close

Вход

Забыли?

вход по аккаунту

?

JP2015171100

код для вставкиСкачать
Patent Translate
Powered by EPO and Google
Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
DESCRIPTION JP2015171100
An object of the present invention is to provide a receiving type piezoelectric element which can
cope with the contradictory action of d31, d32 and d33 with a simple structure using a
piezoelectric body having an appropriate thickness and on which the receiving sensitivity can be
improved. To get. A receiving type piezoelectric element according to the present invention is a
receiving type piezoelectric element 10; a piezoelectric body 12 formed on a curved surface; a
positive electrode 15a disposed on both sides of the piezoelectric body 12; and a negative
electrode. Receiving piezoelectric element 10 is formed from solid 10 'surrounded by said curved
surface, said curved surface forms all or part of the surface of solid 10', and the inner surface
side of said curved surface Space is formed, and the solid 10 'is a closed solid. [Selected figure]
Figure 1
Receiving type piezoelectric element
[0001]
The present invention relates to a piezoelectric element that receives a sound wave, and more
particularly to a reception-type piezoelectric element that enhances the reception sensitivity of
the sound wave.
[0002]
Polymer piezoelectrics, including vinylidene fluoride resins that have been polarized, have
greater flexibility (1) greater film thickness, larger area, longer length, and arbitrary shape
compared to ceramic piezoelectrics. (2) the hydrostatic pressure piezoelectric strain constant dh
04-05-2019
1
is equal or less, but because the dielectric constant ε is small, the hydrostatic pressure power
output coefficient (gh constant determined by dh / ε (gh constant) ) Is extremely large and
therefore has excellent sensitivity characteristics; (3) low density and low elasticity, so the
acoustic impedance (sound velocity × density) is close to the value of water or living body, and
thus between water or living body and the element Have a few reflections on the surface, and can
transmit energy efficiently.
Taking advantage of these characteristics, polymer piezoelectrics are generally electromechanical (acoustic) transducers or elements such as speakers, microphones, ultrasound
probes, hydrophones, vibration meters, strain gauges, sphygmomanometers, bimorph fans, etc.
Application to a wide range of applications has been proposed or put into practical use as a
pyroelectric conversion element.
[0003]
As a receiving type piezoelectric element, a microphone which is usually used by being placed in
these media to receive sound waves propagating in air or gas, as well as to receive sound waves
propagating in water or liquid The hydrophone etc. which are used by being placed in these
media are known.
[0004]
These piezoelectric elements are always required to improve the wave receiving sensitivity.
However, as described above, the polymer piezoelectric material has a problem that the dielectric
constant is small, and the impedance increases as the thickness of the polymer piezoelectric
material is increased in order to enhance the wave receiving sensitivity.
[0005]
Further, the acoustic wave receiving sensitivity of these piezoelectric elements is represented by
a hydrostatic pressure piezoelectric strain constant (dh constant) when the size of the
piezoelectric element is sufficiently smaller than the wavelength of the sound wave, and
naturally, the larger the dh constant is, Excellent sensitivity. In general, the dh constant of the
piezoelectric body is given by the following equation as the sum of the contribution (d33) in the
04-05-2019
2
polarization direction and the contributions (d31 and d32) in two directions orthogonal to the
polarization direction. dh = d 31 + d 32 + d 33 (1) And, in the sheet-like piezoelectric material
generally used, the polarization direction is often taken in the thickness direction because of the
ease of polarization, and the contribution in the thickness direction In d33) and the two-way
contributions (d31 and d32) orthogonal to it, the signs often have opposite or opposite effects.
Such contradictory effects must also be considered in the design of the piezoelectric element.
[0006]
In Patent Document 1, when using a piezoelectric body polarized in the thickness direction to
increase the dh constant (increase the sensitivity), the d31 constant is not the d33 constant but
rather the d31 constant or the d32 constant orthogonal thereto. It is disclosed that the element
configuration positively utilizes the contribution of the above, and in particular, such an element
configuration is formed using a substantially hollow cylindrical piezoelectric body (paragraph
0009, FIG. 1). That is, as shown in FIG. 1, the two opposing side surfaces 2 c and 2 d having a
predetermined area of the cylindrical piezoelectric body 2 are held by the pair of rigid members
4 and 5 having a larger area, thereby forming the cylindrical piezoelectric body 2. The apparent
dh constant is intended to be significantly increased by increasing the effective working area of
the sound pressure which contributes to the axial deformation of the. Furthermore, the blocking
of the sound pressure on the inner surface of the rigid member (rigid cylinder 6) performed for
pressure amplification by the rigid member is, in many cases, the polarization direction of the
piezoelectric body 2 among the dh constants of the piezoelectric body. Contribution of the
thickness direction component (d33 component) having an opposite action to the orthogonal
component (d31 or d32 component of the piezoelectric body polarized in the thickness
direction), that is, the action of sound pressure in the thickness direction of the piezoelectric
body 2 In this aspect as well, it contributes to the apparent increase of the dh constant
(paragraph 0014). However, the above-described piezoelectric element has a problem that its
structure is complicated.
