JP2024070495A - Electromechanical Converter - Google Patents

Abstract

[Problem] To provide an electromechanical transducer that is thin and stable in quality. [Solution] In an electromechanical transducer 10, a piezoelectric element 12 with a weight 13 is placed on a substrate 11, and two opposing spacer plates 14 sandwich the piezoelectric element 12 and weight 13 from both sides, and a sheet film 15 encases them all. The spacer plate 14 is designed to be higher than the total height of the piezoelectric element 12 and weight 13, and a dimension D14 in the depth direction is larger than the dimension D13 in the depth direction of the piezoelectric element 12 and weight 13, so that a space is secured between the piezoelectric element 12 and weight 13 and the sheet film 15. Therefore, only the load from the weight 13 can be applied to the piezoelectric element 12, and even if the sheet film 15 expands or contracts due to environmental factors or changes over time, the performance of the electromechanical transducer 10 is not affected, so that the quality can be stabilized. Even if the electromechanical transducer 10 is provided with the spacer 14, it is possible to achieve a thinness that is sufficient from a practical standpoint. [Selected Figure] Figure 1

Description

The present invention relates to an electromechanical transducer that converts mechanical vibrations into an electrical signal, and in particular to an electromechanical transducer that is used as a sensor or microphone.

When using a piezoelectric element as a sensor, a weight is placed on the piezoelectric element to apply a load, or the piezoelectric element is bent or otherwise deformed to extract an electric charge from the piezoelectric element.

For example, Patent Document 1 discloses an example of a vibration sensor in which a weight is applied to a piezoelectric element. This vibration sensor is configured such that piezoelectric elements are bonded to the top and bottom of a weight inside a sealed case, so that electromotive forces are generated in opposite directions above and below. By reversing the positive and negative of one side on the device receiving the sensor output and adding them together, the effect of noise that may occur when the sensor output is sent to the device is reduced.

Figure 8 shows an example of an acceleration sensor using deformation of a piezoelectric element as a conventional technology. (A) is a perspective view of a sensor with a weight and a sensor without a weight, and (B) is a vertical cross-sectional view of the sensor with a weight. In these acceleration sensors, the entire substrate on which the piezoelectric element is attached is laminated to protect the piezoelectric element. The sensor with a weight uses the output of the piezoelectric element when the piezoelectric element deforms in response to the vibration of a weight attached to the end of the substrate, which acts as a cantilever. The sensor without a weight uses the output of the piezoelectric element when the piezoelectric element deforms in response to contact or collision with an external object.

JP 2015-14530 A

The above vibration sensor has a structure in which piezoelectric elements are arranged above and below the weight, which results in a problem of large structure. In addition, the above acceleration sensor has a problem in that it is difficult to uniformly apply pressure to the piezoelectric element from the laminate film due to the pressure bonding in the lamination process, making it difficult to produce products with uniform quality. In addition, there is a problem in that the laminate film expands and contracts over time and due to environmental influences, causing changes in the pressure applied to the vibrator. These problems are also common to electromechanical transducers that do not have a weight, from the perspective of the size of the structure and the influence of the laminate film on the piezoelectric element.

The present invention aims to provide a thin electromechanical transducer with stable quality.

To solve the above problems, the present invention employs the following electromechanical converter. Note that the words in parentheses below are merely examples, and the present invention is not limited thereto.

That is, the electromechanical transducer of the present invention is an electromechanical transducer that converts vibrations into an electrical signal, and includes a flat or sheet-like substrate, a piezoelectric element provided on the substrate, a film that isolates the space in which the piezoelectric element is disposed from the external environment of the electromechanical transducer, and a structure that protects the piezoelectric element from interference from the film (first embodiment). For example, the structure is a spacer that is provided on the substrate and contains the entire piezoelectric element in an internal space that it surrounds or sandwiches, and the film covers at least the upper part of the spacer (second embodiment).

