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JPH01109257

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DESCRIPTION JPH01109257
[0001]
[Industrial field of application] The present invention relates to a focusing probe for immersion
using a vertical probe, and in particular, the thickness of the beam at the focal point is calculated
by the diameter of the transducer of the used vertical probe. The present invention relates to a
focusing probe suitable for squeezing to a size larger than that. BACKGROUND OF THE
INVENTION Focus probes have traditionally been used to detect microscopic defects in an object,
mainly by means of water immersion, which consist of an ultrasound beam emitted from the
focus probe into water. Is focused to focus within the object, and the increase in sound pressure
at the focus of the subject increases the flaw sensitivity and improves the detection capability for
minute defects. A conventional focus probe has a configuration in which a disc-shaped and a
transducer-shaped concave spherical acoustic lens are made to face each other and combined,
and an ultrasonic beam emitted from the transducer is A so-called point-focusing type focusing
probe focusing on one point is generally used. An example will be described with reference to
FIG. 2. FIG. 0 shows a side sectional view of the focus probe, 1 is a disk-shaped vibrator with
radius Ro, 2 is a damper attached to the back of the vibrator 1 , 3 is an electrode attached to the
damper 2, 4 is a vibrator 1. A holding material for holding the damper 2 and the electrode 3 is
made of a resin such as epoxy resin or acrylic resin, and an acoustic lens 4a having a concave
spherical surface with a radius of curvature r0 is formed at a position facing the vibrator 1
Reference numeral 5 denotes a cylindrical case made of stainless steel, which is fitted to the
outer periphery of the holding member 4. P, the above-mentioned vibrator 1. ダンパ2.
Electrode 3. The focusing probe is composed of the holding material 4 and the case 5. Reference
numeral 6 denotes water for immersing the object and the focus probe P at the time of flaw
detection of the object, and reference numeral 7 denotes a central axis connecting the center of
the vibrator 1 and the curvature center o0 of the acoustic lens 4a. In the focal probe P0 of the
above-described configuration, the ultrasonic wave that has entered the water 6 from the
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transducer 1 through the acoustic lens 4a is focused on the focal point F of the focal distance f.
However, in practice, the focal point F0 is not a point but a finite size because of the wave nature
of the sound wave. As the beam thickness at this focal point becomes larger, the sound pressure
increase rate for fine defects decreases, so that the detectable defects become larger and can not
be distinguished from other large defects. Therefore, the size of the detectable defect is a size
corresponding to the thickness of the beam, and the smaller the beam thickness at the focal
point, the smaller the defect can be detected. The size of the focal spot when it is defined by a
half value angle (-6 dB) is d-6. It is expressed by the following equation, and is determined by the
transducer diameter, the focal length and the wavelength determined by the frequency.
As apparent from the equation 1 where λ = wavelength, f = focal length, R = radius of the
transducer in the above equation, the larger the diameter and frequency of the transducer and
the smaller the focal distance, the smaller the value of d−a And the focus will be narrowed.
However, the vibrator has a problem that it becomes difficult to uniformly vibrate the entire
surface, as well as the problem of back-up which makes it difficult to finish to a uniform
thickness as the diameter becomes larger, and this non-uniform vibration tendency has a
frequency It becomes so remarkable that it becomes high. For this reason, the frequency is also
limited in relation to the transducer diameter. On the other hand, when the ultrasonic wave
emitted from the vibrator 1 is considered to be a plane wave, the focal length f has a relationship
shown by the following equation with the curvature radius r11 of the acoustic lens 4a. Here, C2
冨 the velocity of sound in the acoustic lens 4a, C2 = the velocity of sound in the water 6. As an
example in the case of C1> Cm, the material of the acoustic lens 4a is acrylic resin, and the
following equation (2) becomes f, = □ 0.45, the above equation makes the focal distance smaller
as the curvature radius r0 becomes smaller The 0 radius of curvature r0, which indicates that it
has to be selected in such a dimension as to form a concave sphere of an area to receive the
ultrasonic waves (plane waves) emitted from the transducer 1 without leakage as shown in FIG.