[0007]
Patent No. 3270 616
[0008]
As described above, the conventional piezoelectric element has a problem in that the impedance
increases with the thickness of the piezoelectric body and the structure is complicated.
04-05-2019
3
Therefore, according to the present invention, it is possible to cope with the contradictory effects
of d31, d32 and d33 with a simple structure using a piezoelectric body having an appropriate
thickness, and a wave receiving type piezoelectric element on which the wave receiving
sensitivity can be improved. Intended to provide.
[0009]
According to the study of the present inventors, in order to achieve the above-mentioned
purpose, when a solid having curved surfaces on the surface is a skeleton and a curved surface
portion is formed of a piezoelectric body to constitute a piezoelectric element, the element is
formed with a simple structure. What can be achieved, the area of the piezoelectric body can be
secured, and the capacitance can be increased without increasing the thickness, and even when
using a piezoelectric body polarized in the thickness direction, it is not its d33 constant, but
rather d31 orthogonal to this The present invention has been completed by finding that a device
configuration can be obtained by positively utilizing the contribution of a constant (or d32). In
the present specification, “sound wave” should be interpreted as a wave of pressure vibration,
and is not limited to sound waves in the audible range. That is, “sound waves” are not only
elastic waves propagating in the air, which are the audible frequencies of humans and animals in
a narrow sense, but also any elastic waves propagating in an elastic body regardless of gas,
liquid, or solid in a broad sense Refers to the generic term of
[0010]
The wave receiving type piezoelectric element according to the first aspect of the present
invention is, for example, a wave receiving type piezoelectric element 10 as shown in FIGS. 1 (a)
to (c); and a piezoelectric body 12 formed on a curved surface A positive electrode 15a and a
negative electrode 15b respectively disposed on both sides of the piezoelectric body 12; the wave
receiving type piezoelectric element 10 is formed of a solid 10 'surrounded by the curved
surface, and the curved surface is a solid A whole or part of the surface 10 'is formed, a space is
formed on the inner surface side of the curved surface, and the solid 10' is a closed solid. The
“curved surface” includes not only a continuously curved and non-planar surface, but also a
surface bent by a combination of planes by forming dihedral angles by adjacent two planes by
line segments. If the dihedral angle exceeds 90 °, the curved surface to be formed becomes
smoother, which is preferable. In addition, the curved surface by the combination of 2 planes
adjacent by a point like the vertex of a pyramid is not included. According to this structure, the
04-05-2019
4
piezoelectric body can be compressed and stretched in the circumferential direction to generate
polarization by the sound wave sw (see FIG. 1B) received from the thickness direction of the
piezoelectric body. Also, the piezoelectric element can be formed with a simple structure.
Furthermore, the area of the piezoelectric body can be increased to secure a sufficient
capacitance, and a highly sensitive piezoelectric element can be formed. Furthermore, the
contribution of the d33 constant can be suppressed, and the contribution of the d31 constant
can be mainly used positively.
[0011]
The receiving type piezoelectric element according to the second aspect of the present invention
is the receiving type piezoelectric element according to the first aspect of the present invention,
wherein the curved surface is a cylinder, a polygonal column, a cone, a polygonal pyramid, a
sphere, a polyhedron , An ellipsoid, and a solid selected from the group consisting of a solid
formed by a part of these solid forms a whole surface or a part of a surface of one solid. With this
configuration, it is possible to form a receiving piezoelectric device with a simple shape and
configuration.
[0012]
A receiving type piezoelectric element according to a third aspect of the present invention is the
receiving type piezoelectric element according to the first aspect or the second aspect of the
present invention, wherein the receiving sensitivity / thickness of the piezoelectric body is It is
0.17-10 V / Pa / m. According to this structure, it is possible to obtain a receiving type
piezoelectric element having excellent receiving sensitivity.
