JPS6331300A - Low frequency underwater ultrasonic wave transmitter - Google Patents

Abstract

PURPOSE:To obtain an ultrasonic wave transmitter of high power by disposing inactive columnar members at both sides of an active columnar member, connecting levers to the end parts of the columnar members through hinges and providing convex shells on the levers. CONSTITUTION:A displacement outputted from the active columnar member 31 is transferred to the lever 34 through the hinges 32, 33. The energy of a vertical vibration outputted from the columnar member 31 is transformed to the rotation energy of the lever 34. At this time, the larger the vertical stiffness of the hinges 32, 33 is large, the move vibration energy is efficiently transformed to the rotation energy. When an irregular shell having the large thickness in a part of joining the hinges 35, 35 and a minimum thickness in the center part of the shell is used, a stress concentrated to the root part of the shell can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a low-frequency band, high-power underwater ultrasonic transmitter used for long-distance sonar, marine resource exploration, and the like.

(Prior technology) Low-frequency ultrasonic waves have less propagation loss underwater than high-frequency waves and can reach longer distances. There are many advantages to using ultrasonic waves. Conventionally, electrodynamic transmitters and piezoelectric transmitters have been known as transmitters that emit powerful ultrasonic waves underwater. Although an electrodynamic transmitter can have a large displacement, it is extremely difficult to produce a small transducer with a low frequency because the generated force is small. Furthermore, in the piezoelectric wave transmitter, a silcondethanate-based piezoelectric ceramic is used as an electromechanical energy conversion material. Piezoelectric ceramics themselves have an acoustic impedance that is about 20 times greater than that of water, so although they have the advantage of generating an extremely large force, they have the disadvantage of not being able to take the displacement necessary to exclude the medium during acoustic radiation. . Considering that the acoustic radiation impedance per unit radial area becomes extremely small as the frequency decreases, in order to achieve efficient acoustic radiation at low frequencies, it is necessary to further expand the displacement of the piezoelectric ceramic to increase the acoustic radiation. There is a need to do.

Conventionally, as a high power transmitter in the low frequency band (3K] lz or less), for example, TEEE Trans on II l 1.
ra-5onics Engineering,
pp1]6-]24<1963. ]1)), there is a bending wave transmitter that utilizes the bending vibration of a disk as shown in Fig.
usL,Soc,Am,,vol,6B,No4,
p p 1.046-] D 52 < 1.9 B
As described in [O, ] O) ), a bending and stretching transmitter using an elliptical shell shown in FIG. 6 is known.

(Problems to be Solved by the Invention) The bent wave transmitter using a circular flat plate shown in FIG. 5 uses a circular bimorph oscillator as a wave transmitter, as is well known. In FIG. 2, numeral 10 is a piezoelectric ceramic plate based on zirconate lead titanate, and numeral 11 is a metal plate such as nickel or stainless steel.These constitute a bimorph vibrator, and the bimorph vibrator itself serves as an acoustic radiator. Also, 1
2 is a cavity, and 13 is a housing case. However, in the transmitter shown in FIG. 5, since it is not possible to obtain a piezoelectric ceramic plate with a large area as the ten piezoelectric ceramic plates, a large number of segmented ceramic plates are arranged in a mosaic manner to form the metal plate 11.
Currently, bimorph oscillators are obtained by gluing . In other words, since a large-area porcelain plate cannot be used, the ability to exclude the medium as a transmitter cannot be said to be sufficient.
It is unsuitable for high power transmission. Further, even if a piezoelectric ceramic plate with a large area can be obtained, the structure 1-bimorph resonator has a considerably large bending compliance, and a large medium expulsion ability cannot be expected.

Next, in the bending/extending transmitter shown in FIG. 6, when the active columnar body 20 made of piezoelectric ceramic is stretched and displaced in the long axis direction, the elliptical shell 21 moves toward the columnar body 20 as shown by the arrow in the figure.
This is a wave transmitter that has a kind of displacement amplification mechanism that contracts at a displacement several times zero. (Only a quarter of the elliptical shell is indicated by an arrow.) Since this transmitter uses an elliptical shell as the acoustic radiator, it has structural rigidity far greater than that of a bimorph disk. It is said to be a transmitter that is better at transmitting high-power waves than the transmitter using the bimorph disk shown in Figure 2.

