JPH0392764A - Piezoelectric acceleration sensor - Google Patents

Abstract

PURPOSE:To to improve the temperature characteristics and the output of a sensor by providing a piezoelectric block wherein a plurality of bimorph elements are laminated through insulating layers. CONSTITUTION:In piezoelectric block 13, a plurality of bimorph elements 14 are laminated through insulating layers 15 and a unitary body is formed. In the element 14, two sheets of film-shaped piezoelectric bodies 16 which have the same piezoelectric characteristics and the reverse polarizing directions are laminated through an intermediate electrode 17, and end-part electrodes 18 are stuck to the surfaces which are not in contact with the electrode 17. The electrodes 17 and 18 comprise metal foils such as an aluminum foil and a copper foil and a vapor deposition film of metal. Lead wires 19 are connected to the peripheral part. It is necessary that the planar shapes of the electrodes 17 and 18 have the same shape as the piezoelectric body 16. The piezoelectric body 16 comprises a piezoelectric material in a film state, and the thickness is 10 - 500mum and sufficiently uniform. The entire body is sufficiently homogeneous. Thus, the high output and the excellent temperature characteristics are provided.

Description

[Detailed Description of the Invention] [Field of Application in Industry-12] The present invention relates to a piezoelectric acceleration sensor using a film-like piezoelectric material, which has a particularly simple structure, excellent temperature characteristics, and high output. Moreover, the present invention relates to a piezoelectric acceleration sensor whose output due to acceleration in a direction perpendicular to the sensing axis is very small.

[Conventional technology]

Conventional piezoelectric acceleration sensor (hereinafter abbreviated as sensor).

) is shown in FIG. 19 as an example. This sensor is disclosed in Japanese Unexamined Patent Publication No. 56-10258, in which a disc-shaped vibrating membrane 1 made of a piezoelectric material such as a piezoelectric polymer is fixed to an annular frame 2 at its periphery, and vibration is removed. 1
Load bodies 3, 3 functioning as inertial masses are provided on both sides of the center of the frame body 2, and the frame body 2 is fixed to a pedestal 4.

In this sensor, an axis that is perpendicular to the membrane surface of the vibrating membrane 1 and passes through the center of the silver load body 3 is an acceleration sensing axis G.

In such a sensor, by attaching the pedestal 4 to the object to be measured, it is possible to detect changes in acceleration of the object to be measured in the sensing IIIllllG direction.

3 [Problem to be solved by the invention] However, in this sensor, even when acceleration in a direction perpendicular to the sensing axis G direction is applied, the load body 3 is displaced in that direction, and the vibrating membrane 1 is It had the disadvantage that it caused distortion and resulted in poor electrical output.

There is also the disadvantage that the structure is complicated and manufacturing is troublesome.
It also has the disadvantage that the frequency band that can be changed is narrow and it is difficult to change it.

In order to eliminate these drawbacks of conventional sensors, the present inventors developed a pedestal that is rigidly attached to the object to be measured, and a film that is fixed on the measurement surface perpendicular to the sensing axis of this pedestal. It consists of a load body consisting of a piezoelectric body and a rigid body fixed on the piezoelectric membrane and acting as an inertial mass, and the sensing axis is set in the planar shape of the piezoelectric membrane or in a plane parallel to the measurement surface. The planar shape of the surface in contact with the membrane piezoelectric material is point symmetrical with the center of symmetry being the center of symmetry, and the plane shape of the load body in contact with the membrane piezoelectric material is point symmetrical with the sensing axis as the center of symmetry, and He devised a sensor that is characterized by a line symmetry with the sensing axis as the axis of symmetry for all Itft planes when cross-sectioned through countless perpendicular planes, and previously filed a patent application as Japanese Patent Application No. 1-11-3255. are doing.

Such a sensor is therefore extremely simple in structure;
It has the advantage that the output when acceleration is applied in a direction perpendicular to the sensing axis is extremely small, and the measurable frequency band is wide.

