JPH05344582A - Low frequency underwater transmitter - Google Patents

Abstract

PURPOSE:To obtain a miniaturized and light-weight low frequency underwater transmitter capable of attaining high power radiation. CONSTITUTION:An active disk body 30 formed by a circular piezo-electric unit polarized in the thickness direction generates diameter expanding vibration by applied voltage and an integrated system consisting of the body 30 and metallic disks 31 generates curvature vibration due to the displacement of the body 30. In order to energize the curvature vibration in a state supporting a pin end as close as possible, an O-ring is inserted into a joint part between the two metallic disks 31. Consequently the drop of frequency and the increment of a volume speed can easily be attained. In addition, the body 30 is arranged on the outer surface side of the disks 31 so that tensile stress is not applied to the body 30 under hydrostatic pressure and the size of the body 30 is designed so that the body 30 is arranged on the inside of a conversion point changing compression stress into tensile stress.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-frequency high-power underwater transmitter used for long-distance sonar, marine resource exploration and the like.

[0002]

2. Description of the Related Art Ultrasonic waves of low frequency in water have less propagation loss than those of high frequency waves and can reach farther. Therefore, low frequency ultrasonic waves are used in fields such as sonar, ocean resource exploration, and ocean current research. The use of ultrasound has a number of advantages. BACKGROUND ART Conventionally, an electrodynamic wave transmitter and a piezoelectric wave transmitter are known as wave transmitters that emit intense ultrasonic waves in water. Although an electrodynamic wave transmitter can take a large displacement,
It is extremely difficult to obtain a small-sized transducer at a low frequency because the generated force is small. Further, the piezoelectric wave transmitter uses a lead zircon titanate-based piezoelectric ceramic as an electromechanical energy conversion material. The piezoelectric ceramic itself has an advantage that the generated force is extremely large because the acoustic impedance is about 20 times or more larger than that of water, but there is a drawback that the displacement necessary for removing the medium cannot be taken in acoustic radiation. Considering that the acoustic radiation impedance per unit radiation area becomes extremely small as the frequency becomes low, in order to perform efficient acoustic radiation at low frequencies, the displacement of the piezoelectric ceramic is further expanded to perform acoustic radiation. There is a need.

Conventionally, as a high power transmitter in a low frequency band (3 kHz or less), for example, a journal of
Acoustic Society of America (J.Acoust.Soc.Am., Vol.68,
No. 4, pp1046-1052 (1980.1
As described in (0)), a bending-extension transmitter using an elliptical shell shown in FIG. 5 is known.

[0004]

In the bending-extension transmitter shown in FIG. 5, the elliptical shell 21 is indicated by an arrow in the figure when the active columnar body 20 made of a piezoelectric ceramic is extended and displaced in the major axis direction. Thus, it is a wave transmitter having a kind of displacement magnifying mechanism that contracts with a multiple displacement of the columnar body 20. (Only a quarter portion of the elliptical shell is indicated by an arrow.) The resonance frequency of such a bending and extending transmitter has a stiffness of the active columnar body 20 that is considerably larger than that of the shell. The value is twice the resonance frequency or more. That is, the low frequency miniaturization of the flexural extension transmitter cannot be achieved without considerably reducing the resonance frequency of the elliptical shell 21 itself having a constant dimension with respect to the flexural extension mode. It is desired to further reduce the resonance frequency of itself. However, it is extremely difficult to miniaturize the low frequency of the elliptical shell itself for the reasons described below.

