Electromagnetic signal converter for a bone conduction receiver

Description

FIELD OF THE INVENTION

[0001] The invention relates to an electromagnetic signal converter for a bone conduction receiver, comprising at least one soft magnetic armature which is movable relative to a pole carrying at least one electrical coil, at least one permanent magnet for generating a magnetic bias of the armature, and at least one soft magnetic yoke which, together with the at least one permanent magnet, the at least one pole and the at least one armature, forms at least one magnetic circuit.

[0002] The electromagnetic signal converter should be particularly suitable for use in a bone conduction receiver of a diagnostic device, but also in hearing and communication systems. STATE OF THE ART

[0003] Bone conduction hearing aids, as they are known from the state of the art, convert electrical signals into mechanical vibrations and therefore function as electromagnetic signal transducers and vibration generators. This technology is used in hearing aids, among other things, and is particularly suitable for people with impairments of the outer and middle ear, as in these cases the sound cannot be transmitted as airborne sound to the eardrum and from there by solid-state conduction via the incus and stapes to the cochlea. The acoustic signal to be transmitted to the person is created as an electrical signal or converted from an acoustic signal into an electrical signal, e.g., by being recorded via a microphone. The electrical signal is usually amplified, processed, and passed on to the electromagnetic signal transducer.In the signal converter, the electrical signals are fed to at least one coil, which causes the armature to oscillate accordingly. The oscillator, which serves as the armature, contacts the human body, e.g., at the location of the skull bone. The acoustic signal is transmitted in the form of tactile vibrations, bypassing the middle ear, directly to the inner ear, where it is converted into a nerve impulse in the cochlea.

[0004] High force densities can be achieved with small air gaps, i.e., the working air gaps between the armature and the pole, with low electrical excitation according to the reluctance principle. This shows that the force F acting on the armature is proportional to the square of the air gap induction and thus quadratically dependent on the current supplied to the coil. This quadratic dependence means that the frequency of the force component doubles in the case of a sinusoidal oscillation of the magnetic field. Thus, a signal-accurate reproduction is not possible. In addition, the oscillating movements also change the working air gap, further distorting the transmission behavior.

[0005] By magnetically biasing the armature, where a static magnetic field is generated by one or more permanent magnets, which is superimposed on the dynamic electrically generated field, signal proportionality can be achieved under certain boundary conditions. A solution according to EP 3065420 A1 drastically reduced the magnetic resistance and power consumption by using high-coercivity permanent magnets and thus low magnet heights, as well as by creating secondary flux paths for the electrodynamic excitation. However, the fundamental problems of harmonic distortion and self-adhesion of the armature remain.

[0006] The signal converter of US 2003 / 0034705 A1 also incorporates the principle of superimposing static and dynamic magnetic fluxes in the sense of proportional electromagnetic signal conversion, but with multiple working air gaps, and in one part of the working air gaps, the magnetic fluxes are aligned and in another part, opposite. Furthermore, the signal converter of US 2003 / 0034705 A1 has a different mechanical structure than EP 3065420 A1. On the one hand, an adapter yoke, a coil former, and a coil are connected to each other and act as an armature, and can oscillate relative to a unit consisting of a permanent magnet, yoke, base plate, rod, and counterweight. Thus, in US 2003 / 0034705 A1, there is no armature that is movable relative to the coil.

[0007] The permanent magnet flux creates a reluctance force in the direction of a decreasing magnetic resistance. In some embodiments of US 2003 / 0034705 A1, this reluctance force is compensated by a spring force. In the double-gap systems according to Figs. 4 and 5 of US 2003 / 0034705 A1, no reluctance force occurs when the component acting as the armature is symmetrically positioned. However, this operating point is unstable. As soon as a deflection occurs, a reluctance force also acts in the same direction as this deflection and must be compensated by a spring force. This reluctance force results from the reduction in the total magnetic resistance during deflection, since the decrease in magnetic resistance (increase in magnetic conductance) in the closing working air gap is greater than the increase in resistance in the opening working air gap. The magnetic energy increases, and a force is generated.However, this increase in reluctance force with deflection is not linear and can be described to a good approximation by a third-degree polynomial. The greater the operating point shift of the permanent magnets in the direction of increasing work induction, the greater the reluctance force. The designs according to US 2003 / 0034705 A1 exhibit particularly strong magnetic conductance changes and thus nonlinear reluctance forces. This is because the permanent flux not only closes as shown in US 2003 / 0034705 A1, but also, due to this type of arrangement of the permanent magnets and the air gaps, feeds a secondary path of higher magnetic conductivity to the armature, which generates the electromagnetic flux with its coil.

