JPH0511710B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an underwater broadband transducer, and more particularly to an underwater broadband transducer that is improved in efficiency, broadband, and compactness and weight.

[Conventional technology]

A vertical oscillator using a normal ceramic oscillator or a Lancivin-type oscillator, which is a ceramic oscillator sandwiched between two metals from the front and back in a sandwich-like manner, is formed with multiple surfaces that take into account the directivity and other operating conditions. Transducers and receivers that are arranged in an array and have their sound wave emitting surfaces glued to acoustic windows are widely used in various fields of operation. In this case, the window through which the radiated sound waves pass, the so-called acoustic window, is usually made of water or seawater and its acoustic impedance.
Acoustic rubber (or PC rubber), which is similar to PC, is usually used. Here, P represents the density and C represents the speed of sound.

In addition, such transducers are often required to have a wide band for operational purposes, but in that case, each longitudinal oscillator that constitutes the transducer is a Languevin type oscillator, and back mass )
A common method is to reduce the mechanical Q (selectivity) by setting the wavelength to 1/4 wavelength. The backmass mentioned here refers to the Languevin type oscillator.
It is well known that this refers to the rear part of the metal mass bonded to the front and rear of the ceramic, and the front mass is called the front mass in contrast to the back mass. Further, in consideration of efficient use of the Languevin type vibrator, a bolt-tightening structure is often used so that pre-stress can be applied to the ceramic.

In any case, this Langillevin type resonator has been attracting attention because of its structural feature that it can easily be applied to a wide band, and as a longitudinal resonator for widening the band, a vertical resonator with a 1/4 wavelength Bactomas is basically used.

FIG. 2 is a sectional view showing an example of a conventional underwater broadband transducer. The conventional underwater wideband transducer shown in FIG.
b, 6-c, and these vertical oscillators have a front mass 6 made of metal, such as a vertical oscillator 6-a.
2 cylindrical ceramic 6 with 1 and back mass 63
2 is bolted to apply prestress. Front mass 6 that serves as a sound wave radiation surface
The end face of the vertical vibrator 6-a is bonded to the acoustic rubber 3, and the sound waves from the back mask 63 are prevented from being radiated by the sound insulating material 4, and the vertical vibrator 6-a is entirely housed in the case 5 along with other vertical vibrators. It has a unique structure.

In order to widen the band of such a transducer, the back mass 63 should be set to λ/4 (λ is the wavelength at the resonant frequency), the mechanical Q should be small, and the whole should be set to λ/2.
make it vibrate. Therefore, the total length of the front mass 61 and the ceramic 62 is also λ/4. The dimensions of the front mass 61 are set in consideration of the conditions under which bending vibration does not occur, and the dimensions of the ceramic 62 are set in consideration of the applied voltage.

Now, the wideband transducer mentioned above is usually the one most often used, but in addition to this, a wideband Attempts have been made to improve the
(Tomomasa Matsuki, Journal of the Institute of Electrical Communication Engineers, Vol. 35, No. 12,
P530-533, December 1952), and recently, a proposal for improving the contents of this document has been published in ``A Study of Broadband Underwater Ultrasonic Transducer'' (Takeshi Inoue et al. , IEICE material US85-22, August 27, 1985). This λ/4 acoustic matching layer has a matching member such as epoxy resin interposed between the vibrator radiation surface and the load medium for generating a second vibration mode, and the vibrator has bandpass characteristics due to multiple vibration modes. The purpose is to increase the bandwidth by adding

[Problem that the invention seeks to solve]

However, the conventional broadband transducer described above has the following problems.

That is, in the case of a transducer in which a required number of Languevin type oscillators are housed in a case, a wide band is ensured by setting the back mass to λ/4. In this case, there is a large difference between the acoustic impedance of the sound wave emitting surface of the vibrator and the acoustic impedance of the acoustic rubber used for the acoustic window, so the basic principle is that the efficiency is high and the band is also narrow. There is a problem, and if you try to widen the band by setting the backmass to λ/4 length under these conditions, the size will become very large, and the weight will also become very large. Superimpose. This means that 3000-3500
Compared to the ceramic part, which has a sound velocity of about m/s,
The sound speed of metals such as aluminum used for normal front mass and back mass is approximately 5000 m/s.
This is a self-evident truth if we further consider the density difference between the two.

On the other hand, in the case of a resonator that uses an acoustic matching layer with a thickness of λ/4, it is of course possible to impart broadband characteristics to the resonator itself, but the resonator is usually rarely used as a single unit. In most cases, the device is housed in a case, as shown in FIG. 2, and transmits and receives sound waves through an acoustic window. This is done in consideration of operational environment resistance, so-called weather resistance, robustness, and operability when the vibrator is used as a transducer. Therefore, conventional vibrator with acoustic matching layer There is a problem in that it cannot withstand use in a practical environment if it is used alone.

