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JPH03113362

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DESCRIPTION JPH03113362
[0001]
BACKGROUND OF THE INVENTION The present invention comprises a conical shape for an
ultrasound microscope in which a surface wave and / or a Lamb wave travels through an object
to be examined, having ultrasonic transducers arranged axisymmetrically. It relates to ultrasound
deflection elements. Prior Art and Problems J: An ultrasonic scanning microscope is known from
Zieniuk, A, La1uszek, Ptoc, IEEE Old Trason, Symposium (1986), pages 1037-1039. Attached to
the ultrasound transducer is a frusto-conical sapphire needle, the tip diameter of which is
approximately 1?4 of the ultrasound wavelength in the coupling medium. Thus, the formation of
a predetermined wave in the coupling medium has not been performed, and this arrangement
produces a pass resolution. It is stated to select a cone angle of 20 ░, a tip diameter of 20 ?m
and an ultrasonic frequency of 30 MHz when exciting long waves mainly in the object to be
inspected, but here the cone shape is mainly It is used to transfer the large surface of the
acoustic transducer to a small tip. 1, R5ii1h other, ^ pp1. From Ph7s, Le11 (42), 19113 ░, pp.
411-413, the construction of an ultrasound microscope with surface waves is known, which is
actuated by a conventional spherical ultrasound lens. In the non-focusing state, the longwave
signal contribution is suppressed, while the ultrasonic waves passing through the narrow ring on
the linear lens collide with the surface of the object under inspection at an appropriate angle (socalled Rayleigh angle) to resonantly excite the surface wave. This produces a surface wave with a
circular wavefront. This surface wave joins the surface wave focal point by diffraction.
Furthermore, a transmission device is described which comprises a transmitting and receiving
unit consisting of a lens and an ultrasound transducer. For reflective devices, it has been
proposed to use only a semi-spherical body of a conventional spherical lens / converter unit. In
this case, the lens is not divided, and only one semicircular ultrasonic transducer is provided.
Obviously, it is impossible to set the angle of incidence on the surface of the object to be
inspected to a specific angle, and therefore it is impossible to select, for example, a specific mode
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of surface waves. In this case, only a very small fraction of the energy of the ultrasound waves
generated and acting on the object to be examined is converted into surface waves, so that only a
small amount of energy is available for the generation of the signal. A solution was proposed. A
configuration that overcomes the above drawbacks is described in B, Nongaillard et al., J, Appl,
Ph 7s, 55 (+984), pages 75-79.
Here, a cylinder lens is provided instead of the spherical lens, and the vertical axis is inclined
with respect to the surface of the object to be inspected. The wave front of the cylinder recharge
intersects the surface of the object to be inspected in an elliptical shape. When the tilt angle
corresponds to the Rayleigh angle, surface waves are effectively generated. However, this surface
wave converges on the surface of the object to be inspected to produce a linear focus because the
generation zone is elliptical. For use in a conventional ultrasonic microscope, it is a disadvantage
that the cylinder axis is inclined with respect to the normal direction of the surface of the object
to be inspected. According to U.S. Pat. No. 4,779,241, a flat ultrasound transducer acts on a
cylindrical refracting or reflecting surface in a parabolic manner at an oblique angle, resulting in
a conical wavefront. In this case, the conical axis coincides with the focal line of the reflecting or
refracting surface. The objective is arranged perpendicular to the conical axis, where the conical
wavefront and the tear line of the object to be examined are in the form of a sector. As a result,
point-like foci known from 1, RSm1lh etc. are generated. By changing the angle between the
ultrasonic transducer and the focus plane, the Rayleigh angle for generating surface waves can
be obtained. This method can be implemented using transmission ultrasound transducers and
transmission ultrasound transducers separately or integrally provided in terms of transmission
and reflection. This method also suffers from its use in conventional ultrasound microscopes due
to the tilt angle. In addition, it has been proposed to select the shape of the ultrasonic transducer
so as to obtain the required wave shape. A conical fan-shaped ultrasonic transducer whose
conical axis extends perpendicularly to the surface of the object to be examined is known from S,
y) er, Proe, of 1987 IEEE Ullrason, Symp, pages 301-304. In this case, it is necessary to increase
the manufacturing cost of the ultrasonic transducer. The size of the ultrasound transducer
directly determines the path distance of the ultrasound within the coupling medium to the object
to be examined. This is a problem because of the buffer characteristics. A, Al 5lar et al., Proe,
19881 EEE Ullrason. From Sya + p, pages 771-774, it is known to use an excitation of the Lamb
wave that has spread over the entire surface of the object under inspection to produce an
ultrasonic image. SUMMARY OF THE INVENTION It is an object of the invention to construct the
ultrasound deflection element mentioned at the outset in such a way that ultrasound waves of
one circular wave front are produced in the object to be examined, and the structure is as simple
as possible. The quality of the image is high, and it is to be configured to be applicable to a
conventional ultrasonic microscope.
