Acoustic membrane for an acoustic transducer and related acoustic transducer

Abstract

The present invention relates to an acoustic membrane (14a) for an acoustic transducer, the membrane comprising a substrate (21); and at least one reinforcement layer (23a-23b) of the substrate (21), the at least one reinforcement layer (23a-23b) enabling to improve the stiffness of the membrane (14a). The reinforcement layer (23a-23b) of the substrate (21) corresponds to an amorphous carbon layer belonging to the DLC family and has a stiffness greater than 300 GPa, a density lower than 3400 kg / m 3 and a thickness between 0.5 pm and 6 pm. The reinforcement layer (23a-23b) is attached to the substrate (21) with a bonding layer (22a-22b) having a thickness between 0.1 pm and 1 pm and comprising at least one metallic compound.

Description

Technical Field

[0001] This invention relates to the field of transducers, and more specifically, to acoustic diaphragms for acoustic transducers. Acoustic transducers can correspond to loudspeakers or microphones, such as ribbon microphones, where the ribbon serves as the acoustic diaphragm. The invention also relates to acoustic transducers comprising diaphragms.

[0002] This invention has a variety of applications in fields where it is desirable to obtain transducers with high bandwidth and / or high dynamic characteristics (i.e., acceleration of membrane displacement and / or high frequency).

[0003] For example, the present invention has particularly advantageous applications for loudspeakers capable of producing high-frequency sounds (such as "tweeters") or broadband loudspeakers (such as headphone drivers). Background Technology

[0004] An acoustic transducer includes a sensor and a sound source. The sensor converts acoustic or mechanical quantities into electrical signals, such as a microphone or accelerometer, while the sound source converts electrical signals into acoustic or mechanical quantities, such as a speaker or headphones.

[0005] Loudspeakers typically include a movable diaphragm driven to move by a support member containing a coil, which is displaced under the influence of a magnetic field. The support member is fixed only to a portion of the diaphragm, usually the central circular portion.

[0006] Since the membrane is displaced by a component that is fixed to only a portion of it, it is important that the membrane is stiff enough that the displacement force applied to the membrane causes uniform displacement of the membrane.

[0007] If the membrane is not rigid enough to withstand its own high-frequency vibrations, the membrane will become distorted and generate parasitic noise.

[0008] To achieve high stiffness, naturally rigid materials can be used, or thick layers of medium or low stiffness materials can be formed to construct the membrane. However, using rigid materials or thick layers of these materials typically results in membranes with very high weight.

[0009] However, the greater the weight of the membrane, the greater the electromagnetic force required to displace it, which increases energy consumption and causes inertial problems in the membrane.

[0010] Therefore, a membrane that is both rigid and lightweight is needed to limit distortion and inertia, especially at high frequencies.

[0011] A large portion of today's loudspeakers use diaphragms made of glass, carbon, or aramid fibers, particularly for woofers and midrange speakers, with thicknesses on the order of millimeters. However, for the typical thicknesses (30µm to 60µm) of tweeter diaphragms and headphone drivers, these materials do not allow for high-frequency performance by limiting distortion. To limit distortion, the thickness could be increased significantly, but this would result in a substantial increase in weight, leading to excessive inertia.

[0012] To generate high frequencies while limiting inertial phenomena, it is known to use films with substrates comprising relatively low-density metals or alloys (particularly aluminum or titanium).

[0013] For the same thickness, membranes made from these materials are more rigid than glass fiber membranes, but they are not rigid enough to adequately limit distortion, especially for high-fidelity sound reproduction applications.

[0014] When membranes are made of titanium, they are particularly heavy, which causes inertia problems in the membrane.

[0015] To limit distortion and inertial phenomena, beryllium films can be manufactured because this material combines stiffness (Young's modulus 287 GPa) and low density (1848 kg / m³). Such beryllium films are specifically described in reference FR2854021.

[0016] Due to the cost and availability of this material, alternatives to beryllium are being sought.

[0017] To approximate the properties of beryllium films, it is known to combine lightweight but low-stiffness substrates (e.g., aluminum substrates) with reinforcing layers (e.g., amorphous carbon layers of the DLC family (referred to as "diamond-like carbon" in Anglo-Saxon literature)). In fact, a single aluminum substrate has a strength of 2700 kg / m³. 3 The density and average stiffness (characterized by a Young's modulus of approximately 70 GPa) are high. At typical film thicknesses between 30 µm and 60 µm, this stiffness characteristic does not allow for high frequencies while limiting distortion.

[0018] Theoretically, the stiffness of a membrane can be significantly improved by forming a multilayer structure containing a low-stiffness substrate and a reinforcing layer, since the stiffness of the reinforcing layer may be much higher than that of the substrate. However, due to differences in the mechanical properties of the materials, there is a risk of delamination and interfacial shear between the reinforcing layer and the substrate during membrane fabrication or when the membrane is subjected to high-frequency displacement.

[0019] To keep the reinforcing layer on a low-stiffness substrate, a bonding layer is known from the literature “Effectiveness of Exotic Vapor-Deposited Coatings on Improving the Performance of Hard Dome Tweeters” (Chapman, Peter John, Audio Engineering Society).

