JPS5558697

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DESCRIPTION JPS5558697
Description of the Invention Focusing type ultrasonic probe 1, a disk-shaped oscillator having an
elliptical concave surface 1-1 and an acoustic lens having a concentric groove on the surface
curved 5 Focused ultrasound probe characterized by
Claims
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focusing
ultrasonic probe which has an acoustic lens attached to a disk-shaped oscillator to focus an
ultrasonic beam. In a focusing ultrasound probe using an IQ conventional acoustic lens, a
focusing sound field is realized using a concave spherical lens. For example, when using an
acrylic resin acoustic lens, in order to set the focal length in water to f, a lens shape having a
concave spherical surface with a radius of curvature r given by the following equation is
employed. f / ρ = 212 (1) However, the sound velocity in the acrylic resin is 2740 m / s, and the
sound velocity in water is 1459 m / s. In general, the diameter Δr of the ultrasonic beam on the
focal point (usually referred to as 2 ° 1S resolution) is given by the following equation. Here, λ
is an ultrasonic wavelength. As apparent from the second equation, in order to make Δr small,
that is, to narrow the ultrasonic beam on the focal point, it is understood that the aperture should
be made large with respect to the focal length f. However, as long as a concave spherical lens is
used, sound and waves refracted by the lens surface away from the central axis of the lens will
pass through the sound axis position closer to the focal distance, so the acoustic wave refracted
by the lens surface is focused In order to concentrate in the vicinity, the aperture is usually
limited to be within 40 degrees of curvature radius ρ. As described above, in the case of a
focusing probe using a concave spherical lens, it is impossible to unconditionally increase the
aperture in order to narrow the ultrasonic beam on the 11 points of focus and to increase the
sound pressure. Therefore, in order to solve the problems of the focusing ultrasonic probe using
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the concave spherical lens described above, all sound waves having passed through the lens
surface 20- (2) EndPage: 1 are focused on the focal point. An object of the present invention is to
provide a focused ultrasonic probe according to the present invention, which aims to realize a
thin and high sound pressure ultrasonic beam. The principle of the present invention will be
described below. The focus in the focused sound field indicates the position where the sound
pressure is extremely high compared to the sound pressure in the sound field around it. The
increase in sound pressure is due to the interference phenomenon between the sound waves, and
the sound pressure is increased when the phases of the sound waves coincide. Therefore, in
order to make the sound wave passing through the lens surface be in phase at the focal point and
to increase the sound pressure, the propagation distance of all the sound from the surface of the
oscillator to the focal point to the focal point is a constant multiple of the wavelength. You should
do it. The curved surface of such a lens will be described. A schematic diagram showing a sound
propagation path is shown in FIG. In order to simplify and simplify the explanation, FIG. 1 shows
the resonator 11 and the acoustic lens 2 as a sectional view on a plane including the sound axis,
and the direction of the sound axis is a direction perpendicular to the Y1 sound axis as X It
represented by.
The origin of X, Y coordinates is the boundary between the acoustic lens on the sound axis and
water. The point F indicates the focal point, and the coordinates are (0, f). Since the oscillator is a
flat plate □, the ultrasonic wave emitted from the oscillator 1 propagates in the acoustic lens 2
as a plane wave. Therefore, considering the phase, the X-axis plane in the acoustic lens 2 can be
regarded as a transmission source of ultrasonic waves, and the ultrasonic waves go straight in
the acoustic lens 2 in the Y-axis direction. The number of vibrations ま で until the sound wave
passing through the boundary (x + y) of the acoustic lens 2 and water reaches the focal point F
from the X-axis plane is expressed by the following equation. Here λ. And λ are the ultrasonic
wavelengths in the acoustic lens and the water, respectively. On the other hand, the number of
vibrations until the sound wave that has passed the origin reaches the focal point F is also ν, so
the third equation is as follows. By setting n−λ / 2 ° from the fourth equation, the following
relational equation is obtained. As apparent from the equation (20) (5), the shape of the acoustic
lens is such that the propagation distance of all ultrasonic waves from the oscillator 1 to the focal
point F is a constant multiple of the ultrasonic wavelength. It can be seen that it is elliptical. The
coordinates of the focal point of the ellipse represented by the fifth equation are (0, f), (0, -f) 1 +
n, and it can be seen that one focal point of the ellipse corresponds to the focal point of the
elliptical acoustic lens. . As described above, if an acoustic lens having an elliptic curved surface
represented by the fifth equation is used, all sound waves collected at the focal point F have the
same phase on the focal point. However, in the case of an acoustic lens having an elliptically
curved surface, the sound wave is refracted at the boundary between lens and water, and the
sound wave away from the sound axis passes through the sound axis position closer to the focal
point as in the case of the concave spherical lens. Become. Therefore, a sound wave passing
through the boundary between the acoustic lens and water makes grooves as shown in FIG. 2 on
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the surface of the sound 1 acoustic lens 2 so as to propagate in the 2π direction in the same
direction. However, the depth of the groove should be smaller than the ultrasonic wavelength in
1 acoustic lens and water. By this groove, the ultrasonic waves from the acoustic lens are emitted
in the same direction, but the sound waves propagating in the direction other than the focal point
F do not coincide in phase with the sound waves from the other grooves and cancel each other.