[Means for Solving the Problems and Effects] According to the present invention, in order to
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solve the problems described above, the conical wave front of the ultrasonic wave is directed
toward the object to be inspected, and the ultrasonic transducer and the ultrasonic deflection
element are provided. It is characterized in that the axial disc is inactive (1 naktiv). Preferred
embodiments are described in embodiments 1 to 7 and 1 ░ and 11. In order to operate the
ultrasound microscope with such a configuration effectively, the configurations according to the
embodiments 8 and 9 are advantageous. According to the present invention, the following
conditions for effectively generating a surface wave focus are satisfied. All ranges of ultrasound
have the same constant angle, i.e. Rayleigh angle, with respect to the surface of the object to be
examined. One wave front collides with the surface of the object to be inspected in a circle or a
fan-shape. Or alternatively the conical wavefront of the excited ultrasound wave strikes the
surface of the object to be examined. These conditions include a device having a flat or conical
ultrasonic transducer and a conical deflection element having a common axis of symmetry with
the ultrasonic transducer, and a surface of the object to be inspected. It is filled by positioning
perpendicular to the conical axis. By opening an axisymmetric circle in the ultrasonic transducer
and / or the deflection element, interference by other excitation mechanisms and radiation
mechanisms can be effectively suppressed. It is not necessary to arrange the components
obliquely. In the conventional arrangement with the cylinder surface, the focal point is inclined,
but in the present invention the focal point is located on the conical axis as a line and
perpendicular to the surface of the object to be inspected, ie on the object to be inspected Form a
point. This facilitates image analysis. In particular, the embodiment provided with a refractive
deflection element, ie an ultrasound lens, can be used directly in a conventional ultrasound
microscope. In this case, it can be used instead of the converter / spherical lens unit. The
manufacturing is almost the same as the conventional one, and a concave conical surface is
manufactured instead of the concave spherical surface (1. R, Sm 1 lh, see other above-mentioned
papers). In this case, as a problem of the configuration of the present invention, the incident
angle of the ultrasonic wave to the surface of the object to be inspected is determined by the
opening angle of the cone, and this angle is a surface wave or Lamb wave in a specific object to
be inspected. Although it may not seem to coincide with the angle for generating H, the present
invention solves this problem by frequency adaptation. In particular the waves in the surface
layer known as lamb waves are dispersive, so that by choosing the frequency appropriately, the
angle of the lamb waves can be adapted to the predetermined angle of the conical deflection
element .
Determining this frequency experimentally is straightforward, as the frequency may be varied
until the maximum signal is received. However, since the band of most ultrasound transducers is
not very large, it is necessary to prepare a plurality of devices according to the invention with
different cone angles to inspect all of the objects to be examined. An ultrasound microscope of
such construction has an axial resolution equal to the thickness of the surface layer in which the
excited Lamb wave mode extends. On the other hand, the horizontal resolution can not easily be
determined. The presence of tissue somewhere within the area of the annularly converging
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surface wave always disturbs the received signal. In this case, the obstruction is maximized when
the tissue is in focus. However, for smaller tissues, an improved lateral resolution than the
wavelength of ultrasound is obtained. Next, an embodiment of the present invention will be
described with reference to the attached drawings. FIG. 1 is an embodiment of the invention with
a refractive deflection surface. The piezoelectric ultrasonic transducer 1 is provided with a
terminal 11 for electrically exciting a high frequency. The ultrasonic transducer 1 is mounted on
a lens body 2 made of, for example, sapphire. The coupling medium 3 (for example, water) is
coupling means for transmitting the ultrasonic wave 5 to the object 4 to be inspected. In contrast
to known spherical lenses, the refractive surface 21 is conical in shape, i.e. it is constructed as a
truncated cone with a flat upper surface 22 with a cone angle of [gamma]. The upper surface 22
is coated with an ultrasonic buffer layer to prevent ultrasonic waves from entering at a right
angle. On the other hand, the refracting surface 21 is advantageously coated with an
antireflective layer. The inspection object 4 has a surface layer 41 on a base 42 consisting of
layers. For example, copper fluoride can be adhered to aluminum for inspection. The ultrasonic
wave 5 is refracted by the refracting surface 21 and then penetrates into the connection medium
3. The ultrasound waves 5 all have the same angle ? with respect to the conical axis 6 and their
common wavefront is conical. The angle ? is obtained from the cone angle ? based on Snell's
law of refraction and depends on the velocity of the ultrasonic waves in the lens body 2 and the
coupling medium 3. The conical axis 6 is oriented perpendicular to the surface of the object 4 to
be inspected, so that the wavefront conically cuts the surface of the object 4 to be inspected.