[0020] More precisely, the document presents experimental results, according to which, in order to obtain a laminate attached to the substrate, the bonding layer can be made of chromium nitride with a thickness between 3.2 µm and 9.4 µm or chromium with a thickness between 1.3 µm and 4.7 µm.

[0021] These bonding layers allow for the attachment of reinforcing layers made of DLC or chromium nitride, typically DLC layers with a thickness between 1.5 µm and 2.4 µm or chromium nitride layers with a thickness between 1.4 µm and 5.2 µm, onto aluminum or titanium substrates.

[0022] Using these particularly thick bonding layers (at least 1.3 µm), the membrane resists high-frequency delamination, but the weight of the membrane is also greatly affected by the weight of the bonding layer, while the bonding layer contributes very little to the stiffness of the membrane.

[0023] Therefore, the presence of the bonding layer increases the weight and inertia of the film, limiting the gains obtained by adding the reinforcement layer, as the film properties decrease due to increased inertia. To retain the reinforcement layer with a thin bonding layer, it is known from document DE10038780 to use a bonding layer made of silicon, germanium, or carbon to fix the reinforcement layer made of DLC onto a low-stiffness substrate (e.g., an aluminum substrate). More specifically, this document indicates that the bonding layer made of silicon, germanium, or carbon can have a thickness between 0.001 μm and 10 μm (preferably between 0.002 μm and 4 μm).

[0024] This document describes how the bonding layer allows DLC reinforcement layers with a thickness between 1 μm and 10 μm to be fixed onto an aluminum substrate.

[0025] It should be noted that silicon, germanium, or carbon bonding layers have atomic coordination close to that of C in DLC. Therefore, this literature seems to suggest that in order to anchor DLC layers onto low-stiffness substrates with thin bonding layers, bonding layers with atomic coordination close to that of the reinforcing layer are required.

[0026] However, tests conducted within the scope of this invention have shown that silicon, germanium, or carbon bonding layers do not allow for the attachment of a DLC layer with sufficient stiffness (i.e., greater than 300 GPa) of 4 µm thickness to an aluminum substrate. In fact, delamination of the reinforcement layer has been observed during film fabrication.

[0027] In fact, the DLC layer has residual stress, which is an internal stress associated with its manufacturing process. These stresses are partly related to the thickness and stiffness of the DLC layer and can cause the bonding layer to be biased.

[0028] Typically, the membrane fabrication methods described later require a significant amount of energy to be supplied to the growing deposit during deposition, resulting in high internal compressive stresses in the DLC layer. These internal stresses tend to increase with increasing stiffness of the DLC layer. Furthermore, this energy supply leads to a significant increase in membrane temperature, a phenomenon more pronounced for films with low thermal inertia. Additionally, differences in the coefficients of thermal expansion between the different materials in the membrane generate even greater stresses within it.

[0029] These stresses result in significant elastic potential energy within the DLC layer, which is proportional to the layer's internal stress and thickness. This potential energy can be released by breaking the weakest region of the stack. This region is typically the interface, where the interfacial cohesive energy is lower than the potential energy relaxation resulting from stack failure at that interface. To prevent membrane failure under significant loads caused by the internal stresses of thick and very rigid deposits, it is necessary to optimize the chemical affinity between materials at the interface and maximize the breaking stress in the bonding layer.

[0030] Therefore, as described in the prior art, reinforcing layers with high stiffness (greater than 300 GPa) and large thickness (greater than 4 µm) cannot be attached to low-stiffness substrates using silicon, germanium, or carbon bonding layers. This is related to shear stress, which is greater than the destructive stress of the bonding layer. Consequently, films currently using reinforcing layers either suffer from adhesion problems with the bonding layer, or are at risk of delamination and interfacial shear (e.g., for bonding layers made of silicon, germanium, or carbon), or exhibit distortion (usually due to an excessively thin reinforcing layer), or excessive inertia (especially when the bonding layer is too thick).

[0031] In a completely different field, patent FR3082527 describes an industrial mechanical component, such as a piston pin, cylinder, or tappet, covered with a friction-reducing layer. This friction-reducing layer, made of hydrogen-free amorphous carbon (ta-C type), is fixed to the industrial mechanical component via a bonding layer based on chromium, carbon, and silicon.

[0032] This solution addresses another technical problem: reducing the coefficient of friction in mechanical contact under boundary lubrication conditions. It is intended for use in components that operate primarily in lubricated environments, subjected to high forces (approximately 100 daN) and moving at frequencies far below the acoustic diaphragm frequency (especially below 1 kHz).

[0033] Therefore, those skilled in the field of acoustic membranes who seek to improve the properties of acoustic membranes will not seek solutions for mechanical friction components, because such solutions do not involve the same stresses and do not serve the same purpose.

[0034] In fact, attaching a friction-reducing layer to a heavy steel component that is several centimeters thick and typically weighs more than ten grams is very different from attaching a reinforcing layer to a film that is less than 70 micrometers thick and weighs a few hundred milligrams, because the thermal properties of the component and the mechanical properties of the substrate are very different.