However, the width of the acoustic lens 4a that receives the plane wave is such that the radius of
curvature r6 to be obtained of the diameter 2R or more of the vibrator 1 to be used is selected.
Therefore, the reduction of the focal length f is also about 2.2 times as long as the radius of
curvature r in the case of the above example, with the transducer diameter 2R being limited in
any relation. After all, to reduce the value of d-S in the conventional focusing probe, the
transducer diameter 2R02 frequency and the focal length f. Is selected as appropriate so that the
value of d-6 becomes as small as possible, but as shown in FIG. 2, when the diameter of the
vibrator 1 is determined to be 2R, the curvature is first Since the radius r is selected as described
above, then the focal length f0 is determined by the equation (2) and the frequency is also
determined within a certain range, the limit for squeezing the ultrasonic beam is within the range
calculated by the equation (1) A limited defect which can be detected becomes a large defect
corresponding to a long focal length f as in the above-mentioned example, and has a problem
that fine defects of micron size can not be detected. [Problems to be Solved by the Invention] As
described above, in the conventional focus probe, the radius of curvature of the acoustic lens, the
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focal length and the frequency are determined within a certain range when the transducer
diameter is determined, along with this. The limit at which the ultrasonic beam can be narrowed
is limited within the range calculated by the equation of the focal spot size d-a defined by the half
angle, and it is only possible to detect defects of a size within that range Problem that can not be
detected.
The present invention solves the above-mentioned problems of the prior art, and the focal point
is defined by the half-value angle, the limit at which the ultrasonic beam can be narrowed even
when a transducer of the same diameter as the conventional focal probe is used. The focal length
search made it possible to detect minute defects in the micron unit by reducing the focal length
and reducing the value of da without being limited to the range calculated by the equation d s
The purpose is to provide a feeler. [Means for Solving the Problems] In the present invention, a
cylindrical case in which the inner and outer surfaces of the bottom are formed into a point
focusing type acoustic lens in which the inner and outer surfaces are spherically expanded to the
inner surface and the liquid is injected into the inside. The conventional focal probe is constituted
by a focusing probe composed of a vertical probe smaller in diameter than the bottom diameter
fitted in the case in close proximity to the bottom and concentrically with the bottom. Even when
using a transducer of the same diameter as the probe, reduce the value of dS calculated by the
focal point size equation defined by the half-value angle, and stop the ultrasonic beam to detect
fine defects in the micron unit To make it possible. [Operation] When a pulse voltage is applied
from the ultrasonic generator to the vertical probe, the emitted ultrasonic wave reaches the
acoustic lens through the liquid in the case. In this case, since the vertical probe and the bottom
formed on the acoustic lens are close and concentrically opposed within the near-field limit
distance, a plane wave reaches the inner surface of the acoustic lens, and this surface Other than
the reflected wave, the light enters the acoustic lens and is refracted depending on the velocity of
sound of the liquid in the case and the acoustic lens and the radius of curvature of the inner
surface of the acoustic lens to diffuse the acoustic lens. The ultrasonic waves diffused and passed
through the acoustic lens reach the outer surface of the acoustic lens, where the refraction is
determined by the speed of sound of the liquid in the bath in which the acoustic lens and the
case are immersed and the radius of curvature of the outer surface of the acoustic lens. It is
focused and focused. The ultrasonic beam when entering the liquid in the tank from the outer
surface of the acoustic lens is expanded as if it were a vertical probe as a result of the plane wave
emitted from the vertical probe being diffused by the inner surface of the acoustic lens The same
action as using a large diameter transducer is performed, and at the same time, the ultrasonic
wave reaching from the inner surface to the outer surface of the acoustic lens is not a plane wave
but a spherical wave, and the focal length is also shortened. For this reason, the value of d-6
calculated by the formula of the size of the focal point defined by the half value angle can be
reduced, and the ultrasonic beam is larger than the size calculated by the transducer diameter of
the vertical probe used It becomes possible to narrow down and detect fine defects. An
embodiment of the present invention will be described with reference to FIG.