However, this new type of sensor also has the following disadvantages, which need to be solved. In other words, in order to increase the voltage output of the sensor, it is sufficient to increase the thickness of the film-like piezoelectric material, but it is difficult to perform poling processing on a thick film-like piezoelectric material.
If the dipoles are poorly oriented, the piezoelectric constant may become small or its value may vary.

Additionally, in order to increase the output sensitivity as a charge, it is possible to increase the area of the membrane piezoelectric material, but increasing the area of the membrane piezoelectric material will lead to an increase in the size of the sensor, which will result in a smaller size. It no longer meets the needs of society.

For this reason, the present inventor further developed a sensor having a laminated structure in which a plurality of film-like piezoelectric materials were laminated, as a sensor to solve this problem.
And the laminated interface is in a conductive state, as disclosed in Japanese Patent Application No. 1-13
A patent application has been filed as No. 8323.

However, this improved sensor has the disadvantage that its output fluctuates with fluctuations in the environmental temperature around the sensor, and its temperature characteristics are not necessarily good. That is,
Due to environmental temperature fluctuations, temperature distribution occurs in the thickness direction of each film-like piezoelectric material and the thickness direction of the stacked laminates (membrane piezoelectric materials generally have low thermal conductivity, so it is difficult to maintain a uniform temperature throughout the film. ), a potential difference is generated by the pyroelectric effect based on this temperature distribution, which appears as an output.

[Means for Solving the Problems] The present invention includes a pedestal rigidly attached to an object to be measured, a piezoelectric block fixed to a measurement surface perpendicular to the sensing axis of the pedestal, and this piezoelectric block. The piezoelectric block 7 has a rigid load body fixed to the top and acts as an inertial mass part, and the piezoelectric block 7 has a T-plane shape with the sensing axis as the center of symmetry in a plane parallel to the sub-structure. It is point symmetric,
It has a structure in which a number of stages of bimorph elements are stacked with an insulating layer interposed in between.
Condition ff. Electric bodies hX are stacked, and an intermediate electrode is placed between them.
End electrodes are arranged at both ends, and the electrodes are connected so that the polarization directions of the two membrane piezoelectric bodies are opposite to each other, and the two membrane piezoelectric bodies are parallel. The high morph element outputs of these plural bimorph elements are connected in series to be the detection output of the piezoelectric block, and the Ml body is connected to the piezoelectric block. When the plane shape of the contacting surface is point symmetrical with the sensing axis as the center of symmetry, and when cross-sectioned by countless planes passing through the sensing axis and perpendicular to the measurement surface,
The above-mentioned problem was solved by a sensor that has line symmetry with the sensing axis as the axis of symmetry for all cross sections.

7 This invention will be explained in detail below.

FIG. 1 shows an example of the sensor of the present invention, and the reference numeral 11 in the figure is a pedestal. This pedestal 11 forms the base of the sensor and is rigidly attached to the object to be measured, and is made of a material with sufficient rigidity, such as metal such as steel, brass, and aluminum, glass, ceramic, glass, and hard plastic. It is made.

Further, the elastic modulus of the material forming the pedestal 11 is preferably higher than that of the membrane piezoelectric material described later, and the thickness of the pedestal l1 is desirably several times that of the monomer piezoelectric material.

The pedestal 11 here has a cylindrical shape,
The shape is not limited to this, and may be a plate shape, a rectangular parallelepiped, or the like.

One surface of this pedestal 11 is a flat and smooth measurement surface 1.
2. This measurement plane 12 needs to be a vertical plane that is exactly perpendicular to the acceleration sensing axis G of this sensor.

A piezoelectric block 13 is placed on the measurement surface 12 of this pedestal 11.
are fixed together using epoxy adhesive.

8 - This piezoelectric block 13 is made up of a plurality of piemorph elements l.8 as shown in FIG. 4. , 1. 4
. . are laminated and integrated through an insulating layer 15 .

