JPS594885B2 - bending vibration transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flexural vibration transducer constructed by fixing a polarized piezoelectric ceramic plate to a mechanical resonator.

Mechanical filters have been used in various devices in recent years due to their small size, robustness, stability, and high performance.However, with the advancement of communication technology, there is a desire for smaller size, higher performance, and lower prices. ing.

One of the mechanical filter components is an electro-mechanical transducer, one of which is a flexural vibration transducer.

As shown in Fig. 1, the bending vibration transducer has electrodes 2 and 3 formed on the upper and lower surfaces of a piezoelectric ceramic plate 1 polished into a rectangular flat plate, and residual polarization is generated in the thickness direction as shown by the arrow. Then, as shown in FIG. 2, this piezoelectric ceramic plate 1 is fixed onto a mechanical resonator 4 made of a constant elastic material.

The fixed position of the piezoelectric ceramic plate 1 is such that the longitudinal axis A of the mechanical resonator 4 and the longitudinal axis B of the piezoelectric ceramic plate 1 are aligned, and the lateral center line P of the mechanical resonator 4 is aligned with the longitudinal axis B of the piezoelectric ceramic plate 1. This is where the horizontal center line y of No. 1 is aligned.

When a high frequency alternating voltage is applied between the electrode 2 and the lower electrode 3 provided on the upper side of the piezoelectric ceramic plate 1 of the bending vibration transducer constructed in this way, the piezoelectric ceramic plate 1 expands and contracts due to the piezoelectric transverse effect. do.

Therefore, the entire structure including the mechanical resonator is curved vertically as shown in FIG. 3 due to the bimetal effect, and primary bending vibration is excited.

Now, the equivalent circuit near the resonance frequency of this bending vibration transducer is shown in FIG. 4.

However, in FIG. 4, Cd is the braking capacity exhibited by the piezoelectric ceramic plate 1, m, 8. r is the mechanical equivalent constant of the bending vibration transducer,
A is the force coefficient of the electro-mechanical conversion system.

When the mechanical system of this circuit is converted into an electrical system, it becomes as shown in FIG. 5, and the relationships between m, s, r, C, and R are as shown below.

L=m/A2 ・・・・・・・・・(1)
C=A2/s ・・・・・・・・・(2
)R=r/A2 ・・・・・・・・・(3
) Furthermore, C, R, and Cd are important constants of the bending vibration transducer, and the shapes of the mechanical resonator and piezoelectric ceramic plate are determined from these values.

For example, when the shape of the piezoelectric ceramic plate is sufficiently small compared to the shape of the mechanical resonator, the vibration frequency of the bending vibration transducer is determined by the material constants, length, and thickness of the mechanical resonator.
d/C largely depends on the material, shape, and fixing position of the piezoelectric ceramic plate.

Therefore, in order to eliminate variations in the uniform number of bending vibration transducers to the required value, maximum attention must be paid to the shape of the material, the position and degree of fixation of the piezoelectric ceramic plate to the mechanical resonator, etc. .

However, even with this, a certain degree of variation is inevitable, and constant adjustment becomes necessary in order to obtain the required converter equivalent constant.

In particular, when a bending vibration transducer is used in a mechanical filter, fine adjustment of the equivalent inductance is required for input/output impedance matching.

An object of the present invention is to provide a bending vibrator in which the constants of the bending vibration transducer as described above, particularly the equivalent inductance, are accurately and finely adjusted.

In order to achieve the object, the bending vibration transducer of the present invention includes a rectangular piezoelectric ceramic plate in which the direction of residual polarization matches the thickness direction of the piezoelectric ceramic, and a mechanical resonator. In the bending vibration transducer, the piezoelectric ceramic plate is fixed on the mechanical resonator by making the longitudinal axis of the mechanical resonator coincide with the piezoelectric ceramic plate and the center of the axis of the mechanical resonator and the piezoelectric ceramic plate coincide with the longitudinal axis of the mechanical resonator. The equivalent inductance is finely adjusted to a predetermined value by providing a small area of the electrode surface of the piezoelectric ceramic plate at symmetrical positions in the length direction with respect to the axis extending from the center of the axis in a direction perpendicular to the axis. Examples thereof will be described in detail below.

When an alternating voltage is applied between the electrodes 2 and 3 provided on both sides of the piezoelectric ceramic plate 10 as shown in Figure 1, in the case of fundamental wave vibration, the displacement at both ends is maximum and the displacement at the center is zero. .

