EP0817164B2 - Noise absorbing structures and walls made therefrom - Google Patents

Description

The invention generally relates to structures of noise absorption and walls formed at means of these structures and more particularly such light and compact structures, applicable especially in the aeronautical industry for the equipment of reactors, their nacelles and cabins of aircraft, in the transportation industry, in the industry of the building, etc ...

We have already proposed, in the Patent Application French n ° 94 00539 (published under n ° 2 715 244) lightweight noise absorption structures that include each a support frame on which is fixed and stretched a waterproof membrane, and plates arranged under the membrane to form with them a passive air-laminated shock absorber. The incidence of waves acoustic on the membrane, on the side opposite said plates, causes a vibrational deformation of the membrane which results in laminar flow of air between the membrane and the plates and therefore by a energy absorption. When the acoustic impedance of such a structure is correctly adapted to waves incident acoustics, a large part of the energy of these acoustic waves is absorbed by the structure in a relatively wide frequency band.

The present invention aims to provide important improvements to these structures.

It relates to light structures of the type mentioned above and whose acoustic impedances can be modified, adjustable or controllable and likely to follow changes in the noise sources to be absorbed.

It also relates to light structures of the aforementioned type, comprising modification means, adjusting or controlling their impedances acoustic, which are themselves controllable by a information processing system.

It also relates to light walls and thin, made by juxtaposition and assembly of these structures.

Its purpose is still to compensate influences of pressure and temperature variations exterior on the membrane of the structure noise absorption.

To this end, it offers an absorption structure noise including a support frame on which is stretched and fixed a waterproof membrane of which the outside face of the frame receives acoustic waves, a gas such as air filling a volume delimited by the frame and the membrane, and energy dissipation means housed in this volume, characterized in that the means of dissipation are gas rolling type, electrostatic type or of the electromagnetic type and are modifiable, adjustable or controllable for modification or adaptation of the acoustic impedance of said structure with the characteristics noise to absorb, the above structure is closed so waterproof and contains an expandable volume element and contractile such as a balloon or a bellows for example, filled with air and communicating with the outside through an orifice of static pressure equalization, this occupying element a significant fraction of the volume of said structure.

The structures according to the invention, thanks to the fact that their acoustic impedances are changeable or adjustable, can be designed or adjusted to absorb incident noise or to deflect it by reflection, by example according to the positions they occupy in a noise absorption or protective wall against noise.

In a first embodiment, the energy dissipation means are of the rolling type gas and include plates arranged inside from the frame, a short distance from the membrane, and means for modifying this distance.

In another embodiment, the means at gas rolling dissipation include at least a gas flow passage connecting a chamber closed delimited inside the frame by the membrane to another room located inside said structure.

For example, this passage can be a conduit formed between two superimposed plates associated with means for modifying or adjusting the distance between them for modification or adjustment of the section of passage of the conduit.

According to another embodiment, the gas rolling dissipation means include rods carried by the membrane and extending perpendicularly to it inside the frame in fixed tubes which are closed at their opposite end to the membrane and which delimit with the rods of the conduits gas rolling annulars.

According to yet another embodiment of the invention, the energy dissipation means include electrode plates arranged in parallel to the membrane at a distance from it, and at least another electrode formed on the membrane and connected with said plates to polarization means such that a direct current source associated with a circuit electrical or electronic including elements of energy dissipation by Joule effect.

For example, the membrane may have one or more metallized zones opposite the plates aforementioned electrodes, or else it is made in an electrically charged plastic, to which case the polarization means are not necessary.

Elements of energy dissipation by effect Joule include for example an electrical resistance, advantageously adjustable, the structure according to the invention then comprising controlled means of adjustment of the value of this resistance for adaptation acoustic impedance.

According to another embodiment, the energy dissipation means are of the electromagnetic type and include electrical conductors displaced by the membrane in relation to elements magnetic carried by the frame or made up by it, the aforementioned electrical conductors comprising for example windings connected to the membrane or one or more printed electrical circuits or deposited on the membrane.

Alternatively, a membrane can be used magnetic displaceable with respect to an electrical circuit.

Each structure of the aforementioned type is intended to be juxtaposed and assembled to a plurality of structures of the same type to form a flat or curved wall, convex or concave in which the structures have similar or different acoustic impedances to absorb noise or deflect it by reflection According to the case.

In such a wall, the means of dissipation energy of at least some of the structures are associated to means for controlling, adjusting or control themselves controllable by a processing system some information.

It is thus possible, in particular, to adapt the impedances acoustics of some or all parts the parts of a wall to account for a modification or an evolution over time of the characteristics noise to absorb.

