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JPS60212097

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DESCRIPTION JPS60212097
[0001]
Industrial application Field of application This invention is a super device that is constructed by
combining a parabolic horn with a piezoelectric element having a diaphragm at its central
portion, an electro-acoustic conversion device including a case etc. for housing the piezoelectric
element, and a paraboloid horn. The present invention relates to an acoustic transducer. The
structure of the conventional example and its problems An electro-acoustic transducer
(hereinafter referred to as an ultrasonic sensor) using a piezoelectric element provided with a
diaphragm at the center of the conventional element as an electro-acoustic transducer
(hereinafter referred to as an ultrasonic sensor) Various ultrasonic transducers are known which
are combined with the paraboloid horn made. For example, ultrasonic transducers as disclosed in
Japanese Patent Application Laid-Open Nos. 58-85699 and 58-88999 are known. The ultrasonic
transducer disclosed in Japanese Patent Application Laid-Open No. 58-85699 has a plurality of
ultrasonic transducers on the front surface of an ultrasonic sensor comprising a piezoelectric
element 1, a diaphragm 2, a case 3 and the like as shown in FIG. A thin plate 4 having an opening
is provided, and the ultrasonic sensor and the thin plate 4 are incorporated in the parabolic horn
6. In the figure, reference numeral 6 denotes a connecting shaft for fixing the diaphragm 2 to the
central portion of the piezoelectric element 1. On the other hand, the ultrasonic transducer
disclosed in Japanese Patent Application Laid-Open No. 58-88999, as shown in FIG. 1, has an
elastic diaphragm 2 as the case 3 in comparison with the example shown in the same figure. The
cushioning material 7 is additionally provided with a shock absorbing material 7 to be fixed
thereto. The directional characteristics are improved by forming a circular opening centered on a
line and various other openings arranged concentrically with this opening. In general, an
ultrasonic sensor using a piezoelectric element having a diaphragm at its central portion as an
electro-acoustic transducer has higher sensitivity, lower price, and excellent humidity
characteristics as compared with a conventional capacitor-type ultrasonic sensor. It is known that
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the directivity characteristic is not good although it has advantages such as. The abovementioned proposal is a proposal aiming at improvement of directivity characteristics based on
the above-mentioned recognition, and the cause of directivity characteristics deterioration is the
finite size of the diaphragm 2 which forms a part of an ultrasonic sensor. The size can not be
neglected with respect to the wavelength of the vibration frequency, so even if the end face of
the diaphragm 2 is positioned at the focal point of the parabolic horn, the sound source located
at the non-focal point is necessarily present By blocking the sound source of the non-focus area
by the thin plate 4 as shown in the non-heating point group, and by regarding the thin plate 4 as
an apparent sound source It seems that they are trying to improve the directional characteristics.
Further, according to the above-mentioned proposal, it is described that the directivity
characteristic shown in FIG. 3 can be improved to the characteristic shown in FIG. 3 by providing
the thin plate 4.
However, although the characteristics of the mouth of FIG. 3 are narrower than the
characteristics of FIG. 3 and it can be recognized that the directivity characteristics are surely
improved, the sound source of the non-focus portion described above is completely It can not be
blocked and, as is apparent from the drawing, it still has the characteristic of having a side rope
although it is small. For this reason, the ultrasonic wave transmitting and receiving operation still
has a problem that a malfunction may occur. On the other hand, the practical use of the
ultrasonic transducer in the above-described proposal also has the following problems. First of
all, when the ultrasonic transducer based on the proposal is manufactured and the characteristics
are examined, the generation of side lobes is largely different, and the ultrasonic transmission
and reception having directivity characteristics as shown in FIG. It turned out that it is extremely
difficult to obtain a waver stably. That is, the state of the acoustic circuit formed by the
relationship between the vibration operation of the diaphragm 2 and the thin plate 4 is a change
in the shape and thickness of the diaphragm 2, inclination 1 ambient temperature etc. The
analysis is considered to be extremely difficult because it is considered to be greatly fluctuated,
and therefore, there is a problem that the qualification at the mass production level becomes
extremely difficult. In other words, any of the above-mentioned proposals is improved by
improving the acoustic characteristics of the characteristic gold ultrasonic sensor itself of the
ultrasonic transducer. Considering the fact that it changes extremely easily due to the
deformation of 2 and the change of ambient temperature etc., it is extremely difficult to stably
obtain a product with improved characteristics as an ultrasonic transducer. SUMMARY OF THE
INVENTION The object of the present invention is to solve the problems as described above, and
it is an ultra-high-power piezoelectric element which hardly causes side lobes of -2 s dB or more
to affect the transmission and reception of ultrasonic waves. An acoustic transducer is provided.
