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DESCRIPTION JPH0984172

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DESCRIPTION JPH0984172
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
transducer used in water or seawater, and more particularly to a molded structure of an acoustic
transducer, particularly an ultrasonic transducer, using a piezoelectric element.
[0002]
2. Description of the Related Art A film-like polymer piezoelectric material such as a polarized
vinylidene fluoride resin or a ceramic piezoelectric material such as lead zirconate titanate (PZT)
supplied in a plate shape or a cylindrical shape is used. Application of piezoelectric elements to a
wide range of applications such as microphones, hydrophones, speaker vibrators or pyroelectric
conversion elements has been proposed or put to practical use.
[0003]
When such a piezoelectric element is used as a hydrophone or the like for transmitting and
receiving sound waves in water or seawater, a structure in which the periphery is molded with a
synthetic rubber or a synthetic resin is proposed.
This is mainly to ensure electrical insulation and water resistance, but the molding material is
also required to have other properties such as impact resistance, abrasion resistance, and
adhesion to electrode metals and lead wires. Therefore, the molding material that simultaneously
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satisfies these characteristics is limited, and its selection has been one of the points in the
development of a transducer.
[0004]
There have been attempts to make the mold layer multi-layered to meet various demands on the
molding material. For example, in the ultrasonic transducer disclosed in JP-A-4-48897, a material
having high electrical insulation property is disposed in the inner layer, and a material excellent
in impact resistance and abrasion resistance is disposed in the outer layer. , The mold layer is
configured. Although this ultrasonic wave transmission and reception has a ceramic piezoelectric
body as a constituent requirement, in the case of using a polymer piezoelectric body, in order to
maintain the piezoelectricity, a molding material is cured at normal temperature to about 50 °
C. It is limited to things, and the range of material selection becomes narrower. Not only in this
example, generally, as a molding material for the outer layer, urethane rubber having a relatively
high hardness (60 degrees to 90 degrees in JIS-A hardness) is mainly used from the viewpoint of
durability.
[0005]
On the other hand, the underwater acoustic wave receiver described in JP-A-3-11900 is also a
wave receiver for underwater sound waves having a two-layered mold layer. The mold layer of
this underwater acoustic wave receiver is composed of a soft visco-elastic material in the inner
layer and a hard visco-elastic material in the outer layer to reduce noise caused by acceleration
of the housing vibration received by the wave receiver. Provided for the purpose of
[0006]
However, when synthetic rubber materials or hard visco-elastic materials having relatively high
hardness as described above are used as the molding material for the outer layer, the speed of
sound is greater than the speed of sound of water or seawater as a sound wave propagation
medium. Also, when the wavelength of the sound wave to be transmitted / received is almost
equal to or less than the size of the piezoelectric element, the directivity width of the molded
transducer is the original directivity width of the piezoelectric element. There is a problem that it
becomes considerably narrower than it. Here, the directional width is a region (for example,
angle) of rotation at which a predetermined reception voltage or more can be obtained when the
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transducer or the piezoelectric element is rotated with respect to the sound source.
[0007]
Generally speaking, the relationship between the hardness of the molding material and the speed
of sound does not tend to be as fast as the speed of the hard material, but the speed of sound of
the material is essentially determined by the density and elastic modulus of the material and is
soft The speed of sound is not necessarily slow. Therefore, in the above-mentioned underwater
acoustic wave receiver, in addition to nothing is said about the relationship between the speed of
sound and directivity as focused on in the present invention, in many combinations of soft viscoelastic material and hard visco-elastic material, In order to receive an acoustic wave in an
omnidirectional manner with a narrow directional width of the antenna, there has been a
problem that many receivers have to be arranged.
[0008]
The present invention has been made to solve the above-mentioned problems, and a conventional
high hardness material is preferably used as a molding material for the outer layer, considering
impact resistance and abrasion resistance. Nevertheless, it is an object of the present invention to
provide an excellent transducer having a directional width close to or larger than the original
directional width of the piezoelectric element without narrowing the directional width of the
receiver.
