JPH0235936B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an imaging device using ultrasound energy, and particularly to an ultrasound microscope.

[Background of the invention]

A mechanical scanning sonic microscope has been proposed, for example, in Japanese Patent Laid-Open No. 116058/1983, which utilizes ultrahigh-frequency sound waves with a sound frequency of 1 GHz, which corresponds to a sound wavelength in water of approximately 1 μm.

That is, as shown in FIG.
(For example, cylindrical crystals such as sapphire and quartz glass)
One end surface 21 is an optically polished flat surface, and the other end surface is formed with a lens surface 30 formed by a concave hemispherical hole. An RF pulsed electrical signal applied to the piezoelectric thin film 10 deposited on the end face 21 radiates a plane wave RF pulsed sound wave into the acoustic lens body 20 . This RF lens electric signal is a pulse obtained by extracting several cycles of a continuous sine wave, and the RF pulse sound wave is a so-called burst wave equivalent to this.

This plane sound wave is transmitted between the lens surface 30 and the medium 40.
It is focused onto the sample 50 at a predetermined focus by a positive acoustic lens formed at the interface with water (generally water).

The ultrasonic waves reflected and scattered by the sample 50 are
Sound is collected by the same lens surface 30, converted into a plane wave, propagated within the lens body 20, and finally converted into an RF electric signal by the piezoelectric thin film 10. This RF
The electric signal is diode-detected and converted into a video signal, which is used as the input signal for the above-mentioned cathode ray tube.

The above-mentioned disturbing sound wave energy reflects the elastic properties of the sample, so if the sample is mechanically scanned two-dimensionally and the video signal is displayed on a cathode ray tube in synchronization with this scanning, the A microscopic image will be obtained.

The present invention relates to a so-called reflection type configuration in such an apparatus, in which one piezoelectric thin film is used both for generating an ultrasonic beam and detecting a reflected acoustic beam.

FIG. 2a shows a detection signal in the video region of a received signal when an RF pulse electric signal with a certain repetition period t _R is applied to the piezoelectric thin film 10 in such a reflective configuration. Here, the horizontal axis represents time, and the vertical axis represents signal strength. Further, A shows the applied RF pulse, B shows the reflected signal from the lens surface 30, and C shows the reflected signal from the sample 50. Although the reflected signals B and C do not match in phase, their waveforms and periods are equal to the applied pulse A.

Conventionally, in order to distinguish between the desired reflected signals C and B, the duration time _td of the applied pulse is set as short as possible so that the C and B signals do not overlap on the time axis, and only the C signal is time-selected. A ``width'' mode is employed, which employs a configuration that either gates (FIG. 2b) and integrates, or samples only the C signal.

We will further consider the circumstances during this time. The RF pulse signal applied to the piezoelectric thin film is expressed by the following equation (1).

V(t)=Asinω _p t 0<t<t _d ……(1) Here, if ω _p is the used ultrasonic frequency, the reflected ultrasonic wave C from the sample is Vc(t)=AR ^* sinω _p (t+t _p + 2Z / υ _w ) ...... (2) where t _p + t _s < t < t _p + t _s + t _d where t _p = 2L / υ _L ; L is the axial length of the lens body υ _L is the sound speed of the lens material t _s = 2Z/υ _w ; Z is the distance between the lens surface and the sample, and υ _w is expressed as the speed of sound in water. R ^* is the complex reflectance of the sample, which is determined by the elastic properties of the sample, and can be written as R ^* = Re ^j 〓 ^s (3) (R is the absolute value of R ^* , and θ _s is the phase change upon reflection by the sample).

The conventional "width" mode uses reflected signals from the sample.
The absolute value R of the reflectance of the sample is displayed by video detecting V _c (t). By the way, a constant reflected wave from the lens surface can be obtained if the applied RF pulse is constant. He proposed a device that uses this as a reference wave to make measurements by interfering with the reflected wave from the sample (Japanese Patent Application No. 58,707/1983). A device that can easily change between this interference mode and the conventional amplitude mode can dramatically increase the usefulness of ultrasonic microscope devices.

[Purpose of the invention]

The present invention has been made in view of the above points, and provides an ultrasonic microscope that can easily switch between the conventional "width" mode and "interference" mode with a simple configuration.

