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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electroacoustic transducer, which is used particularly for a long distance sonar, a marine
resource explorer or the like, and has a relatively low frequency and high power transmission
wave among ultrasonic waves. The present invention relates to an acoustic transducer applicable
to an underwater wave transmitter.
2. Description of the Related Art Ultrasonic waves in the low frequency range in water are used
to capture distant targets because they have smaller propagation losses compared to those in the
high frequency range, and they are used not only for sonars, but also for marine resource
exploration etc. Are widely applied in the field of
An example of the structure of an electroacoustic transducer (hereinafter referred to as a
transmitter) used in such fields etc. is disclosed in "3-6-1" etc. of "The 1992 Spring Conference"
of the Acoustical Society of Japan It is done.
The electroacoustic transducer of this type is, as shown in a perspective view in FIG. 5, a discshaped vibrator 22 in which a disc-shaped piezoelectric vibrator 21 is incorporated in a recess,
and a piezoelectric vibrator 21 having a common shape with this. A common-shaped vibrating
body 22 'in which the' is incorporated in the recess is fastened by a bolt 23 via a ring 25 so that
the vibrators 21 and 21 'are directed outward.
Such a transmitter utilizes the radial spread mode of the piezoelectric vibrators 21 and 21 ', and
the vibrators 22 and 22' incorporating these vibrators operate in the bending mode to emit
ultrasonic waves. Do. When the radial expansion mode of the vibrator is converted into bending
vibration, the displacement is expanded, so that it is possible to obtain a single resonance system
transmitter having a high conversion efficiency in a low frequency region.
The first problem with such a transmitter is that not only the rigidity of the disc itself
incorporating the transducer is high, but the transducers 22 and 22 'have a disk shape, so they
have sharp resonance characteristics. And the high Q. This has the disadvantage of not being able
to deliver two different frequencies, or the fact that if there is a variation in the input frequency,
the efficiency of the acoustic wave conversion is significantly reduced.
The second problem is that it can not be used for a transmitter such as a sonar operating at two
frequencies. In this case, the above-described transmitter has the disadvantage that two have to
be prepared. In order to solve this defect, usually, the structure of a single resonance system with
lowered Q is designed to cover each transmission frequency, but since this enlarges the
resonance frequency region, a single frequency A new problem arises that the conversion
efficiency is reduced.
Incidentally, although not a submersible wave transmitter, a speaker as disclosed in JP-A-56152399 comprises a diaphragm and a piezoelectric crystal plate sandwiched between a pair of
electrodes, and the piezoelectric crystal plate The outer periphery of the vibrating face plate to
be vibrated is a shape in which smooth curves or straight lines are connected by smooth curves,
and at least two or more of the centers of these curves are provided.
Such a configuration pursues good voice frequency characteristics as a "talking speaker", and
thus has a flat frequency characteristic in which Q is significantly reduced.
For this reason, the electroacoustic conversion efficiency does not improve, and in particular,
when transmitting only a plurality of specific frequencies, the conversion efficiency is extremely
low and therefore can not be used. Moreover, it does not conform to the water load condition,
high output condition, etc. for using as a submersible wave transmitter, and such a point is not
taken into consideration as a matter of course.
Further, in the ultrasonic transducer disclosed in Japanese Patent Application Laid-Open No. 61234698, the vibration plane of the diaphragm has an anisotropic planar structure having a major
axis direction and a minor axis direction, and the orthogonal biaxial directions are obtained. The
antenna directivity characteristics of are different from each other.
Such a configuration is intended to change directivity characteristics so that the presence or
absence of an obstacle can be easily detected, and is not a configuration as an underwater wave
transmitter, nor a configuration to obtain a plurality of transmission frequencies, It is a
technology without such a need.
Therefore, an object of the present invention is to use a plurality of transmission frequencies
without lowering the electroacoustic conversion efficiency, and to adopt it to a sonar system
operating at two frequencies, and to use water load An object of the present invention is to
provide an electroacoustic transducer which satisfies the conditions.
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the
electroacoustic transducer according to the present invention comprises a piezoelectric vibrator
of a predetermined thickness or this vibrator so as to obtain two resonance frequencies as
transmission frequencies. It has a structure in which the out-of-plane end of the including
diaphragm is made elliptical.
