JPS6040212B2 - bending vibration transducer - Google Patents

Description

Detailed Description of the Invention The present invention provides a flexural vibration transducer, particularly a flexural vibration transducer constructed by connecting thickness-shear mode piezoelectric ceramic plates in the longitudinal direction of the flexural vibration transducer, in which the directions of residual polarization are opposite to each other. By arranging two piezoelectric ceramic plates in the longitudinal direction and supporting the opposing parts of the piezoelectric ceramic plates, we have created a transducer suitable for mechanical filters with low input impedance, wide band, and small spurious. The present invention relates to the constructed bending vibration transducer.

Bending vibration transducers are used mainly in low frequency bands as transducers constituting mechanical filters used in various communication devices and control devices.

A mechanical filter is a filter that uses ultrasonic waves as a medium, and is an electric filter that first converts an electrical signal into a mechanical signal, uses mechanical resonance to generate a signal, and then extracts it again as an electrical signal. . A transducer using a piezoelectric ceramic plate is widely used for converting an electrical signal into a mechanical signal or converting a mechanical signal into an electrical signal in the mechanical filter. Conventionally, a converter as shown in FIG. 1 has been used as this type of converter.

That is, in FIG. 1, 1 is an elastic plate made of a constant elastic material, 2 is a transverse effect piezoelectric ceramic plate having residual polarization in the direction indicated by the white arrow in the figure, and 3 and 4 are support wires that also serve as lead wires. 5 represents a lead wire that supports the transducer. The transducer is supported by support wires 3 and 4, and by applying an alternating electric signal between the lead wire 5 and the support wires 3 and 4 using the support wires 3 and 4 as ground terminals, the piezoelectric ceramic plate 2 moves as shown in the arrows. The transducer is expanded in the direction indicated by the arrow or compressed in the direction opposite to the arrow shown in the figure, and bending vibration occurs in which the entire transducer curves as shown by the dotted line in the figure.

On the contrary, an electric signal is obtained between the support wires 3 and 4 and the lead wire 5 based on the bending vibration as shown by the dotted line in the figure. The converter shown in Figure 1 is mainly used as a low frequency narrow band filter because it has a relatively simple structure, is easy to manufacture, and is stable against temperature changes and changes over time. It is used.

However, since the stretching vibration in the longitudinal direction of the piezoelectric ceramic plate is used, the electrical-mechanical coupling coefficient (k3, in this case) of the piezoelectric ceramic plate is approximately 0. Since the dryness is small, the capacitance ratio of the converter (y=Cd/Co, which will be described later) is large, and as a result, the mechanical filter has a narrow band width. In order to realize a wideband filter using such a converter, it is necessary to add, for example, an LC element to the input and output ends of the converter, making the filter as a whole large and expensive. In order to solve the drawbacks of the converter shown in FIG. 1, the inventors of the present invention previously invented a converter having the configuration shown in FIG.

In Figure 2, 6 and 7 are elastic plates made of a constant elastic material, 8 is a piezoelectric ceramic plate that uses thickness-shear mode vibration with residual polarization in the direction indicated by the white arrow in the figure, and 9 and 1 are respectively It represents a support line that also serves as a lead wire. In the case shown, the transducer is supported by support wires 9, 10 and an alternating electrical signal is applied between the support wires 9 and 10, for example.

In this case, the piezoelectric ceramic plate 8 is subjected to shearing force in the directions of arrows a and b in the figure, and the entire transducer undergoes bending vibration as shown by the dotted line in the figure. In this case, the thickness shear mode vibration is used as the vibration mode of the piezoelectric ceramic plate 8. The electro-mechanical coupling coefficient (k, 5 in this case) of thickness shear mode vibration is about 0.60 to 0.80. For this reason, it is possible to reduce the capacitance ratio of the transducer, and it is possible to provide a mechanical filter with a high Q value and a wide band. Figure 3 shows a general electrical equivalent circuit of a converter, where I, Co, and Ro represent the equivalent inductance, equivalent capacitance, and equivalent resistance near the series resonant frequency of the converter, and Cd represents the damping capacitance. It represents.

The performance of a converter is generally expressed by a capacity ratio y and a quality factor Q, which are defined as follows.

