DE1167389B - Electromagnetic receiver - Google Patents

Description

Electromagnetic Receiver The invention relates to a electromagnetic receiver with an armature, which is on the magnetic pole face of a magnetic circuit facing away from a membrane made of non-magnetic Material lies.

Electromagnetic receivers of this type are known.

The receiver according to the invention is characterized in that the Anchor is arranged in the middle part of the concave surface side of a membrane and that the magnetic circuit passes through an air gap at the front of the central part of the convex Surface side of the membrane separate inner pole and a concentric outer pole has outer pole arranged around the inner pole.

A receiver according to the invention is stable and highly sensitive. Further is the influence of creep strain of the membrane on the receiver due to the magnetically attractive forces, which normally act on the membrane, are reduced. After all, impurities entering the air gap have between them the membrane and the anchor set, little influence.

Further details emerge from the following description with reference to the figures.

F i g. 1 shows a sectional view of a magnetic circuit in one usual recipient; F i g. 2 shows a sectional view of a magnetic circuit of a Receiver according to the invention; F i g. 3 shows a characteristic diagram of a usual recipient; F i g. 4, 5 and 6 show arrangements of the membrane and the anchor; F i g. 7 shows a characteristic diagram of the displacement of the membrane as a function the additional force acting on the membrane; F i g. 8 shows the relationship between the creep of the membrane and time; F i g. 9 and 10 show the Relationships between the magnetic gap between the pole piece faces and the armature and the strength; F i g. 1 shows a view of the spatial association between the membrane and anchor; F i g. 12 shows a section through the arrangement according to FIG. 11; F i G. Figure 13 shows a cross-sectional view of an embodiment of a receiver according to the invention; F i g. 14 shows a characteristic diagram of the receiver of FIG. 13th

For the performance of an electromagnetic telephone receiver of the non-equilibrium type, it is most important that the sensitivity be large over is the required frequency range and that it operates stably.

The formula that represents the sensitivity of a receiver is given as a function of the frequency stiffness by the following formula: In this formula, P = generated sound pressure, Z = receiver impedance, A = force factor of the receiver, K = spatial coefficient of elasticity of the air, So = effective area of the receiver membrane, Vc = volume of the coupling and so = rigidity of the receiver oscillating system. In formula (1) is given by 2 2 so = «) omo, where co, = 2,1rfo = resonance angular frequency and m, = effective mass of the receiver membrane.

If the stiffness of the air chambers in front and back of the membrane is neglected, s, in formula (2) is given by: So = Soo - Sia , (3) where soo = stiffness of the receiving membrane and s ". = Negative stiffness.

In order to increase the sensitivity, the right side of the formula (1) can be made larger. If the dimensions of the telephone receiver have the prescribed value (S, is not changed) and if Z is determined by the formation of the tone circle on the other side, then the arrangement of the receiver can still be changed.

When the relationship of the formula (3) is rewritten as So = Sn (f -1), (4) so is Stability factor. So if s is determined by the formation of the magnetic circuit, it is possible to make it smaller by reducing the stability factor u.

The method of designing a common receiver will be described with reference to FIG. 3 explained. When interpreting common receivers, separate reference is made to the sizes A and, u. In order to make A larger, the magnetic gap g is made smaller so that s, the critical stability force, u "ii, which is assumed at the value s. In the magnetic gap, can be made the critical value of the sensitivity, which - as shown in Fig. 3 - becomes larger and more effective as the magnetic gap becomes smaller. However, this method has a disadvantage. If the normal magnetic gap is g6, the sensitivity can be expected to increase by making it smaller to a magnetic gap ga. If the magnetic gap or the air gap becomes narrower, however, this leads to the following deficiencies: Unless very tight manufacturing tolerances are prescribed, it is difficult to limit g and thus the sensitivity in a given range. Furthermore, g changes due to the creep expansion of the membrane of an electromagnetic receiver that is always present. The fluctuations in sensitivity therefore become large. Finally, the narrower the air gap, the easier it is for dust or dirt to enter or be generated in the air gap during manufacture or use, which easily induces accidental contacts. According to the teaching of the invention, a non-magnetic membrane is placed on the armature side of the magnetic gap so that the magnetic gap can be made larger without the air gap being changed as a result. This enables the sensitivity to be increased without the above-mentioned three defects occurring. In order to demonstrate the effects produced by the invention, accurate measurements were made of the relationship between the magnetic attraction force and the magnetic gap and the displacement of the diaphragm by the force. Further, it was investigated whether the influence of eddy currents caused by the teaching of the invention, which flow to the metallic non-magnetic body in the magnetic gap, can be made small, so that the advantages obtained by the invention are not negated. It has been found that stable and highly sensitive receivers can be constructed using the teachings of the invention.

