JPS62130351A - Acoustic lens for ultrasonic microscope - Google Patents

Abstract

PURPOSE:To improve the SN ratio of a reflected signal by embedding a material which has acoustic impedance nearly equal to the acoustic impedance of an acoustic lens and high ultrasonic wave absorptivity in a recessed part formed in the outer periphery of the acoustic lens at right angles to the acoustic axis. CONSTITUTION:The acoustic lens 4 has the triangular notched recessed part 11 in the outer periphery at right angles to the acoustic axis of the lens 4 and a damper member 12 in the same shape is fitted in the recessed part 11. A signal from a transmitter which is applied to a piezoelectric converter 3 is converted into an ultrasonic wave, which is propagated as a plane wave in the lens 4 and converted by a spherical lens part 4a into a spherical wave, so that the wave travels toward a sample 5 and is propagated in an ultrasonic wave propagation medium 6. Then, a reflected wave P1 reflected at the focus position of the sample 5 passes through the same path as the forward path and reaches the converter 3, so that it is detected signal. Part of the plane wave reaching the spherical surface of the lens part 4a is reflected by the spherical surface and the reflected wave P, is reflected by the side wall of the lens 4 to travel toward the converter 3. This unnecessary reflected wave P2, however, is absorbed 12 and the incidence on the converter 3 is suppressed, so that the SN ratio of the reflected signal is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an acoustic lens for an ultrasound microscope that suppresses multiple reflections within the acoustic lens.

[Conventional technology]

In recent years, unlike optical microscopes or electron microscopes that use electron beams, ultrasound microscopes have been attracting attention because they can obtain acoustic information.

The ultrasonic microscope described above can obtain an ultrasonic microscope image having a resolution on the order of 1 μm by using ultrasonic waves of, for example, 100 MHz to several GHz.

In principle, this ultrasonic microscope mechanically scans the sample surface with a narrowly focused ultrahigh-frequency ultrasonic beam, collects the ultrasonic waves scattered by the sample, and converts them into electrical signals.
The signal is displayed two-dimensionally on a display screen such as a cathode ray tube to obtain a microscopic image. The configuration depends on how the ultrasound is detected; in other words, there are two methods: detecting ultrasound that has passed through the sample while being scattered or attenuated, and detecting ultrasound that has been reflected due to differences in acoustic properties within the sample. Depending on the type, it can be divided into transmissive type and reflective type.

FIG. 3 is a diagram showing the principle of a reflection type ultrasound microscope, and FIG. 4 is a diagram showing the configuration of a conventional acoustic lens. A signal from a transmitter 1 is supplied by a directional coupler or circuit generator 2 to a piezoelectric transducer 3 for both transmitting and receiving purposes. This signal is converted into an ultrasonic wave, and this piezoelectric transducer 3 is attached to one surface (upper end surface) of an ultrasonic focusing lens (acoustic lens) made of an ultrasonic propagation medium material such as sapphire for both transmitting and receiving waves. 4
The wave is radiated inward from one side in the form of a plane wave and transmitted to the other side. The other surface of this acoustic lens 4 is hollowed out into a spherical shape to form a spherical lens portion 4&, and the ultrasonic propagation medium 6 such as water interposed between the sample 5 and the spherical lens portion 4a is formed into a spherical shape. The beam propagates in a wave-like manner and is focused into a beam spot on the surface of the sample 5 (when focused on the surface).

The sample 5 is placed on a sample holder 7.

The ultrasonic waves transmitted to the sample 5 side are transmitted, absorbed, etc. depending on the acoustic characteristics on the sample surface, but some of the reflected waves and scattered waves pass through the same path and pass through the piezoelectric transducer 3. The signal is converted into an electrical signal and input to the receiver 8. The signal is detected by this receiver 8, and the output is sent to the video signal processing section 9.
It is input to a display 10 such as RT. On the other hand, the acoustic lens 4 is scanned, for example, in the X direction by a vibrator (not shown), and the sample holding table 7 side is scanned in the Y direction, and sweep signals synchronized with these scans are displayed on the X and Y axes of the display 10. is applied, and a two-dimensional ultrasound microscope image is displayed on the display screen of the display device 9.