Conversely, the mechanical strain of this piezoelectric ceramic plate 1 is lowest at both ends and highest at the center.

By the way, in order to increase the equivalent inductance without almost affecting the damping capacity Cd and the resonant frequency in a bending-order vibration transducer in which the piezoelectric ceramic plate is fixed to a mechanical resonator as shown in Fig. 2, it is necessary to A possible method is to peel off a part of the electrode 2 and make the electrode surface of the piezoelectric ceramic plate electrodeless at a plurality of small areas.

This means reducing A in formulas 1) to (3) above.

In this case, the amount of adjustment of the equivalent inductance determines how many positions should be made electrodeless.

That is, when the amount of adjustment is small, the vicinity of both ends where mechanical strain is small is made electrodeless, and when the amount of adjustment is large, several places near the center where mechanical strain is large are made electrodeless.

However, when the equivalent inductance of the flexural vibration transducer is adjusted in this way, if the electrodeless part is not symmetrical with respect to the center line P of the mechanical resonator, spurious signals may occur in the flexural vibration transducer. sexuality becomes greater.

For example, in the case of a bending primary vibration transducer, if it is unbalanced with respect to the center line P and made electrodeless, it will be as if the center line P' of the piezoelectric ceramic plate 1 and the center line P of the mechanical resonator 4 are shifted. Therefore, vibration modes other than the primary vibration mode are likely to occur in the mechanical resonator 4.

Therefore, in the present invention, the electrode surfaces on the piezoelectric ceramic plate fixed on the mechanical resonator are peeled off at a plurality of predetermined minute areas to make them electrodeless.In this case, the electrodeless portions 5 and 6 are As shown in Fig. 6, the center line V of the piezoelectric ceramic plate
The electrodes are spaced apart from each other by a distance L1 on the left and right sides, and the number of non-electrode parts is also made equal.

Also, depending on the degree of fine adjustment, the non-electrode portions 7 and 8 may be
If it is necessary to provide them, they are provided at a distance L2 from each other on the left and right sides of the center line P'.

In this case, it goes without saying that the numbers of the electrodeless portions 7 and 8 are equal and are provided symmetrically with respect to the center line P', as described above.

The above embodiment is a bending primary vibration transducer, but if the directions of residual polarization of the piezoelectric ceramic plate are opposite to each other on the left and right sides with respect to the center line V, a bending secondary vibration transducer can be obtained. A vibration transducer can be obtained, and the equivalent inductance of such a bending secondary vibration transducer can be finely adjusted in the same manner as in the bending primary vibration transducer.

In this way, the present invention reduces spurious and improves the equivalent inductance of the bending vibration transducer by making the electrode surface on the piezoelectric ceramic plate a collector electrode with a very small area symmetrical with respect to the lateral center line of the piezoelectric ceramic plate. can be fine-tuned, and a stable bending vibration transducer with uniform characteristics can be provided.

[Brief explanation of drawings]

Fig. 1 is a perspective view of the piezoelectric ceramic plate, Fig. 2 is a perspective view of the bending vibration transducer, Fig. 3 is a side view showing how the bending vibration transducer bends, and Figs. 4 and 5 are the bending vibration transducer. An equivalent circuit diagram of a vibration transducer, FIG. 6 is a front view of an embodiment of the present invention. In the figure, 1 is a piezoelectric ceramic plate, 2 and 3 are electrodes, 4 is a mechanical resonator, and 5, 6, 7, and 8 are non-electrode parts.

Claims (1)

[Claims] 1 A rectangular piezoelectric ceramic plate whose residual polarization direction coincides with the thickness direction of the piezoelectric ceramic and a mechanical resonator are provided, and the longitudinal axis of the piezoelectric ceramic plate and the mechanical resonator are aligned and In a bending vibration transducer in which the piezoelectric ceramic plate is fixed onto the mechanical resonator by aligning the centers of the axes of the piezoelectric ceramic plate and the mechanical resonator, with respect to an axis extending from the center of the axis in a direction perpendicular to the axis. A flexural vibration transducer, characterized in that the electrode surface of the piezoelectric ceramic plate is provided with small electrode-free portions at symmetrical positions in the length direction to finely adjust the equivalent inductance to a predetermined value.