JPH0511719B2 - - Google Patents

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 ultrasound. BACKGROUND ART 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 obtain a small transducer with low frequency because the generated force is small. Furthermore, the piezoelectric wave transmitter uses a zirconate lead titanate piezoelectric ceramic as an electromechanical energy conversion material. Piezoelectric ceramics themselves have an acoustic impedance that is approximately 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 radiation area becomes extremely small as the frequency decreases, in order to achieve efficient acoustic radiation at low frequencies, the displacement of the piezoelectric ceramic must be further expanded to radiate the acoustic radiation. There is a need.

Conventionally, as a high power transmitter in the low frequency band (3KHz or less), for example, I.E.
IEEE Trans.on Ultrasonics Engineering
Ultrasonics Engineering, pp116−124
(1963.11)), there is a bending transmitter that utilizes the bending vibration of a disc as shown in Figure 5, or a bending transmitter using the bending vibration of a disc as shown in Fig. .
Am., vol.68, No.4, pp1046-1052 (1980.10))
As described in , 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 vibrator as a wave transmitter, as is well known. In FIG. 2, 10 is a piezoelectric ceramic plate based on zirconate lead titanate, and 11 is a metal plate made of nickel, stainless steel, etc. These constitute a bimorph vibrator, and the bimorph vibrator itself serves as an acoustic radiator. Further, 12 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 10 piezoelectric ceramic plates, a large number of segmented ceramic plates are bonded to the metal plate 11 in a mosaic style. Therefore, at present, bimorph oscillators have been obtained.
That is, since a large-area ceramic plate cannot be used, the medium exclusion ability as a wave transmitter cannot be said to be sufficient, making it unsuitable for high-power wave transmission. Moreover, even if a piezoelectric ceramic plate with a large area can be obtained, bimorph resonators have a considerable bending compliance due to their structure, and it is undesirable to have such a large medium expulsion ability.

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 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 by several times the displacement. (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 structurally much greater rigidity than a bimorph disk. It is said that this transmitter is superior to the transmitter using the bimorph disk shown in FIG. 2 in transmitting high-power waves.

The resonant frequency of the bending-extension transmitter shown in FIG.
The value is twice or more than the resonant frequency of 1 itself. In other words, the low-frequency miniaturization of the bending-stretch transmitter cannot be achieved without considerably lowering the resonant frequency related to the bending-stretch 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 major 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 z-axis, and a quarter part of the elliptical shell is shown in Figure 7. show. Let the point where the center of the wall thickness of the elliptical shell intersects with the x-axis be (a, 0), and the point where it intersects with the y-axis be (0, b). That is, the major axis of the elliptical shell is a,
Let b be the short axis. Now, when the active columnar body 20 extends and displaces the point P by ξ in the +x direction,
Due to the displacement magnification mechanism of the elliptical shell itself, a displacement several times as large as ξ appears in the -y direction at the Q point, and the entire shell draws 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 taken along the x-axis undergoes only translational displacement parallel to the x-axis, as if wearing a roller, and the rotational displacement around the z-axis is zero. Therefore, as rotation around the z-axis is not allowed, the restriction on the movement of the shell increases, and the resonant frequency of the shell increases. In the bending and stretching transmitter, the resonant frequency of the elliptical shell itself is
Due to the above-mentioned reasons, it is difficult to reduce the frequency, making it extremely difficult to miniaturize low frequencies.

On the other hand, it is of course possible to consider attempts to reduce the size of low frequencies 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. But in this case,
As b/a increases, the displacement magnification rate decreases more significantly than the frequency decrease, so there is no advantage in changing the shape to reduce the size. It is also observed that the resonance frequency decreases when the thickness of the shell is reduced. But in this case,
This has the disadvantage that not only the medium removal 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 these drawbacks of conventional transducers and provide a bidirectional or omnidirectional transmitter that is small in size and has excellent high power characteristics in a low frequency band.

(Means for Solving the Problems) The transmitter of the present invention includes an active columnar body made of piezoelectric ceramic or magnetostrictive material, and inactive columnar states arranged on both sides of the active columnar body. It is 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 low 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 with reference to the drawings.