[0009]
SUMMARY OF THE INVENTION The inventors of the present invention have conducted intensive
studies on underwater acoustic wave transducers.
Then, the sound wave refraction can be expressed by the sound velocity of the molding material
and the sound wave propagation medium, and further, the relationship between the obtained
sound wave refraction and the sound velocity can be analyzed to adjust or control the directivity
width of the transducer. The present invention has been reached. In other words, the adjustment
or control of the characteristic of the directivity width, which is an important characteristic for
the transducer, is based on the speed of sound of the molding material in the inner layer in
contact with the piezoelectric element not to the speed of sound of the molding material on the
outer layer It has been found that this is possible by appropriately selecting.
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[0010]
That is, according to the present invention, the molding material of synthetic resin or synthetic
rubber has two or more layers of molding material layers covering the transmission / reception
wave front of the piezoelectric element, and the molding material of the inner layer facing the
piezoelectric element It is an underwater transducer which is also made of a slow material. The
inner layer molding material is preferably a material whose sound velocity is slower than the
sound velocity of the sound wave propagation medium.
[0011]
In the underwater transducer according to the present invention, the multilayer molding material
layer covering the wave transmitting / receiving wave surface of the piezoelectric element is
designed to have a predetermined speed of sound. The pointing width can be improved to be
close to or higher than the original pointing width of the piezoelectric element.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the underwater transducer
according to the present invention will be described in more detail with reference to the
drawings.
FIG. 1 is a cross-sectional view of an underwater transducer according to a preferred
embodiment of the present invention, wherein the underwater transducer 10 comprises a
polymer piezoelectric body 1 having two main surfaces 1a and 1b and a polymer piezoelectric
body 1 It has the polymer piezoelectric element 3 which consists of the copper foil electrodes 2a
and 2b stuck on the main two surfaces 1a and 1b by the adhesive agent, respectively.
[0013]
In the present invention, one in which electrodes are provided on two opposing surfaces of a
piezoelectric body is referred to as a piezoelectric element. Therefore, in the example of FIG. 1,
the polymer piezoelectric element 3 is composed of the polymer piezoelectric body 1 and the
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copper foil electrodes 2a and 2b, and the sound wave transmitting / receiving wave front is the
surface 3a of the copper foil electrode 2a.
[0014]
In the underwater transducer 10, the inner layer molding material 4 in contact with the
transmission / reception wave 3a of the polymer piezoelectric element 3 and the outer layer
molding material 5 exposed to the sound wave propagation medium are laminated on the inner
layer molding material 4 A backside mold material 6 for protecting 3b and a lead 7 are provided.
The inner layer molding material 4 and the outer layer molding material layer 5 are disposed so
as to cover the transmission / reception wave 3 a of the sound wave of the polymer piezoelectric
element 3.
[0015]
When the underwater transmitter-receiver 10 is used in water in the state of FIG. 1, the
piezoelectric element back surface 3b also naturally functions as a transmission / reception wave
front of the sound wave. However, since the underwater transmitter-receiver 10 is usually used
by attaching it to the housing (not shown) via the back surface molding material 6 or directly to
the back surface 3b of the piezoelectric element, the sound wave from the back surface 3b side
of the piezoelectric element Is substantially blocked. For this reason, in the underwater
transducer 10 shown in FIG. 1, the inner layer molding material 4 is not provided on the
piezoelectric element back surface 3b side.
[0016]
In the present invention, the molding material of the inner layer may be provided so as to be
opposed to at least one transmission / reception wave of the piezoelectric element, and the
underwater transducer is used in the state of FIG. The directivity may be different between the
two transmission and reception wavefronts of the element. Of course, the molding material of the
inner layer can also be disposed on each of the two transmitting and receiving wavefronts of the
piezoelectric element. Furthermore, as the piezoelectric body of the present invention, either a
polymer piezoelectric body or a ceramic piezoelectric body may be used, and besides the foil
electrode, a conductive member such as a vapor deposition electrode or a conductive paint may
be used as the electrode.
