JPS6143896A - Low frequency underwater ultrasonic transmitter - Google Patents

Abstract

PURPOSE:To offer a small-sized two-way or nondirectional echo sounder transmitter excellent in high power characteristic in a low frequency band by providing two-stage displacement enlarging mechanism to said transmitter. CONSTITUTION:An active columnar body 31 is excited for the vertical vibration. A non-active columnar body 41 made of high tensile steel is so designed that it can have a large rigidity with respect to the vertical displacement and can be flexible with respect to a flexible displacement. When the columnar body 31 is displaced by xsi1, a lever 34 rotates inside to develop an enlarged displacement xsi2 at ends P and P'. At this time, the columnar body 41 having a thick base part 31' transmits efficiently the vertical displacement of the columnar body 31 to the lever 34. Even when the lever 34 rotates with respect to the 1st stage displacement enlarging mechanism, structually the flexible moment is canceled out, and the flexible moment arising in the columnar body 31 goes to approximately zero. In terms of the 2nd stage displacement enlarging mechanism, when the displacement by xsi2 occurs at the points P and P', the displacement several times larger than the xsi2 is given as shown by the double arrows owing to the form effect of a convex shell.

Description

[Detailed Description of the Invention] (Industrial Application Field of the Invention) The present invention relates to a bidirectional or omnidirectional low frequency power transmitter used for long-range sonar, marine resource exploration, etc. .

(Prior technology) Low-frequency ultrasonic waves have less propagation loss underwater than high-frequency waves and can reach long distances, so low-frequency ultrasonic waves are used in fields such as sonar, ocean resource exploration, and ocean current research. There are many advantages to doing so. Conventionally, electrodynamic transducers and piezoelectric (electrostrictive) transducers have been known as transmitters that emit powerful ultrasonic waves underwater.

Although electrodynamic transducers are capable of large displacements, they generate small forces, making it extremely difficult to obtain small transducers with low frequencies.

On the other hand, piezoelectric transducers use zirconium lead titanate-based piezoelectric ceramics as the electroacoustic conversion material, and piezoelectric ceramics have an acoustic impedance that is approximately 20 times larger than that of water, so the power generated per unit is extremely large. However, the medium exclusion (acoustic radiation) K has the disadvantage that the required displacement is small. The sound pressure of the ultrasonic wave emitted from the transmitter is so large that the volume velocity of the acoustic radiation surface (defined as the acoustic radiation cross-sectional area x the velocity of the acoustic radiation surface) is large. That is, assuming that the radiation cross-sectional area is constant, the higher the velocity of the acoustic radiation surface of the transmitter, the higher the output sound pressure. In fact, since the time derivative of the displacement of the acoustic radiation surface is the velocity of the acoustic radiation surface, if the vibration velocity is constant, the displacement increases as the frequency decreases, so a large sound pressure can be obtained at low frequencies. If we try to do this, we will need an acoustic radiation surface that can be displaced with a correspondingly large amplitude. moreover,
Considering that the acoustic radiation impedance per unit radiation area becomes extremely small as the frequency decreases, in order to achieve efficient acoustic radiation at low frequencies, K performs acoustic radiation by greatly expanding the displacement of the piezoelectric ceramic. There is a need. below,
A conventional piezoelectric transducer will be explained.

The bolt-on Langevin transducer is a 3kl transducer that transmits powerful ultrasonic waves underwater.
It is well known that it is actively used in the frequency band from lz to several tens of kfTz.

However, if this transducer 1 is to be operated efficiently at a low frequency of 3 kHz or less, the displacement magnification mechanism is required and the weight and dimensions are too large to be of practical use.

Therefore, as a transducer that can be miniaturized at low frequency, for example, R, 8, Woollett, "Trend"
andProblem in 5onar T'ran
sducer Design,” IEF;ETran
s, on Ultrasonics Engineering
ring, pp. 116-124 (1963, 11
) K As described, the bending type transducer using the bending vibration of the disk shown in Fig. 1, or the try
G, Brigham and B, Grass.

“Present 5 status in Flesh
xlensional Tran@ducerTec
hno Iogy'', J, Acoust, 8oc,
Am, Vol. 68.

No, 4. pp. 1046-1052 (1980,
As described in 10), a bending-extension transducer using an oval shell shown in FIG. 2 is known.

