JPH0221690B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vibrator and a piezoelectric filter that utilize bending vibration of a piezoelectric material, and in particular, interdigitated electrodes are formed in parallel to the diagonal on a single square piezoelectric plate, making it easy to support. It relates to something that uses saddle-shaped bending vibration.

Conventionally, vibrators that utilize the bending vibration of piezoelectric materials
It is used in audio frequency acoustics such as telephone receivers, speakers, buzzers, microphones, and pickups, vibration sensors, transducers for airborne ultrasound, and resonators and filter elements in frequency bands of several 100 kHz or less.

As a typical example of a bending vibrator, one having a bimorph structure in which two piezoelectric plates or a piezoelectric plate and a metal plate are bonded together with an adhesive is known. However, due to the presence of an adhesive layer in this bimorph structure, variations in resonance frequency and Q (quality factor)
This is undesirable as it causes a decrease in

On the other hand, as a piezoelectric single bending vibrator without adhesive,
A configuration in which multiple strip electrodes provided on the surface of a piezoelectric ceramic are alternately polarized and driven with alternating current has been proposed, for example, by Tanaka (``Barium titanate and its applications'', published by Ohmsha, 1965, p. 117) and Konno et al. Proceedings of the Acoustical Society of Japan, October 1970, Paper No. 3-4-17, p. 405)
It is stated by. Although these configurations mainly utilize the piezoelectric longitudinal effect, they have rarely been used until now because the capacitance ratio cannot be reduced.

In contrast, Shimizu et al., among the inventors, proposed a normal bimorph resonator that utilizes the piezoelectric transverse effect by providing interdigital electrodes (comb-shaped electrodes) on the surface of a piezoelectric ceramic plate in parallel to the direction of expansion/contraction strain. Patent application No. 57-56313 concerning a single piezoelectric bending vibrator with a small capacitance ratio comparable to , and a single mode bending vibration piezoelectric filter
It is proposed in the issue.

As a result of further research, the inventors of the present invention have developed a single piezoelectric bending vibrator and a piezoelectric filter that do not rely on a bonded structure, which are easier to support than those of the patent application No. 57-56313, and have a much smaller spurious response. It is an object of the present invention to provide a single piezoelectric bending vibrator and a three-terminal or four-terminal bending vibration piezoelectric filter.

In the present invention, a plurality of electrodes are provided on at least one surface of a square piezoelectric plate in parallel with a diagonal line, the plurality of electrodes are connected every other to form an interdigital electrode, and a DC voltage is applied to the interdigital electrode. The piezoelectric plate is polarized by a method of applying , and the square piezoelectric plate undergoes plane-perpendicular bending vibration in opposite phases on two diagonals of the plate, and a saddle-shaped vibration mode with cross-shaped nodal lines is generated. is excited and detected by the interdigital electrodes.

Further, the present invention provides a method of forming interdigital electrodes having electrode fingers parallel to diagonal lines on at least one surface of a square piezoelectric plate, and polarizing the piezoelectric plate by applying a DC voltage to the interdigital electrodes. In the single piezoelectric bending vibrator, the piezoelectric single bending vibrator is configured to perform plane-perpendicular bending vibrations of mutually opposite phases on two diagonals of the square piezoelectric plate, and utilize a saddle-shaped vibration mode having cross-shaped nodal lines. This piezoelectric filter is characterized in that interdigital electrodes are divided into two parts, one for vibration excitation and one for detection, forming a three-terminal or four-terminal filter.

The present invention uses a square piezoelectric plate and additively utilizes not only the piezoelectric transverse effect but also the piezoelectric longitudinal effect.
The object of the present invention is to provide a bending vibrator and filter that can excite saddle-shaped bending vibrations that cannot be driven with ordinary bimorph vibrators, are easy to support, and have extremely low spurious resonance responses.

The operating principle of the present invention will be explained.