[0008] Given the stringent requirements for low distortion in a diagnostic device, nonlinearity in the deflection is unacceptable. A progressive spring characteristic would be required to compensate for this nonlinearity, which is very complex.

[0009] However, not only the low harmonic distortion factor is important, but also the intensity of the vibration (this requires a certain spring stiffness between the armature and the vibrating mass) and the correct resonance frequencies, which result from the spring constant and the vibrating mass. It is necessary to make the vibrating mass of the system as large as possible.

[0010] Since the signal fidelity of bone conduction hearing aids is of utmost importance in diagnostic technology, power consumption is of secondary importance, as these devices are usually mains-powered or there is sufficient space for large batteries. OBJECT OF THE INVENTION

[0011] Therefore, it is an object of the present invention to overcome the disadvantages of the prior art and to find an electromagnetic signal converter, in particular, but not only for diagnostic purposes, which leads to fewer large operating point shifts at the permanent magnet (changes in the magnetic conductance) when the armature is deflected, in order to thereby keep the reluctance force, and thus also the non-linearity of the reluctance force, small. DESCRIPTION OF THE INVENTION

[0012] This object is achieved by an electromagnetic signal converter according to claim 1. The starting point of the invention is an electromagnetic signal converter for a bone conduction hearing aid, comprising at least one soft magnetic armature which is movable relative to a pole carrying at least one electrical coil, at least one permanent magnet for generating a magnetic bias of the armature, and at least one soft magnetic yoke which, together with the at least one permanent magnet, the at least one pole and the at least one armature, forms at least one magnetic circuit.

[0013] It is intended that that at least one first and one second pole is provided, each carrying at least one electrical coil, wherein the two poles are of identical construction and are arranged symmetrically to one another on a common pole axis, that the at least one soft magnetic armature, forming an axial working air gap, is arranged between the at least two symmetrically to one another arranged poles and is movable along the polar axis relative to the poles, that the at least one permanent magnet is magnetized perpendicular to the pole axis and is arranged radially outside the at least one armature, that the outer surface of the at least one armature facing the at least one permanent magnet forms a radial air gap via which the armature is magnetically coupled to the permanent magnet, wherein the axial thickness of the permanent magnet is equal to or greater than the axial distance between the two poles.

[0014] In this way, the axial thickness of the permanent magnet is always greater than the axial thickness of the armature between the poles, so that when the armature moves along the pole axis, at least the part of the armature located between the poles—usually the largest part of the armature—always overlaps with the permanent magnet in the axial direction. Due to the resulting projection of the permanent magnet relative to the armature, as well as the magnetic field of the permanent magnet now running perpendicular to the pole axis and thus perpendicular to the armature's movement, the armature experiences smaller magnetic flux fluctuations during its movement. Fewer operating point shifts occur on the permanent magnet, and the reluctance force, and thus the nonlinearity of the reluctance force, are reduced.

[0015] The axial overlap between the armature and the permanent magnet generates a centering force on the armature, depending on the width of the radial air gap and the maximum deflection of the armature. This force counteracts and at least partially compensates for the reluctance force. The width of the radial air gap remains constant, even when the armature moves relative to the permanent magnet(s).

[0016] This ensures a high degree of constancy of the magnetic flux of the permanent magnet(s), meaning a low dependence of the magnetic field of the permanent magnet(s) on the armature's deflection. At the same time, the inventive design of the signal converter exhibits low magnetic resistance in the electromagnetically excited flux path, thus resulting in a high force / current constant.

[0017] Regarding the terms used: A radial air gap has a length in the direction of the pole axis that corresponds to the greatest extent of the air gap area, and a width that results from the distance between the outer surface of the armature and the adjacent permanent magnet, more precisely its pole face, whereby the width is measured in the radial direction to the pole axis. The term thickness (or height) refers to the axial thickness (or axial height), i.e. the thickness (or height) measured in the direction of the pole axis, while axial distance refers to the distance measured in the direction of the pole axis. The axial thickness of the permanent magnet, which refers here to the structure of the signal converter, is otherwise usually referred to as the width of the permanent magnet, with reference to the permanent magnet, because the length and width of a permanent magnet form its pole face. Otherwise, the thickness, again with reference to the permanent magnet, actually refers to the magnet height, which is measured in the direction of magnetization.