The object of the present invention is to eliminate the above-mentioned drawbacks, and to interpose at least one 1/4 wavelength acoustic matching layer between the acoustic rubber and the sound wave emitting surface of the longitudinal transducer group in a layered adhesive state. An object of the present invention is to provide an underwater wideband transducer which can be significantly improved in efficiency and broadband by providing an acoustic window with a structure in which rubber itself is bonded to a case, and which can be significantly reduced in size and weight.

[Means for solving problems]

The underwater broadband transducer of the present invention is of a type in which a sound wave radiation surface of a group of vertical transducers is bonded to an acoustic window, in which at least one 1/4 wavelength acoustic matching layer is sequentially attached to the sound wave radiation surface. The acoustic rubber is laminated and bonded to the outermost layer of acoustic rubber, and the acoustic rubber is bonded to the longitudinal transducer group housing case to form an acoustic window.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the underwater broadband transducer of the present invention. The embodiment shown in FIG.
The case where there is only one 1/4 wavelength acoustic matching layer to be laminated and bonded is shown as an example, but it is of course possible to form a plurality of layers, and the acoustic matching effect will increase accordingly, as will be described later. This selection can be made arbitrarily by taking into account the trade-off with the external dimensions, weight, and other operational requirements of the transducer to be constructed.

The embodiment shown in FIG.
b, 1-c, an acoustic matching layer 2, an acoustic rubber 3, a sound insulating material 4, a case 5, and the like.

Vertical oscillators 1-a, 1-b, and 1-c are shown as representative parts of vertical oscillators arranged in a plane. For example, vertical oscillator 1-a has a front mass 11, a ceramic 12, and a back mass 13. An acoustic matching layer 2 having a thickness of λ/4 is adhered to the sound wave emitting surface. This acoustic matching layer 2 uses epoxy resin, and its acoustic impedance PC is equal to that of the longitudinal vibrator 1.
The acoustic impedance of the sound wave emitting surface of -a and the acoustic impedance of the acoustic rubber 3 made of a neoprene-based synthetic rubber material are set to take approximately an intermediate value.

Further, the acoustic matching layer 2 is bonded to the acoustic rubber 3,
Furthermore, the acoustic rubber 3 is glued to the case 5,
The acoustic window structure made up of the acoustic rubber 3 and the acoustic matching layer 2 is much more robust than the acoustic window made up of only the acoustic rubber 3 shown in FIG. Note that the case 5 is made of metal and has a cylindrical shape in this embodiment.

Now, in the transducer formed in this way, two vibration modes occur: a vibration mode due to each longitudinal oscillator and a vibration mode due to the acoustic matching layer, and the overall vibration characteristics have broadband characteristics that are a combination of the two vibration modes. It becomes like this. Generally, n+1 vibration modes, which is the number n of acoustic matching layers to be interposed plus 1, are generated.

FIG. 3 is a vibration mode characteristic diagram showing an example of complex vibration mode characteristics when an acoustic matching layer is used. Third
The figure shows the characteristics of complex vibration when there is only one acoustic matching layer, and this is expressed by a first vibration mode a caused by the ceramic and a second vibration mode b caused by the acoustic matching layer. As mentioned above, generally, when n acoustic matching layers are used, n+1 vibration modes appear. The value Ve/Vx indicated by a and b is the vibration velocity distribution of the acoustic matching layer normalized by the vibration velocity of the end face of the ceramic, that is, the sound wave radiation surface. What is meant by FIG. 3 is that this oscillator is a dual mode oscillator in which two resonant modes having mutually different phases by π (180 degrees) exist in close proximity. Regarding the phase relationship, if the acoustic matching layer is doubled, there will be three resonance modes, of which the first and third modes have the same phase, and the second mode differs from these only in π. In-phase modes and anti-phase even modes occur alternately.

In any case, creating multiple vibration modes and vibrating in multiple resonance modes will immediately lead to an expansion of the bandwidth. Additionally, it is recommended that the acoustic matching layer used for this purpose be formed of a plurality of layers having acoustic impedance that gradually decreases from the sound wave emitting surface of the vertical vibrator to the outermost layer of acoustic rubber. This results in better acoustic impedance matching between the load and the longitudinal vibrator.

In this way, it is possible to achieve a wide band through the use of the λ/4 acoustic matching layer, so the backmass is 1
3rd class does not need to be λ/4, and the front mass is 1
The thickness may be approximately the same as that of the first grade, that is, the thickness may be such that unnecessary bending vibrations can be suppressed. Thus, the usable length that can be provided to the ceramic 12 out of the entire λ/2 increases accordingly, and the applied power can also be increased.

