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DESCRIPTION JP2012235445

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DESCRIPTION JP2012235445
The present invention provides an ultrasonic sensor having a directivity angle suited to an
application by changing the structure of a housing. A housing (2) having a base wall (21) and a
peripheral wall (22) surrounding the base wall (21), and a piezoelectric element (3) provided in
the housing (2). An inner surface 211 facing the inner space 20 and an outer surface 212 are
defined, and the inner surface 211 is between the first area screen 213, the first area screen 213
and the peripheral wall 22. The second division screen 214 to be arranged, and the linking
surface 215 connecting the first division screen 213 and the second division screen 214 are
provided, and the distance between the second division screen 214 and the outer surface 212 is
the first The recess 210 is defined by the first partition screen 213 and the linking surface 215
by being longer than the distance between the partition screen 213 and the outer surface 213,
and the piezoelectric element 3 is accommodated in the recess 210 and The ultrasound cell
characterized in that it is fixed to the first area screen 213 Support. [Selected figure] Figure 3
Ultrasonic sensor
[0001]
The present invention relates to sensors, and more particularly to ultrasonic sensors.
[0002]
An ultrasonic sensor can be used to detect the position or movement speed of a target object by
transmitting ultrasonic waves and receiving its reflection, for example, detection of a rear
obstacle in a car or collision prevention system Widely used.
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[0003]
FIG. 1 shows a conventional example of an ultrasonic sensor mounted on a vehicle, as described
in Patent Document 1, and includes a metal case 11 and a piezoelectric element 12 provided in
the case 11. Have.
The housing 11 has a base wall 111, and the base wall 111 is disposed so as to be surrounded by
the thin portion 113 disposed on the periphery thereof and the thin portion 113. And a thick
portion 112 slightly projecting therefrom.
The piezoelectric element 12 is disposed on the thick portion 112.
[0004]
When a voltage is applied, the piezoelectric element 12 is deformed according to the change in
voltage due to the piezoelectric effect, causing the base wall 111 to vibrate, and this vibration
generates an ultrasonic wave. When the ultrasonic waves reach the object to be detected and are
reflected, the reflected ultrasonic waves reach the base wall 111, and the base wall 111
resonates and vibrates again. The piezoelectric element 12 is deformed by this vibration, and an
electric signal is generated by the piezoelectric effect. This electrical signal is detected and
analyzed by a rear end circuit (not shown) electrically connected to the piezoelectric element 12
to measure the distance from the sensor to the object to be detected.
[0005]
JP 2001-326987 A
[0006]
However, such conventional ultrasonic sensors have certain directivity.
That is, the conventional ultrasonic sensor can not transmit ultrasonic waves with an equal
intensity in all directions, and can not receive ultrasonic waves from all directions equally even
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when receiving waves. As described above, the ultrasonic sensor has a direction and angle in
which ultrasonic waves can be transmitted or received as well as an angle, a so-called pointing
angle, but the pointing angle required differs depending on the purpose of use of the sensor.
Therefore, it is desirable for an ultrasonic sensor to have a directional angle suitable for the
purpose of use.
[0007]
Then, this invention aims at provision of the ultrasonic sensor provided with the directivity angle
according to the use purpose by changing the structure of a housing | casing in order to solve
the said subject.
[0008]
In order to achieve the above object, the present invention is an ultrasonic sensor comprising: a
case provided with a base wall and a peripheral wall surrounding the base wall; and a
piezoelectric element provided in the case, The base wall defines an inner space together with the
peripheral wall, and has an inner surface facing the inner space and an outer surface opposite to
the inner surface, the inner surface being a first A second screen, which is disposed between the
first screen and the peripheral wall, and a connecting surface for connecting the first screen and
the second screen, When the distance between the screen and the outer surface is longer than
the distance between the first area screen and the outer surface, a recess is defined between the
first area screen and the linking surface. And the piezoelectric element is accommodated in the
recess and fixed to the first screen. To provide.
