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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
underwater broadband transducer, and more particularly to an underwater broadband
transducer which is improved in efficiency, bandwidth and size and weight. [Prior Art] A
directivity and other operational conditions for forming a longitudinal oscillator using a
lanceypan-type oscillator in which a normal ceramic oscillator or a ceramic oscillator is
sandwiched between two metals in a sandwich form are considered. Transducers of the type in
which a plurality of surface arrangements are taken into consideration and these sound emitting
surfaces are bonded to an acoustic window are widely used in various operation fields. In this
case, a member that constitutes a window that allows radiation sound waves to pass, a so-called
acoustic window, is usually an acoustic rubber (or PC rubber) whose acoustic impedance PC is
similar to water or seawater. Here, P represents the density and C represents the speed of sound.
In addition, such a transducer is often required to have a wide band for the purpose of operation,
in which case each longitudinal transducer to be configured of the transducer is a Langevin type
transducer and the back mass (back It is a general method to reduce mechanical Q (selectivity)
by setting mass) to 1/4 wavelength. Here, back mass refers to the rear one of the metal mass
bonded to the front and back of the ceramic in the lanzy pan type vibrator, and the front one is
called front mass to this back mass. It is also well known that Furthermore, as this Langevin type
vibrator, one having a ported clamp structure is often used so that prestress (pre -5tress) can be
applied to the ceramic in consideration of its efficient use. Anyway, this Lange, · Pan-type vibrator
is focused on features that are structurally easy to cope with wide band degradation, and as a
longitudinal vibrator that performs band broadening, the one with a back mass of 1⁄4 wavelength
is fundamental Are used. FIG. 2 is a cross-sectional view showing an example of a conventional
underwater broadband transducer. In the conventional underwater broadband transducer shown
in FIG. 2, longitudinal transducers 5-a and 5-b are part of a plurality of Langevin type
transducers used as longitudinal transducers. Expressed by 5-c, these longitudinal vibrators are
pre-stressed by bolting a two-stage cylindrical ceramic 62 with a metal front mass 61 and a back
mass 63 like a longitudinal vibrator 5-a, for example. It has a structure. The end face of the front
mass 61 to be the sound wave emitting surface is bonded to the acoustic rubber 3, and the sound
wave from the back mass 63 is considered by the sound insulation material 4 not to emit the
sound wave. It is the structure accommodated in case 5 with a longitudinal vibrator.
In order to broaden the bandwidth of such a transducer, the back mass 63 is made λ / 4 (where
λ is the wavelength at the resonance frequency) and the whole mechanical Q is oscillated at λ /
2. Accordingly, the total length of the front mass 61 and the ceramic 62 is also λ / 4. フロントマ
ス61は1. The ceramic 62 is dimensioned in consideration of the conditions in which no
flexural vibration occurs and in consideration of the applied voltage. By the way, although the
above-mentioned broadband transducer is usually used in a large amount, in addition to this, an
acoustic matching layer of λ / 4 thickness is adhered to the radiation surface of a single vibrator
to form two resonance modes. Attempts have been made to increase the bandwidth, and it has
long been a "band-shaped magnetostrictive ultrasonic wave filter" (Tomomasa Matsuki, Journal
of the Telecommunications Society of Japan, Vol. 35, No. 12). P530∼533. Recently,
improvement proposals for the contents of this document are highly efficient. "A Study on
Broadband Underwater Ultrasonic Transducers" for Broadband Piezoelectric Transducers (Inoue
Takeshi et al.) It is described in detail in the article of the Institute of Electronics and
Communication Engineers, US 85-22 (August 27, 1985). This λ / 4 acoustic matching layer
interposes a matching member such as epoxy resin for generating the second vibration mode
between the vibrator radiation surface and the load medium, and the band pass characteristic by
the plural vibration mode to the vibrator The purpose is to achieve a wide band by [Problems to
be solved by the invention] However, the above-mentioned conventional broadband transducer
has the following problems. That is, the number of Langevin type transducers is accommodated
in the required number arrangement case, and the wide band is secured by setting the back mass
to λ / 4 in the transducer. In this case, the difference between the acoustic impedance of the
sound wave emitting surface of the transducer and the acoustic impedance of the acoustic rubber
used for the acoustic window is large, so that the basic problem is that efficiency can not be
obtained and the bandwidth is narrow. There is also the problem that if the back mass is made λ
/ 4 long under this condition and the band is broadened, the size becomes very large and the
weight becomes very large accordingly. Superimpose. This means that the speed of sound of a
metal such as aluminum used for normal front and back mass is about 5000 m / s, and the
density difference between the two is more than that of a ceramic part having a speed of sound
of about 3000-3500 m / s. It is self-evident if you On the other hand, in the case of a vibrator
using an acoustic matching layer with a thickness of λ / 4, it is of course possible to give wide
band characteristics to the vibrator itself, but the vibrator is rarely used alone as a single
substance. As shown in FIG. 2, it is mostly used to receive and transmit a sound wave through an
acoustic window, housed in a case.
