WO1999051057A1

WO1999051057A1 - Hearing aids with shielding from electromagnetic radiation and method for producing the same

Info

Publication number: WO1999051057A1
Application number: PCT/EP1999/002064
Authority: WO
Inventors: Berthold Bredenbeck; Rolf Flamm; Hans-Peter Hinz
Original assignee: Resound Deutschland Gmbh; Angewandte Plasma-, Vakuum- Und Verfahrenstechnik Gmbh
Priority date: 1998-03-28
Filing date: 1999-03-26
Publication date: 1999-10-07
Also published as: EP1092335B1; AU3600399A; EP1092335A1; DE59903662D1

Abstract

The invention relates to a method for producing a hearing aid with shielding from electromagnetic radiation by applying a metal coating to parts of or all of the housing frame (8) and/or the insides of the housing side parts. Said metal coating is applied using a vapour phase plasma deposition technique with a thermal metal vapour source (25, 26). The invention also relates to the corresponding hearing aid with shielding from electromagnetic radiation.

Description

Hearing aids with a shield against electromagnetic radiation and Vei go to the manufacture

The invention relates to hearing aids with a shield against electromagnetic radiation and a method for producing such aids

Hearing aids in the sense of the invention are to be understood as hearing aids, amplifiers, wireless headphones, hearing glasses with integrated hearing aids

A distinction is made between so-called HDO and IDO hearing devices. HDO hearing devices are placed behind the ear and IDO hearing devices are worn in the ear

Usual hearing aids generally consist of a microphone, an amplifier unit as well as a receiver and a battery. The housings which are worn on the head are made of plastic materials for reasons of weight

With these hearing aids, however, the problem arises that their function is considerably disturbed if the wearer of the device comes into the vicinity of strong electromagnetic radiation sources, for example car telephones, mobile radio devices, radio telephones and microwave devices. In the vicinity of such transmitters, the emitted electromagnetic waves often have a lot high field strengths This electromagnetic radiation penetrates through small openings and gaps in the device, but also through the plastic housing parts into the interior of the device and influences the function of the electronic components of the device considerably

In particular, telephoning with hearing aids in connection with mobile phones is problematic due to the interference. In particular, hearing aids with greater amplification are disturbed by radio telephones to such an extent that telephoning is almost impossible Disorders - 2 -

cause. Interference from radio telephones has a very different behavior depending on the type of telephone and the frequency range used by the telephone.

Telephoning with older type analog radio telephones that work in relatively low frequency ranges is possible in principle with some restrictions. The interference can be greatly reduced here by relatively simple shielding measures and additional interference suppression capacitors. In the case of radio telephones and newer mobile telephones which operate in the so-called DECT standard or GSM standard, interference-free telephoning for hearing aid wearers is not possible despite such measures. This is due on the one hand to the very high signal intensity and on the other hand to the relatively high frequency ranges that are used for signal transmission of the telephone signals.

Various measures for shielding hearing aids against electromagnetic interference radiation are already known from the prior art. DE-OS 43 43 702 describes a hearing aid that can be worn on the head and in which, in order to improve the immunity to interference of the hearing aid against the penetration of high-frequency electromagnetic waves, it is proposed to provide the housing with at least two electrically conductive parts that can be electrically conductively connected via a high-frequency seal . The housing shells are made of plastic, which is made conductive by adding electrically conductive powder, such as graphite. The electrically conductive layers of the abutting edges, which form the elastic high-frequency seal, can consist of an electrically conductive film or else of an electrically conductive lacquer layer. Another high-frequency seal consists of a tubular aluminum foil jacket.

DE-OS 19 54 345 describes a hearing aid in which, in order to improve the immunity to interference from electromagnetic radiation, it is provided that active components of the amplifier and transmission circuit of the hearing aid have electromagnetic shielding, for example in the form of a coating of conductive lacquer a metal foil sheath or a plastic coating with embedded conductive plastic. - 3 -

DE-OS 19 45 760 relates to a digital hearing aid in which an analog to protect against electromagnetic waves. Digital converter is arranged in the microphone housing. This is intended to create a digital hearing aid that is largely insensitive to immissions from electromagnetic waves.

In DE-OS 196 02 453 an electrical hearing aid is described in which it is provided to improve the EMC resistance that high-frequency filters are arranged in sensitive components and / or in interference-sensitive line connections of the circuit of the hearing aid and corresponding electrical derivatives for these high-frequency currents can be switched to a potential-forming ground. The mass can be formed by the metal foil coating or lining of a housing made of plastic.