Another object of the present invention is that the ultrasonic sensor itself consisting of a
piezoelectric element or the like provided with a diaphragm can be considered as a simple
ultrasonic source, that is, a slight deformation, inclination or the like of the diaphragm 2 of the
ultrasonic sensor It is an object of the present invention to provide a mass-productive ultrasonic
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transducer having directivity characteristics which are not greatly affected by the fluctuation of
the ambient temperature or the fluctuation of the ambient temperature. The ultrasonic
transducer according to the present invention comprises an electro-acoustic transducer
comprising a diaphragm and a piezoelectric element provided with the diaphragm, an optional
rigid wall and a cylindrical hollow portion. An acoustic tube positioned in front of the acoustic
conversion element, and a position near the focal point on the horn axis on the horn axis
including the focal point at the center of the hollow portion at one end not facing the electroacoustic conversion element of the acoustic tube And at least a paraboloid horn.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an
ultrasonic transducer using a piezoelectric element provided with a diaphragm as an electroacoustic transducer having a significantly improved directivity characteristic, which will be
described below with reference to the drawings. FIG. 4 is a cross-sectional view showing an
embodiment of an ultrasonic transducer according to the present invention, in which the same
reference numerals as in FIG. 1 indicate the same functional members. Reference numeral 8
denotes a support fixed to the vibration node of the piezoelectric element 1 and supporting the
piezoelectric element 1; 9, a terminal for exchanging electrical energy with the piezoelectric
element 1; and 1o, the piezoelectric element 1 and the terminal 9 electrically Lead wire to
connect to Reference numeral 11 denotes an acoustic tube positioned in front of an
electroacoustic transducer composed of an arbitrary rigid wall 11a and a cylindrical hollow
portion 11b, a piezoelectric element 1 and a diaphragm 2. Although the acoustic tube 11 in the
present embodiment is apparent also from the drawing, it has only one electro-acoustic
transducer, and its central axis corresponds to the horn axis of the electro-acoustic transducer
and the parabolic horn 6. The center of the hollow portion 11 b of the other end 11 c is on the
horn axis of the paraboloid horn 5 so that the one end 11 d is located on the same plane as the
top surface of the diaphragm 2 so as to be coaxial. It is arranged to be located at a position near
the focal point on the horn opening side including the focal position. Furthermore, when the
acoustic tube 11 shown in FIG. 4 is illustrated, it is needless to say that the plan view can be
shown in FIG. 6 and the perspective view can be shown as the mouth of the same figure.
Furthermore, when a forced sound pressure is applied from one end of an acoustic tube having a
cylindrical hollow portion to an arbitrary rigid wall in general, the wavelength of the forced
sound pressure is λ, and the radius of the hollow portion of the acoustic tube is τ. Assuming
that the length is l, 2 r ≦ ˜ bow; · · · · · · · · · (1) l ζ + n λ[email protected] r · · · · · · · ·
·······································································································································································································
··················· (2) (n: positive integer: constant = o, es) Considering the condition that the other end of
the above-mentioned acoustic tube is centered on the hollow portion of the acoustic tube It is
known that a stable spherical wave can be formed, and the acoustic tube 11 according to the
present invention is also configured in consideration of the above equations (1) and (2).
According to the experiments of the inventors of the present invention, r in the equation (1) is
advantageously smaller than r = 4 f 6 j t s-· λ with respect to the occurrence of side lobes, (2)
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The equation 4 can not of course be strictly defined because it contains λ, which changes with
temperature, and the approximation values k and n, but it is intermediate in the general
operating temperature conditions of the equipment used Speed of sound 2 at a predetermined
temperature of 2 For example, considering general use in the natural world, it is set to a value
obtained when general 0.65 is substituted for λ and k based on the speed of sound with 25 ° C.
as the predetermined temperature It has been confirmed that no significant difference occurs in
the occurrence of side lobes due to temperature fluctuations and the like.
