JPH01254859A - Ultrasonic microscope - Google Patents

Abstract

PURPOSE:To make the constitution of the title microscope simpler and inexpensive and, at the same time, to improve the measuring speed of the microscope by suppressing multiple reflection of radio waves in a ultrasonic transducer for reception by obliquely cutting the end face of the transducer and inclining the obliquely cut end face against the plane perpendicular to its central axis. CONSTITUTION:A focusing ultrasonic transducer 16 for transmission which excites leakage surface acoustic waves on the surface of a sample 6 and a planar supersonic transducer 22 for reception which is provided in an inclined state at a prescribed angle against the surface of the sample 6 and receives leakage radiation waves from the leakage surface acoustic waves propagated on the surface of the sample 6 are provided. The end face of the transducer 22 on the sample 6 side is obliquely cut and inclined against the plane perpendicular to its central axis. Therefore, radio waves received by the transducer 22 do not cause multiple reflection in the transducer 22 and only the radio waves returning from the sample 6 are obtained as the output. As a result, a high-frequency oscillator 23 can be used as the signal source instead of a high-frequency pulse oscillator and the relation between the inclined angle of the transducer 22 and its output can be drawn by using an XY plotter 21.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic microscope for measuring the elastic properties of substances. BACKGROUND OF THE INVENTION In recent years, ultrasound microscopes have been developed that utilize ultrasonic waves of several tens of MHz or more instead of light or electron beams. Among these, mechanical scanning reflection ultrasound microscopes use one or two focused ultrasound transducers to obtain images by utilizing reflected ultrasound waves caused by differences in elastic properties at each point of a material. , to quantitatively measure the elastic properties of microscopic parts of materials. FIG. 5 is a block diagram showing an example of a conventional mechanical scanning reflection type ultrasound microscope. In FIG. 5, a pulse modulated wave generated by a high-frequency pulse oscillator 1 passes through a circulator 2, becomes a focused ultrasonic beam by a focused ultrasonic transducer 3, and is irradiated onto a sample 6 on a sample holder 5 via a sound wave propagation liquid 4. be done. The sample holding table 5 is
It is moved in the X and Y directions shown in the figure by the Y force direction moving device 7. The XY direction moving device 7 is controlled by a scanning control circuit 8. Instead of moving the sample holding table 5, the focused ultrasonic transducer 3 can also be moved in the XY force directions. The reflected wave reflected by the sample 6 is again collected by the focused ultrasonic transducer 3, converted into an electric signal, and supplied to the display device 9 via the circulator 2 to obtain an ultrasonic microscope image. Next, FIG. 6 shows a configuration for measuring the sound velocity on the sample surface. In FIG. 6, while moving the sample 6 placed on the sample holding table 5 closer to the focused ultrasonic transducer 3 by the Z-direction moving device 10,
The output of the focused ultrasonic transducer 3 is observed with an oscilloscope 11. When the output of the focused ultrasound transducer 3 is recorded with respect to the moving distance in the Z direction shown in the figure, a curve as shown in FIG. 7 is obtained. This curve is called the V(Z) curve. Figure 8 shows the principle by which the V (Z) curve in Figure 7 is obtained.
゜ In Fig. 8, the sample 6 is arranged so that its surface is close to the focused ultrasonic transducer 3, and the component of the ultrasonic waves irradiated from the focused ultrasonic transducer 3 that returns from the sample surface is oriented along two axes ( Figure 6) Reflected waves from the vicinity (hereinafter referred to as vertical reflected waves) 12 and re-radiated waves of leaky surface acoustic waves excited by the ultrasonic waves 13 incident at the critical angle δ (hereinafter referred to as leaky radiated waves). ) Only 14. The V (Z) curve is obtained by the interference of these two components. When displaying an image with the configuration shown in Figure 5, high contrast can be obtained by measuring the surface of the sample 6 slightly closer to the focused ultrasound transducer 3 from the focal plane, but this is shown in Figure 7. This is because the characteristics of the V (Z) curve shown are utilized. Next, the leakage radiation wave 14 will be explained with reference to FIG. The ultrasonic wave 13 that is incident on the sample surface at an angle specific to the substance, that is, at a critical angle δ, excites a leaky surface acoustic wave 15 that propagates on the sample surface while releasing energy into the sound wave propagation liquid 4 . Specifically, the emitted energy is a longitudinal sound wave, called a leakage radiation wave 14, and as shown in FIG. It propagates in the direction. As shown in FIG. 8, only the component of the leakage radiation wave 14 emitted from a position symmetrical to the incident position with respect to the beam center from the focused ultrasonic transducer 3 is collected. In other words, the incident ultrasonic wave 13 undergoes mode conversion, propagates on the sample surface as a surface wave, and then is converted back into a longitudinal sound wave and is collected.
