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The present invention relates to a broadband piezoelectric transducer capable of transmitting
ultrasonic waves with high power in water. Conventionally, a bolt-clamped Langevin transducer
as shown in FIG. 3 is known as an ultrasonic transducer capable of high power transmission in a
frequency band of several kilohertz to several tens of kilohertz in water. As shown in FIG. 3, this
bolted Langevin transducer includes a front mass 31 made of a high rigidity material such as Al
alloy, Ti alloy, steel, etc., and a ring-shaped piezoelectric ceramic 32 disposed between the front
mass 31 and the rear mass 33. Rear mass 33 made of high rigidity material such as stainless
steel as well as front mass 31, and bolt 34 made of high tensile strength steel such as Cr-Mo
steel, which has a function to apply compressive stress to ring-shaped piezoelectric ceramic 32,
Nats 35 And has a great feature that high power drive is possible. Here, the ring-shaped
piezoelectric ceramic 32 uses a longitudinal effect vibration mode (33 mode) in which an electrolow mechanical coupling coefficient is obtained as compared with the transverse effect
longitudinal vibration mode (31 mode). Adjacent piezoelectric ceramic rings 32 are polarized in
opposite directions to each other as indicated by arrows in the drawing, and are electrically
connected in parallel to achieve matching with the power amplifier. In addition, since
piezoelectric ceramics are generally vulnerable to tensile stress compared to compressive stress,
static bias stress is applied in advance by the bolts 34 and nut 35, and the structure is
sufficiently durable even at high power conditions. ing. Such a bolt-clamped Langevin transducer
uses a half-wave resonant mode, as is well known. Problem to be Solved by the Invention Usually,
this bolted Langevin transducer is designed and manufactured so that the acoustic radiation
surface performs piston vibration. The vibration stress acting on the conventional bolt-clamped
Langevin transducer is mostly applied to the ring-shaped piezoelectric ceramic and the bolt
portion, and the front mass 31 and the rear mass 33 only perform piston translational
displacement. That is, the front mass which emits acoustic radiation is displaced by the same
amount as the displacement generated by the piezoelectric ceramic, and this displacement is
generally small, and the input mechanical impedance seen from the acoustic radiation surface is
acoustic radiation that uses water as a medium. It is considerably larger than the impedance.
This creates an acoustic impedance mismatch between the water and the transducer, which limits
the bandwidth of the transducer. Therefore, it has been difficult to make the bolted Langevin
transducer 3 dB relative bandwidth 20% or more. The present invention aims at realizing a
broadband underwater ultrasonic transducer with high electro-acoustic conversion 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 is formed in the through hole provided in the piezoelectric ceramic laminate. The
laminate is provided with a bolt for applying a compressive stress, a slit or groove is formed from
the outer edge to the central portion in the front mass portion, and the inertial mass of each
opposing front mass portion divided by the slit or groove is equalized. In addition, it is an
underwater ultrasonic transducer in which the inertial masses of adjacent front mass portions are
made different from each other through slits or grooves to achieve broadening. The present
invention positively utilizes the shear force generated between the piezoelectric ceramic laminate
and the bolt, contrary to the conventional bolted Langevin transducer, and rotates the rigid body
of the front mass in which the groove or the slit is formed in advance. By exciting the bending
vibration accompanied by the above, it is characterized in that acoustic radiation is efficiently
performed in a form in which the translational displacement of the front mass and the bending
vibration are combined. 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 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 translational displacement due to the
extension of the piezoelectric ceramic laminate, the final bending front mass 11 is displaced as
shown by the broken lines aa 'to bb'. It will improve further. Although the principle of operation
of the transducer according to the present invention has been described above, it is possible to
effectively eliminate the medium by providing the slit 16 or the groove from the outer edge of
the front mass to the central portion as shown in FIG. Become. By providing the slit 16, the point
of contact between the bolt and the front mass, the point of contact between the neck 17
protruding from the piezoelectric ceramic laminate and the front mass, that is, the arm between
these two points of contact, the neck by the principle By rigidly rotating the front mass portion
outside of 17, the vibration displacement can be significantly expanded at the front mass outer
edge. Furthermore, by providing such a slit, the inertial mass of each partial front mass divided
by the slit 16 can be set arbitrarily. As means for setting the inertial mass, it is conceivable to
change the distribution of the mass of the divided partial front mass, to change the shape of the
partial front mass, and to change the position of the contact point of the neck 17 and the front
mass. Is possible. In this case, it should be noted that the inertial mass is not asymmetrically
distributed with respect to the central axis of the transducer. If the distribution of the inertial
mass of the front mass becomes asymmetric with respect to the central axis, non-axisymmetric
vibrations are excited, which adversely affects the acoustic radiation. Therefore, in the transducer
of the present invention, the inertial mass of each opposing partial front mass divided by the slit
is equalized. As described above, in the transducer according to the present invention, by making
the inertia mass of the adjacent partial front mass different, the transducer of the multiple
resonance system having a plurality of resonance frequencies in the band is formed. Can be
It can be said that the transducer of the present invention is a transducer which is essentially
different from the bolted Langevin transducer which is a conventional single-resonance system.
Thus, in the transducer of the present invention, the medium displacement can be increased
based on the principle of leverage, and a wide band high power transducer can be achieved by
the multi-resonance system. Even if the acoustic emission surface is a complete square front
mass, the adjacent partial fronts can be formed by changing the setting of the distance from the
central axis as shown in FIG. It goes without saying that the inertial mass of the mass can be
varied. Embodiment An underwater ultrasonic transducer shown in FIG. 1 will be described as an
embodiment of the present invention. The transducer center frequency shown in FIG. 1 is 7 KHz,
and the acoustic radiation surface is a rectangle having a long side of 14.5 cm and a short side of
9.5 cm. The piezoelectric ceramic used for the piezoelectric ceramic laminate is a lead zirconate
titanate ceramic having an electromechanical coupling coefficient of 0.61 and a relative
permittivity of 833 T / Co of 1080. 7o7) A1 alloy for mass 11, stainless steel for rear mass 12,
Cr-Mo rigid for bolt 14 and nut 15, and Cr-Mo rigid for neck 17 were used. Further, a slit 16
having a width of 0.4 mm was formed in the front mass 11. The transducer was then mounted in
a watertight housing and the electroacoustic conversion efficiency, 3 dB relative bandwidth in
water, was measured. The results are shown in Table 1 in comparison to a bolted Langevin
transducer having a resonance at 7 KHz. Table 1. Comparison of the present transducer and the
conventional bolted Langevin transducer The present transducer has high efficiency as well as
the bolted Langevin transducer, and a wide band is achieved. Although the example of the slit
was shown in this embodiment, substantially the same effect was obtained even with the groove.
In addition, as for a front mass, as for the resonant frequency of the bending vibration, 0.5 times
to 1.5 times of the resonant frequency of translational vibration is desirable. 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. It is not effective if it is less than 3 times. (Effects of the Invention) As
described above, according to the present invention, a highly efficient and wide-band underwater
ultrasonic transducer is obtained, and the industrial value is also great.
Brief description of the drawings
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.
In the figure, 11 is a 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 formed in the front mass, 17 is a neck, broken line
a- a 'and b-b' indicate the vibrational displacement of the front mass. FIG. 2 shows a square
shaped front mass used in a transducer according to the invention. FIG. 3 shows a conventional
bolted Langevin transducer. In the figure, 31 is a front mass, 32 is a piezoelectric ceramic ring,
33 is a rear mass, 34 is a bolt, and 35 is a nut. Figure 2
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