(Problems with the Prior Art) The bending transducer using a circular flat plate shown in FIG. 1 uses two VC circular bimorph vibrators as a transmitter, as is well known. In Fig. 1, 10 is a zirconium titanate-based piezoelectric ceramic plate, 11 is a metal plate such as nickel or stainless steel, and 10.11 constitutes a bimorph resonator, and these two bimorph resonators are both acoustic media. It performs bending vibrations that push out or pull in (water), and ultrasonic waves are emitted from both sides of the bimorph oscillator. Further, 13 is a housing case. However, since it is not possible to obtain a piezoelectric ceramic plate with a large area as shown in Table 10,
Metal plate 11VC in mosaic style with many segmented porcelain plates
At present, bimorph resonators are obtained by bonding.

Therefore, the medium rejection ability as a transmitter is insufficient, making it unsuitable for high power transmission VCFi. Even if a piezoelectric ceramic plate with a large area could be obtained, the bimorph resonator has a large bending compliance due to its structure, and good medium expulsion ability cannot be expected.

In the bending-elongation transducer using an elliptical shell shown in FIG. 2, when the piezoelectric ceramic columnar body 20 is elongated and displaced in the longitudinal direction, one shell 21 is several times larger than the columnar body 20, as shown by the double arrow in the figure. This is a transducer that has a kind of displacement amplification mechanism that contracts uniformly with a displacement of . (Only a quarter portion is indicated by an arrow.) Regarding such a bending-extension transducer, the displacement of the piezoelectric ceramic columnar body 20 is expanded several times, and ultrasonic waves are transmitted from the outer surface of the shell, and compared to a bimorph disk, the displacement of the piezoelectric ceramic columnar body 20 is expanded several times. Since the elliptical shell has great rigidity, it is said to be a transducer that is superior to the transducer shown in FIG. 1 in transmitting high-power waves. However, due to the force, the performance of the flex-extension transducer shown in FIG. 2 is strongly dependent on the shape of the elliptical shell. A flat elliptical shell in which the minor axis a is smaller than the major axis bK, in other words, the eccentricity is large, theoretically provides better acoustic matching and better acoustic radiation efficiency. However, for the reasons explained below, this elliptical shell cannot take any arbitrary shape. First, when the first K shape becomes flat, stress is concentrated near the portion with large curvature.

This is due to the fact that M2 must have a storage space for the piezoelectric ceramic columns and electronic equipment. For this reason, in practice, the ratio a/b of the short axis to the long axis of the elliptical shell is set to 0.
．． It is impossible to reduce the number to 3 or less.

Therefore, the part of the elliptical shell that is displaced the most with respect to the displacement of the piezoelectric ceramic columnar body 20 is the short axis part, and a / b
> 0.3, this part is so K that at most a 5-7 times magnified displacement occurs.

(Object of the Invention) An object of the present invention is to eliminate the drawbacks of the conventional transducer and provide a bidirectional or omnidirectional transmitter that is compact and has high power characteristics in the low frequency band. be.

(Structure of the Invention) The present invention is capable of exciting longitudinal vibration, and consists of an active columnar body connected to two hinge parts at each end thereof, a hinge part, and a pace part, which are arranged in parallel across the active columnar bodies. two inactive columnar bodies, a first lever part connected to both ends of one inactive columnar body and the active columnar body via a hinge part, and similarly the other inactive columnar body and active columnar body. A second lever part connected to both ends of the lever part via a hinge part, and a Humpex-type shell or an h-concape-type shell formed at the ends of the first and second lever parts, respectively. This is a low frequency underwater ultrasonic transmitter characterized by the following.

(Detailed description of the structure) The transmitter of the present invention solves the problems of the prior art by having the above-mentioned two-stage displacement amplifying mechanism. The details are explained below according to the drawings.