[0013]
A receiving type piezoelectric element according to a fourth aspect of the present invention is the
receiving type piezoelectric element according to any one of the first to third aspects of the
present invention, wherein the space is filled. The filler has a rubber hardness of A0 to A90 based
on JIS K6253 or ASKER C 0 to 90 based on SRIS 0101. With this configuration, it is possible to
form a receiving type piezoelectric element in which the non-piezoelectric element forming the
outer surface can withstand external water pressure or the like. Therefore, the hydrophone which
receives the sound wave propagating especially in water or liquid It can be used as
04-05-2019
5
[0014]
According to the present invention, the piezoelectric element can be formed with a simple
structure. Furthermore, the area of the piezoelectric body can be increased to secure a sufficient
capacitance, and a highly sensitive piezoelectric element can be formed. Furthermore, the
contribution of the d33 constant can be suppressed, and the contribution of the d31 constant
can be mainly used positively.
[0015]
(A) is a partially cutaway perspective view showing a cylindrical solid 10 ′ which is a skeleton of
the reception type piezoelectric element 10. (B) is a partially cutaway perspective view showing
the actual dimensions of the produced reception type piezoelectric element 10. (C) is a
fragmentary sectional view of wave receiving type piezoelectric element 10 in a field parallel to
bottom face 11b. It is a photograph of the receiving type piezoelectric element 10 completed
actually. It is an illustration of the three-dimensional shape which can become frame | skeleton of
a receiving type piezoelectric element. It is a block diagram of the receiving type piezoelectric
element created by carrying out parallel lamination | stacking of the polymeric piezoelectric
material. It is an impedance conversion circuit direct connection hydrophone circuit diagram. It is
a photograph showing an overview of a hydrophone. It is a hydrostatic pressure sensitivity
measurement principle figure. It is a figure which shows an acoustic sensitivity measurement
system. It is a figure which shows the frequency characteristic of acoustic sensitivity. It is a
principle view of a hydrostatic pressure piezoelectric distortion constant measuring device. It is a
figure explaining the external pressure concerning a cylinder. It is a block diagram of the wave
receiving type piezoelectric element using a flat-plate-like piezoelectric material.
[0016]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings. In the drawings, the same or corresponding parts are denoted by the same or similar
reference numerals, and redundant description will be omitted. Further, the present invention is
not limited to the following embodiments.
04-05-2019
6
[0017]
The wave receiving type piezoelectric element according to the first embodiment of the present
invention includes a piezoelectric body 12 formed in a cylindrical shape as a curved surface, as
shown in FIGS. 1 (a) to (c); inside and outside of the piezoelectric body 12 It comprises a positive
electrode 15a and a negative electrode 15b respectively disposed on the surface. The cylindrical
shape forms the outer peripheral portion of the wave receiving type piezoelectric element 10.
The top surface 11a and the bottom surface 11b of the case 11 form a cylindrical top surface
and a bottom surface, and the cylindrical shape is closed from above and below. As described
above, the receiving-type piezoelectric element of the present application is a solid whose threedimensional structure serving as its framework is closed, and a part or all of the solid surface is
formed of a piezoelectric body formed in a curved surface. Furthermore, a space is formed on the
inner surface side of the piezoelectric body.
[0018]
With reference to FIGS. 1 (a) to 1 (c), the case where the wave-receiving piezoelectric element 10
of the present invention is formed from a cylindrical (cylindrical) solid 10 'will be further
described. FIG. 1A is a partially cutaway perspective view showing a cylindrical solid 10 ′ which
is a skeleton of the reception type piezoelectric element 10. The cylindrical solid 10 ′ is a
cylinder formed by winding a PVDF piezo film 12 as a piezoelectric body around a bobbin-like
metal case 11. The case 11 forms a cylindrical upper surface 11a and a lower surface 11b, and
the upper surface 11a and the lower surface 11b are supported by a central support 11c. The
PVDF piezo film 12 forms the side of a cylinder. Since the top surface 11 a and the bottom
surface 11 b have an outward protrusion from the support 11 c, a space is formed on the inner
surface side of the PVDF piezo film 12. The top surface 11a and the bottom surface 11b close the
space in the cylinder from above and below to form a closed cylindrical solid 10 '. Thus, a closed
solid is used for the skeleton of the receiving type piezoelectric element 10. Al electrodes (15a,
15b) are deposited on both surfaces of the PVDF piezo film 12 as positive and negative
electrodes in a range smaller than the entire surface of the film 12 (for example, with margins at
the top, bottom, left and right of the surface). In the case of a cylindrical piezoelectric element as
shown in FIG. 1, vapor deposition may be continued in the circumferential direction.