When an insulating adhesive is used to laminate and integrate these bimorph elements 14, this becomes an insulating layer 15, and a sheet or filly (insulating layer 15) made of an insulating material is used.
) may be formed into a layer using a conductive adhesive. In addition, as shown in FIG.
Laminated through 7, middle electrode l of fetal piezoelectric body 16.16
The end electrodes 18 and 18 are attached to the surface not in contact with the electrode 7. Both the intermediate electrode 17 and the end electrode 18 are made of metal foil such as aluminum foil or copper foil, or a metal vaporized film, and lead wires 19 are connected to their peripheral edges. The piezoelectric film 16, 16, the intermediate electrode 17, and the end electrodes 18, j8 may be laminated and integrated using either an insulating adhesive or a conductive adhesive.

The two film-like piezoelectric materials 16.16 must both have the same shape and the same piezoelectric properties, but their polarization directions are opposite to each other (as shown by the arrows in FIG. 3). (in the opposite direction).

Further, although the thicknesses of the individual film-like piezoelectric bodies {6 within one pymorphelement 14 do not need to be strictly the same, it is desirable that the variation be within ±10%. Furthermore, it is desirable that the thickness of the intermediate electrode 17 and the end electrodes 18.18 be uniform, and it is necessary that their planar shape is, in principle, the same as that of the piezoelectric film 16.16.

The film-like piezoelectric material I6 used here is a film-like material made of a piezoelectric material with a thickness of 10 to 500 μm, whose thickness is sufficiently uniform and whose whole is sufficiently homogeneous. It will be done.

Examples of piezoelectric materials include polyvinylidene fluoride,
Polyvinylidene chloride, polyvinyl fluoride, polyvinyl chloride, nylon with nylon 11 and polymetaphenylene isophthalamide, polyvinylidene fluoride with ethylene, trifluoroethylene, vinyl fluoride, etc. Polymer, vinyl acetate, vinyl blobionate, copolymer of vinyl benzoate and vinylidene cyanide, polyph,
In addition to polymers such as blend polymers of vinylidene chloride and polycarbonate 1, vinylidene polyfluoride, and polyvinyl polyphfluoride, piezoelectric material powders such as metal titanate and metal silconate titanate can be used. Those added to or dispersed in polymers are used.

The planar shape of the crotch-shaped piezoelectric material j6, that is, the piezoelectric material block 13, is important for reducing crosstalk.

In this invention, the cross 1--k refers to the output P1 and the sensing 'Pll' when the sensor receives acceleration in the direction of the sensing axis G.
l Output P of Ojr subjected to acceleration in the direction perpendicular to G
, the ratio P2/P. It is expressed as follows.

In order to reduce this crosstalk, the film-like piezoelectric material 16 has a planar shape or a sensing axis G in a plane parallel to the sub-plane l2.
It must be point symmetric with the center of symmetry. In the example shown in Fig. 1, it is circular, but other planar shapes that do not satisfy the condition L are, for example, those shown in Figs. 4 to 9.
There is something like the one shown in the figure. Figure 4 is a parallelogram,
The figure is a square, the figure 6 is an ellipse, the figure 7 is a hexagon, the figure 8 is an octagon, and the figure 9 is a ring. In these figures, the symbol G indicates the sensing axis G. All of these planar shapes are point symmetrical with respect to the sensing axis G as the center of symmetry. Of course, planar shapes other than these can also be used if the above conditions are met.

A load body 20 made of a rigid body and functioning as an inertial mass section is integrally fixed onto the piezoelectric block 13. This load body 20 is displaced in response to acceleration and causes strain or stress on the piezoelectric block 13, that is, the membrane piezoelectric body 16, and its weight is related to the electrical output per unit stroke of the sensor. Therefore, there is no particular limitation, or it is set within a range that does not cause creep in the piezoelectric film 16. The load body 20 and the piezoelectric block 13 are fixed together using an epoxy adhesive or the like.

