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JPH0835955

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DESCRIPTION JPH0835955
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic probe used as a sensor of a flaw detection apparatus.
[0002]
2. Description of the Related Art An ultrasonic flaw detector concentrates and radiates a
directional ultrasonic plane wave on a subject, and flaws on the surface and inside (nonuniform
points or boundaries with different media) It is a device that receives the wave reflected by the
sensor and detects information about the object from the measurement of its intensity and
propagation time, and has been widely put to practical use in recent years by the development of
ultrasonic technology and signal processing technology. In a flaw detection apparatus for
observing internal defects such as steel materials, a frequency of 0.4 to 10 MHz is used. On the
other hand, a high frequency of 0.1 to 5 GHz is used for an ultrasonic microscope which
performs finer sample observation such as pattern observation of a semiconductor.
[0003]
[0003] These ultrasonic flaw detection devices generally have an electric system including a
pulse voltage transmitting unit, a signal receiving unit, a signal synchronization unit, and a data
display unit, and a probe which is an ultrasonic sensor. The probe receives an pulse voltage to
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generate an ultrasonic beam, and an ultrasonic element having a function of converting a
reflected wave into an electric signal, and an acoustic lens having a function of focusing the
ultrasonic beam and emitting it to an object. And consists of
[0004]
FIG. 2 shows the main part structure of a conventional probe for an ultrasonic microscope. The
upper end surface of the cylindrical acoustic lens 12 consists of a plane perpendicular to the
central axis (cylindrical axis), and the ultrasonic element 11 is disposed in close contact
therewith. In the ultrasonic element 11, the piezoelectric transducer 13 and its upper electrode
14 and lower electrode 15 are arranged concentrically. Electrically independent conductive wires
are connected to the upper and lower electrodes 14 and 15, respectively, but are omitted for
simplicity in FIG. The upper electrode 14 is narrower than the lower electrode 15, and its
diameter is DE. The excitation and reception of ultrasonic waves occur in the area of the
piezoelectric transducer 13 directly below the upper electrode 14.
[0005]
A tapered area 17 and a concave lens 16 are provided at the lower end of the acoustic lens 12.
The tapered region 17 functions to prevent multiple reflection of ultrasonic waves in the acoustic
lens and to prevent the emission of excess ultrasonic waves that cause noise on the object
surface. The concave lens 16 (curvature R, aperture CL) functions to narrow the ultrasonic waves
emitted from the acoustic lens 12 to the subject (not shown) in a point shape.
[0006]
Now, when a pulse voltage is applied to the ultrasonic element 11 from the external circuit
through the conducting wire, an area corresponding to the upper electrode 14 of the
piezoelectric transducer 13 generates an ultrasonic wave, and a plane wave (longitudinal wave)
propagates to the acoustic lens 12. Do. The directivity of the plane wave becomes sharper as the
wavelength λ is shorter and as the electrode diameter DE is larger. A so-called first zero
radiation angle θ0 is often used as an index indicating this radiation directivity (region in which
energy is concentrated).
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[0007]
FIG. 3 is a view for explaining the ultrasonic beam radiation and the first zero radiation angle
θ0. As shown in FIG. 3A, the ultrasonic wave excited by the ultrasonic element includes a
surface wave propagating on the surface of the acoustic lens, a transverse wave having a small
amount of energy distributed in a region close to the surface, and an acoustic lens. There is a
longitudinal wave (plane wave) emitted from the acoustic lens. By making the DE relatively large
and increasing the frequency (shortening the wavelength λ), it is possible to make most of the
ultrasonic waves propagating to the concave lens side account for the longitudinal waves.
[0008]
FIG. 3B is a calculation result showing the radiation angle θ dependency of the directivity
coefficient DC of the plane wave. DC is a ratio of the sound pressure on the central axis of the
acoustic lens to the sound pressure at any one point sufficiently far, and can be expressed as
follows by using the first Bessel function. As the radiation angle gets farther and farther away
from the central axis, DC falls and becomes zero initially when y = k (DE / 2) sin θ = 3.83.
Therefore, the radiation angle θ at this time is referred to as a first zero radiation angle θ0. θ0
is approximately given by As shown in FIG. 3B, it can be seen that DC does not exceed 0.1 in a
radiation angle region larger than θ0, and in fact the radiation energy of the plane wave
converges almost in an angle region smaller than θ0. The region of 0 ≦ y ≦ 3.83 is referred to
as the main pole, and the other bulge is referred to as the sub pole.
[0009]
FIG. 2 also shows the locus of the wave reflected by the concave lens 16 of the plane wave
radiated from the ultrasonic element 11 at the first zero radiation angle θ 0. However, for
simplicity, only one-side reflected wave is shown. The first zero radiation angular plane wave
reflected by the concave lens 16 is once reflected by the upper end face of the acoustic lens 12
and then rereflected by the tapered region 17, and is reflected by the side face of the acoustic
lens 12 to be the upper electrode of the upper end face The light is incident on the area directly
below 14, that is, the detection area (position P 1) of the piezoelectric transducer 13. As a result,
as shown in FIG. 5, the electric signal train may be interrupted as unnecessary echo noise (SE)
other than the signal wave.