This is nothing but the consideration of operational environment resistance when using the
transducer as a transducer, so-called weatherability and robustness, and operability, and
therefore only a conventional transducer with an acoustic matching layer Then, there is a
problem that it is unbearable to use in the practical environment as it is. The object of the
present invention is to eliminate the above-mentioned drawbacks and to interpose at least one
quarter-wave acoustic matching layer between the sound wave emitting surface of the
longitudinal vibrator group and the acoustic rubber in the stratified adhesion state, An object of
the present invention is to provide an underwater broadband transducer in which high efficiency
and wide band are significantly improved by providing an acoustic window having a structure in
which rubber itself is adhered to a case, and further, a significant reduction in size and weight
can be achieved. [Means for Solving the Problems] The underwater broadband transducer
according to the present invention is an underwater broadband transducer of the type in which
the sound wave emitting surface of the longitudinal transducers is bonded to the acoustic
window. A wavelength acoustic matching layer is sequentially laminated from the acoustic wave
emitting surface to the outermost acoustic rubber layer and adhered, and the acoustic rubber is
adhered to the longitudinal vibrator group storage case, and the acoustic window is formed. Ru.
The present invention will now be described in detail with reference to the drawings. FIG. 1 is a
cross-sectional view showing an embodiment of the underwater broadband transducer according
to the present invention. Although the embodiment shown in FIG. 1 shows the case where the
quarter-wave sound bonding layer to be laminated and bonded is 1 '+ I'i as an example, it is
needless to say that it may be formed as a plurality. Although the acoustic matching effect is
increased as will be described later, this selection can be arbitrarily set in consideration of the
trade-off with the external dimensions 2 weight of the transducer to be configured and other
operation requirement specifications. In the embodiment shown in FIG. 1, longitudinal oscillators
1-a, 1-b. 1- C2 acoustic matching layer Acoustic Gono-3. The sound insulation material 4 and the
case 5 etc. are formed and formed. The longitudinal oscillators 1-a, 1-b and 1-c are
representatively shown as part of the surface-arranged longitudinal oscillators. For example, the
longitudinal oscillator 1-a is a front mass 11.. The acoustic matching layer 2 of λ / 4 thickness is
adhered to the sound wave emitting surface, which is constituted by the ceramic 12 and the back
mass 13. The acoustic matching layer 2 uses an epoxy resin, and the acoustic impedance PC is an
acoustic impedance of the sound wave emitting surface of the longitudinal transducer 1-a and a
sound utilizing a neoprene-based synthetic gono! a) It is set so as to take an approximately
middle value of the acoustic impedance of the rubber 3. The acoustic matching layer 2 is bonded
to the acoustic rubber 3, and the acoustic rubber 3 is bonded to the case 5, and the acoustic
window structure formed by the acoustic rubber 3 and the acoustic matching layer 2 is shown in
FIG. The acoustic window composed of the acoustic rubber 3 alone is much more robust.
In the case of the present embodiment, the case 5 is made of cylindrical metal. The transducer
thus formed has two vibration modes, that is, the vibration mode by each longitudinal vibrator
and the vibration mode by the acoustic matching layer, and the comprehensive vibration
characteristic has a wide band characteristic combining the two vibration modes. It will be. In
general, n + 1 vibration modes are generated in which the number nK1 of acoustic matching
layers to be interposed is added. FIG. 3 is a vibration mode characteristic diagram showing an
example of composite vibration mode characteristics when using an acoustic matching layer. FIG.
3 shows the characteristics of the composite vibration in the case where the acoustic matching
layer is a single layer, which is expressed by a first vibration mode a by ceramic and a second
pregnancy mode b by the acoustic matching layer. As described above, generally, n + 1 vibration
modes appear when n acoustic matching layers are used. The values Ve / Vx indicated by a and b
are obtained by normalizing the vibration velocity distribution of the acoustic matching layer
with the vibration velocity of the end face of the ceramic, that is, the sound wave emitting
surface. The meaning of FIG. 3 is that this oscillator is a dual mode oscillator in which two
resonant modes having phases different from each other by π (180 degrees) exist in close
proximity to each other. In terms of the phase relationship, assuming that the acoustic matching
layer is doubled, there are three resonance modes, of which the first and third order have the
same phase, and the second order differs from these only by π. The in-phase in the odd mode
and the anti-phase in the even mode occur alternately. In any case, such multiple vibration modes
and multiple resonance modes lead to an immediate increase in bandwidth. Furthermore, the
acoustic matching layer used for such purpose is formed of a plurality of acoustic impedances
that gradually decrease from the sound emitting surface of the longitudinal vibrator to the sound
θS rubber of the outermost layer. The impedance matching between the load and the vertical
vibrator can be achieved. In this manner, the broadband can be achieved through the use of the
λ / · 1 sound-b matching M, so that the pack mass 13 etc. need not be λ / 4, and the thickness
immediately before the front mass 11 etc., That is, it may be set to such an extent that generation
of unnecessary stagnation vibration can be suppressed. Thus, the available length that can be
provided to ceramic 12 in the entire λ / 2 may be increased, and the applied power may also be
increased. The numerical example is as follows. That is, as the -V / 1j of the vertical vibrator of
the conventional example shown in FIG. ! ! The length of the back mass of λ / 4 among I is about