According to this embodiment of the electromechanical transducer, the entire piezoelectric element is contained in the space surrounded or sandwiched by the spacer, so the spacer secures a space between the piezoelectric element and the film, and can protect the piezoelectric element from interference from the film. In such a structure, even if the film expands or contracts due to environmental factors or changes over time, the performance of the electromechanical transducer is not affected. Therefore, the electromechanical transducer of this embodiment has stable quality. Furthermore, although the electromechanical transducer of this embodiment is equipped with a spacer, it can be made thin enough from a practical standpoint.

The electromechanical converter of the above aspect may further include a converter provided in the internal space for impedance conversion of the output of the piezoelectric element.

When impedance conversion is performed in a space that is not shielded from the external environment, parasitic capacitance (stray capacitance) may occur in the path, resulting in reduced sensitivity and susceptibility to noise. With this type of electromechanical converter, the converter is provided in a space that is shielded from the external environment of the electromechanical converter, so that the effects of external environmental factors that may affect the converter can be suppressed, and the performance of the electromechanical converter can be improved.

More preferably, in any of the above-mentioned aspects of the electromechanical transducer, a weight is further provided that is attached to and overlaps the piezoelectric element, and the spacer accommodates the weight in the above-mentioned internal space. In addition, the weight has a mass that corresponds to the frequency characteristics of the electromechanical transducer.

In this embodiment of the electromechanical converter, the mass of the weight corresponds to the frequency characteristics of the electromechanical converter. From another perspective, when manufacturing this embodiment of the electromechanical converter, the frequency characteristics (frequency range) of the electromechanical converter can be adjusted by changing the mass of the weight used. This embodiment of the electromechanical converter can be used, for example, as an acceleration sensor.

More preferably, in the electromechanical converter of the second aspect described above, a dual-purpose weight is attached to the piezoelectric element and is integrated with a converter that converts the impedance of the output of the piezoelectric element into a weight that applies a load to the piezoelectric element, and the spacer accommodates the dual-purpose weight in the internal space described above.

With this type of electromechanical converter, the converter is integrated with the weight, eliminating the need for space to place the converter as a standalone unit, making it possible to further miniaturize the electromechanical converter.

Also, preferably, in the electromechanical transducer of the first aspect described above, the structure is a weight that is large enough to cover the entire upper surface of the piezoelectric element and is attached to the piezoelectric element in a layered manner, and the film envelops the entire substrate on which the piezoelectric element and the weight are provided.

In this embodiment of the electromechanical converter, the weight covers the entire top surface of the piezoelectric element, protecting the piezoelectric element from interference from the film, so the piezoelectric element can be protected without the need for a spacer, which contributes to the miniaturization of the electromechanical converter.

As described above, the electromechanical transducer of the present invention can provide a thin electromechanical transducer with stable quality.

1A and 1B are a perspective view and a plan view showing an electromechanical transducer 10 according to a first embodiment. 2 is a vertical cross-sectional view of the electromechanical transducer 10 (a cross-sectional view taken along line II-II in FIG. 1). FIG. 4 is a cross-sectional view showing an electromechanical transducer 20 according to a second embodiment. 11A and 11B are a perspective view and a plan view showing an electromechanical transducer 30 according to a third embodiment. 5 is a vertical cross-sectional view of the electromechanical transducer 30 (a cross-sectional view taken along line VV in FIG. 4). FIG. 11 is a cross-sectional view showing an electromechanical transducer 40 according to a fourth embodiment. 7A and 7B are a perspective view and a vertical cross-sectional view (a cross-sectional view taken along line VII-VII in FIG. 7) showing an electromechanical transducer 50 according to a fifth embodiment. 1A and 1B are a perspective view and a cross-sectional view showing an acceleration sensor of the prior art;

The following describes an embodiment of the present invention with reference to the drawings. Note that in order to facilitate understanding of the invention, the dimensions of the components are exaggerated in the drawings, and the relative ratios of height (thickness), width, and depth of each component and the relative ratios of size between components do not correspond to the actual ones.