FIG. 1 shows an example of a transmitter of the present invention using a convex type shell. The operating principle of the transmitter shown in FIG. 1 will be explained in detail. In FIG. 1, numeral 31 is an active columnar body made of piezoelectric ceramic or magnetostrictive material, and longitudinal vibration is excited by inputting voltage or current. This active columnar body 31 has hinges 32,3
2' to the lever 34. In addition, the inactive columnar body 31' is the active columnar body 31'.
are arranged in parallel to each other and connected to the lever 34 via hinges 33, 33'. The system consisting of the hinge and the inactive column 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 column is displaced by ξ ₁ as indicated by the arrow in FIG. 1, the lever 34 rotates inward by an angle θ and an enlarged displacement ξ ₂ occurs at the lever ends P, P'. In this case, by using a material with sufficient rigidity (for example, high-strength stainless steel) for the lever, the lever exhibits a movement almost like a rigid body rotation, and the distance between the hinges 32, 33 or 32', 33' can be reduced by l. ₁ , the distance between the hinge 33 and P or 33' and P' is l ₂ , then the geometrically expanded displacement ξ ₂ is |ξ ₂ |=l ₂ /l ₁ |ξ ₁ | (1) Become. For example, if l ₂ =3l ₁ , a displacement that is three times larger than the displacement ξ ₁ of the active columnar body occurs at points P and P'. At this time, in order to efficiently transmit the longitudinal vibration excited by the active columnar body 31 to the lever 34, the non-active columnar body that functions as the fulcrum needs to have considerably high rigidity with respect to longitudinal vibration as described above. be. Also, when the lever 34 rotates around the lever fulcrums Q and Q' by an angle θ, the hinge 3 that comes into contact with the lever
The portions 2, 32', 33, and 33' are also deflected by an angle θ, and a deflection moment is generated. The magnitude of this bending moment is determined by the hinges 32, 32', 33,
The smaller the deflection compliance of 33', the greater. That is, the smaller the bending compliance of the hinges 32, 32', 33, 33', the more the rotation of the lever 34 is inhibited, and the hinges 32, 32', 33, 33'
33, 33', the vertical compliance is small;
A hinge with a large bending compliance (for example, a flat hinge) is preferable. Moreover, the first aspect of the present invention
Even if the lever 34 rotates by an angle θ with respect to the step displacement magnifying mechanism, the bending moment is canceled out due to the structure, and the bending moment generated within the active columnar body 31 is almost zero, which is a remarkable feature. That is, since almost no bending deformation occurs in the active columnar body, it is possible to realize a robust first stage displacement amplifying mechanism.

Regarding the second stage displacement magnification mechanism, when vertically displacing ξ ₂ at points P and P', due to the shape effect of the convex shell via the hinges 35 and 35', a displacement ξ ₃ that is further expanded than ξ ₂ is generated as shown in the figure. given as indicated by the arrow. In this case, the hinge 35,3
5' effectively transmits the vertical displacement from the lever 34 to the shell, so it is necessary to design it with high rigidity against vertical displacement. Furthermore, in order to downsize the transmitter at low frequencies, it is necessary to lower the resonance frequency of the system consisting of the shells 36, 36' themselves and the hinges 35, 35', so the hinges 35, 35' themselves are flexible against bending deformation. It is more effective to work in That is, Ciel 36,
Compared to the case where 36' is supported by a roll that does not allow rotation at the contact points with hinges 35 and 35', when the bending compliance of the hinge is designed to be flexible to rotation as in accordance with the present invention, It was experimentally revealed that the resonant frequency of a system consisting of a shell and a hinge was reduced to approximately one-half. Therefore, the hinges 35, 35'
Directly connect the convex shell 3 to the lever 34 without going through the
Compared to the configuration in which the 6 and 36' elements are bonded 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), and it can be said that it is small and has 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 multiplied by n (n≫) at the acoustic radiation end.
Since the displacement in 1) can be expanded, the mass of the acoustic radiation end becomes n ² times when converted to 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. Therefore, in this 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 present transducer.

The displacement output from the active columnar body is transmitted to the lever 34 via the hinges 32, 33, 32', 33'.
is transmitted to. In order to efficiently convert the energy of longitudinal vibration output from the active columnar body into the rotational energy of the lever 34, the hinges 32, 3
The dimensions and shapes of 3, 32', and 33' are extremely important. The hinges 32, 33, 32', 33' must effectively transmit the force output from the active column 31 to the lever in the longitudinal direction; , the larger the vertical stiffness, the better.

