CN103646642B - Many sap cavities broad band low frequency underwater acoustic transducer - Google Patents

Abstract

The invention provides a multi-cavity low-frequency broadband underwater acoustic transducer. It includes a Janus-type composite rod transducer composed of an active driver and two horn-shaped radiation heads installed at both ends of the active driver through prestressed bolts. It also includes two cylindrical shells, and the two cylindrical shells are respectively covered in Outside the two trumpet-shaped radiating heads, the middle part of the cylindrical shell and the Janus-type composite rod transducer forms an inner Helmholtz cavity, and the cylindrical shell and the outer side of the Janus-type composite rod transducer form two symmetrical external Helmholtz cavities . The invention utilizes the low-frequency liquid cavity resonance of the Helmholtz resonance cavity and the longitudinal resonance of the Janus transducer to form a broadband emission effect, so that the transducer has the characteristics of low frequency, small volume, broadband, high power, and deep-water operation, and can be applied to low-frequency active sonar , long-distance underwater acoustic communication, low-frequency underwater acoustic experiment, ocean acoustic tomography, seabed geological and landform exploration and other fields.

Description

Multi-cavity low-frequency broadband underwater acoustic transducer

technical field

The invention relates to an underwater acoustic transducer, in particular to an underwater acoustic transducer with multiple liquid cavities.

Background technique

Sound waves are the only energy carrier known to man so far that can be transmitted over long distances in seawater. Acoustic methods are the main means of exploring the ocean, developing the ocean, and conducting underwater confrontation. Underwater target detection, positioning, identification, navigation, communication, offshore oil and gas resource exploration, seabed geological and geomorphic imaging, research and measurement of hydrological conditions in sea areas, sound waves and sound wave generators, namely underwater acoustic transducers, all play a pivotal role.

In the application field of underwater acoustic transducers, a single transmitting transducer often cannot meet the requirements of directivity, transmitting sound power and information processing, etc., and often needs to be composed of multiple transducers to form a matrix of various shapes. Task. These arrays are usually fixed on ships or work in a towed manner, so they are limited by the installation platform. In order to facilitate the arrangement and installation, the volume and weight of the transmitting transducer element must be greatly reduced.

However, there is a theoretical contradiction between the small size of the underwater acoustic transducer and the low-frequency, high-power emission. For example, in order to improve the emission efficiency and radiation power, the transducer usually works in a resonant state, and the size of the classic longitudinal vibration transducer is proportional to the wavelength of the radiated sound wave, that is, the lower the operating frequency, the smaller the size of the transducer. The larger the volume, the greater the weight. In addition, the radiation sound power of the low-frequency transducer is proportional to the square of the frequency and radiation area, which means that the radiation frequency or radiation area is reduced by 10 times, and the radiation sound power will be reduced by 100 times. Therefore, while reducing the frequency while keeping the radiated sound power of the transducer constant or increasing, the vibration velocity of the radiating surface must be greatly increased to obtain sufficient volume velocity, and due to the power of the drive module and the transducer Due to the limitation of its own mechanical strength, it is often difficult to achieve low-frequency high-power transmission by greatly increasing the vibration velocity of the radiation surface.

Therefore, reducing the operating frequency and realizing a small size are a pair of contradictions; increasing the radiated sound power and reducing the frequency are also a pair of contradictions.

At present, the main methods to solve the above contradictions are as follows:

One is to replace the traditional longitudinal vibration mode with the bending vibration mode to reduce the resonance frequency of the structure. Typical representatives are seven types of flexural transducers, among which type IV flexural transducers are the most common. In addition, there is also a non-resonant transducer of the electric (magnetic) type to achieve ultra-low frequency broadband transmission. However, the sound power radiated by this kind of transducer is small, the electroacoustic conversion efficiency is low, the structural design and driver are very demanding when transmitting high power, and the nonlinear effect is obvious.

The second is to use new energy-transforming materials to replace traditional piezoelectric ceramic materials. At present, emerging new transducer materials include rare earth giant magnetostrictive materials such as Terfenol-D and Gafenol, and relaxor ferroelectric single crystal materials such as lead magnesium niobate titanate (PMN-PT) and lead niobate zincate titanate (PZN-PT), etc. These materials have greater flexibility, greater strain capacity and high electromechanical coupling coefficient, and are very suitable for making low-frequency and high-power underwater acoustic transducers. device.

