Ceramic Resonators

Abstract

In a ceramic resonator of the type comprising an outer casing, a disc shaped ceramic resonator element, a pair of resilient terminal members on both sides of the resonator element, each including a projection for supporting the resonator element, and a split inner casing contained in the outer casing for containing the resonance element and terminal members, one half of the split inner casing is provided with an annular rib on its mating surface and a cylindrical recess inside the annular rib, and the other half of the split inner casing is provided with a cylindrical recess on its mating surface for receiving the annular rib whereby when the resonator and the terminal members are assembled in a space defined by the recesses of the inner casing halves, the resonator element is resiliently supported between the projections of the terminal members at its geometrical center.

Description

This invention relates to a ceramic resonator and more particularly to a ceramic resonator for use in a filter wherein a ceramic resonator element disposed in a space of an inner casing is securely supported by two resilient terminal plates.

In the so-called ceramic resonator, a ceramic element is utilized as a resonator element and the expansion vibration or contour vibration of the element is utilized for performing the filtering function. Thus for example, in the case of a resonator in the form of a circular disc shaped ceramic element, as the geometrical center of the element coincides with the nodes of respective vibrations, it is possible to provide the desired filtering characteristics by supporting the element at its physical center because such method of supporting does not disturb the mode of vibration of the resonator element.

According to a prior art supporting mechanism, a pair of resilient supporting members are provided with opposing projections adapted to engage and support the geometrical center of the element. According to another supporting mechanism, lead wires are soldered directly to the geometrical center thus supporting the element by the lead wires.

Although both of these supporting mechanisms have been used widely because of their simple construction, they are not yet satisfactory. Thus, with the mechanism utilizing the resilient supporting members, as the projections are urged against the element merely by the resiliency of the supporting members, the supporting force is not sufficient so that the outer ends of the projections may disengage the geometrical center of the element thus varying the filter characteristics. Further, with the supporting mechanism using lead wires it is necessary to reduce as far as possible the diameter of the lead wires for minimizing the effect thereof upon the vibration of the element. However, fine lead wires are liable to be broken by mechanical vibrations and shocks.

It is an object of this invention to provide an improved ceramic resonator wherein a ceramic resonance element contained in a space of an inner casing of a special construction is stably supported by resilient leaf terminal plates.

Another object of this invention is to provide a new and improved ceramic resonator which can well withstand mechanical vibrations and shocks and has stable operating characteristics not affected by such vibrations and shocks.

According to this invention there is provided a ceramic resonator of the type comprising an outer casing, a disc shaped ceramic resonator element, a pair of resilient terminal members on both sides of the resonator element, each one of the terminal members including a projection for supporting the resonator element, and a split inner casing for containing the resonator element and terminal members, the inner casing being contained in the outer casing, characterized in that one half of the split inner casing includes an annular rib on its mating surface and a cylindrical recess inside the annular rib and the other half includes a cylindrical recess on its mating surface for receiving the annular rib whereby when the resonator element and the terminal members are assembled in a space defined by the recesses of the inner casing halves, the resonator element is resiliently supported between the projections of the terminal members at its geometrical center.

The recesses of the outer casing halves are dimensioned to snugly receive the terminal members and the resonator element so as to minimize their lateral displacement when subjected to mechanical vibrations or shocks.

The present invention can be more fully understood from the following detailed description when taken in conjunction with the appended drawings, in which:

FIG. 1 shows an exploded perspective view of various component elements of one example of the ceramic filter embodying the invention;

FIG. 2 shows a section of one half of the split type inner casing shown in FIG. 1 and taken along a line II--II;

FIG. 3 shows a longitudinal section of the assembled ceramic filter; and

FIG. 4 shows a perspective view of one half of a modified split type inner casing.

The ceramic resonator shown in FIGS. 1 to 3 comprises a circular disc shaped ceramic resonator element 1 having electrodes 2 coated on the opposite sides thereof by firing silver films. Two resilient terminal plates 11a and 11b are made of resilient electroconductive material such as phosphor bronze for example, and respectively comprise circular enlarged portions 11a.sub.1 and 11b.sub. 1 of equal diameter and leads 11a.sub. 2 and 11b.sub. 2 integral with and extending from the enlarged portions. Enlarged portions are provided with projections 12 and 14 respectively. One of the terminal plates 11b is formed with a U shaped slot around the projection 14, thus forming a cut out tongue 13.

The inner casing comprises split halves 5a and 5b of generally rectangular configuration. Each half is formed of strong insulating material, polyacetal resin for example, and each provided with a recess so that when two halves are assembled together there is formed a cavity adapted to receive resonator element 1 and two resilient terminal plates 11a and 11b. The assembly is contained in an outer casing 3 with tongues 3b.sub.1 and 3b.sub.2 which are used to mount the resultant assembly on a chassis or a printed board.

One half 5a of the inner casing is provided with an annular rib 4 at its mating surface, the diameter of the inner cylindrical surface or recess 4' of the rib 4 being slightly larger than the diameter of the resonator element 1, by for example 0.2 to 2 millimeters. At the bottom of recess 4' is formed a second circular recess 4" of smaller diameter to contain the enlarged portion of the resilient terminal plate. A portion of rib 4 is notched as at 4a and a tangential rib 7 is provided in parallel with one side edge of the half 5a. Ribs 4 and 7 have the same height.