That is, y=Cd/Co Q=Noshi)/Ro On the other hand, when configured as a mechanical filter, the passage band width Δf is inversely proportional to the capacity ratio y.

That is, L of △f. Therefore, as mentioned above, in the case of the configuration shown in FIG. 2, it is possible to select the capacity ratio y by 4. becomes possible.

The configuration shown in FIG. 2 has the excellent advantages as described above, but has disadvantages in that the braking capacity Cd is relatively small and the input impedance is relatively high.

When this converter is used in a mechanical filter,
This is because if the damping capacitance is small, it is susceptible to the influence of external stray capacitance, and if the impedance is high, there are many problems in matching with the external circuit.

For this reason, a converter having the configuration shown in FIG. 4 was devised. In FIG. 4, numerals 6, 7, 9, and 10 correspond to those in FIG. 11 represents a lead wire.

In the configuration shown in FIG. 4, an alternating electrical signal is applied across the support lines 9, 1 and between the support lines 9, 10 and the lead line 11.

In the illustrated case, the two piezoelectric ceramic plates 8-0 and 8-- are configured to have residual polarization in opposite directions, and therefore the piezoelectric ceramic plates 8-0 and 8-1 are Arrows A, B
When subjected to shear forces such as C and D, the transducer bends as shown by the dotted line in the same way as in the case shown in FIG. Fourth
In the case of the illustration, it is said that the structure shown in the second figure is taken, but the second
It has a structure in which the illustrated piezoelectric ceramic plate 8 is divided into two.

In the case shown in FIG. 4, piezoelectric ceramic plates 810 and 811 are electrically inserted in parallel, and the braking capacities shown in FIG. 3 exist in parallel (i.e., braking Capacity Cd
), making it possible to reduce input and output impedance. However, on the other hand, the equivalent capacitance Co shown in FIG. 3 increases as the braking capacitance Cd increases, and the capacitance ratio y, that is, Cd/Co, does not substantially change. Therefore, the advantages of the structure shown in FIG. 2 and the advantage of widening the band can be enjoyed as they are. In the case shown in Fig. 4, the lengths of the elastic plates 6 and 7 are selected to be equal, so that when the frequency is taken as the key, the response level of the transducer is as shown in Fig. 5, which is the even-order bending vibration. It becomes a form in which only the modes of .

The configuration shown in FIG. 4 has the advantage of being able to select a small input impedance as described above, but has the following mechanical drawbacks.

That is, it is necessary to connect the lead wire 11 to the boundary between the piezoelectric ceramic plates 8-0 and 8-1.

[B) In the case of the structure shown in Fig. 4, the support plates 9 and 10 are attached to the layer where the vibration displacement is zero, that is, at the node, but as shown in Fig. 6, the horizontal axis represents the length of the transducer, and the vertical axis When the vibration displacement and bending moment displacement are taken as , it can be seen that the position where the vibration displacement becomes zero does not necessarily become zero as the bending moment displacement.

That is, torsional moments act on the support lines 9 and 10 shown in FIG. 4, respectively, and this has the possibility of imparting spurious vibrations to the transducer. FIG. 7A shows an embodiment of the present invention that solves this problem.

The symbols 6, 7, 8 - 0, 8 in the figure correspond to those in Figure 4,
17 is a support plate made of constant elastic metal;
8 represents the pillar. In the case shown, the support plate 17 is
As shown in a plan view in FIG. 7B and a side view in FIG. 7C, it is configured in a so-called battledore shape. And support plate 1
A piezoelectric ceramic plate 8-0 is attached to one side of the transducer 7, and a piezoelectric ceramic plate 8-1 is placed on the other side, and the entire transducer is supported by the support 18. Assuming that lead wires X and Y are attached to the elastic plates 6 and 7, respectively, and an alternating electric signal is applied between one lead wire X and Y and the column 18, the same result as shown in FIG. 4 will be obtained. Become something.

