JP2011064651A - Acceleration detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration detector which is easy to manufacture and has high accuracy and high sensitivity. <P>SOLUTION: This acceleration detector 10 includes a base 20 which has a movable part 24 to be displaced by acceleration given perpendicularly to the main surface and a fixed part 22 supporting the movable part 24 through the medium of a narrow part 26, and a pressure-sensitive element 30 which has a pressure sensing part 32 having a detection axis in the direction of detection of a force perpendicular to the direction of the acceleration and being connected to a pair of base parts 34 and 35 lined up along the detection axis. The paired base parts 34 and 35 are fixed to the movable part 24 and the fixed part 22 of the base 20, and the narrow part 26 is formed between the movable part 24 and the fixed part 22 in the direction intersecting the direction of the detection axis in a region located between the paired base parts 34 and 35. The pressure-sensitive element 30 is so formed that it is extended from either one of the paired base parts 34 and 35 to the other over the narrow part 26 and has beam parts 36 having free ends. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an acceleration detector using a high-precision and high-sensitivity piezoelectric vibrator in which the degree of design freedom of the size and area of a weight portion is expanded.

Conventionally, an accelerometer as disclosed in Patent Documents 1 to 3 including a pressure-sensitive element using a piezoelectric vibrator and a weight portion is disclosed.
In the acceleration sensor of Patent Document 1, a weight 104 is connected to one base 102 of a pressure-sensitive element 101 via a constriction 103 as shown in FIG. As shown in (2) and (3), the weight 104 is disposed at a position opposite to the pressure sensitive element 101 with the constriction 103 as a base point. The constriction 103 is formed on each of the front and back surfaces of the substrate 105.

  As shown in FIG. 8, the accelerometer disclosed in Patent Document 2 is connected to a weight 203 connected to a base 202 by a hinge coupling 201 so as to freely rotate in the X-axis direction, and connected to the weight 203 and the base 202 to detect the accelerometer. A pressure-sensitive element 204 having an axis formed in the Y-axis direction orthogonal to the X-axis direction is provided, and the pressure-sensitive element 204 is formed on the front and back of the weight 203 and the base 202.

  Patent Document 3 discloses an accelerometer having a beam resonator force transducer. As shown in FIG. 9, an accelerometer 301 having a beam resonator force transducer includes a base 304 connected to a weight 303 by a hinge 302, and a cantilever having one end connected to the weight 303 and the other end extending from the base 304. A pressure sensitive element 307 connected to the free end 306 of the beam 305 is provided. A stop 309 for stopping the displacement of the weight 303 at the breaking limit is formed on the free end 308 side of the weight 303 with a predetermined distance from the weight 303.

US Pat. No. 5,165,279 JP-A-1-302166 JP 59-126261 A

  However, in Patent Document 1, since the size of the weight 104 that can be secured is restricted by the size of the pressure-sensitive portion of the pressure-sensitive element 101, there is a problem that the sensitivity that satisfies the specification cannot be obtained depending on the required specifications of the accelerometer. It was.

  Further, since the constriction 103 is provided on each of the front and back surfaces of the substrate 105, the constriction 103 must be formed on each of the main surfaces of the substrate 105 by a photolithographic etching method. Therefore, there is a problem that the work is complicated and the cost is increased.

  In addition, an acceleration sensor of a cantilever type as disclosed in Patent Document 2 has an upper limit on sensitivity because the acceleration that is the destructive limit is reduced by increasing the sensitivity. As a result, sufficient crystal performance could not be achieved especially for sensors for low acceleration. This is caused by a structure in which stress is linearly applied to acceleration.

  Further, Patent Document 3 is provided with a stopper 309 that serves as a stopper for the weight 303, but the base 304, the weight 303, and the stopper 309 cannot be integrally formed. In addition, due to the problem of processing accuracy, it is difficult to set the weight 303 at a predetermined interval in the gap between the stoppers.

  Furthermore, when a stop (stopper) as shown in Patent Document 3 is applied to an accelerometer as shown in Patent Document 2, a stopper is provided separately from the pressure sensitive element. This stopper has a configuration in which one end of the stopper is fixed to the base in the same manner as the pressure-sensitive element provided on the base, and a free end contacting the weight is cantilevered so as to provide a predetermined distance from the weight. Therefore, there is a problem that it is difficult to position the free end of the stop at a predetermined distance from the weight.