First Embodiment
The structure of an electromechanical transducer 10 according to a first embodiment will be described with reference to Figures 1 and 2. Figure 1 is a perspective view and a plan view of the electromechanical transducer 10, and Figure 2 is a vertical cross-sectional view (cross-sectional view taken along line II-II in Figure 1) of the electromechanical transducer 10.

The electromechanical transducer 10 is mainly composed of a flat substrate 11, a piezoelectric element 12 placed on the substrate 11, a weight 13 attached so as to overlap the piezoelectric element 12, two spacer plates 14 that sandwich the piezoelectric element 12 and weight 13 from both sides in the horizontal direction (a specific direction perpendicular to the thickness direction), and a sheet film 15 that encases the entire assembly to form an enclosed space inside. An environmentally resistant polymeric material is suitable for the sheet film, and a PET material is preferable. In addition, a lamination method using the sheet film can be considered to ensure performance and reliability. The sheet film needs to be set so that the resonant frequency, which is determined by the mass and tension, is equal to or higher than the upper limit frequency for measurement.

1A, the horizontal shape of the weight 13 is designed to be substantially the same as that of the piezoelectric element 12 so as to efficiently apply a load to the piezoelectric element 12. Also, as shown in Fig. 1B, the dimension _D14 in the depth direction of the spacer plate 14 is designed to be larger than the dimension _D13 in the depth direction of the piezoelectric element 12 and the weight 13, and as shown in Fig. 2, the height of the spacer plate 14 is designed to be higher than the height of the piezoelectric element 12 and the weight 13 when they are stacked together.

By making the spacer plates 14 this size, the entire piezoelectric element 12 with the weight 13 attached can be contained within the space formed between the two spacer plates 14. As a result, the sheet film 15 that encases the entire structure comes into contact with the upper end faces of the two spacer plates and covers the upper part of the space in which the piezoelectric element 12 with the weight 13 is contained, and is always separated from the piezoelectric element 12 with the weight 13 attached.

Looking at it from another perspective, in the first embodiment, the spacer is composed of two spacer plates 14, and the entire piezoelectric element 12 with the weight 13 attached is contained in the space formed between the two opposing spacer plates 14 (the space partitioned by the two spacer plates 14), so that the spacer protects the piezoelectric element 12 from interference from the sheet film 15.

Although not shown, the ground (hereinafter referred to as "GND") and output terminal of the piezoelectric element 12 are pulled out to the bottom or end of the substrate 11. When the substrate 11 to which the piezoelectric element 12, weight 13, and spacer plate 14 are attached is wrapped in sheet film 15, a hole is made in the sheet film 15 so as not to block the pulled out GND and output terminal, and the substrate 11 and sheet film 15 are tightly attached around the hole. This makes it possible to isolate the space wrapped in the sheet film 15 from the outside environment and maintain airtightness.

A thin metal plate or the like may be attached to the bottom surface of the substrate 11 (the surface opposite to the surface on which the piezoelectric element 12 is arranged) for reinforcement. The substrate 11 may also be a sheet film made of a polymer or the like, or a sheet film made of the same material as the sheet film 15 or a different material.

The electromechanical transducer 10 can be used, for example, as an acceleration sensor. As described above, in the electromechanical transducer 10, the sheet film 15 does not interfere with the piezoelectric element 12, so only the load from the weight 13 can be applied to the piezoelectric element 12. Even if the sheet film 15 expands or contracts due to environmental factors such as temperature and humidity or due to changes over time, the performance of the sensor is not affected, so a sensor with stable quality can be manufactured.

In addition, the structure of the electromechanical transducer 10 is somewhat thicker than the sensor of the prior art described above (Figure 8), but is thin enough for practical use.

Furthermore, when the electromechanical transducer 10 is used as a sensor, the frequency characteristics of the sensor can be adjusted by changing the mass of the weight 13.

