JP2985509B2 - Low frequency underwater transmitter - Google Patents

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 Low-frequency ultrasonic waves in water have less propagation loss than high-frequency ultrasonic waves and can reach farther away, so low-frequency ultrasonic waves are used in sonar, marine resource exploration, ocean current research, and other fields. Using ultrasonic waves has many advantages. 2. Description of the Related Art Conventionally, an electrokinetic transmitter and a piezoelectric transmitter have been known as transmitters that emit strong ultrasonic waves in water. Electrokinetic transmitters can take large displacements,
It is extremely difficult to obtain a small transducer at low frequencies due to the small power generated. In addition, the piezoelectric type transmitter uses a lead zirconate titanate-based piezoelectric ceramic as an electromechanical energy conversion material. The piezoelectric ceramic itself has an acoustic impedance of about 20 times or more as large as that of water, and thus has an advantage that the generated force is extremely large. However, there is a disadvantage that it is not possible to take a displacement necessary for removing a medium in acoustic radiation. Considering that the acoustic radiation impedance per unit radiation area becomes extremely small as the frequency decreases, in order to perform efficient acoustic radiation at low frequencies, the acoustic radiation is performed by further expanding the displacement of the piezoelectric ceramic. 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. Acoustic Soc. Am., Vol. 68,
No. 4, pp 1046-1052 (1980.1
As described in (0)), a flexural elongation transmitter using an elliptical shell shown in FIG. 5 is known.

[0004]

The elliptical shell 21 of the bending / extending transmitter shown in FIG. 5 is indicated by an arrow in the drawing when the active columnar body 20 made of a piezoelectric ceramic expands and displaces in the longitudinal direction. As described above, this is a transmitter having a kind of displacement enlarging mechanism that contracts at a multiple of the 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 flexural extension transmitter is substantially higher than that of the elliptical shell 21 because the stiffness of the active columnar body 20 is considerably higher than that of the shell. The value is twice or more the resonance frequency. That is, without considerably lowering the resonance frequency of the elliptical shell 21 having a certain dimension with respect to the bending-elongation mode, the low-frequency miniaturization of the bending-elongation transmitter cannot be achieved. It is desired to further reduce its own resonance frequency. However, it is extremely difficult to reduce the size of the elliptical shell itself at low frequencies for the reasons described below.

To explain the operation of the elliptical shell,
The major axis of the elliptical shell is x-axis, the minor axis is y-axis, and the depth direction is z
A quarter of the elliptical shell, corresponding to the axis, is shown in FIG. The point at which the center of the thickness of the elliptical shell intersects the x axis is (a, 0), and the point at which 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 is extended and the point P is displaced by ｘ in the + x direction, the displacement magnifying mechanism of the elliptical shell itself causes a displacement several times as large as ξ in the −y direction at the point Q. The medium will be drawn in as a whole shell. On the other hand, when the active columnar body is contracted, the shell as a whole acts in a 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 rotational displacement about the z-axis is zero only by the translational displacement as if the roller were worn. Therefore, as much as the rotation about the z-axis is not permitted, the constraint on the movement of the shell is increased, and the resonance frequency of the shell is increased. The flexural elongation transmitter has been extremely difficult to miniaturize at a low frequency because the resonance frequency of the elliptical shell itself is unlikely to decrease for the reasons described above.

On the other hand, when the shape of the elliptical shell is changed, b
As / a increases and approaches a circle, the shell resonance frequency certainly decreases. However, in this case, the larger the value of b / a, the more the displacement enlargement ratio is reduced as compared with the decrease in the frequency. Therefore, there is no merit of reducing the size by changing the shape. Also, it is recognized that the resonance frequency is reduced when the thickness of the shell is reduced. However, in this case, not only the medium excluding ability of the shell is reduced, but also the water pressure resistance is remarkably deteriorated.