By the way, the above-mentioned ultrasonic microscope has X,
The focus position in the Z-axis direction perpendicular to the Y plane is changed. In other words, if the acoustic lens 4 is used close to the sample side and focused on the inside of the sample, an ultrasonic microscope image of the inside of the sample can be obtained.

[Problem that the invention seeks to solve]

However, in the ultrasonic microscope with the above configuration, the fourth
As shown in the figure, in addition to the reflected wave P1 from the focus position of the sample 5, the reflected wave P2 reflected by the spherical lens portion 4a of the acoustic lens 4 and the reflected wave P2 reflected from the focus position of the sample 5, for example, from the surface of the sample 5. Reflected waves Pa and the like are generated, and these reflected waves P2.degree. Pa are multiple-reflected on the wall surface of the acoustic V-lens 4, enter the piezoelectric transducer 3, and are detected as one reflected signal. In particular, the reflected wave P1 from sample 5
However, at the time when it re-enters the acoustic lens 4 via the ultrasonic propagation medium 6 and reaches the piezoelectric transducer 3, the reflected waves Pg and Pa due to multiple reflections as described above reach the piezoelectric transducer 3, and a particularly coherent wave is generated. Since it is an acoustic system, interference may occur, and the reflected wave P1 from the sample 5 may reach the customer. Therefore, in conventional acoustic lenses, the reflected waves due to multiple reflections become noise components, and the S/N of the reflected signal is
This has the drawback that it is difficult to extract only the reflected waves from the accurate sample as reflected signals.

Therefore, in Japanese Patent Laid-Open No. 58-96248, the present applicant proposed that the acoustic impedance of the acoustic lens be relatively reduced by adding a layer to the outer peripheral surface of the acoustic lens excluding the spherical lens part in contact with the sound field medium and the electrode part to which the piezoelectric transducer is attached. We propose an acoustic lens coated with a material with similar acoustic impedance and high ultrasound absorption. According to this, unnecessary reflected waves within the acoustic lens can be absorbed to some extent and the reflected waves that become noise components can be suppressed from entering the piezoelectric transducer, but unnecessary reflected waves cannot be completely removed. isn't it.

[Object of the Invention] The present invention has been made in view of the above circumstances, and is aimed at reducing the S/N of one reflected signal by removing multiple reflected waves that become noise components.
It is an object of the present invention to provide an acoustic lens for an ultrasonic microscope that can improve the image quality and selectively extract information about only the focal position.

[Means and effects for solving the problem] The acoustic lens for an ultrasonic microscope according to the present invention has a concave portion circularly provided on the outer periphery perpendicular to the acoustic axis of the acoustic i-lens, and the acoustic impedance of the acoustic lens is provided in the concave portion. This material has an acoustic impedance approximately equal to that of the material and has a material embedded therein that has a high absorption of ultrasonic waves.

That is, the multiple reflected waves that become noise components passing through the ultrasound absorbing material embedded in the recess are absorbed by the ultrasound absorbing material, and as a result, only the reflected waves from the sample are detected as reflected signals.

[Embodiments of the invention]

The present invention will be described in detail below with reference to one drawing. .

FIG. 1 is a configuration diagram of an acoustic lens according to a first embodiment of the present invention.

The acoustic lens 4 of this embodiment is made of sapphire or the like, as in the conventional one, on its outer periphery perpendicular to the acoustic axis.
A triangular cut recess 11 whose cross section in the acoustic axis direction is a triangle whose base is on the outer circumferential side of the acoustic lens is provided in a circumferential manner, and a damper member 12 having the same shape as the recess 11 is fitted into the recess 11 .