The resonant frequency of the bending-extension transmitter shown in FIG.
The value will be twice or more -L. In other words, the low-frequency miniaturization of the bending-stretching transmitter cannot be achieved without considerably lowering the resonant frequency related to the bending-stretching mode of the elliptical shell 21 itself, which has a certain size. Further reduction of its own resonant frequency is desired. However, for the reasons described below, it is extremely difficult to miniaturize the elliptical shell itself at low frequencies.

In order to explain the operation of this elliptical shell, the long axis of the elliptical shell corresponds to the X axis, the short axis corresponds to the y axis, and the depth direction corresponds to the y axis, and a quarter part of the elliptical shell is shown in Figure 7. show. The point where the center of the thickness of the elliptical shell intersects with the X axis is (a, O),
Also, the point that intersects with the y-axis is set to <0. b). That is, the major axis of the elliptical shell is a, and the minor axis is b. Now, when the active columnar body 20 extends and displaces point P by ξ in the +X direction, due to the displacement magnification mechanism of the elliptical shell itself, a displacement several times ξ appears in the -y direction at point Q. The shell as a whole will draw in the medium. On the other hand, when the active columnar body contracts, the shell as a whole acts in a direction to exclude the medium. In this case, the cross section of the elliptical shell cut along the X axis is parallel to the
The rotational displacement around the axis is zero. The more rotation around the 4Z axis is not allowed in the secondary position, the greater the restriction on the movement of the shell becomes, and the resonant frequency of the shell becomes higher. It is extremely difficult to reduce the size of low-frequency transmitters in bending and stretching transmitters because the resonant frequency of the elliptical shell itself is difficult to decrease due to the following two reasons.

On the other hand, it is naturally possible to consider attempts to achieve low-frequency miniaturization by changing the shape and wall thickness of the elliptical shell.

First, when changing the shape of an elliptical shell, the shell resonance frequency certainly decreases as b/a increases and approaches a circle. However, in this case, as b/a increases, the displacement magnification rate decreases significantly compared to when the frequency is low, so there is no advantage of changing the shape to reduce the size. It is also observed that the resonance frequency decreases when the shell thickness is reduced. But in this case,
This has the disadvantage that not only the medium exclusion ability of the shell is reduced, but also the water pressure resistance properties are significantly deteriorated.

The object of the present invention is to eliminate the drawbacks of the conventional one to two-way transmitter and provide a bidirectional or omnidirectional transmitter that is small in size and has excellent high power characteristics in the low frequency band.

(Means for Solving the Problems) The transmitter of the present invention includes an active columnar body using a piezoelectric ceramic or a magnetostrictive material, an inactive columnar state sandwiching the active columnar body, and disposed on both sides of the active columnar body. A low riser characterized by comprising a lever connected to each end of the active columnar body and the inactive columnar body via a hinge, and a convex shell connected to each of the two levers via a hinge. It is a high frequency underwater ultrasonic transmitter.

(Function) The transmitter of the present invention improves the problems of the prior art by having the above two-stage displacement amplifying mechanism. This will be explained below according to the drawings.

FIG. 1 shows an example of a transmitter of the present invention using a convex shell. The operating principle of the transmitter shown in FIG. 1 will be explained in detail. In Fig. 1, numeral 31 is an ac-dip columnar body made of piezoelectric ceramic or magnetostrictive material.
Longitudinal vibration is excited by inputting voltage or current. This active columnar body 31 is connected to the hinge 3
2.32' to the lever 34. In addition, the inactive columnar body 31'' is arranged in parallel with the active columnar body 31, and the inactive columnar body 31''
It is connected to the collar 34. The system consisting of the hinge and the inactive columnar body is made of a material with high mechanical strength such as high-strength steel, and has considerable rigidity against longitudinal displacement and is designed to act flexibly against bending displacement. Designed.