[0019]
FIG. 1 (b) is a partially cutaway perspective view showing the actual dimensions of the produced
04-05-2019
7
reception type piezoelectric element 10. As shown in FIG. 1 (b), the outer surface of the PVDF
piezo film 12 is preferably coated with a polyolefin film 14 as a protective film. FIG. 1C is a
partial cross-sectional view of the receiving piezoelectric device 10 in a plane parallel to the
bottom surface 11 b. As shown in FIG. 1 (c), the receiving type piezoelectric element 10 has a
space (or a filler) around the support 11c, an Al deposited electrode 15a (positive electrode), a
PVDF piezo film 12, an Al deposited electrode. 15b (negative electrode), and the structure
laminated | stacked in order of the polyolefin film 14 have. Either of the Al vapor deposition
electrodes 15a and 15b may be a positive electrode, one of which may be a positive electrode
and the other may be a negative electrode. FIG. 2 is a photograph of a receiving type
piezoelectric element actually completed by connecting lead wires to positive and negative
electrodes, and is made using a screw, a flat plate, a nut, and the like. As shown in FIG. 1B, the
space formed on the inner surface side of the PVDF piezo film 12 may be filled with
polyurethane 13 as a filler. By supporting the PVDF piezo film 12 from the inside by the
polyurethane 13, it can withstand water pressure from the outside, etc., and the wave receiving
type piezoelectric element 10 can be used as a hydrophone.
[0020]
[Piezoelectric Body] As the piezoelectric body of the present application, a polymer-based
piezoelectric body which is excellent in flexibility, can be easily made into a thin film, a large
area, and a long size, and can be made into any shape and form is preferable. As the polymer
piezoelectric material, a vinylidene fluoride resin piezoelectric material having excellent
piezoelectric properties is preferable. Above all, vinylidene fluoride (VDF) alone necessary for
uniaxial stretching for β-type crystallization suitable for piezoelectricity expression is used alone
Coalescence is preferred. In addition, VDF copolymers capable of β-type crystallization under
normal crystal conditions (for example, superior amount of VDF and inferior amount of vinyl
fluoride (VF), trifluoroethylene (TrFE) or tetrafluoroethylene (TFE) (Copolymers of (1) and (2)),
and copolymers of a predominant amount (particularly 70 to 80 mol%) of VDF and a subordinate
amount (especially 30 to 20 mol%) TrFE are most preferably used. In addition, vinylidene
cyanide-vinyl acetate copolymer having relatively high heat resistance is also suitably used.
[0021]
These polymer-based piezoelectric materials are formed into films or sheets after film formation
by melt extrusion etc. and then subjected to polarization treatment by uniaxial stretching or heat
treatment at a softening temperature or less, and application of an electric field at a softening
temperature or less as necessary. Be done. The polymer-based piezoelectric material used in the
04-05-2019
8
present invention may be used as a single layer of these films or sheets, or may be used in the
same polarization direction or in the reverse direction through an intermediate electrode layer.
Although the number of laminations is not limited in principle, for example, a laminated body of
about 2 to 20 layers can be mentioned.
[0022]
The thickness (thickness in the polarization direction) of the piezoelectric body is 10 μm to 2
mm, more preferably 40 μm to 1 mm. If it is 10 μm or more, it is possible to suppress
deterioration of the shape self-holding property, and reduce the necessity of relying on shape
retention on other structural materials, so most structural stress can be received by other
structural materials and piezoelectric material It can be avoided that the stress generated inside
is reduced and the sensitivity can not be sufficiently obtained. If the thickness is 2 mm or less, it
is possible to avoid that the rigidity is too large and the molding process becomes difficult, and
the rigidity is appropriately reduced to facilitate the molding process. Furthermore, it is
preferable that the thickness is 40 μm or more because the shape self-holding property is
further increased. There is no particular limitation on the size of the piezoelectric body (the size
when the curved surface-shaped piezoelectric body is spread in a flat plate shape), and the size is
such that the piezoelectric body can be manufactured and formed as all or part of a threedimensional surface It should be as large as possible.