[0009]
In the above means, preferably, the ratio of the depth of the recess to the distance between the
second screen and the outer surface is more than 0% and 50% or less.
[0010]
Moreover, it is preferable that the ratio of the area of the said 1st division screen with respect to
the area which united the said 1st division screen and the said 2nd division screen is 36% or
more and 90% or less.
[0011]
Furthermore, the depth of the recess is preferably more than 0.05 mm.
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[0012]
According to the above configuration, on the inner surface of the base wall for disposing the
piezoelectric element, a recess whose depth and size are adjusted to obtain a desired directivity
angle is defined, and the piezoelectric element is formed in the recess By being accommodated, it
is possible to provide an ultrasonic sensor having a pointing angle suitable for the purpose of
use.
[0013]
It is a local sectional view of an ultrasonic sensor of a conventional example.
It is a top view which shows one Embodiment of the ultrasonic sensor which concerns on this
invention.
FIG. 3 is an enlarged view of a portion along line III-III in FIG. 2;
It is the figure which showed the area of each part in FIG.
It is the graph which showed the change of the horizontal directivity angle of the ultrasonic
sensor concerning the present invention.
It is the graph which showed the change of the resonance frequency of the ultrasonic sensor
concerning the present invention.
It is a polar-coordinate figure which shows the horizontal directivity angle of each of the
ultrasonic sensor which concerns on this invention, and the ultrasonic sensor of a prior art
example. It is a graph which shows the change of the horizontal directivity angle of the ultrasonic
sensor which concerns on this invention. It is the graph which showed the change of the
resonance frequency of the ultrasonic sensor concerning the present invention.
[0014]
Hereinafter, embodiments of the present invention will be described in detail with reference to
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the accompanying drawings.
[0015]
As shown in FIG. 2 and FIG. 3, the ultrasonic sensor according to the embodiment of the present
invention is composed of a housing 2, a piezoelectric element 3 and a sealing material 4.
[0016]
The housing 2 has a base wall 21 and a peripheral wall 22 provided around the base wall 21. An
internal space 20 is defined in the housing 2 by the base wall 21 and the peripheral wall 22. .
In addition, although aluminum was used as a material of the housing | casing 2 in a present
Example, this invention is not limited to this.
[0017]
The base wall 21 is made so as to vibrate to generate an ultrasonic wave, and has an inner
surface 211 facing the inner space 20 and an outer surface 212 opposite to the inner surface
211.
[0018]
The inner surface 211 has a first section screen 213 disposed substantially at the center, a
second section screen 214 disposed between the first section screen 213 and the peripheral wall
22, a first section screen 213 and a second section screen 214. And an interlocking surface 215
connecting the
In addition, since the distance between the first area screen 213 and the outer surface 212 is
shorter than the distance between the second area screen 214 and the outer surface 212, the
first area screen 213 and the linking surface 215 A recess 210 is defined on the inner surface
211 side of the base wall 21, and the piezoelectric element 3 is accommodated in the recess 210
and fixed to the first screen 213.
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In the present embodiment, the second division screen 214 is provided to be substantially
elliptical.
[0019]
Here, assuming that the depth of the recess 210 is h1 and the distance between the second area
screen 214 and the outer surface 212 is h2, the resonance frequency of the housing 2 is
maintained at a suitable value for the ultrasonic sensor and good simultaneously. In order to
obtain a horizontal pointing angle, the ratio of h1 to h2 is preferably more than 0% and not more
than 50%. Moreover, in order to obtain a good sensor effect, it is preferable that the depth h1 of
the recess 210 exceeds 0.05 mm.