On the other hand, in recent years, an acceleration detector capable of detecting a low acceleration while being able to detect an acceleration up to, for example, 100 G is desired. However, the pressure-sensitive element whose sensitivity is increased to detect low acceleration has a problem that it breaks when high acceleration is applied.
In order to solve the above-mentioned problems of the prior art, an object of the present invention is to realize an acceleration detector that is easy to manufacture and has high accuracy and high sensitivity.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
[Application Example 1] A force that is perpendicular to the main surface and is displaced by an acceleration, a base that includes a fixed portion that supports the movable portion via a constriction, and a force that is perpendicular to the direction of the acceleration. A pressure sensing element having a pressure sensing direction as a detection axis and connected to a pair of bases arranged along the detection axis, wherein the pair of bases and the movable part of the base Fixed to the fixed portion, the constricted portion is a region sandwiched between the pair of base portions, and is formed in a direction intersecting the direction of the detection axis between the movable portion and the fixed portion, The pressure sensing element is formed so as to extend from one of the pair of base portions to the other and straddle the constricted portion, and has a beam portion whose end portion is a free end. vessel.

  As a result, the beam is configured to extend from a pair of base portions of the pressure-sensitive element to the other base portion, so that the pressure-sensitive element and the beam can be formed simultaneously and integrally. Therefore, in the present invention, the beam and the weight can be easily positioned as compared with the configuration in which the pressure-sensitive element and the beam are separately provided and it is difficult to adjust the gap between the beam and the weight.

  In addition, even when a large acceleration is applied to a highly sensitive acceleration detector that detects low acceleration, the beam portion can stop the displacement of the movable portion at the breaking limit, and the detector can be prevented from being broken.

Application Example 2 The beam portion is formed so as to extend from one of the pair of base portions of the pressure-sensitive element on one main surface of the base to the other and straddle the constricted portion. A first beam portion whose portion is a free end, and the other main surface of the base opposite the first beam portion, with one end being a free end and the other end being either a movable portion or a fixed portion of the base The acceleration detector according to Application Example 1, further comprising: a second beam portion serving as a fixed end fixed to one side.
Thereby, even when a large negative acceleration G is applied, the second beam portion can stop the displacement of the movable portion at the destruction limit, and the detector can be prevented from being destroyed.

Application Example 3 The pressure-sensitive element is formed such that the first pressure-sensitive element formed on one main surface of the base and the first pressure-sensitive element facing the other main surface of the base. The acceleration detector according to Application Example 1, wherein the acceleration detector includes a formed second pressure-sensitive element.
As a result, the acceleration can be detected in a differential manner, so that the acceleration can be detected with higher sensitivity.

[Application Example 4] In any one of Application Examples 1 to 3, the beam portion may have a variable length between the fixed end and the free end according to a fracture limit. Accelerometer.
Thus, the design of the breakage limit point of the acceleration detector can be arbitrarily changed.

It is the schematic of the acceleration detector of Example 1. FIG. It is explanatory drawing of an effect | action of the acceleration detector of Example 1. FIG. It is the schematic of the acceleration detector of Example 2. FIG. It is explanatory drawing of an effect | action of the acceleration detector of Example 2. FIG. It is the schematic of the acceleration detector of Example 3. FIG. It is explanatory drawing of an effect | action of the acceleration detector of Example 3. FIG. It is explanatory drawing of the conventional acceleration sensor. It is explanatory drawing of the conventional pendulum type accelerometer. It is explanatory drawing of the accelerometer which has the conventional beam resonator force converter.

Embodiments of an acceleration detector according to the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram of an acceleration detector according to a first embodiment, (1) is an exploded perspective view seen from one main surface side of the base, and (2) is a side view.

As shown in the figure, the acceleration detector 10 of the first embodiment has a base 20 and a pressure-sensitive element 30 as the main basic configuration.
The base 20 mainly includes a fixed portion 22, a movable portion (weight portion) 24, and a constricted portion 26.

  The fixing portion 22 is a member that is not displaced by application of the acceleration G and fixes the base 20 to a substrate (not shown). The movable portion 24 serving as a weight is supported by the fixed portion 22 and is displaced (movable) in the application direction (Z-axis direction) when the acceleration G is applied. The fixed portion 22 and the movable portion 24 include mounting portions 29 a and 29 b that support a pair of base portions of the pressure-sensitive element 30 when a pressure-sensitive element 30 described later is bonded to the one main surface 27 side of the base 20. Yes.

