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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a conventional focusing
method, FIG. 2 is a view for explaining the principle of the present invention, and FIG. 3 is a view
showing a configuration of an embodiment of the present invention .
DETAILED DESCRIPTION OF THE INVENTION The present invention is a sound wave focusing
hand generally used in a microscope, particularly a microscope using high frequency sound
energy. On the stage. In recent years, since the generation and detection of high-frequency sound
waves to the IG) IZ has become oT-capable, approximately 1 micron of sound wave wavelength in
water can be obtained, and therefore, it is possible to study a priming mirror using sound wave
energy. Nine. Such an apparatus requires how to produce a narrow focused sound beam, as
shown in FIG. A conventional example will be described. That is, Aphire et al. (1) 9.7... '' Column O
crystal 20 company One end face company Optically polished plane, and concave hole is garbled
on the other end face. An RF electric signal is applied from the signal source 1 G to the
piezoelectric element 15 formed on the flat surface, and a plane wave RF sound wave is emitted
into the crystal 20. This plane acoustic wave is focused by the positive lens formed by the
interface 25 of the crystal-medium 30 formed in the above-mentioned concave hole, its
predetermined focal point PK :. As is well known, if the focal length to aperture ratio, i.e., the fnumber of the lens, is sufficiently small, this arrangement can produce a very narrow acoustic
beam. Since this focused sound wave is subject to disturbances such as reflection, scattering, and
transmission attenuation by a sample placed near the focal point, to detect this irregular wave
energy K. It is possible to obtain an electrical signal that reflects the elastic properties of the
sample. The crystal system described above may be used again for the detection of acoustic
energy, or a similar crystal system may be made to face in a confocal manner. As is clear from
the above description, the acoustic lens uses the difference in the speed of sound between the
crystal and the medium as its focusing principle. (2) In such a case, in order to operate as an
acoustic lens, it is desirable that a plane wave having a sound pressure and phase distribution as
uniform as possible be incident on the interface between the crystal and the medium. In the case
of the conventional configuration of FIG. 1, the aperture diameter of the piezoelectric element is
2p, and the distance normalized from 素 子 · 8 / λ (λ used sound wave frequency) as the
distance tL from the element to the acoustic lens interface FIG. 2 schematically shows the sound
pressure distribution of the sound wave beam. It can be seen that the sound pressure distribution
shows a complicated pattern from the surface of the piezoelectric vibrator to% I @ '' / λ.
Therefore, conventionally, first, the distance t between the lens portion and the piezoelectric
element is narrowed to about several times the used acoustic wavelength, or secondly, it is
determined by い わ ゆ る − / λ. Distance) was taken. When the lens material is sapphire, since
the acoustic wave wavelength is about 11 microns at I GHz, the first method requires a sapphire
plate of several lθμ, which is extremely difficult.
Also, in the case of # 'ip · = 1 mm by the method of ・ 2, · · · · · λ must have a very long crystal of
99 mm! になる。 In this case, a long distance leads to a large attenuation in the crystal (0).
Therefore, in the case of a crystal of about 1 (about 1 mm, a piezoelectric element with an
extremely small opening of −− = 9.1 mm is required. As described above, according to the
conventional method, it is required to produce a piezoelectric element having a very long crystal
or a very small aperture, and it is difficult to produce a high frequency probe. The present
invention has been made in view of the above points, and it is an object of the present invention
to obtain the same focused beam as that of the conventional example by using a sonic wave
having a length which is narrower than 狭 く, '/ λ. That is, as can be seen from FIG. 2 (noting
that a simple part of the beam is clasped within, for example, A3 within the range of A ′ ′ / J, a
concave lens is formed at one end of the crystal of this length. is there. The Fresnel focal
distance, point B, point A corresponds to a distance which is peaked in terms of sound pressure
on the axis. Describing in detail, the on-axis sound pressure bank of the disk imaging element of
the opening of radius p, I is given by I = wP (-(JT '+ p, 1-by rare (1) λ) t is (4)-(bJlj-1) = (n + 1)
πn = 0.1. H2 is satisfied, that is, 2n + 111− (□) 冨 λ 鵞 (2fl + 1) J ′ ′ ′ ′ ′ ′ ′ 0 (3). In
equation (3), n = 0 and L = I)-/ λ, that is, the Fresnel focal distance t is given, and when n = 1, t *
#-/ 3λ, that is, the A3 point is given. Generally, a human wing point is given by 1 / λ 3 N. 0 The
invention according to the present invention satisfies the following formula: O at the length of
the crystal II @ "/ 3 λ, 815 λ, 3/7 λ. · · · By selecting one of the · · · relatively uniform lens
opening surface. Sound wave is going to be incident. In this case, in the case of 10 = 1 m 1 n 11
GHz described in the conventional example, it will be apparent that the size becomes 11 mm in t
at ・ · 8/7 λ, and the number of practical dimensions becomes clear. As can be seen in FIG. 2, in
the case of points such as ρ and shif λ, so-called submaximities are large and if this submaximal
part is also incident on the lens, an unnecessary beam is generated, so 5) I It is desirable to
squeeze the aperture and attach a sound absorbing agent to the portion where the submaximal
beam hits. Hereinafter, an embodiment of the present invention will be described according to
FIG. The piezoelectric element 45 is formed on the end face of the columnar crystal 50 such as
sapphire or fused quartz, and the concave lens 55t is formed on the other end face. Assuming
that the aperture diameter t-2A of the piezoelectric element is used, the lens aperture is selected
as ・ · / N when using the AM point (N = 3.5.7 · old ···).
Also, the length of the crystal is p, '/ λ NIC cutting. Under such pressure, Gaussian sound waves
are incident on the lens interface to obtain a good focused beam. By adding an opening of the
lens to the lens opening 10 / NKL, and adding a sound absorbing agent 60 (such as a PETSEDIC
(epoxy resin)), it prevents the -1 beam from entering the medium (water) 70 from the lens
interface. In this embodiment, the crystal part corresponding to the sub pole is further tapered to
prevent the sub pole beam from entering the medium. As described above, according to the
present invention, since a crystal shorter than Fresnel focus and spot distribution is used, an
acoustic wave focusing action can be realized with a short crystal, and L @ ss in the crystal and
the difficulty in production (6) There is a large reduction, and a large contribution to the socalled sonic microscope or other ultra high frequency acoustic wave device.