[0020]
FIG. 4 is a top view of the concave portion 210, schematically showing the area of the first
division screen 213 and the area of the second division screen 214. As shown in FIG. Here,
assuming that the area of the first section screen 213 is A1 and the area of the second section
screen 214 is A2, in order to obtain good horizontal directivity angles while maintaining the
resonance frequency of the housing 2 suitable for ultrasonic sensors. The ratio of A1 (area of the
first division screen 213) to A1 + A2 (area of the first division screen 213 and the second division
screen 214) is 36% or more and 90% or less. preferable. Further, the bottom surface area (that is,
A1) of the recess 210 is required to be larger than the bottom surface of the piezoelectric
element 3 in order to allow the recess 210 to accommodate the piezoelectric element 3, but the
presence of the recess 210 is the present invention A1 should not be equal to the sum of A1 and
A2, as
[0021]
The piezoelectric element 3 is made of a ceramic material so as to be able to be deformed
according to the applied electric field.
[0022]
The sealing material 4 fills the internal space 20 and covers the piezoelectric element 3, whereby
the piezoelectric element 3 is fixed to the first screen 213.
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[0023]
With the above configuration, in the ultrasonic sensor according to the present invention, the
base wall 21 vibrates as the piezoelectric element 3 is deformed by the application of the electric
field, and the ultrasonic wave is transmitted by the vibration of the base wall 21 .
Alternatively, the base wall 21 vibrates by receiving ultrasonic waves, and the piezoelectric
element 3 is deformed with the vibration of the base wall 21 to generate an electric field.
[0024]
The ultrasonic sensor according to the present invention includes electronic components such as
a capacitor and a wire, for example, in addition to the above-mentioned configuration, but these
are well known techniques and therefore will not be described here.
[0025]
Hereinafter, in the ultrasonic sensor according to the present invention, various experimental
results obtained by examining how the directivity angle and the resonance frequency change by
changing the parameters h1, h2, A1, and A2 are shown in FIG. This will be described with
reference to FIG.
[0026]
FIG. 5 shows how the horizontal pointing angle is changed by changing the ratio of the depth
(h1) of the recess 210 to the distance (h2) between the second screen 214 and the outer surface
212 in the ultrasonic sensor according to the present invention. It is a graph which shows the
experimental result which investigated whether it changed.
[0027]
In the above experiment, a microphone was placed at a distance of 30 cm from the second
division screen 214 to measure the sound pressure.
In the configuration of the present experimental example, the distance (h2) between the second
section screen 214 and the outer surface 212 is 0.8 mm, the area (A1) of the first section screen
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213 is 35 mm <2>, and the second section screen 214 The area (A2) was 45 mm <2>.
[0028]
As can be seen from FIG. 5, when the ratio of h1 to h2 is 0%, that is, when the recess 210 is not
formed on the inner surface 211, the horizontal pointing angle is 83 degrees.
Also, as the depth (h1) of the recess 210 increases, the horizontal pointing angle also increases,
and when the ratio of h1 to h2 reaches 50%, the horizontal pointing angle reaches 140 degrees.
In addition, when it exceeded 55%, the horizontal directivity angle became about 180 degrees,
that is, the horizontal directivity angle could not be obtained.
As this result shows, a recess 210 for housing the piezoelectric element 3 is formed on the inner
surface 211 of the base wall 21 of the ultrasonic sensor, and the recess for the distance (h2)
between the second screen 214 and the outer surface 212 By appropriately adjusting the ratio
(h1 / h2) of the depth (h1) of 210, it is possible to provide an ultrasonic sensor having a
horizontal pointing angle suitable for the purpose of use.
[0029]
6 shows an ultrasonic sensor according to the present invention, in which the ratio of the depth
(h1) of the recess 210 to the distance (h2) between the second screen 214 and the outer surface
212 changes the resonance frequency of the housing 2 It is a graph which shows the
experimental result which investigated how it changed. Generally, an ultrasonic sensor uses
sound waves with a frequency in the range of 40 kHz to 70 kHz, and since the lower the
frequency, the smaller the attenuation with propagation, the ultrasonic waves can be propagated
over a long distance.