Therefore, it is easy to consider a structure as shown in FIG. 2 as a small transmitter that overcomes such disadvantages of the conventional transducer. In the transmitter shown in FIG. 2, a disk-shaped vibrator in which an active disk 40 made of a piezoelectric ceramic is fitted in a metal disk 41 having a depressed main surface is used.
It has a structure in which a plurality of sheets are prepared and they are bolted together so that the active disks 40 are on the outer surface sides. As a driving principle of the transmitter, a radial spreading vibration in which the active disk body 40 is displaced in the radial direction is used, and the vibration is converted into a disk-shaped vibration composed of the active disk body 40 and the metal disk 41 into which the active disk body 40 is fitted. The system is designed to increase displacement by converting it into bending vibration of the body. This transmitter structure has an advantage that it is easy to reduce the thickness and weight without deteriorating the water pressure resistance. However, since the periphery of the metal disk is fixed, there is a limit in reducing the frequency and increasing the power, and further improvement in reducing the frequency and increasing the power is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide an omnidirectional low-frequency transmitter which is small and lightweight and has excellent high power characteristics.

[0009]

According to the present invention, there is provided a transmitter comprising two disk-shaped vibrators each including an active disk using a circular piezoelectric ceramic and a disk into which the active disk is fitted. A low-frequency underwater transmitter characterized in that active discs are connected to each other on the outer surface side via a ring made of a high-strength material.

[0010]

The transmitter according to the present invention has the above-mentioned structure to solve the problems of the prior art. This will be described below with reference to the drawings.

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

[0012] When the active disk body is displaced in the radial direction by xi] _1, the bonding portion or O-ring portion of the two metal discs becomes a support end, the active disk body and the metal disc integral system only xi] ₂ Displaced in the direction of the central axis. 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 takes bending vibration.

In the transmitter according to the present invention, an O-ring 32 made of a high-strength material is sandwiched between two metal disks so that the angular displacement of the peripheral portion of the metal disk is close to free (pin end support). Since the active disk body and the metal disk vibrate integrally, a thin and light weight, low frequency, and high power can be easily achieved. FIGS. 3A and 3B show the O-ring 32.
Shows the vibration modes with and without (axial symmetry,
This is shown by a half model. ). 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 displacements 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 can
This is performed in a state close to the in-end support, and the frequency can be reduced. Further, as shown in FIG. 3, θ _a > θ _b
In addition, since the amplitude of the vibration mode can be increased, that is, the amount of removed medium can be increased, and a large sound pressure can be generated.

Although the active disk used in the transmitter of the present invention tends to be slightly fragile with respect to tensile stress, in the present invention, as shown in FIG. The active disc 30 is fitted to the outer surface, and the diameter of the active disc 30 is determined to be about 60 to 75% of the diameter of the entire transmitter by stress analysis by the finite element method. , Only compressive stress can be applied. Therefore, the low-frequency underwater transmitter according to the present invention is excellent in water pressure resistance and has a depth (500 m depth).
Degree) can be used. In the present invention, the outer shape of the active body is preferably a disk in terms of excellent simplicity, but is not limited thereto. For example, 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 in order to positively utilize the longitudinal effect longitudinal vibration of the piezoelectric ceramic.

The invention of claim 3 will be described in detail with reference to FIGS. 4 (a) and 4 (b). 4A and 4B, reference numeral 50 denotes 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 the adjacent segments are opposite. By inputting a voltage along the polarization direction,
The longitudinal effect longitudinal vibration (33 mode) is excited.
The active segments are bonded to the inside of the depression of the metal disk 51 made of a material having high mechanical strength such as high-tensile steel by a strong adhesive. FIG. 4 (a),
In (b), two metal disks into which such active segment groups are fitted are prepared, and are joined by a spring band 55 via an O-ring 52 made of a high-strength material. Further, the outer periphery is protected via a protection plate 53.
It is molded with urethane resin 54 or the like.