  The constricted portion 26 is a thin-walled portion formed between the fixed portion 22 and the movable portion 24 and having a concave end surface shape in the X-axis direction of the planar rectangular base 20. The constricted portion 26 displaces the movable portion 24 in the direction opposite to the direction in which the acceleration G is applied (direction of inertial force) when the acceleration G is applied to the movable portion 24 and expansion / contraction / compression stress is applied to the pressure-sensitive element 30. It is configured as follows. The constricted portion 26 shown in FIG. 1 is a groove formed by cutting the other main surface 28 of the base 20 into a concave end surface shape.

  As long as the constricted portion 26 has a shape in which a part of the base 20 is thinned so as to have flexibility, in addition to the concave groove formed on the other main surface 28 of the base 20 as illustrated, A concave groove may be formed on one main surface 27 side, and for example, the front and back surfaces of the base 20 may be formed in a semicircular shape.

  Further, the fixed portion 22, the movable portion 24, and the constricted portion 26 constituting the base 20 can be integrally formed by cutting the thinned constricted portion 26 using a rectangular metal material in plan view.

The pressure sensitive element 30 mainly includes a pressure sensitive part 32, a pair of base parts 34 and 35, and a beam part 36.
The pressure-sensitive element 30 has a pair of base portions 34 and 35 arranged at both ends, and a pressure-sensitive portion 32 having a vibration region provided between the pair of base portions 34 and 35, and an excitation electrode (not shown) on the vibration region. Is forming.

  The pressure-sensitive part 32 of the present embodiment has a configuration in which one vibrating arm is provided between the pair of base parts 34 and 35 so as to be connected to the base parts 34 and 35. The pressure sensing unit 32 may be a double tuning fork vibrating piece that has a large frequency change with respect to the applied force and can detect the pressure with high sensitivity. That is, the double tuning fork vibrating piece is a vibrating piece having a flexural vibration mode, and has a structure in which the end faces on the free end sides of two tuning fork type vibrating pieces are opposed to each other, and are parallel to each other in the Y axis. It is good also as a structure which has two bases which are connected to the both ends of the longitudinal direction of this vibration arm, and the vibration arm extends in the direction, and two bases arranged in a line with the vibration arm.

  The resonating arm is elongated in the Y-axis direction and is a portion that is flexed and vibrated by applying a driving voltage by an excitation electrode (not shown) provided on the surface thereof. This is the part where the frequency changes when tension is applied. Therefore, the acceleration can be detected by detecting the frequency change.

  The pressure-sensitive element 30 is a force perpendicular to the direction of acceleration, and the pair of base portions 34 and 35 are fixed to the mounting surfaces 29a and 29b on the base 20 so that the detection direction of the force is a detection axis. Yes. That is, the detection axis of the pressure sensitive element is in the Y-axis direction.

  Further, the constricted portion 26 of the base 20 with respect to the pressure-sensitive element 30 is an area sandwiched between the pair of base portions 34 and 35 and intersects the direction of the detection axis between the movable portion 24 and the fixed portion 22. It becomes the relationship arranged in.

  The beam portion 36 includes a fixed end 37 connected to one of the pair of base portions 34 and 35, and a free end 38 extending to the other base portion. In the beam portion 36 shown in FIG. 1, the fixed end 37 is connected to the base portion 35 on the fixed portion 22 side.

  The length of the beam portion 36 is configured to arbitrarily change the length between the fixed end 37 and the free end 38 in accordance with a predetermined breaking limit of the acceleration detector 10. The breakage limit of the acceleration detector 10 is, for example, that excessive acceleration is applied to the movable portion 24 of the base 20 to increase the amount of displacement, and the expansion and contraction stress acts on the pressure-sensitive element 30 connected to the base 20 to break the element. That means. Specifically, when the length of the beam portion 36 is increased, the free end 38 is likely to come into contact with the displaced movable portion 24, and the displacement amount of the movable portion 24 can be reduced (the displacement range of the movable portion 24 is reduced). it can. On the other hand, when the length of the beam portion 36 is shortened, the free end 38 does not come into contact unless the movable portion 24 is largely displaced, so that the width of the displacement range of the movable portion 24 is widened.