34 IrIm, and that of the ceramic is about 11-1 so that the mass length is about 12 marks.
In this embodiment, the front mass and the back mass are both 8 nn, and the ceramic is
approximately 30 closed to reduce the total length to about 46 nnh. Along with this, the sound 9
of the λ / 4 epoxy resin (the length of about 17 old n of the Bz composite 5 layer is required, but
the thickness of the acoustic rubber can be compressed to about 13 nvn by the combined
window configuration with the acoustic matching layer As a whole, in addition to the reduction in
weight due to the reduction of back mass, the total length is also reduced by several tens of
meters, and in addition, the ceramic part can be provided with about three times the length. The
above is a comparison with the conventional example in which the band is broadened by setting
the back mass to λ / 4, but in the case of another conventional example, that is, one in which an
acoustic matching layer of λ / 4 thickness is adhered to a longitudinal vibrator, Is used as it is or
in a form simply adhered to the acoustic rubber in consideration of weather resistance and the
like. That is, the acoustic rubber 3 of the conventional structure shown in FIG. 2 is divided into
upper and lower parts as shown by dotted lines, the upper part being the acoustic rubber, and
the lower part the acoustic matching layer. In such a structure, the acoustic matching layer using
an epoxy resin is usually exposed to the environment, and the weather resistance is lower than
that of the neoprene-based acoustic rubber, and it is difficult to completely adhere to the case. It
becomes. The solution of this problem is merged and this is the main point of the present
invention, one embodiment of which is shown in FIG. The relative bandwidth of the transducer
thus obtained is as high as 40 to 50% even as a single acoustic matching layer, and a wide band
can be easily implemented. Specifically, this means that the bandwidth can be increased by two
to three times or more as compared with the case where the back mass is set to λ / 4. Regarding
the degree of acoustic impedance matching in the transducer with such structure, the bandwidth
that can be designed, and the optimum matching layer thickness, a synthesis method of
multimode filters is introduced, and the longitudinal oscillator is connected to its electrical
terminal. The values are determined by assuming that the load is connected to the input and
output terminals as a multi-mode filter. The gist of this synthesis method is that the image
impedance Zim when this vertical oscillator is viewed from the load side of the vertical oscillator
which can be expressed by a 4-terminal network using a special circuit is a real value based on
the filter theory of the image parameters If it is an imaginary number, it will be a stop zone, and
it will be a method of combining longitudinal oscillators with little ripple in the passband?
Determine the specific acoustic impedance and layer thickness of the acoustic matching layer so
that Zim is equal to the load impedance ZL at the center frequency and Zim can take real values
continuously over the wide band as far as possible by C. The number of acoustic matching layers
and the thickness of acoustic rubber are finally determined through the trade-off between the
conditions and the operating conditions.
[Effects of the Invention] As described above, according to the present invention, in the
underwater broadband transducer of the type in which the sound wave emitting surface of the
longitudinal vibrator group is bonded to the acoustic window, the acoustic wave is generated
between the sound emitting surface and the acoustic rubber. By making at least one acoustic
matching layer of a material whose impedance has almost an intermediate value between the
layers, and forming the acoustic window by bonding the outermost layer of acoustic rubber to
the case, the efficiency and the bandwidth are significantly increased. It is possible to realize a
compact, lightweight and robust underwater broadband transducer that can greatly increase the
input power while being able to
Brief description of the drawings
FIG. 1 is a sectional view showing an embodiment of the underwater broadband transducer
according to the present invention, FIG. 2 is a sectional view showing an example of a
conventional underwater broadband transducer, and FIG. 3 is a composite when using an
acoustic matching layer It is a vibration mode characteristic view which shows an example of a
vibration mode characteristic.
'-A + 1 b, 1-c · curved · vertical holding element, 2 · · · · · · sound rim (gold layer, 3 · · · · · · acoustic
rubber, 4 · · · · · · sound insulation,訃 · · ° ° case, 6-a, 5-b, 5-c-· · Longitudinal oscillator, 11.61 · · ·
· · · · · · · · · · · · · · · · · · · · · · · ceramic, 13.63 ......... back mass. Agent Patent Attorney Yen Hara 2 'Day
1- to 7'-', '-C ---- 4 f' t 't 7 r' th hand / f ---- Front Mass, '2- ----<-Lami-Shif / 3-----Panic 1 '(Fig. 1 乙 a, 乙 -4,6-(:- /---------------------------------------------------------------------- Dynamic velocity V χ---spring and
matching layer (7) velocity joint part α---e-7 s so 21: according to one child hioka mode eachone-sound igq gold layer (: cattle due to Figure 3 Figure 3
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