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[0010]
Problem to be Solved by the Invention As shown in FIG. 5, echo noise (SE) is relatively identified
when the distance between the ultrasonic probe and the object is constant (in the case of FIG. 5).
Although it is possible, in the search for flaw detection of a subject, there is a problem that the
probe interferes with the signal wave to degrade the resolution because the probe is brought
close to the subject.
[0011]
FIG. 5 is a view showing a pattern of received wave voltage (after conversion by an ultrasonic
element) when a plane wave is radiated according to the concave lens focus of the ultrasonic
probe shown in FIG. is there.
As described above, most of the conversion energy is radiated to the narrow region within the
first zero radiation angle θ0 of FIG. The wave with the highest energy density among the main
poles is θ = 0, ie, a plane wave radiated along the central axis of a cylindrical acoustic lens (peak
intensity is a function of D2C). Assuming that the transmission wave pulse is T, T is reflected at
the center of the concave lens, follows the same path, and is detected by the ultrasonic element
as the primary reflected wave L1, and part of L1 is the upper end face of the acoustic lens. Is
reflected back to the inside of the acoustic lens, and the detection wave reflected by the concave
lens end face again is L2, and in the same manner, L3 and L4 appear. Therefore, intervals
between T1 and L1, L1 and L2, L2 and L3, and L3 and L4 are equal. A part of the transmission
wave T is emitted from the concave lens without becoming the reflected wave L1, is partially
reflected on the surface of the object and returns, and the signal wave detected by the ultrasonic
element is f. SE in FIG. 5 is echo noise due to reflection from the side surface of the acoustic lens,
and in principle all waves of 0 <θ ≦ θ0 contribute.
[0012]
An object of the present invention is to provide an ultrasound probe capable of suppressing echo
noise so that resolution does not decrease.
[0013]
SUMMARY OF THE INVENTION In the present invention, a cylindrical acoustic lens having a
concave lens on its lower end surface and having an upper end surface consisting of a plane
perpendicular to the cylindrical axis, and the above-mentioned upper end surface In an ultrasonic
probe comprising an ultrasonic element comprising a closely-formed lower electrode, a
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piezoelectric transducer, and an upper electrode, the energy of a plane wave (longitudinal wave)
excited from the piezoelectric transducer is concentrated The component reflected by the
concave lens among the ultrasonic waves radiated with a so-called first zero radiation angle θ0,
which is an index indicating a region (radiation directivity), is a component of the upper end face
The dimensions of the cylindrical acoustic lens are LL ≒ (MA / X1) · (DL / 2) + (Y1-R) −MA,
where LL is the axial acoustic lens axis so as to reach the edge. , DL is cylindrical The diameter of
the sounding lens, R is the concave lens curvature, X1 is the length of the perpendicular from the
reflection point of the first zero radiation angle ultrasonic wave to the central axis of the
cylindrical acoustic lens, Y1 is the center of curvature of the concave lens The distance between
the perpendicular and the center axis of the cylindrical acoustic lens, MA is the center of the
cylindrical acoustic lens in which the locus of the reflected wave from the reflection point of the
first zero radiation angle ultrasonic wave at the concave lens is extended to the concave lens side
An ultrasonic probe is disclosed, which is configured to satisfy the following equation: a distance
between a point intersecting an axis and a cylindrical acoustic lens central axis intersection point
of the perpendicular.
[0014]
When the shape and dimensions of the cylindrical acoustic lens are determined so as to satisfy
the above equation, the first zero radiation angle θ0 wave is of course relatively small, so θ0 is
relatively small, so the angle θ near θ0 (θ00 , ΘS), and the first reflected wave of the plane
lens concave lens reaches the upper end edge of the substantially cylindrical acoustic lens.
Then, in this narrow area, they interfere with each other to lose energy, and the primary reflected
wave that contributes to the echo noise component as a side reflected wave is significantly
attenuated.
[0015]
EXAMPLES The present invention will be described in more detail based on the following
examples.
FIG. 1 is a cross-sectional view showing the shape of an ultrasound probe according to an
embodiment. 6 is an enlarged view of the vicinity of the concave lens of the ultrasonic probe of
FIG. In the figure, 1 is an ultrasonic element, 2 is a cylindrical acoustic lens made of quartz,
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sapphire or the like, 3 is a thin plate piezoelectric transducer made of ZnO, lead titanate or the
like, and 4 and 5 are Cr and Au, respectively. Etc., 6 is a concave lens having a curvature R and an
aperture CL, and 7 is a tapered region. The ultrasonic element 1 comprises a piezoelectric
transducer 3 and electrodes 4 and 5. Also, DL is the diameter of the acoustic lens 2, LL is the
axial length of the acoustic lens 2, DE is the upper electrode diameter, θ 0 is the first zero
radiation angle, and θ I is the incidence of the first zero radiation wave on the concave lens 6,
reflection The angle θ is an angle between the normal to the concave lens reflection point of the
first zero radiation angle wave and the lens center axis. There is a relationship of θI = θ0 + θ.