An electro-acoustic transducer according to another aspect of the present invention is an electroacoustic transducer including a pair of diaphragms to which a piezoelectric vibrator is fixed,
wherein at least one of the piezoelectric vibrator and the diaphragm is flat. It has a structure in
which the outer end has an elliptical shape.
Here, a groove is formed on the main surface of the vibrating plate on the side to which the
piezoelectric vibrator is not fixed to lower the rigidity in the elliptical long / short axis direction
and sharp resonance characteristics, that is, Two high resonance characteristics of Q are
In addition, by forming the groove at a total of four locations on the main surface excluding the
region of a predetermined width including the long / short axis of the ellipse and the
circumferential region of the ellipse, the long / short shaft portion is made thicker and vibration
is generated. It is possible to obtain characteristics of small level reduction, that is, high
conversion efficiency and sharp resonance characteristics.
The pair of diaphragms are fixed to each other with a ring having a lower Young's modulus than
the diaphragms.
Reference is made to the plan view of FIG. 1 showing an embodiment of the present invention.
In FIG. 1, in this transmitter, a diaphragm 2 having a larger elliptical shape is fixed to an elliptical
piezoelectric vibrator 1 and covered with a mold resin 4 to form a watertight structure.
Elliptical circumference is a locus of points equidistant from two focal points at a constant
distance, and the ellipses forming the outer ends on the plane of the piezoelectric vibrator 1 and
the diaphragm 2 differ in the dimension of the equidistant. All of them have this elliptical
It is preferable that the major axis 10 of the ellipse indicating the major axis, the minor axis 11 of
the ellipse indicating the minor axis, and two focal points not shown are common to the
piezoelectric vibrator 1 and the diaphragm 2.
Referring to FIG. 2 showing a cross-sectional view taken along the line AA 'of FIG. 1, this wave
transmitter is an elliptical piezoelectric vibrator 1' common to the piezoelectric vibrator 1 and the
diaphragm 2 described above and The diaphragms 2 'are fixed to each other, and the upper and
lower diaphragms 2 and 2' are fastened to each other by eight bolts 3 via a ring 5 at a
predetermined distance.
Here, the mold resin 4 covers the entire surface.
Although not shown, cables for supplying power to the piezoelectric vibrators 1 and 1 'are
connected to the upper and lower surfaces of these vibrators.
By supplying power to the piezoelectric vibrators 1 and 1 ', radially spreading vibration is
excited. The diaphragms 2 and 2 'are made of a material having high mechanical strength such
as high tensile strength steel, each having a recess formed therein, in which the transducers 1
and 1' are respectively fitted, and strong adhesion is achieved. It is fixed by an agent to form a
plate-like or disc-like vibrator.
If the above-described elliptical shape long / short diameter ratio is, for example, √2 (square
root of 2): 1, the upper limit frequency is approximately twice the lower limit frequency. The
surface area occupied by the vibrations 1 and 1 'in the plate-like vibrating body consisting of the
vibrating plates 2 and 2' to which the vibrators 1 and 1 'are fixed respectively is substantially
equivalent to the tensile stress on the vibrator 1 or 1' In order not to be added, it is preferable to
set about 64%.
The ring 5 is a concavo-convex type ring made of a fiber-reinforced plastic which has a lower
Young's modulus than the diaphragms 2 and 2 'and a high strength. The diaphragms 2 and 2 'are
fixed to each other by bolts 3 so that they face each other.
One of the characteristic parts of this embodiment is that four grooves 6 are formed on the main
surface of the diaphragms 2 and 2 'opposite to the side to which the vibrators 1 and 1' are fixed. .
Referring to the plan view of FIG. 3 showing the shape of the grooves 6, four grooves 6 are
formed in the diaphragm 2 viewed from the opposite side of the plane of FIG. Here, four grooves
6 of a predetermined depth are formed on the main surface excluding the region of the width W1
along the minor axis and the width W2 along the major axis and the outer peripheral region of
the diaphragm 2. The outer periphery 7 of each groove 6 is an elliptical periphery common to
the focal point.
