JPH0452677B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a bonded piezoelectric vibrator made by bonding two piezoelectric elements.

Conventional structure and its problems An application example of a bimorph piezoelectric vibrator, which is one of the bonded piezoelectric vibrators, uses the inverse piezoelectric effect to vibrate by applying electrical input using its flexural vibration. There are two types: those that use external mechanical vibrations to generate electrical signals, and those that utilize piezoelectric effects. Typical examples of applications in the former case include ultrasonic and sonic wave transmitters, vibration generators, etc., and in the latter case, typical examples include ultrasonic and other sonic wave receivers and vibration pickups.

Conventionally, there are two types of bimorph piezoelectric vibrators. This will be explained with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view of a bimorph piezoelectric vibrator using a parallel connection method and FIG. 2 a series connection method. In FIG. 1, numerals 1 and 2 are piezoelectric elements polarized in the direction of the arrow, and the two pieces are electrically and mechanically connected at an interface 3. As can be seen from the direction of the arrow, the polarization direction of both sheets is oriented in the same direction. Electrodes are provided on the main surfaces 4, 5 of the piezoelectric elements 1, 2, respectively, and electrical connections connect the surfaces 3, 5 and 4, 5 to a power supply V.

Now, if we consider the case where this vibrator is used with the inverse piezoelectric effect, piezoelectric element 1 extends in the length direction because an electric field with the polarization direction opposite is applied, and piezoelectric element 2 extends in the length direction because an electric field is applied in the same direction. It contracts, so one side extends and the other contracts, causing a bending movement as shown in the figure.

Conversely, if we consider the case where the piezoelectric effect is used, if an external force is applied to cause the deflection as shown in Figure 1, the piezoelectric element 1 will be extended in the length direction, so the charge on the surface 3 and the surface 4 is charged. Moreover, since the piezoelectric element 2 is conversely contracted in the length direction, electric charges on the surfaces 3 and 5 are charged, and a voltage is generated between the surfaces 3 and 4 and 5.

Next, FIG. 2 shows a method of series connection in which the piezoelectric elements 6 and 7 are connected in directions in which the polarization directions are different from each other by 180°. In this case as well, the two piezoelectric elements 6 and 7 have an interface 9
The two plates are electrically and mechanically connected, and as in FIG. 1, electrodes are provided on opposing surfaces 8, 9, and 10 perpendicular to the polarization direction, respectively. In this case, the electrical input/output terminals are connected to the surfaces 8 and 10. Now considering the case of use in the inverse piezoelectric effect, when a voltage is applied to planes 8 and 10, the elements of piezoelectric element 6 extend in the length direction and the elements of piezoelectric element 7 extend in the length direction, as in FIG. It contracts and performs a flexural vibration as shown in Figure 2. Conversely, when looking at the use of the piezoelectric effect, if an external force is applied and the piezoelectric element 6 is bent as shown in Figure 2, the piezoelectric element 6 is extended in the length direction, so the piezoelectric Element 7 is on surface 9,
The charge on surface 10 is charged and a voltage is generated on surfaces 8-10.

Now, in order to compare the deflection characteristics and electrical characteristics, let us assume that the shapes and dimensions of the piezoelectric elements in Figures 1 and 2 are the same, and the capacitance of each is c, and the thickness of the piezoelectric element is t. The deflection due to the inverse piezoelectric effect is ξ ₁ The case shown in Figure 2 is ξ ₂ The voltage generated due to the piezoelectric effect is
Let V ₁ and V ₂ be V 1 and V 2 be the input voltage of the inverse piezoelectric effect, and F be the external force due to the piezoelectric effect, then ξ ₁ = A×d ₃₁ ×V/π, ξ ₁ = A×d ₃₁ ×V, respectively. /2t V ₁ =B×d ₃₁ ×F, V ₂ =2×B×d ₃₁ ×F. Moreover, if the electrical impedance is below the resonance frequency, Z ₁ =1/2ωC and Z ₂ =1/ωc, respectively.

Therefore, in the case of the inverse piezoelectric effect, the input charge is doubled and distorted in the case of parallel connection (FIG. 1) than in the case of series connection (FIG. 2). In addition, in the case of the piezoelectric effect, the output charge of parallel connection (Fig. 1) is the same as that of series connection (Fig. 2), and the generated voltage is twice (6 dB) higher than that of series connection (Fig. 2). Become. For this reason, when using the inverse piezoelectric effect, it is generally more advantageous to use parallel connections, and this is often used, since parallel connections cause more distortion than series connections with the same applied voltage. Conversely, when utilizing the piezoelectric effect, it is advantageous to use series connection.

However, in applications where the same vibrator uses both the piezoelectric effect and the inverse piezoelectric effect (for example, when transmitting and receiving ultrasonic waves using the same element), one or the other must be used. Therefore, either input voltage or output sensitivity is sacrificed.

OBJECTS OF THE INVENTION The present invention provides a bonded piezoelectric vibrator that can simultaneously satisfy both input voltage and output sensitivity.

Structure of the Invention The present invention includes first and second piezoelectric vibrators having two or more polarizations whose polarization directions differ by 180 degrees from each other in the thickness direction, and in which the polarization directions of the mutually overlapping portions of the piezoelectric vibrators are in the same direction. This is a bonded piezoelectric vibrator that is bonded together so that

DESCRIPTION OF EMBODIMENTS FIG. 3 shows an embodiment of the present invention. In FIG. 3, piezoelectric elements 11 and 12 are polarized so that their polarization directions differ by 180° approximately in the middle, and electrodes 13 to 18 are provided on a plane perpendicular to the polarization plane according to their respective polarization regions. are electrically and mechanically connected by electrodes.

When it is desired to use the piezoelectric vibrator of the present invention with the piezoelectric effect, if an external force is applied and the element is bent as shown in the figure, the piezoelectric element 11 will extend, and electric charges will be applied to the electrodes 13, 14, 17, and 16. When the electrodes 14 and 17 are connected, the same voltage as in the case of FIG.
Occurs between 18 and 18. Therefore, the output voltage when the terminals between the electrodes 13 and 18 and between the electrodes 15 and 16 are set as both terminals is the same example of series connection as in the case of FIG. 2.

In addition, if you want to use the inverse piezoelectric effect, connect electrodes 13 to 15 to electrode 14, electrodes 16 to 17 to
If a voltage is applied to each of 18, a parallel bimorph configuration will be obtained, which is exactly the same as the parallel connection shown in FIG. If electrodes 13 to 18 are connected using memory or IC switches, it is very easy to switch between parallel and series connections depending on how to use the inverse piezoelectric effect and piezoelectric effect.
This is very advantageous for uses such as transmitting and receiving ultrasonic waves.

Effects of the Invention The bonded piezoelectric vibrator of the present invention is a single transducer, and when transmitting, it is connected in parallel to obtain a large power with the same input voltage, and as soon as the transmission is finished, it is connected in series as a bimorph, and when receiving, the reception sensitivity is improved. It can be taken in large quantities.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views of conventional parallel-type and series-type piezoelectric vibrators, respectively, and FIG. 3 is a cross-sectional view of a piezoelectric vibrator according to an embodiment of the present invention. 11, 12... piezoelectric vibrator, 13-18... electrode.

Claims (1)

[Claims] 1. First and second piezoelectric vibrators having two or more polarizations whose polarization directions differ by 180 degrees from each other in the thickness direction, and the polarization directions of the overlapping parts of the first and second piezoelectric vibrators are the same. A bonded piezoelectric vibrator that is bonded in the same direction.