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JP2006174003

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DESCRIPTION JP2006174003
PROBLEM TO BE SOLVED: To narrow directivity and shorten reverberation time with an isotropic
ultrasonic transducer. SOLUTION: An ultrasonic transducer 10 includes a bottomed cylindrical
case 11 and a piezoelectric element 12 provided substantially at the center of the inner surface
of the bottom of the case 11. The hollow cross section of the case 11 is a substantially perfect
circle, and the thickness of the bottom of the case 11 is thicker at the portion where the
piezoelectric element 12 is provided, and gradually becomes thinner toward the side wall surface
of the case 11 In the thickness of the bottom of 11, the ratio t1 / t2 of the minimum thickness t1
to the maximum thickness t2 is 0.43 or more and 0.57 or less. [Selected figure] Figure 1
Ultrasonic transducer
[0001]
The present invention relates to an ultrasonic transducer, and more particularly, to a back sonar
and a corner sonar of a car, and a parking slot sensor attached to the side of the car and
detecting presence or absence of a space with an obstacle such as a side wall in parallel parking.
The present invention relates to an ultrasonic transducer.
[0002]
The ultrasonic transducer performs sensing using ultrasonic waves, intermittently transmits an
ultrasonic pulse signal from the piezoelectric vibration element, and uses the piezoelectric
vibration element to reflect the reflected wave from an obstacle present in the periphery. It is
something which detects the object by receiving.
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1
[0003]
Among such ultrasonic waves, an ultrasonic transducer 1 as shown in FIG. 6 is known as a
vehicle-mounted one.
(See Patent Document 1) The ultrasonic transducer 1 includes a case 2.
The case 2 is a bottomed cylindrical shape having a hollow portion with a perfectly circular cross
section, and the flat plate-like piezoelectric element 4 housed in the hollow portion is fixed to the
inner surface of the bottom portion 2 a of the case 2. Signal wire 6 is connected to one electrode
of the piezoelectric element 4 and the other signal wire 6 of the connector cable 5 is electrically
conducted to the other electrode of the piezoelectric element 4 via the metal case body 2. .
[0004]
The piezoelectric element 4 is covered with a sound absorbing material 7, and the piezoelectric
element 4 and the sound absorbing material 7 are sealed by an insulating resin 8 having
elasticity such as silicon rubber or urethane rubber.
[0005]
The bottom of the case 2 has a step shape in which the thickness of the portion to which the
piezoelectric element 4 is fixed is increased and the thickness to which the piezoelectric element
4 is not attached, that is, the portion around the piezoelectric element 4 is reduced. ing.
The step is provided to prevent the piezoelectric element 4 from being broken by external stress.
[0006]
Also, an invention of an ultrasonic transducer has been made for the purpose of reducing the
reverberation time while giving anisotropy to the directivity. Although this prior art is not shown
in particular in this prior art, while the level | step difference is provided in the part which a
piezoelectric element adheres similarly to patent document 1, in order to give anisotropy to
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directivity, the hollow part of a case is provided. However, the cross section of the case inner wall
is formed to be long on one side and short on the other side. Further, paragraph 0036 of the
same document states that the structure of the step may be a smooth inclined structure instead
of being stepped. JP 2000-152388 A JP 2001-326987 A
[0007]
However, in the above-mentioned conventional ultrasonic transducer, the reverberation
characteristic is unstable and the reverberation time is long, the ultrasonic wave reflected from
the object close to the ultrasonic transducer interferes with the reverberation, and the presence
of the close object is In some cases, it is not possible to detect, or it becomes impossible to
accurately grasp the distance to a close object.
[0008]
In particular, with the further miniaturization of the ultrasonic transducer and the development
of the application to the parking slot sensor, an anisotropy is not obtained, that is, the directivity
is directed to the isotropic ultrasonic transducer as illustrated in FIG. There is a need to reduce
the gender and further shorten the reverberation time.
[0009]
In order to solve the above problems, an ultrasonic transducer according to the present invention
is an ultrasonic transducer including a bottomed cylindrical case and a piezoelectric element
provided substantially at the center of the inner surface of the bottom of the case. The internal
cross section forming the hollow of the case is a substantially perfect circle, and the thickness of
the bottom of the case is thicker at the portion where the piezoelectric element is provided, and
gradually becomes thinner toward the side wall surface of the case In addition, in the thickness
of the bottom of the case, the ratio t1 / t2 of the minimum thickness t1 to the maximum
thickness t2 is 0.43 or more and 0.57 or less.
[0010]
The ultrasonic transducer thus configured has a shorter reverberation time as compared with the
conventional ultrasonic transducer, and therefore, it is possible to more accurately grasp the
distance to an adjacent object.
More specifically, the ultrasonic transducer according to the present invention is suitable for use
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in a parking slot sensor as an isotropic ultrasonic transducer with the hollow cross section of the
case as a substantially perfect circle, and the minimum at the bottom of the case By defining the
ratio of thickness to the maximum thickness to be 0.43 or more and 0.57 or less, it is possible to
obtain a short reverberation time and to narrow the directivity of the ultrasonic transducer, so
that the parking slot sensor The invention can be applied to various sensors using the ultrasonic
transducer.
[0011]
The features of the present invention will be described in more detail with reference to the
following examples of the present invention.