• la figure 1 est une vue schématique en perspective avec arrachement partiel d'une structure d'absorption de bruit selon l'invention ;
• la figure 2 est une vue schématique en coupe selon la ligne II-II de la figure 1 ;
• la figure 3 est une vue schématique partielle en perspective d'une variante de réalisation ;
• les figures 4 à 13 représentent schématiquement divers modes de réalisation des moyens de dissipation d'énergie.

The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of example with reference to the appended drawings in which:

• Figure 1 is a schematic perspective view with partial cutaway of a noise absorption structure according to the invention;
• Figure 2 is a schematic sectional view along line II-II of Figure 1;
• Figure 3 is a partial schematic perspective view of an alternative embodiment;
• Figures 4 to 13 schematically represent various embodiments of the energy dissipation means.

The noise absorption structure according to the invention, a first embodiment of which is shown by way of example in FIGS. 1 and 2, essentially comprises a thin gas-tight membrane 10 which is stretched and fixed on the upper face of a frame support 12, the upper part of which is formed with partitions perpendicular to the membrane and whose part lower 16 has a parallel bottom wall 18 to the membrane.

The membrane 10 can be produced in particular plastic, elastomer, metal or in any material allowing a membrane to be produced thin enough and flexible to be deformable by acoustic waves to absorb. This membrane being fragile, acoustically transparent means (not shown) are provided to cover and protect it external mechanical attack, these means being for example constituted by a metallic fabric associated with a layer of glass wool or the like.

The support frame 12 is made of any material rigid suitable, in particular of metal or material plastic, depending on the applications to which the structure according to the invention is intended.

The membrane 10 can be fixed on the frame 12 by its edges 20 folded over the periphery of the part upper part of the frame 12. An surround 22 can be attached to the periphery of the frame 12 as shown schematically in Figure 1 to ensure the connection structures between them, for example thanks to attachment or assembly means 24 such as tenons and dovetail grooves.

When the structure according to the invention forms a waterproof enclosure, can be provided at the bottom of frame 12, as shown diagrammatically in FIG. 2, an element 26 liable to contract and expand according to variations in pressure static and / or temperature outside the structure of noise absorption according to the invention, this element 26 can be constituted by a flexible balloon or a bellows connected to the outside by a passage or orifice 28 of static pressure equalization, crossing for example the bottom wall 18 of the frame 12.

This element 26 occupies a relatively significant volume delimited by frame 12 and the membrane 10, for example about a third of this volume. When pressure or temperature increases or decreases outside the structure, the pressure or the gas temperature increases or decreases so corresponding to the interior of element 26 and compensates at least partially the pressure variations at inside the structure, which makes it possible to membrane 10 almost insensitive to variations in external static pressure and temperature.

In addition, when the internal surface of a duct fluid passage comprises structures according to the invention or is formed of such structures, the elements 26 allow each structure to be adapted to changes static pressure in the duct.

The membrane 10 can be fixed by gluing on the upper peripheral part of the frame 12, as already indicated, as well as on the upper edges of the partitions internal 14 of frame 12.

Alternatively, and as shown schematically in FIG. 3, the internal partitions 14 of the frame 12 can be replaced by perpendicular studs 30 at the membrane and on whose ends the membrane can be fixed by gluing.

The studs 30 can be carried by a plate openwork 32, by a grid, or by any other means appropriate.

The noise absorption structure according to the invention also includes means of dissipation of energy of which various embodiments are represented by way of example in FIGS. 4 to 13.

In Figure 4, the means of energy dissipation are of the gas rolling type (for example air). The internal partitions 14 of the frame 12 delimit with the membrane 10 of the chambers 34 closed by a wall bottom 36 and which communicate with the lower volume of the frame 12 by a conduit 38 of relatively cross section small and relatively long compared to to its section, allowing energy dissipation by laminar gas flow.

In the variant embodiment of FIG. 5, the conduit 38 is replaced by a channel 40 formed in hollow in the upper face of the bottom wall 36 to which is associated with a cover plate 42 which constitutes the upper wall of channel 40. An orifice 44 of the plate 42 connects the chamber 34 to the channel 40, while an orifice 46 of the bottom wall 36 connects the channel 40 at the lower volume of the frame 12.

As best seen in Figure 6, which is a top view of the energy dissipation means In FIG. 5, the channel 40 can be formed in a spiral in the bottom wall 36 of the chamber 34.

Under the effect of the pressure of acoustic waves incident, the membrane 10 deforms and behaves like a very damped oscillator whose frequency central is a function of the membrane tension, of its density and thickness, between other. The deformation of the membrane causes a laminar gas flow in the dissipating means of energy constituted by the conduit 38 or the channel 40.

