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JPS62176399

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DESCRIPTION JPS62176399
[0001]
BACKGROUND OF THE INVENTION The present invention relates to a piezoelectric transducer
capable of transmitting ultrasonic waves with high power in water. 2. Description of the Related
Art A bolt-clamped Langevin transducer as shown in FIG. 2 is known as an ultrasonic transducer
capable of high power transmission in a frequency band of 3 to several tens of KHz in water. As
shown in FIG. 2, this bolt-clamped Langevin transducer is a ring-shaped piezoelectric ceramic
disposed between the front mass 21 and the front mass 21 and the rear mass 23 made of a high
rigidity material such as aluminum alloy, titanium alloy or steel. 22. A bolt 24 made of a high
tensile strength alloy such as Cr-Mo steel which has a function to apply a compressive stress to
the rear mass 23 and the ring-shaped piezoelectric ceramic 22 made of a high rigidity material
such as stainless steel like the front mass 21 25 and has a great feature that high power drive is
possible. Here, the ring-shaped piezoelectric ceramic 22 uses a longitudinal effect longitudinal
vibration mode (33 mode) that can obtain an electromechanical coupling coefficient much larger
than the transverse effect longitudinal vibration mode (31 mode). Adjacent piezoelectric ceramic
rings 22 are polarized in opposite directions as shown by the arrows in the figure, and
electrically connected in parallel to achieve matching with the power amplifier. Also, since
ceramics are generally weak against tensile stress compared to compressive stress, static bias
compressive stress is applied in advance by bolts 24 and nut 25. This structure is sufficiently
durable even at high power conditions. . In the bolt-clamped Langevin oscillator with such a
structure, as is well known, a half-wave resonant mode is used, there is an oscillation node at the
piezoelectric ceramic 22 portion, and stress is concentrated at the piezoelectric ceramic ring 22
and bolt 24 portion. To work. (Problems to be Solved by the Invention) The above-mentioned
bolt-clamped Langevin transducer uses half-wavelength resonance, so if the shape is the same,
the resonant frequency and the length of the transducer are in inverse proportion to each other.
If the frequency is halved, the length is doubled. Furthermore, this transducer is usually used in
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large numbers in order to obtain the desired directivity, and such a large number array is
necessarily larger and heavier than those used at low frequencies. . For this reason, in recent
years there has been a strong demand for reduction in size and weight of the bolt-clamped
Langevin transducer.
In order to reduce the size and weight of the transducer, it is better to make the front mass as
thin as possible in terms of the front mass [Ftm] of the cross-sectional area of the piezoelectric
ceramic. However, if the front mass is made thin, the front mass itself is likely to be bent and
efficient acoustic radiation becomes difficult. On the other hand, it is conceivable to make the
bolt diameter sufficiently small to reduce the deflection of the front mass. That is, if the diameter
of the bolt is reduced (the moving shear force can be reduced). The shear force is generated
because the bolt tries to prevent the expansion and contraction of the piezoelectric ceramic when
the piezoelectric ceramic ring is expanded and contracted piezoelectrically. However, if the
diameter of the bolt is reduced, it is impossible to apply sufficient bias stress to the piezoelectric
ceramic ring as is well known. As described above, there are certain limitations in attempting to
reduce the size and weight of the transducer with the bolt-clamped Langevin transducer. It is an
object of the present invention to solve such an illumination point and to realize a small and
lightweight transducer having high acoustic radiation efficiency. (Means for Solving the
Problems) In the present invention, a piezoelectric ceramic laminate having a through hole is
disposed between a front mass and a rear mass, and a piezoelectric ceramic laminate is provided
through the through holes provided in the piezoelectric ceramic laminate. A bolt is provided to
apply compressive stress to the body, and the front mass portion is, in addition to the
translational displacement, a joint between the bolt and the front mass, a piezoelectric ceramic
laminate, or a neck and front mass disposed between the laminate and the front mass. It is a
submersible ultrasonic transducer characterized in that the bending displacement is made based
on both the joint portions of the joint portion with the joint portion, and the vibrational
displacement of the outer edge portion of the front mass is largely taken by this principle to
enhance the acoustic radiation efficiency. In the present invention, contrary to the conventional
bolt-clamped Langevin transducer, the shear force generated between the piezoelectric ceramic
laminate and the bolt is positively utilized to excite the bending vibration accompanied by the
rigid body rotation of the front mass. Thus, the present invention is characterized in that acoustic
radiation is efficiently performed by combining the translational displacement of the front mass
and the bending vibration. An example of an underwater ultrasonic transducer according to the
invention is shown in FIGS. 1 (a), (b). The figure (a) is a front view, and the figure (b) is a sectional
view. In FIG. 1, 11 is a front mass for flexural vibration, 12 is a rear mass, 13 is a piezoelectric
ceramic laminate, 14 is a bolt, 14 'is a bolt head, 15 is a nut, 16 is a slit, 17 is a piezoelectric
ceramic laminate. It is a neck that transmits the generated displacement to the front mass 11.