DE-GM 296 08 215 describes a hearing aid in which the integrated circuit is provided with a shield which forms a radio frequency block. This shielding consists of a metallic cage, a metal foil sheathing, a coating of conductive varnish or a plastic sheathing with embedded conductive material.

Finally, it is also known from DE-PS 34 13 891 and DE-PS 41 00 541 to produce metallic shielding layers by means of vacuum arc discharge and anodic evaporation in order to shield the housing against electromagnetic radiation. According to DE-PS 43 07 740, flat plastic plates are provided with a metallic shielding layer and then softened to form the actual housing. The method does not guarantee a complete, self-contained shielding layer in finished housings, since the deformation no longer guarantees the homogeneity of the metallic coating and miniature cracks or "pin holes" for the electromagnetic radiation create entry openings. A further disadvantage is therefore the need for relatively thick layers with a large unevenness over large areas and an inevitable heating of the plastic material, which also has a negative effect on the homogeneity of the metal coating.

From DE-PS 44 40 521 a device for coating substrates with an ionized metal vapor is known. With this device is under negative pressure - 4 -

or vacuum is generated by heating metal vapor, from which a metal vapor plasma is generated by ionization in an arc discharge supported by the metal vapor between the cooled anode and the cooled cathode. From this plasma, the metal is deposited on the flat or flat substrate. The electrical decoupling of the metal vapor source and the ionization device allows the evaporation rate and the degree of ionization to be changed and optimized. It has been shown that the latter method allows a very homogeneous thin metallization on flat plastic objects. However, in order to coat very complicated spatial structures with narrow and comparatively large elevations or depressions, measures must be found to further develop the method in order to adapt the angular divergence and the degree of scatter to the specific application.

Various measures are therefore known from the prior art for shielding hearing aids against electromagnetic radiation. These are either measures such as the provision of electrically conductive coatings on housing components or else the installation of special electronic filter media within the electrical circuit of the hearing aid. The disadvantage of these measures of the prior art, however, is that, on the one hand, as far as the electrical circuit of the hearing aids is changed by an additional arrangement, they are very complex and, on the other hand, the aluminum foil due to the previous shielding measures. Use conductive varnish and conductive plastics, adequate shielding is not possible. Corresponding tests by the applicant have shown that hearing aid wearers with new-type mobile telephones cannot make interference-free calls using this shielding method.

The prior art therefore essentially describes the measures mentioned in order to shield hearing aids against electromagnetic radiation. This includes EMC interference suppression of the microphone by means of interference suppression capacitors, interference-proof constructions of the hearing aid amplifier, shielding the strands between the amplifier and the listener, and the microphone or shielding the housing with appropriate protective layers made of aluminum foils, conductive varnishes or conductive plastic.

The technical object of the invention is therefore to improve the electromagnetic shielding of hearing aids so that the interference radiation into them Hearing aids, for example, of new types of cell phones and other electronic and electrical devices can be suppressed in a simple, inexpensive manner. It should be ensured that even housings and housing seals with a very complicated and versatile shape can be uniformly provided on all sides with an absolutely closed, very thin metal coating of high conductivity.

This object of the invention is achieved by a method for producing a hearing aid shielded against electromagnetic radiation by partially or completely applying a uniformly thin metal layer on the surface of the housing frame and / or the inside of the housing parts by using a plasma vaporization method, with the implementation of the vaporization method metal vapor is generated by heating in a vacuum or vacuum, from which a metal vapor plasma is built up by separate ionization in an arc discharge supported by the metal vapor between the cooled cathode and the cooled anode, from which the metal is deposited on the surfaces. This is achieved according to the invention in that a thermal evaporator unit with a crucible containing at least one metal containing evaporation material is arranged above the anode, the anode encompassing the crucible at least on two sides, that the cathode is positioned at right angles above the anode in such a way that the evaporation lobe of the metal ionized in the cathodic plasma vacuum arc that forms between them extends to a rotating holder for the housing frame and / or housing side parts, that the parameters are set for a closed metal layer thickness of 20 nm to 500 nm such that a) the distance between Anode and evaporator unit between 1 cm to

5 cm and the distance between the anode and cathode is between 10 cm and 20 cm, b the distance between the evaporator unit and the holder is 20 cm to 50 cm. c) the arc power at a vacuum of 2 × 10 ^" * bar and less is between 0.05 and 0.5 kW, the maximum of the ion energy distribution curves being between 0.5 eV and 50 eV. - 6 -

