JPS6322484B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an edge mode mechanical filter having a configuration in which a resonator and a transducer using an edge mode as a vibration mode are elastically coupled by a coupler.

Conventionally, filters for intermediate frequency (IF) in the medium wave band include ceramic filters that utilize the contour vibration of a disc or square plate, or flexural vibration of a disc.
A mechanical filter is used that utilizes the longitudinal vibration of a rod and the torsional vibration of a cylinder. In such conventional ceramic filters and mechanical filters, supporting the resonator and transducer and attaching the input/output lead wires are generally done by soldering the support wires or lead wires to the vibration nodes, or by using protrusions. This has been carried out by methods such as pressure-welding terminal plates having a terminal plate.

However, although the displacement is zero at the vibration node, the stress is not zero. For example, if solder is added to the vibration node, the solder acts as stiffness and causes an increase in the resonant frequency. Furthermore, if supports and lead wires are attached to the bending vibration nodes of the rectangular plate, even if the displacement is zero, the influence of the rotational moment on the vibration cannot be avoided. On the other hand, when using a method of pressure-welding the terminal plate, there are serious problems in practice, such as variations in characteristics due to misalignment of the contact portions and poor contact due to vibrations and shocks.

In order to fundamentally solve these problems, the inventors of the present invention have filed Japanese Patent Application Nos. 54-156067 and 1982-156068.
As shown in the issue, we proposed the use of edge modes, which have a vibrational energy distribution concentrated only at the edges of the piezoelectric plate. In addition, we have actually developed edge mode piezoelectric resonators and three-terminal filters using this technology, and these have achieved resonance for medium-wave bands with small dimensions and good characteristics that are almost unaffected by support and lead wire attachment. It was shown that ceramic filters and ceramic filters can be obtained.

The present invention further applies such an edge mode to a mechanical filter, and is particularly characterized in that the edge mode is used as the vibration mode of a resonator or a transducer that is a component of a mechanical filter.

Hereinafter, the present invention will be explained in more detail using the drawings.

First, before entering into a description of the mechanical filter of the present invention, the characteristics of the edge mode resonator disclosed in Japanese Patent Application No. 156067/1988 will be briefly described.

FIG. 1 shows an edge mode vibration pattern of a thin rectangular plate. FIG. 2 shows the calculation results of the areal strain distribution in this mode. The numerical values shown in FIG. 2 are relative values of areal strain when the maximum value is 10. From these figures, the vibration energy of this mode is extremely concentrated at the edges, and at a distance of approximately 1.5 times the plate width or more from the edge, both displacement and stress become almost zero.
It can be seen that supporting and fixing this part has no effect on vibration.

An example of the configuration of a resonator using such an edge mode is shown in FIG.

FIG. 3 is a plan view showing an example of the electrode structure of a piezoelectric ceramic resonator used at least as an input or output resonator in the present invention. a is a front electrode, and 2 is a back electrode.

Drive electrodes 2 and 3 are formed by sputtering or the like on both the front and back surfaces near the ends of a piezoelectric ceramic plate (length L, width 2H) polarized in the thickness direction (perpendicular to the plane of the paper). In order to effectively excite edge mode vibration, the drive electrodes 2 and 3 are approximately semicircular to match the shape of the areal strain distribution, as shown in FIG.

In addition, in the areal strain distribution shown in FIG. 2, there are two areas opposite to each other on both sides near the end of the porcelain plate where the sign of the areal strain of the portion corresponding to drive electrodes 2 and 3 is opposite and the relative value is large. Set of opposite phase drive electrodes 4, 6
and form 5 and 7.

The surface electrodes 4 and 6 are leaded and connected to the other end which has almost no effect on vibration. And terminal 2'
An electrical signal is input or output between 4' and 6'.

In this case, a piezoelectric ceramic plate polarized in the thickness direction is used as the resonator material. By shaping the drive electrode as shown in the figure to match the areal strain distribution shown in FIG. 2, effective excitation of the edge mode becomes possible. The resonator frequency of this edge mode resonator 1 is almost determined by the width 2H of the rectangular plate 1a. When using a piezoelectric ceramic plate, the resonance frequency is 455K.
Hz, the width 2H of the plate will be approximately 3 mm. Therefore, the length L of the rectangular plate 1a including the fixed part will be the width 2
If it is taken to be about 2.5 times H, the total length L of the plate is about 7.5
mm. Therefore, it can be seen that by utilizing the edge mode, a very small and easily supported resonator can be realized even in this frequency band.

Next, the edge mode mechanical filter of the present invention will be explained.

The edge mode resonator has the most basic structure in which two edge mode resonators 1 and 1' configured as shown in FIG. 3 are elastically coupled by a coupler 8.
Mechanical filters are shown in Figures 4 and 5. In Figure 4, the resonators 1 and 1' are arranged in the direction perpendicular to the board surface, and the position for attaching the coupler 8 is selected at the edge of the board, and in Figure 5, the resonators 1 and 1' are arranged in the horizontal direction. A connector 8 is attached to the side of the board. In FIGS. 4 and 5, the electrodes 4a and 6 of the resonator 1 on the input side
Connect a and the output side electrodes 4a' and 6a', and use these as a common ground terminal.A lead wire is attached to the input resonator's electrode 2a, and a lead wire is attached to the input terminal P and the output side resonator's electrode 2'a. and set it as the output terminal Q. Furthermore, as described above, in the edge mode, the vibrational energy is concentrated at the edge of the substrate, so the resonators 1, 1' are supported and fixed at the other end 9 of the substrate where no vibrational energy is present.