The third is to adopt the Helmholtz structure. The Helmholtz resonant cavity is one of the main ways to obtain low-frequency and very low-frequency vibrations with a small volume. In water, the Helmholtz cavity is filled with water to form a liquid cavity. The working depth of this type of transducer is not limited by the structure, and the electromechanical coupling coefficient at the resonance of the liquid cavity is high, which can radiate relatively large acoustic power. The disadvantage is that the Q value is high, and the bandwidth of the liquid cavity resonance is narrow, which is not conducive to forming the broadband emission required in the field of underwater acoustic communication. However, if the liquid cavity resonance can be coupled with other structural vibration modes, and the shape, size, boundary conditions, and additional fluid impedance of the cavity can be optimized at the same time, it is expected to expand the working frequency band of the transducer and design a small-volume, Low-frequency, broadband, high-power, deep-water underwater acoustic transducer.

Contents of the invention

The purpose of the present invention is to provide a multi-cavity low-frequency broadband underwater acoustic transducer with the characteristics of low frequency, small volume, broadband, high power and deep water operation.

The object of the present invention is achieved in that it comprises a Janus (Jenus) type composite rod transducer composed of an active driver and two horn-shaped radiation heads installed at the two ends of the active driver through prestressed bolts, and also includes Two cylindrical shells, the two cylindrical shells are respectively covered outside the two horn-shaped radiation heads, the middle part of the cylindrical shell and the Janus type composite rod transducer constitutes the internal Helmholtz cavity, which is the inner liquid cavity, and the cylindrical shell and the outside of the Janus-type composite rod transducer form two symmetrical external Helmholtz cavities, which are external liquid cavities.

The present invention may also include:

1. The active driver includes two, the prestressed bolts also have two, and also includes an intermediate mass block, the intermediate mass block is cylindrical and has a threaded through hole in the center, and the ends of the two prestressed bolts are screwed on the In the threaded through holes, two active drivers and two horn-shaped radiating heads are mounted on both sides of the intermediate mass by two prestressed bolts.

2. A radial threaded hole is set on the intermediate mass, and one end of the support rod is installed in the radial threaded hole. The two cylindrical shells are directly connected to the support beam, and the other end of the support rod is connected to the support beam.

3. The active driver is a piezoelectric crystal stack, and the piezoelectric crystal stack is formed by bonding n pieces of piezoelectric ceramic discs, n is an even number ≥ 2, and the piezoelectric ceramic discs are polarized along the thickness direction. Electrode sheets are arranged between the ceramic discs.

4. The active driver is a round rod made of rare earth giant magnetostrictive material, a group of excitation coils are wound around the round rod, and the excitation coil is enclosed in a closed magnetic circuit made of high magnetic permeability material.

The invention provides an underwater acoustic transducer composed of a Janus composite rod transducer and a plurality of Helmholtz resonance cavities. The low-frequency liquid cavity resonance of the Helmholtz resonant cavity and the longitudinal resonance of the Janus transducer are used to form a broadband emission effect, so that the transducer has the characteristics of low frequency, small size, broadband, high power, and deep-water operation.

The invention overcomes the disadvantage that traditional composite rod transducers are difficult to realize small-sized low-frequency emission, and simultaneously utilizes the advantages of high electromechanical coupling coefficient of longitudinal vibration mode, high emission efficiency and high radiation sound power.

The invention overcomes the shortcomings of the traditional Helmholtz resonator, such as narrow emission response bandwidth, which is not conducive to realizing broadband emission, and utilizes the advantages of low resonant frequency and high sound source level of liquid cavity resonance.

In the present invention, a pair of external liquid chambers are added at both ends of the Janus-Helmholtz underwater acoustic transducer, and the liquid chamber is used to generate high-frequency liquid chamber resonance, which expands the upper limit of the working frequency band of the Janus-Helmholtz underwater acoustic transducer, which is called multiple Liquid cavity Janus-Helmholtz hydroacoustic transducer.

The invention can be applied to the fields of low-frequency active sonar, long-distance underwater acoustic communication, low-frequency underwater acoustic experiment, ocean acoustic tomography, seabed geological and landform exploration and the like.

Description of drawings

Fig. 1 is a schematic diagram of the extended working frequency band of the multi-cavity Janus-Helmholtz underwater acoustic transducer in the present invention.

Fig. 2 is a sectional view of the multi-cavity Janus-Helmholtz underwater acoustic transducer in the present invention.

Fig. 3 is a schematic diagram of a multi-chamber Janus-Helmholtz underwater acoustic transducer with a shell supporting device in the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

In conjunction with Fig. 2, the multi-cavity Janus-Helmholtz underwater acoustic transducer provided by the first embodiment of the present invention includes a Janus-type composite rod transducer and two cylindrical shells 5; the Janus-type composite rod transducer It consists of an intermediate mass 1, two piezoelectric crystal stacks 2, two horn-shaped radiation heads 4 and two prestressed bolts 3, each crystal stack consists of n pieces (n is an even number ≥ 2) of piezoelectric ceramic circles The sheets are glued together. The piezoelectric ceramic discs are polarized along the thickness direction, and electrode sheets can be arranged between every two ceramic discs. The intermediate mass 1 , the piezoelectric crystal stack 2 and the trumpet-shaped radiation head 4 are connected together in sequence, and the piezoelectric crystal stack 2 is prestressed by pressing the prestressed bolt 3 .