[0023]
[Electrode] As the positive electrode and the negative electrode disposed on both sides of the
piezoelectric body, a vapor deposition electrode as generally used, a foil electrode affixed with an
adhesive, or a metal spray electrode can be used. However, preferably, those satisfying the
requirements such as (1) not inhibiting the compressive deformation of the piezoelectric body,
(2) that the shaping of the piezoelectric body formed on the curved surface is easy, etc. An
electrode which can secure flexibility such as a conductive paint is preferable. For example, an Al
vapor deposition electrode and a copper foil electrode can be mentioned. The thickness of the
electrode is 30 nm to 70 μm, more preferably 60 nm to 40 μm. When the thickness is 30 nm
or more, the value of the electrical resistance decreases, and when it is 70 μm or less, flexibility
can be maintained.
[0024]
04-05-2019
9
[Protective Film] The outer surface of the piezoelectric body is preferably provided with a
protective film such as a coating for protecting the electrode. As such a protective film, it is
possible to exemplify a coating of a resin which is excellent in waterproofness and water vapor
barrier property, and in which the polymer piezoelectric body and acoustic impedance are close
to each other or which is homogeneous or compatible. For example, polyolefin films, PVDF films,
vinylidene chloride films, polyester films, polyurethane coatings, epoxy coatings and the like can
be mentioned.
[0025]
[Filler] As shown in FIG. 1A, a space is formed on the inner surface side of the piezoelectric body
12. The internal space formed in the solid constituting the wave receiving type piezoelectric
element is preferably vacuum if the piezoelectric body can withstand the pressure difference
between inside and outside. Alternatively, it may be filled with any gas (air, nitrogen, etc.) or any
liquid (water, etc.) as a filler, or any resin of excellent elasticity such as polyurethane, or any
foamed resin such as urethane foam. It can also be filled with a buffer material. When the wave
receiving type piezoelectric element is used as a hydrophone, any filler capable of supporting
hydrostatic pressure may be used. In addition, although the gas, the liquid, and the solid are
mentioned as the filler, they may be appropriately selected according to the environment where
the external pressure is different, for example, the shallow region and the deep region in the
water. Alternatively, the thickness of the piezoelectric body may be adjusted to withstand
external pressure. When the solid filler is based on JIS K6253 (durometer type A (Shore A)), the
rubber hardness is preferably A0 to A90. Alternatively, when based on SRIS 0101 (standard by
Japan Rubber Association, soft rubber (expandable rubber), spring type Asker C type), it is
preferable that the rubber hardness (sponge hardness) is ASKER C0 to C90.
[0026]
[Three-Dimensional Body] The wave-receiving piezoelectric element of the present application
includes a piezoelectric body formed in an aspect. The piezoelectric body formed on the curved
surface forms a three-dimensional surface to be a skeleton of the reception type piezoelectric
element. Therefore, the piezoelectric body is compressed and expanded in the circumferential
direction by the sound wave received from the thickness direction to cause polarization. For
example, the piezoelectric body 12 forms the side of a cylinder shown in FIG. Alternatively, it
may be the side of the cone shown in FIG. 3 (b) or the side of the truncated cone shown in FIG. 3
(c). In addition, the entire circumference of the side surface may be formed, or a part (for
04-05-2019
10
example, a half circumference) may be formed. Alternatively, the piezoelectric body 12 may form
the surface of a sphere shown in FIG. 3D, or may form the surface of an ellipsoid. Also, the
piezoelectric body may form the entire surface or may form a part of the surface. In the case of a
sphere or an ellipsoid, compression and expansion in the circumferential direction of the
piezoelectric body can be performed in any direction without being limited to one direction,
which is more preferable. The three-dimensional shape may be a three-dimensional shape formed
of a portion of a three-dimensional body such as a sphere or a cylinder as in a hemisphere or a
half pipe shown in FIG. Thus, the curved surface formed by the piezoelectric body constitutes a
continuously curved non-planar surface and forms the entire surface or a part of the closed solid.
[0027]
Alternatively, the curved surface formed by the piezoelectric body may be a curved surface
formed by a combination of flat surfaces by two adjacent flat surfaces forming a dihedral angle.
For example, the piezoelectric body 12 forms the side surface of the prism shown in FIG.
Alternatively, it may be the side surface of the pyramid shown in FIG. In addition, the entire
circumference of the side surface may be formed, or a part (for example, a half circumference)
may be formed. If the dihedral angle exceeds 90 °, it is preferable because the curved surface
formed of the piezoelectric body becomes more gentle. Therefore, it is preferable that it is a
prism with five or more angles and a pyramid with five or more angles. Furthermore, as a solid
surrounded by a curved surface, a polyhedron can be mentioned. For example, the piezoelectric
body 12 may form the surface of the polyhedron shown in FIG. 3 (h), or may form the surface of
the polyhedron shown in FIG. 3 (i). Also, the piezoelectric body may form the entire surface of the
polyhedron or may form a part of the surface.