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[0017]
The outer layer molding material 5 in FIG. 1 is a member that contacts water or seawater as a
sound wave propagation medium, and in terms of protecting the piezoelectric element 3 from the
external environment, it has excellent properties such as impact resistance, abrasion resistance
and water resistance. Preferably, it is formed of synthetic resin or synthetic rubber. On the other
hand, the inner layer molding material 4 is formed of a material made of synthetic resin or
synthetic rubber having a sound velocity slower than that of the outer layer molding material 5,
and it is preferable to select a material having good adhesion with the electrode 2a. Urethane
rubber or silicone rubber having a predetermined sound velocity may be used. Further, the
selection of the materials for the inner layer molding material 4 and the outer layer molding
material 5 is also preferable in consideration of the required directivity width since there are
problems such as the adhesiveness between the layers and the migration of additives. An
adhesive layer or a primer layer may be provided between the electrode 2 a and the inner layer
molding material 4 to strengthen mutual adhesion. On the other hand, the outer layer molding
material 5 and the rear surface molding material 6 are the same in order to ensure the bonding
on the bonding surface 5a (6a) of the two and as a result keep the piezoelectric element 3
airtight from the external environment. It is good to be made of material.
[0018]
The underwater transducer of the present invention is particularly preferably used for
transmission and reception of ultrasonic waves, but may be used for sound waves in the audible
range as long as the wavelength is equal to or less than the size of the piezoelectric element. The
molding material layer may have three or more layers, and in this case, it is preferable that the
molding materials of the outer layer be sequentially laminated so that the sound velocity of the
member decreases.
[0019]
As the polymer piezoelectric material of the present invention, a vinylidene fluoride-vinyl acetate
copolymer or polyamide resin having relatively high heat resistance is suitably used, and in
addition, a vinylidene fluoride resin (PVDF resin having excellent piezoelectric characteristics) In
particular, as compared to vinylidene fluoride (VDF) homopolymer which requires the use of a
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strong solvent or uniaxial stretching at the time of film forming for .beta.-type crystallization
suitable for piezoelectric expression, it is preferable to use conventional crystallization
conditions. VDF type copolymers capable of β-type crystallization [eg superior amount of VDF
and inferior amount of vinyl fluoride, ethylene trifluoride (TrFE), ethylene tetrafluoride, ethylene
trifluoride chloride, ethylene hexafluoride or Copolymer with propylene etc.] is preferable, and
furthermore, a copolymer of a superior amount (especially 70 to 80 mol%) of VDF and a inferior
amount (especially 30 to 20 mol%) of TrFE is particularly preferably used. Ru. Further, as the
ceramic piezoelectric material, PZT having a perovskite crystal structure and a ferroelectric
ceramic typified by barium titanate can be mentioned.
[0020]
These polymer piezoelectric materials are formed into films or sheets by film formation of a resin
by melt extrusion etc., then subjected to uniaxial stretching or heat treatment at a softening
temperature or less, and polarization treatment by an electric field application at a softening
temperature or less as necessary. Be done. Although the thickness of the polymer piezoelectric
material is not particularly limited, it is usually supplied at about 50 to 2000 μm.
[0021]
EXAMPLES The present invention will be described more specifically by the following Examples
and Comparative Examples.
[0022]
With regard to the underwater transducer and piezoelectric element manufactured in these
examples, using the type 8103 manufactured by Brüel & Kj ー r as a transmitter, the
manufactured underwater transducer and piezoelectric element are used as a receiver and
pointing of the receiver The width was measured and determined by the following method.
First, the wave receiving surface of the wave receiver was placed opposite to the wave
transmitter at a distance of 50 cm, and both were set at a depth of 20 cm in a water tank at
normal temperature. Subsequently, transmission of ultrasonic waves with a frequency of 45 kHz
was started from the transmitter, and the receiving voltage was measured while rotating the
receiver. Then, the left and right angles at which the reception voltage becomes half of the peak
voltage are read, and the angle obtained by adding them is set as a directivity width (half angle)
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of -6 dB.
