JPS58212300

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DESCRIPTION JPS58212300
[0001]
The present invention relates to an ultrasonic transducer having a small size, sharp directional
characteristics, and a pulse characteristic (transient '1. 1' 4 fl) '. Piezoelectric ceramic bonded
elements are often used in devices for transmitting and receiving ultrasonic waves in the air. -It is
made to use at the resonance point and anti-resonance point of flexural vibration of the element.
In addition, since the mechanical impedance of air is much smaller than that of the piezoelectric
ceramic, the laminated piezoelectric element is bonded to the diaphragm to reduce the
mechanical impedance. The structure and characteristics of a conventional ultrasonic transducer
are shown in FIGS. 1 and 2 respectively. As shown in FIG. 1, the connecting shaft 2 is fixed to the
center of the bonding type piezoelectric element 1 in a penetrating manner, and the diaphragm 3
is attached to the connecting shaft 2. Then, the node of vibration of the bonding type
piezoelectric element 1 is fixed to the tip of the support 4 with the elastic adhesive 5. 6, 6 'are
terminals, 7 is a case covering the bonding type piezoelectric element 1, etc., 8 is a protective
mesh attached to a through hole formed in the upper part of the case 7, 9.9' is a bonding Lead
wire electrically connecting the piezoelectric element 1 and the terminal 6.6 '. FIG. 2 shows
transmission and reception waveforms when the ultrasonic transducer of the above structure is
driven by a plurality of pulses, and the rise and fall times are delayed and extend over 2
milliseconds or more. . When it is necessary to obtain measurement information at short time
intervals using such a conventional ultrasonic wave 11 transmission i-wave device, the signal
received by the wave receiver is received because the rise and fall times are long. It takes time at
1 for the signal to reach its peak value. Alternatively, accurate measurement information could
not be obtained, for example, the next signal was received before the falling of the received
signal. In addition, when transmitting and receiving waves are performed by a single element, it
takes a considerable amount of time to be transmitted immediately after being transmitted and it
becomes ready for reception, during which measurement information was not obtained.
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Furthermore, if the directional characteristics of the ultrasonic transducer using piezoelectric
ceramics are dampened, the diaphragm, the bonding type piezoelectric element and the support
for supporting the bonding type piezoelectric element become remarkably large. There was a
drawback. Even with a large diaphragm, it was not possible to sharpen the directional
characteristics significantly because it is difficult to vibrate the piston L1. Therefore, when trying
to sharpen the directivity characteristics using a horn, the mechanical Q is lowered to make the
pulse characteristics, J, t6 j & N: 9,?
In the present invention, a diaphragm is provided at the center of the bonded piezoelectric
element, and the periphery of the diaphragm is elastically fixed to the case with an elastic
material such as elastic rubber so as to suppress mechanical vibration, and the opening is
formed. By adding the provided thin plate and horn, an ultrasonic transducer having sharp
directional characteristics and sharp pulse characteristics is realized, and the above problems are
solved. Hereinafter, an embodiment of the present invention will be described with reference to
the drawings. FIG. 3 is a cross sectional view of this embodiment. A diaphragm 13 made of metal
or resin is attached to a joint shaft 12 disposed at the center of the bonded piezoelectric element
11. The peripheral portion of the diaphragm 13 is elastically fixed to the inner side surface of the
cylindrical case 17 via a buffer material 2o such as an elastic rubber formed in an annular shape
so as to suppress mechanical vibration. A sound absorbing material 21 is provided at the bottom
of the case 1. In front of the diaphragm 13, a thin plate 23 having a circular opening 22 at the
center and another opening 22 'provided concentrically around a straight line passing through
the connecting shaft 12 is installed ing. The thin plate 23 and the case 17 for covering the
bonding type piezoelectric element 11 and the like are inserted into and held by the throat
portion of the parabolic horn 24 so as to be 6,. Reference numerals 19 and 19 'denote lead wires
electrically connecting the bonding type piezoelectric element 11 and the terminals 16 and 16'.
The shapes of the open portions 22 and 22 'of the thin plate 23 differ depending on the size and
thickness of the bonding type piezoelectric element 11, the size, thickness and central angle of
the diaphragm 13, the inner diameter of the shock absorbing material 20, etc. . When the
diameter of the bonding type piezoelectric element 11 is about 9.1 mm, the thickness is 0, 6 mm,
and the diaphragm 13 has a conical shape with a diameter of 17 mm on the bottom, the essential
resonance frequency of this super 11 wave transducer As a result of various investigations, the
thin plate 13t showing the best directivity characteristics, a plurality of circular openings 22 with
a diameter of 0.8 mm in the center, and a diameter of 8 ml + 1 on the circumference It is of the
shape shown in FIG. 4 in which a plurality of circular 1j old 1 portions 22 'of 0.6 mm are
provided. Next, pointing of the ultrasonic transducer according to the above-mentioned structure
of the present invention '1! One is shown in FIG. This figure ((8) shows the directivity
characteristic of the thin plate 23 installed in front of the diaphragm 13, and the same figure (G))
shows the directivity characteristic of the one before installation. From this it can be seen that
the half-angle, the zide rope has decreased significantly. In addition, in terms of space, for
example, up and down, left and right, nearly uniform directivity characteristics can be obtained.
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Furthermore, the transmission sensitivity also increased by about edB.