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In the figure, the same reference numerals as in FIG. 2 indicate the same things. 8 is a cylindrical
case, a screw 8a is processed on the upper inner periphery of the figure, a bottom 9 is provided
on the lower side of the figure, Liquid 10 (eg, water, alcohol, etc.) is injected as a medium. The
bottom 9 is formed of a point focusing type acoustic lens in which both the inner surface 9a and
the outer surface 9b are spherically expanded toward the inner surface 9a, and the outer
diameter of the bottom 9 is larger than the diameter of the portion where the screw 8a is
processed It is a dimension. Both case 8 and bottom 9 are manufactured to a thickness of about 1
to 3 in consideration of strength, processability, acoustic properties, etc. using homogeneous
quartz glass, acrylic resin, aluminum alloy, etc. . The radius of curvature r1 of the inner surface
9a of the bottom 9 and the radius of curvature r of the outer surface 9b are determined so as to
satisfy r, ≦ r, and usually, the relationship of rl <rt is established. 11 is a vertical probe. A screw
is processed on the outer periphery so as to be able to be screwed into the screw 8a, and when it
is fitted in the case 8, it is immersed in the liquid 10 and the axis is the curvature center 01, 0.
And concentric with the central axis 7. Further, the distance between the vertical probe 11 and
the inner surface 9a is adjustable, and the distance is close to the near sound field limit distance.
When a pulse voltage is applied to the vertical probe 11 from an ultrasonic oscillator (not
shown), the emitted ultrasonic waves reach the inner surface 9 a through the liquid 10. In this
case, a plane wave arrives at the inner surface 9a and enters the bottom 9 except for the
reflected wave reflected by the inner surface 9a. The incident ultrasonic waves are diffused
depending on the velocity of sound C of the liquid 10, the velocity of sound C2 of the bottom 9
and the radius of curvature r of the inner surface 9a, and are diffused in the bottom 9. The
diffusion of the ultrasonic beam is due to the fact that the focal length calculated by the equation
(2) becomes negative because of Ct <Cm and becomes closer to the vertical probe 11 than the
inner surface 9a. From the law, the smaller the radius of curvature r1, the larger it becomes. The
diffused ultrasonic beam passes through the bottom 9 and reaches the outer surface 9 b. The
outer surface 9b is refracted into the water 6, but the sound velocity C9 of the bottom 9 and the
sound velocity Ca of the water 6 (C3 = C when the liquid 10 is water) and the curvature radius r
of the outer surface 9b. In this case, the focal distance f in this case can not be calculated in the
above equation (2) because the ultrasonic waves at the outer surface 9b are spherical waves
instead of plane waves, and they are spherical This is a fairly small value due to wave refraction.
Also, the ultrasonic beam upon entering the water 6 from the outer surface 9 b is emitted from
the vertical probe 11 at the radius R 6 of its transducer and then diffused in the bottom 9 to
become the radius R, as if the transducer diameter is It becomes the same as the diameterexpanded state, and works the same as using the vertical probe with a large diameter transducer
as the vertical probe 11.
For this reason, the value of ci-s calculated by the equation (1) has a relationship in which the
transducer radius is R, <R and the focal distance f is f,> f. Since the value at the focal point F of
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the ultrasonic beam is narrowed to the ratio of R, / H or more, the minute defects can be
detected. [Effects of the Invention] As described above, according to the present invention, the
inner and outer surfaces of the bottom of the case are formed into a point-focusing acoustic lens
in which the inner and outer surfaces are spherically expanded to the inner surface, and the
cylindrical The conventional focus probe is a focal probe composed of a case and a vertical probe
with a diameter smaller than the bottom diameter fitted in the case in close proximity to the
bottom and concentrically with the bottom. Even when using a transducer of the same diameter
as that of the laser, the value of ci-a calculated by the focal point size equation defined by the
half-value angle can be reduced, and There is a practical effect of being able to detect defects.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a side sectional view of one embodiment of a focusing probe according to the present
invention.
FIG. 2 is a side sectional view for explaining an example of a conventional focusing probe. Patent
Assignee Hitachi Construction Machinery Co., Ltd. Attorney Attorney Akimoto Michiaki Minoru
(1st day) 8- 1-8-γ-s 9-1 base (Acoustic lens 9a-inner surface 9b-outer surface fO-base狡 11-one
sound a search 1 chi
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