The ratio of the area of widths W1 and W2 surrounded by the four grooves 6 to the major
surfaces of the four grooves 6 is set to 1: 1. The groove 6 ′ of the lower diaphragm 2 ′ also
has a groove shape common to the groove 6.
In this structure, since the piezoelectric vibrators 1 and 1 'and the diaphragms 2 and 2' have an
elliptical shape, the upper limit of the resonance frequency of the transmitter is substantially
determined by the minor axis and the lower limit is substantially determined by the major axis.
The resonant frequency in the radial direction of the vibrator tries to change continuously along
the elliptical circumference, but when, for example, the piezoelectric vibrator 1 or 1 'is driven at a
frequency at which a bending mode occurs in the major axis direction In directions other than
the long axis direction, an effect of suppressing the bending mode in the long axis direction is
generated in proportion to the rigidity of the structure. However, in this embodiment, the
formation of the groove 6 reduces the thickness of the area other than the cruciform surface area
on the long / short axis, so the rigidity as the structure is small. From the viewpoint of the
oscillation source, this is equivalent to the reduction in load.
Therefore, the lower limit resonance frequency determined by the major axis length has a small
conversion loss, and a large mechanical displacement can be obtained. The above effects are
common to the upper limit resonance frequency determined by the minor axis length.
In FIG. 4 showing the frequency characteristics of the above embodiment, the horizontal axis
shows normalized frequency, ie, frequency divided by the conventional resonance frequency
shown by dotted line, and vertical axis shows vibration level relative value, ie, divided by
conventional resonance frequency level. Indicates the level. The characteristic shown by the solid
line is the case according to this embodiment, and the measurement point of the vibration level is
the center point of the ellipse.
Conventionally, because of a single resonance system, a peak occurs at a resonance frequency
determined by the diameter of the circle, and the vibration level is low at other frequencies, and
substantially no resonance occurs. On the other hand, in this embodiment, peaks occur at two
frequencies substantially determined by the length / short axis length. Such two frequency
differences can be enlarged by increasing the length / breadth ratio of the ellipse. Also, Q of the
two resonance frequencies can be improved by appropriately making the groove deep and wide.
In this embodiment, although the outer periphery 7 of the groove 6 is defined to be along the
elliptical periphery, it is not limited thereto, and may be a polygon such as a triangle or a square.
Although both of the piezoelectric vibrators 1 and 1 'and the diaphragms 2 and 2' have an
elliptical shape, the present invention is not limited to this, and if either one exhibits an elliptical
shape, the characteristics shown in FIG. Have an effect.
In the embodiment described above, a pair of diaphragms is provided. However, the present
invention is not limited to this. Two resonance frequencies can be obtained even if there is only
one diaphragm on which the piezoelectric vibrator is fixed. Further, although the case where the
groove is formed is shown, the invention is not limited thereto, and the groove may not be
formed in applications where sharp resonance characteristics are not required.
As described above, since the electroacoustic transducer according to the present invention is
provided with an elliptical piezoelectric vibrator or diaphragm, two transmission frequencies can
be obtained, and in particular, the piezoelectric vibrator When both or one of the flat outer edges
of the diaphragm is elliptical and it is equipped with a pair, it is possible not only to obtain two
delivery frequencies with high output and high Q but also to process it into an oval Since the
grooves are formed to the extent that they can be easily manufactured and can be reduced in
weight, all the above-described objects can be achieved.
Brief description of the drawings
1 is a plan view showing an embodiment of the electro-acoustic transducer according to the
present invention.
2 is a cross-sectional view showing a cut surface of the line AA of FIG.
3 is a plan view showing the opposite main surface of the diaphragm of FIG.
4 is a characteristic diagram showing the frequency characteristics of an embodiment of the
present invention and a conventional example.
5 is a perspective view showing a conventional underwater wave transmitter.
Explanation of sign
1, 1 ', 21, 21' piezoelectric vibrator 2, 2 'diaphragm 3, 23 bolt 4, 24 mold resin 5, 25 ring 6, 6'
groove 7 outer periphery 10 major axis 11 minor axis 22, 22 'vibrator
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