The measures of the invention are based on the cathodic plasma coating method, in which the material to be evaporated is thermally evaporated in an arc discharge between a cold cathode and a cold anode and ionized in the arc, very advantageously for producing very homogeneous metal coatings with preferably between 200 nm and 500 nm lying layer operation are used, which have a very high conductivity when using gold as a coating material, for example with a layer thickness of 400 nm has a surface resistance of only 0.3 to 0.4 ohm / D. This means that by applying metal layers produced according to the invention to housing parts (hereinafter also referred to as substrate parts) of hearing aids, excellent electromagnetic shielding is achieved. The layers deposited using the method have a very high adhesive strength, the temperature load on the plastic substrates being very low given the layer thicknesses achieved, because of the low particle temperature near the substrate. A very high coating rate of approximately 40 nm / s to 50 nm / s with a relatively low arc power also contributes to this. Furthermore, the applied layers are compact and highly abrasion-resistant, which enables the housing parts coated in this way to be further processed.

The high density of the layers also leads to better corrosion resistance of the metallization. Since hearing aids are generally worn behind the ear or in the ear and skin sweat is also present to a greater extent, there is often corrosion of the metallic components of the devices, which can affect the function but also the shielding against electromagnetic radiation . In devices with plastic housings metallized according to the invention, it was found that due to the density of the layer there is considerably better corrosion resistance.

The density of the layer also means that less metallic material has to be used for adequate shielding, since layers of 100 nm to 1000 nm already have a very good shielding effect. This means a considerably cheaper way to shield hearing aids against electromagnetic radiation.

Adapted to a special embodiment or application requirements, different metal layers are used: selected from the group: Copper. Gold. Silver, platinum, aluminum, cobalt, nickel or alloys thereof. It is further preferred to apply a corrosion layer to the metal layer, which can consist, for example, of silicon oxide or aluminum trioxide or titanium dioxide. These layers are also preferably applied by means of the plasma vapor deposition process.

Depending on the plastic materials to be coated, it may furthermore preferably be necessary to apply an adhesion promoter layer made of metal, such as titanium or chromium, before coating or to carry out a plasma pretreatment of the housing parts in a vacuum chamber by means of arc discharge.

With most enclosures, it is not necessary to coat the entire enclosure with metal. According to the invention it is therefore provided that the metal layer is only partially applied. In these cases, the areas not to be coated can be masked by using appropriate shapes or covers, for example silicone molds or coatings, which cover the areas not to be coated. After the coating, these covers are removed.

Another object of the invention is a hearing aid with a shield against electromagnetic radiation, which can be obtained by partially or completely applying a metal layer to the housing frame and the inside of the housing parts, the metal layer being applied by means of the plasma vapor deposition method with a thermal metal vapor source according to the invention becomes.

In a preferred embodiment, the hearing aids are hearing aids, hearing glasses with integrated hearing aids, hearing amplifiers or wireless headphones. Hearing amplifiers are standardized hearing aids that are not individually adapted to the wearer.

The invention is explained in more detail in the following description with reference to the drawing. Show it

Figure 1 is an exploded view of an HDO hearing aid for an arrangement behind the ear.

2 shows the exploded view of an IDO hearing device which is arranged in the ear: - 8th -

Fig. 3 is a schematic representation of an apparatus used for the method according to the invention.

The method according to the invention is carried out in a device according to FIG. 3 as follows. The housing parts to be coated 1; 8 are placed in a vacuum chamber 20, which is then evacuated. By briefly contacting the electrode inserted in the chamber in an electrically insulated manner, namely the cathode and the anode or with the aid of a separate ignition electrode, a plasma vacuum arc is ignited, which burns between the cathode 22 and the anode 23. For cooling, the electrodes are traversed with cooling coils 24. The coating material 26 is thermally evaporated from a crucible 25 located within the vacuum chamber. For this purpose, the crucible 25 is heated via a resistance heater 27. The energy required for this is supplied by a power supply 28 with which the evaporation power can be controlled. The vaporized material, in the present example gold, reaches the arc burning between cathode 22 and anode 23 and is ionized there. The ionized material vapor strikes the surfaces of the housing parts 1 to be coated; 8 down. For this purpose, the housing parts, in the case shown the housing frame 8, are fastened on rotatable mounting disks 30, each mounting disk carrying, for example, six housing frames, which in turn are mounted on a turntable 32. This ensures that all parts pass through different positions of the vaporization lobe.