Furthermore, the three-dimensional shape of the load body 20 is important in reducing the cross 1 and loke.

First, the surface of the charged body 20 in contact with the piezoelectric block 13 (hereinafter referred to as the bottom surface) is exactly perpendicular to the sensing axis G, and the planar shape of the bottom surface is a line with the sensing axis G as the center of symmetry. Must be symmetrical.

Therefore, as the shape that satisfies this condition, the shapes shown in FIGS. 4 to 9, for example, can be adopted, similar to the planar shape of the film-like piezoelectric body 13 described above. However, when introducing the membrane piezoelectric body 16 and the load body 20, the planar shape of the bottom surface of the load body 20 and the plane shape of the membrane piezoelectric body 16 do not necessarily have to be the same. The piezoelectric bodies l6... may have a square planar shape, and the bottom surface of the load body 20 may have a circular planar shape, as long as the sensing axes G are the same, as will be described later.

At the same time, when the load body 20 is cross-sectioned through numerous planes passing through the sensing axis G and perpendicular to the bottom surface, it is necessary that all the cross sections have line symmetry with the sensing axis G as the axis of symmetry. Figures 10 to 1 satisfy this line symmetry condition.
There is one shown in Figure 6. The one shown in Fig. 10 is plate-shaped, the one shown in Fig. 11 is columnar, the one shown in Fig. 12 is conical, and the one shown in Fig. 13 is columnar.
The one shown in the figure is a sphere cut out on a plane, the one in Fig. 14 is an ellipsoid cut out on a plane, the one in Fig. 15 is a column with a space inside it, and the one in Fig. 16 is a sphere cut out on a plane. It is a combination of a column and a plate.

In these figures, the symbol S indicates the bottom surface and G is the axis of symmetry that coincides with the sensing axis. Furthermore, the load body 20 that satisfies this condition of line symmetry has its center of gravity located on the sensing axis G.

Moreover, the load body 20 can be made of a composite material made of different materials in addition to being made of the same material as a whole, but in this case, each material is firmly fixed and the whole is rigid. They must be able to be regarded as such, and each must not undergo different displacements when subjected to acceleration.

Under such conditions, that is, the load body 20 having symmetry has its axis of symmetry aligned with the pair J31 of the piezoelectric block 13,
In other words, the sensor G1'. The center of symmetry of the piezoelectric block 13 and the axis of symmetry of the load body 20 are arranged to coincide with each other, and the piezoelectric block 13 is fixed.

Such a sensor is used with its pedestal 11 attached to a fixed object, and the acceleration in the direction of the sensing axis G can be determined.

FIG. 17 shows the high morph element 1 of the sensor in this example.
4 shows the square wire between the two end electrodes 1
8.18 is connected across to serve as the terminal A for taking out the output of one of the elements 1 and 14, and the intermediate electrode 17 is used as it is as the terminal B for taking out the output of the other element 14.

That is, the two membrane piezoelectric bodies 16.1.6 are connected in parallel.

Moreover, FIG. 18 shows such a pymorph element 1.
14 - A pair of output take-out terminals A. Terminal A of the first high morph element 14 in contact with the load body 20 is used as one output terminal of the sensor I5, and terminal B1 is connected to the piezoelectric block 13 for B. is connected to the terminal A of the second pymorph element 1 and 14, and the terminal B
, or the third Highmorph Element!・14 terminal A3
In the same manner, the terminal B of the n-th Novimorph element 14 is connected to the other output terminal as the cassette 7, that is, the output terminals A and B of the plurality of Pimorph elements 1 are connected in series.

In a sensor with such a structure, the pedestal 11, the piezoelectric block 13, and the load body 20 are simply laminated, so the structure is simple, manufacturing is easy, and miniaturization is possible. .