[0016]
Applying geometrical optics to the reflected wave path of the first zero radiation angle wave
shown in FIGS. 1 and 6, the following relationship is obtained. ## EQU3 ## where X 1 is the
length of the perpendicular from the reflection point P at the concave lens of the first zero
radiation angle ultrasonic wave to the central axis of the acoustic lens, Y1 is the distance between
the curvature center N of the concave lens and the acoustic lens central axis intersection point Q
of the normal, MA is the reflection point P of the first zero radiation angle ultrasonic wave at the
concave lens to the locus of the reflected wave Rc and to the concave lens side The distance
between the point M where the extended line intersects the acoustic lens central axis and the
acoustic lens central axis intersection point Q of the perpendicular. As can be seen from FIG. 6,
since the axial end Q0 of the acoustic lens 2 and the point Q do not completely coincide with
each other, the equation (5) is an approximate value. However, the distance between the point Q
and Q0 is negligible for the axial length LL. That is, the shape of the ultrasonic probe of the
present invention shown in FIG. 1 is such that the dimensions of the acoustic lens and the
concave lens curvature are designed so as to satisfy (Equation 5).
[0017]
According to this embodiment, the first zero-axis wide angle wave is reflected from the point P to
the edge E of the end face of the acoustic lens 2. At this edge E, the reflected wave from point P is
scattered to reduce the intensity. In FIG. 2 of the conventional example, the light is reflected from
the side surface of the cylinder and is incident on the piezoelectric transducer to become noise,
but in the embodiment of FIG.
[0018]
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Of the echo noise SE due to the side reflection wave shown in FIG. 5, the component for reducing
the resolution is not only the plane wave emitted at the first zero radiation angle θ0. However, if
θ0 is relatively small, the primary reflected wave of the concave lens, which becomes the echo
noise SE, is determined mostly by satisfying the equation (5), and the primary reflected wave of
the concave lens is mostly the upper end face of the acoustic lens. The echo noise SE is
significantly attenuated since it concentrates at the edge and interferes with each other and
cancels out.
[0019]
The received wave voltage pattern (concave lens focal point is the object surface, ie, z = 0) when
the acoustic lens is produced with the dimensions of FIG. 1 satisfying the equation (5) is as
shown in FIG. Although it corresponds to FIG. 5 which is a received wave voltage pattern when
the conventional acoustic lens (FIG. 2) is used, the echo noise SE is hardly detected.
[0020]
As described above, according to the present invention, it is possible to remarkably suppress the
echo noise due to the reflected wave from the side surface of the acoustic lens, and to suppress
the factor that affects the resolution at the time of flaw detection. be able to. As a result, high
resolution flaw detection becomes possible.
[0021]
Brief description of the drawings
[0022]
It is a figure which shows the reflective wave path of the ultrasonic probe shape by the FIG. 1
Example, a dimension, and a 1st zero radiation wave.
[0023]
2 is a diagram showing the shape, size and reflection wave path of the first zero radiation wave
of the ultrasonic probe according to the conventional example.
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[0024]
3 is a diagram for explaining the directivity of the ultrasonic radiation beam from the ultrasonic
element.
FIG. 3A is a calculation diagram showing the type of radiation wave and its energy distribution,
and FIG. 3B is a calculation diagram showing the radiation angle dependency of the directivity
coefficient Dc of the longitudinal wave (plane wave).
[0025]
4 is a diagram showing a received wave voltage pattern of an ultrasonic probe using the acoustic
lens of the embodiment shown in FIG.
[0026]
5 is a diagram showing a received wave voltage pattern of the ultrasonic probe using the
acoustic lens of the conventional example shown in FIG.
[0027]
6 is an enlarged view around the lower end surface of the acoustic lens of FIG.
[0028]
Explanation of sign
[0029]
DESCRIPTION OF SYMBOLS 1, 11 Ultrasonic element 2, 12 Acoustic lens 3, 13 Piezoelectric
transducer 4, 14 Upper electrode 5, 15 Lower electrode 6, 16 Concave lens 7, 17 Taper area DE
Upper electrode diameter DL Acoustic lens diameter LL Acoustic lens axial length R Concave lens
curvature CL Concave lens aperture θ0 Reflected wave at the first zero radiation angle Rc θ0
wave concave lens Incident of the concave lens of the wave θI θ0 wave, reflection angle θ θ0
wave concave lens normal point of the reflection point of concave lens Make angle T Transmitted
wave pulse L1 to L4 Reflected wave at concave lens of θ = 0 wave Signal wave from object
surface of wave θ = 0 wave SE Echo noise by side reflected wave
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