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JP2004032107

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DESCRIPTION JP2004032107
A receiver for receiving a wide range of ultrasonic signals in a wide frequency band is provided.
SOLUTION: A hemispherical surface baffle 21 made of a 180 degree hemispherical surface for
reflecting an ultrasonic signal, a wave receiving element 11 arranged at a predetermined distance
Dr from a center point 101 of the hemispherical surface baffle 21, and a hemispherical surface A
receiver including a molding material 31 for fixing the wave receiving element 11 to the baffle
21. The diameter Db of the hemispherical surface baffle 21 is set to about 1 wavelength or more
of the sound wave, and Dr / Db <1.2 is satisfied. Deploy. [Selected figure] Figure 1
Wave receiver
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
receiver for detecting an ultrasonic signal in water, and more particularly to a receiver for
reducing size and weight and improving directivity in a wide frequency band. 2. Description of
the Related Art FIG. 6 is a longitudinal sectional view of a conventional wave receiver. The
conventional wave receiver includes the wave receiving element 14, the flat baffle 25, the
molding material 34, the sound absorbing material 42, and the electronic circuit 62. The wave
receiving element 14 is disposed on the vertical axis 204 at a distance Dr (wave receiving
element distance) from the flat baffle 25. In this type of receiver, the mounting surface of the
receiver element 14 serves as a sound wave reflection plate for ultrasonic signals, and the
reflected wave generated by this sound wave reflection plate causes the front (0 degrees <θ <90
degrees) to be horizontal. Since the sensitivity in the direction (θ = 90 degrees) is not uniform
and a large sensitivity deviation occurs in directivity, one of the important factors is to reduce the
reflected wave. [0004] For this purpose, usually, the mounting surface of the wave receiving
element 14 is provided with a sound absorbing material 42, and the reflected wave is reduced to
make the sensitivity in the lateral direction uniform from the front and suppress the deviation of
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directivity. Is adopted. However, this method relies on the characteristics of the sound absorbing
material 42. As a typical sound absorbing material method, there is a method of attenuating by
diffuse reflection by a weir, or a method of converting an acoustic wave into heat by
mechanically vibrating it by the sound wave during transmission which contains additives and
microvoids in impedance material close to water. Etc. However, the former requires a size that is
adapted to the wavelength of the frequency to be used and is very large, and can not be reduced
in size and weight when used in a low frequency band. Also, the latter has a good sound
absorption effect at a specific frequency but hardly becomes effective at other frequency bands,
so it can not be said that it is sufficient for improving directivity in a wide frequency band.
Therefore, for example, in a sound absorbing material of a method in which an additive or
microvoid is included in a material having impedance close to water, and the additive or
microvoid is mechanically vibrated by the sound wave passing through to convert the sound
wave into heat. It is possible to make a sound absorbing material corresponding to the frequency
of (1) into a laminated structure to widen the frequency band and improve the sound absorption
coefficient. Since this technology utilizes the resonance characteristic of the additive inside the
sound absorbing material, the thickness of the sound absorbing material can be reduced
particularly in the case of a low impedance additive such as a void. In addition, if a sheet of sound
absorbing material in which the corresponding sound absorbing frequency is changed is made to
have a laminated structure, a certain effect can be achieved also for broadening the frequency
band to some extent.
However, materials of impedance close to water contain additives and microvoids, and the
additives and microvoids are mechanically vibrated by the sound waves being transmitted to
convert the sound waves into heat. The sound absorbing material of the method brings about the
problem of the enlargement by the increase in the number of laminations newly in the point of
further widening the frequency band. This is because a sheet of sound absorbing material that is
suitable for the frequency band to be used is prepared and all of them are laminated.