[0028]
The solid shown in FIG. 3 is an example, and the solid forming the skeleton of the receiving type
piezoelectric element of the present application may be a solid which can form a curved surface
on the piezoelectric body and can form a space on the inner surface side of the piezoelectric
body. . When the piezoelectric body forms a part of a three-dimensional surface, as shown in FIG.
1A, the remaining surface may be formed of a rigid member such as metal. By using the case 11
shown in FIG. 1 (a), it is possible to easily form a stronger solid. Further, as in the case 11 shown
in FIG. 1A, a support for maintaining the shape may be provided inside the three-dimensional
structure. The material of the rigid member is not particularly limited, as long as it has a strength
enough to maintain a three-dimensional shape.
04-05-2019
11
[0029]
[Receiver Sensitivity and Piezoelectric Thickness] The receive type piezoelectric element of the
present application satisfies 0.17 ≦ Receiver sensitivity / thickness ≦ 10 V / Pa / m in relation
to the receiver sensitivity and the thickness of the piezoelectric body. Is preferred. The receiving
type piezoelectric element satisfying this range can increase the receiving sensitivity while
securing the capacitance.
[0030]
[Estimation of Wave Receiving Sensitivity] The method of verifying the wave receiving sensitivity
used in the embodiments of the present application will be described in detail by taking a flat
type PVDF-based polymer piezoelectric material as an example of a hydrophone. An impedance
conversion circuit was directly connected to a 12 mm diameter piezoelectric element (FIG. 4) to
produce a hydrophone. The gradient of the output voltage with respect to the pressure change
generated by pressurizing it in the pressure vessel was calculated and the hydrostatic pressure
sensitivity was calculated, and the method was considered as the receiving sensitivity (acoustic
sensitivity).
[0031]
[Configuration of Piezoelectric Element] As shown in FIG. 4, copper foil electrodes were applied
to a 500 μm thick P (VDF / TrFE) piezoelectric body to form parallel piezoelectric layers. When
the piezoelectric sensitivity (reception sensitivity) is estimated from the gh constant (0.14 Vm /
N), the following formula (2) is obtained (s: piezoelectric sensitivity, t: thickness). s = gh × t = 70
μV / Pa (2)
[0032]
[Impedance Conversion Circuit] FIG. 5 is an impedance conversion circuit directly connected
hydrophone circuit diagram. An impedance conversion circuit based on a FET source follower of
input resistance 1 GΩ was directly connected to the element of FIG. The measured value of the
04-05-2019
12
capacitance of the element is 30 pF (31 pF in calculation). From the time constant determined by
multiplication with the input resistance value, the cutoff frequency of the low band is 5.3 Hz (see
FIG. 5). FIG. 6 is a photograph showing an overview of the hydrophone. The piezoelectric element
and the impedance conversion circuit were molded with urethane rubber to prepare a
hydrophone. The cable length is 5m.
[0033]
[Hydrostatic pressure sensitivity measurement method and hydrostatic pressure sensitivity] The
hydrophone is pressurized quasistatically, and the gradient of the voltage generated at that time
to the pressure change is considered to coincide with the acoustic sensitivity within the range of
the linearity of the piezoelectric element. . Based on this idea, we add our hand to the
measurement method of dh constant of the piezoelectric material which has been done
conventionally, devise the measurement method of hydrostatic pressure piezoelectric constant,
and use it as a simple method to estimate acoustic sensitivity (reception sensitivity). We
examined the usefulness of As a means of applying pressure semi-statically, the hydrophone was
set in a liquid-filled pressure vessel leaving a slight gap, and pressurized gas was injected and
pressurized. As the liquid, a fluorine-based one having excellent insulation was used as the
compressed gas, and N 2 gas was used. The pressure gradient of the output voltage is taken as
the hydrostatic pressure sensitivity. (In the dh constant measurement, the generated charge is
measured by a charge amplifier. ) In order to pressurize to about 0.5 MPa, the generated voltage
becomes about 40 V and exceeds the amplifier power supply voltage, and in order to match the
time constant to the boosting speed, the attenuator capacitors are connected in parallel.