When the active columnar body is displaced by ξ as indicated by the arrow in FIG. 1, the lever 34 rotates inward by an angle θ, and an enlarged displacement ξ2 is generated at one end of the lever P, P'. In this case, the lever should be made of a material with sufficient rigidity (
For example, by using high-strength casdenless steel), the lever exhibits a movement almost like a rigid body rotation, and the hinge 32
．． 33 (or 32°, 33°) as Q3,
If the distance between the hinges 33 and 1] (or 33゛ and l]') is Q2, the geometrically expanded displacement ξ2 becomes ]ξ21-quasi J-1ξ11 (]-1. For example, u2=3Ql Then, a displacement that is three times larger than the displacement ξ1 of the active columnar body occurs at points p and p'.At this time, the inactive columnar body that acts as this fulcrum is the active columnar body 31. In order to efficiently transmit the excited longitudinal vibration to the lever 34, it is necessary to increase the rigidity with respect to the longitudinal vibration considerably as described above.

Also, the lever 34 is at an angle θ about the lever fulcrum Q, Q'm.
When the hinge is rotated by 32゜32'', it comes into contact with the lever.
, 33 and 33' portions also undergo deflection deformation by an angle θ, and a deflection moment is generated. The magnitude of this bending moment increases as the bending compliance of the hinges 32, 32', 33, 33' decreases. That is, hinge 32°32',
33. The smaller the bending compliance of 33°, the more the rotation of the lever 34 is inhibited, and the hinges 32, 32
″, 33. The vertical compliance is small at 33°,
A hinge with a large bending compliance (for example, a flat hinge) is preferred. Furthermore, even if the lever 34 is rotated by the angle θ regarding the first displacement expanding mechanism of the present invention, the bending moment is canceled out due to the structure, and the bending moment I generated within the active columnar body 31 is significantly reduced to almost zero. It has excellent characteristics. That is, since almost no bending deformation occurs in the active columnar body, it is possible to realize a robust first stage displacement expander side.

Regarding the second displacement extension mi, at points p and p', ξ
2, a displacement ξ3 which is further enlarged than ξ2 is given by the shape effect of the convex shell via the hinges 35, 35' as shown by the arrow in the figure. In this case, the hinges 35, 35' must be designed to have high rigidity against vertical displacement in order to effectively transmit the vertical displacement from the lever 34 to the shell. In addition, in order to reduce the size of the low frequency transmitter, the shell itself is 36.36" and the hinge is 35.35".
Since it is necessary to lower the resonant frequency of the system consisting of the At the contact point of the shell and hinge, if the bending compliance of the hinge is designed to be large enough to be flexible against rotation as in the present invention, compared to the case where it is supported by a roll that does not allow rotation, the system consisting of the shell and the hinge will be It has been experimentally found that the resonance frequency is reduced to approximately one-half. Therefore, the convex shell 36.36" is connected directly to the lever 34 without going through the hinge 35.35'.
Compared to a structure in which the transmitter is glued together, the transmitter based on the present invention can be further miniaturized at low frequencies. 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), making it a small device with excellent acoustic radiation ability.

Furthermore, another excellent feature of the underwater ultrasonic low-frequency transmitter according to the present invention is that the displacement of the active columnar body is expanded by n times (n>>]) at the acoustic radiation end. Therefore, the mass of the acoustic radiation end becomes 12 times that of the active columnar body side, making it possible to obtain a small, lightweight, low-frequency transmitter.

The operating principle of the low-frequency ultrasonic transmitter based on the present invention has been explained above, and the acoustic radiation load is defined as the characteristic acoustic impedance (defined as the product of density and sound speed) of 1.5X.
Because the water is 106MKS rayls,
Book 1 - In the transducer, there are various restrictions in order to perform efficient acoustic radiation.

A perspective view is shown in FIG. 2 to clarify the three-dimensional shape of the tree transducer.

The displacement output from the active columnar body is transmitted to the hinge 32,
33 (32°, 33') to the lever 34. In order to efficiently convert the longitudinal vibration energy output from the active columnar body into the rotational energy key of the lever 34, the dimensions of the hinges 32, 33 (32'', 33')
Shape is extremely important. The hinges 32j3 (32', 33'') must effectively transmit the force output from the active columnar body 31 to the lever in the vertical direction, but in this case, the hinges 32, 33<32', 33°) , the larger the vertical stiffness, the better.