The transmitter of the present invention is characterized in that a longitudinal effect longitudinal vibration (33 modes) having high conversion efficiency is positively used. Therefore, the active body portion formed by the piezoelectric ceramic is formed by radially polarizing segments polarized in the radial direction from the center, and a voltage is radially input to each segment. At this time, the input voltage depends on the power consumption and the electric field strength of the piezoelectric ceramic.
It can be adjusted by making the distance between the electrodes of each segment appropriate. It is also characterized in that each segment is pressure-compensated by a bolt 57 at the center of the 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 30 is set to 104.
mmφ, thickness 7 mm, diameter of the metal disk 31 is 160
mmφ, 14 mm where the thickness is thick, 7 where the thickness is thin
mm, the inner diameter of the insertion O-ring 32 is 140 mmφ, and the thickness is 8
mmφ, the gap between the two vibrators was designed to be 4 mm.
Therefore, the overall size of the transmitter before molding is 160
mmφ × 32 mm. The active disk 30 is made of a lead zirconate titanate-based piezoelectric ceramic, the metal disk 31 is made of an aluminum alloy A7075-T6, and the insertion O-ring 32 is made of maraging steel. The resonance frequency of this transmitter in air is 3125 Hz. With respect to the radial displacement of the active disk, about 1 unit on the central part of the system in which the active disk and the metal disk are integrated, that is, on the central axis of the transmitter.
7.1 times the displacement is obtained.

Next, according to the characteristics of this transmitter in a water tank, the sound pressure at a point 1 m away from the acoustic radiation surface is 2500 Hz.
, A sound pressure of 202 dBre1 μPa is obtained. The Q value in water can be as low as about 5.1. The directivity is almost omnidirectional.

[0019]

Embodiment 2 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 thickness is 14 mm when the thickness is large, 7 mm when the thickness is small, the inner diameter of the insertion ring 52 is 180 mmφ, and the thickness is 8 mmφ. The gap between the two vibrators was designed to be 4 mm. Therefore, the overall size of the transmitter is about 200 mmφ × 32 mm. In FIG. 1, the outer shape of the active segment group 50 is configured as an octagon, but is not necessarily limited to an octagon and may be a regular polygon. The active segment group 50 employs a lead zircon titanate piezoelectric ceramic, the metal disk 51 employs an aluminum alloy A7075-T6, and the insertion ring 52 employs maraging steel. The resonant frequency of this transmitter in air is 2
579 Hz.

Next, regarding the characteristics of this transmitter in a 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 non-directional.

[0021]

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

[Brief description of the drawings]

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

FIG. 2 is a partial cross-sectional perspective view of a basic structure of a transmitter in which a conventional structure is improved.

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

FIG. 4 is a 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 flexural extension transmitter.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 20 Active columnar body 21 Oval shell 30 Active disk body 31 Metal disk 32 High-strength material O-ring 33 Protective plate 34 Urethane resin 35 Spring band 36 Bolt 40 Active disk body 41 Metal disk 42 Bolt 50 Active disk body 51 Metal disk 52 High-strength material O-ring 53 Protective plate 54 Urethane resin 55 Spring band 56 Bolt 57 Pressure compensating bolt 58 Tapered spacer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-122400 (JP, A) JP-A-55-74189 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04R 1/44 330 H04R 17/00 332

Claims (3)

(57) [Claims] 1. An active disk using a circular piezoelectric ceramic and two disk-shaped vibrators each including a disk into which the active disk is fitted are connected to a pin end via a ring made of a high-strength material. A low-frequency underwater transmitter characterized by being supported and coupled such that the active disks are on the outer surface side of each other. 2. The low-frequency underwater transmitter according to claim 1, wherein the two disk-shaped vibrators are joined at their outer peripheral portions. 3. A disk-shaped vibrator in which a large number of piezoelectric ceramic segments as active bodies are radially arranged from the center to the outer periphery in the concave portion of a disk having a regular polygonal concave portion formed on the main surface. The low-frequency underwater transmitter according to claim 1, wherein the transmitter is a body.