[0018] The pole surfaces of the poles facing the armature have surface normals (=pole axes) that point in the direction of the width of the working air gaps and thus lie in the direction of movement.

[0019] The armature has at least two pole faces parallel to each other and at least one outer surface, which is generally perpendicular to the pole faces of the armature. The pole face of the permanent magnet(s) facing inward, toward the armature, faces the outer surface of the armature and forms a radial air gap.

[0020] The armature's outer surface will generally have a straight line parallel to the pole axis in longitudinal section, i.e., a section parallel to the pole axis. Likewise, the pole face of the permanent magnet, which is adjacent to the armature's outer surface and creates the radial air gap with it, will run parallel to the pole axis and thus parallel to the armature's outer surface. This ensures that the radial air gap between the armature's outer surface and the permanent magnet's pole face has a constant width along the pole axis.

[0021] The magnetic flux generated by the permanent magnet(s) closes a first magnetic circuit via the armature, across a working air gap between the armature and one pole, across this pole, and across the soft magnetic yoke. The second magnetic circuit closes via the armature, across the other working air gap between the armature and the other pole, across the other pole, and across the soft magnetic yoke.

[0022] The armature is designed symmetrically to a plane perpendicular to the pole axis. The permanent magnet(s) are also designed symmetrically to this plane. When the armature is at rest, where no movement is induced by the coils, it is held by a suspension so that the first and second working air gaps are equal.

[0023] In its simplest form, the signal converter according to the invention comprises an armature surrounded by one or more permanent magnets.

[0024] The armature is arranged between two similar, symmetrically arranged poles. A soft magnetic yoke closes the two magnetic circuits. The armature, poles, and permanent magnets can be rotationally symmetrical around the pole axis. The permanent magnet(s) would then be ring-shaped or, together, would form a ring.

[0025] The armature could also be rectangular, viewed in the direction of the polar axis. In this case, permanent magnets, e.g., bar magnets, would be arranged on at least two parallel sides of the armature, particularly on the wide sides, parallel to each other in a plane normal to the polar axis, so that the radial air gap between the armature and the permanent magnets is the same size in each case. The bar magnet would then be at least as long as the corresponding side of the rectangle. Preferably, a single bar magnet is used per side.A square armature could also be conceivable as a special case of the rectangular armature, in which case, while maintaining a constant radial gap, bar magnets are provided either for each side of the square, preferably one bar magnet per side of the square, which is at least as long as one side of the square armature, or bar magnets are provided only for two parallel sides of the square, preferably one bar magnet per side of the square, which is at least as long as one side of the square armature. In general, the armature can have the shape of a regular n-gon surrounded by n bar magnets corresponding to one side length of the n-gon, while maintaining a constant radial gap. The poles and coils are generally rotationally symmetrical about the pole axis, regardless of the shape of the armature.

[0026] The pole for an armature can be composed of several sub-poles with their own coils. For example, instead of one pole, four sub-poles could be provided, covering a rectangular armature. It would also be conceivable to divide the armature into several sub-armatures. The coil of a pole can be constructed from several sub-coils, especially of similar types.

[0027] However, the signal converter according to the invention can also comprise multiple units—each composed of an armature, two poles, and a surrounding arrangement of permanent magnets, as well as a soft magnetic yoke. These units can be arranged one behind the other along a common pole axis. And / or these units can be arranged side by side, each with its own pole axis.

[0028] In order to obtain the largest possible oscillating mass, it is preferably provided that the at least one armature belongs to a fixed part of the signal converter, in particular is firmly connected to a housing surrounding the magnetic circuit, while the at least two poles, the at least two coils, the at least one permanent magnet and the at least one soft magnetic yoke are firmly connected to one another and form the oscillating mass of the signal converter relative to the armature.

[0029] The signal converter according to the invention then has, in its simplest form, an armature which is firmly connected to a housing, as well as an oscillating mass which comprises the two poles, the coils of the poles, the permanent magnet(s) surrounding the armature and a soft magnetic yoke.