In addition, the planar shape of the piezoelectric film 16, that is, the piezoelectric block 13 is point symmetrical with respect to the sensing axis G, and the planar shape of the bottom surface of the load body 20 is symmetrical with the sensing axis G as the center of symmetry. At the same time, the three-dimensional shape of the load body 20 is linearly symmetrical in a plane passing through the sensing axis G with the sensing axis G as the axis of symmetry, so the cross 1·-k is slight.

Generally, when acceleration is applied to a sensor in a direction other than the direction of its sensing axis, it is divided into at least two components, one in the direction orthogonal to the sensor and the other in the direction of the sensing axis, according to the law of vector decomposition. This component in the direction perpendicular to the sensing axis acts on the center of gravity of the load body 20, and a bending moment about the center of gravity acts on the load body 20. Therefore, a compressive force acts on a part of the membrane piezoelectric body 16, that is, a part of the piezoelectric body block 13, and a tensile force acts on the remaining part. Each piezoelectric film 16 generates charges of opposite signs due to compressive force and tensile force, but if the amounts of charges are equal, they cancel each other out and no output is produced. Therefore, if a compressive force and a tensile force of equal magnitude act on each piezoelectric membrane 16, the output from the piezoelectric membrane 16 will be 7, and acceleration in a direction other than the sensing direction will be detected. It disappears.

In this invention, since the shapes of the piezoelectric block 13 and the load body 20 have the above-mentioned symmetry, even if acceleration in a direction other than the direction of the sensing axis G is applied, the individual membrane piezoelectric bodies 16... are subjected to compressive force and tensile force of equal magnitude, and the individual membrane piezoelectric bodies 16...
・There is no output from the sensor, and crosstalk is extremely small.

Further, this sensor has a high upper limit of its measurable frequency and a wide measurable frequency band.

The second limit of the measurable frequency of this type of sensor is determined by the sensor's resonant frequency. The resonance frequency of the sensor in this invention is determined by the elasticity of the piezoelectric block 13 and the adhesive layer that adheres it to the pedestal 11 and the load body 20 due to its structure. Since it is proportional to the value obtained by dividing the rate by the mass of the load body 20, the resonant frequency is more than two orders of magnitude higher than the resonant frequency of a conventional vibrating membrane type sensor, and is on the order of kilohertz. However, it should be noted that as the elastic modulus of the adhesive layer decreases, the resonance frequency decreases.

Therefore, the piezoelectric block 13 itself and the pedestal 1
Regarding the adhesive used for fixing to the load body 20, the elastic modulus of the adhesive layer is EA, the total thickness is tA, the elastic modulus of the membrane piezoelectric material 16 is E1, and the total thickness is tp. In this case, it is necessary to satisfy the relationship expressed by the following formula.

(EA/tA)/(Er/tp)≧0.
1 What this formula means is the condition for the force generated on the load body 20 due to acceleration to be well transmitted to the membrane piezoelectric material 6... without being absorbed by the adhesive layer 1. When the value of the formula is less than 0.1, absorption relaxation by the adhesive layer cannot be ignored, and the resonance frequency decreases as described above, narrowing the measurable frequency range.

In addition, when the types of adhesives are different and the elastic modulus is also different, the ratio between the elastic modulus and the thickness of each adhesive layer may be determined, the sum of these ratios may be substituted into the above equation.

Therefore, the adhesive used here should be a hardening type such as Epoquin type, phenol type, or cyanoacrylate type and has a high elastic modulus, and adhesive type such as rubber type is inappropriate.