[0035] The problem this invention aims to solve is to propose a rigid and lightweight acoustic transducer film that overcomes the limitations of the prior art by fixing the reinforcing layer to the substrate, thereby limiting distortion and inertia at high frequencies, resisting the risks of delamination and interface shear, and ensuring the adhesion of the reinforcing layer to the substrate with the help of an optimized bonding layer. Summary of the Invention

[0036] The present invention proposes to solve this technical problem by using a thin bonding layer containing at least one metal compound, so as to ensure good chemical affinity with the substrate on the one hand, and good chemical affinity with the DLC reinforcement layer on the other hand.

[0037] The chemical affinity is further enhanced by creating a chemical composition gradient within the bonding layer and between the two interfaces, which allows for the avoidance of chemical or mechanical discontinuities. Furthermore, a material with good toughness is required to prevent cohesive failure within the bonding layer.

[0038] Therefore, the combination of these different parameters (i.e., interfacial cohesion and toughness) allows for optimization of the adhesion between the reinforcing layer and the substrate, and thus increases the thickness of the reinforcing layer.

[0039] This invention is therefore the result of an observation that a thin bonding layer containing at least one metal compound can be used to fix the reinforcing layer, contrary to the technical bias of the literature “Effectiveness of Exotic Vapor-Deposited Coatings on Improving the Performance of Hard Dome Tweeters” (Chapman, Peter John, Audio Engineering Society), which indicates the use of very thick metal bonding layers.

[0040] Similarly, the present invention allows for limiting the risk of delamination and interface shearing of these layers, in contrast to the technical bias of document DE10038780, which suggests the use of bonding layers with atomic coordination close to the reinforcing layer.

[0041] Therefore, according to a first aspect, the present invention relates to an acoustic diaphragm for an acoustic transducer, comprising:

[0042] - Base; and

[0043] - At least one reinforcing layer, which is used to reinforce the substrate so as to allow for improved membrane stiffness.

[0044] The invention is characterized in that the at least one reinforcing layer corresponds to an amorphous carbon layer belonging to the DLC family, which has a stiffness greater than 300 GPa and a stiffness less than 3400 kg / m². 3 The density and thickness are between 0.5µm and 6µm; the reinforcing layer is fixed to the substrate by a bonding layer with a thickness between 0.1µm and 1µm and containing at least one metal compound.

[0045] Advantageously, the substrate has a stiffness of less than 150 GPa, and the bonding layer has a stiffness between that of the reinforcing layer and that of the substrate.

[0046] Therefore, this embodiment is the result of observation that, for stacks containing amorphous carbon DLC reinforcement layers, even if they can have a thickness of up to 6 µm and a high stiffness greater than 300 GPa, bonding layers containing at least one metal compound, having a stiffness between that of the reinforcement layer and the substrate, and a thickness between 0.1 µm and 1 µm can provide the expected anti-delamination and anti-interfacial shear stress properties.

[0047] DLC (Diamond Like Carbon, as referred to in Anglo-Saxon literature) is a carbon coating that possesses some of the properties of diamond, although it does not have the typical crystal structure of diamond.

[0048] These layers are composed of carbon and have an amorphous (non-crystalline) structure containing a mixture of atomic sp bonds. 3 (such as in diamond) and sp 2 (e.g., in graphite).

[0049] The density of the DLC amorphous carbon layer depends on sp 3 and sp 2 The bond ratio and the possible presence of hydrogen, impurities, and porosity. Pure diamond (100% sp. 3 The density of the bond is approximately 3520 kg / m³. 3 The density of graphite is approximately 2267 kg / m³. 3 If the DLC amorphous carbon layer has a density below 3400 kg / m³, then... 3 The density of indicates that it has a specific sp ratio. 2 Bonds, and / or contain impurities or pores.

[0050] Therefore, this embodiment is the result of observation that having the bonding layer with an intermediate stiffness between the stiffness of the substrate and the stiffness of the reinforcing layer is particularly advantageous for improving the adhesion between the reinforcing layer and the substrate by limiting the risk of delamination and interfacial shear between the layers.

[0051] Specifically, this bonding layer can effectively fix a stiffness greater than 300 GPa and less than 3400 kg / m². 3 The density and thickness of the DLC amorphous carbon layer are between 0.5µm and 6µm.

[0052] Typically, ta-C type DLC amorphous carbon layers have internal compressive stresses ranging from 2 GPa to over 8 GPa. The DLC amorphous carbon layer of the film according to the invention has a minimum internal stress close to 2 GPa. Similarly, the thermal stress is on the order of 1 GPa to 2 GPa.

[0053] These specific technical choices allow for the production of membranes with significant improvements in substrate stiffness and limited increases in weight and inertia.

[0054] Therefore, the acoustic membrane according to the invention provides an effective trade-off between membrane stiffness and lightweight requirements, since for a membrane of a fixed diameter, lightweight depends directly on thickness and density.

[0055] For example, the substrate has a thickness between 5 µm and 70 µm and comprises at least one polymer and / or one composite material, wherein the at least one polymer and / or one composite material has a stiffness greater than 2 GPa and less than 2800 kg / m². 3 Density. Preferably, the substrate comprises at least one material selected from the group consisting of: carbon composites, carbon fiber reinforced polymers, graphite and composites thereof, graphene and composites thereof, graphene oxide, carbon nanotubes, and mixtures thereof.