In order to explain the operation of this elliptical shell,
The major axis of the elliptical shell is the x-axis, the minor axis is the y-axis, and the depth direction is z.
Corresponding to the axis, a quarter of the elliptical shell is shown in FIG. The point where the center of the wall thickness of the elliptical shell intersects the x axis is (a, 0), and the point where it intersects the y axis is (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 the point P by ξ in the + x direction, the displacement magnifying mechanism of the elliptical shell itself causes a displacement of several times ξ in the −y direction at the point Q. The medium as a whole will pull in the medium. On the other hand, when the active columnar body contracts, the shell as a whole works in the direction of eliminating the medium. In this case, the cross section of the elliptical shell cut along the x-axis is parallel to the x-axis,
The translational displacement is zero, and the rotational displacement about the z-axis is zero, as if the roller were worn. Therefore, since the rotation about the z axis is not allowed, the constraint on the movement of the shell is increased and the resonance frequency of the shell is increased. In the flexural extension wave transmitter, the resonance frequency of the elliptical shell itself is difficult to decrease for the above reasons, and it is extremely difficult to downsize the low frequency wave.

On the other hand, when the shape of the elliptical shell is changed, b
The shell resonance frequency surely decreases as / a is increased and approaches a circle. However, in this case, as b / a is increased, the displacement enlargement ratio is significantly reduced as compared with the frequency reduction, and therefore there is no merit of changing the shape and reducing the size. It is also recognized that the resonance frequency is lowered when the thickness of the shell is reduced. However, in this case, there is a drawback in that not only the medium excluding ability of the shell is lowered but also the water pressure resistance characteristic is significantly deteriorated.

Therefore, it is easy to consider the structure shown in FIG. 2 as a small-sized transmitter that overcomes the drawbacks of the conventional transducer. In the wave transmitter shown in FIG. 2, a disc-shaped vibrating body in which an active disc body 40 made of a piezoelectric ceramic is fitted in a metal disc 41 having a depressed main surface is used.
A single piece is prepared, and the active disk bodies 40 are bolted together so that they are on the outer surface side of each other. As a driving principle of this wave transmitter, radial expansion vibration in which the active disc body 40 is displaced in the radial direction is used, and the vibration is a disc-shaped vibration composed of the active disc body 40 and a metal disc 41 into which the vibration is carried. The system is designed to expand the displacement by converting it into bending vibration of the body. This wave transmitter structure has an advantage that it can be easily made thin and lightweight without deteriorating the water pressure resistance characteristic. However, since the periphery of the metal disk is fixed, there is a limit to lowering the frequency and increasing the power, and further improvement is required for lowering the frequency and increasing the power.

An object of the present invention is to provide an omnidirectional low frequency transmitter which is compact and lightweight and has excellent high power characteristics.

[0009]

A wave transmitter according to the present invention comprises two disk-shaped vibrating bodies each including an active disk body using a circular piezoelectric ceramic and a disk in which the active disk body is fitted. It is a low-frequency underwater transmitter characterized in that active disk members are connected to each other via a ring made of a high-strength material so that they are on the outer surface side.

[0010]

The wave transmitter according to the present invention has the above-mentioned structure to solve the problems of the prior art. The following is a description with reference to the drawings.

FIG. 1 shows an example of the wave transmitter of the present invention. The operating principle of the transmitter of FIG. 1 will be described in detail. In FIG. 1, reference numeral 30 is an active disk body using a circular piezoelectric ceramic. The active disk body 30 is polarized in the thickness direction, and the radial expansion vibration is excited by inputting a voltage along the polarization direction. In addition, this active disk body is a strong adhesive,
It is bonded inside the recess of the metal disk 31 made of a material having high mechanical strength such as high-strength steel. In Figure 1,
Two metal disks in which such an active disc body is fitted are prepared and joined by a spring band 35 on the end face via an O-ring 32 made of a high-strength material. Further, the outer periphery thereof is molded with urethane resin 34 or the like via a protective plate 33.

When the active disc body is displaced by ξ _{1 in the} radial direction, the joint portion of the two metal discs, that is, the O-ring portion becomes the supporting end, and the system of the active disc body and the metal disc is only ξ _2. Displaces in the central axis direction. At this time, xi] ₂ becomes ξ _2> ξ ₁ have been expanded compared to xi] _1. This is repeated, and the system in which the active disk body and the metal disk are integrated undergoes bending vibration.

