with open or closed cells, such as for example basotect type G + melamine foam from BASF, polyurethane foam, foam with shape memory, foam comprising polyester fibers, Stratocell Whisper foam, polyester foam, ethylene-propylene-diene monomer foam. Foams, such as those made from polyethylene, can be obtained by a cross-linking process. These foams have an internal structure with open cells. Obviously, the foam may be obtained by a method other than the crosslinking method.

The porous matrix may have a porosity between 0.5 and 0.99. In particular, the porosity may be between 0.7 and 0.99. The increase in porosity makes it possible to provide flexibility to the matrix of the material, thus increasing the attenuation of very low frequencies.

It is important that all of the acoustic energy be mechanically transmitted to the material. If it is a homogeneous material, this transmission occurs naturally, but if it is a material that does not ensure such transmission, such as a porous material with open pores, the first face exposed to the sound source must be made airtight by applying a thin layer of a non-penetrating material, for example by adding an airtight film. This will prevent energy from propagating in the open pores of the material and thus prevent the propagation of sound waves according to the law of airborne acoustics. Coatings that can be used to form the hermetic film 16 are, for example: all films from 0.05mm to 0.5mm thick, in particular laminated, inlaid or textured aluminium films, polymer films, PVC, vinyl, polypropylene type films and films having a thickness of more than 50000N.m^-4S air through any material of resistance.

In the

acoustic panels

10a, 12a according to the present invention, longitudinal waves (i.e., compressional waves) and transverse waves (i.e., shear waves) are propagated. However, the applicant of the present application notes that the shear wave proves to be the slowest wave in the

panels

10a, 12 a. In order to obtain optimum acoustic isolation, whilst accurate dimensioning is theoretically mandatory, the applicant of the present application notes that it is possible to have a significant sound transmission reduction effect when the spatial separation a between the

units

10e, 12e is equal to half the shear wavelength:

wherein f is₀Is the center frequency of the frequency range to be processed, and V_TRepresenting the velocity of a shear wave in said material.

In fact, the applicant of the present application noted that a relationship can be established between the shear wave velocity in the panel and the pitch of the cells, as long as the thickness of the panel is substantially equal to the pitch between the cells. It should be noted that in the case of fig. 1, the spacing between cells (all the same) is the same as the spacing between diffusers. In the case where a cell includes a plurality of diffusers and all cells are identical, the spacing between a given diffuser and the diffuser corresponding to the given diffuser in an adjacent cell is equal to the spacing between cells.

Using this criterion makes it possible to simplify the definition of the panel, since no finite element calculations are needed to know the arrangement and dimensions of the diffuser to have good absorption properties.

In the example set forth in fig. 1, the diffusers 10f are laterally spaced apart by 6cm, and the foam is melamine with a young's modulus of 100 kPa. The diffusers all had the same diameter, i.e. 1.2cm, and the support sheet was made of wood with a young's modulus of 1GPa and a thickness of 1 cm. The dimensional parameters of the acoustically isolated panel are summarized in the following table:

[ Table 1]

The graph of fig. 2 obtained through the experiment includes a plurality of curves. Each curve represents the amount of vibration transmission in dB as a function of frequency and for a given angle of incidence of the sound waves on the first face of the panel. The angle of incidence is shown on the graph. It should be noted that for low angles of incidence, the amount of transmission is low. On these curves, it can be seen that there is a low amount of vibration transmission between about 250Hz and 750Hz, so that little energy is transmitted through the layer.

The curve of fig. 3 obtained by experiment shows the transmission loss on the y-axis as a function of frequency. Curve 18 represents the transmission loss (ratio between the source-side sound intensity and the receive-side sound intensity) in the panel of fig. 1, and curve 20 represents the transmission loss in a reference panel formed from a matrix made of the same material as the panel of fig. 1 but without the diffuser and air seal.

At about 400Hz, the presence of peaks in transmission loss can be observed, extending between 300 and 800Hz, which proves the effectiveness of the proposed construction for acoustic isolation at low frequencies, that is, at audible low frequencies.

Fig. 4 shows a second embodiment of a panel 12b according to the utility model, in which each cell 12e comprises two diffusers, the cells 12e being positioned side by side to form a periodic structure. Each cell 12e includes a first diffuser having a first radius and a second diffuser having a second radius greater than the first radius. The first diffuser 12f1 is located closer to the first face 12c, while the second diffuser 12f2 is located closer to the second face 12 d. The unit 12e is periodically repeated according to the law of a given spacing α shown previously.