[0056] Alternatively, the substrate has a thickness between 20 µm and 60 µm and comprises at least one metal or alloy having a stiffness greater than 30 GPa and a stiffness less than 2800 kg / m³. 3 The density. For example, the substrate may include aluminum and / or its alloys and / or magnesium and / or its alloys.

[0057] Alternatively, the substrate comprises at least one material selected from the group consisting of titanium and its alloys, and the substrate has a thickness between 10 µm and 30 µm (more preferably between 15 µm and 25 µm).

[0058] Preferably, the reinforcing layer has a strength of less than 3200 kg / m². 3 The density. The density is less than 3200 kg / m³. 3This means that the DLC amorphous carbon layer has a high proportion of sp 2 Bonds (typically greater than 10% for ta-C type DLC), and / or contain impurities or porosity.

[0059] This definition can include hydrogenated forms of DLC, such as ta-C:H (referred to as "Tetrahedral Amorphous Carbon – Hydrogenated" in Anglo-Saxon literature) and DLCH (referred to as "Diamond-Like Carbon – Hydrogenated" in Anglo-Saxon literature).

[0060] ta-C:H and DLCH coatings are hydrogenated variants of DLC, in which a certain proportion of hydrogen atoms are incorporated into the carbon structure. Adding hydrogen alters some properties of the DLC coating, such as hardness, friction, and abrasion resistance. Typically, incorporating hydrogen into the carbon structure results in a decrease in density.

[0061] In addition to the hydrogenated form, ta-C type DLC (referred to as "Tetrahedral Amorphous Carbon" in Anglo-Saxon literature) can also be used, because the density of ta-C is typically between 2600 kg / m³. 3 With 3200kg / m 3 between.

[0062] The characteristic of ta-C is its amorphous structure, i.e., non-crystalline, in which most carbon bonds are sp. 3 Type (greater than or equal to 50%), similar to the bonds present in diamond.

[0063] This bond, which leads to coordination of the first nearest tetrahedron (hence the “t” in ta-C), endows ta-C with certain diamond-like properties.

[0064] Within the scope of this invention, hydrogenated forms of DLC or ta-C have been found to be particularly effective in improving membrane stiffness, even at very small thicknesses. According to embodiments of the invention, it can be noted that for DLC amorphous carbon layers with a thickness between 3 µm and 6 µm and a stiffness greater than 300 GPa, the membrane stiffness is significantly improved. To test acoustic membranes with reinforcing layers made of ta-C or ta-C:H, the density of the carbon layer can be looked for rather than its stiffness. Indeed, it is known that a layer with a stiffness greater than 300 GPa corresponds to a density greater than 2.6 g / cm³ for ta-C:H. 3 The density corresponding to ta-C is greater than 2.4 g / cm³. 3Therefore, by weighing before and after the deposition of the reinforcement layer, and given the component surface area and layer thickness, the density of the reinforcement layer was found to be greater than 2.4 g / cm³. 3 Then the stiffness of the reinforcing layer should be greater than 300 GPa.

[0065] In the context of this invention, the stiffness of a material or a composite of materials is defined by its elastic modulus, or Young's modulus, which corresponds to a measure of the material's resistance to elastic deformation. Importantly, it should be noted that the value of the elastic modulus can vary slightly depending on the purity of the material and its microstructure (dense or columnar, i.e., having very long grains in the crystallographic direction).

[0066] Preferably, the reinforcing layer has a stiffness greater than 300 GPa (or even 450 GPa) and / or an indentation hardness (HIT) greater than 30 GPa. Preferably, the reinforcing layer has a stiffness less than 700 GPa.

[0067] According to the present invention, HIT hardness measurement is performed using a nanoindentation method, as described in document FR2796150. This method involves applying a measuring load to the material surface using a tip to induce material deformation, and then measuring the deformation induced by the tip under different loads to determine the hardness and stiffness of the material. This yields a load-based displacement curve, allowing for the extraction of hardness and stiffness.

[0068] Preferably, the reinforcing layer has a sp content greater than or equal to 50%. 3 Bond ratio.

[0069] According to the present invention, measuring sp 3 The bond ratio was determined using Raman spectroscopy. Specifically, Raman spectroscopy utilizes measurements of spectra at different excitation wavelengths of laser light (325 nm, 442 nm, 488 nm, and 633 nm) to obtain the spline ratio of the layer. 3 The average content of hybrid atoms. Laser power is limited to prevent material modification under irradiation. Intensity spectra based on Raman shifts are obtained by adjusting the G peak (elongation mode) and D peak (vibrational mode) of carbon bonds using two Gaussian functions. Plotting the position of the G peak (using a Raman shifter) based on the excitation wavelength yields a straight line; the slope of this line represents the dispersion of the G peak (in cm⁻¹). -1 / nm). This dispersion is related to the sp of the analyzed material. 3 The content of hybrid atoms is proportional. For materials belonging to the DLC family, sp... 3Analysis of bond content is described, for example, in the article “Structure of diamond-like carbon films deposited by femtosecond and nanosecond pulsed laser ablation” by Sikora et al., Journal of Applied Physics, Vol. 108, p. 113516 (2010).