FIG. 1 shows the basic structure of a bending vibrator according to the present invention, in which interdigital electrodes 2 and 3 are configured to be parallel to the diagonal direction of a square piezoelectric plate 1.
Every other electrode is connected to an extraction electrode at the periphery. Then, a voltage is applied between the interdigital electrodes 2 and 3 to polarize the electrodes in a direction perpendicular to the length direction of the electrodes.

When this structure is driven by applying AC voltage to 2 and 3, the driving forces of the piezoelectric longitudinal effect and the piezoelectric transverse effect are added, and the two diagonal lines as shown in Fig. 2 A saddle-shaped vibration mode having cross-shaped nodal lines (M-M', N-N' lines) that performs plane-perpendicular bending vibration in opposite phases on AB and CD is excited. That is, when the end of one diagonal line AB is displaced upward in the plane, the end of the other diagonal line CD is displaced downward in the plane. Such a vibration mode is difficult to excite using a normal bimorph structure.

The resonance frequency waveform and vibration mode of the piezoelectric vibrator according to the present invention were calculated using the finite element method. Figure 3a is a two-dimensional representation of the distribution of displacement Uz in the direction perpendicular to the surface (Z direction) in the 1/4 area of the piezoelectric plate (for example, the area surrounded by OM'BN' in Figure 2). be. The size of the diagonal line represents the size of Uz. From this figure, along the x (or y) direction, from the node line O-M' (or O-N'), plate 1
The displacement increases as it approaches the edge of O, and also increases as it moves away from the center O on the diagonal line.

Similarly, figure b shows the displacement amounts of Ux and Uy in the x and y directions on the surface of the plate for the 1/4 area.For convenience, only the changes in the outline are shown, and the displacement is 10 times that of figure a. The illustration is enlarged. Ux,
Uy is equal in magnitude on the top and bottom surfaces of the plate, and is in antiphase with each other.

As is clear from FIGS. 3a and 3b, in the piezoelectric bending vibrator according to the present invention, the displacement of the contour vibration in the x and y directions is extremely small, and it is clear that the bending vibration mainly vibrates in the vertical direction of the piezoelectric plate. It is.

As described above, the strain distribution on the surface of the square piezoelectric plate was calculated in order to find the electrode shape for effectively exciting the vibration mode of the saddle-shaped bending vibration according to the present invention. According to this result, the slip strain Sxy is about two orders of magnitude larger than the expansion and contraction strains Sxx and Syy, except for the peripheral area. (However, Sxx is the expansion/contraction strain in the x direction, Syy is the expansion/contraction strain in the y direction, and Sxy is the sliding strain in the xy plane.) The sliding strain Sxy decreases rapidly in the peripheral area. The calculation result of Sxy is shown in Fig. 4. Sxy
is expressed as the sum of mutually opposite phase expansion and contraction strains in both diagonal directions, so it is understood that for excitation in this mode, interdigital electrodes should be arranged parallel to the diagonals of the square piezoelectric plate. In other words, the expansion/contraction strain in the direction parallel to the electrode finger (direction of one diagonal line) due to the piezoelectric transverse effect and the expansion/contraction strain in the direction perpendicular to the electrode finger (direction of the other diagonal line) due to the piezoelectric longitudinal effect are in opposite phase. , and both act additively on the excitation of the saddle-shaped vibration mode.

In order to determine the shape and size of the active region of the interdigital electrode of the system that efficiently excites the saddle-shaped bending vibration mode in the present invention, the following calculations were performed.

As clarified in the above-mentioned Japanese Patent Application No. 57-56313, in the case of utilizing the piezoelectric effect, when the ratio a/p of the electrode width a and the electrode period p is 0.5, the capacitance ratio is the minimum, and the piezoelectric vertical In the case of effective use, the smaller a/p is, the smaller the capacity ratio is, so if a/p is set to 0.3, the capacity ratio in horizontal effect use is approximately 1/2 of that in vertical effect use. be. Therefore, the principal values of strain that are linearly connected to the piezoelectric transverse effect and the piezoelectric longitudinal effect (the principal directions are mostly diagonal directions) are S ₀₁ and S ₀₂ , and |S ₀₁ |+|S ₀₂ /√2| and |S ₀₁ / √2｜＋｜
The distribution of S ₀₂ | was calculated. The results for half of the piezoelectric plate are shown in FIG. In the figure, the maximum value at the center O is set as 10 and is expressed as an isovalue line. (however,
The arrows in the figure indicate the direction of the interdigital electrodes. ) Based on the above results, we fabricated a bending vibrator.