Become. As a result, among the acoustic waves emitted from all parts of the acoustic lens, only
the acoustic wave incident on the focal point F has the same phase on the focal point, and a high
sound pressure and a narrow ultrasonic beam can be realized on the focal point. An embodiment
of the focusing ultrasonic probe according to the present invention based on the above principle
will be described. The external view of the focusing ultrasonic probe of the present invention is
shown in FIG. In FIG. 3, the acoustic lens 2 is made of an acrylic resin, the aperture is 30 wφ,
and the underwater focal length f is between 1 and 50.
The resonant frequency of oscillator 1 is 3 MHZ. The depth of the V-shaped groove 3 is 0.1 mm.
In FIG. 3, a cross-sectional view taken along the XY plane is shown in FIG. The concave surface of
the acoustic lens 2 is a surface formed of an elliptical body (rotational axis is sound axis)
arranged with a major axis of 39.2 m and a minor axis of 277. EndPage: 2 The diameter of the
ultrasonic beam on the focal point by the above-described focused ultrasonic probe according to
the present invention is 2 mmφ. On the other hand, in a conventional probe using a concave
spherical lens, when the underwater focal length is 501 m, the aperture is at most 10 rm nφ 5
and therefore the focal beam diameter can not be made within 5 cabinets. Moreover, the sound
pressure on the focal point at this time is 1/9 or less of the sound pressure by the focusing probe
of the present invention. As described above, in the focusing ultrasonic probe according to the
present invention, the sound pressure on the focal point is 9 times or more, and at least 1/2 or
less in the focusing diameter, as compared with the conventional probe of the same focal length.
Ultrasonic beam can be realized. Next, an example in which the present invention is applied to a
line focusing type ultrasonic probe will be described. An example in which the present invention
is applied to a line focusing ultrasonic probe is shown in FIG. In this probe, the ultrasonic waves
are focused on the focal line FF '. The cross-sectional view by the XY plane of the probe shown in
FIG. 5 is the same as FIG. As for the line-focusing ultrasonic probe, the focusing ultrasonic probe
according to the present invention has the same effect as in the embodiment shown in FIG. 3 as
compared to the conventional line-focusing probe (7) or more. As compared with an ultrasonic
probe using a conventional concave spherical acoustic lens, the sound pressure at the focal point
can be increased, and a thin ultrasonic beam can be realized.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a propagation path
of ultrasonic waves in a focused ultrasonic probe in the present invention. FIG. 2 is a schematic
view showing the propagation direction of the ultrasonic wave by the groove in the acoustic lens
having the groove on the elliptic curved surface. FIG. 3 is a view showing an embodiment of a
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focused ultrasonic probe in the present invention. FIG. 4 is a cross-sectional view of the probe
shown in FIG. 3 along the X-Y plane. FIG. 5 is a view showing an example in which the present
invention is applied to a line focusing type ultrasonic probe. 1 is a probe, 2 is an acoustic lens, 3
is a groove. −・(8)EndPage: 3
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