[0070] The stiffness of the membrane can be improved by using only one reinforcing layer on one side of the membrane. Preferably, the membrane includes two reinforcing layers disposed on both sides of the substrate and fixed to the substrate by two bonding layers. This embodiment allows for improvement of membrane stiffness by using two reinforcing layers fixed on both sides of the membrane.

[0071] The one or more bonding layers may comprise at least one material selected from the group consisting of chromium and its alloys, titanium and its alloys, tantalum and its alloys, aluminum and its alloys, tungsten, compounds comprising nitrides, silicides, or carbides of these metals, and mixtures thereof. Preferably, the bonding layer comprises chromium and / or at least one chromium alloy. These materials possess particularly effective technical properties to allow for the adhesion of carbon to the metal and to mitigate shear stress between the DLC layer and the substrate with a very thin bonding layer.

[0072] The stiffness of the bonding layer is advantageously between that of the substrate and the reinforcing layer.

[0073] Preferably, one or more bonding layers have a thickness between 0.1 µm and 0.3 µm. This limited thickness of the bonding layers allows for limiting the total weight of the acoustic membrane. Greater thicknesses are possible, but would increase the weight of the membrane.

[0074] Alternatively, the membrane may include at least one protective layer disposed between the substrate and the bonding layer of the reinforcing layer. Alternatively or additionally, the at least one protective layer may be fixed to at least one side of the reinforcing layer, opposite to the side fixed to the substrate by the bonding layer.

[0075] According to a second aspect, the present invention relates to an acoustic transducer comprising a support (preferably cylindrical), a drive motor configured to generate a magnetic field for moving the support, and an acoustic diaphragm according to a first aspect of the invention, the acoustic diaphragm being fixed to the support and configured to generate or capture sound waves.

[0076] Preferably, the technical selection of different layer sizes results in an acoustic membrane with a mass of less than 220 mg.

[0077] According to a specific embodiment, the transducer is a high-frequency loudspeaker, i.e., it is configured to emit sound in a frequency range greater than 1 kHz, the transducer having a maximum frequency greater than 30 kHz, a diameter less than 6 cm, and an acoustic diaphragm with an equivalent Young's modulus greater than 200 GPa (preferably greater than 250 GPa).

[0078] In another variation of the invention, the transducer is a broadband loudspeaker, i.e., configured to emit sound in a frequency range greater than 20 Hz, the transducer having a maximum frequency greater than 30 kHz, a diameter less than 8 cm, and an acoustic diaphragm with an equivalent Young's modulus greater than 200 GPa (preferably greater than 250 GPa). Attached Figure Description

[0079] The manner in which the invention is practiced and the advantages thereby obtained will become apparent from the following embodiments, given in a non-limiting manner and with the aid of the accompanying drawings, wherein:

[0080] [ Figure 1 This is a schematic cross-sectional view of an acoustic transducer according to an embodiment of the present invention.

[0081] [ Figure 2 According to the first embodiment Figure 1 A schematic cross-sectional view of the diaphragm of an acoustic transducer;

[0082] [ Figure 3 According to the second embodiment Figure 1 A schematic cross-sectional view of the diaphragm of an acoustic transducer; and

[0083] [ Figure 4 According to the third embodiment Figure 1 A schematic cross-sectional view of the diaphragm of an acoustic transducer. Detailed Implementation

[0084] Figure 1 An acoustic transducer 11 is shown, which includes a frame 12 designed to be fixed within a housing to form a speaker enclosure. The frame 12 supports a drive motor 20 for a diaphragm 14a. For this purpose, the acoustic transducer 11 includes a cylindrical support 13 that can be translated using a magnetic field generated by the motor 20.

[0085] The cylindrical support 13 is connected to the membrane 14a via the inner annular edge 18 fixed to the upper end of the cylindrical support 13.

[0086] In the instruction manual, the relative terms "upper" or "lower" refer to, for example, Figure 1 The speaker is shown in its typical orientation, with the motor 20 positioned at the bottom and the diaphragm 14a positioned at the top of the acoustic transducer 11. Clearly, the acoustic transducer 11 can be inverted without altering the invention.

[0087] The annular outer edge 15 of the membrane is connected to the upper support surface 16 of the frame by means of a suspension member 17. Thus, the frame 12 is fixed to the motor 20 at its lower end, while its upper end surrounds the cylindrical support member 13 and the membrane 14a.

[0088] At the lower part of the acoustic transducer 11, the cylindrical support 13 preferably has an upper surface 19, which is provided with a dome, such as an inverted dome.

[0089] At the upper part of the acoustic transducer 11, the upper support surface 16 of the frame 12 has a diameter, for example, between 1 cm and 17 cm.

[0090] In one embodiment, the acoustic transducer 11 is a high-frequency loudspeaker, i.e., it is configured to emit sound in a frequency range greater than 1 kHz. In this embodiment, the acoustic transducer 11 has a maximum frequency, for example, greater than 30 kHz, has an upper support surface 16 of frame 12 with a diameter of less than 6 cm, and has a diaphragm 14a with an equivalent Young's modulus greater than 200 GPa (preferably greater than 250 GPa).