By the way, although not shown, by removing the weight 13 from the electromechanical converter 10 or adjusting the mass of the weight, the electromechanical converter of this structure can be used as a microphone in which the air layer between the sheet film 15 and the piezoelectric element 12 serves as an anterior chamber and the sheet film 15 acts as a vibrating membrane. With a microphone of this structure, even if the sheet film 15 expands or contracts due to environmental factors such as temperature and humidity or due to changes over time, the performance of the microphone is not affected, so a microphone of stable quality can be manufactured. In addition, it is preferable to make the gap formed between the spacer and the piezoelectric element as thin as possible so that the resonant frequency is equal to or higher than the highest audible frequency.

Second Embodiment
FIG. 3 is a cross-sectional view showing an electromechanical transducer 20 according to the second embodiment.
The electromechanical transducer 20 of the second embodiment is a modification of the electromechanical transducer 10 of the first embodiment (FIGS. 1 and 2), and differs from the electromechanical transducer 10 in that an impedance converter is further disposed between two spacer plates, and in relation to this, the dimensions of some of the components are also different. Note that a description of the points in common with the electromechanical transducer 10 will be omitted as appropriate. Also, illustration of the internal structure of the impedance converter will be omitted.

Compared to the electromechanical converter 10 (Figure 2), the electromechanical converter 20 has a larger gap between the two spacer plates 14, and an impedance converter 26 is placed between the piezoelectric element 12 with the weight 13 and one of the spacer plates 14, resulting in larger dimensions for the substrate 21 and the sheet film 25.

The spacer plate 14 is higher than the combined height of the piezoelectric element 12 and the weight 13, and higher than the height of the impedance converter 26. Although not shown, the depth dimension of the spacer plate 14 is larger than the depth dimension of the piezoelectric element 12 and the weight 13, and larger than the depth dimension of the impedance converter 26. Therefore, the sheet film 25 does not interfere with the impedance converter 26, in addition to the piezoelectric element 12 and the weight 13.

Although not shown, the GND and output terminal of the piezoelectric element 12 are connected to the impedance converter 26, and the GND and output terminal of the impedance converter 26 are pulled out to the bottom or end of the substrate 21. When the substrate 21 to which the piezoelectric element 12, weight 13, spacer plate 14, and impedance converter 26 are attached is wrapped in sheet film 25, holes are made in the sheet film 25 so as not to block the pulled out GND and output terminal, and the substrate 21 and sheet film 25 are tightly attached around the holes. This isolates the space wrapped in the sheet film 25 from the outside environment, maintaining airtightness.

In the electromechanical converter 20, the impedance converter 26 is housed in an enclosed space, so that the effects of external environmental factors (e.g., humidity changes, sudden temperature changes, etc.) that may affect the impedance converter 26 can be suppressed, making it possible to improve the performance of the electromechanical converter 20.

In addition, in the electromechanical converter 20, if a component (dual-purpose weight) is provided in which the impedance converter 26 is integrated with the weight 13 and this component is placed on top of the piezoelectric element 12 in place of the weight 13, this component also functions as an impedance converter, eliminating the need for space to place a standalone impedance converter, thereby making it possible to further miniaturize the electromechanical converter.

Third Embodiment
Next, the structure of an electromechanical transducer 30 according to a third embodiment will be described with reference to Fig. 4 and Fig. 5. Fig. 4 is a perspective view and a plan view of the electromechanical transducer 30, and Fig. 5 is a vertical cross-sectional view (a cross-sectional view taken along line V-V in Fig. 4) of the electromechanical transducer 30.

The electromechanical converter 30 of the third embodiment is a modification of the electromechanical converter 10 of the first embodiment described above, and differs from the electromechanical converter 10 in that a cylindrical spacer is used instead of a spacer consisting of two spacer plates. Note that explanations of points common to the electromechanical converter 10 will be omitted as appropriate.

The electromechanical converter 30 is mainly composed of a flat substrate 31, a piezoelectric element 32 arranged on the substrate 31, a weight 33 attached so as to overlap the piezoelectric element 32, a cylindrical spacer 34 that surrounds the periphery of the piezoelectric element 32 and the weight 33 (surrounding the surface perpendicular to the thickness direction of the piezoelectric element 32 and the weight 33), and a sheet film 35 that is attached to the upper end surface of the cylindrical spacer 34 and closes the upper end of the cylindrical spacer 34.