FIG. 3 shows an example of the transmitter of the present invention using a convex shell. The operating principle of the transmitter shown in FIG. 3 will be explained in detail. In FIG. 3, reference numeral 31 denotes an active columnar body made of piezoelectric ceramic or magnetostrictive material, whose longitudinal vibration is excited by inputting a voltage or current. A hinge portion 33, 33' and a pace portion 31' are arranged in parallel to the active columnar body 31.
The inactive column, which is made of a high mechanical strength material such as high-strength steel, is designed to have considerable stiffness against longitudinal displacement and flexibility against deflection displacement. When the active column is displaced by ξ, as indicated by the double arrow in FIG. 3, the lever 34 rotates inward by an angle θ, and an enlarged displacement ξ2 occurs at the lever ends P, P'. In this case, by using a material with sufficient rigidity for the lever (for example, high tensile stainless steel), the lever exhibits a movement close to the rotation of a rigid body, and the hinges 32, 33 (or Fi 32', 33
') the distance between! 1. Hinge 33 and P (or Fi33
' and p') distance! , then the geometrically expanded displacement ξ, kel! 1ξzl=lξ+l (1). For example, if it is 4"34, then the displacement P is three times the displacement ξ1 of the active columnar body.

This occurs at point P'. At this time, in order to efficiently transmit the longitudinal vibration excited by the active columnar body 31 to the lever 34, the inactive columnar body that functions as the fulcrum needs to have considerably high rigidity with respect to longitudinal vibration as described above. be.

This is precisely why the pace portion 31' is so thick. ``Also, the lever 34 is the lever Q,
When rotated around Q' by an angle θ, the hinges 32, 32', 33, and 33' that contact the lever are also deflected by an angle θ, and a bending moment is generated in the inactive columnar body. The magnitude of this deflection moment is 32
．． 32', 33. The smaller the deflection compliance of 33', the greater. i.e. hinges 32.32', 33.3
The smaller the deflection compliance of lever 34
This will inhibit zero rotation, and the hinges 32, 32', 3
3.33', a hinge with a small vertical compliance and a large bending compliance (for example, a plate-shaped hinge) is suitable. Furthermore, even if the lever 4 rotates by an angle θ in the first stage displacement magnifying mechanism of the present invention, the bending moment is canceled out due to the structure and a bending moment a? '! It has a remarkable feature of being almost zero. That is, since bending deformation is extremely unlikely to occur in the active columnar body, it is possible to realize a robust first installation position enlarging mechanism.

Regarding the second installation position expansion mechanism, when the point p and p' is displaced by ξ, due to the shape effect of the convex shell, an expanded displacement of several times ξ is given as shown by the double arrow in the figure. That's why. As described above, since the transmitter of the present invention has a two-stage displacement amplification mechanism, an extremely large displacement is given to the acoustic radiation surface (outer surface of the shell), and it can be said to be compact and have excellent acoustic radiation ability.

Next, FIG. 4 shows an example of an active columnar body used in the transmitter of the present invention using a piezoelectric ceramic ring.

In FIG. 4, 41 is a piezoelectric ceramic ring, and adjacent piezoelectric ceramic rings are arranged so that their polarization directions are opposite to each other and are electrically arranged in parallel.
The 43Vi nut serves to apply static compressive stress to the piezoelectric ceramic ring 41. The reason for this is that although piezoelectric ceramics have high mechanical strength against pressure, they are vulnerable to tension, so they are used to generate tension in the piezoelectric ceramic ring 41 during excitation to improve performance. As a result, it is possible to drive at several times the tension limit inherent to piezoelectric ceramics.The active columnar body with such a structure has the polarization and electric field vector directions uniformly in phase within all piezoelectric ceramic rings 41. Alternatively, by being in reverse phase, the whole can expand and contract uniformly. In the transmitter of the present invention, it is of course possible to use a high-performance magnetostrictive material containing a rare earth element instead of the piezoelectric ceramic as the active columnar body.

The transmitter based on the present invention using a convex shell has been described above, but the transmitter using a concave shell 35' shown in FIG. It is clear that the shell operates in exactly the same way as the shell, except that the phase of acoustic radiation differs by π. In Fig. 5, 31 is an active columnar body, 31' is a base part, 32.32', 33.33' are hinge parts,
The 34 lever part and 35' are concave type shells.

As mentioned above, another excellent feature of the underwater low-frequency transmitter based on the present invention is that the displacement of the active columnar body is increased by n times (n >> 1) at the acoustic radiation end. Therefore, the mass of the acoustic radiation end is 0.2 times that of the active columnar body side, and a small, lightweight, low-frequency transmitter can be obtained. It can be said that the transmitter of the present invention is a transmitter that can achieve low frequency, size and weight reduction, and high efficiency at the same time and easily.