As an example, assuming, for example, that the electro-acoustic transducer is transmitted to the
conical diaphragm with a tip diameter of 7φ with the vibration frequency of the piezoelectric
element being 76 KHz and the air temperature is 26 ° C. = = 1.74 m ++ Any value sufficiently
small can be set, for example, 1 cabinet by an experiment of measuring the directivity
characteristic. Further, if r = 1 mm is set, equation (2) can be expressed as 1.63 m assuming n =
1. Therefore, for example, the value 1.63 mm can be set as l. Needless to say, in order to obtain
better results, it is possible to select an appropriate value by an experiment to measure the
directivity characteristics for the value in the vicinity of the value of 1.63 mm. Since one
embodiment of the ultrasonic transducer according to the present invention is configured as
described above, when electrical energy is supplied from the terminal e, an electro-acoustic
transducer comprising the piezoelectric element 1 and the diaphragm 2 Generates a sound wave,
which is supplied to the one end 11d of the acoustic tube 11 as a forced sound pressure and
transmitted to the outside through the hollow portion 11b. Here, when the directivity
characteristics at the time of driving as described above were measured, the directivity
characteristics as shown in FIG. 6 were obtained. It is needless to say that the directivity angle is
the characteristic when the diameter of the parabolic horn 6 is set to be similar to that of the
embodiment shown in FIG. Although it is apparent from FIG. 6, the side lobes of −25 dB or more
have only a slight first side lobe, and even when compared with the directivity characteristics of
the device with extremely sharp directivity characteristics, FIG. One unit of the directivity
characteristic chart of FIG. 1 was 10 dB when it was actually manufactured and confirmed. It is
clear that the second side rope has been generated and improved. Here, consider the reason why
the directivity characteristics as described above are obtained. First, at the time of driving as
described above, the vibration wave transmitted to the outside from the end of the hollow
portion 11b of the other end portion 11c of the acoustic tube 11 has a configuration in which the
acoustic tube 11 takes into consideration the above-described relational expression. It is needless
to say that it is a spherical wave centered on the end opening center of the portion 11b. On the
other hand, the end 11C side center of the hollow portion 11b of the acoustic tube 11 is
positioned at a position near the focal point on the horn opening side including the focal position
on the horn axis of the parabolic horn 5 as described above. Accordingly, it is considered that the
spherical wave transmitted to the outside mentioned above will travel parallel to the horn axis in
the paraboloid horn 5, and as a result, the opening of the paraboloid horn 6 travels to the outside
It is considered that the sound waves that have been transmitted have extremely sharp directivity
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characteristics as shown in FIG.
In other words, in the ultrasonic transducer according to the present invention, the spherical
sound source is provided by the acoustic tube 11 in the vicinity of the focal point on the horn
opening side including the focal position on the horn axis of the parabolic horn 6, It can be
considered that extremely sharp directivity characteristics are obtained because the sound
source clearly located in the non-focus area is largely reduced. By the way, in the embodiment of
FIG. 4 mentioned above, although good results were obtained as shown in FIG. 6 with respect to
directivity characteristics, it is considered to be good when examining transmission and reception
sensitivity. However, when considering the use as a device, there are problems in practical use
that are limited to extremely special applications. Also, as mentioned above, although r in the
above equation (1) works for the side ropes as it is smaller as it is certain, it is certain that if it is
too small, the transmission and reception sensitivity drops. The inventors of the present
invention have also confirmed through experiments that a decrease in sensitivity is similarly
observed when n is made too large for l in (2). As a result of the inventor of the present invention
performing various experiments to address the above problems, if an appropriate acoustic space
is provided between the acoustic tube 11 and the diaphragm 2, transmission and reception
sensitivity will be remarkable. It has been confirmed that the directivity characteristic is also
further improved. Furthermore, according to the experiment of the inventor of the present
invention, the above-mentioned acoustic space is simply formed with respect to the directivity
characteristic, so that the side rope level is further lowered and the lowering rate is a change in
the size of the space and the length etc. Although the transmission and reception sensitivity can
be increased by providing it as in the embodiment of FIG. 4, the transmission and reception
sensitivities are greatly fluctuated by the change of the size, and conversely the size is changed. It
has been confirmed that the characteristics have a property of being largely fluctuated by the
change of the vibration frequency and the shape of the diaphragm 2 if fixed. From this fact, it can
be considered that the change in sensitivity as described above is caused by the change in sound
pressure level applied to one end 11 d of the acoustic tube 11 since there is no large change in
directivity characteristics. The reduction in sensitivity in the case as described above can be
achieved by suppressing the actual or apparent sound pressure level applied to the one end 11d
by shortening the configuration itself or by shortening r and increasing l. It is thought that it is
because it becomes a thing. It is considered that the improvement of the directivity characteristic
is caused by the fact that supply of forced sound pressure in a more stable phase state to the one
end portion 11 d of the acoustic tube 11 becomes possible by the acoustic space.
Hereinafter, another embodiment of the ultrasonic transducer according to the present invention
made based on the above fact will be described with reference to the sectional view of FIG. In FIG.