[Summary of the invention]

Rewriting equation (2), the reflected signal from the sample V _c
is V _c (t) = ARsinω _p (t + t _p + 2Z / υ _w + θ _s ) (4) where t _p + t _s < t < t _p + t _s + t _d , and the reflected signal V _B from the lens surface is V _B (t)=AQsinω _p (t+t _p ) (5) where t _p <t<t _p +t _d Q is expressed by the reflectance between the lens and the medium. If the duration time t _d of the applied RF pulse is increased so that t _d > 2Z/υ _w (=t _s ), the reflected signal B
and C overlap (dashed line area in Figure 3a). Equation (4),
From (5), in the time domain t _p +t _s <t<t _p +t _d ......(6), this sum signal is V(t) = ARsinω _p (t+t _p +2Z/υ _w +θ _s ) (7) +AQsinω _p (t+t _p ), and in the video domain where this is square-law detected by diode, V(t)=A ² R ² 2A ² RQcosω _p (2Z/υ _w +θ _s )+A ² Q ² ………(7′ ) becomes. Displaying this signal provides an "interference" mode.

Next, in this state, V (t) = AQsinω _p (t + t _p ) ...... (5') where t _p < t < t _p + t _d The electric signal (Fig. 3b) is expressed in the RF domain by formula (7). ), the two subtracted signals become V(t)=ARsinω _p (t+t _p +2Z/υ _w +θ _s ) (4') as shown in Figure 3c, which is equivalent to (4) above. ) is the same as the formula, so the "width" mode used in the conventional example can be obtained.

Contrary to the above explanation, if the applied pulse duration time t _d is shortened so that t _d <2Z/υ _w , the reflected signal from the sample is V _c in equation (2), and in the conventional amplitude mode be.
By adding the end face corresponding to the reflected wave V _B from the lens shown in equation (5) to this, a sum signal shown in equation (7) is obtained, and an "interference" mode is obtained.

In either case, the same gate signal can be used, as is clear from FIG.

As described above, in the present invention, a signal reflected from the lens surface or a signal equivalent thereto, that is, a signal having the same period and waveform as the applied pulse, is generated electrically or acoustically, and this is added and subtracted from the reflected wave from the sample. By doing so, both the "width" and "interference" modes are realized.

[Embodiments of the invention]

Embodiments of the present invention will be described using the drawings.

FIG. 4 is a diagram showing a first embodiment of the present invention.

An RF continuous wave electrical signal (for example, 1 GHz) generated by an oscillator 100 is converted into an RF pulsed electrical signal of duration t _d via an analog switch 105 .
The ON/OFF control of the analog switch 105 and the setting of the repetition period are performed by a pulse oscillator 210 which also supplies a time gate gate signal. Here, the duration time t _d is set so that t _d >2Z/υ _w . This RF pulse signal is divided into two systems by a power divider 110, one of which is applied to a sensor system consisting of a lens 125 and a sample 126 via a directional coupler 120. At this time, the reflected ultrasonic signal obtained from the sensor is
As shown in Figure a, the reflected echo C from the sample and the lens echo B are obtained in a superimposed manner, and the directional coupler 1
After being amplified by the receiving amplifier 150 via the RF signal 20, the signal is input to the RF subtracter 160. Another system of RF pulse electrical signals is passed through an RF delay device 130, a variable gain RF amplifier 140, and an analog switch 135.
It is input to the RF subtractor 160 (FIG. 5b). In this embodiment, a signal equivalent to a lens echo is electrically generated by an RF delay device 130 and a variable gain amplifier 140, and the delay amount is set to t _p and the gain is set to Q. Of course, it is also necessary to adjust the influence of the delay and gain of the analog switch 135 and the like.
In this way, when the analog switch 135 is ON, the subtracter 160 uses these two types of RF signals.
The output is as shown in FIG. 5c, and only the reflected signal C from the sample can be extracted with the gate signal (FIG. 5d) and provided as an image in the "width" mode. Also, when the analog switch 135 is OFF, the output of the RF subtracter 160 is as shown in FIG. 5a, so
At this time, the part extracted by the gate signal is in "interference" mode. In either case, in this configuration, the output of the RF subtracter 160 is converted into a video band by the diode detector 170 and then introduced into the time gate circuit 200 via the analog multiplexer 180 to provide a video signal.

As described above, in this embodiment, the duration time of the RF pulse is completely different from that in the conventional example, and is made long until the reflected signals B and C overlap. You can switch between "width" and "interference" modes.

Furthermore, in this embodiment, as in the conventional example, if the duration of the RF pulse is shortened until the reflected signals B and C do not overlap, or by providing a matching layer on the lens surface, the reflected wave from the lens surface can be obtained. If this is not possible, the amount of delay caused by the RF delay device 130 may be set to t _p +t _s , and the RF subtracter 160 may be used as an RF adder.

