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JP2000295694

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DESCRIPTION JP2000295694
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic sensor applied to, for example, an ultrasonic imaging apparatus for imaging using a
plurality of sensors.
[0002]
2. Description of the Related Art An ultrasonic sensor used for an ultrasonic imaging apparatus
or the like is required to have wide directivity and a wide sensitivity frequency band. In order to
improve the directivity of the ultrasonic sensor, it is sufficient to reduce the aperture area, that is,
to be close to a point wave source, but in this case, there arises a problem of insufficient
transmission energy.
[0003]
As a method of realizing wide directivity and a wide sensitivity frequency band while sufficiently
securing the aperture area of an ultrasonic sensor, there is a method of using an acoustic lens as
seen in JP-A-9-298795. .
[0004]
By the way, according to the ultrasonic sensor described in Japanese Patent Application LaidOpen No. 9-298795, a plurality of random inclined cross sections are formed on the ultrasonic
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1
receiving surface of the protective plate of the ultrasonic transducer. By forming the grooves
concentrically, the acoustic lens is formed at the portion corresponding to each sensor, so that
the structure becomes complicated and there is a problem that it takes time to design and
process the acoustic lens.
[0005]
The present invention has been made in view of such circumstances, and an object thereof is to
provide an ultrasonic sensor capable of realizing wide directivity and wide sensitivity frequency
band with a simple configuration.
[0006]
The ultrasonic sensor according to the present invention is characterized in that the piezoelectric
vibrator is joined to a flat plate having a larger area than the piezoelectric vibrator, and such a
structure is adopted. By doing this, wide directivity and wide sensitivity frequency band can be
realized.
[0007]
That is, when the piezoelectric vibrator is vibrated in a state where the piezoelectric vibrator is
joined to a flat plate (for example, a stainless steel disc) having a larger area than the
piezoelectric vibrator, the rigidity of the flat plate joined to the piezoelectric vibrator causes
piezoelectricity. The shape of the vibrator is a sine curve, and the vibrating surface is in a bent
state, and a leaky wave (leakage wave) is transmitted to a flat plate around the piezoelectric
vibrator.
These phenomena improve the directivity of the ultrasonic sensor and broaden the sensitivity
frequency band.
[0008]
Here, in the ultrasonic sensor of the present invention, even if a flat plate having a larger area
than the piezoelectric vibrator is bonded to only one side of the piezoelectric vibrator, the object
can be sufficiently achieved, but the piezoelectric vibrator If flat plates are joined to both sides,
the Q value of the entire sensor decreases, and the sensitivity frequency band can be further
extended.
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[0009]
Further, in the ultrasonic sensor according to the present invention, if a spiral slit having an
inclination with respect to the radiation direction of the piezoelectric vibrator is processed in a
portion other than the joint portion of the flat piezoelectric vibrator, The propagation of leaky
waves in the radial direction is delayed, so that the size of the flat plate (for example, the radius
of the stainless steel disc) can be reduced, and the sensor can be miniaturized.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described below based on the drawings.
[0011]
FIG. 1 is a general perspective view of an embodiment of the ultrasonic sensor of the present
invention, and FIG. 2 is a side view of the embodiment.
[0012]
The ultrasonic sensor according to the present embodiment includes a cylindrical piezoelectric
vibrator 1 and two stainless steel disks 2 having a larger area than that of the piezoelectric
vibrator 1. The disc 2 is joined.
The centers of the piezoelectric vibrator 1 and the two stainless steel disks 2 coincide with each
other.
[0013]
The piezoelectric vibrator 1 is an element in which an electrode layer is formed on both sides of a
thickness vibration type piezoelectric element such as lead zirconate titanate (PZT), and in this
example, one having a diameter of 2.4 mm and a thickness of 1 mm is used. .
Further, as the stainless steel disc 2, one having a diameter of 11 mm and a thickness of 0.1 mm
is used.
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3
[0014]
The vibration state of the ultrasonic sensor of the above shape and size is shown in FIG.