[0030] Only the armature, perhaps in the form of an armature plate, is firmly connected to the housing, through which the vibrations are transmitted to the human body. All other active components, such as permanent magnets, soft magnetic yoke, poles, and the coil, belong to the oscillating mass, which oscillates relative to the armature and the housing. This maximizes the oscillating mass.

[0031] If the signal converter according to the invention comprises several units - each composed of an armature, two poles and a surrounding arrangement of permanent magnets and a soft magnetic yoke - on the one hand the armatures are connected to each other or all to a housing, just as on the other hand the oscillating masses are connected to each other to form a common oscillating mass.

[0032] To further increase the oscillating mass, the oscillating mass can contain at least one additional mass that is less magnetizable than the poles, the armature, or the soft magnetic yoke. The additional mass should not play a role in the magnetic circuit, so it could be non-magnetizable or at least less magnetizable than the magnetizable elements of the magnetic circuit.

[0033] Typically, the stationary part of the signal converter is connected to the oscillating mass of the signal converter via spring elements. The spring elements hold the armature between the two poles in the resting state, ensuring that the first and second working air gaps are equal. Preferably, the armature is elastically connected to the oscillating mass via at least one spring, particularly a leaf spring. Preferably, one spring is provided axially outside each soft magnetic yoke, thus providing a total of two springs. The armature is suspended from the spring(s), and the resonant frequency of the oscillating system is determined by the spring constant of the spring(s) and the oscillating mass.

[0034] The nonlinearity of the reluctance force is advantageously reduced if the greatest dimension of the armature measured radially to the pole axis is greater than the greatest dimension of the poles measured radially to the pole axis. In particular, the greatest dimension of the armature measured radially to the pole axis can be greater than the greatest dimension of the end face of the pole, i.e., the pole face facing the armature, measured radially to the pole axis.

[0035] In one embodiment of the invention, the armature is plate-shaped, at least in the region radially within the poles. Plate-shaped means that the end faces are flat and parallel to one another, and the distance between the end faces, i.e., the axial height or thickness of the armature, is smaller than its radial extent. Even if the armature extends radially beyond the poles, it can have the same height in this region as between the poles. The armature would then be entirely plate-shaped. The plate shape of the armature results in a flat design of the signal converter.

[0036] In one embodiment of the invention, the axial thickness of the armature expands radially outside the poles toward the outer surface of the armature. This improves the magnetic coupling to the permanent magnet(s) and reduces the nonlinearity of the restoring force. This expansion occurs symmetrically in both directions of the pole axis.

[0037] In one embodiment of the invention, the poles are plate-shaped and have a recess for the coil, which is accommodated within the plate thickness. The pole then has a pole core that supports the coil and a pole plate or pole shoe that does not support a coil and faces the armature. Here, too, "plate-shaped" means that the end faces of the pole, also called pole faces, are flat and parallel to one another, and the distance between the end faces, i.e., the axial thickness of the pole, is smaller than its greatest radial dimension. The plate shape of the yoke promotes a low overall height of the signal converter.

[0038] In one embodiment of the invention, it is provided that the soft magnetic yoke has a plate-shaped cover for each pole, which rests against the pole in the axial direction and covers it in the radial direction, as well as at least one wall which adjoins the covers and encloses the poles with coil, the armature and the at least one permanent magnet radially outwardly, and to which the at least one permanent magnet is attached. There are thus two covers and at least one common wall which connects the two covers to one another. In particular - viewed in the circumferential direction around the pole axis - walls are provided at least where permanent magnets are located. In particular, the permanent magnets are countersunk on this wall or, radially wholly or partially, into this wall. For example, if there is a rectangular armature that only has permanent magnets on the broad sides of the rectangle, a wall could only be provided on one broad side of the armature.The two lids and the two walls would then have the shape of a cuboid shell.

[0039] It is also conceivable that a closed, circumferential wall is provided around the pole axis. This way, the armature and the poles are completely surrounded by soft magnetic material. The two covers and the circumferential wall would then have the shape of a hollow cylinder or a hollow cuboid, for example.

