JPS59161113A - Mechanical filter - Google Patents

Abstract

PURPOSE:To eliminate and suppress a spurious by a mechanical simplex by a constituting so that the thickness of piezoelectric ceramics used fro a converting piece for forming a mechanical filter is different from each other. CONSTITUTION:A converting piece 8 consists of a piezoelectric ceramic 5 whose residual polarization is performed in the thickness direction, and constant elastic metallic plates 6, 7 for pinching it in the shape of a sandwhich. In the same way, a converting piece 13 consits of a piezoelectric ceramic 12 and the constant elastic metallic plates 6, 7. These converting pieces 8, 13 are coupled through a connector 9 and form a mechanical filter. In this case, the thickness only of the piezoelectric ceramics 5, 12 is made different from each other. However, the width and length are of the same dimensions. In this way, a supurious is dispersed and suppressed. Accordingly, the spurious is eliminated and suppressed by a mechanical simplex.

Description

Detailed Description of the Invention (a) Technical Field of the Invention The present invention relates to the structure of a mechanical filter, and in particular improves the spurious characteristics of a mechanical filter by improving the structure of an electro-mechanical transducer (hereinafter abbreviated as the transducer). The aim is to suppress the

(b) Background of the Technology Mechanical filters have been widely used as frequency selection devices in carrier/radio equipment, etc., and have greatly contributed to the miniaturization, economicalization, and performance improvement of equipment. Improvements in semiconductor technology and transportation in recent years.

With the digitalization of radio equipment, the trend towards miniaturization and economicalization of equipment is rapidly progressing, and the demands on the parts used are becoming stronger.In particular, mechanical filters are desired to have improved spurious characteristics.

(0) Conventional technology and problems The prior art will be explained below with reference to the drawings.

FIG. 1 is a structural diagram of a mechanical filter using a conventional longitudinal vibration mode converter, in which (5) is a perspective view of the converter, a3) is a perspective view of the mechanical filter, and (a3) is a perspective view of the mechanical filter.
C) is a side view of (6). The transducer shown in FIG. The piezoelectric ceramic 1 is constructed by bonding both sides of the piezoelectric ceramic 1 with constant-elasticity metal plates 2 and 3 having the same shape and thickness, which face each other in the thickness direction. A mechanical filter consisting of a combination of a piezoelectric ceramic 5 and a constant elastic metal plate 6 bonded to the opposite surface in the thickness direction.
Two sets of transducers 8 consisting of The electrode terminal/supporter 10 is integrated with the constant elastic metal plate 6 at the vibration node at the center of one side of the same, and the same electrode terminal/supporter 10 is integrated with the constant elastic metal plate 6 at the central part of the elastic metal plate 7 corresponding to both the electrode terminal/supporter 10. The figure shows a structure in which an electrode terminal/supporter 11 having a shape of '' is integrally connected to a constant elastic metal plate 7, and only the constant elastic metal plate 6 is connected by two connectors 9.

1) and (0) of the conventional example shown in Fig. 1. An arbitrary value is selected depending on the desired filter characteristics. Because of this structure, it can be easily realized even if the thickness of the transducer is about 1 mm, and since the electrode terminal can also be used as a support, it is structurally highly reliable, and integrated formation is easy to manufacture. There are advantages such as being a high quality product.However,
On the other hand, there is a drawback that spurious waves peculiar to the transducer adversely affect the filter characteristics. For example, in the case of the transducer 4 configured as shown in Fig. 1(a), the Longitudinal vibration mode co-synchronization generates odd-numbered high-frequency vibrations such as 1st, 3rd, 5th, etc., respectively. Each of these resonant frequencies corresponds to the transducer 4
In general, the desired frequency range of the transducer used in a mechanical filter is relatively narrow, about 2 to 3 times the passband center wave number; Since there was a relatively large margin in the size of the mechanical filter, it was relatively easy to remove spurious signals by connecting a 3-LC bandpass filter to the input/output section of the mechanical filter.