The acoustic impedance of a structure according to the invention is perfectly suited to the characteristics incident noise when it is completely absorbed, without reflection by the membrane.

The invention provides means for modify, adjust or control this acoustic impedance.

For example, if the means of energy dissipation include a channel 40 of the type shown in Figures 5 and 6, modification or adjustment acoustic impedance can be obtained by variation of the cross section of channel 40. For this, as shown schematically in Figure 7, we can form, on the face of the plate 42 which is turned on the side of the bottom wall 36, ribs in projection 48 engaged with a small clearance in the channel 40 of the plate 36, and means 50 are provided for modification the distance between the plate 42 and the wall of bottom 36, these means 50 being for example of the type memory of shape or piezoelectric type, controlled by an appropriate electrical circuit.

Changing the distance between the plate 42 and the wall 36 modifies the cross section of the channel 40 and therefore the laminar gas flow conditions in this channel, which changes the impedance accordingly acoustics of the structure according to the invention.

When the means of energy dissipation are of the type represented in figure 4, one can modify the acoustic impedance of the structure by acting on the volume of the lower part of the frame 12 (volume under the wall 36) for example using an element inflatable similar to element 26 of Figure 2, which one connects to pressure adjustment means.

In the variant embodiment of FIG. 8, the membrane 10 carries rods 52 which extend inside of the support frame, perpendicular to the membrane, and which are engaged in tubes 54 carried by an intermediate wall 36 of the support frame, so that the displacement of the rods 52 in the tubes 54 caused by deformations of the membrane 10 results in a laminar gas flow in the tubes 54 and by a corresponding energy dissipation.

In the alternative embodiment of FIG. 9, the means of energy dissipation are also gas rolling type and include horizontal plates 56 arranged parallel to the membrane 10 and a short distance from it inside the frame support, these plates 56 being carried by means 58 making it possible to modify the distance d between the membrane 10 and the plates 56. For example, these means 58 are carried by the intermediate wall 36 and include controlled shape memory elements by an appropriate electrical circuit 60.

Changing the distance d between a plate 56 and the membrane 10 causes a modification of the acoustic impedance of the structure according to the invention.

In the embodiment of FIG. 10, the energy dissipation means include plates electrodes 62 arranged inside the frame of support, parallel to the membrane 10 and at a short distance of it, and for example carried by the wall intermediate 36 of the support frame through dielectric elements 64. The membrane 10 comprises electrodes associated with the plates 62, such as example that metallized zones 66 of its surface, these zones 66 and the plates 62 being connected to the poles from a direct current source 68 via an energy dissipating element such as a resistor electric 70 which is advantageously a resistance variable controlled by an appropriate means 72, resistance 70 absorbing energy by the Joule effect and variation of its value allowing to modify the impedance acoustics of the structure according to the invention.

Preferably, holes 74 are drilled in the electrode plates 62 to avoid any rolling effect gas between them and the membrane 10.

The electrostatic attraction exerted by plates 62 on the membrane plays the role of an anti-stiffness dynamic which opposes the stiffness of the contained gas in the structure. This reduces the thickness (or height) total of the structure and therefore its size.

As a variant, the membrane 10 and / or the plates electrodes 62 could consist of an electret, such as for example a plastic material of the polyurethane type or PVDF permanently electrically charged, the means for biasing the electrodes being then deleted.

In the embodiment of FIG. 11, the energy dissipation means are of the electromagnetic type. The membrane 10 is connected, inside the frame, to electric windings 76 movable relative to magnetic elements 78 constituting by example the intermediate wall 34 of the support frame. To avoid any gas rolling effect, parts 78 protruding towards the membrane can be pierced with through holes 80.

In the variant embodiment of FIG. 12, magnetic elements 82 (e.g. permanent magnets) are arranged under the membrane 10 and electrical conductors 84 are carried by the latter, by being constituted for example by a or electrical circuits printed or deposited on the membrane. The displacement of these electrical conductors 84 in the magnetic field lines of elements 80 results in energy dissipation.

In the variant embodiment of FIG. 13, it is a part of the support frame 12 which can be produced made of magnetic material and constitute a permanent magnet whose field lines can be cut by the electrical conductors 84 of the membrane 10 for an energy dissipation effect.

In another variant, a membrane is used magnetic which moves relative to a circuit electric to dissipate energy.