[0040] To ensure the connection of the permanent magnet(s) to the at least one magnetic circuit and to minimize the installation space in the radial direction, it can be provided that the at least one permanent magnet is arranged inside a recess in the wall. In particular, the at least one permanent magnet will be flush with the wall or the surfaces of the recess. SHORT DESCRIPTION OF THE CHARACTERS

[0041] The invention will now be explained in more detail using exemplary embodiments. The drawings are exemplary and are intended to illustrate the inventive concept, but in no way restrict it or represent it exhaustively. They show: Fig. 1 shows a longitudinal section through a schematically illustrated signal converter according to the invention in a first embodiment, Fig. 2 shows a longitudinal section through a schematically illustrated signal converter according to the invention in a second embodiment, Fig. 3 shows a longitudinal section through a schematically illustrated signal converter according to the invention in a third embodiment. WAYS OF IMPLEMENTING THE INVENTION

[0042] The signal converter in Fig. 1 essentially consists of two identical poles 1a, 1b, each with an electric coil 2, two permanent magnets 3 in the form of cuboid magnets, the longitudinal direction of which is normal to the plane of the drawing, and a plate-shaped armature 4. The poles 1a, 1b and the coils 2 are rotationally symmetrical about the pole axis 5. The armature 4 is not rotationally symmetrical about the pole axis 5, but rather rectangular. Each pole 1a, 1b extends with its pole face 6 to the armature 4 up to an operating air gap 7 for the armature 4. The poles 1a, 1b are plate-shaped and have a recess with a trapezoidal cross-section for a coil 2 on the end face facing away from the armature 4. Of course, the poles 1a, 1b and the coils 2 can also be constructed differently.

[0043] In Fig. 1 the radial length of the armature 4 is greater than that of the poles 1a, 1b. The permanent magnets 3 are arranged in the radial direction at the same distance from the pole axis 5 and here - measured in the direction of the pole axis 5 - are thicker or higher than the armature 4. The armature 4 is entirely plate-shaped. The permanent magnets 3 are arranged radially outside the armature 4 with respect to the pole axis 5 and, with its outer surface 15 (which here consists of four rectangles), form a radial air gap 14 via which the armature 4 is magnetically coupled to the permanent magnets 3. The air gap 14 has a constant width over the height of the outer surface 15 of the armature 4, both in a state where no electrical signal is applied to the coils 2 and in a state where an electrical signal is applied to the coils 2 and the armature 4 is deflected from its rest position.

[0044] To close the two magnetic circuits, a soft magnetic yoke 8 is provided, which consists of two similar U-shaped or bridge-shaped parts and is essentially designed as a cuboid shell. In other words, the soft magnetic yoke 8 is composed of two plate-shaped covers 9, which axially bear against the poles 1a, 1b and here also against their coils 2 and cover the poles 1a, 1b in the radial direction, as well as two flat, straight walls 10 (shown left and right in Fig. 1 ), which connect to both covers 9 and enclose the poles 1a, 1b with coils 2, the armature 4, and the permanent magnets 3. In this example, no walls 10 (and no permanent magnets 3) are provided parallel to the plane of the drawing, so the yoke 8 is open here. However, it would be conceivable that two more walls 10 (with or without permanent magnets 3) could be provided parallel to the plane of the drawing, so that the yoke 8 would have the overall shape of a hollow cuboid.

[0045] On the inside of the wall 10 there is a recess in which the permanent magnet 3 is fixed at least with its outer pole face.

[0046] The soft magnetic yoke 8 can also be formed in two parts in another way, e.g. by a cover 9 and the wall 10 forming a part in the shape of a pot, onto which the other cover 9 is then placed.

[0047] The permanent magnets 3 are magnetized perpendicular to the pole axis 5 and are designed, for example, as Sm2Co17 or NdFeB magnets. The poles 1a, 1b can be made of soft magnetic metal. The armature 4 and the soft magnetic yoke 8 can be made of the same material as the poles 1a, 1b.

[0048] A housing that encloses all of the mentioned and illustrated parts of the signal converter, protects them against environmental influences, and can be placed on the body of the patient to be examined is not shown here. The armature 4 is firmly connected to this housing and resiliently connected to the oscillating mass of the signal converter, so that it can move freely relative to the oscillating mass, i.e., relative to the poles 1a, 1b with coils 2, the permanent magnets 3, and the soft magnetic yoke 8, along the pole axis 5. The poles 1a, 1b, the coils 2, the permanent magnets 3, and the soft magnetic yoke 8 are firmly connected to one another and together form the oscillating mass. Of course, additional masses 16 can also be arranged on the oscillating mass, as shown in Fig. 3 is shown.