However, for filters used in the timing extraction section of digital communication devices, it is necessary to consider the desired frequency range to be approximately 10 to 15 times the passband center frequency, and there are also demands for smaller and more economical filters. Therefore, it is desirable to obtain characteristics that do not generate spurious signals with a single mechanical filter, which has been difficult to achieve with conventional structures.

(d) Purpose of the Invention In view of the above-mentioned drawbacks of the conventional filter, it is an object of the present invention to provide a structure of a compact, high-performance mechanical filter that takes advantage of the conventional advantages, suppresses spurious characteristics, and suppresses spurious characteristics. be.

(e) Structure and object of the invention According to the present invention, a plurality of vibrators each having a piezoelectric ceramic having residual polarization in a predetermined direction and a constant elastic metal plate bonded to the upper and lower surfaces of the piezoelectric ceramic are used. Constituent Mechanicus 4- A mechanical filter characterized in that the thickness of the piezoelectric ceramic of at least one vibrator is different from the thickness of the piezoelectric ceramic of the other vibrators.

(f) Embodiment of the Invention An embodiment of the mechanical filter of the invention will be described in detail below with reference to FIGS. 2 to 4. In the top view, parts corresponding to those in FIGS. 1(B) and 1(C) are designated by the same reference numerals, and redundant explanation thereof will be omitted.

FIG. 2 is a structural diagram of a mechanical filter using a longitudinal flute-order vibration mode converter according to the present invention, in which (8) is a perspective view and (8) is a side view. Diagram (B)
The only difference is that the thickness of the piezoelectric ceramic 5 of one of the transducers 8 in FIG.
In this example, the transducer shown in FIG. For example, if the constant elastic metal plates 2 and 3 have a thickness of 0.25, a width of 1.0, and a length of 11.2 mm, the frequency characteristics will be as shown by the solid line in the frequency characteristics in Figure 3. The second-order vibration mode resonance frequency fc occurs near 200'Hz, and the first-order vibration mode frequency frm in the thickness direction significantly occurs near 2100 KHz.

However, two sets of converters of the same size as this are shown in Figure 1 (B).
If a mechanical filter with a center frequency of 200 <' Hz is realized with a structure of In order to do this, it is sufficient to use a combination of transducers such that the vertical flute-order vibration mode frequencies in the length direction are the same and the thickness direction flute-order vibration mode frequencies are different.

For example, when considering the transducers 8 and 13 shown in FIG. If it is made thicker or thinner than the thickness of the piezoelectric ceramic 5, the first vibration mode frequency in the thickness direction becomes the fT-B point lower than the fTA point or a higher point (not shown), as shown in FIG. 4, and the filter characteristics are as shown by the dotted line. The spurious can be suppressed by dispersion.

(g) Effects of the Invention As explained in detail above, according to the mechanical filter of the present invention, by changing the thickness of the piezoelectric ceramic used in the transducer, the spurious that previously had an adverse effect on the characteristics can be eliminated from the mechanical filter alone. Since removal and suppression can be performed with

[Brief explanation of drawings]

FIG. 1 is a structural diagram of a conventional mechanical filter of a vertical flute-order vibration mode, in which (5) is a perspective view of a basic transducer, and (B) is a perspective view of the mechanical filter. (C) shows a side view of (B) ○ Figure 2 is a structural diagram of the mechanical filter according to the present invention;
) shows a side view. FIG. 3 shows an example of frequency characteristics of a transducer, and FIG. 4 shows an example of filter characteristics.

Claims (1)

[Claims] A mechanical filter configured using a plurality of oscillators each having a piezoelectric ceramic having residual polarization in a predetermined direction, and a constant elastic metal plate bonded to the upper and lower surfaces of the piezoelectric ceramic. A mechanical filter characterized in that the thickness of the piezoelectric ceramic of at least one of the vibrators is different from the thickness of the piezoelectric ceramic of the other vibrators.