The other half 5b of the inner casing is provided with three cylindrical recesses 6, 6' and 6" of decreasing diameters thus forming a stepped construction. The outermost recess 6 snugly receives annular rib 4 of first half 5a, the intermediate recess 6' has the same diameter as said cylindrical recess 4' and the innermost recess 6' receives the enlarged portion of the resilient terminal plate. At the bottom of recess 6" is formed a rectangular recess 8. Further, this other half 5b is provided with a relatively shallow slot 9 at a position corresponding to notch 4a of rib 4 and a relatively deep groove 10 adapted to receive straight rib 7. Recess 8 is dimensioned to receive tongue 13 of the resilient terminal plate 11b when the tongue is slightly bent down.

Component parts of the ceramic resonator described above are assembled together as shown in FIG. 3. More particularly, enlarged portion 11a.sub.1 of terminal plate 11a is fitted in recess 4" of the half 5a and then the resonator element is placed in recess 4' inside rib 4 so that the geometric center of the element 1 is supported by projection 12 of terminal plate 11a. The enlarged portion 11b.sub.1 of terminal plate 11b is placed in recess 6" of the other half 5b such that upon assemblage, the projection 14 will come to engage the geometrical center of the other electrode 2. Thereafter, two halves are assembled together by fitting ribs 4 and 7 in recess 6 and groove 10 respectively. Then, lead 11b.sub. 2 will be firmly held between rib 7 and groove 10 and lead 11a.sub.2 will be received in notch 4a and groove 9.

Furthermore, as the enlarged portions of respective terminal plates are firmly held in the bottom of respective recesses, the resiliency of tongue 13 firmly holds the element in position. As shown in FIG. 3, the thickness of the cavity defined by recesses 4' and 6' is designed to be slightly larger than the thickness of the element 1. After assembling both halves in this manner to form the inner casing, the assembly is disposed in the outer casing 3. The opening of the outer casing is sealed by a casting resin 15 such as epoxy resin.

With this construction, the resonator element is clamped between resilient terminal plates with a sufficient pressure. Further, as the lateral movement of the resonator element is prevented by recesses 4' and 6' of the inner casing halves, the resonator element is always maintained in position with its geometrical center aligned with the projection of the terminal plates regardless of large vibrations or shocks, whereby variation of the characteristics of the resonator caused by vibrations or shocks can be positively prevented.

When the ceramic resonator of this invention was subjected to a vibration test wherein the vibrating frequency was varied continuously from 55Hz to 10Hz under an acceleration of 10g where g represents the acceleration due to gravity of the earth and to a shock test wherein the ceramic resonator was dropped 10 times on a concrete floor from a height of 1500mm, variation in the resonance frequency fr and in the mechanical quality coefficient Q.sub.M were only 0.01 percent and 2 to 5 percent, respectively which are sufficiently small for the practical purpose.

Even, under the most adverse condition, the periphery of the resonator element engages the inner surfaces of the recessed 4' and 6' so that it is possible to limit the lateral displacement of the element or hence the variations in fr and Q.sub.M to a minimum.

The continuous annular rib 4 shown in FIG. 1 may be replaced by a plurality of circumferentially spaced apart segments of rib 41 as shown in Fig. 4. Further, it is clear that ribs 4 and 7 on one half 5a and grooves 9 and 10 on the other half 5b may be interchanged, and that tongue 13 may be formed for both terminal plates.

Claims

What is claimed is:

1. A ceramic resonator comprising:

an outer casing;

a disc shaped ceramic resonator element adapted to vibrate in the radial expansion mode;

a pair of resilient terminal members on both sides of said resonator element, each one of said terminal members having a projection for electrically contacting and supporting said resonator element;

an inner casing contained in said outer casing having a cavity for containing said resonator element and said terminal members therein, said cavity having a diameter slightly larger than that of said resonator element, said inner casing including two members, the first inner casing member being provided with an annular rib and a cylindrical recess inside of said annular rib on one surface thereof, and the second inner casing member being provided with a cylindrical recess for receiving said annular rib of the first inner casing member, said first and second inner casing members being mated with each other to define said cavity by said recesses thereof, said ceramic resonator element and resilient terminal members being mounted within said cavity such that said ceramic resonator element is resiliently supported between said projections of said resilient terminal members at its geometrical center, with a space between said ceramic resonator element and the walls of said cavity.

2. The ceramic resonator according to claim 1 wherein said cavity of said inner casing has a diameter which is 0.2 to 2 millimeters larger than that of said ceramic resonator element.

3. The ceramic resonator according to claim 1 wherein said inner casing is of polyacetal resin.

4. The ceramic resonator according to claim 1 wherein said annular rib on the first inner casing member comprises a plurality of circumferentially spaced apart segments.

5. The ceramic resonator according to claim 1 comprising an additional recess formed substantially centrally of the inner wall of at least one of said first and second inner casing members for receiving at least a portion of a resilient terminal member.