Furthermore, this sensor does not produce an output due to the pyroelectric effect. That is, in one pymorphelement electrode 14, the +9 polarization directions of the membrane piezoelectric film [6, +6 and +9] are opposite to each other (opposite directions), and their thicknesses are almost equal, so that the end electrodes 18, If a temperature difference of Δt occurs between the electrodes 18 and 18, one end electrode 18 and the intermediate electrode 1
A temperature difference of Δt/2 occurs between the intermediate electrode 17 and the other end electrode 18, and a temperature difference of Δt/2 also occurs between the intermediate electrode 17 and the other end electrode 18. Due to this temperature difference, a voltage of ■ is generated in one of the membrane piezoelectric bodies 16 due to the pyroelectric effect, and the other membrane piezoelectric body 1
Similarly, a voltage of -■ is generated at 6. And the 17th
Since the output connection is made as shown in the figure, ■ and -■ cancel each other out, and no output due to the pyroelectric effect appears between the output terminals AB. Similarly, in each of the pymorph elements 1 and 14, the output terminals A and B
Since the output due to the pyroelectric effect does not appear in between, the output due to the pyroelectric effect also does not appear in the sensor output when these are connected in series. Therefore, the output does not fluctuate due to acceleration due to temperature changes, resulting in good temperature characteristics.

Furthermore, in this sensor, since the outputs from the plurality of bimorph elements 14 are connected in series, the outputs of each bimorph element 14 are added up, and the output as a sensor becomes large. Sensitivity.

Hereinafter, specific examples will be shown to clarify the effects.

(Example 1) (Creation of bimorph element) Thickness I]. 0μm, length 5.0mm, width 5.0mm polyvinylidene fluoride-1 (elastic modulus 2.7X) 09Pa
) using two sheets, thickness 30 μm, length 5.0 mm, width 5.0
Using three pieces of copper foil of mm
．． A pymorph element 1 as shown in FIG. 3 was prepared using 6XIQ'' Pa), and its electrodes were connected as shown in FIG. 17 to form an output J terminal.

Three of these bimorph elements were superimposed and glued together using an Evokin adhesive to form a piezoelectric block, and the piezoelectric block I was adhered to a temporary alumina plate having a thickness of inn as a pedestal. Next, a 40 mm thick, 5. 0mm, Maki 50mm, weight 0
A 84 g brass load body was bonded with an epoxy adhesive with the axes of symmetry aligned to form a sensor. The thickness of all adhesive layers was approximately 10 μm. Three pymorph elements 1.
The output terminals of the two were connected in series as shown in FIG.

(Comparative Example 1) In Example 1, only one bimorph element constituted the piezoelectric block.

(Comparative Example 2) Three sheets of the polyphthovinylidene of Example 1 were stacked together using a conductive adhesive, and then two sheets of the copper foil were laminated on the front and back sides of the pedestal of Example 1. They were glued together and the same load bodies were stacked to form a seven-piece assembly (Patent application No. 1-13832).
(corresponds to the sensor shown in No. 3).

For these three sensors, the excitation frequency was 10QHz,
A continuous sine wave excitation test was conducted with an excitation acceleration IG, and the output was determined when the ambient temperature was varied under the following conditions during the test.

20°C (room temperature) ↓Rapid heating for 1 minute 400C ↓Hold temperature for 1 minute Cool to room temperature The results are shown in Table 1.

The outputs J shown in Table 1 are expressed as relative values, with the output before heating (time 0 minutes) being 1 for each sensor in each example.

Table 1 The output of each sensor at room temperature is shown in Table 2.

Table 2 As is clear from the results in Tables 1 and 2, the sensor of the present invention does not produce output due to the pyroelectric effect even when there is a sudden change in ambient temperature, and the true output changes based on acceleration. It can be seen that the temperature characteristics are excellent. It can also be seen that the output voltage is high and the sensitivity is high.

In addition, for both sensors, the crosstalk is in the range of 3 to 5%, and the measurable frequency band is 0.1%.
The frequency was Hz to 2KHz.