  It is only necessary that the beam portion 36 can be configured to come into contact with the movable portion 24 at the failure limit and stop the displacement of the movable portion 24. Two beam portions 36 shown in FIG. In addition to the formed structure, one may be used.

  The pressure-sensitive element 30 can integrally form the bases 34 and 35, the pressure-sensitive part 32, and the beam part 36 by using a photolithography technique and an etching technique as a piezoelectric material. Lithium acid or the like can be used.

  The pressure-sensitive element 30 formed in this way has a pair of base portions 34 bonded to the mounting portions 29a and 29b of one main surface 27 of the base 20 with a predetermined interval between the base 20 and the bonding means 40. It is fixed.

The predetermined interval that is the gap between the pressure sensitive element 30 and the base 20 is set to a distance at which the pressure sensitive portion 32 and the base 20 do not interfere with each other.
The acceleration detector according to the first embodiment having the above-described configuration operates as follows. FIG. 2 is an explanatory diagram of the operation of the acceleration detector according to the first embodiment.

  When a positive acceleration G acts on the base 20 of the acceleration detector 10 as shown in (1), it is a force perpendicular to the direction of the acceleration G, and the sense of the pressure-sensitive element 30 having the detection direction of the force as a detection axis. A compressive stress is applied to the pressure part 32. The pressure sensitive element 30 can detect the acceleration G by changing the frequency due to the compressive stress.

  When an excessive acceleration G exceeding the breaking stress is applied to the acceleration detector 10 according to the first embodiment, compressive stress is applied to the pressure-sensitive portion 32 of the pressure-sensitive element 30 according to the displacement of the movable portion 24. On the other hand, the beam portion 36 fixes the fixed end 37 to the fixed portion 22 of the base 20 through the base 35 and the free end 38 is not fixed, so that it is not affected by the compressive stress of the movable portion 24. Therefore, the free end 38 of the beam portion 36 comes into contact with the displaced movable portion 24 and functions to stop the displacement of the movable portion 24.

  The fixed end 37 of the beam portion 36 of the pressure-sensitive element 30 only needs to be connected to one of the base portions 34 and 35, and the fixed end 37 is connected to the base portion 34 on the movable portion 24 side as shown in (2). In addition, the free end 38 can be formed so as to extend to the base portion 35 on the fixed portion 22 side. In this case, when an excessive acceleration G exceeding the fracture stress is applied, the beam portion 36 fixes the fixed end 37 to the movable portion 24 of the base 20 through the base portion 34, and the free end 38 is not fixed. There is no influence of the stretching stress of the portion 24. Accordingly, the free end 38 of the beam portion 36 comes into contact with the fixed portion 22 and functions to stop the displacement of the movable portion 24 as in (1).

  According to the acceleration detector of the first embodiment, even when the acceleration G exceeding the destruction limit acts on the acceleration detector 10, the beam portion 36 becomes a stopper of the movable portion 24 and is destroyed by the excessive acceleration G. The acceleration can be detected within a preset measurement range.

  In addition, the present invention is characterized in that the pressure-sensitive portion 32, the base portions 34 and 35, and the beam portion 36 constituting the pressure-sensitive element 30 are integrally formed by etching and photolithography so as to provide a predetermined distance from the movable portion 24. Compared with the configuration in which the beam portion 36 is provided alone, the beam portion 36 can be positioned easily.

Next, an acceleration detector according to the second embodiment will be described below.
FIG. 3 is a schematic view of the acceleration detector according to the second embodiment. (1) is an exploded perspective view seen from the other main surface side of the base, and (2) is a side view.

As shown in the figure, the acceleration detector 100 of the second embodiment has a configuration in which the second beam portion 50 is provided in the configuration of the first embodiment which is a basic configuration.
The second beam portion 50 has one end as a fixed end 52 connected to the other main surface 28 of the base 20 and the other end as a free end 54 extending from the fixed end 52. The second beam portion 50 shown in FIG. 3 is a plane including only the beam portion 36 and the base portion 35 on the fixed portion 22 side except the base portion 34 and the pressure sensitive portion 32 on the movable portion 24 side from the pressure sensitive element 30 of the first embodiment. The fixed end 52 is formed on a surface facing the base portion 35 on the fixed portion 22 side.