(Example) As an example of the present invention, an underwater ultrasonic wave transmitter using a convex shell will be described with reference to FIG. The transducer using the convex type shell shown in Fig. 3 is housed in an FRP housing case 61 with a wall thickness of 10aII to prevent acoustic coupling between the transducer and the nosing case, and to prevent rotational movement of the lever. For this purpose, an acoustic decoupling material 62 mainly made of cork and synthetic rubber is placed on the side of the lever. The convex shell used for acoustic radiation has a radius of curvature larger than the outer diameter, and its planar shape is 5.
Qcm×40cIL1 thickness 1.5 to 2.0C1fi.

Note that the planar shape is not limited to this. The lever, hinge and convex shell are all made of high tensile strength. The resonant frequency of the prototype transmitter in the air is 810 Hz, and the mass Fi is 47~. The displacement of the active columnar body is about 12 times greater in the central part of the convex shell. Here, the piezoelectric ceramic ring described above was used as the active columnar body.

When this transducer was placed in a water tank and driven with no power and the sound pressure was measured at a point 1 m away from the sound emitting surface, a sound pressure of 180 dBrelμPa was easily obtained. In addition, the directivity is close to omnidirectional at low frequencies, but becomes close to bidirectional as the frequency increases.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to obtain a bidirectional insulator and omnidirectional high-power transmitter that is small and lightweight and has excellent acoustic radiation efficiency.

[Brief explanation of drawings]

FIG. 1 shows a conventional bending transducer, FIG. 2 shows a conventional bending-extension transducer, FIG. 3 shows a transmitter of the present invention using a convex shell, and FIG. 4 shows an active FIG. 5 is a view showing an example of a columnar body, FIG. 5 is a view showing an example of a transmitter according to the present invention using a concave shell, and FIG. 6 is a view showing an embodiment of the transmitter according to the present invention. In the figure, IO is a piezoelectric ceramic plate, 11 is a metal plate, 12 is a cavity, 13 is a housing case, 20 is a piezoelectric ceramic columnar body, 21 is an elliptical shell, 31 is an active columnar body, 3
1'C base portion of inactive columnar body, 32.32'
, 33.33' is a hinge, 34 is a lever, 35#'i funpex type shell, 35'H concave type shell, 4
1tj piezoelectric ceramic ring, 42 is a bolt, 43 is a nut,
81 is a housing case, and 82 is an acoustic decoupling material. O 1 Figure O 2 Figure 3 Figure 4 41 41 41 41 41 4+ 71su Figure 5 procedural amendment (voluntary) Commissioner of the Japan Patent Office rg＞bρyearρp＞＞E3
2. Title of the invention: Low-frequency underwater ultrasonic wave transmitter 3. Relationship with the amended case: Applicant No. 5-33 Shiba, Minato-ku, Tokyo (423) NEC Corporation Representative: Tadahiro Sekimoto 4 , Agent Sumitomo Sanda Building, 37-8 Shiba 5-chome, Minato-ku, Tokyo Telephone: Tokyo 0
3-456-3111 (main representative) (contact information: Patent Department, NEC Corporation) 5 Detailed explanation of the invention in the specification subject to amendment column 6, content of amendment / section 2nd page I3h of the specification (The phrase "electrostrictive transducer" is corrected to "piezoelectric (electrostrictive) transducer." .42 with bolts.'' In the 6th line of page 14 of the specification, the statement ``Tension is used'' is corrected to ``High-tensile steel is used.'' Jino Specification Honor No. 1. f 810HzJ on page 4, line 8
Correct it to [510HzJ. ! ++

Claims (1)

[Claims] An active columnar body capable of exciting longitudinal vibrations and connected to two hinge parts at each end thereof, and two inactive columnar bodies each consisting of a hinge part and a base part and arranged in parallel across the active columnar body. A first lever part that connects the body to both ends of one inactive columnar body and an active columnar body via a hinge part, and similarly connects both ends of the other inactive columnar body and active columnar body to the hinge part. A low-frequency underwater device characterized by having a structure consisting of a second lever part connected through the interface, and a convex-type shell or a concave-type shell formed at the ends of the first and second lever parts, respectively. Ultrasonic transmitter.