FIG. 3 is a cross-sectional view showing a state of being cut along the radial direction from the
center of the ultrasonic sensor.
[0015]
In the vibration state shown in FIG. 3, the piezoelectric vibrator 1 is contracted vertically and
expanded laterally, and it can be seen that the vibration surface of the piezoelectric vibrator 1 is
bent.
This is a deformation (sine curve) caused by the rigidity of the stainless steel disc 2 to the
piezoelectric vibrator 1, and in the case where a flat plate such as a stainless steel disc is not
attached to the piezoelectric vibrator 1, the piezoelectric vibrator 1 is There is no large deflection
of the vibrating surface of.
Further, in the vibration state shown in FIG. 3, it can be seen that leaky waves are transmitted to
the stainless steel disc 2 around the piezoelectric vibrator 1 and it can be seen that energy is
efficiently radiated.
[0016]
Here, when the directivity characteristic of the ultrasonic sensor of the present embodiment was
measured, the result as shown in FIG. 4 was obtained.
From the directivity characteristic diagram shown in FIG. 4, it is understood that the ultrasonic
sensor of the present embodiment exhibits a wide directivity of 1 dB down at 30 degrees.
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[0017]
FIG. 5 is a plan view of another embodiment of the ultrasonic sensor of the present invention,
and FIG. 6 is a side view of that embodiment.
[0018]
The ultrasonic sensor according to the present embodiment has a structure in which the stainless
steel disc 2 is joined to both surfaces of the piezoelectric vibrator 1 as in the previous
embodiment, and the piezoelectric vibrator of the stainless steel disc 2 is A feature is that a
plurality of spiral slits 3... 3 having an inclination with respect to the radiation direction of the
piezoelectric vibrator 1 are processed in portions where 1 is not joined.
[0019]
As the shape of the slit 3, as shown in FIG. 7, a circle a having a diameter of a portion 2A of the
stainless steel disc 2 to which the piezoelectric vibrator 1 is not joined is along the fixed circle b
(joined portion 2B) When rolling, it is obtained from the locus (cycloid) drawn by one point p on
the circle a.
[0020]
Then, by processing the slits 3 in the above shape on the stainless steel disc 2, the propagation of
leaky waves in the radial direction of the stainless steel disc 2 is delayed, and the stainless steel
circle is made. The radius of the plate 2 can be reduced.
[0021]
The shape of the slit 3 is not limited to the shape shown in FIG. 5, and any shape may be adopted
as long as it has a spiral shape having an inclination with respect to the radiation direction of the
piezoelectric vibrator 1.
[0022]
Here, in the above embodiment, although the stainless steel disc 2 is bonded to both surfaces of
the piezoelectric vibrator 1, even in the configuration in which the stainless steel disc 2 is bonded
to any one surface of the piezoelectric vibrator 1. The object of the present invention can be
sufficiently achieved.
[0023]
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Moreover, although the example of one ultrasonic sensor is shown in the above embodiment, it is
needless to say that the present invention can be applied to a multi ultrasonic sensor in which a
plurality of sensors are arranged.
[0024]
As described above, according to the ultrasonic sensor of the present invention, the piezoelectric
vibrator is simply connected to a flat plate (for example, a stainless steel disc) having a larger
area than the piezoelectric vibrator. Thus, wide directivity and wide sensitivity frequency band
can be realized.
[0025]
In the ultrasonic sensor of the present invention, if flat plates having a larger area than that of
the piezoelectric vibrator are bonded to both surfaces of the piezoelectric vibrator, the Q value of
the entire sensor becomes smaller, and the sensitivity frequency band becomes wider.
[0026]
Further, in the ultrasonic sensor according to the present invention, if a spiral slit having an
inclination with respect to the radiation direction of the piezoelectric vibrator is processed in a
portion other than the joint portion of the flat piezoelectric vibrator, The propagation of leaky
waves in the radial direction is delayed, and the size of the flat plate can be reduced, that is, the
sensor can be miniaturized.
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