  The second beam portion 50 is formed to face the pressure sensitive element 30 with the base 20 sandwiched between the other main surface 28 of the base 20. At this time, the fixed end 52 and the free end 54 of the second beam portion 50 are extended from one of the pair of base portions 34 and 35 on the one main surface 27 side to the other and straddle the constricted portion 26. It is formed.

  Note that the length of the second beam portion 50 is configured such that the length between the fixed end 52 and the free end 54 is arbitrarily set and changed according to a predetermined breaking limit of the negative acceleration G of the acceleration detector 100. .

  The second beam portion 50 only needs to be configured to come into contact with the movable portion 24 at the fracture limit to stop the displacement of the movable portion 24. As shown in FIG. 3, two (plural) free ends are formed. In addition to the configuration, one may be used.

  The second beam portion 50 formed in this manner is bonded to the mounting portion 29a on the other main surface 28 of the base 20 with the fixed end 52 spaced apart from the mounting portion 29c facing the base 20 with a predetermined interval therebetween. 40 is adhered and fixed. The predetermined interval that is a gap between the second beam portion 50 and the base 20 is set to a distance at which the base 20 and the second beam portion 50 that are displaced when the acceleration in the measurement range is applied do not interfere with each other.

The acceleration detector according to the second embodiment having the above-described configuration operates as follows. FIG. 4 is an explanatory diagram of the operation of the acceleration detector according to the second embodiment.
When an excessive positive acceleration G exceeding the breaking stress is applied to the acceleration detector 100 according to the second embodiment, a compressive stress is applied to the pressure-sensitive portion 32 of the pressure-sensitive element 30 according to the displacement of the movable portion 24. On the other hand, the beam portion 36 fixes the fixed end 37 to the fixed portion 22 of the base 20 through the base 35 and the free end 38 is not fixed, so that it is not affected by the compressive stress of the movable portion 24. Therefore, the free end 38 of the beam portion 36 comes into contact with the displaced movable portion 24 and functions to stop the displacement of the movable portion 24.

  On the other hand, when an excessive negative acceleration G exceeding the destructive stress is applied to the acceleration detector 100 according to the second embodiment, an extensional stress is applied to the pressure-sensitive portion 32 of the pressure-sensitive element 30 according to the displacement of the movable portion 24. Since the second beam portion 36 fixes the fixed end 52 to the fixed portion 22 of the base 20 and the free end 54 is not fixed, the second beam portion 36 is not affected by the stretching stress of the movable portion 24. Accordingly, the free end 54 of the second beam portion 50 comes into contact with the displaced movable portion 24 and functions to stop the displacement of the movable portion 24.

Thereby, even when a large negative acceleration G is applied, the second beam part can stop the displacement of the movable part at the destruction limit, and the acceleration detector can be prevented from being destroyed.
The fixed end 52 of the second beam part 50 may be formed on the other main surface 28 side facing the mounting surface 29b of the movable part 24 in addition to the structure formed on the fixed part 22 of the base 20. The same effect is produced.

Next, the acceleration detector of Example 3 will be described below.
FIG. 5 is a schematic view of an acceleration detector according to the third embodiment. (1) is an exploded perspective view seen from one main surface side of the base, and (2) is a side view.

  As illustrated, the acceleration detector 200 of the third embodiment has a configuration in which a second pressure-sensitive element 60 is provided instead of the second beam portion 50 of the second embodiment. The second pressure-sensitive element 60 is composed of the same shape and material as the pressure-sensitive element 30 of the first embodiment, exhibits the same action, and a detailed description thereof is omitted. The second pressure-sensitive element 60 is provided on the other main surface 28 of the base 20 so as to be symmetric with respect to the first pressure-sensitive element 30 on the one main surface 27 of the base 20 and the base 20.

The acceleration detector according to the third embodiment having the above-described configuration operates as follows. FIG. 6 is an explanatory diagram of the operation of the acceleration detector according to the third embodiment.
Since the acceleration detector 200 according to the third embodiment includes the first and second pressure-sensitive elements 30 and 60 on one and the other main surfaces 27 and 28 of the base, for example, a positive acceleration G is applied. Then, the first pressure-sensitive element 30 is subjected to compressive stress, and the second pressure-sensitive element 60 is subjected to tensile stress. Therefore, a positive / negative detection signal is reversed, and by taking this difference, highly sensitive acceleration detection can be performed.