Further, when the lever 34 rotates, the hinge flexes and deforms as the lever rotates, and in this case, the smaller the flexural stiffness of the hinge, the easier the lever can rotate.

In other words, the hinges 32, 33 (32", 33') can be said to be better if their longitudinal stiffness is large and their deflection stiffness is small. Ideally, a hinge with a longitudinal stiffness of ω and a deflection stiffness of O is ideal. However, when the width W of the hinge and the height h of the hinge are defined, the greater the width W, the greater the deflection stiffness, but also the greater the longitudinal stiffness.Also, the greater the height l], the greater the deflection stiffness. , both longitudinal stiffness becomes smaller.

A detailed study of energy transfer efficiency reveals that there is an optimum value for the hinge dimensions w and h, and when the value of the dimension ratio h/w is between 1.5 and 4.2, the efficiency can be reduced without much loss. It has been found that energy is transferred from the active column 32 to the lever 34.

The hinge 35 functions to transmit the rotational displacement of the lever 34 to the shell 3G, but when the entire transmitter is immersed in water, the hinge 35 undergoes bending deformation via the shell 36, and the hinge 35
If the strength of No. 5 is insufficient, the water pressure resistance characteristics will deteriorate. On the other hand, as described above, in the case of a rigid structure that does not allow rotation of the lever, it is difficult to miniaturize the transmitter at low frequencies.

As a countermeasure against this, as shown in FIG. 2, the lever 34 is tapered so that the tip of the lever 34 and the shell 36.
It is extremely effective to join them via the hinge 35 so that their bottom surfaces partially or completely overlap. This makes it possible to achieve both improved water pressure resistance and miniaturization at low frequencies.

In addition, the lever 34, the hinges 35, 35', and the shell 36.
It goes without saying that 36'' is acceptable even if it is integrated.

Next, FIG. 3(a) shows the structure of a conhex shell used in a typical flexural I transmitter. The thickness of the seal is the same everywhere. This will be referred to as a uniform shell. Shell short axis 1], long axis a divided by 1)/
a is an important factor that determines the shape of the shell.

1) It is known that when /a is large, the displacement ξ3 of the shell center portion does not become thicker with respect to the output displacement ξ2 of the lever 34, and in order to increase ξ3/ξ2,
The value of b/a must be 0.5 or less.

On the other hand, if 1) /a is made small and the shell is flat,
ξ3/ξ2 can be increased, but 1)/a is 0
．． If it is less than 2, there is a problem that the water pressure resistance deteriorates rapidly. Another problem was that vibration stress was concentrated at the base of the shell during high-power wave transmission.

That is, the uniform shell has various problems such as not being able to obtain a large ratio of ξ3/ξ2, and vibration stress being concentrated at the base of the shell.

Therefore, in the transmitter based on the present invention, as shown in FIG. 3(b), the shell is thickened at the portion where it joins the hinges 35, 35', and the thickness is minimized at the center of the shell. These problems are solved by using non-uniform shells.

FIG. 4 shows, as an example, the vibration displacement distribution of a shell with b/a of 0.35, comparing a uniform shell and a non-uniform shell. In Figure 4, the center of the shell is taken as the origin,
The long sleeve of the shell is taken as the X axis, and the short axis is taken as the Y axis, and the vibration displacement distribution of the shell when the shell is compressed by the displacement ξ2 output from the lever 34 is shown. At this time, the center of the shell thickness is selected as the representative value. The material of the shell is steel alloy.

