US3803521A

US3803521A - Electromechanical band-pass filter

Info

Publication number: US3803521A
Application number: US00366590A
Authority: US
Inventors: M Hetzel
Original assignee: ELRESOR
Current assignee: ELRESOR
Priority date: 1972-06-12
Filing date: 1973-06-04
Publication date: 1974-04-09
Anticipated expiration: 1991-04-09
Also published as: CH566091A5; FR2188362B1; JPS5652492B2; US3914719A; DE2330288A1; CH571291A5; DE2330288C3; NL7308120A; JPS4963361A; FR2188362A1; DE2330288B2; GB1427537A; USB366589I5; DE2330287A1

Abstract

An electromechanical band-pass filter is provided with transducers to convert electrical energy to mechanical motion, or convert mechanical motion to electrical energy. Each transducer includes a magnetic member and a coil member movable relative to each other. The magnetic member is supported on a leaf spring for movement in a plane parallel to the surface of a ferromagnetic member. Each coil member comprises a flat coil mounted on a ferromagnetic member, each coil having straight conductor segments extending at a right angle to the relative motion.

Description

United States Patent Hetzel Apr. 9, 1974 3,529,414 9/l970 Ganter et a] 310/25 X Primary Examiner-Archie R. Borchelt [75] Inventor: Max Hetzel, Bienne, Switzerland Assistant Exammer-Marvm Nussbaum [73] Assignee: Elresor SA, Bienne, Switzerland Attorney, Agent, or FirmGriffin, Branigan and Butler [22] Filed: June 4, 1973 l N 366 590 [57] ABSTRACT [21 1 App An electromechanical band-pass filter is provided with transducers to convert electrical energy to mechanical [30] Foreign Application Priority Data motion, or convert mechanical motion to electrical June 12, 1972 Switzerland 8684/72 gy- Each transducer includes a g ic er June 12, 1972 Switzerland ..8685/72 and a oil member movable relative to each other. 7 The magnetic member is supported on a leaf spring [52] U.S. Cl. 333/71, 333/30 R for movement in a plane parallel to the surface of a [51] Int. Cl. H03h 9/04, H03h 9/26 ferromagneti member. Each coil member comprises [58] Field of Search 333/71, 30 R; 310/25 a flat coil m u d n a ferromagnetic m h coil having straight conductor segments extending at a [56] References Cited right angle to the relative motion.

UNITED STATES PATENTS 10 Claims, 6 Drawing Figures 3,485,035 l2/l969 Ganter et al. 310/25 UX I s N 1? g N s 9 41 c 9 7 i I y Y '15 I I MEI 1 BF 3 SHEET 2 BF 3 Fig.2

I 2 1: gig/7L w M N N RE: W

fATENTEDAPR 9 1974 SHEET 3 [IF 3 ELECTROMECHANICAL BAND-PASS FILTER these resonators an electromagnetic transducer in form of a coil with a permanent magnet located therein is provided to convert an electrical signal into a mechanical motion of the resonator.

The other resonator is also provided with a coil and a permanent magnet core to convert mechanical motion of the second resonator into an electrical output signal. As is usual on such electromechanical filters, the resonator is moved toward the coil and back therefrom, so that a relatively large air gap is required to prevent touching of the resonator at the coil. U.S. Pat. No. 3,480,809 shows a prior art filter of this type.

If the air gap between coil and resonator is large, the coupling factor is small. However, if a small coupling factor is present, the filter cannot be adjusted by means of electric terminating resistances to the desired pass curve. As a result thereof only relatively small bandwidths are possible because each resonator generates for itself a pass curve. If an attempt is made to increase the bandwidth, an undesired ripple occurs in the middle of the pass region. A filter of relatively small bandwidth or with a relative large ripple in the pass region is not suitable for certain applications, for instance as the band-pass filter in a central remote control system, where low frequency signals are transmitted over the power mains.

A further consideration is that the low coupling factor of the transducer of the prior art filter has an effect such that the damping curve does not ascendto an infinite value at low frequencies, but attains a fixed value for the frequency zero, i.e., for DC current. The prior art filter is therefore not capable of blocking low frequencies, which again makes this filter unsuitable for certain applications. I

It is an object of the present invention to provide an electromechanical filter which does not have the cited disadvantages and which, particularly in the lower low frequency region (100 to 1,000 hertz) has a' relatively large bandwidth but only a very small ripple in the pass region of the damping curve.