Therefore, it is necessary to correct the actual sensitivity by the capacitance ratio. FIG. 7 shows a
hydrostatic pressure sensitivity measurement principle diagram. As a result of measuring using
this method, the hydrostatic pressure sensitivity became 74 μV / Pa, -202.6 dB (re 1 V / μPa).
[0034]
[Frequency Characteristics of Acoustic Sensitivity] FIG. 8 shows the measurement system when
the acoustic sensitivity of the present hydrophone is actually measured, and FIG. 9 shows the
results. It can be confirmed that the level shows good agreement with the hydrostatic pressure
sensitivity. In addition, I think that the attenuation by a long cable is not seen either. A dip is seen
around 35 kHz in Fig. 9, but it is thought that the relationship between the hydrophone outer
diameter (D = 20 mm) and the wavelength in water at that time (λ = 42 mm), D λ λ / 2, is
attributable . As described above, it has been shown that the acoustic sensitivity (reception
sensitivity) can be estimated by measuring the hydrostatic pressure piezoelectric sensitivity.
04-05-2019
13
[0035]
First, as an example of a wave receiving type piezoelectric element provided with a piezoelectric
body formed on a curved surface, a mechanism capable of increasing the wave receiving
sensitivity while securing electrostatic capacitance by using the cylindrical hydrophone shown in
FIG. 1 will be described. Do.
[0036]
Example 1 A PVDF uniaxially stretched polarized film (Kureha KF, piezo film, manufactured by
Kureha Co., Ltd.) was used as a piezoelectric body.
Thickness: 110 μm, width: 10 mm, length: 19 mm (stretching direction). An aluminum (Al) vapor
deposition electrode was used for the electrode. Polyurethane was used as the filler. Polyolefin
was used for the protective film. FIG. 2 is a photograph of the hydrophone (Example 1) created
this time. The element structure is as shown in FIGS. 1 (a) to 1 (c). A cylinder was formed of a
PVDF piezo film 12 in a metallic case 11, filled with polyurethane 13, lead wires were drawn, and
a protective film of a polyolefin film 14 was coated on the outermost layer. Al vapor deposition
electrodes were deposited on both sides of the PVDF piezo film 12 leaving some margins at the
top, bottom, left, and right of the film. The case 11 was actually formed of a screw, a flat plate
and a nut. The rubber hardness of the filled polyurethane was A28.
[0037]
[Hydrostatic Piezoelectric Strain Constant Measurement Device] The principle of the hydrostatic
pressure piezoelectric strain constant measurement device for estimating the receiving sensitivity
is shown in FIG. This device measures the hydrostatic pressure piezoelectric strain constant dh of
the piezoelectric body. The sample (piezoelectric element) is put into the inert liquid and
pressurized, and the gradient with respect to the pressure of the polarization density generated
at that time becomes dh. FIG. 10 is a simplified view of the principle of FIG.
[0038]
04-05-2019
14
[Theoretical wave receiving sensitivity] When dh is divided by the dielectric constant (ε0ε ′),
the hydrostatic pressure piezoelectric output constant gh is obtained, and the product of the
piezoelectric body thickness t times this becomes the theoretical wave receiving sensitivity s.
That is, s = gh × t (3) This s and the measured receiving sensitivity show good agreement. On the
other hand, (3) is s = gh × t = dh / (ε0ε ′) × t = dh × S / (ε0ε ′ × S / t) Therefore, s = dh
× S / C (4) For example, the theoretical sensitivity can also be determined using equation (4) (S:
electrode area, C: capacitance).
[0039]
[Received Wave Sensitivity] The theoretical receive sensitivity was determined by measuring dh
of the cylindrical piezoelectric element (Example 1) and the flat piezoelectric element (piezo film,
FIG. 12). The comparison results are shown in Table 2. The cylindrical shape is about 35 times
larger. Here, regarding the piezoelectric element of Example 1, it is estimated that the modulus of
elasticity of polyurethane having hardness A28, which is the filling material in the cylinder, is
smaller by about 1 to 2 digits than PVDF, and considering the shape of the case, We consider the
mechanism of sensitivity increase by considering the pressure distribution in an infinite-length
cylindrical wall with no filler material. FIG. 11 shows a cylinder to which the external pressure is
applied (curved surface of the piezoelectric body to which the external pressure is applied). In the
case where the wavelength is sufficiently larger than the element size, it is sufficient to consider
the state of hydrostatic pressure application with zero internal pressure and external pressure P.