The structure of this embodiment is an axisymmetric structure, and at the center of the intermediate mass 1, it is symmetrical with respect to a plane perpendicular to the axis of symmetry; the intermediate mass 1 is centered, with piezoelectric crystal stacks 2 on both sides, and horn-shaped radiation Head 4, the side of the smallest outer diameter of the horn-shaped radiation head 4 is bonded to one side of the piezoelectric crystal stack 2, and the prestressed bolt 3 is inserted through the central hole of the horn-shaped radiation head 4, passing through the piezoelectric crystal stack 2, and the end The thread and the thread of the intermediate mass 1 are tightened to form a Janus-type composite rod transducer; the horn-shaped radiation head 4 is covered with a cylindrical shell 5, and the middle part of the cylindrical shell 5 and the Janus-type composite rod transducer constitutes the inner Helmholtz The cavity is called the inner liquid cavity, and the outer side of the cylindrical shell 5 and the Janus type composite rod transducer forms two symmetrical outer Helmholtz cavities, which are called the outer liquid cavity.

There may be two piezoelectric crystal stacks 2 in this embodiment, and there may be two corresponding prestressed bolts 3 , and each crystal stack is formed by bonding n pieces (n is an even number ≥ 2) of piezoelectric ceramic discs. The piezoelectric ceramic discs are polarized along the thickness direction, and the polarization directions of every two adjacent piezoelectric ceramic discs are opposite. Electrode sheets can be arranged between the ceramic discs, and the piezoelectric ceramic discs are connected in parallel on the circuit.

There may be only one piezoelectric crystal stack 2 in this embodiment. When there is only one piezoelectric crystal stack 2, there is no intermediate mass 1. There is only one prestressed bolt 3, which runs through the piezoelectric crystal stack 2 and the horn-shaped radiation head 4, and one end is tightened by a nut at the end face of the horn-shaped radiation head.

The piezoelectric crystal stack 2 in this embodiment can also be replaced by round rods made of rare earth giant magnetostrictive materials, and the round rods can be one group or two groups. A set of exciting coils is wound around the periphery of each set of round rods, and the coils are enclosed in a closed magnetic circuit made of high-permeability materials such as pure iron.

In conjunction with Fig. 3, another embodiment of the present invention is based on the previous embodiment, on which radial threaded holes are set on the intermediate mass 2, and also includes a support rod 7 and a support beam 8, and the support rod 7 and the support beam 8 can be multiple groups, and the quantity and size should ensure the support strength without affecting the radiation of the inner liquid cavity. One end of the support rod is installed in the radial threaded hole, and the two cylindrical shells are directly connected with the support beam. The other end of the support rod One end is connected to the support beam.

In the above-mentioned technical solution, a through hole is provided in the center of the horn-shaped radiation head 4 for the passage of prestressed bolts, and the outer diameter of the smallest outer diameter end is the same as the outer diameter of the piezoelectric crystal stack 2 .

In conjunction with FIG. 1 , a schematic diagram of the multi-cavity Janus-Helmholtz underwater acoustic transducer in the present invention to expand the working frequency band. The dotted line shows the frequency response curve of the Janus-Helmholtz underwater acoustic transducer, which has two peaks produced by the resonance of the inner liquid cavity and the longitudinal resonance of the Janus transducer; the solid line shows the multi-cavity Janus-Helmholtz water The frequency response curve of the acoustic transducer, which has three peaks produced by the resonance of the inner liquid cavity, the longitudinal resonance of the Janus transducer, and the resonance of the outer liquid cavity. According to the phase relationship of the sound pressure generated by the three vibrations on the sound axis, the resonant frequency of the external liquid chamber is generally set at a high frequency that is greater than the longitudinal resonant frequency of the Janus transducer.

Concrete implementation process of the present invention comprises:

The intermediate mass 1 is processed into a cylindrical shape from a metal material, and a threaded through hole is provided in the center for installing a prestressing bolt 3 . In order to facilitate the installation of the supporting devices 7 and 8 of the cylindrical shell 5 , radial threaded holes can be arranged at equal intervals along the circumferential direction of the intermediate mass 1 .

Each crystal stack is formed by bonding n pieces (n is an even number ≥ 2) of piezoelectric ceramic discs, and the polarization direction of each adjacent two piezoelectric ceramic discs is opposite to ensure the polarity of the two end faces of the entire crystal stack. The polarity is negative. Electrode sheets can be arranged between the piezoelectric ceramic discs, and the piezoelectric ceramic sheets are connected in parallel on the circuit.