FIG. 6 shows the pulse characteristics of this ultrasonic transducer. The rise and fall times of the
pulse are 0.2 milliseconds or less. 7 (A), (B), and (Q represents the diameter and sound pressure
half angle of the bottom of the conical diaphragm 13 when the inner diameter of the shock
absorbing material 2o is changed to 12 mm, 13 mm, and 14 mm. The relationship between time
and transmitted sound pressure level is shown. In any case, the curve a101 is when the inner
diameter of the buffer material 2o is 12 mm, and the curve 102 ° 103 is when the inner
diameter is 1311 m and 14 mm, respectively. As apparent from the figure, as the diameter of the
diaphragm 13 increases, the transmission sound pressure level generally increases, but the rise
time is also long: ',,,. As for the sound pressure half angle, according to the structure of the
present invention, the shock absorbing material 201. There were no significant changes in the
diameter of 121 nm, 13 mm and 14 mm and the diameter of the diaphragm 13 in the range of
14 to 18 mm. Therefore, the diameter of the diaphragm 13 is 13 mm or less, which is
disadvantageous in terms of the transmission sound pressure level and the point 11 of the first
case. When the diameter of the diaphragm 13 is 20 mm or more, not only the large effect can
not be seen in terms of sound pressure half angle, rise time, transmission sound pressure level
111, and bonding is optimum for the above large diaphragm 13 The size of the piezoelectric
element 11 also increases and the size of the ultrasonic transducer increases. Aren't you? The
diameter of the bonding type piezoelectric element 11 is 9.1 mm, thickness EJ, '0.6111111 X 2
sheets, and it is an experimental value in the case of the parabolic horn 24i1 diameter
55111111. FIG. 8 shows the relationship between the inner diameter of the old buffer 20 and
the characteristics when the diameter of the diaphragm 13 is changed to 16 [11111-, "ffIIIls 17
mm". The curve 111 in the figure is the characteristic when the diameter of the diaphragm 13 is
15 mm, and the curve 112 ° 113 is the characteristic when the diameters are 16 mm and 17
mm, respectively. As is apparent from the figure, the decrease in the inner diameter of the shock
absorber 20 1 ffl ':: With the decrease in the rise time generally, the feed j "? 11. Levels also
tend to decrease. □ However, when the ratio of the inner diameter of the buffer A 2 o to the
diameter of the diaphragm 13 is about 0.8, the transmission sound pressure level takes a
maximum value, and at this time, the sound pressure half angle also shows the minimum value.
Furthermore, if the inner diameter of the shock absorbing material 2o is reduced, the side rope
also increases and the transmission sound pressure level decreases and the rise time does not
decrease significantly. The relationship between the diameter of the horn 24 of the ultrasonic
transducer according to the present invention and the half pressure of sound pressure is shown
in FIG. 9 at a driving frequency of 7 okH +.
In the figure, the curve is a calculated value of the sound pressure half angle in the case of a
circular diaphragm which performs piston oscillation. In this case, the directivity coefficient R
(represented by the following equation, where ■ 1 is the first Bet-7 function, a is the radius of
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the sound source, and K is the wave number. When R (in the equation (1) is solved for the sound
pressure half angle θh as − (% of the equation), it can be approximated by the following
equation. Where d is the diameter of the sound source C mm], f is the operating frequency C klk],
and C is the speed of sound C m / s]. 101, the curve in the diagram is taken as in equation (2).
Also, at this time, the first tide lobe drops by about 1y, edB, as compared with the main rope,
according to the equation 0). Therefore, the ultrasonic transducer according to the present
invention is 1 "as compared to the calculated factor which is analyzed as a circular diaphragm
which performs piston vibration. Pressure half-angles: It became clear that the side ropes also
showed small Ill'r. For example, when used for an autofocus 4-cas in a video camera, the angle of
view of the camera, the possible range-finding range, the range-finding scale in terms of degrees,
the side 1- 1 1 Narrow directivity characteristics, high sensitivity characteristics, good transients
with reduced 1- 111 is required. In order to realize narrow directivity, it is necessary to enlarge
the size of the sound source and make the operating frequency Q, as is apparent from Jl and
equation (2). However, the size of the sound source is limited as a consumer part. On the other
hand, as the use frequency goes up, it is released into air: It increases and the possible distance
range decreases. Therefore, in the case of the above-mentioned example: in the example of use,
according to the present invention, the ultrasonic transducer having the structure of 70 ± 10 klb
is desirable. As described above, the ultrasonic transducer according to the present invention has
sharp directional characteristics and good pulse characteristics, and it is necessary for ultrasonic
applied measurement where sharp directional characteristics are required such as a distance
meter using a sound wave. It is very useful.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a sectional view showing an example of a conventional ultrasonic transducer, and FIG. 2
is a view showing its pulse characteristics.
FIG. 3 is a cross-sectional view showing an embodiment of the ultrasonic transducer according to
the present invention, FIG. 4 is a perspective view showing an example of a thin plate which is a
component thereof, and FIG. FIG. 6 shows the pulse characteristics of this ultrasonic transducer,
FIGS. 7 (to 7), (B), (where Q is the diameter of the diaphragm and the sound pressure half angle
in the ultrasonic transducer of the present invention, Fig. 8 (5), (B) and (C) show the relationship
between the inner diameter of the shock absorber and the characteristics of the shock absorber,
Fig. 8 (5), (B) and (C) respectively FIG. 9 is a diagram showing the relationship between the
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diameter of the wheel 1 and jllun and the sound pressure half angle. 11 · · · Bonding type
piezoelectric element, 13 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · sound absorption
Material 22, 22 '··········································· Thin plate, 24 ······· Horn. Name of agent Attorney Nakao
Toshio One other person 1111. Fig. 1 Fig. 3 @ 5 Fig. C α ((ν) Fig. 7 tA tZ IA 16 1θ 2θ オ J J
(flame (fI-J Fig. 8 (^ IQ 12 14 I6A speed [Dai 2 L つ P 3 J ヒ 9 9 · Hen 9 Figure 46 5 θ 60, f,-レ
[9]
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