In this second embodiment of the panel according to the utility model the diffusers 12f1, 12f2 are laterally spaced apart by 6cm, the foam being melamine having a young's modulus of 100 kPa. Two diffusers are used and have different diameters. The support sheet was made of wood having a Young's modulus of 1GPa and a thickness of 1 cm. The dimensional parameters of the acoustically isolated panel of fig. 4 are summarized in the following table:

[ Table 2]

The graph of fig. 5 obtained by digital simulation includes a plurality of curves. Each curve represents the vibration transmission loss in dB as a function of frequency and for a given angle of incidence of the acoustic wave on the first face 10c of the panel 10 a. The angle of incidence is shown on the graph. It should be noted that for low angles of incidence, the amount of transmission is low. On these curves, it can be seen that there is a low vibration transmission between about 400Hz and 1000Hz, so that little energy is transmitted through the layer.

The curve of fig. 6 obtained by digital simulation shows the transmission loss on the y-axis as a function of frequency. Curve 22 represents the transmission loss in the panel of fig. 4, and curve 24 represents the transmission loss for the wood sheet only.

It can be seen that up to about 1000Hz, the transmission losses are greater than about 5dB for the panel according to the utility model, which proves the effectiveness of the proposed construction for low frequency acoustic isolation.

The two examples above clearly show that with the construction of the acoustic insulation panel according to the utility model, the acoustic insulation at very low frequencies can be significantly improved.

Unlike the prior art configuration, good insulation is possible even with the single row diffuser 10f (FIG. 1). This is due to the fact that there are multiple waves propagating simultaneously on a fairly thin layer. So that they have a very high probability of encountering the diffuser. To obtain even better results, the addition of several rows of diffusers 12f1, 12f2 (fig. 4) can further improve the performance of the assembly, as shown in fig. 5, where the frequency band is broadened with greater transmission amplitude. Obviously, however, it will be appreciated that this is also done at the expense of greater thickness or weight.

The following table summarizes the numerical ranges that can be used to produce the material. The variability of the parameters shown in the table below is due to the fact that: the exact geometry can only be obtained after optimization by taking into account the parameters of the substrate and the frequency range to be treated.

[ Table 3]

Use of

Software and a sizing tool was developed by the finite element method. For this purpose, the material of the matrix is considered as an elastic solid, and its equivalent mechanical parameters are entered as information. The vibration mode of a single cell is calculated for all angles of incidence, thereby making it possible to identify the stop band: there is no band of modes regardless of the angle of incidence. The geometry of the individual cells, in particular the periodicity of the tubes, can then be tuned according to the desired stop band. When the vibration composed of longitudinal wave and transverse wave in the elastic solid is not transmitted to the sheet material, the result is thatThe people are satisfied. The frequency range in which the material is effective can be modified by modifying the following parameters:

thickness of the substrate

Periodicity of the inclusions

Radius of the inclusions

Young's modulus of the matrix

Density of the matrix

Geometry of the inclusions

Material and thickness of the gastight film

-sound reduction factor of the material used for the seal.

Figure 7 shows a different form of diffuser which may be used in the present invention. The first row represents a hollow diffuser 28 in the form of a cylindrical or tubular wall. The second row represents a diffuser 30 comprising a hollow cylindrical or tubular wall 32 having an internal reinforcing wall 34 joining the inner surfaces of the cylindrical wall 32. The third row comprises a diffuser 36 with a hollow structure that houses internally a mass-spring mechanical resonator 38, i.e. a mechanical absorber, in which energy is dissipated under the resonance action of a mass-spring system (mass-black central mass and spring-inner stiffening wall). The resonator or inner mass includes an outer cylindrical wall 40, the inner surface of which is joined to the resonator 38 via a plurality of bridges 42. The principle is to connect a weight to a spring, so that the initial displacement exerted on the mass is gradually absorbed by the displacement of the mass attached to the spring. It is the dynamic absorber principle that makes it possible to process frequency bands other than the stop band, i.e. at the resonance frequency of the mass-spring system. Therefore, the working principle is different from an acoustic resonator (Helmholtz resonator) that obtains air resonance in the cavity. The fourth row represents a diffuser 44 having a hollow structure similar to the third row. However, in these embodiments, each inner mass 46 is joined to the tubular wall 48 or outer cartridge wall via a single joint bridge 50. Thus, this type of diffuser 44 has the lower stiffness of the mass 46 and bridge 50 assembly, thus allowing for better energy dissipation than the third row embodiment where each mass 38 is joined to the outer cartridge wall 40 by several bridges 42.

In the above embodiment, each of the bridges may be a flat wall extending from one end to the other end of the cylindrical wall.

