JPH0457975B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an ultrasound microscope.

Various types of ultrasonic microscopes have been proposed in the past, including one having the configuration shown in FIG. 1, for example. In this ultrasound microscope, a high frequency pulse generator 1
An ultra-high frequency burst wave electrical signal is generated,
This electric signal is supplied to a piezoelectric transducer 3 via a circulator 2, where the electric signal is converted into an ultrasonic wave. 5, the beam is projected as a minute spot onto a sample 8 placed on a sample stage 7 that moves two-dimensionally in the X-axis and Y-axis directions by a scan control device 6. Further, ultrasonic waves are reflected from the sample 8 according to its acoustic characteristics, and the reflected waves are collected by the acoustic lens 4 through the liquid 5 and transmitted to the piezoelectric transducer 3.
is converted into an electrical signal by This electrical signal is supplied to the gate circuit 9 via the circulator 2, where unnecessary signals other than sample information are removed. The output signal of the gate circuit 9 is amplified and detected by the amplification/detection circuit 10 to obtain a detection signal corresponding to the intensity of the reflected wave from the sample, and this detection signal is synchronized with the scanning of the sample stage 7 by the scan control device 6. The brightness signal at the corresponding position on the sample surface is recorded in the scan converter 11, and the recorded brightness signal is displayed on the cathode ray tube 12 as an ultrasonic image.
Note that the high frequency pulse generator 1, the scan control device 6,
The operations of gate circuit 9 and scan converter 11 are controlled by control circuit 13.

In the ultrasonic microscope described above, the ultrasonic waves emitted from the piezoelectric transducer 3 to the acoustic lens 4 undergo multiple reflections between the concave lens portion of the acoustic lens 4 and the piezoelectric transducer 3, and The reflected waves are each converted into electrical signals by the piezoelectric transducer 3 and supplied to the gate circuit 9 via the circulator 2.

FIG. 2A shows the distribution of signals input to the gate circuit 9 when the high-frequency pulse generator 1 generates an ultra-high frequency burst wave electrical signal for a short period of time under the control of the control circuit 13. Something,
P ₀ represents the leakage signal that reaches the gate circuit 9 directly from the high-frequency pulse generator 1 through the circulator 2, and P ₁ , P ₂ and P ₃ represent the leakage signal between the piezoelectric transducer 3 and the lens part of the acoustic lens 4. represents the first, second and third reflected wave signals at . Therefore, in this type of ultrasound microscope, the acoustic lens 4 is arranged such that the sample reflected wave signal S is located between the first reflected wave signal _P1 and the second reflected wave signal _P2 .
is designed, and a second
A gate control signal as shown in FIG. 2B is supplied to extract only the sample reflected wave signal S as shown in FIG. 2C.

Now, focusing on the output signal of the gate circuit 9 (Fig. 2C), when the focal point of the acoustic lens is sent into the sample, the reflected wave from the sample consists of the reflected wave from the surface and the reflected wave from inside. It's on,
Generally, as shown in FIG. 3, the reflected wave S ₁ from the sample surface is stronger than the reflected wave S ₂ from inside, and the amplification/detection circuit 10 amplifies the output signal of the gate circuit 9.
Since the envelope is detected and its peak is detected, the image displayed on the cathode ray tube is an ultrasonic image from the surface of the sample. In other words, conventional ultrasound microscopes can only display images of the sample surface where ultrasound is most strongly reflected or the internal position where ultrasound is most strongly reflected, regardless of the reflected ultrasound intensity. It was not possible to selectively display an image at any arbitrary position on or inside the sample.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic microscope capable of selectively displaying images of arbitrary positions on and inside a sample.

The ultrasound microscope of the present invention changes the relative position between the focus of the acoustic lens and the sample in the direction of ultrasound generation,
means for moving the focal point of the acoustic lens to a desired position on the surface of the sample or inside the sample; means for envelope detection of an electrical signal corresponding to the ultrasonic wave reflected from the sample; and the envelope detection. The present invention is characterized by comprising means for automatically extracting only a portion corresponding to the sample information at the position where the focus of the acoustic lens is located from the output signal of the means.

The invention will be explained below with reference to the drawings.

FIG. 4 shows an example of the ultrasonic microscope of the present invention. In FIG. 4, elements corresponding to those in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

According to the present invention, a mechanism (not shown) is provided for driving the acoustic lens 4 in the direction in which ultrasonic waves are emitted from the acoustic lens, and this driving mechanism causes the focal point of the acoustic lens 4 to be located on the surface of the sample. This acoustic lens is moved so that the focal point is at a desired position inside the sample based on the position of the acoustic lens, this moving distance is detected by the sensor device 21, and this sensor device outputs an output at a time related to this moving distance. Generate a pulse.

As mentioned above, the signal generated from the gate circuit 9 is as shown in FIG. 3, and in the present invention, this signal is amplified and envelope-detected in the amplification/detection circuit 10'. The output waveform of this circuit 10' is shown in FIG. 5A. According to the present invention, the sample internal reflection wave S ₂ of the output signal of this circuit 10' is sampled and held in the sample and hold circuit 22 by the output pulse of the sensor device 21 (FIG. 5B),
This sampled and held value (FIG. 5C) is recorded in the scan converter 11 as a luminance signal at a desired position within the sample, and this signal is displayed on the cathode ray tube 12 as described above.

The signal generated from the amplification/detection circuit 10' (FIG. 5A) is converted into an output pulse of the sensor device 21 (FIG. 5B).
A method of configuring the sensor device 21 so that the value obtained by sampling corresponds to information on a desired position (focal position) within the sample will be described below.