Component 4 causes a significant phase change or is attenuated due to changes in the elastic properties of the sample surface. Therefore, the periodicity of the V (Z) curve obtained by the interference of the components of the leakage radiation wave 14 and the vertically reflected wave 12 (FIG. 8) depends on the elastic properties of the material surface, and the periodicity shown in FIG. By measuring ΔZ, the sound speed of the leaky surface acoustic wave 15 of the substance can be calculated. The relationship between this period ΔZ and the speed of sound is approximately given by the following equation. is, Z = V L / (2f (1cosθ)
) θ = 5in-' (Vr/Vc) where ■, is the longitudinal sound velocity of the sound wave propagation liquid 4, V is the sound velocity of the leaky surface acoustic wave 15, and f is the used ultrasonic frequency. However, these This method has the following problems: (1) The component of the vertically reflected wave 12 may not have sufficient intensity to interfere with the leaky radiation wave 14. This is the case for materials, biological tissues, etc. In this case, the contrast of the image decreases and V (Z)
The curve also shows no periodicity. (2) In the conventional method of determining the sound velocity of a leaky surface acoustic wave from the period ΔZ of the V(Z) curve, in a sample where multiple leaky acoustic wave modes exist, the waveform of the V(Z) curve is disturbed; The sound speed of leaky surface acoustic waves cannot be measured without using waveform analysis techniques such as Fourier transform. (3) The pulse width of the pulse modulated wave generated by the high-frequency pulse oscillator should be long in order to cause interference, but there is a limit to the pulse width in order to separate it from unnecessary echoes generated within the focused ultrasound transducer. , so that the pulse width used may not produce the desired interference effect. Therefore, a receiving ultrasonic transducer for receiving leaky radiation waves from the leaky surface acoustic waves is provided separately from a focused ultrasonic transducer for transmitting waves that excites leaky surface acoustic waves on the sample surface, and This receiving ultrasonic transducer has been proposed to be arranged so as to be inclined at a predetermined angle with respect to the sample surface so that it can selectively detect only leaked radiation waves at a predetermined radiation angle. FIG. 10 is a block diagram showing such an ultrasonic Bm mirror, which uses a flat type as an ultrasonic transducer for receiving waves. In FIG. 10, an electric signal from a high-frequency pulse oscillator l becomes a focused ultrasound beam by a focused ultrasound transducer 16 for transmitting waves, and a sound wave propagating liquid 4
The sample 6 is irradiated through the sample 6, and a leaky surface acoustic wave is excited on the surface of the sample 6. The leakage radiation wave re-radiated from the leakage surface acoustic wave is radiated at an angle specific to the material, propagates in that direction, and reaches the wave-receiving planar ultrasonic transducer 17. The angle of the receiving planar ultrasonic transducer 17 with respect to the sample surface is changed by a tilt angle variable device 18 that is controlled by a tilt angle controller 19 . When the end face of the receiving planar ultrasonic transducer 17 has an inclination angle that is perpendicular to the direction of the temple of the leaked radiation wave, the output of the receiving planar ultrasonic transducer 17 shows a peak. The output of the receiving planar ultrasonic transducer 17 passes through a high frequency amplification detector 20 and is sent to an XY plotter 21 at the same time as the tilt signal from the tilt angle control device 19. The inclination angle θ at which the output reaches its peak is a value unique to each material, and the sound velocity (2) of the leaky surface acoustic wave can be determined from the inclination angle θ at that time using the following equation. V (=V, The receiving planar ultrasonic transducer 17 is arranged at an inclination angle θ where the output peaks.The sample holding table 5 on which the sample 6 is fixed is moved in the X and Y directions by the XY moving device 7. The XY moving device 7 is controlled by a scanning control circuit 8. The output from the high frequency amplification detector 20 is sent to the display device 9 in synchronization with the position information signal from the scanning system?'f1 circuit 8, and an image is displayed. If the sample 6 is homogeneous and has no surface irregularities, there will be no change in the output of the receiving planar ultrasonic transducer 17 even if the ultrasonic beam is scanned over the sample surface. If a sample has cracks or defects near the subsurface, the sound waves will be disturbed or scattered at that location, resulting in a drop in output.Furthermore, if the sample is polycrystalline and has grain boundaries, or if each crystal grain has a crystal plane or The same applies to those whose elastic properties have changed, and images with high contrast can be obtained by changing the output of the planar ultrasonic transducer 17 for receiving waves. Although a planar type ultrasonic transducer is used, the same effect can be obtained by using a linear focused ultrasonic transducer for wave reception.' [Problem H that the invention seeks to solve] However, as mentioned above, Conventional ultrasound microscopes require the use of a high-frequency pulse transmitter as a signal source.This eliminates unnecessary signals due to multiple reflections of sound waves within the receiving plane ultrasound transducer or the receiving linear focused ultrasound transducer. This is because it is necessary to separate temporally by using a high frequency signal (burst wave) as a signal source. However, using a high frequency pulse signal involves the following problems: (1) High frequency pulse Since high-performance equipment is required to generate and amplify the signal, the equipment itself is large and expensive. (2) When taking images or drawing output curves against tilt angles, one pulse Since only one piece of information (pixels, etc.) can be obtained, a long measurement time is required.This invention has a simple configuration by mechanically suppressing unnecessary signals caused by multiple reflections within the receiving ultrasonic transducer. The object of the present invention is to provide an ultrasonic microscope that is inexpensive and capable of high-speed measurement.