In order to obtain a homogeneous, closed layer thickness of approximately 20 nm to approximately 500 nm of the desired quality, it is expedient to adhere to the following parameters. The distance between the anode 23 and the evaporation unit 23-27 should be between 1 cm and 5 cm, the anode 23 being mounted under the crucible 25 and encompassing it at least on two sides so that it ends in or above the level of the crucible.

The cathode 22 is at a distance of between 10 cm and 50 cm from the anode 23 and is positioned at a right angle such that the evaporation lobe of the metal ionized in the cathodic plasma vacuum arc which forms between them as far as the rotating holder 30; 32 extends for the housing frame and / or housing side parts. It is considered particularly advantageous if the distance between the evaporator unit 23-27 and the holding amg 30, 32 is approximately 20 to 50 cm and the mounting disks 30 rotate in the opposite direction to the turntable 32. In this way, the frame and / or side parts can be moved at 20 rpm to 100 rpm. In addition to the vertical arrangement shown, a horizontal hanging arrangement can also be selected, the area of the crucible cavity being able to be adapted accordingly.

The thickness of the metal layer can be continuously monitored by layer thickness monitoring sensors during the process and can be regulated by changing the metal evaporation at the metal vapor source and / or the arc power in the vacuum system and, if appropriate, the opening angle of cover plates.

For the control of the arc power it is provided that it is between 0.05 kW and 0.5 kW at a vacuum of 2 x 10 ^" ^ bar and less, the maximum of the ion energy distribution curve should be between 0.5 eV and 50 eV. The control input takes place with the aid of the power supply source 29.

1 shows an exploded view for an HDO hearing aid which is to be worn behind the ear. The housing consists of the housing side parts 1 and a housing frame 8. The housing side parts are provided on the inside with a metal layer, whereas the surfaces of the housing frame 8 are almost completely metallized. The layer thickness of the metallization is preferably 400 nm to 500 nm, as a result of which surface resistances of 0.2 to 0.4 ohm / D can be achieved, which results in a very high shielding performance. 1 also shows a battery drawer 2 for receiving the battery for the hearing aid, an audio contact cover 3 and a battery axis 4a and an axis 4b for the audio contact cover. A microphone cover 5 and a hearing angle 6 are to be attached to the housing frame 8, in which an amplifier group 7 can be used. A hearing tube 9, a receiver 10, a receiver mounting 11, a silicone tube 12, a microphone tube 13, a microphone 14, a microphone mounting 15 and a silicone tube 16 are also accommodated in the housing frame.

2 describes the structure of an IDO hearing aid. that is worn in the ear canal. The hearing aid shell 41 is completely metallized on the inside. In it, a hearing tube 42 is housed a receiver 43 with the receiver strands 44, which with a - 10 -

Amplifiers 45 are connected. Microphone strands 46 lead to the microphone 47. A faceplate 48 is also metallized on the inside and contains battery contacts which are connected to the amplifier 45 via battery wires 49.

With the hearing aids according to the invention and the method for producing an EMC shield in these aids, it is possible for the first time to effectively shield the electromagnetic radiation from mobile telephones of more recent technology. This makes it possible for users of such devices to also be able to use mobile telephones.

The proposed measure of metallizing the housing by means of the vacuum arc process is simple, inexpensive and considerably more effective than previous measures such as the application of EMC lacquers, the use of aluminum foils, the use of metal grids or the shielding of individual switching components or the change in circuitry of the electronic components in the hearing aids. In particular, the usual galvanic and thermal coating processes are unsatisfactory because the parts to be coated are exposed to increased temperature loads.

The following example is intended to explain the invention further.

The following hearing aids were manufactured and tested.

1. IDO hearing aid (in the ear) with EMC protective lacquer in the inner shell area;

2. IDO device with amplifier wrapped in aluminum foil; 3- IDO device with interference suppression capacitors;

4. IDO device with interference suppression capacitors and EMC protective lacquer in the inner shell area;

5. IDO comparison device without shielding;

6. HDO device (behind the ear) with the EMC protective lacquer in the inner shell area;

HDO device with IDO device with amplifier wrapped in aluminum foil;

8. HDO device with interference suppression capacitors; - 11 -

9. HDO device with interference suppression capacitors and EMC protective layer in the inner shell area;

10. HDO device according to the invention with an EMC protective layer of gold applied using the cathodic vacuum arc process;

11. HDO device according to the invention with an EMC protective layer and interference suppressors, the protective layer consisting of gold and applied by means of the cathodic vacuum arc process;

12. HDO comparison device without shielding.

With the hearing aids mentioned above, tests were carried out with DECT radio telephones and GSM mobile telephones of a more recent design. The interfering effect on the test hearing aids was subjectively tested by listening to the devices with a listening fork under the influence of the radiation from the telephones. The radio telephones and mobile phones were moved around the test hearing aids in different positions and the interference was assessed acoustically. Two devices of each hearing aid variant were tested. As the results are almost identical, the individual results are not listed separately.