When the angle ? matches the Rayleigh angle for a particular surface wave, ie, the Lamb wave
51, the Lamb wave 51 is strongly excited. Since the surface is circular at the intersection with the
surface, the Lamb wave 51 which is a surface wave propagates in the radial direction and
connects the focal point 52. In particular, Lamb waves propagating only in the one surface layer
41 are excited.
The Lamb wave is diffusive, that is, by changing the frequency of the ultrasonic wave, it is
possible to extensively adjust the Rayleigh angle for the Lamb wave mode, which corresponds to
the angle 0 made by the lens body 2. Also, Lamb waves are leaky (l @ ckead), i.e. strongly
reflected into the connecting medium 3, giving rise to detectable ultrasonic signals. The above
apparatus can be used as a transmitter or a receiver in an ultrasound reflection microscope. In
this case, known circuit arrangements for dissociating the excitation and measurement signals
must be employed. By means of the length of the lens body 2, it is possible to separate the
transmitting wave and the measuring wave in time. It can likewise be provided as a transmitter in
an ultrasound transmission microscope. In this case, a known device of the same or a pond is
provided as a receiver on the side of the oppositely inspected object. It is known from the article
by RSm 1th et al. That a reflector that is completely circularly symmetric about the conical axis 6
produces a maximum signal at the tissue free surface. This is true even in the case of an ideal
reflector at the focal point 52. Image information as signal attenuation occurs when there is little
tissue next to the focal spot 52. On the other hand, an improvement can be obtained by
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substantially trisecting the device into 180 'sectors. Thus, in addition to dividing the entire device
in the plane of symmetry including the conical axis 6, half of the refracting surface 21 is covered
with an absorbing material, and / or the ultrasonic transducer is limited to a 180 ░ sector.
Improvement is also obtained by this. However, if it deviates from the 180 'fan shape, the
utilization effect decreases accordingly. In this case, a zero measuring device is provided which
does not emit a signal when there is no defect in the focal point 52 and produces a maximum
signal when there is a defect in the focal point 52. Such an ultrasonic lens body 2 provided with
the refracting surface 21 can be manufactured by a known manufacturing technology of a
spherical ultrasonic lens body, and can be attached to an ultrasonic microscope as a substitute
for the spherical ultrasonic lens body. Conical devices having a cone diameter of 10 pm or less
may be manufactured to obtain high resolution. In this case, the minimum diameter of the cone is
usually chosen to be several times the wavelength of the ultrasound in the coupling medium at
the frequency used. At this time, if the angle 0 is small, the path distance of the ultrasonic wave 5
in the coupling medium 3 can be considerably shortened as compared with the case of the
spherical lens body. This means that the available ultrasound frequency is GH! Range, which
means that the resolution is improved. The preferred ultrasound frequencies for this ultrasound
deflection element are 1 MH ? to I GH t.
The focus is limited to the surface layer 41 in the axial direction. Also, for example, even if the
distance between the lens body 4 and the inspection object 4 changes during scanning of the
microscope, the rectangular arrangement does not shift the focus to the side, so the stability
against disturbance is large, that is, the condition for the scanning device Will be reduced. FIG. 2
shows a variant of the device with a conical reflector 7 (for example made of a metal such as
polished aluminum). The same members as in FIG. 1 are given the same reference numerals. The
ultrasound transducer 1 is adapted at its shape Q to the deflection element 7 and is configured as
a torus. This torus (Kreisring) covers the projection of the reflector surface onto that surface. The
axial disc is passiv. Accordingly, the output of the generated ultrasound is used to avoid the
reception of the ultrasound 5 reflected normally on the surface of the object 4 to be inspected.