Assuming that the inner diameter of the cylinder is a and the outer diameter is b, the stress σr in
the inner radial direction of the wall and the stress σθ in the circumferential direction (the axial
direction is not considered), σr = −b <2> (1−a <2> / r < 2>) P (5) σθ = −b <2> (1 + a <2> / r
<2>) P (6) Thus, the voltage V generated on the inside and the outside of the cylindrical wall has
piezoelectric output constants g31 and g33. Expressed by using the following equation, V = ∫
(σθg31 + σrg33) dr (integral from integral a to b) = − {g31 + (b−a) g33 / (a + b)} bP (7)
Therefore, since the sensitivity s is V / P, s = − {g 31 + (b−a) g 33 / (a + b)} b (8) In the case of
PVDF, the signs of g31 and g33 are opposite and in the canceling direction, but when the
thickness of the piezoelectric body is thin, (b−a) / (b + a) << 1, the contribution of g31 becomes
dominant It can be understood that the generated voltage is increased by multiplying the outer
size sufficiently large compared to the thickness. When the sensitivity in the case of the present
element is calculated by equation (8), s = 634 μV / Pa. Actually, although it is necessary to
consider in consideration of the compressive modulus of the filler in the cylinder and the
modulus of the protective layer, the mechanism of the sensitivity increase is understood
qualitatively. In the case of the cylindrical hydrophone shown in FIG. 1, the axial stress
(contribution of g32) is supported by the pressure applied to the upper and lower surfaces by the
inner shaft (central axis, support) as a rigid body. It is considered that no stress in this direction
is generated in the piezoelectric body. Thus, a rigid body may be used to block the contribution
04-05-2019
15
of g32. In the case where the shaft is not a rigid body but is soft to a certain extent, even if there
is a contribution of g32, it is a contribution of the + direction (sensitivity increase), which is
preferable.
[0040]
[Capacitance] Here, the capacitance of the flat plate in the case where the reception sensitivity is
equal will be examined. In order to obtain the same sensitivity with a flat plate, it is necessary to
make the piezoelectric body about 35 times thicker. The values of capacitance in the case of the
same size (9 mm × 18 mm) are calculated as shown in Table 3, and the capacitance is about 35
times smaller than that of a cylinder.
[0041]
It has been shown that a cylindrical hydrophone using a thin piezoelectric film formed on a
curved surface can increase the receiving sensitivity while securing the capacitance.
[0042]
[Received Wave Sensitivity and Piezoelectric Body Thickness] Table 4 further shows a
comparison of the cylindrical hydrophone (Example 1) shown in FIG. 2 with various plate-like
piezoelectric elements (Comparative Examples 1 to 3). .
FIG. 12 shows the piezoelectric element used in Comparative Example 1 and Comparative
Example 2. FIG. 4 shows the piezoelectric element used in Comparative Example 3. As
Comparative Examples 1 to 3 show, in order to increase the sensitivity of the hydrophone, it is
preferable that the piezoelectric body is thicker. However, at the same time, the capacitance
decreases. In Example 1, the sensitivity could be increased without thickening the piezoelectric
body (by securing the capacitance). The sensitivity is approximately 34 times that of Comparative
Example 1 of the same thickness. In addition, since the sensitivity can be remarkably increased,
even if the thickness of the piezoelectric body is increased to a certain extent (even if the
capacitance is slightly decreased), the excellent sensitivity can still be maintained. Here,
considering the relationship between the wave receiving sensitivity and the thickness of the
piezoelectric body, in Example 1 in which the wave receiving sensitivity could be increased while
securing the capacitance, the sensitivity to the thickness was set to Comparative Examples 1 to 3
and It turns out that it is remarkably large by comparison.
04-05-2019
16
[0043]
Reference Signs List 10 (cylindrical) wave receiving type piezoelectric element 10 'solid body 11
case 11a upper surface 11 b bottom surface 11 c pillar 12 piezoelectric body, PVDF piezo film
13 polyurethane 14 polyolefin film 15 a positive electrode, Al evaporation electrode (Positive)
15b Negative electrode, Al deposited electrode (Negative) 20 (Parallel layer) Receiving type
piezoelectric element 21 Polymer piezoelectric material 22 Copper foil electrode 30 (Flat plate
type) Receiving type piezoelectric element sw Sound wave
04-05-2019
17
Документ
Категория
Без категории
Просмотров
0
Размер файла
33 Кб
Теги
jp2015171100
1/--страниц
Пожаловаться на содержимое документа