JPH0412824B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an ultrasonic microscope, and particularly to an ultrasonic microscope that is suitable for observation using ultrasonic waves having a wide range of frequencies.

[Background of the invention]

Regarding ultrasonic microscopes, various configurations are being developed as described in Japanese Patent Application Laid-Open No. 116058/1983. The configuration of these conventional ultrasonic microscopes will be explained with reference to FIG. In the figure, 1 is made of cylindrical fused silica or the like, optically polished on one side,
This is an acoustic lens having a hemispherical hole lens surface 15 formed on the other surface. 2 is a piezoelectric thin film (ZnO, etc.) attached to the optically polished surface of the acoustic lens 1, and the acoustic lens 1 is sandwiched between the upper and lower electrodes 3.
installed on. The acoustic lens 1, piezoelectric thin film 2, and upper and lower electrodes 3 are collectively referred to as a sensor 16. Reference numeral 4 denotes a pulse oscillator that emits necessary continuous wave pulses 5 to the upper and lower electrodes 3. When a pulse 5 oscillated by the pulse oscillator 4 is applied to the upper and lower electrodes 3, the piezoelectric thin film 2 is excited and an ultrasonic wave 6 is generated.
occurs. 7 is the lens surface 1 of the acoustic lens 1
A sample placed on the sample stage 14 facing the 5 side, 8
is a medium (for example, water) that fills the gap between the acoustic lens 1 and the sample 7. The ultrasonic wave 6 generated by the piezoelectric thin film 2 propagates within the acoustic lens 1 as a plane wave. When the plane wave of the ultrasonic wave 6 reaches the lens surface 15, a refraction effect occurs due to the difference in the propagation speed of sound between the material of the acoustic lens 1 and the medium 8, and the plane wave of the ultrasonic wave 6 is focused onto the surface of the sample 7. irradiated. The ultrasonic waves 6 irradiated to the sample 7 in this way are reflected within the sample 7 and transmitted to the medium 8, and the lens surface 15
The sound is collected and phased in the plane wave, which reaches the piezoelectric thin film 2 and is converted into an RF signal (high frequency electric signal) 9 by the piezoelectric thin film 2. 10 receives the RF signal 9 and performs diode detection to output the video signal 1.
1, a receiver 21 converts the video signal 11 into
This echo processing section performs amplification, level adjustment, and A/D conversion on the signal and outputs the result to the digital image memory 23. Reference numeral 13 denotes a drive device that scans the sample stage 14 that supports the sample 7, and the drive device 13 is configured to digitize the scanning position information when scanning the sample stage 14 and output it to the digital image memory 23. ing. and,
In the digital image memory 23, the video signal from the echo processing section 21 and the driving device 1 are processed.
Image information is formed and stored in synchronization with the scanning position information from 3. Then, the image information in the digital image memory 23 is transferred to a CRT (cathode ray tube) 12.
Display and observe. Note that 22 is an echo display section that displays the degree to which the video signal 11 is amplified and level-adjusted by the echo processing section 21, and the displayed state is used as a guide for observation.
On the other hand, as mentioned above, when the ultrasonic waves 6 generated in the piezoelectric thin film 2 propagate through the acoustic lens 1 and reach the lens surface 15, some of them are irradiated onto the sample 7, and some of them are irradiated onto the acoustic lens 1 and the medium 8. It is reflected due to the difference in acoustic impedance between the If the medium 8 is not filled between the acoustic lens and the sample, the difference in acoustic impedance between the acoustic lens 1 and the air will be extremely large.
The ultrasonic waves are totally reflected by the lens surface 15.

In an ultrasound microscope configured as described above,
The sensor 1 uses various different frequency ranges depending on the material of the sample, etc., and corresponds to each frequency range.
6, more effective observation can be made. When performing observation using various sensors 16, it is necessary to find the optimum frequency in the corresponding frequency range of the sensor 16, that is, the frequency with the best propagation efficiency of ultrasonic waves. Conventionally, the frequency selection operation in each sensor 16 is performed without filling the lens surface 15 of the acoustic lens 1 with the medium 8, and while manually converting the frequency, the frequency selection operation in the hemispherical hole 15 is
The operator judges the intensity of the reflected echo totally reflected by the echo display section 22 and selects the optimum frequency. This operation is very complicated and takes a lot of time, as it is necessary to change the frequency as described above and judge the maximum reflected echo by looking at the echo display section 22 for each frequency. . Furthermore, this process has to be performed every time the sensor 16 is replaced, which also poses a problem.

[Purpose of the invention]

An object of the present invention is to provide an ultrasonic microscope that has a function of automatically selecting the optimum frequency for each sensor when performing observations using different sensors in various frequency ranges.