[0012]
An ultrasonic transducer according to an embodiment of the present invention will be described
with reference to FIGS. 1 to 3.
[0013]
The ultrasonic transducer 10 shown in FIG.
The case 11 is formed of, for example, a metal material such as aluminum, and has a bottomed
cylindrical shape having a true circular cross section and a hollow portion.
In the hollow portion of the case 11, the flat piezoelectric element 12 is fixed to the inner surface
of the bottom of the case 11.
Electrodes which do not appear on the drawing are provided on both main surfaces of the
piezoelectric element 12 and are fixed to the bottom of the case 11 through the electrodes
formed on one of the main surfaces.
[0014]
The piezoelectric element 12 is connected to one signal line 14 a of the connector cable 13 on
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the other main surface.
Further, the piezoelectric element 12 connects another signal line 14 b of the connector cable 13
to the inner wall side surface of the metal case 11, thereby providing the connector cable 13 via
the case 11 on one main surface of the piezoelectric element 12. It is connected to another signal
line 14b.
[0015]
Inside the case 11, a sound absorbing material 15 made of felt or the like is provided so as to
cover the piezoelectric element 12. In addition, an insulating resin 16 having elasticity such as
silicon rubber or urethane rubber is provided in the case 11 so as to seal the piezoelectric
element 12 and the sound absorbing material 15.
[0016]
The bottom of the case 11 increases the thickness of the portion to which the piezoelectric
element 12 is fixed, and approaches the side wall surface of the case 11 from the portion to
which the piezoelectric element 12 is not attached, that is, the peripheral portion of the
piezoelectric element 12 Therefore, it has an inclined structure in which the thickness is
gradually reduced.
[0017]
Here, in the ultrasonic transducer having an outer diameter of 14 mm, an inner diameter of **
mm and a maximum thickness of 7 mm at the bottom, the conventional ultrasonic wave
transmission and reception in which the bottom of the case 2 shown in FIG. The half-full angle
and reverberation time of the vessel 1 and the ultrasonic transducer 10 shown in FIG. 1 in which
the bottom of the case 11 has a sloped structure are compared.
The half-full angle is an angle between directions which are 20 log 0.5 dB (about 6 dB) lower
than the transmission / reception sensitivity of the direction (the direction of 0 °) facing the
bottom of the case. In any of the conventional ultrasonic transducer 1 and the ultrasonic
transducer 10 of the present invention, the maximum thickness of the bottom of the case is t2,
the minimum thickness is t1, and the minimum thickness t1 is changed. I confirmed the
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characteristics. The comparison results are shown in FIGS.
[0018]
As is clear from the graph showing the relationship between the thickness ratio of the bottom of
the case and the half-full angle shown in FIG. 4, the half-full-angle characteristic is different
between the conventional ultrasonic transducer 1 and the ultrasonic transducer 10 of the
present invention. Can not be seen. When an ultrasonic transducer is used for a parking slot
sensor, it is desirable that the half-full angle be 40 ° or less. In the ultrasonic transducer of the
present invention, the ratio t1 of the minimum thickness to the maximum thickness of the case
bottom portion It is desirable to set / t2 to 0.57 or less.
[0019]
On the other hand, as is clear from the graph showing the relationship between the thickness
ratio of the case bottom and the reverberation time shown in FIG. 5, the reverberation time is the
same as the ultrasonic transducer of the conventional step structure and the ultrasonic
transmission / reception of the inclined structure of the present invention. A big difference was
seen in the wave. That is, it has become clear that the reverberation time of the ultrasonic
transducer 10 of the present invention is shorter than that of the conventional ultrasonic
transducer 1. In particular, in the conventional ultrasonic transducer 1, the reverberation time is
1.2 milliseconds (msec) or more when the ratio t1 / t2 of the minimum thickness to the
maximum thickness of the case bottom is 0.58 or less However, in the ultrasonic transducer 10
of the present invention, the reverberation time was 1.15 milliseconds even when the ratio t1 /
t2 of the minimum thickness to the maximum thickness of the case bottom was 0.15. When an
ultrasonic transducer is used as a parking slot sensor, it is desirable that the reverberation time is
1 millisecond or less, so in the ultrasonic transducer of the present invention, the ratio of the
minimum thickness to the maximum thickness of the case bottom It is desirable to set t1 / t2 to
0.43 or more.
[0020]
From the above, the isotropic ultrasonic transducer having a half full angle of 40 ° or less and a
reverberation time of 1 millisecond or less has an inclined structure in which the bottom surface
of the case gradually becomes thinner with the piezoelectric element forming portion as the
maximum thickness. Thus, an ultrasonic transducer having a ratio t1 / t2 of the minimum
thickness t1 to the maximum thickness t2 of 0.43 or more and 0.57 or less is provided.
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[0021]
It is a sectional view showing the structure of the ultrasonic transducer concerning the example
of the present invention.
It is a top view which shows the case body concerning the ultrasonic transducer of this invention.
FIG. 3 is an explanatory view of line AA in FIG. 2; It is a graph which shows the relationship
between the ratio of the thickness of a case bottom part, and a half-full angle. It is a graph which
shows the relationship between the ratio of the thickness of a case bottom part, and
reverberation time. It is sectional drawing which shows the structure of the conventional
ultrasonic transducer.
Explanation of sign
[0022]
10 ultrasonic transducer 11 case 12 piezoelectric element
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