JPH02310463A - Ultrasonic microscope - Google Patents

Abstract

PURPOSE:To prevent the degradation in resolving power in the case of internal observation by impressing high-frequency pulse electric signals (RF pulses) in duplex and obtaining an interference signal with the multiple reflection signals as a reference signal. CONSTITUTION:The high-frequency continuous wave electric signal generated in an RF generator 1 is converted by a pin diode switch 2 to the RF pulses. The double repeating pulses which have the same repeating period tr and the same pulse width td and are deviated in time by shift time ts are sent as a control signal to the switch 2 from a pulse oscillator 3. Gate signal pulses are sent at the timing delayed by the time tg from the double pulses to a gate circuit 4 from the oscillator 3. The RF pulses which are the output of the switch 2 are impressed to a transducer 12 via a circulator 5. The resulted reflection signal is passed through a circulator 5 and is amplified in a receiving amplifier 6; thereafter, the signal is converted to a video band by a diode detector 7 and is applied to the circuit 4, by which the video signal is formed.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a reflection-type ultrasonic microscope that irradiates a sample with ultrasonic waves and observes the inside of the sample from the reflected image.

[Conventional technology]

FIG. 3 shows the general configuration of a focused ultrasonic transducer, which is a part of an ultrasonic microscope that generates an ultrasonic beam. In the figure, the focused ultrasonic transducer 11 is composed of a transducer I2 made of a piezoelectric element and an acoustic lens medium 13 made of sapphire or the like.The lower end of the acoustic lens medium 13 facing the sample 14 has a spherical surface (acoustic lens) 13a. is formed by optical polishing. 15 is a medium such as water filled between the acoustic lens medium 13 and the sample 14 for propagating sound waves. In such a configuration, when a high frequency pulsed electrical signal (hereinafter referred to as an RF pulse) is applied to the transducer 12, ultrasonic waves are emitted into the acoustic lens medium 13. This ultrasonic wave is refracted by the acoustic lens 13a, propagates through the medium [15], and is focused inside the sample 14. The scratches 14a inside the sample 14, the acoustic lens 13a and the medium 1
A part of the ultrasonic waves reflected and scattered at the interface with the acoustic lens medium 13 is collected by the acoustic lens medium 13, and is converted back into an electric signal by the transducer 12. Figure 4 shows the signal waveform of the reflected signal obtained in this way in the video band, where the horizontal axis is time, the vertical axis is signal strength, L is the pulse width of the RF pulse, and t is the same. It is a repetition period. In the figure, A shows the applied RF pulse itself, B shows the reflected signal from the interface between the lens 13a and the medium 15, and C shows the reflected signal from near the focal point inside the sample. An ultrasound microscope that obtains information from the amplitude intensity of a reflected signal as shown in FIG. 4 is called an amplitude mode. On the other hand, there is a mode called interference mode in which information is obtained by interfering a reflected signal with a reference signal. Ultrasonic microscopes in this interference mode are roughly divided into types that electrically interfere the reference signal and reflected signal and types that acoustically interfere, but in the former type, the reference signal and reflected signal are separated from generation to interference. Since different electrical signal paths are followed, the obtained image may be disturbed due to disturbances such as electromagnetic noise mixed into the reference signal, so the latter method is better because it is less susceptible to disturbances and can easily configure an interference mode. Regarding the ultrasonic microscope that causes acoustic interference,
1-88142, as shown in FIG. 5, the pulse width t of the applied RF pulse A is
4 is made sufficiently long, the reflected signal B from the interface between the acoustic lens 13a and the medium 15 is temporally superimposed on the reflected signal C from the sample 14 as a reference signal, and an interference signal Z is obtained.