As shown in FIG. 4, the cylindrical spacer 34 has a cylindrical shape (in the illustrated example, it is a square cylindrical shape) and is fixed to the substrate 31 so that the piezoelectric element 32 and the weight 33 are housed in the hollow portion extending inward. Note that in the illustrated example, the cylindrical spacer 34 surrounds the piezoelectric element 32 and the weight 33 without any gaps, but a gap may be provided between the piezoelectric element 32 and the weight 33 and the cylindrical spacer 34.

As shown in FIG. 5, the height of the cylindrical spacer 34 is designed to be higher than the combined height of the piezoelectric element 32 and weight 33. In addition, since the sheet film 35 is attached to the upper end surface of the cylindrical spacer 34, it is always separated from the piezoelectric element 32 with the weight 33 attached.

From another perspective, in the third embodiment, the cylindrical spacer 34 houses the piezoelectric element 32 with the weight 33 in its hollow portion 34a (the space formed inside the cylindrical spacer 34, the space partitioned by the cylindrical spacer 34), thereby protecting the piezoelectric element 32 from interference by the sheet film 35. In addition, the lower end of the cylindrical spacer 34 is blocked by the substrate 31, and the upper end is blocked by the sheet film 35, so that the hollow portion 34a of the cylindrical spacer is isolated from the external environment.

Although not shown, the GND and output terminal of the piezoelectric element 32 are pulled out to the bottom or end of the substrate 31. Instead of blocking the upper end of the cylindrical spacer 34 with the sheet film 35, the entire substrate 31 to which the piezoelectric element 32 with the weight 33 and the cylindrical spacer 34 are fixed may be wrapped in the sheet film to form an airtight space inside, as in the first embodiment. In that case, a hole is made in the sheet film 35 so as not to block the pulled out GND and output terminal, and the substrate 31 and the sheet film 35 are tightly attached around the hole.

Fourth Embodiment
FIG. 6 is a cross-sectional view showing an electromechanical transducer 40 according to the fourth embodiment.
The electromechanical transducer 40 of the fourth embodiment is a modification of the electromechanical transducer 30 of the third embodiment (FIGS. 4 and 5), and differs from the electromechanical transducer 30 in that an impedance converter is further disposed in the hollow portion of the cylindrical spacer, and in relation to this, the dimensions of some of the components are also different. The electromechanical transducer 40 of the fourth embodiment can also be regarded as a modification of the electromechanical transducer 20 of the second embodiment (FIG. 3), and differs from the electromechanical transducer 20 in that a cylindrical spacer is used instead of the spacer composed of two spacer plates. Note that the description of the points common to the electromechanical transducers 20 and 30 will be omitted as appropriate.

Compared to the electromechanical converter 30 (Figure 5), the electromechanical converter 40 has a larger width dimension of the cylindrical spacer 44 (more precisely, the dimension of the hollow portion 44a), and an impedance converter 46 is placed next to the piezoelectric element 32 with the weight 33 attached, so that the dimensions of the substrate 41 and the sheet film 45 are larger.

The cylindrical spacer 44 is higher than the combined height of the piezoelectric element 32 and the weight 33, and is also higher than the height of the impedance converter 46. Therefore, the sheet film 45 does not interfere with the impedance converter 46, as well as the piezoelectric element 32 and the weight 33. In addition, the lower end of the cylindrical spacer 44 is blocked by the substrate 41, and the upper end is blocked by the sheet film 45, so that the hollow portion 44a of the cylindrical spacer is isolated from the external environment. With this structure, it is possible to obtain the same effect as the electromechanical converter 20 (Figure 3) of the second embodiment described above.

Although not shown, the GND and output terminals of the piezoelectric element 42 are connected to an impedance converter 46, and the GND and output terminals of the impedance converter 46 are pulled out to the bottom or end of the substrate 41.