[Summary of the invention]

The frequency range of ultrasonic waves used in ultrasound microscopes is wide from 50 MHz to 1 GHz and even 2 GHz, depending on the azimuth resolution, depth resolution, etc., and the frequency range is selected as appropriate depending on the target sample and the observation position of the sample. are doing. In conjunction with the selection of the frequency range, the optimal sensor is also used. In determining the frequency range and sensor in this way, there is a frequency most suitable for each sensor, that is, a frequency with the best propagation efficiency. The present invention selects the optimal frequency for each sensor by changing the oscillation frequency stepwise, and then sequentially comparing and determining the intensity of the total reflection echo in the hemispherical hole of the spherical lens to determine the maximum value of the reflection echo. It is characterized by the fact that it is carried out by determining the

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In the figure, the same reference numerals as in the conventional example indicate the same members. 24 is a lens echo determination unit connected to the oscillator 4 and the echo processing unit 21, which outputs a command to the oscillator 4 to change the frequency of the pulse 5 oscillated by the oscillator 4 in steps, and also changes the frequency mentioned above in steps. The intensity of the total reflection echo from the lens surface 15 at each stage of change is sequentially compared and judged to determine the maximum value, and the frequency at which the reflected echo reaches the maximum value is set in the oscillator 4. Note that when the optimum frequency is selected in the lens echo determination section 24, the determination is made using the total reflection echo at the lens surface 15, so the lens surface 15 is not filled with the medium 8. By the way, when the lens echo determination section 24 performs the above-mentioned determination, the reflected echo received by the piezoelectric thin film 2 includes an oscillation signal, a reflected echo reflected by the lens surface 15, an electrical reflected signal, and a multiplexed signal within the acoustic lens 1. Contains multiple reflected echoes. Among these, what is necessary for the above judgment is the lens surface 15.
Only the reflected echo reflected by the beam is unnecessary, and the following operations are performed to obtain this reflected echo. That is, since the electrical reflected signal arrives much faster than the reflected echo from the lens surface 15, it is sufficient to slightly delay the gate opening time. Therefore, the time period during which the output from the piezoelectric thin film 2 is acquired by the lens echo determination section 24 is determined by the elapsed time from the oscillation of the pulse 5 from the oscillator 4 until it is reflected by the lens surface 15 of the various sensors 16. The maximum value of the echo intensity is determined by capturing reflected echoes during this time period. Note that when reflected echoes are captured during the above time period, the multiple reflected echoes may also be captured in some cases, but since the multiple reflected echoes have a sufficiently small value, they do not affect the determination of echo intensity.

As described above, each time the sensor 16 is replaced, the lens echo determination section 24 outputs an oscillation frequency conversion command to the oscillator 4 at predetermined intervals, and captures the reflected echo from the lens surface 15 at each frequency. , the values are sequentially determined to find the frequency at which the reflected echo is at its maximum value, and this frequency is set in the oscillator 4 to complete the frequency selection operation. At this point, the sample 7 is set on the sample stage 14, the medium 8 is filled between the sample 7 and the acoustic lens 1, and observation is performed.

By the way, in the lens echo determination section 24,
The maximum value of the reflected echo from the lens surface 15 of each sensor 16 is determined, but the reflected echo must have a value greater than the required value for that sensor 16. The intensity of the reflected echo may also be determined. By determining the intensity of this reflected echo,
The sample 7 can be observed while constantly making pass/fail judgments for each sensor.

With this configuration, when observing various samples in a wide frequency range of 5MHz to 2GHz,
By setting the sensor 16 according to the selected frequency range, the optimal frequency for the sensor 16 can be automatically selected, eliminating the need for complicated frequency selection operations. Therefore, observation work can be performed quickly and efficiently.

In the above embodiments, a reflective type was described, but similar effects can be obtained with a transmissive type.

〔Effect of the invention〕

As explained above, according to the present invention, when the frequency range is changed in a wide frequency range depending on the material of the observation sample or the observation depth, etc., and when observation is performed using a sensor corresponding to the frequency range, Frequency selection can be done easily and accurately.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an ultrasound microscope according to the present invention, and FIG. 2 is a block diagram showing a conventional ultrasound microscope. DESCRIPTION OF SYMBOLS 1... Acoustic lens, 2... Piezoelectric thin film, 4... Oscillator, 10... Receiver, 16... Sensor, 21...
...Echo processing section, 22...Echo display section, 23...
...Digital image memory, 24...Lens echo determination section.

Claims (1)

[Claims] 1 An oscillator that oscillates pulses, an acoustic lens that irradiates the sample with the ultrasonic wave, which has an oscillator that oscillates pulses, a piezoelectric thin film that generates ultrasonic waves using the pulses from the oscillator, and an ultrasonic wave that is irradiated from the acoustic lens and is transmitted by the sample. an acoustic lens having a piezoelectric thin film that receives and phases the disturbed sound waves; a sample stage that supports the sample; a drive device that scans the sample stage and outputs scanning information; and the acoustic lens. a receiver for converting sound waves received by the receiver into a video signal; a digital image memory for storing image information by synchronizing the video signal from the receiver with the scanning information; and a digital image memory for displaying the image information in the digital image memory. In an ultrasonic microscope consisting of a display device for observation, the frequency of the oscillation pulses of the oscillator is changed stepwise and oscillated sequentially, and the ultrasonic waves generated in the piezoelectric thin film by each pulse are transmitted to the lens of the acoustic lens. An ultrasonic microscope characterized by being provided with a lens echo determination unit that sequentially captures reflected echoes reflected from a surface, sequentially compares the intensities of the captured reflected echoes, and determines a frequency at which the intensity of the echoes reaches a maximum value.