7, the same reference numerals as in FIG. 4 indicate the same functional members, and 12 is an
acoustic space formed between the diaphragm 2 and the acoustic tube 11. As is apparent from
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the drawing, the configuration of the embodiment shown in FIG. 7 is the same as that of the
embodiment of FIG. 4 except that the acoustic space 12 is present, and the other configuration is
completely the same. By the way, the acoustic space 12 is marked in the hollow portion 11b of
the one end 11d of the acoustic tube 11 by the above-mentioned experimental confirmation so
that the sound pressure level that can be 77Il becomes stable and large, that is, the diaphragm 2
It is desirable to form so that the sound pressure by the vibration of can be efficiently
transmitted. In the present embodiment, as a result of various experiments, for example, the
shape is cylindrical and the length and diameter are the same as those of the specific numerical
example described above for the conditions of the acoustic tube 11 etc. Cabinet, is set to -10 tran.
That is, 1) An ultrasonic transducer having a cylindrical acoustic space with various lengths and
diameters is created, and the directivity characteristics, transmission and reception sensitivity
characteristics of each transducer are measured, and the results are as described above. I set it to
the value. It is needless to say that it is desirable that the value of the above-mentioned acoustic
space can be variously changed in consideration of the degree of influence on transmission and
reception sensitivity when the expected characteristic condition or the condition of the acoustic
tube 11 or the like is changed. . Now, looking at the directivity characteristics, transmission and
reception sensitivity in the embodiment shown in FIG. 7 having the values as described above in
the acoustic tube 11 and the acoustic space 12 etc. It can be confirmed that the above
characteristics and the transmission and reception sensitivity characteristics are each increased
by 8 dB as compared with the embodiment shown in FIG. As is clear from the drawing, it is clear
that the directivity is improved without the side rope of -25 dB or more, and that the
transmission and reception sensitivity also increase by 8 dB. In terms of output level, a signal of
about six times can be obtained, and the range of use as a device can be greatly expanded. In the
embodiments shown in FIG. 4 and FIG. 7, the acoustic tube 11 is described as being independent,
but the length and the radius of the hollow portion are the equations (1) j (2) described above. It
is needless to say that as long as it can be set in consideration, it may be integrated with a case in
which the parabolic horn 6 or the piezoelectric element 1 or the like is enclosed to form a part of
the ultrasonic sensor.
According to the present invention, as described above, the sound wave obtained by the
ultrasonic sensor comprising the piezoelectric element, the diaphragm and the like is
appropriately determined in consideration of the wavelength of the sound wave obtained by this
sound wave and an appropriate temperature condition. A non-focusing position is obtained
because the spherical sound source is converted to a sound source via an acoustic pipe that can
be set, and the obtained spherical sound source is located near the focal point on the horn
opening side including the focal position on the horn axis of the parabolic horn. Since it is
possible to make the sound source located at a very small amount, it is possible to stably provide
an ultrasonic transducer having extremely sharp directivity characteristics. Furthermore,
according to the present invention, directivity characteristics are further improved by providing
an appropriate acoustic space between the above-mentioned acoustic tube and an electro-
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acoustic conversion element consisting of a piezoelectric element and a diaphragm, and in
addition, transmission and reception are performed. It has the effect of being able to provide an
ultrasonic transducer of extremely high practical value that has significantly increased wave
sensitivity. It is a thin plate located in front of the conversion element, and therefore it is vibrated
by the vibration of the diaphragm during driving, which adversely affects the transmission
characteristics of ultrasonic waves, ie, to the electro-acoustic conversion element. Even if the
vibration energy supply to the diaphragm 2 is stopped and the vibration of the diaphragm 2
stops, the thin plate continues to vibrate by inertia, and on the contrary, the vibration energy is
supplied to the diaphragm, unnecessary vibration of the diaphragm In the ultrasonic transducer
according to the present invention, the one positioned in front of the electro-acoustic transducer
is an acoustic pipe having a certain length, and On the contrary, it also has the effect that
vibration does not cause << deterioration of the transmission characteristics as described above.
[0002]
Brief description of the drawings
[0003]
Sectional drawing which shows one Example of a wave speed receiving device, FIG. 6 a.
The mouth is a plan view and a perspective view of an example of the acoustic tube shown by the
numeral 11 in FIG. 4, FIG. 6 is a directional characteristic view of the embodiment shown in FIG.
4, and FIG. FIG. 8 is a cross-sectional view showing another embodiment of the wave device, and
FIG. 8 shows directivity characteristics of the embodiment shown in FIG. DESCRIPTION OF
SYMBOLS 1 ···· Piezoelectric element, 2 ··················································· , 12 ... ... acoustic space. Name
of agent Attorney Nakao Toshio and 1 other person Fig. 1 (Waba D Fig. 2 (λ λ [ニ 3 〔儂 儂]
αS 4 Fig. R degree) Fig. 7
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