According to the invention this is obtained on a filter of the type described above by providing that each resonator comprises a leaf spring to which a permanent magnet system forming the magnet member of the transducer is attached, that the coil member of the transducer comprises a flat coil lying in a plane arranged practically parallel to the oscillation plane of the resonator, that the permanent magnet system comprises a permanent magnet of high coercitive material located above the conductors of each half of the flat coil, both magnets being connected together by a yoke of ferromagnetic material and arranged in such a way that the free ends of the permanent magnets are of opposite polarities, and that the direction of magnetization of the permanent magnets extends parallel to the plane of the leaf spring and vertically to the plane of the coil, and that a ferromagnetic part is provided underneath the flat coil to complete the magnetic circuit of the permanent magnet system.

in a band-pass filter according to the invention, the air gap between permanent magnet system and flat coil of each transducer can be kept very small. The magnetic circuit of the transducer carries from one permanent magnet over a short yoke to the other permanent magnet and from there over the air gap containing the windings of one half of the flat coil to the ferromagnetic part and from there again over the air gap with the windings of the other half of the coil back to the first mentioned permanent magnet. This advantageous design of the magnetic circuit has only small losses and permits, in combination with permanent magnets of high coercitive material, preferably a samarium cobalt alloy, the production of a very strong magnetic field in the air gaps. Thus, it is important that the permanent magnets magnetized vertically to the plane of the coil are not located adjacent to each other over a single half of the coil, as is frequently the arrangement on tuning fork oscillators where magnetic coupling is of secondary importance. Since the permanent magnets are located at a distance from each other, this prevents a large part of the magnetic flux from extending directly from a north pole to a south pole without vertically passing through the windings.

The high electromagnetic coupling factor of the transducers of the inventive band-pass filter permits attainment of the desired relatively wide bandwidth. For a good filter it is important that it can be adjusted by electrical terminating resistances to the desired bandpass curve to avoid the undesirable ripple in the pass region.

In prior art filters the use of high coercitive materials creates great difficulties or is impossible, because of the danger that the high attraction forces may cause the parts movable relative to each other to touch and block the resonator. On the other hand, in the band-pass filter according to this invention the direction of magnetization parallel to the plane of the leaf spring has the advantage that the forces act edgewise on the leaf spring, so that it can hardly be deformed by th high coercitive forces. In this way, a constantly, equal air gap is assured.

According to a preferred embodiment of the invention the ferromagnetic part carrying the flat coil extends on both sides further than the flat coil in the direction of the relative movement of the magnet system and the flat coil. The magnetic force lines of the permanent magnet system can enter practically vertically into the ferromagnetic part after having crossed the relatively small air gap containing the flat coil, and by the relative motion between the permanent magnet on one side of the flat coil with the ferromagnetic part on the other side, the magnetic force lines are moved vertically to their direction back and forth. The magnetic force lines also retain their original configuration during the movement because they are not deflected from their direction by the ferromagnetic part extending further than the coil. In this way, it is possible to obtain very high flux changes in the coil. The ferromagnetic part preferably comprises a material with small eddy current losses.

According to a preferred embodiment of the invention the windings of the flat coil comprise straight conductor sections located substantially parallel to each other and approximately at a right angle to the relative motion, the straight conductor section representing the active part of the flat coil. This provides that in the operation of the transducer the magnetic field remains substantially limited to this active part. In this way, a good coupling factor of the transducer is assured.

An embodiment of the invention will now be described by reference to the drawing.

FIG. 1 is a top view of an electromechanical band filter comprising two electrodynamic transducers;

FIG. 2 shows a view of an electrodynamic transducer of an electromechanical band-pass filter;

FIG. 3 is a sectional view taken along the line II of FIG. 2;

FIG. 4 is a perspective view of the basic parts of the electrodynamic transducer;

FIG. 5 shows a view of the transducer on which a leaf spring is used to mount the permanent magnet system at a small distance above the flat coil; and,

FIG. 6 is a side view of the transducer shown in FIG. 5.

FIG. 1 shows a band-pass filter provided'with two electrodynamic transducers l and 1a. One transducer serves to convert electrical energy into mechanical motion of a first resonator, and the other transducer serves to convert mechanical motion into electrical energy.

The mass of a permanent magnet system 2 serves together with the mass of a leaf spring 41 as oscillating mass, so that the unit comprising permanent magnet system 2 and the leaf spring 41 represents a mechanical resonator.

In the example of the band-pass filter shown, the leaf springs 41 are connected to a support 43 which represents a mass coupling the resonators. Also mounted on the support 43 is part 5 (FIG. 3) with flat coils 3. The whole is suspended on supporting means (not shown) by suitable means such as thin rods 51, 53 and 55, for example. Other suspension means may be used provided that a high coupling factor can be obtained.

The design and operation of a single electromagnetic transducer'of the band-pass filter will now be explained with reference to FIGS. 2 to 6. As can be seen from the drawing, the electrodynamic transducer basically comprises three parts, namely a permanent magnet system 2, a flat coil 3 and a ferromagnetic part 5.