FIGS. 6, 7, and 8 show the structure of a mechanical filter in which the structure shown in FIGS. 4 and 5 is expanded to have a multi-stage configuration, that is, a plurality of resonators and transducers are elastically coupled by a coupler. and are shown in Figure 9, respectively. Here, FIG. 6 shows a case in which the resonators arranged in the thickness direction of the plate are coupled by a connector 8 attached to the end of the plate, and FIG. This is the configuration for the case where the child 8b is used. On the other hand, FIGS. 8 and 9 show configurations in which the resonators are arranged laterally and are elastically coupled by the connectors 8 on the sides, but in FIG. 9, unlike in FIG. 8,
The coupler 8 and the resonator are integrated and can be manufactured by punching out a single substrate. By increasing the number of resonators 10 in this way, a correspondingly steeper cutoff characteristic can be realized.

The resonator 10 inserted between the two input and output transducers 1 and 1' does not necessarily need to be provided with a drive electrode, and a constant elastic alloy such as Elinvar can also be used as the resonator material.

FIG. 10 shows an embodiment of the mechanical filter of the present invention, which has the configuration shown in FIG. , shows the filter characteristics when connected by a connector with a diameter d=0.3 mm and a length l _c =2.5 mm. As shown in the figure, a guaranteed attenuation value of approximately 30 dB was obtained, and good characteristics were also achieved in terms of cutoff characteristics and passband loss.

Although specific configuration examples of the present invention have been described above, the configuration of a mechanical filter based on this principle is not limited only to the above configuration examples.
In addition to the shape of the electrode of the above-mentioned transducer, the present inventors have already disclosed the shape of the electrode in Japanese Patent Application No. 54-156067~.
Of course, as proposed in No. 8, a rectangular electrode or a semicircular electrode adapted to the area strain distribution of the edge mode may be used at the end of the vibrator.

Furthermore, a constant elastic alloy such as Elinvar or the same piezoelectric material as the transducer can be used as the material of the resonator. When Elinbar is used, a piezoelectric film such as ZnO or a thin piezoelectric ceramic film can be applied to the resonator at both ends, and this can be used as a transducer. Furthermore, although a transducer using edge mode was used as an input/output transducer, it is also possible to use a transducer using other vibration modes such as bending vibration, which is conventionally used in mechanical filters. It is possible.

As described above, according to the present invention, it is possible to support and fix or pull out the lead without affecting vibration at all, and as a result, it is extremely easy to manufacture, has good filter characteristics, has small variations, and has shock resistance.・We can provide high-quality, highly reliable mechanical filters with good vibration resistance, and the value this provides to industry is extremely large.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of edge mode vibration, FIG. 1 is a vibration pattern of edge mode vibration, and FIG. 2 is an area strain distribution diagram. FIG. 3 shows the electrode configuration of an edge-mode ceramic resonator for explaining the progress of the present invention, where a shows the front surface and b shows the back surface, and FIG. 4 shows the edge-mode mechanical filter according to the present invention. This is an example of the basic configuration. FIG. 5 shows another basic configuration example of the present invention. FIGS. 6 to 9 are also perspective views showing other embodiments of the present invention. FIG. 10 shows filter characteristics of an embodiment of the mechanical filter having the configuration shown in FIG. 1, 1'... Edge mode converter, 1a... Substrate,
2, 3, 3a, 3b...drive electrode, 4, 5, 6, 7
... Opposite phase drive electrode, 8, 8a, 8b... Connector, 9
... Fixed part, 10... Resonator, 11... Groove, L... Length of resonator (transducer), 2H... Width of resonator (transducer),
P...Input terminal, Q...Output terminal, l _g ...Groove depth, w _g
...Width of the groove.

Claims (1)

[Claims] 1 Two or more rectangular (length L, width 2H, thickness T, where L≫2H, T≪2H) piezoelectric ceramic plates polarized in the thickness direction are fixed at intervals, and these piezoelectric ceramic plates are In order to transmit the edge mode in which the vibration energy is concentrated only near the longitudinal ends of the piezoelectric ceramic plates and the corners of the piezoelectric ceramic plates expand and contract in an arc shape and are displaced, the ends or sides of the piezoelectric ceramic plates are elastically connected to each other using connectors. furthermore, two of the two or more piezoelectric ceramic plates are used as input and output resonators, and these input and output resonators include a portion at the end of the piezoelectric ceramic plate and at the center in the width direction. The edge mode is characterized in that at least an arc-shaped drive electrode is formed in a portion where area strain due to vibration is large centered around the piezoelectric ceramic plate, and a point located at a distance of more than 1.5 times the width of the piezoelectric ceramic plate is supported and fixed. mechanical filter.