Instead of sealing the top of the cylindrical spacer 44 with the sheet film 45, the piezoelectric element 32 with the weight 33, the impedance converter 46, and the substrate 41 to which the cylindrical spacer 44 is fixed may be entirely wrapped in a sheet film to form an enclosed space inside, as in the second embodiment. With this configuration, the hollow part of the cylindrical spacer 44 can be more reliably isolated from the external environment, and the influence of external environmental factors that may affect the impedance converter 46 can be more reliably suppressed.

Fifth Embodiment
Finally, the structure of an electromechanical transducer 50 according to a fifth embodiment will be described with reference to Fig. 7. Fig. 7A is a perspective view of the electromechanical transducer 50, and Fig. 7B is a vertical cross-sectional view of the electromechanical transducer 50 (a cross-sectional view taken along line VII-VII in Fig. 7A).

In the electromechanical transducers of the first to fourth embodiments described above, a spacer is provided on the substrate, and the spacer sandwiches or surrounds the piezoelectric element, thereby protecting the piezoelectric element from interference with the sheet film. In contrast, the electromechanical transducer 50 of the fifth embodiment is characterized in that a spacer is not provided on the substrate, and instead the weight also serves to protect the piezoelectric element from interference with the sheet film.

The electromechanical converter 50 is mainly composed of a flat substrate 51, a piezoelectric element 52 placed on the substrate 51, a weight 53 attached so as to overlap the piezoelectric element 52, and a sheet film 55 that encases the entire assembly and forms an enclosed space inside.

As shown in FIG. 7 (A), the horizontal shape of the weight 53 is designed to be approximately the same as that of the piezoelectric element 52 so that a load can be efficiently applied to the piezoelectric element 52, and the weight 53 is placed closely on top of the piezoelectric element 52, so that the upper surface of the piezoelectric element 52 is completely covered by the weight 53. The horizontal shape of the weight 53 may be slightly larger than the horizontal shape of the piezoelectric element 52. This makes it possible to more reliably protect the piezoelectric element 52 from interference from the sheet film 15.

In addition, since the substrate 51 is larger than the piezoelectric element 52 and the weight 53, when the substrate 51 and the weight 53 are entirely wrapped in the sheet film 55, as shown in FIG. 7B, a space is created around the side of the piezoelectric element 52, and the sheet film 55 is always separated from the piezoelectric element 52. With this structure, it is possible to obtain the same effect as the electromechanical converters 10 (FIGS. 1-2) and 30 (FIGS. 4-5) of the first and third embodiments described above. In addition, by adopting a component (dual-purpose weight) in which an impedance converter is integrated into the weight instead of the weight 53 and attaching such a dual-purpose weight to the piezoelectric element 52, it is possible to obtain the same effect as the electromechanical converters 20 (FIGS. 3) and 40 (FIG. 6) of the second and fourth embodiments described above.

[Advantages of the present invention]
As described above, according to the electromechanical transducer of each of the above-mentioned embodiments, the following effects can be obtained.

(1) In the first to fourth embodiments, the piezoelectric element is housed in an internal space sandwiched or surrounded by the spacer, which prevents the sheet film from interfering with (applying pressure to) the piezoelectric element. This means that even if the sheet film expands or contracts due to environmental factors or changes over time, the performance of the electromechanical transducer is not affected, making it possible to manufacture an electromechanical transducer with stable quality. Furthermore, even an electromechanical transducer equipped with a spacer can be thin enough for practical use.

(2) When manufacturing an electromechanical transducer to be used as a sensor, the frequency characteristics of the sensor can be adjusted by changing the mass of the weight used.

(3) In the second and fourth embodiments, the impedance converter is placed in a space isolated from the external environment, so that the effects of external environmental factors that may affect the impedance converter can be suppressed, thereby improving the performance of the electromechanical converter.