The flat coil 3 and the ferromagnetic part 5 form a mechanical unit. The permanent magnet system 2 is located above the flat coil 3 at a small distance in such a way that the permanent magnet system and the flat coil can move relative to each other.

The flat coil 3 comprises a number of windings 7 which preferably comprise insulated copper wire. The design of the coil as a flat coil has the advantage that the air gap between the permanent magnet system 2 and the ferromagnetic part 5 can be kept small. A flat coil can also be safely fastened in a simple way on the ferromagnetic part 5. Fastening is preferably accomplished by glueing in such a way that the individual windings 7 of the flat coil.3 extend parallel to the surface 11 of the ferromagnetic part 5. The flat coil 3 has a form such that the windings 7 have straight conductor sections 9, as best shown in FIG. 4. In the embodiment shown, each winding has two straight conductor sections 9 lying in the flux region l3, 15 (FIG. 4) of the magnetic circuit 17 (FIG. 3). These straight conductor sections form the active part of the flat coil 3. The straight conductor sections are located at approximately a right angle to the relative motion.

The permanent magnet system 2 preferably comprises a plate-like part or yoke 21 on one side of which two arms are provided at a distance from each other. These arms, 23 and 25, are preferably permanent magnets. The permanent magnets may, for example, comprise a samarium cobalt alloy, and are magnetized in such a way that one magnet has at its free end a magnetic north pole and the other magnet has at its free end a magnetic south pole. It would eventually also be possible to utilize a one piece permanent magnet system, if a magnetic path 17 is provided which is of such form that the magnetic flux lines extend approximately perpendicularly to the surface 11 of the ferromagnetic part.

The permanent magnet system 2 is designed such that the magnetic field is substantially limited to the active part, that is to the straight conductor sections 9, of the flat coil 3. This provides that the magnetic flux lines intersect, on a relative motion of the permanent magnet system 2 and the flat coil 3, only the straight conductor sections 9 of the windings 7. This provides for a high coupling factor.

Either the permanent magnet system 2 or the flat coil 3 may form the movable part. It would also be possible to move both parts. However, it is necessary for the mutual influence that there by relative motion between permanent magnet system 2 and flat coil 3. This can be a back and forward movement. It is important that the air gap 29 remains constant during relative motion be tween permanent magnet system 2 and flat coil 3, and this is the case when the permanent magnet system 2 is moved parallel to the surface 11 of the ferromagnetic part 5. To provide a forward and backward movement parallel to the surface of the ferromagnetic part 5 a leaf spring 41 (FIG. 5) can be provided, which is arranged in such a way that its flexing axis is perpendicular to the surface 11 of the ferromagnetic part 5. Accordingly, the permanent magnet system can only move parallel to the surface 11 of the ferromagnetic part 5. According to the embodiment shown in FIGS. 5 and 6 the ferromagnetiepart 5, together with the flat coil, is supported on a support 43 comprising an arm 45. One end of the leaf spring 41 is mounted on the arm 45, whereas the other end of the leaf spring 41 carries the permanent magnet system 2. In this arrangement of the leaf spring the permanent magnet system can be moved parallel to the surface 11 of the ferromagnetic part, whereas a movement in the direction of the coil is impossible, because in this direction the leaf spring is stiff. Therefore, the permanent magnet system 2 cannot be drawn into contact with the flat coil by the acting magnetic forces.

The electrodynamic transducer shown, particularly according to the embodiment of FIGS. 5 and 6, is admirably suitable for use in a resonator system of the type required in electromechanical filters.

For mechanical to electrical transducing, an induced voltage is generated at the terminals of the flat coil 3 according to the law of induction. This voltage U (FIG. 4) is proportional to the relative velocity V, and the number of conductors N and the length Iof the conductors in the field.

Because the straight conductor sections 9 in both flux regions 13 and 15 are connected in series it follows that:

One recognizes proportionality between velocity V and voltage U.

For electrical to mechanical transducing, a current I is applied to the flat coil 3 and a force K acts on the straight conductor sections 9 in the flux regions 13 and 15 of the magnetic field lines B of this field. The force K is determined by the following formula:

whereby l is the length of the conductor in the field and N is the number of conductors. The force K accelerates the permanent magnet system 2 relative to the flat coil 3.

The described electrodynamic transducer is, because of its small size and its high ratio of magnetic field energy to magnetic mass, particularly well suited for band-pass filters requiring a relatively large bandwidth.