The system includes a focused ultrasonic transducer for transmitting waves that excites leaky surface acoustic waves on the sample surface, and a focused ultrasonic transducer for transmitting waves that excites leaky surface acoustic waves on the sample surface, and a focused ultrasonic transducer that is arranged at a predetermined angle with respect to the sample surface to excite leakage from the leaky surface acoustic waves that propagates on the sample surface. A planar ultrasonic transducer for receiving radiation or a linear focused ultrasonic transducer for receiving radiation is provided. Suppose that is inclined with respect to the axis perpendicular to the central axis. [Function] By canting the end face of the ultrasonic transducer for receiving waves diagonally and making the end face inclined with respect to the plane perpendicular to the central axis of the ultrasonic transducer, multiple reflections of sound waves inside the ultrasonic transducer are prevented. suppressed. [Example] The present invention will be described in detail below based on FIGS. 1 to 4. Note that the same parts as those in the conventional example are denoted by the same reference numerals, and the explanation thereof will be omitted. FIG. 1 shows a block diagram of an embodiment of the invention. In FIG. 1, the receiving planar ultrasonic transducer 22 has an end face on the sample side cut obliquely, and the end face is inclined with respect to a plane perpendicular to the central axis as shown. For this purpose, a receiving planar ultrasonic transducer 22
The sound waves received at This allows the XY block 21 to draw a curve of the relationship between the inclination angle and the output of the planar ultrasonic transducer 22 for wave reception in a short time. ,
The high frequency amplification detector 20 can also be used with a narrow band, and together with the use of the high frequency oscillator 23, the configuration becomes simple and inexpensive. FIG. 2 is an enlarged view of the arrangement of the focused ultrasonic transducer 6 for transmitting waves and the planar ultrasonic transducer 22 for receiving waves. The surface of the sample 6 is placed at the focal point of the focused ultrasonic transducer 16 for transmitting waves or closer to the lens. Further, the receiving planar ultrasonic transducer 22 is arranged so that the detection tilt area A is located at a position away from the incident ultrasonic spot by a certain surface wave propagation path length. The rotation center R and the rotation axis 24 are determined so that the length of the surface wave propagation path does not change when the wave receiving planar ultrasonic transducer 22 is rotated in the direction of arrow P to change the inclination angle θ. FIG. 3 is an example for obtaining an image. In this configuration as well, the high frequency oscillator 23 can be used as a signal source, which simplifies the circuit configuration and
The time required to obtain an image on the display device 9 can be shortened. FIG. 4 shows an example in which a linear focused ultrasonic transducer 25 is used for wave reception. In this case as well, the end surface of the linear focused ultrasonic transducer 25 on the sample side is cut obliquely. In FIG. 4, the sample surface is included in the illustrated XY plane, and the central axis of the focused ultrasonic transducer 16 for transmitting waves is included in the YZ plane. The receiving linear focused ultrasonic transducer 25 has its focusing direction aligned with the X direction, and is inclined at a predetermined angle with respect to the sample surface in a plane (YZ plane) perpendicular to the focusing direction. At this time, a beam spot 27 of the focused ultrasonic transducer 16 for transmitting waves is included on a line 26 where a plane perpendicular to the focusing direction and the sample surface intersect. Effects of the Invention According to the present invention, the sample-side end surface of the planar ultrasonic transducer for receiving waves or the linear focused ultrasonic transducer for receiving waves is inclined with respect to the plane perpendicular to the central axis. Multiple reflections of sound waves inside the transducer can be suppressed, high-speed measurement can be performed, and an inexpensive ultrasonic microscope can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is an enlarged layout diagram of the transmitting ultrasonic transducer and the receiving ultrasonic transducer in FIG. A block diagram showing the configuration of an embodiment of
The figure is an enlarged layout diagram of a transmitting ultrasonic transducer and a receiving ultrasonic transducer when a linear focused ultrasonic transducer is used for receiving waves, and FIG. 5 is a block diagram showing the configuration of the first conventional example. , FIG. 6 is a block diagram showing the configuration of the second conventional example, FIG. 7 is a diagram showing the V (Z) curve, FIG. 8 is an explanatory diagram showing the principle of obtaining the V (Z) curve, and FIG. Figure 9 is an explanatory diagram showing the leakage radiation waves in Figure 8;
FIG. 10 is a block diagram showing the configuration of the third conventional example;
FIG. 1 is a block diagram showing the configuration of a fourth conventional example. 6: Sample, 16: Focused ultrasonic transducer for wave transmission,
22: Planar ultrasonic transducer for receiving waves, 25: Linear ultrasonic transducer for receiving waves. Figure 3 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] 1) A focused ultrasonic transducer for transmitting waves that excites leaky surface acoustic waves on the sample surface, and leakage from the leaky surface acoustic waves that are arranged at a predetermined angle with respect to the sample surface and propagate on the sample surface. A planar ultrasonic transducer for receiving radiation or a linear focused ultrasonic transducer for receiving radiation is provided. An ultrasonic microscope characterized in that the plane is inclined with respect to a plane perpendicular to the central axis.