The elementary noise absorption structures which have just been described can be assembled together to form flat, curved, concave or convex walls, of large dimension. For example, the elementary structures of FIGS. 4, 5, 8 and 9 can have dimensions, on the surface, of the order of 5 × 5 cm ² and can be combined to form a structure of the type of that represented in FIG. 1 having a surface of the order of 20 x 20 cm ² , the heights of these structures generally being between 15 and 50 mm. The acoustic impedances of elementary structures can be adjusted individually or in small groups of structures. Adjusting the acoustic impedances makes it possible to have an impedance well suited for certain surface areas of a wall with maximum absorption of the incident noise, while other surface areas of the wall will have different impedances to partially absorb the noise incident and partially reflect it in a determined direction.

In addition, the possibility of impedance adjustment acoustics of each elementary structure allows to obtain a spatial evolution of the characteristics acoustics of a wall. We can also get a wall with non-localized acoustic impedance when the lower parts of elementary structures are interconnected, the acoustic impedance of connecting means being a parameter for adjusting the acoustic frequency bands to be processed. Moreover, as already indicated, the structures according to the invention such as those of figure 2, adapt automatically to variations in external static pressure and for example to the evolution of the static pressure in a conduit.

Claims (14)

1. A noise-absorption structure comprising a support frame (12) over which a gastight membrane (10) is tensioned and fixed, the outside face of the membrane receiving soundwaves, a gas such as air, for example, filling an internal volume defined by the frame (12) and the membrane (10), and energy-dissipation means housed in said volume, characterized in that the energy-dissipation means are of the laminar gas-flow type, of the electrostatic type, or of the electromagnetic type, and are modifiable, adjustable, or controllable in order to modify the acoustic impedance of said structure as a function of the characteristics of the noise to be absorbed and the structure is closed in gastight manner and contains an expandable and contractible volume element (26) such as a balloon or a bellows, for example, filled with air and communicating with the outside via a static pressure equalizing orifice (28), said element (26) occupying a considerable fraction of the inside volume of said structure.
2. A structure according to claim 1, characterized in that the laminar gas flow type dissipation means comprise plates (56) disposed inside the frame (12), a short distance from the membrane (10), and means (58, 60) for modifying this distance.
3. A structure according to claim 1, characterized in that the laminar gas flow dissipation means comprise at least one gas flow passage or duct (38) connecting a closed chamber (34) defined inside the frame (12) by the membrane (10) to another chamber inside said structure.
4. A structure according to claim 3, characterized in that said passage is a channel (40) formed between two superposed plates (36, 42).
5. A structure according to claim 4, characterized in that the structure comprises means (48, 50) for modifying the section of the channel (40) by modifying the distance between the two superposed plates (36, 42).
6. A structure according to claim 1, characterized in that the laminar gas flow dissipation means comprise rods (52) carried by the membrane (10) and extending perpendicularly therefrom inside the frame in fixed tubes (54) which are closed at their ends remote from the membrane (10) and which co-operate with the rods (52) to define annular gas-flow channels.
7. A structure according to claim 1, characterized in that its internal volume defined by the membrane (10), the support frame (12) and a bottom wall (18) carried by the frame (12) is adjustable, for example by means of an inflatable element housed inside by the frame.
8. A structure according to claim 1, characterized in that the dissipation means of the electrostatic type comprise electrode plates (62) disposed parallel to the membrane (10) at a distance therefrom, and at least one other electrode formed on the membrane and connected together with said plates (62) to bias means (68) including energy-dissipation elements, such as a resistor (70) for example.
9. A structure according to claim 8, characterized in that the structure comprises means (72) for adjusting the resistance of the resistor (70).
10. A structure according to claim 8 or 9, characterized in that the membrane (10) includes one or more metal-coated zones (66) facing said electrode plates (62).
11. A structure according to claim 1, characterized in that the dissipation means of the electrostatic type comprise electrode plates disposed parallel to the membrane at a distance therefrom and at least one electrode formed by the membrane (10), said electrode and/or the plates being permanently electrically charged.
12. A structure according to claim 1, characterized in that the dissipation means of the electromagnetic type comprise a magnetic membrane moved relative to an electric circuit or electric conductors moved by the membrane (10) relative to magnetics elements (78, 82) carried by the frame (12) or constituted thereby, the electric conductors comprising for example coils (76) connected to the membrane (10) or electric circuits (84) printed or deposited on the membrane.
13. A structure according to any one of claims 1 to 12, characterized in that the structure is juxtaposed and assembled with a plurality of structures of the same type to form a wall that is plane or curved, convex or concave, in which the structures have acoustic impedances that are similar or different for absorbing the incident noise or for deflecting it by reflection, as appropriate.
14. A wall comprising a plurality of structures according to claim 13, characterized in that the energy dissipation means of at least some of said structures are associated with modification, adjustment, or control means themselves controllable by a data processor system, and are, for example, adaptable to the noise that is to be absorbed and to variation thereof.

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