Finally, fig. 8 shows a possible variant of the first embodiment, as an example. Here, each cell 24 includes two

diffusers

26a, 26b spaced apart by a distance a, the cell 24 being spaced apart from an adjacent cell by the distance a. The

diffusers

26a, 26b are here identical, but may also be different, i.e. may have different radii, different positions or even the form as shown in fig. 7.

It will be appreciated that the positioning, location and dimensions of the panels, i.e. diffusers, can be precisely defined by finite element simulations. There are therefore many possible combinations in terms of positioning, position and dimensions of the diffuser, which can have good acoustic insulation as long as the panel has the features according to the utility model.

In summary, according to the utility model, the gas-tight membrane makes it possible to create a gas-tight barrier. This is applied (by gluing or by other mechanical fixing means) to the first face of the layer housing the diffuser, in order to create a covering layer and improve the acoustic insulation (that is to say reduce the amount of vibration and acoustic transmission on either side) by combining a plurality of acoustic phenomena, of which the main two are:

generating a vibration decoupling between the incident acoustic wave and the supporting sheet by means of the porosity of the film and of the layer, the film and the layer acting as a double wall, one of which is formed by the sheet and the other by the film, the film having to have a thickness sufficiently low as previously described,

the conversion of the acoustic waves coming from the source into vibration waves (in particular transverse and shear waves) in the layer of elastomeric material, which are then blocked by the presence of the diffuser.

Claims

1. An acoustic insulation panel (10) comprising a layer (10a), characterized in that said layer comprises a first face (10c) and a second face (10d) and comprises a plurality of diffusers interposed between said first face and said second face, said diffusers (10f) being arranged in said layer so as to form a periodic array of cells positioned side by side in a direction parallel to said first face (10c) and said second face (10d), wherein each cell (10e) comprises at least one diffuser (10f), said panel further comprising sealing means (16) able to prevent the entry of air into said layer (10a) from outside said panel.

2. The panel of claim 1, wherein the young's modulus of the diffuser is greater than the young's modulus of the material of the layer.

3. The panel of claim 2, wherein the young's modulus of the diffuser is at least ten times the young's modulus of the material of the layer.

4. Panel according to any one of claims 1 to 3, in which the Young's modulus of the layer is between 1kPa and 100MPa and/or the density of the layer is 5kg/m³And 1000kg/m³In the meantime.

5. A panel according to any one of claims 1 to 3, wherein the layer (10a) is a porous matrix with open or closed cells.

6. A panel as claimed in any one of claims 1 to 3, wherein the layer is a polyurethane foam, a foam with shape memory or a polyester fibre.

7. The panel of claim 5, wherein the porosity of the porous matrix is between 0.5 and 0.99.

8. The panel of claim 5, wherein the porosity of the porous matrix is between 0.7 and 0.99.

9. A panel as claimed in any one of claims 1 to 3, wherein the layer is a non-porous matrix.

10. A panel as claimed in any one of claims 1 to 3, wherein the layer is a rubber-based non-porous matrix.

11. A panel as claimed in any one of claims 1 to 3, wherein the diffuser (10f) is a cylinder of straight cylinder whose generatrix is substantially parallel to the first (10c) and second (10d) faces of the layer (10a) of material containing the diffuser (10 f).

12. A panel as claimed in any one of claims 1 to 3, wherein all the diffusers (10f) are identical.

13. A panel as claimed in any one of claims 1 to 3, wherein the diffuser (10f) has an internal structure that is hollow, solid or with internal stiffening walls.

14. A panel as claimed in any one of claims 1 to 3, wherein said sealing means comprises an air-isolating film covering said first face (10c) of said layer (10 a).

15. The panel of claim 14 wherein the air barrier film has a thickness at least equal to 0.05 mm.

16. The panel of claim 15 wherein the air barrier film has a thickness of less than 0.5 mm.

17. A panel as claimed in any one of claims 1 to 3, wherein the sealing means has a thickness of at least more than 50000n.m^-4S air passing resistance.

18. A panel as claimed in any one of claims 1 to 3, wherein the spacing a between the cells is such that

Wherein f is₀Represents the center frequency of the target frequency range and V_TIs the velocity of the shear wave.

19. A panel as claimed in any one of claims 1 to 3, wherein said layer of material comprises at least one zone having a thickness with a positive young's modulus gradient oriented from said first face (10c) towards said second face (10 d).

20. An assembly comprising a panel as claimed in any one of claims 1 to 19 wherein the second face is pressed against a face of a support sheet.

21. The assembly of claim 20, wherein the young's modulus of the support sheet is greater than the young's modulus of the layer.

22. The assembly of claim 21, wherein the young's modulus of the support sheet is at least ten times the young's modulus of the layer.