The horn-shaped radiation head 4 is made of light metal such as aluminum alloy, and the outer diameter of the smallest outer diameter end is the same as that of the piezoelectric crystal stack 2 .

Set the intermediate mass 1, a piezoelectric crystal stack 2, and a trumpet-shaped radiation head 4 in order, put them into the prestressed fixture and clamp them, penetrate the bolts 3 and tighten them to form a composite rod transducer, and then loosen the fixture and turn it upside down In the direction of the composite rod transducer, another piezoelectric crystal stack 2 and horn-shaped radiation head 4 are arranged in sequence, the clamp is clamped, and another prestressed bolt 3 is inserted and tightened to make a Janus type composite rod transducer.

The cylindrical shell 5 is set on the outside of the horn-shaped radiation head 3, and the cylindrical shell 5 and the Janus-type composite rod transducer constitute an inner liquid cavity, two outer liquid cavities, and a total of three Helmholtz cavities.

A pluggable or threaded underwater connector is drawn out from the intermediate mass 1 to connect with the transmission cable. In order to achieve watertightness, a polyurethane watertight layer is coated on the periphery of the two piezoelectric crystal stacks 2, and the polyurethane watertight layer can also be replaced by other sealing materials such as epoxy resin layer.

When the transducer is working, an alternating electric field is applied to the piezoelectric crystal stack 2, and the piezoelectric ceramic wafer produces stretching vibration in the thickness direction under the excitation of the alternating electric field, which is reflected in the entire crystal stack as longitudinal stretching vibration. When the frequency of the variable signal reaches the longitudinal resonance frequency of the Janus type composite rod transducer, the frequency response curve in water has a maximum value. When the Janus-type composite rod transducer performs stretching vibration, the fluid in the inner and outer liquid chambers is excited to generate liquid chamber vibration. At the resonant frequency of the inner and outer liquid chambers, the frequency response curves in the water respectively appear maximum.

Referring to FIG. 3 , in the actual application of the underwater acoustic transducer, a support structure of a cylindrical shell 5 needs to be provided. The support structure includes support rods 7 and support beams 8 . One end of the support rod 7 is connected to the intermediate mass 1 , and the other end is connected to the support beam 8 . Both ends of the supporting beam 8 are respectively connected to the cylindrical shell 5 by bolts. The support rods 7 and the support beams 8 can be in multiple groups, and the quantity and size should ensure the support strength without affecting the radiation of the inner liquid cavity.

Finally, it should be noted that the above examples are only used to illustrate the technical solution of the present invention and not to limit. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent replacements to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all should be included in the scope of the present invention. within the scope of the claim.

Claims (4)

1. the underwater acoustic transducer of sap cavity broad band low frequency more than a kind, comprise one by active drive, the Janus type composite bar energy converter of two tubaeform radiation head compositions at active drive two ends is installed on by pre-stressed bolt, it is characterized in that: also comprise two cylindrical shells, two cylindrical shells cover on outside two tubaeform radiation heads respectively, the center section of cylindrical shell and Janus type composite bar energy converter forms inner Helmholtz cavity, for interior sap cavity, the outside of cylindrical shell and Janus type composite bar energy converter forms two symmetrical outside Helmholtz cavitys, for outer sap cavity,

Described active drive comprises two, described pre-stressed bolt also has two, also comprise intermediate mass block, intermediate mass block is that cylindrical, center is provided with tapped through hole, the end thread of two pre-stressed bolts is tightened against in tapped through hole, and two active drive and two tubaeform radiation heads are arranged on the both sides of intermediate mass block by two pre-stressed bolts.

2. many sap cavities broad band low frequency underwater acoustic transducer according to claim 1, it is characterized in that: above intermediate mass block, radial screw bore is set, one end of support bar is arranged in radial screw bore, and two cylindrical shells are directly connected with supporting traverse, and the other end of support bar is connected with supporting traverse.

3. many sap cavities broad band low frequency underwater acoustic transducer according to claim 1 and 2, it is characterized in that: described active drive is stack of piezo crystals, stack of piezo crystals forms by n sheet piezoelectric ceramic wafer is bonding, n is the even number of >=2, piezoelectric ceramic wafer through-thickness polarizes, and is provided with electrode slice between every two panels ceramic disks.

4. many sap cavities broad band low frequency underwater acoustic transducer according to claim 1 and 2, it is characterized in that: described active drive is the pole that rare earth ultra-magnetostriction material is made, pole periphery is wound around one group of drive coil, and drive coil is enclosed in the closed magnetic circuit that high-permeability material makes.