[0049] The armature 4 is elastically connected to the oscillating mass via two leaf springs 17, which Fig. 1 is not shown, but Fig. 3 can be removed. The two working air gaps 7 are adjusted by the preload of the leaf springs 17. The magnetic flux electrically excited by the coils 2 is superimposed on the permanent magnetic flux, which has the opposite direction in both working air gaps 7. The magnetic flux goes, for example, from the armature 4 to the pole faces 6 of the poles 1a, 1b. The electrically excited magnetic flux runs along the pole axis 5 from top to bottom or vice versa. In this way, it reduces the magnetic flux in one working air gap 7 and increases it in the other working air gap 7. This leads to different forces on both sides and the armature 4 moves by reducing the working air gap 7 with the stronger magnetic flux. The movement of the armature 4 is transmitted to the human body via the housing (not shown).

[0050] The signal converter according to Fig. 2 is very similar to that in Fig. 1 , it is therefore important to Fig. 1 Said and therefore only the differences are explained. The coils 2 are located in Fig. 2 in the rectangular cross-section recesses of the poles 1a, 1b. The recesses for the coils 2 in Fig. 1 und 2 are, however, interchangeable.

[0051] The anchor 4 is in Fig. 2 plate-shaped only between the poles 1a, 1b. Outside of the poles 1a, 1b, the axial height or thickness of the armature 4 expands symmetrically in both directions of the pole axis 5, namely by approximately a quarter of the height or thickness of the armature 4 between the poles 1a, 1b. The height of the outer surface 15 is preferably greater than the axial distance between the pole faces of the two poles 1a, 1b. However, the height of the outer surface 15 is preferably smaller than the axial thickness of the permanent magnets 3, more precisely smaller than the axial dimension of the pole face of the permanent magnets 3 facing the armature 4. The shape of the armature 4 in Fig. 1 und 2 are interchangeable.

[0052] Concentrically around the pole axis 5, a bore 12 is provided through the poles 1a, 1b, the soft magnetic yoke 8 and through the armature 4 itself, in order to connect the armature 4 to the housing (not shown), e.g., by screwing it. In addition, several smaller bores 13 are provided to screw the soft magnetic yoke 8 to the poles 1a, 1b. Of course, the soft magnetic yoke 8 could also be connected to the poles 1a, 1b in a different way, such as by gluing. Corresponding bores 12 and / or smaller bores 13 (or gluing instead of the bores 13) are also possible for the design according to Fig. 1 necessary.

[0053] In the cover 9 of the soft magnetic yoke 8, a total of four threads 11 are marked, which are also shown in the design according to Fig. 1 and 3 These are used to screw on and pre-tension the leaf springs 17 using screws 19, see Fig. 3 .

[0054] The execution according to Fig. 3 is similar to that according to Fig. 1 , so that only the differences or features that are beyond Fig. 1 go out. In Fig. 3 It is shown how the fixed part and the oscillating part of the signal converter are connected to each other by means of leaf springs 17. This is the case with the versions according to Fig. 1 und 2 should also be provided.

[0055] Clearances must be provided at yoke 8, pole 1a, 1b and armature 4 to establish a connection between armature 4 and leaf springs 17. These clearances are to be achieved through a central bore 12 in Fig. 2 realized, as well as by two corresponding holes next to the pole axis 5 in Fig. 3 . In these holes of the Fig. 3 One threaded pin 20, each of which runs through the entire assembly and thus through the armature 4, and two threaded sleeves 22 are inserted, each of which runs through the cover 8 and a pole 1a, 1b. The leaf springs 17 are placed on the threaded pins 20 and secured with nuts 21. The threaded pins 20 then also serve to couple the armature 4 to a housing. Of course, the connection between the armature 4 and the leaf springs 17 can also be made in another way.

[0056] Yoke 8 and poles 1a,1b are in Fig. 3 glued so that holes 13, as they are in the execution according to Fig. 2 are omitted.

[0057] Additional masses 16 are in the design according to Fig. 3 radially between the poles 1a, 1b and the wall 10 of the soft magnetic yoke 8 and axially between the permanent magnet 3 and the cover 9 of the soft magnetic yoke 8. Also in the versions according to Fig. 1 und 2 Additional masses 16, e.g. on the Fig. 3 appropriate bodies.