In FIG. 4, the solid line shows the shell before being deformed, the dashed line shows the vibration displacement distribution of the non-uniform shell, and the dotted line shows the vibration displacement distribution of the conventional uniform shell. This displacement distribution is ξ
2 is plotted assuming a constant displacement, and the actual displacement is magnified 500 times. The value of displacement magnification ξ3/ξ2 for the non-uniform shell is 4.67, and ξ for the uniform shell.
The value of 3/ξ2 is 346, which clearly indicates that the use of a non-uniform shell is more advantageous for acoustic radiation. Furthermore, from the results of experiments and numerical calculations using the finite element method (FEM), it was found that this kind of displacement distribution does not depend on the materials such as iron, aluminium alloy, glass fiber reinforced plastics, and carbon fiber reinforced plastics. . Furthermore, in a nonuniform shell, the maximum thickness/
A material having a minimum thickness ratio of 1.4 to 5.2 can provide particularly effective acoustic radiation.

In the transmitter based on the present invention, the problem is how efficiently the vibration energy of the active columnar body made of piezoelectric ceramic or rare earth magnetostrictive material, which has a much higher specific acoustic impedance than water, can be acoustically radiated into water. This is an important point in ``obtaining a wave device''. The conventional flexural elongation (flexural FIe) shown in Figure 3
In the case of a (xLensional) transmitter, the displacement magnification rate is at most 7 times because it has only the displacement magnification mechanism of the shell itself. However, when actually performing efficient acoustic radiation underwater, such a displacement magnification rate is insufficient.

In the case of this transmitter, as described above, a displacement magnification ratio ξ3/ξ1 which is much larger than that of the bending-extension transmitter can be realized. When performing acoustic radiation underwater, the acoustic radiation surface is subjected to considerable pressure from the loading medium, water. This is the so-called pressure based on acoustic radiation impedance. In this transmitter,
If an extremely large displacement magnification rate ξ3/ξ is achieved, the power to exclude the medium will be insufficient and high power wave transmission will become difficult. As a result of analysis using the finite element method (FEM) and several types of experiments regarding this transmitter, there is an overall optimal value for the displacement magnification rate ξ3/ξ1, which is 10≦ξ3/ξ1≦2.
5, the acoustic impedance matching with water is sufficient,
It was found that high-efficiency transmission over a wide band can be achieved. Note that when ξ and /ξ1 are less than 10, there is no significant difference in performance from the conventional bending-stretch transmitter.

The transmitter according to the present invention has a symmetrical structure, and can radiate sound evenly on the left and right sides. When this transmitter is immersed in water, the shell is deformed by hydrostatic pressure such that it becomes flat, and at this time, the lever 34 is deformed such that it is pressed toward the plane of symmetry. However, with this transmitter, Fl?? between the left and right levers? Water pressure resistance can be easily improved by inserting a P round rod or an acoustic springing material (for example, onion skin paper). In addition, in this transmitter, compressive force is applied to the active columnar bodies 31 made of piezoelectric ceramics or magnetostrictive material due to water pressure, but the material constituting these active columnar bodies 31 has a strength several times higher than the tensile force. Lick with compressive strength strength of
The structure of this transmitter is inherently excellent in water pressure resistance, and it also has the advantage that no water pressure is applied to the active columnar body. The reason for this is that the water pressure applied from the lever 33 to the hinge 35 and from the lever 33'' to the hinge 35' creates tension in the active columnar body 31, and the water pressure applied to the shell 36.
1 does not produce any compressive force, because they cancel each other out.

In addition, one of the other great advantages of this transmitter is that as shown in Fig. 2, the lances 1 to 1 can be accommodated in the inactive columnar bodies 3], 31'' by normal means such as Pol I~. It is possible to realize a transmitter with a built-in transformer.By incorporating a transformer, power can be supplied from the power supply to the transmitter via a cable at low voltage, and its advantages are immeasurable. Note that in the bending/extension transmitter shown in FIG. 6, it is impossible to incorporate a 1-lance due to its structure.

(Example) As an example of the present invention, an underwater ultrasonic transmitter using a convex shell will be described with reference to FIG.