[Problem to be solved by the invention]

However, conventional interference mode ultrasonic microscopes, especially those that use acoustic interference, have the following problems. (1) Since an RF pulse with a long pulse width is used as the applied signal, the depth resolution decreases when observing the inside of the sample. The reflected signal contains integral information from the sample surface to the focal plane, and in amplitude mode, the reflected signal from near the focal point and other signals are temporally separated and detected. However, in an interference mode with a longer pulse width, it is impossible to temporally separate the reflected signals, and the reflected signal from the sample surface is also included in the interference signal. A more detailed explanation with reference to Fig. 7 is as follows.In Fig. 6, the applied RF pulse A
Let E be the component of the sound wave excited by the waveform reflected by the unevenness of the sample surface and collected again. In addition, the mode is converted at the interface of the sample 14 having a layered structure, propagates through the interface as an elastic boundary wave, and after being further reflected at the interface, the mode is converted again and the component is collected by the acoustic lens medium 13 as F. . Note that B is a reflected signal from the interface between the acoustic lens 13a and the medium 15, and C is a reflected signal from near the focal point. FIG. 7 shows these signals separated and arranged on the time axis. As can be seen from FIG. 7, both components E and F are detected temporally earlier than the reflected signal C from near the focal plane. However, in the time domain L8, which is treated as an interference signal, components E and F exist, and the resulting interference signal has component B (
This is a waveform in which the reference signal) and components C, E, and F interfere with each other. In amplitude mode, the pulse width of the applied signal is made as short as possible in order to increase the depth resolution, and component C is temporally separated from components E and F, but this is not possible in interference mode. In this way, the interference mode that is supposed to improve the resolution may actually reduce the depth resolution during internal observation. (2) Since the reflected signal B from the interface between the acoustic lens 13a and the medium 15 is used as the reference signal, the reference signal has a constant amplitude intensity regardless of the sample. Therefore,
If the reflected signal C from the sample has only a weak amplitude intensity, for example when observing the interface between two materials with a small difference in acoustic impedance, component C will be extremely small compared to component B, so the component to the interference signal will be The contribution rate of C decreases, and the contrast of the observed image decreases. This invention aims to solve these problems by making it possible to temporally separate the reflected signal from the vicinity of the focal point inside the sample from other reflected signals, thereby preventing a decrease in resolution during internal observation. Furthermore, the amplitude strength of the reference signal can be selected according to the amplitude strength of the reflected signal from the vicinity of the focal point, making it possible to obtain good images with high contrast even when observing samples with weak amplitude strength. Its purpose is to provide a microscope.

[Means to solve the problem]

In order to achieve the above object, in the present invention, two RF pulses having the same repetition period and pulse width and shifted by a fixed shift time are applied to the transducer,
Moreover, one reflection signal in the reflection signal train of multiple reflections within the acoustic lens medium caused by one of the RF pulses and the other reflection signal from near the focal point inside the sample due to the other RF pulse overlap in time. The shift time is set.

[For use]

RF pulse A and RF with the same repetition period and pulse width but delayed by a certain shift time ts
A double signal with pulse A° is applied to the transducer, and one reflection signal Dm of the multiple reflections in the acoustic lens medium due to RF pulse A is reflected, (nxl, 2.3...). As a signal, an interference signal is obtained by superimposing the reflected signal C'' from the vicinity of the focal point inside the sample due to the RF pulse A''.Thereby, even if the pulse width t4 of the RF pulse is shortened, an interference signal can be obtained. It becomes possible to temporally separate the reflected signal C' from the vicinity of the focal point from other reflected signals.In addition, the multiple reflected signal used as a reference signal is
By setting the shift time t, it is possible to select an appropriate signal from the reflected signal sequence D7, so that the amplitude intensities of the reference signal Dk and the reflected signal C' can be made to be approximately the same.