This damper member 12 is made of a material that has an acoustic impedance substantially equal to that of the acoustic lens and that absorbs large ultrasonic waves. Although it is difficult to find such a simple substance, it is possible to create such a substance in one equivalent manner. For example, it is well known that the acoustic impedance can be varied over a wide range by mixing tungsten metal powder and epoxy resin in ultrasonic diagnostic probes and the like. In addition, the damper member 1 can be prepared by mixing not only tungsten metal powder but also a powder having an acoustic impedance larger than the acoustic impedance of the lens constituent material and an organic resin in an appropriate proportion.
2 can be formed.

Further, the damper member 12 itself forms an entrance pupil and an exit pupil of the acoustic lens 4.

In the acoustic lens 4 configured in this way.

The signal from the transmitter 1 applied to the piezoelectric transducer 3 is converted into an ultrasonic wave, becomes a plane wave, and passes through the acoustic lens 4.
is converted into a spherical wave by the spherical lens portion 4a, and propagated toward the sample 5 through an ultrasonic propagation medium 6 such as water. Then, the reflected wave Pl reflected at the focus position of the sample 5 passes through the same path as the outward path, reaches the piezoelectric transducer t3, and is detected as one reflected signal.

On the other hand, a part of the plane wave that has arrived at the spherical surface of the spherical lens portion 4a of the acoustic lens 4 is reflected by the spherical surface, and this reflected wave P2 is reflected by the side wall of the acoustic lens 4 and is directed toward the piezoelectric transducer 3. However, this unnecessary reflected wave P
Since the damper member 12 is disposed on the path of the second damper member 12, the first reflected wave P2 is largely absorbed by the damper member 12 when passing through the damper member 12, resulting in an unnecessary reflected wave P2.
2 to the piezoelectric transducer 3 is sufficiently suppressed. As a result, noise is reduced and the S/N of one reflected signal is improved.

Further, a part of the spherical wave toward the sample 5 is reflected at a point other than the focus position of the sample 5, for example, the surface of the sample 5. This reflected wave P3 is also reflected by the side wall of the acoustic lens 4 and directed toward the piezoelectric transducer 3 in the same manner as the reflected wave P2 described above, but is largely absorbed by the damper member 12 and is prevented from entering the piezoelectric transducer 3. be done. As a result, it is possible to selectively extract only information near the focus position of the sample 5.

The material forming the damper member 12 is required not only to have high ultrasonic absorption but also to have an acoustic impedance approximately equal to the acoustic impedance of the acoustic lens. 1. If the acoustic impedance of the two is greatly different, the reflectance of ultrasonic waves will increase at the interface between the two, and unnecessary reflected waves will not enter the damper member 12. As a result, unnecessary reflected waves will be absorbed. This is so that you will not be disappointed. To explain this in detail, 1. For example, regarding the reflection of ultrasonic waves.

If the ultrasonic wave is incident from the first medium to the second medium, the reflectance R of 1 intensity is when it is perpendicularly incident.

R= ((Zl − Zz )/(Z1+Z2 ) )”
is given by However, zl is the acoustic impedance of the first medium, and Z2 is the acoustic impedance of the second medium.

Also, the acoustic impedance 2 of the medium is:

2=ρC. However, ρ is the density of the medium, and C is the speed of sound in the medium. According to the above 4 formulas, if Zl = Z2, the reflection of vertically incident ultrasonic waves becomes 0. Therefore, as in the present invention,
When the acoustic impedance of the acoustic lens and the acoustic impedance of the damper member are approximately equal, unnecessary reflected waves P2
, Pa enters the damper member from the acoustic lens with almost no reflection at the interface, and is absorbed by the damper member.

FIG. 2 is a block diagram of an acoustic lens according to a second embodiment of the present invention.

The acoustic lens 4 of this embodiment has an outer periphery perpendicular to the acoustic axis.
A recess 11 having a rectangular cross section in the acoustic axis direction is provided in a circumferential manner from near the piezoelectric transducer 3 to near the curved lens part, and a damper member 12 having the same shape is fitted into the recess 11. be. As in the first embodiment, the damper member 12 is made of a material that has approximately the same acoustic impedance as the acoustic impedance of the acoustic lens and has high ultrasonic absorption.