The transmission band of the sensitivity of the receiver is through the resonance frequency f determined. The upper limit frequency of the transmission band must have the value given by the design conditions. For example is at a receiver with a system oscillating in three degrees of freedom specified deviation of about 3 db in the range of 300 to 3600 Hz from the sensitivity frequency characteristic the resonance frequency f, about 1700 Hz. To increase the sensitivity, therefore at the same time so and m, are made smaller, these values satisfying the formula (2).

A highly sensitive and stable receiver is obtained by makes it larger, for which purpose the membrane is designed and arranged as described above, and it is made to vibrate, as also described above.

In Fig. 1 is a magnetic circuit for a common receiver shown. In Fig. 2 is a magnetic circuit for a receiver according to the Invention shown. 1 is an armature, 2 is an outer pole, 3 is an inner pole, 4 is a bobbin, 5 is a bobbin. In the F i g. 1 and 2 is the inner pole 3 cylindrical. The coil 4 is wound on the coil carrier 5, and the coil carrier 5 is fitted to the outside of the inner pole 3. In the arrangement according to FIG. 1, the outer pole 2 is concentric and cylindrical on the outside of the coil 4 wrapped. The armature lies opposite the upper boundary surface of the inner pole 3 and the outer pole z. In the arrangement according to FIG. 2, however, is the outer pole 2 bent inwards, the anchor 1 is smaller, and the opposite area of the armature 1 and the outer pole 2 is the same as before. Still has the coil 4 the same size.

If the outer diameter of the inner pole 3, the thickness of the outer pole 2, the dimensions of the coil 4 and the thickness of the armature 1 of the arrangement according to FIG. 2 dimensioned in the same way as in the arrangement according to FIG. 1, on the other hand, in the arrangement according to FIG. 2 the outer pole 2 is bent inwards and the outer diameter of the armature 1 is made smaller, this results in the electrical performance, that is the value - in the formula (1), when measured, the same values as in FIG. 1. Without reducing the driving forces, the mass of the armature can be made smaller.

On the other hand, mo = Aa + ma, (5) where md = effective mass of the non-magnetic body part of the membrane and m " = mass of the armature. Md is so closely related to soo and the creep resistance of the membrane that it is not made sufficiently small Therefore, m ″ can only be made smaller by making m ″ smaller, as can be seen from FIG.

Next, consider the membrane. It is known that in membrane structures according to FIGS. 4, 5 and 6, in which a flexible part 6 is provided within the clamping surface on the circumference and whose inner part is spherical, conical or horn-shaped, i.e. in which the flexible part and the inner part swing together, so in formula (1) are made large can. However, if the characteristics of force and displacement in such a membrane, as shown in Figs. 5 and 6 is shown, clamped, measured, the result in FIG. 7 relationships shown. Curves 7 , 8 and 9 relate to membranes with a thickness of 0.06, 0.08 and 0.1 mm. The displacement under the action of a force acting on the diaphragm is therefore small when the force is small, or when the thickness of the diaphragm is large or, in other words, when the stress exerted on the material of the diaphragm is small. However, when the thickness of the diaphragm becomes smaller, the displacement deviates from linearity even with a small force.

The deviation is also not symmetrical if the direction of force is changed. Rather, as shown in FIG. 7 recognizable - the shift is smaller, when the diaphragm is pushed towards its convex surface as if it were is pushed in the opposite direction.

In the case of using a membrane in an electromagnetic receiver, a magnetic attraction force acts statically on the membrane and, furthermore, a restoring force generated by the deformation of the membrane acts in the opposite direction to the magnetic attraction force. Both forces keep each other in balance. If a membrane 0.06 mm thick is used, it is brought into an equilibrium position which corresponds to points A or B in FIG. 7 corresponds. In order to reduce soo and m, - these are the conditions for obtaining high sensitivity, as described above - it is necessary to use a membrane that is thinner than 0.1 mm and therefore does not shift linearly. It makes a difference whether such a membrane works around working point A or around working point B. The former case - that is, the case where the magnetic circuit is on the side of the convex surface of the diaphragm - is more advantageous. In particular, there are two stability advantages, as will be described below.