Furthermore, considering the application to the receiver, the problem is that the sound absorbing
material becomes quite expensive and the receiver becomes expensive due to the increase in the
types of the sound absorbing material sheet. One of the main objects of the present invention is
to provide a compact and lightweight receiver capable of receiving a wide range of ultrasonic
signals in a wide frequency band. Another main object of the present invention is to provide an
inexpensive receiver capable of receiving a wide range of ultrasonic signals in a wide frequency
band. A receiver according to the present invention comprises an acoustic wave reflection plate
having a partial curved surface, and a wave reception element disposed at a predetermined
distance from a center point of the acoustic wave reflection plate. , And. A receiver according to
the present invention is characterized by comprising a sound wave reflection plate having a
partial elliptic surface, and a wave reception element disposed at a predetermined distance from
a center point of the sound wave reflection plate. . A receiver according to the present invention
is characterized by comprising a sound wave reflection plate which is a partial spherical surface,
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and a wave reception element arranged at a predetermined distance from the center point of the
sound wave reflection plate. A receiver according to the present invention is characterized by
comprising a sound wave reflection plate having a hemispherical surface of 180 degrees, and a
wave reception element disposed at a predetermined distance from the center point of the sound
wave reflection plate. I assume. A receiver according to the present invention is a receiver for
detecting an ultrasonic signal in water, and includes a sound wave reflection plate having a
hemispherical surface for reflecting the ultrasonic wave signal, and a central point of the sound
wave reflection plate A free sound field and an omnidirectional receiving element disposed at a
predetermined distance, and when the predetermined distance is Dr and the diameter of the
hemispherical surface is Db, then Dr / Db <1.2 It arranges so that it may be satisfied. The wave
receiver according to the present invention is characterized in that a plurality of the sound wave
reflection plates are arranged around the wave receiving element. The wave receiver according to
the present invention is characterized in that two of the sound wave reflection plates are
arranged to face each other around the wave receiving element.
The wave receiver of the present invention is characterized in that a sound absorbing material is
present between the wave receiving element and the sound wave reflection plate. The receiver
according to the present invention is characterized in that the inside of the sound wave reflection
plate is hollow. The wave receiver of the present invention is characterized in that the diameter
of the sound wave reflection plate is equal to or more than the length of the wavelength of the
sound wave. The wave receiver of the present invention is characterized in that the wave
receiving element is arranged radially from the center point of the sound wave reflection plate.
The wave receiver of the present invention is characterized in that the wave receiving element is
fixed to the sound wave reflection plate with a molding material. The receiver of the present
invention is characterized in that the molding material is a material having an acoustic
impedance equivalent to water or urethane. A receiver according to the present invention is
characterized in that the directivity of the wave receiving element is non-directional. BEST MODE
FOR CARRYING OUT THE INVENTION A receiver (FIG. 1) having a hemispherical baffle 21
according to the present invention is a mounting surface for the wave receiving element 11 in a
receiver for detecting an ultrasonic signal in water. Compared to the conventional configuration
(FIG. 6) in which the sound absorbing material 42 is provided between the wave receiving
element 14 and the flat baffle 25 to eliminate the influence of the reflected wave from the flat
flat baffle 25, the sound absorbing material 42 is eliminated. A hemispherical baffle 21 having a
diameter of about 1 wavelength or more is provided as a sound wave reflection plate for
reflecting a sound wave on a free sound field and a non-directional light receiving element 11. In
order to clarify the above and other objects, features and advantages of the present invention,
embodiments of the present invention will now be described with reference to the drawings, such
as a longitudinal sectional view of a conventional receiver shown in FIG. I will explain in detail. <<
First Embodiment >> FIG. 1 is a longitudinal sectional view of a wave receiver according to a first
embodiment of the present invention. The wave receiver according to the first embodiment of the
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present invention includes a wave receiving element 11, a hemispherical surface baffle 21 as a
sound wave reflecting plate including a cylinder connected to a hemispherical surface connected
with 180 degrees, a sound wave reflecting plate, a molding material 31, and an electronic circuit.
61 is comprised. A free sound field omnidirectional receiving element 11 formed of a spherical
shell piezoelectric ceramic or the like is directly in front of the center point 101 of the hollow
hemispherical surface baffle 21 formed of a metallic hemispherical shell (θ = 0 The acoustic
impedance is molded and fixed with a molding material 31 such as urethane equivalent to water
in the direction (radial direction). The signal lead wire of the wave receiving element 11 passes
through the inside of the molding material 31 and is connected to an electronic circuit 61 such
as a preamplifier disposed in a watertight container which penetrates the metal hemispherical
shell and doubles as the hemispherical surface baffle 21.
The center point 101 and the wave receiving element 11 are arranged on the vertical axis 201.
Then, assuming that the diameter Db (baffle diameter) of the hemispherical surface baffle 21 is 1
wavelength or more and the distance between the wave receiving element 11 and the
hemispherical surface baffle 21 is Dr (wave receiving element distance), then Dr / Db < It is 1.2.
