TECHNICAL FIELD OF THE INVENTION

The present invention is related to a membrane according to the pre-characterizing part of claim 1, to a hearing device with such a membrane and to methods for manufacturing membranes.

DESCRIPTION OF THE RELATED ART Membrane based transducer protection systems are used in the field of hearing aids to prevent cerumen entering into the hearing aid housing via sound inlet or sound outlet.

The working principle of these systems is a passive

membrane that covers the sound inlet or the sound outlet of the hearing aid. Besides the protective functions of the membrane, it is envisaged that the membrane is acoustically transparent, i.e. no damping occurs, and linear in its behavior, i.e. no distortions occur, up to high sound pressure levels. By such a membrane, the transducer beneath the membrane would be fully protected against moisture and cerumen, while the overall acoustic behavior of the hearing aid is not affected. However, this aim is hardly achieved because dirt or cerumen is deposited on the membrane changing the acoustic behavior of the membrane. Of course, the membrane can be cleaned by wiping with a cloth or tissue if it is dirty or if there are deposits of cerumen. Furthermore, the required acoustic behavior asks for very thin and lightweight membranes having a favorable surface structure.

EP-8 350 042 A2 describes a protection system for sound inlets or outlets based on a thin-walled membrane which can have a surface structure comprising concentric rings embossed into it. The known membrane has a wall thickness of 20 μπι. In addition, the membrane has an uneven surface comprising bumps and dents resulting in deposition of dirt and cerumen.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a membrane that does at least not have one of the above-mentioned drawbacks while the acoustic behavior is still optimal. The foregoing and other objects of the present invention are achieved by a membrane according to the characterizing part of claim 1. Further embodiments, a hearing device as well as methods for manufacturing are given in further claims . In particular, a membrane for protecting a sound inlet or a sound outlet of a hearing device is disclosed, the membrane comprising :

- an outer surface facing towards surroundings when

mounted on the hearing device;

- an inner surface facing towards inside when mounted on the hearing device;

wherein the inner surface comprises a surface structure and that the outer surface is substantially flat.

The main idea of the present invention is to provide a membrane that comprises a surface structure but only on one side, namely on the side pointing towards the inside of the hearing device. The surface of the membrane pointing to surroundings is flat giving no possibility for dirt and cerumen to deposit. In the event that dirt or cerumen is nevertheless deposited on the membrane, an easy cleaning is possible by using a tissue or the like. The single-sided surface structure provides excellent acoustic performance due to the precise micro-machining by laser, for example.

In an embodiment of the membrane according to the present invention, a peripheral section is thicker than a central section .

Further embodiments of the membrane according to the present invention comprise concentric rings as surface structure. In further embodiments of the membrane according to the present invention, a thickness is gradually decreasing from the peripheral section towards a geometrical center. In further embodiments of the membrane according to the present invention, it is made of a thermoplastic elastomer or of a silicon rubber.

In still further embodiments of the membrane according to the present invention, a maximal thickness of 15 μπι and a minimal thickness of 3 μπι, particularly of 5 μιη.

In still further embodiments of the membrane according to the present invention, the surface structure of the inner surface is made by one of the following method:

- hot melting;

- micro injection molding;

- laser ablation;

- combination of laser ablation with hot melting or

injection molding.

Furthermore, a hearing device is described comprising at least one membrane according to the present invention, the at least one membrane covering at least one of a sound inlet and a sound outlet, whereas an inner surface of the membrane comprises a surface structure, the inner surface facing towards inside of the hearing device and that an outer surface of the membrane is substantially flat, the outer surface facing towards surroundings of the hearing device. A further embodiment of the hearing device according to the present invention comprises a carrier element to which the membrane is bonded at peripheral sections of the membrane.

Finally a first method for manufacturing a membrane

according to the present invention is described, comprising one of the following techniques for obtaining a surface structure on an inner surface of the membrane:

- hot melting;

- micro injection molding;

- laser ablation;

- combination of laser ablation with hot melting or

injection molding.

Finally a first method for manufacturing a membrane

according to the present invention is described, comprising the steps of:

- supplying a membrane foil on a carrier foil, the

membrane foil being uncovered on one side,

- machining surface structure into the uncovered side of the membrane foil,

- attaching a carrier element to the membrane foil by a bonding technique, such as laser welding or adhesive bonding,

- removing the carrier foil,

- singularizing membranes by cutting or punching, for example . In an embodiment of the method according to the present invention, the step of machining the surface structure into the uncovered side of the membrane foil uses one of the following techniques:

- hot melting;

- micro injection molding;

- laser ablation;

- combination of laser ablation with hot melting or

injection molding.

It is expressly pointed out that also all combinations of the above-mentioned embodiments are possible and herewith disclosed. Only those embodiments or combinations of embodiments are excluded that would result in a

contradiction.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is further described by referring to drawings showing exemplified embodiments of the present invention .

Fig. 1 shows a BTH- (Behind-The-Ear) hearing device in a perspective view,

Fig. 2 shows, in cross-sectional view, a first

embodiment of a membrane according to the present invention mounted on a carrier, shows, in cross-sectional view, a second

embodiment of a membrane according to the present invention mounted on the carrier, Fig. 4 shows, in cross-sectional view, a third

embodiment of a membrane according to the present invention again mounted on the carrier, and Fig. 5 shows inventive manufacturing steps for

manufacturing membranes according to the present invention .