A square piezoelectric ceramic plate with a side of 10 mm and a thickness of 0.5 mm (lead zirconate titanate N6 manufactured by Tohoku Metal Industry Co., Ltd.)
material), p = 0.5 mm, a/p = 0.3, and the fifth
Interdigital electrodes were formed on both sides of the plate as shown in FIG. 6a, and the capacitance ratio was measured by forming interdigital electrodes whose outlines of the active regions were approximately aligned with contour lines 9, 8, 7, and 6 in the figure. (9, 8, 7, 6 representing the electrode pattern in Figure 6a are the fifth
Same as the values 9, 8, 7, and 6 of the isovalue lines in the figure. )
The result is shown in figure b, electrode pattern 7 or 6.
By doing so, that is, by widening the active region of the drive electrode, it was shown that a vibrator with a capacitance ratio as small as 11 to 12 could be obtained.

Next, the admittance characteristics of double-sided drive and single-sided drive were measured using the vibrator with electrode pattern 7 among the above vibrators, and the results are shown in FIGS. 7a and 7b, respectively. With single-sided drive, the resonant frequency is 10.293kHz.
It has been shown that almost no spurious response appears up to 120kHz, and in double-sided drive, almost no spurious response appears up to 260kHz.

The above has been explained using the embodiment of the vibrator according to the present invention, but by forming interdigital electrodes in parallel to the diagonal direction on a square piezoelectric plate, the piezoelectric transverse effect and the piezoelectric longitudinal effect can be utilized additively. It was revealed that a single piezoelectric bending vibrator can be obtained that has a small capacitance ratio comparable to that of conventional bimorph vibrators, and is easy to support without an adhesive layer.

Next, a piezoelectric filter, which is another aspect of the present invention, will be explained.

Applying the above bending vibrator, 3-terminal or 4-terminal
This constitutes a single mode filter for the terminal.

The piezoelectric filter according to the present invention has two types of interdigital electrodes formed in parallel with the diagonal lines on one square piezoelectric plate, and a signal is input from one electrode to excite bending vibration, which is then transmitted to the other electrode as an electric signal. It is converted into and extracted.

A specific example thereof is shown in FIG. 8 and subsequent figures.

In Fig. 8, an interdigital electrode is formed on one side of the piezoelectric plate 1, and the electrode is divided into two electrodes 4 and 6 approximately at the center, one for input and the other for output. This is a 3-terminal (or 4-terminal) filter with 5 as a common electrode. Figure b is A- of figure a.
The cross section taken at A' is shown, and symbols 7 and 8 are input and output terminals connected to the electrodes 4 and 6.
Symbol 9 is a ground terminal connected to the common electrode.

In FIG. 9, electrodes similar to those in FIG. 8 are formed on both sides of a piezoelectric plate 1 so that the front and back sides face each other.
Reference numerals 8 denote input and output terminals connected to the corresponding electrodes 4 and 6 on the front and back, respectively, and 9 is a common terminal connected to the electrodes 5 on the front and back.

In Figures 8 and 9, the interdigital electrodes are divided into two approximately at the center to serve as input and output electrodes, but in Figures 10 and 11, the way the electrodes are divided is changed.
This shows an example in which input electrodes and output electrodes are alternately arranged in a complicated manner. That is, the common electrode 5 has a meander line (zigzag line) shape, and the input electrode 4 and the output electrode 6 are arranged on both sides thereof. With this electrode arrangement, good symmetry is maintained between the input and output electrodes, so spurious resonance responses are significantly reduced compared to the electrodes shown in Figures 8 and 9, and the characteristics are improved. is improved. In addition, as shown in Fig. 12, interdigital electrodes are formed on both sides of the piezoelectric plate 1, and without dividing them within the plane of the plate 1, the electrodes on one side are used for input and the electrodes on the other side are used for output. This is a 4-terminal filter. 7 and 7' are input terminals, and 8 and 8' are output terminals.