In the acoustic lens 4 of this embodiment, unnecessary reflected waves P2,
The distance that Pa passes through the damper member 12 becomes longer,
The unnecessary reflected waves P2 and P3 are absorbed more completely, and the reflected waves traveling in a direction deviating from the direction parallel to the acoustic axis are absorbed by the damper member 12, and the reflected waves traveling substantially parallel to the acoustic axis are absorbed. can be detected by the piezoelectric transducer 3. That is, only information near the focus position of the sample 5 can be extracted more selectively. Other functions and effects are similar to those of the first embodiment.

As explained above, the length of the damper member 12 embedded in the acoustic lens 4 in the direction perpendicular to the acoustic axis.

By adjusting the length in the direction parallel to the acoustic axis, the buried position, and the shape, it is possible to selectively extract the information of the primary phase phase ultrasound, that is, only the focus position.

In addition, the entrance pupil and output waterfall of the acoustic lens are damped by the damper member 1.
2. Therefore, when attaching a piezoelectric transducer 3 or an exciter for vibrating the acoustic lens 4 to the acoustic lens 4, it is possible to form the acoustic lens 4 outside the range limited by the entrance pupil and the exit 11iVC of the acoustic lens 4. This makes it easier to attach the piezoelectric transducer 3, vibrator, etc. In addition, since the damper member 12 forms an entrance pupil and an exit pupil, the piezoelectric transducer 3
The size of the piezoelectric transducer can be limited, making it easier to form the piezoelectric transducer.

〔Effect of the invention〕

As explained above, according to one aspect of the present invention, a concave portion is provided in a circumferential manner on the outer periphery perpendicular to the acoustic axis of an acoustic lens, and the concave portion has an acoustic impedance substantially equal to the acoustic impedance of the acoustic lens, and Since a highly absorbing material is buried, it is possible to absorb and remove noise components and multiple reflected waves passing through the ultrasonic absorbing material buried in the recess.

The S/N of the reflected signal can be improved.

In addition, by adjusting the size of the ultrasonic absorbing substance,
Information about only the focus position can be selectively extracted.

In addition, since the entrance pupil and exit pupil of the acoustic lens can be formed from an ultrasonic absorbing material, it becomes easier to attach a piezoelectric transducer or an exciter that vibrates the acoustic lens. The size of the transducer can be limited and the work of forming the piezoelectric transducer becomes easier.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the first embodiment of the present invention, Fig. 2 is a block diagram of the second embodiment of the present invention, Fig. 3 is a principle diagram of a reflection type ultrasound microscope, and Fig. 4 is a diagram of the conventional ultrasonic microscope. FIG. 2 is a configuration diagram of an acoustic lens. 1...Transmitter, 2...Circulator. 3...Piezoelectric transducer. 4...acoustic lens, 4&...spherical lens section. 5... Sample, 6... Ultrasonic propagation medium. 7... Sample holding stand, 8... Receiver. 9...Video signal processing section. 10... Display portion, 11... Recessed portion. 12...Damper part.ゝ゛-2-・' 21!1 Figure 3 Figure 4

Claims (1)

[Claims] Transmits ultrasonic waves emitted from an ultrasonic transducer installed on one end surface, sends them to the sample side through a liquid interposed on the other end surface, and captures the reflected ultrasound waves.
In an acoustic lens for an ultrasound microscope used to transmit ultrasound images to the ultrasound transducer side, a concave portion is provided in a circumferential manner on the outer periphery perpendicular to the acoustic axis of the acoustic lens, and the acoustic lens is placed in the concave portion. 1. An acoustic lens for an ultrasonic microscope, characterized in that a material having an acoustic impedance substantially equal to an acoustic impedance and having a large absorption of ultrasonic waves is embedded therein.