For this purpose, it is appropriate to select the distance 2 between the ultrasonic transducer 1
and the surface of the inspection object 4 as Z <R / 1ano. Here, R is the outer radius of the
reflecting surface of the reflector, and ? is the incident angle of the ultrasonic wave on the
object to be inspected. The incident angle O is related to the cone angle ? of the reflector 7 by
the refraction law. The inner radius r of the ultrasonic transducer 1 or the reflection surface must
be selected such that r> R?Zlan? / 2 in order to prevent the reflector from being placed on the
object 4 to be inspected. FIG. 3 shows a modification including the conical ultrasonic transducer
1. The point of the pond corresponds to the embodiment of FIG. 1 with the ultrasound lens 2.
Therefore, the same reference numerals are given to the same members. The lens body 2 is. It
has a second conical surface 23 to which the ultrasonic transducer 1 is attached. Accordingly, the
radiation of the ultrasonic wave is conical, and the energy density at the refractive surface 21 is
higher than the energy density at the ultrasonic transducer 1. This is because the energy from
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the torus of the ultrasound transducer 1 whose central radius is rl concentrates on the smaller
torus of the refractive surface 21 whose central radius is r l. This embodiment is suitable for
lenses with the smallest diameter, but it is of course also advantageous to construct it as a 180 ░
sector. Next, embodiments of the present invention will be listed. (1) The ultrasonic transducer
(1) is flat, and the conical axis (6) of the deflection surface (21, 7) is perpendicular to the
ultrasonic transducer (1) (FIGS. 1 and 2) The conical ultrasound deflection element according to
claim 1, characterized in that (2) The ultrasonic transducer (1) has a conical shape, and its
conical axis is in contact with the conical axis (6) of the deflection surface (21) (FIG. 3) Conical
ultrasound deflection element as described.
(3) The conversion element is a lens (2) having a conical concave surface (21) on the side of the
object to be inspected. Conical ultrasound deflection element. (4) Conical concave (21) is a
truncated cone. Conical ultrasonic deflection element according to claim 3, characterized in that
its flat upper surface (22) is coated with an ultrasonic buffer layer (FIG. 1). (5) The deflecting
element is a reflector (7) having a concave surface in a conical shape toward the ultrasonic
transducer (1), and the ultrasonic transducer (1) is the ultrasonic transducer (1). 2), characterized
in that it is shaped and arranged to cover the projection of the conical concave surface of the
reflector (7) onto the surface) (FIG. 2). Conical ultrasound deflection element. (6) The ultrasound
transducer (1) and / or the transforming element (2, 7) are configured as a sector with a 1806
sector angle, according to one or more of the previous claims. A conical ultrasound deflection
element according to any one of the preceding paragraphs. (7) The conical ultrasonic deflection
element according to the above paragraph 4 or 6, characterized in that it is used simultaneously
as a transmitter and a receiver in an ultrasonic reflection microscope. (8) The conical ultrasonic
deflection according to any one of the above (1) or (1) to (7), wherein the frequency of the
ultrasonic wave is set so that the image signal is maximum-. element. (9) In the above item 8,
characterized in that Lamb wave is excited in the surface layer (41) using the inspection object
(4) having the layer structure (41, 42>) Conical ultrasound deflection element as described. A
conical ultrasound deflection element according to claim 1, characterized in that the smallest
diameter of the conical ultrasound deflection element (2, 7) is several times the wavelength of
the ultrasound used. 11. The conical ultrasound deflection element according to claim 1,
characterized in that it is adapted to ultrasound frequencies ranging from IMlh to I GHt.
[0002]
Brief description of the drawings
[0003]
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FIG. 1 is a cross-sectional view of a deflection element according to the invention with a conical
lens, FIG. 2 a cross-section view of a deflection element according to the invention with a conical
reflector, and FIG. 3 a conical ultrasound transducer It is a figure which shows the example of
combination of a conical lens.
1 ииииии Ultrasonic transducer 2 ░ 7 и Ultrasonic deflection element и Inspection object
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