[0023]
Examples 1 to 4 An underwater transducer 10 having a structure substantially as shown in FIG. 1
was manufactured as follows. First, a VDF / TrFE (75/25 molar ratio) copolymer (manufactured
by Toha Chemical Industry Co., Ltd.) is sheet extruded at a die temperature of 265 ° C., heat
treated at 125 ° C. for 13 hours, and then under an electric field of 75 MV / m. A polarization
process was carried out for a total of 1 hour including the holding time at 5 ° C. for 5 minutes
and the elevation time, to obtain a 500 μm thick polymer piezoelectric sheet.
[0024]
Then, a copper foil having a thickness of 70 μm was attached to both sides of the sheet with a
polyester adhesive, and the disc-like piezoelectric element 3 having a diameter of 40 mm was cut
out from the obtained sheet with electrodes. Furthermore, the operation of forming a mold,
attaching the disc-shaped piezoelectric element 3 having lead wires wired thereto, pouring the
mold material into it and curing it is repeated, and the underwater transmitter-receiver of the
structure substantially shown in FIG. 10 was manufactured.
[0025]
The underwater transducer 10 thus obtained has an outer diameter dimension of about 12 mm
in thickness and about 80 mm in diameter, and the thicknesses of the inner layer molding
material 4, the outer layer molding material 5 and the back molding material 6 are 3 mm and 3
mm, respectively. , 6 mm. The outer layer molding material 5 and the back surface molding
material 6 are made of urethane rubber having a hardness (JIS-A) of 80 degrees and a sound
velocity of 1983 m / sec at normal temperature, and the rubber material of the inner layer
molding material 4 is changed to repeat the experiment. The measurement results as shown in
Table 1 were obtained for the directivity width (half angle) of -6 dB at. Incidentally, the sound
velocity of water as a sound wave propagation medium at normal temperature is 1490 m / sec.
[0026]
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Comparative Example 1 Underwater wave transmission / reception in the same configuration as
in Example 1 except that the inner layer molding material 4 is not provided, and the transmission
/ reception wavefront 3a of the piezoelectric element 3 is covered with the same outer layer
molding material of 3 mm in thickness The vessel was manufactured. The -6 dB pointing width
(half angle) of this underwater transducer was 62 degrees.
[0027]
Comparative Example 2 In the underwater transducer of Comparative Example 1, a piezoelectric
element was manufactured in which the outer layer molding material was not provided, and the
transmission / reception wave 3a of the sound wave was exposed. The -6 dB pointing width (half
angle) of this piezoelectric element was 93 degrees.
[0028]
From the above results, if the sound velocity of the inner layer molding material 4 is slower than
that of the outer layer molding material 5, the directivity width is wider than in the case of only
the outer layer molding material 5 shown in Comparative Example 1, and the sound velocity of
the inner layer molding material 4 is It can be seen that the slower the distance, the wider the
directivity. In addition, it is also understood that when silicon rubber whose sound velocity is
slower than the sound velocity of water is used for the inner layer molding material 4, a
directivity width wider than the intrinsic directivity width of the piezoelectric element shown in
Comparative Example 2 can be obtained.
[0029]
According to the present invention, the directivity width of the transducer can be freely designed
by appropriately selecting the sound velocity of the multi-layered molding material layer
covering the wave transmitting / receiving wave front of the piezoelectric element. It is also
possible to obtain an underwater transducer having a wide pointing width close to or greater
than the pointing width of.
[0030]
Brief description of the drawings
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[0031]
1 is a sectional view of an embodiment of the underwater transducer according to the present
invention.
[0032]
Explanation of sign
[0033]
1: Piezoelectric body 2a, 2b: Foil electrode 3: Piezoelectric element 3a: Wave transmitting /
receiving wave surface 4: Inner layer molding material 5: Outer layer molding material 6: Back
surface molding material 10: underwater transducer
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