FIG. 13 shows an example of filter characteristics when a single mode three-terminal filter is constructed using the electrodes shown in FIG. 10.

The structure of the piezoelectric filter of the present invention has been described above.According to the present invention, a relatively low-frequency, low-loss filter can be realized with relatively small dimensions, and it does not have an adhesive layer like a bimorph resonator. Therefore, variations in characteristics are reduced, and since the vibration mode takes a saddle-shaped vibration mode, the vibration nodes are formed in a cross shape including the center, making it extremely easy to support.

Furthermore, spurious resonance responses are suppressed up to high frequency ranges, making it possible to provide high-quality piezoelectric filters.

It should be noted that the electrodes in the present invention can be formed by conventional techniques such as silver powder screen printing, sputtering, and vapor deposition, and the interdigital electrodes in the filter can be formed by any strain distribution as shown in FIG. 6a. Of course, it is possible to use a value that lies along the isovalue line, and there is no restriction in any way.

In addition, in the single mode filter obtained by the present invention, a filter with high selectivity can be easily obtained by directly connecting a plurality of filters with the same characteristics in cascade without using a coupling capacitance or the like. Naturally, these are also included in the present invention.

[Brief explanation of drawings]

Fig. 1 is a plan view showing the basic structure of the bending vibrator according to the present invention, Fig. 2 is a diagram explaining the vibration mode of the piezoelectric plate, and Fig. 3 is a quarter section of the piezoelectric plate in the same vibration mode. Figure 4 shows the vibration displacement distribution in the direction perpendicular to the plane (z direction), Figure b shows the displacement in the side direction (x, y direction), and Figure 4 shows the vibration displacement in the direction perpendicular to the surface (z direction). Figure 5 showing the surface slip strain in the same vibration mode for 1/4 section of the piezoelectric plate.
The figure shows the strain distribution in the same vibration mode for half of the piezoelectric plate. Plan view, Figure 6b shows actual measured values showing changes in capacitance ratio due to electrode pattern shape, Figure 7 is an admittance frequency characteristic diagram of a vibrator using electrode pattern 7, Figure a is for double-sided drive, Figure b is 8, 9 and 12 show different embodiments of the piezoelectric filter, in which figure a is a plan view and figure b is a line A-A' in figure a. The sectional views, FIGS. 10 and 11, are views showing other embodiments of the piezoelectric filter, and FIGS.
The figure is a graph showing the filter characteristics of the three-terminal filter shown in FIG. 1... Piezoelectric ceramic plate, 2, 3, 4, 5, 6... Interdigital electrode, 7, 7', 8, 8', 9, 9'... Terminal.

Claims (1)

[Scope of Claims] 1. A plurality of electrodes are provided on at least one surface of a square piezoelectric plate in parallel with a diagonal line, and the plurality of electrodes are connected every other to form an interdigital electrode, and the interdigital electrode The piezoelectric plate is subjected to polarization treatment by applying a DC voltage to the electrodes, and two of the square piezoelectric plates are polarized.
A piezoelectric single body bending vibration characterized in that a saddle-shaped vibration mode having cross-shaped nodal lines is excited and detected by the interdigital electrodes, and the plane-perpendicular bending vibration is performed in opposite phases on two diagonals. Child. 2. An interdigital electrode having electrode fingers parallel to the diagonal is formed on at least one surface of a square piezoelectric plate, and the piezoelectric plate is polarized by a method of applying a DC voltage to the interdigital electrode. In a single piezoelectric bending vibrator that performs plane-perpendicular bending vibration in opposite phases on two diagonals of a square piezoelectric plate and utilizes a saddle-shaped vibration mode having cross-shaped nodal lines, the interdigital electrodes A piezoelectric filter characterized in that it is divided into two parts, one for vibration excitation and one for detection, to form a three-terminal or four-terminal filter.