[0091] In another embodiment, the acoustic transducer 11 is a broadband loudspeaker, i.e., it is configured to emit sound in a frequency range greater than 20 Hz. In this embodiment, the acoustic transducer 11 has a maximum frequency greater than 30 kHz, has an upper support surface 16 of the frame 12 with a diameter less than 8 cm, and has a diaphragm 14a with an equivalent Young's modulus greater than 200 GPa (preferably greater than 250 GPa).

[0092] Membrane 14a is a result of a technological choice that preferably allows for a weight of less than 220 mg to limit the membrane's inertia. Therefore, according to the invention, membrane 14a is formed by bonding a substrate 21 with at least one reinforcing layer 23a-23b fixed to the substrate 21 by bonding layers 22a-22b.

[0093] like Figure 2 , 3 As shown in Figure 4, membranes 14a-14c preferably have two reinforcing layers 23a-23b, which are fixed to both sides of the substrate 21 by two bonding layers 22a-22b. Alternatively, the membrane may comprise a single reinforcing layer without altering the invention.

[0094] According to the present invention, the substrate 21 has a stiffness of less than 150 GPa. For this purpose, the substrate 21 can be made of a polymer or composite material having a stiffness greater than 2 GPa, a density of less than 2800 kg / m³, and a thickness between 5 µm and 70 µm. In this embodiment, it can be made of a material selected from the group consisting of: carbon composite materials, carbon fiber reinforced polymers, graphite and composites thereof, graphene and composites thereof, carbon nanotubes and mixtures thereof.

[0095] According to another embodiment, the substrate 21 may be made of metal or alloy having a stiffness greater than 30 GPa, a density less than 2800 kg / m³, and a thickness between 20 µm and 60 µm. For example, the substrate 21 may be made of a material selected from the group consisting of aluminum and its alloys or from the group consisting of magnesium and its alloys.

[0096] The acoustic membranes 14a-14c also include at least one layer 23a-23b for reinforcing the substrate 21 to improve the stiffness of the membranes 14a-14c.

[0097] According to the present invention, the reinforcing layers 23a-23b correspond to the DLC amorphous carbon layers, which have a stiffness greater than 300 GPa, a density less than 3400 kg / m³, and a thickness between 0.5 µm and 6 µm.

[0098] Preferably, it has a thickness between 3µm and 6µm, a density of less than 3200 kg / m³, a stiffness greater than 450 GPa, and / or a HIT hardness greater than 30 GPa. For example, the reinforcing layers 23a-23b correspond to tetrahedral amorphous carbon ta-C.

[0099] The reinforcing layers 23a-23b are fixed to the substrate 21 by bonding layers 22a-22b, which contain at least one metallic compound and have a stiffness between that of the reinforcing layers 23a-23b and that of the substrate 21, and a thickness between 0.1 µm and 1 µm. Preferably, they have a thickness between 0.1 µm and 0.3 µm and are made of a material selected from the group consisting of chromium and its alloys, titanium and its alloys, tantalum and its alloys, aluminum and its alloys, tungsten, nitride or carbide compounds, and mixtures thereof.

[0100] exist Figure 3 In one embodiment, two protective layers 24a-24b are fixed to one side of two reinforcing layers 23a-23b, opposite to the side that is fixed to the substrate 21 by means of bonding layers 22a-22b.

[0101] In one embodiment, the protective layer is made of a two-component polyurethane varnish and applied by spraying. It has a thickness between 5 µm and 20 µm. It is necessary to reduce the thickness of the protective layer to minimize its mass. Different varnishes can be applied depending on the desired aesthetic properties. For example, the protective layer may correspond to a parylene layer.

[0102] Figure 4 One embodiment is shown in which two protective layers 25a-25b are placed between the substrate 21 and the two bonding layers 22a-22b of the reinforcing layers 23a-23b.

[0103] In one embodiment, the protective layer is formed by anodizing the surface of a substrate (for magnesium or aluminum alloy) after immersion in an electrolytic bath to form a protective oxide layer on the surface.

[0104] Different layer deposition methods can be used to manufacture the acoustic membranes 14a-14c according to the present invention.

[0105] For the deposition of bonding layers 22a-22b on substrate 21, electrolytic deposition, chemical deposition (electrolysis-free), physical vapor deposition, or chemical vapor deposition can be used, as described in patent FR3082526.

[0106] For example, electrolytic deposition (also known as electroplating) involves immersing a substrate in an electrolytic solution containing ions for which a bonding layer is to be deposited. By applying a voltage, the ions are reduced and deposited on the surface of the substrate, forming a uniform bonding layer.

[0107] In electrochemical deposition, the substrate is immersed in a solution containing the metal ions to be deposited. Unlike electrolytic deposition, the ions are reduced on the substrate surface through an electrochemical reaction due to the action of a reducing agent.

[0108] Physical vapor deposition (PVD) involves vaporizing the constituent materials of the bonding layer under vacuum and depositing the vaporized particles onto the surface of the substrate 21. For example, cathodic arc deposition is a type of PVD.

[0109] Chemical vapor deposition (CVD) involves introducing gaseous precursors that form the binding layers 22a-22b into the substrate 21. These gaseous precursors react and decompose to form the binding layers 22a-22b.

[0110] Plasma-assisted chemical vapor deposition (PACVD or PECVD), plasma-assisted physical vapor deposition, or reactive PVD can also be used, which combines PVD and CVD.