  As shown in (1), when an excessive positive acceleration G exceeding the breaking stress is applied to the acceleration detector 200 according to the third embodiment, the pressure-sensitive portion 32 of the first pressure-sensitive element 30 according to the displacement of the movable portion 24. Compressive stress is applied. On the other hand, the beam portion 36 of the first pressure-sensitive element 30 is fixed to the fixed portion 22 of the base 20 by disengaging the fixed end 37 from the base portion 35, and the free end 38 is not fixed. Not affected. Accordingly, the free end 38 of the beam portion 36 comes into contact with the displaced movable portion 24 and functions to stop the displacement of the movable portion 24.

  On the other hand, as shown in (2), when an excessive negative acceleration G exceeding the breaking stress is applied to the acceleration detector 200 of the third embodiment, the pressure sensitivity of the second pressure sensitive element 60 according to the displacement of the movable portion 24. The portion 32 is subjected to compressive stress. The beam portion 36 of the second pressure-sensitive element 60 is fixed to the fixed portion 22 of the base 20 with the fixed end 37 removed from the base portion 35, and the free end 38 is not fixed. Not receive. Accordingly, the free end 38 of the beam portion 36 comes into contact with the displaced movable portion 24 and functions to stop the displacement of the movable portion 24.

  As a result, the acceleration can be detected in a differential manner, so that the acceleration can be detected with higher accuracy. In addition, even when excessive plus or minus acceleration is applied to the acceleration detector, the beam parts formed on both main surfaces of the base at the fracture limit can stop the displacement of the movable part, and the acceleration detector It can be prevented from being destroyed.

10, 100, 200 ......... Acceleration detector, 20 ......... Base, 22 ......... Fixed part, 24 ......... Moving part, 26 ......... Necked part, 27 ......... One main surface, 28 ... ... the other main surface, 29 ......... mounting part, 30 ......... pressure-sensitive element, 32 ......... pressure-sensitive part, 34, 35 ......... base, 36 ......... beam, 37 ......... fixed End, 38 ......... Free end, 40 ......... Adhesion means, 50 ......... Second beam portion, 52 ......... Fixed end, 54 ......... Free end, 60 ......... Second pressure sensitive element 101 ......... Pressure-sensitive element, 102 ......... Base, 103 ......... Constriction, 104 ......... Weight, 105 ...... Substrate, 201 ......... Hinge coupling, 202 ......... Base, 203 ......... Weight, 204 ......... Pressure sensitive element, 301 ......... Accelerometer, 302 ......... Hinge, 303 ......... Weight, 304 ...... Base, 305 ... Cantilever, 06 ......... free end, 307 ......... pressure-sensitive element, 308 ......... free end, 309 ......... stop.

Claims (4)

A movable part that is displaced by acceleration applied perpendicularly to the main surface, and a base that includes a fixed part that supports the movable part via a constricted part;
A pressure-sensitive element having a pressure-sensitive portion connected to a pair of bases that are forces perpendicular to the direction of acceleration, the detection direction of which is the detection axis, and arranged along the detection axis;
With
The pair of base portions is fixed to the movable portion and the fixed portion of the base;
The constricted portion is a region sandwiched between the pair of base portions, and is formed in a direction intersecting the direction of the detection axis between the movable portion and the fixed portion,
The pressure-sensitive element has a beam portion that extends from one of the pair of base portions to the other and straddles the constricted portion, and has a beam portion whose end portion is a free end. Detector. The beam portion is
A first beam that is formed so as to extend from one of the pair of bases of the pressure-sensitive element on one main surface of the base to the other and straddle the constricted part, and whose end is a free end And
The second beam having the other main surface of the base opposite to the first beam portion, one end as a free end, and the other end as a fixed end fixed to either the movable portion or the fixed portion of the base. And
The acceleration detector according to claim 1, comprising: The pressure sensitive element is:
A first pressure sensitive element formed on one main surface of the base;
A second pressure sensitive element formed on the other main surface of the base so as to face the first pressure sensitive element;
The acceleration detector according to claim 1, comprising:   The acceleration detector according to any one of claims 1 to 3, wherein the beam portion has a variable length between the fixed end and the free end according to a fracture limit.

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