〔Effect of the invention〕

As explained above, the piezoelectric acceleration sensor of the present invention includes a pedestal rigidly attached to an object to be measured, a piezoelectric block fixed to a measurement surface perpendicular to the sensing axis of the pedestal, and a piezoelectric block. The piezoelectric block has a rigid front body fixed to the top and acts as an inertial claw, and the piezoelectric block has a planar shape or a point symmetry with the sensing axis as the center of symmetry in a plane parallel to the creation plane. and
The bimorph element has a structure in which nine bimorph elements are stacked with an insulating layer interposed between them.
I'J-shaped piezoelectric bodies are stacked, and an intermediate electrode is placed between them.
End electrodes are disposed at both ends, and the polarization directions of the two film-like piezoelectric bodies are opposite to each other, and the two film-like piezoelectric bodies are arranged in an IF: row between the electrodes. The high-morph element outputs of these multiple bimorph elements are connected in series to provide the detection output of the piezoelectric block, and the load body is the piezoelectric block. When the planar shape of the surface in contact with is point symmetrical with the sensing axis as the center of symmetry, and cross-sectioned by countless planes passing through the sensing axis and perpendicular to the measurement surface,
All cross sections are line symmetrical with the sensing axis as the axis of symmetry, so the structure is simple, it is easy to downsize, the rho characteristic is excellent, the output is high, and Crosstalk becomes extremely small. Furthermore, the measurable frequency band is wide, it is easy to design a design that matches the measurement purpose, and there is a large degree of freedom in design.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing an example of a piezoelectric acceleration sensor according to the present invention, FIG. 2 is a sectional view showing an example of a piezoelectric block according to the present invention, and FIG. 3 is an example of a pymorph element according to the present invention. 4 to 9 are all plan views showing examples of the planar shape of the membrane piezoelectric material used in this invention, and each of FIGS. 10 to 16 is a cross-sectional view showing the load used in this invention. 17 is a cross-sectional view showing an example of the three-dimensional shape of the body; FIG. 17 is a diagram showing connections for outputting the bimorph element in the present invention;
FIG. 18 is a diagram showing the wiring for taking out the output of the piezoelectric block according to the present invention, and FIG. 19 is a schematic structural diagram showing an example of a conventional piezoelectric acceleration sensor. 1l...Pedestal, 12...Measurement surface, 13...Piezoelectric block, 14...Bimorph element, l5...Insulating layer, 16...Membrane piezoelectric body, 17 intermediate electrode, 18... end electrode, 20... load body.

Claims (2)

[Claims] (1) A pedestal that is rigidly attached to the object to be measured, a piezoelectric block fixed to the measurement surface perpendicular to the sensing axis of this pedestal, and a rigid body fixed to the piezoelectric block and acting as an inertial mass part. The piezoelectric block has a planar shape that is point symmetrical with respect to the sensing axis as the center of symmetry in a plane parallel to the measurement surface, and has a plurality of bimorph elements laminated with an insulating layer interposed therebetween. The bimorph element has a structure in which two membrane-like piezoelectric materials are stacked on top of each other.
An intermediate electrode is arranged in the middle, and end electrodes are arranged at both ends thereof, and the polarization directions of the two film-like piezoelectric materials are opposite to each other, so that the two film-like piezoelectric materials are arranged in parallel. The above electrodes are connected to form a bimorph element output, and the bimorph element outputs of these plural bimorph elements are connected in series to form the detection output of the piezoelectric block, and the load body is If the planar shape of the surface in contact with the piezoelectric block is point symmetrical with the sensing axis as the center of symmetry, and when cross-sections are taken through countless planes passing through the sensing axis and perpendicular to the measurement surface, the sensing axis for all cross sections is A piezoelectric acceleration sensor characterized by line symmetry with respect to an axis of symmetry. (2) In the piezoelectric acceleration sensor according to claim (1), the pedestal, the piezoelectric block, the load body, the membrane piezoelectric material, the intermediate electrode, and the end electrode are fixed with an adhesive, and the total of these adhesive layers is The thickness is t_A, its elastic modulus is E_A, the total thickness of the piezoelectric film is t_P, and its elastic modulus is E_P.
A piezoelectric acceleration sensor that satisfies the following relationship. (E_A/t_A)/(E_P/t_P)≧0.1