While a preferred embodiment of the invention has been disclosed in specific detail, various modifications and substitutions in the preferred embodiment may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. An electromechanical band-pass filter having transducers for converting electrical energy into mechanical motion of a resonator, and for converting mechanical motion of a resonator into electrical energy, each transducer comprising a magnet member and a coil member movable relative to each other, characterized in that:

each resonator comprises a leaf spring to which a permanent magnet system forming the magnet member of the transducer is attached;

the coil member of the transducer comprises a flat coil lying in a plane parallel to the oscillation plane of the resonator;

the permanent magnet system comprises a permanent magnet of high coercitive material located above the conductors of each half of the flat coil;

both magnets are connected together by a yoke of ferromagnetic material and arranged in such a way that the free ends of the permanentmagnets are of opposite polarities;

the direction of magnetization of the permanent magnets extends parallel to the plane of the leaf spring and vertically to the plane of the coil; and,

that a ferromagnetic part is provided underneath of the flat coil to complete the magnetic circuit of the permanent magnet system.

2. An electromechanical band-pass filter as claimed in claim 1, characterized in that the permanent magnets consist of a samarium-cobalt-alloy.

3. An electromechanical band-pass filter as claimed in claim 1, characterized in that the windings of the flat coil comprise straight conductor section located substantially parallel to each other and approximately at a right angle to the relative motion, said straight conductor sections representing the active part of the flat coil; and that the permanent magnets are of such design that the magnetic field remains substantially limited to said active part of the fiat coil.

4. An electromechanical band-pass filter as claimed in claim 1, chracterized in that the ferromagnetic part extends on both sides further than the flat coil in the direction of the relative movement, so that the form of the flux path in the air gap between the permanent magnet system and ferromagnetic part remains substantially the same in every position of the relative movement thereof.

5. An electromechanical band-pass filter as claimed in claim 1, characterized in that the ferromagnetic part consists of a material with low edge current losses.

6. An electromechanical band-pass filter as claimed in claim 5, characterized in that the ferromagnetic part consists of ferroxcube.

7. An electromechanical band-pass filter as claimed in claim 6, characterized in that the ferromagnetic part consists of lamellar iron.

8. An electromechanical band-pass filter as claimed in claim 2, characterized in that the windings of the flat coil comprise straight conductor sections located substantially parallel to each other and approximately at a right angle to th relative motion, said straight conductor sections representing the active part of the flat coil; and that the permanent magnets are of such design that the magnetic field remains substantially limited to said active part of the flat coil.

9. An electromechanical band-pass filter as claimed in claim 3, characterized in that the ferromagnetic part extends on both sides further than the flat coil in the direction of the relative movement, so that the form of the flux path in the air gap between the permanent magnet system and ferromagnetic part remains substantially the same in every position of the relative movement thereof. 1

10. An electromechanical band-pass filter as claimed in claim 9, characterized in that the ferromagnetic part extends on both sides further than the flat coil in the direction of the relative movement, so that the form of the flux path in the air gap between the permanent magnet system and ferromagnetic part remains substantially the same in every position of the relative movement thereof.

Claims

1. An electromechanical band-pass filter having transducers for converting electrical energy into mechanical motion of a resOnator, and for converting mechanical motion of a resonator into electrical energy, each transducer comprising a magnet member and a coil member movable relative to each other, characterized in that: each resonator comprises a leaf spring to which a permanent magnet system forming the magnet member of the transducer is attached; the coil member of the transducer comprises a flat coil lying in a plane parallel to the oscillation plane of the resonator; the permanent magnet system comprises a permanent magnet of high coercitive material located above the conductors of each half of the flat coil; both magnets are connected together by a yoke of ferromagnetic material and arranged in such a way that the free ends of the permanent magnets are of opposite polarities; the direction of magnetization of the permanent magnets extends parallel to the plane of the leaf spring and vertically to the plane of the coil; and, that a ferromagnetic part is provided underneath of the flat coil to complete the magnetic circuit of the permanent magnet system.

3. An electromechanical band-pass filter as claimed in claim 1, characterized in that the windings of the flat coil comprise straight conductor section located substantially parallel to each other and approximately at a right angle to the relative motion, said straight conductor sections representing the active part of the flat coil; and that the permanent magnets are of such design that the magnetic field remains substantially limited to said active part of the flat coil.

4. An electromechanical band-pass filter as claimed in claim 1, characterized in that the ferromagnetic part extends on both sides further than the flat coil in the direction of the relative movement, so that the form of the flux path in the air gap between the permanent magnet system and ferromagnetic part remains substantially the same in every position of the relative movement thereof.

9. An electromechanical band-pass filter as claimed in claim 3, characterized in that the ferromagnetic part extends on both sides further than the flat coil in the direction of the relative movement, so that the form of the flux path in the air gap between the permanent magnet system and ferromagnetic part remains substantially the same in every position of the relative movement thereof.