In the wave transmitter of the present invention, by sandwiching an O-ring 32 made of a high-strength material between two metal disks, the angular displacement of the metal disk peripheral portion is close to free (pin end support). Since the active disc body and the metal disk vibrate integrally, it is possible to easily reduce the thickness and weight, reduce the frequency, and increase the power. The O-ring 32 is shown in FIGS.
Indicates vibration modes with and without (axial symmetry,
It is shown with a model of one half. ). Note that FIG.
In each of (a) and (b), a solid line shows a structural displacement diagram by modal analysis, a broken line shows a structural prototype diagram, and θ _a and θ _b show angular displacement in each case.
By inserting the O-ring 32, the bending vibration of the system in which the active disk body and the metal disk are integrated causes p
Since it is performed in a state close to the in-end support, the frequency can be lowered. Furthermore, as shown in FIG. 3, θ _a > θ _b
Since the amplitude of the vibration mode can be made large, that is, the amount of excluded medium also becomes large, it is possible to produce a large sound pressure.

Although the active disc body used in the wave transmitter of the present invention tends to be slightly fragile in tensile stress, in the present invention, as shown in FIG. 1, the active disc body 30 is composed of two metal discs. By fitting to the outer surface and determining the diameter of the active disk 30 to be about 60 to 75% of the diameter of the entire transmitter by stress analysis by the finite element method, the active disk 30 is It is possible to apply only compressive stress. Therefore, the low-frequency underwater transmitter according to the present invention is excellent in water pressure resistance and has a deep depth (water depth of 500 m).
It is possible to use the In the present invention, the outer shape of the active body is preferably a disc in terms of excellent simplicity, but the outer shape is not limited to this. For example, in order to positively utilize the longitudinal effect longitudinal vibration of the piezoelectric ceramic, a structure in which a large number of piezoelectric ceramic segments are radially arranged from the center as shown in FIGS. 4A and 4B is also effective.

The invention of claim 3 will be described in detail with reference to FIGS. 4 (a) and 4 (b). In FIGS. 4A and 4B, 50 is a piezoelectric ceramic segment group which is an active body. Each segment is polarized in the radial direction of the transmitter,
Furthermore, the polarization directions of adjacent segments are opposite. By inputting a voltage along the polarization direction,
Vertical effect Vertical vibration (33 mode) is excited.
This active segment group is bonded to the inside of the recess of the metal disk 51 made of a material having high mechanical strength such as high-strength steel by a strong adhesive. FIG. 4 (a),
In (b), two metal disks in which such an active segment group is fitted are prepared and joined by a spring band 55 via an O-ring 52 made of a high-strength material. In addition, the outer periphery of the
It is molded with urethane resin 54 or the like.

The wave transmitter of the present invention is characterized by positively utilizing the longitudinal effect longitudinal vibration (33 mode) having high conversion efficiency. For this reason, the active body portion of the piezoelectric ceramic is formed by radially attaching segments polarized in the radial direction from the center, and a voltage is input to each segment in the radial direction. At this time, the input voltage is a combination of power consumption and electric field strength of the piezoelectric ceramic,
It can be adjusted by making the distance between the electrodes of each segment appropriate. Another feature is that each segment is pressure-compensated by a bolt 57 in the central portion of the wave transmitter via a tapered spacer 58 so that a compressive stress is always applied.

[0017]

[Embodiment 1] An embodiment of the present invention will be described with reference to FIG. In FIG. 1, the diameter of the active disc body 30 is set to 104
mmφ, thickness 7 mm, diameter of metal disk 31 is 160
mmφ, 14 mm thick, 7 thick
mm, the insertion O-ring 32 has an inner diameter of 140 mmφ, and a thickness of 8
mmφ, the gap between the two vibrators was designed to be 4 mm.
Therefore, the size of the whole transmitter is 160 before molding.
It becomes mmφ × 32 mm. A lead zirconate titanate-based piezoelectric ceramic is applied to the active disk body 30, an aluminum alloy A7075-T6 is applied to the metal disk 31, and maraging steel is applied to the insertion O-ring 32. The resonance frequency of this transmitter in air is 3125 Hz. The radial displacement of the active disk body is about 1 at the central part of the system where the active disk body and the metal disk are integrated, that is, on the central axis of the transmitter.
A displacement of 7.1 times is obtained.