A subjective rating scale of the interference from 1 to 6 with the gradings 1 = very good, 2 = good, 3 = satisfactory, 4 = sufficient, 5 = poor, 6 = insufficient.

The tests were carried out with the IDO devices with IC4 technology and with HDO devices with BT4 technology. Similar results have also been achieved in experiments with other amplifiers of hearing aids, so that it can be assumed that there is transferability to all other amplifier technologies.

The results shown in Table 1 below were determined in the tests: 12

Number of the test device Rating DECT rating GSM

1 6 6

2 6 6

3 6 6

4 5 5

5 6 6

6 6 6

7 6 6

8 6 6

9 5 5

10 2 2

11 1 1

12 6 6

The experiments clearly show that interference can only be sufficiently shielded with the hearing aids number 10 and 11 according to the invention, so that interference-free telephoning with radio or mobile telephones is possible. With all other tested variants, only a poor shielding is achieved, so that the wearer of such hearing aids cannot make interference-free calls with radio or mobile phones.

Claims

- 13 -patent claims

1. A method for producing a hearing aid shielded against electromagnetic radiation by partially or completely applying a uniform metal layer to the surfaces of the housing frame (8) and / or the inside of the housing side parts (1) using a plasma vaporization method, whereby to carry out the plasma vaporization method by Heating in vacuum or vacuum produces metal vapor, from which a metal vapor plasma is built up by separate ionization in an arc discharge supported by the metal vapor between the cooled cathode and the cooled anode, from which the metal is deposited on the surfaces, characterized in that

- That a thermal evaporator unit (23-27), which is designed as an at least one metal-containing evaporation material (26) receiving crucible (25), above which the crucible (25) is arranged at least on two sides, anode (23),

- That the cathode (22) over the anode (23) is positioned at right angles such that the exhaust lobe of the ionized metal in the cathode plasma vacuum arc forming between them up to a rotating holder (30, 32) for the housing frame and / or extends housing side parts,

- And that for a closed metal layer thickness of 20 nm to 500 nm, the parameters are set such that a) the distance between the anode (23) and evaporator unit (23 to 27) between 1 cm to 5 cm and the distance between the anode (23) and the cathode (22) is between 10 cm and 20 cm, b) the distance between the evaporator unit (23-27) and the holder (30, 32) is 20 cm to 50 cm. - 14 -

c) the arc power at a vacuum of 2 x 10 "* bar and less is between 0.05 to 0.5 kW, the maximum of the ion energy distribution curve being between 0.5 eV and 50 eV.

2. The method according to claim 1, characterized in that the evaporation material is selected from the group consisting of copper, gold, silver, platinum, aluminum, cobalt, nickel or alloys thereof.

3. The method according to claim 1 or 2, characterized in that the on the bracket (30, 32) suspended housing frame (8) and / or housing side parts (1) are rotated at 20 rpm to 100 rpm.

4. The method according to claims 1 to 3, characterized in that an additional corrosion protection layer is applied to the metal layer by means of the plasma vacuum arc process.

5. The method according to claim 4, characterized in that the corrosion protection layer consists of silicon dioxide or aluminum trioxide.

6. The method according to claims 1 to 5, characterized in that an adhesion promoter layer made of suitable metals such as titanium or chromium is applied before the coating. - 15 -

Method according to one or more of claims 1 to 6, characterized in that a plasma pretreatment of the housing parts is carried out in a vacuum chamber before the coating.

8. The method according to any one of claims 1 to 7, characterized in that when a metal layer is partially applied, a masking of the surfaces not to be coated takes place.

9. The method according to claim 8, characterized in that silicone molds or sheet metal parts are used for the masking.

10. The method according to one or more of claims 1 to 9, characterized in that the hearing aid is a hearing aid, a pair of hearing glasses with an integrated hearing aid, a hearing amplifier or a wireless headphone, and that gold is used as the coating metal.

11. Hearing aid manufactured according to one or more of claims 1 to 10, with a shield against electromagnetic radiation.