[0111] The deposition of reinforcing layers 23a-23b on bonding layers 22a-22b can be performed using the previously described PVD or CVD techniques or other techniques not mentioned.

[0112] For example, deposition using an electric arc (referred to as "Cathodic Arc Deposition" in Anglo-Saxon literature, or CAD for short) can be used to deposit reinforcement layers 23a-23b on bonding layers 22a-22b.

[0113] This technique involves evaporating / sublimating a graphite target using an electric arc in an inert gas atmosphere (typically argon). Carbon ions are accelerated toward a substrate 21 coated with bonding layers 22a-22b, on which reinforcing layers 23a-23b are formed.

[0114] Using these deposition techniques, the bonding layers 22a-22b can be very thin relative to the reinforcing layers, so that the properties of the acoustic membranes 14a-14c can be anticipated by considering only the substrate 21 and one or more reinforcing layers 23a-23b.

[0115] exist Figure 2 In the example, two reinforcing layers 23a-23b are fixed on both sides of the substrate 21. A magnesium substrate 21 with a stiffness of 42 GPa and a thickness of 31 µm can be used, which is combined with two ta-C reinforcing layers 23a-23b with a stiffness of 500 GPa and a thickness of 4 µm and two bonding layers 22a-22b with a thickness of 0.3 µm.

[0116] Using these thicknesses and stiffnesses, the equivalent stiffness of the acoustic diaphragm 14a can be estimated as 270 GPa according to the following formula:

[0117]

[0118] Where E represents the equivalent Young's modulus of the acoustic membrane.

[0119] Eskin represents the Young's modulus of the reinforcing layer.

[0120] Ecore represents the Young's modulus of the substrate.

[0121] hskin represents the thickness of the reinforcement layer, and

[0122] hcore represents the thickness of the substrate.

[0123] Furthermore, considering that the density of ta-C is 2900 kg / m³ 3The density of magnesium is 1740 kg / m³. 3 The density of acoustic membrane 14a can be characterized as 1980 kg / m³ according to the following formula. 3 :

[0124]

[0125] Where P represents the density of the acoustic diaphragm,

[0126] Pskin indicates the density of the reinforcement layer.

[0127] Pcore represents the density of the substrate.

[0128] hskin represents the thickness of the reinforcement layer, and

[0129] hcore represents the thickness of the substrate.

[0130] A key factor in predicting the behavior of the acoustic diaphragm 14a is the velocity of sound at its output end. This velocity can be estimated by the square root of the ratio of stiffness to density. In the example described earlier, the velocity of sound is estimated to be 11683 m / s.

[0131] These values ​​are close to the measured values ​​for beryllium films, which typically have a stiffness of 287 GPa and a strength of 1848 kg / m³. 3 Its density and the speed of sound are 12455 m / s.

[0132] For use Figure 2 Another example of the structure can be achieved by combining an aluminum substrate 21 with a stiffness of 70 GPa and a thickness of 25 µm with two ta-C reinforcing layers 23a-23b with a stiffness of 500 GPa and a thickness of 4 µm. Using these thicknesses and stiffnesses, the equivalent stiffness of the acoustic diaphragm 14a can be estimated as 313 GPa according to [Equation 1]. Furthermore, considering that the density of aluminum is 2700 kg / m³... 3 According to [Formula 2], the density of the acoustic diaphragm 14a can be characterized as 2750 kg / m³. 3 In this example, the speed of sound is estimated to be 10670 m / s.

[0133] If the thickness of ta-C on each side is increased by one micrometer in the previous example, the equivalent stiffness of the acoustic membrane 14a can be estimated to be 342 GPa, and the sound velocity is 11147 m / s.

[0134] Therefore, an acoustic membrane 14a with mechanical properties equivalent to that of a beryllium membrane can be obtained.

[0135] This invention therefore allows for the acquisition of rigid and lightweight acoustic diaphragms 14a-14c by fixing the reinforcing layer to the substrate 21. These acoustic diaphragms 14a-14c exhibit limited distortion and inertia at high frequencies. Furthermore, they effectively resist delamination and interfacial shear risks. Thus, this invention allows for the provision of acoustic diaphragms 14a-14c that are particularly effective for forming high-resolution acoustic transducers 11.

Claims

1. An acoustic diaphragm (14a-14c) for an acoustic transducer (11), comprising: - Base (21); as well as - At least one reinforcing layer (23a-23b) for reinforcing the substrate (21) thereby allowing for improved stiffness of the membrane (14a-14c); The feature is that the at least one reinforcing layer (23a-23b) corresponds to an amorphous carbon layer belonging to the DLC group, which has a stiffness greater than 300 GPa and a stiffness less than 3400 kg / m. 3 The density and thickness are between 0.5µm and 6µm; The reinforcing layers (23a-23b) are fixed to the substrate (21) by means of bonding layers (22a-22b), the bonding layers (22a-22b) having a thickness between 0.1µm and 1µm and containing at least one metal compound.

2. The acoustic diaphragm for an acoustic transducer according to claim 1, wherein, The substrate (21) has a stiffness of less than 150 GPa, and the bonding layer (22a-22b) has a stiffness between that of the reinforcing layer (23a-23b) and that of the substrate (21).