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows a perspective view of a hearing device 10 of the type BTH- (Behind-The-Ear) . The hearing device 10 comprises a housing 14 and a hook 12 that is attached to the housing 14 and that guides sound waves generated by a receiver in the housing 14 via a sound outlet 13 to the ear of a user. To prevent cerumen from entering into the hook 12, the sound outlet 13 is covered by a membrane according to the present invention.

In addition, a sound inlet 11 is provided in the housing 14, which sound inlet 11 is covered by a membrane according to the present invention to prevent dirt from entering into the housing 14 or microphone inlets. Even though only a BTE-type hearing device is depicted in Fig. 1, the inventive membrane protection element can also be used for other hearing device styles, such as for an ITE- ( In-The-Ear) hearing device and for a RIC- (Receiver-In- the Canal) hearing device.

Fig. 2 shows a cross-sectional view of a membrane 1 cut perpendicular to an outer surface 4 of the membrane 1. The membrane 1 covers an opening of a housing, e.g. a housing of a hearing device, of which only carrier elements 2 are visible. The membrane 1 is affixed to the carrier elements 2 by means of adhesive bonding or laser welding, for example . A rotational axis 3 is drawn as a dashed line indicating a rotational symmetry of the membrane 1 covering a round opening. However, it is pointed out that a rotational symmetry is not mandatory. Any other forms of the opening and therewith the corresponding membranes covering such openings are possible.

The orientation of the membrane 1 is important in that the already mentioned outer surface 4 of the membrane 1 is pointing to surroundings when mounted on the carrier elements 2. As a consequence, an inner surface 5 of the membrane 1 is pointing towards the inside of the housing. This orientation is essential for the present invention in that only the inner surface 5 may comprise a surface structure and the outer surface 4 is substantially flat so that no dirt - or in case of a hearing device no cerumen is deposited on the outer surface 4, and if so, easy cleaning of the membrane 1 by wiping with a tissue or cloth is possible . In order to provide optimal acoustical behavior of the membrane 1, a surface structure is machined into the inner surface 5 of the membrane by micro machining, for example.

Fig. 2 shows a first embodiment for a membrane 1 having a central section 6 with reduced thickness compared to a peripheral section that is bonded to the carrier element 2. The central section 6 having reduced membrane thickness almost extends over the complete surface of the membrane 1 resulting in a reduced mass or density of the membrane 1.

Fig. 3 shows a second embodiment for a membrane 1 according to the present invention comprising concentric rings 7 leaving its original thickness at the center of the

membrane 1. The concentric rings 7 may be cut into the membrane 1 with a laser, for example.

Fig. 4 shows a third embodiment for a membrane 1 according to the present invention, wherein the thickness of the membrane 1 decreases continuously from the peripheral section towards the center 3 of the membrane 1 where the thickness reaches a minimum.

All the surface modifications of the original flat membrane 1 are realized, for example, by means of laser- micromachining reducing the membrane thickness from its original 15μπι down to less than 7pm, while the outer surface 4 of the membrane 1 is not modified and still smooth, thus facilitating the cleaning during use in the ear in case of implementing the present invention in the technical field of hearing devices.

Thus, the main idea of the present invention, when

implemented in the technical field of hearing devices, is to improve the acoustic performance of membrane-based cerumen protection systems by single-sided laser- micromachining of the membrane. Laser-micromachining of polymers by means of "cold ablation" using a pico-second laser can be used. All materials being used have an

ablation threshold, meaning a point where they are directly vaporized when hit with a laser beam of sufficient peak optical intensity. This allows micromachining and surface patterning of materials with minimal thermal and mechanical distortion. For a given pulse energy, the peak energy increases as the pulse width gets shorter. Typical pulse durations of solid-state lasers are 10 to 15 pico-seconds with pulse repetition rates of 50 kHz to 1 MHz. Additional parameters that need to be optimized for micromachining of a given material substrate are power and wavelength.

For modifying a membrane by providing a surface structure on the inner surface 5 of the membrane this technology has some distinct advantages:

Very local material ablation without "melting" the surrounding area; - High resolution and high accuracy of material

ablation;

- Machining of uneven membranes is possible due to lar Reyleigh-length of laser;

- A high manufacturing throughput is possible.

Fig. 5 schematically shows the main four steps of a metho for manufacturing membranes according to the present invention using laser micromachining, for example. The manufacturing process allows to produce membranes in a hi production rate resulting in reduced manufacturing costs while a high quality and improved acoustical behavior is obtained for the membrane-based cerumen protection system In a first step 1, a foil assembly 60 is provided

comprising a membrane foil 62 and a carrier foil 61

attached to each other. The membrane foil 62 can be made of a thermoplastic elastomer, for example, (e.g. TPU) .

Therewith, the membrane foil 62 is prepared for further processing. The membrane foil 60 is attached to the carrier foil 61.

In a second step 2, a respective surface structure 63 is machined into the membrane foil 62 from the uncovered side by means of a pico-second laser. An attachment region remains unstructured, which allows more stability in a subsequent step for attaching the membrane foil 62 to the carrier elements 64. In a third step 3, the carrier elements 64 are attached to the membrane foil 62 by laser welding or adhesive bonding, for example. In a fourth and final step 4, the carrier foil 61 is removed first and the membrane foil 62 that is bonded to the carrier elements 64 is cut or punched along designed line to obtain the single membranes 65 attached to its carrier elements 64.

Such a manufacturing approach allows to reasonably handle a very thin (less than 5 μπι) foil for mass manufacturing, potentially allowing to realize protection membranes with smaller outer diameters.