The transmitter using the convex shell shown in FIG. 1 was housed in a rubber boot with a wall thickness of 1.0 cm. At this time, an acoustic decoupling material mainly composed of cork and synthetic rubber is applied to the lever 34 and the housing in order to prevent acoustic coupling between the transmitter and the housing case and to prevent rotational movement of the lever 34. placed between the cases. The convex shell that performs acoustic radiation is a half of an elliptical shell with a ratio of 0.4 of the short axis 2b to the long axis 2a, the length 2a of the long axis of the shell is 50 cyn, and the depth is 4 cyns.
0 cnl, and the thickness is 1.0 cm to 2.0 cm. The lever, hinge and convex shell are all made of high-strength steel. The resonant frequency of the prototype transmitter in the air is 470! lz. A displacement approximately 12 times greater than that of the active columnar body is obtained in the central portion of the convex shell. In addition, piezoelectric ceramic rings polarized in the thickness direction were stacked and tightened with bolts as the active columnar bodies.

Next, this transmitter was placed in a water tank and driven at high power, and the sound pressure at a point 1 m away from the acoustic radiation surface was measured, and it was found to be 1.90 dB re1μ at 400 II z.
A sound pressure of Pa was easily obtained. 6 in transmit voltage sensitivity
The dB specific bandwidth was 32%. The directivity is almost omnidirectional at low frequencies, but as the frequency increases, it becomes almost bidirectional.

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

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the operating principle of the transmitter of the present invention, Fig. 2 is a perspective view of an embodiment of the transmitter of the present invention, and Fig. 3 is an example of a convex shell used in the transmitter of the present invention. Fig. 3(a) is a perspective view of the conventional uniform shell, and Fig. 3(b) is a perspective view of the conventional uniform shell.
Figure 4 shows the non-uniform shell used in this transmitter, Figure 4 does not show the displacement distribution of the convex shell, Figure 5 shows the conventional bent wave transmitter, and Figure 6 shows the conventional bent type transmitter. FIG. 7 is a diagram showing an elliptical shell used in a conventional bending/extension transmitter. In the figure, 10 is a piezoelectric ceramic plate, 11 is a metal plate, 12 is a cavity, 13 is a case, 20.31 is an active columnar body, 21 is an elliptical shell, 31' is an inactive columnar body, 32.32°, 33. 33'', 35.35' are hinges, 36.36'' are FIG. .36; Convex shell Fig. 2 31; Active columnar body 31'; Inactive columnar bodies 32, 32, 33, 33; Hinge 34; Lever 35.35; Hinge 36.36; Convex shell 37; Transformer Fig. 3 (a) (b) Fig. 4, Fig. 5, Fig. 10; Piezoelectric ceramic plate 11; Metal plate 12; Cavity 13; Case Fig. 6, 20; Active columnar body 21; Oval shell

Claims (1)

[Claims] 1. An active columnar body made of piezoelectric ceramic or magnetostrictive material, an inactive columnar body placed on both sides of the active columnar body, and each of the active columnar body and the inactive columnar body. A low-frequency underwater ultrasonic transmitter comprising: a lever connected to an end of the lever via a hinge; and a convex shell connected to each of the two levers via a hinge. 2. In the low-frequency underwater ultrasonic transmitter according to claim 1, the shape of the hinge provided at each end of the active columnar body and the inactive columnar body is such that the height of the hinge is equal to the width of the hinge. A low frequency underwater ultrasonic transmitter characterized in that the value divided by is 1.5 to 4.2. 3. In the hinge portion provided at the tip of the lever of the low-frequency underwater ultrasonic transmitter according to claim 1 or 2, the tip of the lever and the bottom surface of the convex shell partially or completely overlap. A low-frequency underwater ultrasonic transmitter characterized by being joined via a hinge. 4. The convex shell portion of the low-frequency underwater ultrasonic transmitter according to claim 1, 2, or 3 has a shape that is gradually thinner from the bottom to the center, and the ratio of maximum thickness / minimum thickness is A low frequency underwater ultrasonic transmitter characterized in that the frequency is 1.4 to 5.2. 5. Claims 1, 2, 3, or 4
A low frequency underwater ultrasonic transmitter according to item 1, characterized in that a round rod or an acoustic decoupling material is inserted between the two levers. 6. In the low frequency underwater ultrasonic transmitter according to claim 1, 2, 3, 4 or 5,
A low-frequency underwater ultrasonic transmitter characterized by having a transformer attached to an inactive columnar body.