3. The acoustic diaphragm for an acoustic transducer according to claim 1 or 2, wherein, The substrate (21) has a thickness between 5 µm and 70 µm and comprises at least one polymer and / or one composite material, wherein the polymer and / or the composite material has a stiffness greater than 2 GPa and a stiffness less than 2800 kg / m². 3 The density.

4. The acoustic diaphragm for an acoustic transducer according to claim 3, wherein, The substrate (21) includes at least one material selected from the group consisting of: carbon composites, carbon fiber reinforced polymers, graphite and composites thereof, graphene and composites thereof, graphene oxide, carbon nanotubes, and mixtures thereof.

5. The acoustic diaphragm for an acoustic transducer according to claim 1 or 2, wherein, The substrate (21) has a thickness between 20 µm and 60 µm and comprises at least one metal and / or an alloy having a stiffness greater than 30 GPa and a strength less than 2800 kg / m². 3 The density.

6. The acoustic diaphragm for an acoustic transducer according to claim 5, wherein, The substrate (21) comprises at least one material selected from the group consisting of aluminum and its alloys.

7. The acoustic diaphragm for an acoustic transducer according to claim 5, wherein, The substrate (21) includes at least one material selected from the group consisting of magnesium and its alloys.

8. The acoustic diaphragm for an acoustic transducer according to any one of claims 1 to 3, wherein, The substrate (21) comprises at least one material selected from the group consisting of titanium and its alloys, and the substrate (21) has a thickness between 10 µm and 30 µm.

9. The acoustic diaphragm for an acoustic transducer according to any one of claims 1 to 8, wherein, The at least one bonding layer (22a-22b) comprises at least one material selected from the group consisting of chromium and its alloys, titanium and its alloys, tantalum and its alloys, aluminum and its alloys, tungsten, compounds containing nitrides, silicides or carbides of these metals, and mixtures thereof.

10. The acoustic diaphragm for an acoustic transducer according to any one of claims 1 to 9, wherein, The at least one bonding layer (22a-22b) has a thickness between 0.1µm and 0.3µm.

11. The acoustic diaphragm for an acoustic transducer according to any one of claims 1 to 10, wherein, The reinforcing layers (23a-23b) have a strength of less than 3200 kg / m³. 3 The density.

12. The acoustic diaphragm for an acoustic transducer according to any one of claims 1 to 11, wherein, The reinforcing layers (23a-23b) have a thickness between 3µm and 6µm.

13. The acoustic diaphragm for an acoustic transducer according to any one of claims 1 to 12, wherein, The reinforcing layers (23a-23b) have a stiffness greater than 450 GPa.

14. The acoustic diaphragm for an acoustic transducer according to claims 1 to 13, wherein, The reinforcing layers (23a-23b) have a sp content greater than or equal to 50%. 3 Bond ratio.

15. The acoustic diaphragm for an acoustic transducer according to any one of claims 1 to 14, wherein, The reinforcing layers (23a-23b) correspond to tetrahedral amorphous carbon ta-C.

16. The acoustic diaphragm for an acoustic transducer according to any one of claims 1 to 14, wherein, The membrane (14a-14c) includes two reinforcing layers (23a-23b) arranged on both sides of the substrate (21) and fixed to the substrate (21) by two bonding layers (22a-22b).

17. The acoustic diaphragm for an acoustic transducer according to any one of claims 1 to 16, wherein, The membrane includes at least one protective layer (25a-25b) disposed between the substrate (21) and the bonding layer (22a-22b) of the reinforcing layer (23a-23b).

18. The acoustic diaphragm for an acoustic transducer according to any one of claims 1 to 17, wherein, The membrane includes at least one protective layer (24a-24b) fixed to at least one side of the reinforcing layer (23a-23b), opposite to the side fixed to the substrate (21) by means of the bonding layer (22a-22b).

19. An acoustic transducer (11), comprising: - Support component (13); - Drive motor (20), which is configured to generate a magnetic field to move the support (13); as well as - The acoustic diaphragm (14a-14c) according to any one of claims 1 to 18, the acoustic diaphragm (14a-14c) being fixed to the support (13), the acoustic diaphragm (14a-14c) being configured to generate or capture sound waves.

20. The acoustic transducer according to claim 19, wherein, The transducer is a high-frequency loudspeaker, i.e., configured to emit sound in a frequency range greater than 1 kHz. The transducer (11) has a maximum frequency greater than 30 kHz, a diameter less than 6 cm, and an acoustic diaphragm (14a-14c) with an equivalent Young's modulus greater than 200 GPa, preferably greater than 250 GPa.

21. The acoustic transducer according to claim 19, wherein, The transducer is a broadband loudspeaker, i.e., configured to emit sound in a frequency range greater than 20 Hz. The transducer (11) has a maximum frequency greater than 30 kHz, a diameter less than 8 cm, and an acoustic diaphragm (14a-14c) with an equivalent Young's modulus greater than 200 GPa, preferably greater than 250 GPa.

22. The acoustic transducer according to any one of claims 19 to 21, wherein, The acoustic membrane (14a-14c) has a mass of less than 220 mg.

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