In this case, as is clear from FIG. 6, the position of the support column 18 is approximately x = 1/2, where both the vibration displacement and the bending moment displacement are zero, and the support column 18 has an undesired No significant moment or vibration is applied. In addition, the support plate 17 supports two piezoelectric ceramic plates 8-1 and 8-1.
It becomes possible to supply power to When constructing a mechanical filter using the transducer shown in FIG. 7A, it is not necessary to provide the lead wires X and Y shown in FIG. 7A.

Figure 8 shows the mechanical conversion using the transducer shown in Figure 7A.
An example of a filter configuration is shown. Codes 6A, 6B in the figure; 7A, 7B: 8-OA, 8-OB: 8-I
A, 8-IB; 17A, 17B; 18A, 18B are the numbers 6, 7, 8-0.8-1, 17, 1 shown in FIG. 7A, respectively.
It corresponds to 8. Further, 19 is an elastic plate, 20 is a support line, 21, 22, 23, and 24 are connectors, and 25 is a connecting position between the mechanical vibrator and the connectors. Further, 31 constitutes an input side transducer, 32 constitutes an output side transducer, and 33 constitutes a resonator. In the illustrated case, the input side transducer 31 and the resonator 33 are mechanically loosened at points 25 and 27, 26 and 28, where the vibration displacement is generally maximum, by the couplers 21 and 23, respectively.

Further, the resonator 33 and the output side transducer 32 are connected to the coupler 2, respectively.
2, 24, the point 27 where the vibration displacement is generally maximum
and 29, 28 and 30 are mechanically connected. Then, an alternating electric signal is applied between the support line 18A and the support line 20, and an electric signal is output from between the support line 20 and the support line 18B. When an alternating electric signal is applied between the support column 18A and the support wire 20, the support wire 2
0 and the elastic plates 6A, 7A are electrically short-circuited.

As a result, an alternating electrical signal is applied to the lead wires ○ and Y and the support 18 shown in FIG. 7A, and the input side converter 3
1 vibrates as shown by the dotted line in the figure. The vibration of the input side transducer 31 is transmitted to the resonator 33 via the couplers 21 and 23, and the resonator 33 also vibrates as indicated by the dotted line in the figure. Similarly, the vibration of the resonator 33 is transmitted to the output transducer 3 via the couplers 22 and 24.
2 as shown by the dotted line in the figure, and the piezoelectric ceramic plates 8-OB and 8
Vibration is applied to 1B and 1B. As a result, the lead wires
An electric signal corresponding to the vibration of the output side transducer 32 is output between Y and the support column 18B. Although the case of the secondary bending vibration mode has been described in FIG. 8, the present invention is not limited thereto.

As described above, according to the present invention, it is possible to provide a bending vibration transducer using a thickness-shear mode piezoelectric ceramic plate, and it is possible to keep its input impedance small.

In addition, problems in supporting the converter and mechanical problems have been completely solved.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are explanatory diagrams explaining the prerequisite problems of the present invention, Figure 4 is a configuration to which the present invention is applied, and Figure 5 is the frequency/response level of the transducer shown in Figure 4. Show characteristics. Further, FIG. 6 is an explanatory diagram for explaining the mechanical problems of the configuration shown in FIG. 4, FIGS. 7A, B, and C are examples of the configuration of the present invention, and FIG. An example will be shown in which a mechanical filter is constructed using a transducer. In the figure,
6 and 7 are elastic plates, 8-0 and 8-1 are piezoelectric ceramic plates, 9 and 1 are support wires, 11 is a lead wire, 17 is a support plate, 18 is a column, 19 is an elastic plate, 20 'Ma support line, 21
None, 24 is a connector, 31 is an input side converter, 32
3 represents an output side transducer, and 33 represents a resonator. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1 A pair of elastic plates 6 and 7 having the same length, and residual polarization directions between the elastic plates 6 and 7 are perpendicular to the longitudinal direction of the elastic plates 6 and 7 and opposite to each other. At least two thickness-shear mode piezoelectric ceramic plates 8-
0,8-1, and the thickness shear mode piezoelectric ceramic plate 8-0,
and a support plate 17 disposed between 8-1, and the support plate 17
and the thickness shear mode piezoelectric ceramic plates 8-0 and 8-1 with an electrical signal applied between them.
1. A bending vibration transducer characterized in that 0,8-1 is energized.