The first benefit relates to the creep resistance of the membrane. If a membrane is used in an electromagnetic receiver, the magnetic gap becomes of the receiver becomes smaller over time due to the creeping of the membrane. This lies the magnetic forces of attraction that constantly act on the membrane. Will If this effect is large, the sensitivity and other characteristics of the Until it is no longer usable.

The creep of the same membrane in the case of operating at the working point A in Fig. 7 and at working point B was measured. An example of the measurement results shows Fig. B. Curve A shows creep when the concave surface part alone was loaded and when a force was acting in the direction of the convex surface. the Curve B indicates the creep of the diaphragm when a force is applied in the opposite direction to which the curve A worked. The amount of creep is about half of in the first case that in the second case. It follows that in case A, the receiver is particularly stable are formed.

A second advantage in terms of stability results from the consideration of u. To do this, refer to the diagram in Fig. 9, in which the abscissa represents the magnetic gap between the pole piece surfaces and the armature and the ordinate represents the force. The curve a in FIG. 9 represents the magnetic attraction force acting on the armature. Curves b to d represent the restoring forces due to the displacement of the diaphragm. Curve b applies to the case where the magnetic circuit is on the side of the concave surface of the diaphragm lies. It shows that when the forces of attraction of the magnetic circuit are not effective, the magnetic gap g3 is changed to the gap g, when these forces of attraction set in and come into equilibrium with the restoring force F. g, thus indicates the state of equilibrium. As in Fig. 7 is curve b in FIG. 9 curved downwards. If a non-magnetic body of a thickness corresponding to the magnetic gap 92 is in the air gap, for example on the surface of the armature or the pole piece and the minimum value of the magnetic gap is g2 (the air gap is zero), curve b is always above curve a, and the The restoring force of the membrane is always stronger than the magnetic force of attraction. These relationships are shown in curves a and b in FIG. 9 in relation to the magnetic gaps g2 and g, can be seen. As soon as the armature comes into contact with the surface of the pole piece with any vibration, it is therefore returned to the original position by the restoring force of the membrane, and a stably operating receiver is therefore obtained. The stability factor, u results from the ratio the tangent soo of curve b at point P to tangent s "of curve a at point P. If the equilibrium position at point P is selected by changing the stiffness of the membrane by changing the thickness or any other dimensions of the membrane, one of the results is obtained Curve corresponding to curve b by rotating curve b about point P. For example, a curve such as curve b 'is obtained for the restoring force As described above, it is necessary for the stability of the receiver that these curves not correspond to curve a between magnetic gaps g2 and g, cut. in order to make, and the smallest in the range satisfying this requirement, obviously, the curve of the curve must be selected b. in the case b the critical stability force that can be reduced.

If the magnetic circuit is on the side of the convex surface of the membrane, the curve in FIG. 7 the restoring force, for example as a curve e. If such a curve is to lead to the critical stability force by reducing the stiffness of the membrane in the same way as in the case described above, curve d is obtained. The stability factor, among others in this case, obviously has a lower value than the value, ub, which was previously obtained. It was found that the expected increase in sensitivity actually occurred. The curve c also has the property that its tangent soo at point P is equal to that of the curve b described above. The stability, u and the sensitivity are therefore the same in both cases. However, the difference between the restoring force of the diaphragm and the magnetic attraction force in curve c is so much larger than in curve b that curve c can be considered to be more stable.

The effect of the non-magnetic body in the air gap will now be described. It has already been explained in the explanation of FIG. 9 emphasizes that a non-magnetic plate of a thickness corresponding to g2 is inserted into the air gap. Since the magnetic gap in FIG. 9 may also be zero instead of g ", it is readily understood that even if a non-magnetic plate is inserted, the same effect occurs and the same explanation of the effect applies in this connection. The non-magnetic plate, however, is effective to increase the stability factor to lessen u. Magnetic gap s "Critical AA Stability force - mm 108 dynes / cm p. dyn / amp so Operation at point P2 on curve d. . . . . . . . . . 0.20 0.185 0.320 1.73 1.0-106 0.19 Operation at point Pl on curve b. . . . . . . . . . 0.15 0.242 0.627 2.59 1.1 - 108 0.14 As can be seen from the table, the effect of lowering the stability li due to a non-magnetic plate is greater than the lowering of the force factor due to the necessity of increasing the air gap. The value for is about 1.36 times larger. Will this value When used in the formula (1), it is found that the sensitivity increases by about 2.6 db. In the course of these tests, quantities other than A and so in formula (1) were not changed.