[0058] This signal transducer is used in hearing and communication systems as well as for audio diagnostics. The associated bone conduction receiver (osteophone) is worn and applied to the human or animal skull. The size of the bone conduction receiver and thus of the signal transducer must be dimensioned according to its application. In some designs of this signal transducer, the latter is very small; in this case, its external height, measured from cover 9 to cover 9 along axis 5, is approximately 8-10 mm. The diameter of the soft magnetic element 8, i.e. from the outside of wall 10 to the outside of the opposite wall 10, is 15-25 mm, e.g., 20 mm. The permanent magnet 3 has, for example, an axial height of 2-5 mm, e.g., 3 mm, and a radial dimension of 1-2 mm, e.g., 1.5 mm. LIST OF REFERENCE SYMBOLS

[0059] 1a, 1bPole 2Coil 3Permanent magnet 4Armature 5Pole axis 6Pole face of pole 1a, 1b 7Working air gap 8Soft magnetic yoke 9Cover 10Wall 11Thread 12Bore 13Bore 14Air gap 15Surface of armature 4 16Additional mass 17Leaf spring 18Spacer 19Screw 20Threaded pin 21Nut 22Threaded sleeve

Claims

1. Electromagnetic signal converter for a bone conduction receiver, comprising - at least one soft-magnetic armature (4) which is movable relative to a pole (1a, 1b) that supports at least one electric coil, - at least one permanent magnet (9) for generating a magnetic bias of the armature (4), as well as - at least one soft-magnetic yoke (8), which forms at least one magnetic circuit together with the at least one permanent magnet (3), the at least one pole (1a, 1b) and the at least one armature (4), characterized - in that at least one first pole (1a) and one second pole (1b) are provided, each of which carries at least one electric coil (2), wherein the two poles are identical in design and are arranged symmetrically with respect to one another on a common pole axis (5), - in that the at least one soft-magnetic armature (4) is arranged between at least two poles (1a, 1b) arranged symmetrically with respect to one another, thereby forming in each case an axial working air gap (7), and is movable along the pole axis (5) relative to the poles (1a, 1b), - in that the at least one permanent magnet (3) is magnetized perpendicularly to the pole axis (5) and is arranged radially outside the at least one armature (4), - in that the lateral surface (15) of the at least one armature (4) facing the at least one permanent magnet (3) forms a radial air gap (14), via which the armature (4) is magnetically coupled to the permanent magnet (3), wherein the axial thickness of the permanent magnet (3) is equal to or greater than the axial distance between the two poles (1a, 1b).

2. Signal converter according to claim 1, characterized in that the at least one armature (4) belongs to a fixed part of the signal converter, in particular is fixedly connected to a housing surrounding the magnetic circuit, while the at least two poles (1a, 1b), the at least two coils (2), the at least one permanent magnet (3) and the at least one soft-magnetic yoke (8) are fixedly connected to one another and form the oscillating mass of the signal converter, relative to the armature (4).

3. Signal converter according to claim 2, characterized in that the oscillating mass contains at least one additional mass which is less magnetizable than the poles (1a, 1b), the armature (4) or the soft-magnetic yoke (8).

4. Signal converter according to claim 2 or 3, characterized in that the armature is elastically connected to the oscillating mass via at least one spring, in particular a leaf spring (17).

5. Signal converter according to one of the preceding claims, characterized in that the largest extension of the armature (4) measured radially to the pole axis (5) is larger than the largest extension of the poles (1a, 1b) measured radially to the pole axis (5).

6. Signal converter according to one of the preceding claims, characterized in that the armature (4) is plate-shaped at least in the region radially inside the poles (1a, 1b).

7. Signal converter according to one of the preceding claims, characterized in that the axial thickness of the armature (4) expands radially outside the poles (1a, 1b) towards the lateral surface (15) of the armature (4).

8. Signal converter according to one of the preceding claims, characterized in that the poles (1a, 1b) are plate-shaped and have a recess for the coil (2) accommodated within the plate thickness.

9. Signal converter according to one of the preceding claims, characterized in that the soft-magnetic yoke (8) has, for each pole (1a, 1b), a plate-shaped cover (9) which abuts the pole (1a, 1b) in the axial direction and covers it in the radial direction, and at least one wall (10) which adjoins the cover (9), which encloses the poles (1a, 1b) with coil (2), the armature (4) and the at least one permanent magnet (3) radially outside and to which the at least one permanent magnet (3) is fastened.