A numerical example is shown below. That is,
As an example of the conventional longitudinal vibrator shown in Fig. 2,
At a frequency of 30KHz, the total length is approximately 57mm, the back mass of λ/4 is approximately 34mm, and the ceramic is approximately 11mm.
mm, so the front mass length is approximately 12 mm. In this embodiment, the front mass and back mass are both 8 mm, the ceramic is approximately 30 mm, and the total length is reduced to approximately 46 mm. Along with this, the length of the acoustic matching layer of λ/4 epoxy resin is required to be approximately 17 mm, but the thickness of the acoustic rubber can be compressed to approximately 13 mm by using a window configuration in combination with the acoustic matching layer. In addition to the weight reduction due to weight reduction, the total length is also 10-odd mm.
In addition to being shortened, the ceramic portion can now be approximately three times as long.

The above is a comparison with a conventional example in which the backmass is set to λ/4 to achieve a wide band.However, regarding another conventional example, that is, one in which an acoustic matching layer with a thickness of λ/4 is bonded to a longitudinal vibrator, this is the same. It can be used as is, or if weather resistance is taken into consideration, it can be simply glued to acoustic rubber. In other words, the acoustic rubber 3 of the conventional structure shown in FIG. 2 is divided into upper and lower halves as shown by dotted lines, with the upper part being the acoustic rubber and the lower part being the acoustic matching layer. Such structures usually have the problem that the acoustic matching phase, which uses epoxy resin, is exposed to the environment, has lower weather resistance than neoprene-based acoustic rubber, and is difficult to ensure perfect adhesion to the case. Become. The solution of this problem by merging processing is the gist of the present invention, an embodiment of which is shown in FIG. The fractional bandwidth of the transducer thus obtained can be easily 40 to 50% even as a single acoustic matching layer, and widening the band can be easily achieved. Specifically, this means that the band can be made 2 to 3 times wider than when the backmass is set to λ/4.

In addition, regarding the degree of acoustic impedance matching, possible design bandwidth, and optimal matching layer thickness in a transducer with such a structure, a multimode filter synthesis method is introduced, and the longitudinal oscillator is connected to its electrical terminal. The value is determined by assuming that it is a multi-mode filter with loads connected to the input and output terminals. The gist of this synthesis method is that the image impedance Zim when looking at this resonator from the load side of the longitudinal resonator, which can be expressed by a four-terminal network using a special circuit, is
However, based on the filter theory of image parameters, when it is a real number, it becomes a passband, and when it is an imaginary number, it becomes a stopband. When trying to secure a longitudinal oscillator with few ripples in the passband by the synthesis method, Zim is loaded at the center frequency. The specific acoustic impedance and layer thickness of the acoustic matching layer are determined so that it is equal to the impedance Z _L and that Zim can take continuous real values over as wide a band as possible, and the final The number of acoustic matching layers and the thickness of the acoustic rubber are determined accordingly.

〔Effect of the invention〕

As explained above, according to the present invention, in an underwater broadband transducer in which the sound wave radiation surface of the vertical transducer group is bonded to the acoustic window, the acoustic impedance between the sound wave radiation surface and the acoustic rubber is approximately equal to that of the two. By layering at least one acoustic matching layer made of a material with an intermediate value and adhering the outermost layer of acoustic rubber to the case to form an acoustic window, it is possible to achieve significantly higher efficiency and a wider range of input signals. This has the effect of realizing a small, lightweight, and robust underwater broadband transducer that can significantly increase power.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of the underwater wideband transducer of the present invention, Fig. 2 is a sectional view showing an example of a conventional underwater wideband transducer, and Fig. 3 is a composite diagram when an acoustic matching layer is used. FIG. 3 is a vibration mode characteristic diagram showing an example of vibration mode characteristics. 1-a, 1-b, 1-c... longitudinal vibrator, 2...
Acoustic matching layer, 3... Acoustic rubber, 4... Sound insulation material, 5
...Case, 6-a, 6-b, 6-c...Longitudinal vibrator, 11,61...Front mass, 12,62...
...Ceramic, 13,63...Batukumas.

Claims (1)

[Claims] 1. In an underwater wideband transducer in which the sound wave radiation surface of a group of vertical transducers is bonded to an acoustic window, at least one 1/4 wavelength acoustic matching layer is sequentially formed from the sound wave radiation surface to the outermost layer of acoustic rubber. 1. An underwater wideband transducer comprising: an acoustic window formed by layering and adhering the acoustic rubber to the longitudinal transducer group housing case.