Next, according to the characteristics of this transmitter in the water tank, the sound pressure at a point 1 m away from the acoustic radiation surface is 2500 Hz.
At, a sound pressure of 202 dBre 1 μPa is obtained. Also, the Q value in water can be as low as about 5.1. As for directivity, it is almost omnidirectional.

[0019]

Second Embodiment Next, an embodiment of the present invention will be described with reference to FIGS. 4 (a) and 4 (b). In FIG. 4, the diagonal length of the active segment group 50 is 180 mm, the thickness is 7 mm, the diameter of the metal disk 51 is 200 mmφ, the thick portion is 14 mm, the thin portion is 7 mm, the inner diameter of the insertion ring 52 is 180 mmφ, and the thickness is 8 mmφ. The two vibrating body gaps were designed to be 4 mm. Therefore, the overall size of the wave transmitter is about 200 mmφ × 32 mm. Although the active segment group 50 has an octagonal outer shape in FIG. 1, it is not necessarily limited to an octagon and may be a regular polygon. A lead zircon titanate-based piezoelectric ceramic is applied to the active segment group 50, an aluminum alloy A7075-T6 is applied to the metal disk 51, and maraging steel is applied to the insertion ring 52. The resonance frequency of this transmitter in air is 2
It is 579 Hz.

Next, regarding the characteristics of this transmitter in the water tank, the sound pressure at a point 1 m away from the acoustic radiation surface is 20
A sound pressure of 205 dBre1 μPa is obtained at 00 Hz. The Q value in water is about 5.6, and the directivity is almost omnidirectional.

[0021]

As described above, according to the present invention, it is possible to obtain an omnidirectional high-power low-frequency transmitter that is small in size, lightweight, and has excellent acoustic radiation efficiency.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional perspective view showing a structural example of a wave transmitter of the present invention.

FIG. 2 is a partial cross-sectional perspective view of the basic structure of a wave transmitter with an improved conventional structure.

FIG. 3 is a diagram showing vibration modes of the wave transmitter of the present invention.

FIG. 4 is a cross-sectional view and a plan view showing another example of the wave transmitter of the present invention.

FIG. 5 is a cross-sectional view showing a conventional bending and stretching wave transmitter.

FIG. 6 is a cross-sectional view showing an elliptical shell used in a conventional bending and stretching wave transmitter.

[Explanation of symbols]

 20 Active Columnar Body 21 Elliptical Shell 30 Active Disc Body 31 Metal Disc 32 High Strength Material O-ring 33 Protective Plate 34 Urethane Resin 35 Spring Band 36 Bolt 40 Active Disc Body 41 Metal Disc 42 Bolt 50 Active Disc Body 51 Metal Disc 52 High-strength material O-ring 53 Protective plate 54 Urethane resin 55 Spring band 56 Bolt 57 Pressure compensation bolt 58 Tapered spacer

Claims (3)

[Claims] 1. An active disk comprising two disk-shaped vibrating bodies, each of which is composed of an active disk body using a circular piezoelectric ceramic and a disk in which the active disk body is fitted, and a ring made of a high-strength material. A low-frequency underwater transmitter characterized in that the plates are connected to each other on the outer surface side. 2. The low-frequency underwater transmitter according to claim 1, wherein the two disk-shaped vibrating bodies are connected at their outer peripheral portions. 3. A disk-shaped vibrating body in which a large number of piezoelectric ceramic segments that are active bodies are radially arranged from the center to the outer peripheral portion of a disk having a regular polygonal concave portion formed on the main surface of the vibrating body. The low-frequency underwater transmitter according to claim 1, which is a body.