FIG. 6 is a diagram showing a second embodiment of the present invention, and unlike the previous embodiment, this is an example in which subtraction of lens echoes is created acoustically. That is, the RF continuous wave electrical signal generated by the oscillator 300 is transmitted to the analog switch 30.
5 into an RF pulsed electrical signal of duration _td . The pulse oscillator 41 controls the ON/OFF of the analog switch 305, controls the repetition frequency and duration, and provides the time gate signal.
done by 0. Of course, here the duration t _d
is made long so that t _d > 2Z/υ _w . This RF pulse electric signal is divided into two systems by a power divider 310,
One of them is connected to the lens 3 via a directional coupler 320.
25 and a sample 326. At this time, the reflected ultrasonic signal obtained from the sensor via the directional coupler 320 is obtained in the form of a superimposed reflection echo C from the sample and lens echo B, as shown in FIG. 7a. Further, one other system is applied to another sensor system 323 via a directional coupler 321. This sensor has no concave hole on the other end surface and its lens axis length L' is approximately equal to the lens 325, and the reflected ultrasonic signal obtained through the directional coupler 321 is 2L'/υ as shown in FIG. 7b. The result is multiple echoes B', B'', ... with a period of _L. In this embodiment, the first lens echo B' is RF-delayed so that its amplitude and phase difference match the lens echo B of the sensor 327. amplifier 330, and RF variable gain amplifier 3
40, and then subtracted from each other in an RF subtracter 360, to obtain the reflected echo from the sample as the output of the RF subtracter, as shown in FIG. 7c. In this embodiment, the other configurations are the same as in the previous embodiment except that acoustically created lens echoes are used. That is, 350 is an RF amplifier, 34
5 analog switch, 360 RF subtracter, 37
0 diode detector, 400 a time gate circuit, and 390 an RF multiplier 390. Thus,
In this configuration, the analog switch 345
"Width" and "Interference" modes can be obtained by turning ON/OFF.

Although separate sensors are used in this embodiment, as shown in FIG.
10 and 520 may be provided, and one may be provided with a concave lens 530 and the other may be provided with a polishing plane 540 at locations facing each other to form an integral structure.

FIG. 9 shows another embodiment of the sensor section, showing a cross-sectional view a and a perspective view b of the lens system. The lens body 610 has a cylindrical shape, one end of which is optically polished, and a lower electrode 710.
(Au, Ti, etc.) is provided, and a piezoelectric thin film 6 is provided on it.
80 is sputter deposited. On top of this, an inner electrode 700 and an outer electrode 690 are provided in a concentric column. The other end has a concave hole 620 in the center, and an outer circle 630 is optically polished. A beam of 650 beams is focused on the sample 600 by the action of an ultrasonic lens 620 generated from a piezoelectric thin film sandwiched between an inner electrode 700 and a lower electrode 710. In addition, the outer electrode 690
Ultrasonic waves generated from the piezoelectric thin film sandwiched between the lower electrode 710 and the lower electrode 710 cause multiple reflections by the opposing inner surface 640. That is, the functions of the embodiments described above are realized by an integrated concentric lens configuration.

Also in the embodiments shown in FIGS. 6 to 9 above, when the duration of the RF pulse is shortened,
Alternatively, when a reflected wave from the lens surface is obtained, the RF subtracter 360 is used as an RF adder to calculate the sum of both signals, as described in the embodiment of FIG.

〔Effect of the invention〕

As described above, according to the present invention, by electrically or acoustically creating a signal equivalent to a lens echo, and adding and subtracting it with the reflected signal from the sample, "width",
Video information for each mode of "interference" can be easily obtained.

[Brief explanation of drawings]

Figure 1 is a diagram showing the configuration of a conventional probe system, Figure 2 is a diagram explaining a method of detecting an image, and Figure 3 is a diagram showing the configuration of a conventional probe system.
The figures are for explaining the principle of the present invention, FIG. 4 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 5 is a diagram for explaining the principle of the present invention.
FIG. 6 is a diagram showing the configuration of another embodiment of the present invention, FIG. 7 is a diagram explaining the operation, and FIGS. 8 and 9 are diagrams for explaining the operation. It is a figure which shows the structure of another Example of the principal part of this invention.

Claims (1)

[Claims] 1. A means for generating a focused ultrasonic beam using ultrasonic waves emitted from a piezoelectric thin film, and detecting reflected waves of the beam reflected from a sample by the piezoelectric thin film, and a means for two-dimensionally converting the sample into a focal region of the beam. a means for electrically or acoustically generating a signal equivalent to the signal obtained from the ultrasonic beam; a means for adding/subtracting this signal and the detection signal; An ultrasonic microscope characterized by comprising means for controlling addition and subtraction, and a gate circuit for extracting the detection signal or the added and subtracted signal within a required range.