【Example】

FIG. 1 is a system block diagram of an embodiment of the present invention. In FIG. High frequency continuous wave electric signal is passed through pin diode switch 2
is converted into an RF pulse. The pin diode switch 2 is supplied with the same repetition period 1. A double repetitive pulse having the same pulse width t4 and shifted by the shift time is sent as a control signal. Also, the time t from the above double pulse from the pulse oscillator 3 to the gate circuit 4. The gate signal pulse is sent at a timing delayed by . During this time t9, the ultrasonic wave excited by the transducer 12 (FIG. 3) propagates through the acoustic lens medium 13, the medium 15, and further inside the sample, is reflected near the focal plane, and propagates along the same path again to the transducer 12. This is the time it takes to reach the target. R which is the output of pin diode switch 2
The F pulse is applied to the transducer 12 via the circulator 5. Further, the obtained reflected signal is amplified by a receiving amplifier 6 via a circulator 5, and then converted into a video band signal by a diode detector 7, and then is converted to a video band signal by a gate circuit 4.
It becomes a video signal. FIG. 2 shows the waveform of the detection signal shown in FIG. 1, where the horizontal axis is time and the vertical axis is signal intensity. In the figure, A,
A" is the RF pulse 1, B, B' is the reflected signal from the interface between the acoustic lens 13a and the medium 15, c, c' is the reflected signal from near the focal point inside the sample, Dn, p, + (n=
1.2.3.) is inside the acoustic lens medium 13, that is, the interface between the acoustic lens 13a and the medium 15 and the transducer 1.
This is a reflected signal train due to multiple reflections between the second mounting surface and the second mounting surface.
In the figure, the components are shown separately for each of the double RF pulses A and A', but the signal actually introduced into the gate circuit 4 is a superposition of these components. In the illustrated example, the second multiple reflection signal D2 due to the RF pulse A and the RF
The shift time Ls is set so that the reflected signal C° from the vicinity of the focal plane due to the pulse A° overlaps with the reflected signal C° in the time domain, thereby obtaining an interference signal using the multiple reflected signal D2 as a reference signal. In this way, in the illustrated embodiment, an interference signal can be obtained without increasing the pulse width t4 of the RF pulse. In addition, the reference signal can be freely selected according to the amplitude strength of the reflected signal C'', and is not limited to D2.
It is possible to set the shift time so that C overlaps with ff, further, , D, .

【Effect of the invention】

According to this invention, in an acoustic interference type ultrasound microscope that is not affected by external electromagnetic noise, etc., an RF pulse is applied twice and an interference signal is obtained using a multiple reflection signal as a reference signal. Since there is no need to increase the pulse width of the RF pulse, it is possible to prevent a decrease in depth resolution, and since the reference signal can be selected according to the strength of the reflected signal from the sample, it is possible to obtain high-contrast images of any sample. Obtainable.

[Brief explanation of drawings]

Figure 1 is a system block diagram of an embodiment of this invention, Figure 2 is a system block diagram of an embodiment of this invention.
The figure shows the waveform of each component of the reflected signal in the embodiment of Fig. 1, Fig. 3 is a vertical cross-sectional view showing the general configuration of a focused ultrasound transducer, and Fig. 4 shows an amplitude mode ultrasound microscope. Figure 5 shows the waveform of the detection signal of a conventional interference mode ultrasound microscope. Figure 6 shows the path of the ultrasound beam when the focus is inside a sample with a layered structure. FIG. 7 is a diagram showing the waveform of each component of a reflected signal of a conventional interference mode ultrasound microscope. l...RF oscillator, 2...pin diode switch, 3...pulse oscillator, 4...gate circuit, 5...
... Circulator, 6... Receiving amplifier, 7... Diode detector, 11... Focused ultrasound transducer, 12... Transducer, 13... Acoustic lens medium, 14... Sample, 15...・Medium, A, A'・
・・High frequency pulse electric signal, t, ・・Repetition period, t
6...Pulse width, t,...Shift time. fa 2 Figure 1K 3 Figure 4

Claims (1)

[Claims] 1) In an ultrasound microscope equipped with a focused ultrasound transducer consisting of a transducer that generates ultrasound by applying a high-frequency pulsed electrical signal and an acoustic lens medium that focuses the ultrasound and irradiates it onto the sample, the repetition period and pulse Applying two high-frequency pulsed electrical signals with the same width and shifted by a fixed shift time to the transducer,
Moreover, one reflection signal in the reflection signal train of multiple reflections within the acoustic lens medium caused by the high-frequency pulse electric signal and the other reflection signal from near the focal point inside the sample due to the high-frequency pulse electric signal are temporally different. An ultrasonic microscope characterized in that the shift time is set to overlap with .