In FIG. 6A, the focus of the acoustic lens 4 is located on the surface of the sample, and the ultrasonic waves generated from the piezoelectric transducer 3 pass through the ultrasonic acoustic lens 4 and the ultrasonic transmission medium 5, and are reflected on the surface of the sample 8. A case is shown in which the signal is transmitted through the ultrasonic transmission medium 5 and the acoustic lens 4 again and converted into an electric signal by the piezoelectric transducer 3. Here, l is the length of the acoustic lens, f is the focal length of the acoustic lens, c ₁ is the speed of sound within the acoustic lens, and c ₂
indicates the speed of sound within the ultrasound transmission medium. in this case,
The waveform of the signal supplied from the amplification/detection circuit 10' to the sample/hold circuit 22 is shown by a broken line in FIG. 6C. In this FIG. 6C, S ₁ ' is information on the sample surface, and S _t is a start pulse generated from the control circuit 13. This start pulse causes the high frequency generator 1 to generate a high frequency signal and performs calculation in the sensor device 21. Starts processing (described later). Time t ₁ from the moment the high frequency generator 1 generates the signal until the sample surface information reaches the sample and hold circuit 22 (Figure 6C)
can be regarded as the time from when the ultrasonic wave is generated from the piezoelectric transducer 3 until it enters the piezoelectric transducer 3 again, since the transmission time of the electric signal in the electric circuit can be ignored. Therefore, the following equation is satisfied.

t ₁ = 2l/c ₁ + 2f/c ₂ ...(1) According to the present invention, in order to obtain information inside the sample,
The acoustic lens 4 is moved by a distance h so that the focal point of the acoustic lens 4 reaches a desired position X inside the sample as shown in FIG. 6B. In this case, the waveform of the signal supplied to the sample and hold circuit 22 is
Figure C shows the solid line waveform. In this Figure 6C,
S ₁ is the information on the sample surface, and S ₂ is the information on the point X inside the sample.
This is the information. Therefore, the time t ₂ is equal to the time it takes for the ultrasound to pass through the ultrasound transmission medium 5 by a distance of 2h, and the formula t ₂ =2h/c ₂ (2) is satisfied. Also, in FIG. 6B, from the time when the information on the surface of the sample 8 reaches the sample/hold circuit 22, the information on the point
The time until reaching the hold circuit 22, that is, the time t ₃ between the information S ₁ and S ₂ in FIG. 6C
is equal to the time from when the ultrasonic wave is incident on the surface of the sample to when it is reflected at point X and emitted from this surface, and when the sound speed inside the sample is _c3 , the following equation holds true.

t ₃ = 2h/c ₃ …(3) From the moment the start pulse S _t occurs to point X in the sample
As is clear from FIG. 6C, the time T until the information S ₂ reaches the sample-and-hold circuit 22 is T = t ₁ - _{t 2} + t ₃ ...(4), and this equation (4) is replaced by the equation ( By substituting 1), (2) and (3), the following equation (5) is obtained.

T=2(l/c ₁ +f-h/c ₂ +h/c ₃ )...(5) Since c ₁ , c ₂ , c ₃ , l and f in this equation (5) can be set in advance, the sensor device If the moving distance h of the acoustic lens 4 is measured by a known method using 21, the calculation of equation (5) can be easily achieved in this sensor device 21, and in this time T, as shown in FIG. All you have to do is generate a sampling pulse.

As is clear from the above, according to the present invention, by adjusting the focal position of the acoustic lens 4 to a desired position within or on the sample, sample information at this desired position can be automatically displayed on the cathode ray tube. Can be done.

It goes without saying that the present invention is not limited to the above-mentioned example, and can be modified in many ways. For example, instead of moving the acoustic lens, the sample stage 7 can be moved in the same direction. Alternatively, the sensor device 21 may not detect the amount of movement of the acoustic lens, but instead may apply a desired amount of movement to the device 21 from the outside, so that the device 21 automatically performs only the arithmetic processing described above.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing a conventional ultrasound microscope, Figure 2 is a waveform diagram to explain the operation of Figure 1, and Figure 3 is a waveform diagram to explain the operation of Figure 1.
The figures are a waveform diagram showing the waveform in Figure 2C in detail, Figure 4 is an explanatory diagram showing an example of the ultrasonic microscope of the present invention, and Figure 5 is a waveform diagram showing the waveform of Figure 2C in detail.
The figure is a waveform diagram for explaining the operation of FIG. 4, and FIG. 6 is a diagram for explaining the principle of the present invention. 1... High frequency pulse generator, 2... Circulator, 3... Piezoelectric transducer, 4... Acoustic lens, 5... Liquid (ultrasonic transmission medium), 6...
Scanning control device, 7...sample stage, 8...sample, 9...
...Gate circuit, 10,10'...Amplification/detection circuit,
11...Scan converter, 12...Cathode ray tube, 13...Control circuit, 21...Sensor device, 2
2...Sample/hold circuit.

Claims (1)

[Scope of Claims] 1. means for changing the relative position between the focal point of the acoustic lens and the sample in the ultrasonic generation direction, and moving the focal point of the acoustic lens to a desired position on the surface of the sample or inside the sample; detection means for envelope-detecting an electric signal corresponding to an ultrasound reflected from a sample; a calculation means for generating a signal synchronized with the ultrasonic reflection time; and a calculation means for sample-holding the output signal of the detection means in synchronization with the output signal of the calculation means, and detecting a signal on the surface or inside of the sample where the focal point of the acoustic lens is located. An ultrasound microscope characterized by comprising: sample holding means for extracting only ultrasound images at arbitrary positions;