The principle of operation of the transducer according to the invention will be described on the
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basis of FIG. The front mass 11 is pushed forward when the piezoelectric ceramic laminate 13
'extends in a piezoelectric manner. However, since the bolt 14 is not piezoelectrically stretched,
when the piezoelectric ceramic laminate 13 is stretched, a force is generated in the bolt 14 to
prevent the stretching of the piezoelectric ceramic laminate 13. The reaction force increases as
the diameter of the bolt 14 increases. Thus, the front mass shear force is eventually generated
and the front mass is bent. When the front mass 11 bends, the phases of the front mass portion
outside and the front mass portion inside the piezoelectric ceramic laminate become opposite to
each other. In the transducer according to the present invention, even if the phase of the
vibrational displacement is reversed in the central portion and the outer edge portion of the front
mass, the amount of medium displacement of the outer edge portion of the bending front mass
11 is the inner portion of the bending front mass 11 If it is overwhelmingly larger than the
amount of medium excluded, the total amount of medium excluded will be considerable.
Furthermore, since the rigid frontal displacement 11 is additionally subjected to a rigid body
translational displacement due to the extension of the piezoelectric ceramic laminate, the
bending front mass 11 is finally displaced as shown by the broken line aa 'to bb'. It will improve
further. The working principle of the transducer according to the present invention has been
described above, but as shown in FIG. 1, if the slits or grooves 16 are provided from the outer
edge of the front mass toward the central part, more effective medium removal is possible. It
becomes. By providing such a slit or groove 16, the contact between the bolt and the front mass,
the neck 17 protruding from the piezoelectric ceramic laminate or the piezoelectric ceramic
laminate or the contact with the front mass, that is, between the two contacts As this arm, due to
the principle of leverage, the vibration displacement can be significantly expanded at the outer
edge of the front mass. In this way, high efficiency and high power transducers can be achieved
in the present invention by increasing the amount of medium displacement and increasing the
acoustic radiation. Also, in the conventional bolted Langevin transducer, only the translational
displacement of the portion of the front mass is performed in the rigid body, but in the present
invention, since the outer edge portion of the front mass is rigidly rotated, rotational inertia is
given to the front mass. In order to obtain a lightweight transducer, it can be easily realized by
setting the outer diameter of the bending front mass 11 to a value several times as large as the
outer diameter of the piezoelectric laminate 13.
EXAMPLE An underwater ultrasonic transducer shown in FIG. 1 will be described as an example
of the present invention. First we will talk about transducers that are not slit in the front mass.
This transducer is a square whose resonance frequency is 7.8 KHz and whose acoustic emission
surface is 10.5 cm on a side. As a piezoelectric ceramic of the piezoelectric ceramic laminate 13,
a lead zirconate titanate piezoelectric ceramic having an electromechanical coupling coefficient
of 0.61 and a relative dielectric constant e33T / eO of 1080 was used. Also, an Al alloy was used
for the bending front mass 11, stainless steel for the rear mass 12, Cr-Mo @ for the bolt 14 and
nut 15, and stainless steel for the neck 17. The transducer had a length of 13.2 cm and a weight
of 1736 g. A measure of displacement magnification according to the principle is given by the
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ratio of the diameter of a circle having an area equal to the bending front mass to the diameter of
the neck 17. In the case of the transducer of this example, the ratio is 3.7. Incidentally, when the
ratio was 3 or less, it was not possible to experimentally obtain a transducer excellent in acoustic
radiation performance as compared with the conventional bolted transducer. Furthermore, in the
present transducer, the shape and size of the front mass were determined such that the
resonance frequency of the bending vibration mode of the front mass came near the resonance
frequency of the piston vibration mode which is the vibration mode of the conventional bolted
Langevin transducer. Next, this transducer was mounted in a watertight housing, and the
electroacoustic conversion efficiency, Q in water, was measured. Next, an underwater ultrasonic
transducer having a slit 16 with a width of 0.5 mm formed in the front mass 11 was produced. At
this time, in air, the resonant frequency of the transducer decreased by 700 Hz as compared to
when the slit was not formed. The operating characteristics in water were measured in the same
manner as described above. The results are shown in Table 1 in comparison with the
conventional bolted Langevin oscillator used in the 7 KHz band. The transducers of the present
invention are particularly advantageous for weight reduction as compared to the conventional
bolted Langevin transducer, and it was difficult for the conventional transducers to have a Q
value of 5 or less in water However, since the present transducer is excellent in terms of
matching of acoustic impedance with water in water, it has a wide band and high electroacoustic
conversion efficiency. Although the example of the slit was shown in this embodiment, it may be
a groove.
In addition, as for a front mass, the resonant frequency of the bending vibration is desirable
about 0 to 5 times to about 1.5 times compared with the resonant frequency of translational
vibration. The shape of the front mass is preferably a circle having a size of 8 to 10 times the
diameter of the neck or an area equal to this circle. (Effects of the Invention) As described above,
the transducer according to the present invention actively utilizes not only the translational
displacement of the front mass performing acoustic radiation but also the rigid body rotational
displacement associated with the bending deformation, so that it is lightweight and has an
acoustic radiation efficiency. You can get an excellent transducer.
[0002]
Brief description of the drawings
[0003]
1 (a) and 1 (b) show an underwater ultrasonic transducer according to the present invention,
wherein (a) is a front view and (b) is a cross-sectional view.
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In the figure, 11 is a bending front mass, 12 is a rear mass, 13 is a piezoelectric ceramic
laminate, 14 is a bolt, 14 'is a bolt head, 15 is a nut, 16 is a slit or groove formed in the front
mass, and 17 is a neck. FIG. 2 shows a conventional bolted Langevin transducer, in which 21 is a
front mass, 22 is a piezoelectric ceramic ring, 23 is a rear mass, 24 is a bolt, and 25 is a nut.・ ・
・・・
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