The F i g. 11 and 12 show an embodiment of the invention in which a non-magnetic plate is provided. An armature 1, to which some compression bodies are attached (16), lies in the middle of a conical membrane 10. The magnetic circuit lies in the direction of the convex surface of the membrane 10 (at the bottom in FIG. 12) and is also from this side operated out. To explain this, reference is made to FIG. 10, in which curve a represents the magnetic forces of attraction and curves b to d represent restoring forces of the membrane. The curves are curved like the curves explained above. (In FIG. 10, the curves are shown in a simplified straight line in order to avoid complications which arise from the fact that curves in both directions and straight lines had to be shown in their entirety. Exactly the same explanation as for FIG. 9 applies for all curves according to FIG. 10.) The critical value to which the stiffness of the membrane can be reduced in the present case if a magnetic gap g1 is used and without the non-magnetic plate, which is arranged in a conventional receiver , is given by the karve b, which intersects the point P3. The critical stability force at point P1 is in this case, ub. If the non-magnetic plate g2 is inserted, the critical value of the restoring force of the diaphragm is obtained from curve c, and the critical stability force, uc, becomes obviously smaller than, ub. In this case, however, the width of the air gap is g, -g2 and less than the air gap width g1 in the case of curve b. If dust or dirt or other impurities accidentally enter the air gap for any reason, the receiver will work poorly. For this reason, the measures described so far are not always recommended. Therefore, if the non-magnetic plate g2 is inserted and the magnetic circuit becomes longer by the thickness of the plate and it is further operated at g1 ', the critical rigidity is as in the curve d, and the stability factor is lid in this case.

Measurement results relating to the stability factor will now be given below and other characteristics in the event that the membrane uses curve d at point P2 was compared with measured values for curve b at point P1. In the following table are the measured values in the case of a thickness of the non-magnetic plate of 0.05 mm specified. The thickness of the membrane material corresponds to g2 in FIG. 9 and 10. It there is an advantage that even if the strength of the connection between membrane and anchor is weaker than with a conventional receiver in which the armature is directly opposite the magnetic pole face, the armature through the magnetic attraction is not released. There is also the advantage that the magnetic attraction force at point g1 'in F i g. 10 so much lower is than in g that the risk of the membrane creeping is less.

F i g. 13 shows an embodiment of an electromagnetic receiver according to the invention. A coil 4 is wound on a bobbin 5 which is fitted on the outside of a cylindrical inner pole. An outer pole 2 lies on the outside of the coil 4. The front end of the outer pole 2 is bent inward. A magnet 12 is located outside of the bobbin 5. A magnetic circuit is formed from these parts. The inner pole, the bobbin, the outer pole, a ring 11 and a yoke 13 are encompassed by a frame 14 in such a way that they combine to form the magnetic circuit. An armature 1 is glued to the center of a membrane 10 made of a non-magnetic body. The anchor is .mit some compression bodies 16 occupied. After the armature 1 is arranged on the side of the membrane facing away from the magnetic circuit, the membrane is fastened by means of a housing 15 and a cover 17.

F i g. 14 shows the frequency characteristic of the receiver according to FIG Invention as shown in FIG. 13 is shown.

Claims (6)

Claims: 1. Electromagnetic receiver with an armature, the side facing away from the magnetic pole face of a magnetic circuit a membrane made of non-magnetic material, characterized in that the armature (1) is arranged in the central part of the concave surface side of a membrane (10) and that the magnetic circuit is one through an air gap from the central part of the convex surface side of the membrane separate inner pole (3) and one concentric has outer pole (2) arranged around the inner pole on the outside. 2. Electromagnetic receiver according to claim 1, characterized in that the armature (1) is fitted into the concave surface side of a conical membrane (10) and that a magnetic circuit (2, 11, 13, 3) with an air gap on the side of the convex surface of the conical membrane lies. 3. Electromagnetic receiver according to claim 2, characterized characterized in that the anchor (1) on the concave surface side of the conical Membrane (10) is covered with pressed bodies (16). 4. Electromagnetic receiver according to claim 1 to 3, characterized in that the magnetic circuit (2, 11, 13, 3) has an inwardly curved outer pole (2). 5. Electromagnetic receiver according to one of claims 1 to 4, characterized by a magnetic circuit with an inner pole (3), a coil (4) and an inwardly bent outer pole (2). 6. Electromagnetic receiver according to one of the preceding Claims, characterized in that the outer pole (2) is bent inwards. References considered: U.S. Patent No. 2,535,757.