[0030]
As can be seen from FIG. 6, when the ratio of h1 to h2 is 0%, that is, when the recess 210 is not
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formed on the inner surface 211, the resonance frequency of the housing 2 is approximately 65
kHz. As the ratio of h1 to h2 increases, that is, as the recess 210 becomes deeper, the resonant
frequency of the housing 2 decreases, and when the ratio of h1 to h2 reaches 50%, the resonant
frequency decreases to about 50 kHz.
[0031]
FIG. 7 is a polar coordinate diagram showing an ultrasonic sensor according to the present
invention as an experimental example, and an ultrasonic sensor having no recess as shown in the
conventional example as a comparative example and comparing horizontal directivity angles
thereof . The line orthogonal to the base wall 21 was used as the original line (0 degrees in the
figure), and the attenuation amount (unit dB) of the sound pressure intensity was measured from
-90 degrees to 90 degrees, and the results are shown in radial coordinates.
[0032]
In the present experimental example, the respective numerical values of h1, h2, A1 and A2 were
determined as follows. h1=0.11mm h2=0.64mm A1=40mm<2>
A2=40mm<2>
[0033]
As can be seen from FIG. 7, the experimental example according to the present invention has a
directivity angle larger than that of the comparative example.
[0034]
FIG. 8 shows the ultrasonic sensor according to the present invention, in which the ratio of the
area (A1) of the first division screen 213 to the area (A1 + A2) of the total area of the first
division screen 213 and the second division screen 214 is changed. It is a graph which shows the
experimental result which investigated how a pointing angle changes.
In the present experimental example, h1 was 0.11 mm and h2 was 0.64 mm, and the sum of A1
and A2 was fixed, and the value of A1 was changed.
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[0035]
As can be seen from FIG. 8, as the ratio of A1 to the sum of A1 and A2 increases, the horizontal
directivity angle also increases. As described above, by adjusting the ratio of the area of the first
division screen 213 to the total area of the first division screen 213 and the second division
screen 214, it is also possible to provide a desired directivity angle that matches the purpose of
use. An acoustic wave sensor can be provided.
[0036]
FIG. 9 shows an ultrasonic sensor according to the present invention, in which the ratio of the
area (A1) of the first division screen 213 to the total area (A1 + A2) of the first division screen
213 and the second division screen 214 is changed. It is a graph which shows the experimental
result which investigated how the resonant frequency of the body 2 changes.
[0037]
As shown in FIG. 9, the ratio of A1 to the sum of A1 and A2 is approximately inversely
proportional to the resonance frequency, but if the ratio is in the range of 36% to 90%, the
resonance frequency is always 61.5 kHz or less .
[0038]
As described above, the ultrasonic sensor according to the present invention defines the recess
210 by providing the first screen 213 and the second screen 214 having different distances from
the outer surface 212 on the inner surface 211 of the base wall 21. And by disposing the
piezoelectric element 3 in the recess 210, the ratio of the depth of the recess 210 to the distance
between the second screen 214 and the outer surface 212, and the first screen 213, as described
above. By appropriately adjusting the ratio of the area of the first division screen 213 to the total
area of the second division screen 214, it is possible to give the ultrasonic sensor a desired
directivity angle suitable for the purpose of use.
[0039]
While the present invention has been described in detail in connection with specific
embodiments, the present invention is not limited to the above embodiments and the attached
drawings, but covers various modifications included in the widest scope of interpretation. It
should be understood that it is intended.
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[0040]
The ultrasonic sensor according to the present invention can have a directivity angle suitable for
the application, and thus can be used as various object detection sensors such as a collision
prevention sensor and a parking sensor provided in a vehicle, for example.
[0041]
DESCRIPTION OF SYMBOLS 2 Casing 20 internal space 21 base wall 210 recessed part 211
inner surface 212 outer surface 213 1st screen 214 2nd screen 215 connecting surface 22
peripheral wall 3 piezoelectric element 4 sealing material A 1 area of 1st screen A2 2nd screen
Area h1 Depth of recess h2 Distance between 2nd screen and outer surface
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