When the hemispherical surface baffle 21 has the side to which the wave receiving element 11 is
attached as the front (0 degrees <θ <90 degrees), the water is spread from the front without the
hemispherical surface baffle 21 to the lateral direction (θ = 90 degrees) With respect to the
direct wave 51 of the propagating ultrasonic signal, the reflected wave 52 reflected by the
hemispherical surface baffle 21 reradiates approximately equally from the front to the lateral
direction. Therefore, the received signal added to the direct wave 51 by the receiving element 11
in front of the hemispherical baffle 21 has a substantially constant sensitivity from the front to
the lateral direction. On the other hand, the ultrasonic signal from the rear (90 degrees <θ <180
degrees) with the hemispherical baffle 21 has a diameter of the hemispherical baffle 21 of 1
wavelength or more and the transmitted wave of the sound wave by diffraction is backward from
the lateral direction The transmitted wave becomes minimum because the shadow gradually
becomes smaller, and behind the baffle (θ = 180 °). Therefore, the received signal added to the
direct wave 51 by the wave receiving element 11 in front of the hemispherical baffle gradually
decreases from the lateral direction to the rear, and has a minimum sensitivity right behind. For
this reason, Cardioid (Heart-shaped curve) directivity is obtained in a frequency range of a
wavelength shorter than the diameter of the hemispherical surface baffle 21. Referring to FIG. 6,
when the sound absorbing material 42 is omitted in the conventional configuration, the distance
between the wave receiving element 14 and the flat baffle 25 is Dr (wave receiving element
distance), and the diameter of the flat baffle 25 is When Db (baffle diameter), Dr / Db ≧ 1.2, the
distance Dr between the wave receiving element 14 and the flat baffle 25 becomes large, and the
influence of the reflected wave becomes small. The distance Dr between the wave receiving
element 11 and the hemispherical surface baffle 21 shown in FIG. 1 is set to Dr / Db <1.2.
Further, as a result of making the shape of the baffle a hemispherical surface, the reflected wave
52 from the front to the lateral direction re-radiates almost equally to an arbitrary frequency, so
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that cardioid directivity can be obtained in a wide frequency band. This will be described with
reference to actual measurement figures 2 and 3 and 7 and 8 of the embodiment. Each of FIGS.
2, 3, 7 and 8 shows sensitivity deviation in the range from the front (θ = 0 degrees) to the lateral
direction (θ = 90 degrees), that is, the smoothness of directivity.
2 and 3 are characteristic values according to the first embodiment (FIG. 1) of the present
invention, and FIGS. 7 and 8 are characteristic values when the conventional wave receiver (FIG.
6) does not have the sound absorbing material 42. 7 are frequency characteristics, and FIGS. 3
and 8 are distance characteristics between the wave receiving element and the baffles. The
frequency characteristic is a graph that expresses the normalized distance as a variable, where
the receiving element distance Dr between the receiving element and the baffle is normalized by
the baffle diameter Db, to the normalized frequency where the wavelength λ is normalized by
the baffle diameter Db. The distance characteristic is a graph representing the normalized
frequency as a variable with respect to the normalized distance. The frequency characteristics of
the first embodiment according to the invention (FIG. 2) have a normalized frequency 1 or baffle
diameter, except in the case where the normalized distance is 0.14, ie the distance between the
receiving element and the baffle approximately The sensitivity deviation is suppressed to about 8
dB or less in a frequency band in which Db is one wavelength or more. On the other hand, in the
case of the frequency characteristic (FIG. 7) of the conventional wave receiver (FIG. 6), the
normalized distance is 1.17, ie, when the wave receiving element distance Dr between the wave
receiving element 14 and the planar baffle 25 is large. Except that the sensitivity deviation is
about 8 dB or more in the frequency band where the normalized frequency is 1 or more. In
addition, the distance characteristic (FIG. 3) of the first embodiment (FIG. 1) according to the
present invention is smaller than the distance characteristic (FIG. 8) of the conventional receiver
(FIG. 6). The sensitivity deviation is improved by 10 dB or more within the normalized distance of
1.2, including the case where the distance between the receiving element and the baffle is
substantially in contact, that is, 0.14. The data in FIG. 3 is in the range of the standardized
distance 0.1 to 0.6, but a tendency of decreasing downward to the right is obtained, and further,
the standardized distance 0.6 in which the receiving element distance Dr becomes larger. It is
apparent that the influence of the reflected wave is further reduced in the range of -1.2, and the
sensitivity deviation is further reduced in the standardized distance 1.2. Therefore, it can be seen
that the directivity of the receiver having the hemispherical surface baffle 21 of the present
invention is remarkably improved in the frequency range in which the baffle diameter Db is 1
wavelength or more. Moreover, in the first embodiment, with regard to directivity improvement
in a wide frequency range, it is possible to extremely reduce the receiving element distance Dr
between the receiving element 11 and the hemispherical surface baffle 21 without a sound
absorbing material, The effects of small size, light weight and low cost can be obtained. Second
Embodiment FIG. 4 is a longitudinal sectional view of a wave receiver according to a second
embodiment of the present invention. The wave receiver of the second embodiment includes a
wave receiving element 12, hemispherical baffles 22 and 23, and a molding material 32.