Furthermore, 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. That is, the hinges 32,3
3, 32', and 33' can be said to be superior as the longitudinal stiffness is greater and the deflection stiffness is smaller. Vertical stiffness is ∞, flexural stiffness is O
It can be said that the hinge is ideal. however,
If the width of the hinge is w and the height of the hinge is h, then the width w
The larger the value, the greater the flexural stiffness, but also the greater the longitudinal stiffness. Furthermore, as the height h increases, both the deflection stiffness and the longitudinal stiffness decrease.

When we investigate the energy transfer efficiency in detail, we find that there is an optimal value for the hinge dimensions w and h.
It has been found that energy can be transmitted from the active columnar body 32 to the lever 34 without significantly reducing efficiency when the value of the size ratio h/w is 1.5 to 4.2.

The hinge 35 controls the rotational displacement of the lever 34 from the shell 3.
However, when the entire transmitter is immersed in water, the hinge 35 is subjected to bending deformation via the shell 36, and if the strength of the hinge 35 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 for this, as shown in FIG. 2, the lever 34 is tapered and the tip of the lever 34 and the bottom surfaces of the shells 36, 36' overlap partially or completely, and are joined via a hinge 35. , is extremely effective. This makes it possible to achieve both improved water pressure resistance and miniaturization at low frequencies.

Note that even if the lever 34, hinges 35, 35', and shells 36, 36' are integrated,
Needless to say, it is inevitable.

Next, FIG. 3a shows the structure of a convex shell used in a normal flextension transmitter. The thickness of the shell is uniform everywhere. this,
Let's call it uniform shell. Short diameter b of the shell,
The value b/a divided by the major axis a is an important factor that determines the shape of the shell.

It is known that when b/a is large, the displacement ξ ₃ of the shell center portion does not become large with respect to the output displacement ξ ₂ of the lever 34, and in order to increase ξ ₃ /ξ ₂ , b/ The value of a must be 0.5 or less.

On the other hand, if b/a is made small and a flat shell is used, ξ ₃ /ξ ₂ can be made large, but b/a
When a is 0.2 or less, there is a problem that water pressure resistance rapidly deteriorates. 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 the inability to obtain a large ratio of ξ ₃ /ξ ₂ and the concentration of vibration stress at the base of the shell.

Therefore, in the transmitter based on the present invention, FIG.
As shown in FIG. 2, by using a non-uniform shell in which the shell is thick at the part where it joins with the hinges 35, 35', and the thickness is minimal at the center of the shell,
These problems have been resolved.

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 FIG. 4, the center of the shell is taken as the origin, the long axis 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 ξ ₂ output from the lever 34. shows. At this time, the center of the thickness of the shell 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 plotted with the displacement of ξ ₂ constant, and the actual displacement is magnified 500 times. Displacement magnification rate of non-uniform shell ξ ₃ /
The value of ξ ₂ is 4.67, and the value of ξ ₃ /ξ ₂ for the uniform shell is 3.46, which clearly shows that the use of a non-uniform shell is more advantageous when performing acoustic radiation. Additionally, the results of experiments and numerical calculations using the finite element method (FEM) revealed that this displacement distribution is almost independent of materials such as iron, aluminum alloys, glass fiber reinforced plastics, and carbon fiber reinforced plastics. Furthermore, the maximum thickness/minimum thickness ratio in non-uniform shells is 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 larger specific acoustic impedance than water, can be acoustically radiated into water. This is an important point in obtaining a high-performance transmitter. The conventional flexural elongation shown in Figure 3
In the case of a Flextensional (Flextional) transmitter, the displacement magnification rate is at most 7 times because it only has 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 mentioned above, a much larger displacement magnification ratio ξ ₃ /ξ ₁ than that of the bending-extension transmitter can be achieved. 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 ratio ξ ₃ /ξ ₁ is achieved, the power to exclude the medium will be insufficient, making high-power wave transmission difficult. As a result of finite element method (FEM) analysis and several types of experiments regarding this transmitter, we found that there is an overall optimal value for the displacement magnification rate ξ ₃ /ξ ₁ , and when 10≦ξ ₃ /ξ ₁ ≦25, the water It was found that the acoustic impedance matching was sufficient and that highly efficient transmission over a wide band could be achieved. Note that when ξ ₃ /ξ ₁ is 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 so as to be pushed toward the plane of symmetry. However, in this transmitter, the water pressure resistance can be easily improved by inserting an FRP round rod or an acoustic decoupling material (for example, onion skin paper) between the left and right levers. In addition, in this transmitter, compressive force is applied to the active columnar bodies 31 made of piezoelectric ceramics or magnetostrictive material by water pressure, but the material making up these active columnar bodies 31 has a strength several times higher than the tensile force. Since the transmitter has a compressive force resistance of , the present wave transmitter has excellent water pressure resistance due to its structure, and also has the advantage that water pressure is not directly applied to the active columnar body. The reason is lever 33
from hinge 35 and lever 33' from hinge 3
The water pressure applied to the 5' portion is applied to the active columnar body 31.
This is because the water pressure applied to the shells 36, 36' creates a compressive force in the active column 31, and these forces cancel each other out.