(4) In the second and fourth embodiments, a component that integrates the impedance converter with the weight is provided and is attached to the piezoelectric element in a layered manner, eliminating the need for space to place the impedance converter as a stand-alone component, thereby making it possible to further miniaturize the electromechanical converter.

(5) In the fifth embodiment, the weight covers the entire top surface of the piezoelectric element, protecting the piezoelectric element from interference with the sheet film, eliminating the need for a spacer and allowing the electromechanical converter to be made smaller.

(6) In the above-mentioned conventional sensors, the coefficient that links the change in force in the length direction and the change in charge, called the piezoelectric constant _d31 , is used, resulting in a cantilever-shaped structure and a large structure. In contrast, in the first to fifth embodiments, the coefficient that links the change in force in the thickness direction and the change in charge, called the piezoelectric constant _d33 , is used in the piezoelectric element, and a weight is placed on the piezoelectric element, making it possible to reduce the size.

The present invention is not limited to the above-described embodiments and can be implemented in various modifications.

In each of the above-described embodiments, the substrate, the piezoelectric element, and the weight are all substantially rectangular flat plates, but the shapes of the substrate, the piezoelectric element, and the weight are not limited to this and can be changed as appropriate depending on the situation. Also, in each of the embodiments, a transparent sheet film is used, but the sheet film does not have to be transparent.

In the third and fourth embodiments described above, the spacer has a rectangular tube shape, but the spacer in these embodiments may have any shape as long as it is cylindrical, and may have, for example, a cylindrical or elliptical tube shape instead of a rectangular tube shape.

In the first and second embodiments described above, the spacer is composed of two spacer plates, and the piezoelectric element with the weight attached is sandwiched between the two opposing spacer plates. Alternatively, the spacer may be composed of three or more spacer plates, and the spacer plates may be intermittently or continuously arranged around the piezoelectric element with the weight attached to it.

In addition, the configurations and numerical values given in the description of the electromechanical converters 10, 20, 30, 40, and 50 are merely examples, and it goes without saying that they can be modified as appropriate when implementing the present invention.

10, 20, 30, 40, 50 Electromechanical converter 11, 21, 31, 41, 51 Substrate 12, 32, 52 Piezoelectric element 13, 33, 53 Weight 14, 34, 44 Spacer 15, 25, 35, 45, 55 Sheet film 26, 46 Impedance converter

Claims (7)

An electromechanical transducer for converting vibration into an electrical signal,
A flat or sheet-shaped substrate;
A piezoelectric element provided on the substrate;
a film that isolates a space in which the piezoelectric element is disposed from an external environment of the electromechanical transducer;
and a structure that protects the piezoelectric element from interference with the film. 2. The electromechanical transducer of claim 1,
The structure comprises:
a spacer provided on the substrate and enclosing the entire piezoelectric element in an internal space that the spacer surrounds or sandwiches;
The film is
An electromechanical transducer covering at least an upper portion of the spacer. 3. The electromechanical transducer of claim 2,
The electromechanical transducer further comprises a transducer provided in the internal space for impedance conversion of an output of the piezoelectric element. 4. The electromechanical transducer according to claim 2,
A weight is further provided which is attached to the piezoelectric element in a superimposed manner.
The spacer is
An electromechanical transducer, characterized in that the weight is contained in the internal space. 5. The electromechanical transducer of claim 4,
The weight is
An electromechanical transducer having a mass corresponding to the frequency characteristics of the electromechanical transducer. 3. The electromechanical transducer of claim 2,
The piezoelectric element further includes a dual-purpose weight that is attached to the piezoelectric element and that applies a load to the piezoelectric element and that is integrated with a converter that converts the impedance of an output of the piezoelectric element,
The spacer is
An electromechanical transducer, characterized in that the dual-purpose weight is accommodated in the internal space. 2. The electromechanical transducer of claim 1,
The structure comprises:
a weight that is large enough to cover the entire upper surface of the piezoelectric element and is attached to overlap the piezoelectric element;
The film is
An electromechanical transducer comprising: a piezoelectric element and a weight disposed on the substrate;