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The difference from the first embodiment described above is that the hemispherical baffle 23 is
added at a position in the direction of θ = 0 degrees from the central point 102 of the
hemispherical baffle 22, and the central point 102 and the central point are added. An
arrangement 103 is opposed to the wave receiving element 12 in between. The center point 102,
the wave receiving element 12, and the center point 103 are arranged on the vertical axis 202.
That is, two sound wave reflection plates (hemispherical surface baffles 22 and 23) are disposed
to face the periphery of the wave receiving element 12. By adopting the two hemispherical
baffles 22 and 23 as described above, the sensitivity is suppressed in a specific direction (that is,
the direction in which the hemispherical baffle 23 is present) other than the device body on
which the electronic circuit etc. is mounted. The effect of being able to In the second
embodiment, two or more hemispherical baffles are used, but it is possible to arrange two or
more hemispherical baffles around the wave receiving element 12 without being limited to two.
It is. Further, in the second embodiment, since the sensitivity can be suppressed in a specific
direction without requiring signal processing such as special wave receiving element
configuration such as a wave receiving element array or directivity synthesis, the present
invention In addition to achieving the purpose of (1), it has a synergistic (excellent) effect of
reducing unnecessary noise such as sea surface reverberation. Third Embodiment FIG. 5 is a
longitudinal sectional view of a wave receiver according to a third embodiment of the present
invention. The wave receiver of the third embodiment includes the wave receiving element 13,
the hemispherical surface baffle 24, the molding material 33, and the sound absorbing material
41. The difference from the first embodiment described above is that the sound absorbing
material 41 is added between the molding material 33 and the hemispherical baffle 24, and the
center point 104 and the wave receiving element 13 are added. Are arranged on the vertical axis
203. As described above, it is a feature that the sensitivity deviation is further improved by
adopting the configuration in which the sound absorbing material 41 is added. In the present
embodiment, even if the performance of the sound absorbing material 41 is low, the sensitivity
deviation is already small due to the effect of the hemispherical surface baffle 24, which is
effective. The present invention is not limited to the above embodiments, and it is apparent that
each embodiment can be appropriately modified within the scope of the technical idea of the
present invention. For example, the hemispherical surface described in the hemispherical baffles
21, 22, 23, 24 serving as a sound wave reflection plate for reflecting the sound wave in each
embodiment is a partial curved surface which is a part of a curved surface or a partial ellipse
which is a part of an elliptical surface It is possible to replace the surface with a partial spherical
surface that is part of a spherical surface.
As described above, according to the present invention, a hemispherical baffle having a diameter
of about 1 wavelength or more is provided as a sound wave reflection plate in a free-field
omnidirectional receiving element. If the distance between the wave receiving element and the
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hemispherical baffle is Dr and the diameter of the hemispherical baffle is Db, then the electronic
circuit, power supply, power source, etc. It becomes possible to receive a wide range of ultrasonic
signals in a wide frequency band while maintaining the effect of the conventional receiver baffle
that blocks the self noise generated from the Since the wave element array, the signal processing
circuit and the like are not required, it is possible to realize a reduction in size, weight and cost.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of a wave receiver
according to a first embodiment of the present invention. FIG. 2 is a frequency characteristic of
the receiver of the present invention. FIG. 3 is a distance characteristic of the receiver of the
present invention. FIG. 4 is a longitudinal sectional view of a wave receiver according to a second
embodiment of the present invention. FIG. 5 is a longitudinal sectional view of a wave receiver
according to a third embodiment of the present invention. FIG. 6 is a longitudinal sectional view
of a conventional wave receiver. FIG. 7 is a frequency characteristic of a conventional wave
receiver. FIG. 8 is a distance characteristic of a conventional receiver. [Description of the code]
11, 12, 13, 14 Receiving elements 21, 22, 23, 24 Hemispherical baffles 25 Flat baffles 31, 32,
33, 34 Mold materials 41, 42 Sound absorbing materials 51 Direct waves 52 Reflected waves 61,
62 Electronic circuit 101, 102, 103, 104 Center point 201, 202, 203, 204 Vertical axis
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