In addition, as one of the other great merits of this transmitter, as shown in Fig. 2, the inactive columnar body 3
By attaching a transformer to 1 and 31' by a conventional means such as bolts, it is possible to realize a transmitter with a built-in transformer. The built-in transformer allows power to be supplied to the transmitter via the cable at low voltage from the power supply, which has immeasurable advantages. Note that in the bending/extending transmitter shown in FIG. 6, it is impossible to incorporate a transformer due to its structure.

(Embodiment) As an embodiment 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 Figure 1 was housed in a rubber boot with a wall thickness of 1.0 cm. At this time, in order to prevent acoustic coupling between the transmitter and the housing case, and to prevent rotational movement of the lever 34, an acoustic decoupling material mainly composed of cork and synthetic rubber is applied to the lever 34 and the housing case. It is placed between. The convex shell that emits sound is half the size of an elliptical shell with a ratio of the major axis 2a to the minor axis 2b of 0.4.
The length 2a of the long axis of the shell is 50
cm, depth is 40cm, and thickness is 1.0cm~2.0cm
And so. The lever, hinge, and convex shell were all made of high-strength steel. The resonant frequency of the prototype transmitter in the air is 470Hz. The displacement of the central part of the convex shell is about 12 times that of the active columnar body. In addition, as the active columnar body, piezoelectric ceramic rings polarized in the thickness direction were stacked and tightened with bolts.

Next, we put this transmitter in a water tank and drove it with high power, and measured the sound pressure at a point 1m away from the acoustic radiation surface, which was 190 dB at 400 Hz.
A sound pressure of re1μPa was easily obtained. The 6 dB specific bandwidth in terms of transmit voltage sensitivity 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 a transmitter according to an embodiment of the present invention;
The figure is a perspective view of an example of a convex shell used in the transmitter of the present invention, FIG. 3a is a diagram showing a conventional uniform shell, and FIG. 3b is a diagram showing a nonuniform shell used in the present transmitter. , Figure 4 is a diagram showing the displacement distribution of the convex shell, Figure 5 is a diagram showing a conventional bending type transmitter, Figure 6 is a diagram showing a conventional bending extension wave transmitter, and Figure 7 is a diagram showing a conventional bending type transmitter. The figure which shows the elliptical shell used for the bending extension transmitter of. In the figure, 10 is a piezoelectric ceramic plate, 11 is a metal plate, 12 is a cavity, 13 is a case, 20, 3
1 is an active columnar body, 21 is an elliptical shell, 3
1' is an inactive columnar body, 32, 32', 33,
33', 35, 35' are hinges, 36, 36' are convex shells, and 37 is a transformer.

Claims (1)

[Claims] 1. An active columnar body made of piezoelectric ceramic or magnetostrictive material, inactive columnar bodies 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 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 divided value 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 of the convex shell partially or completely overlap. A low-frequency underwater ultrasonic transmitter characterized by being connected 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 gradually becomes thinner from the bottom to the center, and the ratio of maximum thickness/minimum thickness is
A low frequency underwater ultrasonic transmitter characterized by a frequency of 1.4 to 5.2. 5. The low-frequency underwater ultrasonic transmitter according to claim 1, 2, 3, or 4, characterized in that a round rod or an acoustic decoupling material is inserted between the two levers. Low frequency underwater ultrasonic transmitter. 6. A low frequency underwater ultrasonic transmitter according to claim 1, 2, 3, 4 or 5, characterized in that a transformer is attached to an inactive columnar body. Frequency underwater ultrasonic transmitter.