JPH0390857A - Ultrasonic microscope - Google Patents

Abstract

PURPOSE:To improve the azimuth resolution and depth resolution and to obtain an image with high resolution by providing a high-frequency band correcting means which increases in gain as the frequency characteristics of electric signal amplification increase. CONSTITUTION:A waveform generating circuit 20 generates a bias voltage, which is applied to a variable high frequency band correcting circuit 10. Consequently, the high frequency band of a reflected wave which is reflected at a deeper position in a sample 104 and received a longer delay time later is amplified large and the attenuation of the spectrum intensity in the high frequency band can be corrected. Therefore, the azimuth resolution of an internal image of the sample 104 can be improved and the depth resolution when a three- dimensional image is formed can be improved, so that the image with extremely high resolution is obtained. Further, data after the attenuation in the sample is corrected can be obtained and this data is outputted to an instrument 114 for material property quantitative measurement, which is carried out to enable extremely accurate measuring operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic microscope capable of quantitatively measuring the physical properties of a sample and observing the internal state of the sample.

[Conventional technology]

BACKGROUND ART Ultrasonic microscopes are conventionally known that focus an ultrasonic beam onto a minute spot, relatively scan a sample with the ultrasonic beam, process reflected signals obtained, and observe the internal state of the sample.

FIG. 7 shows an example of the configuration of a conventional ultrasound microscope.

Reference numeral 100 shown in the figure is a control section, which transmits a command signal for generating a transmission signal to the pulse transmission section 101. When the pulse transmitter 101 receives the command signal, it generates a transmit pulse wave. A transmission pulse wave generated from the pulse transmission unit 101 is applied to the piezoelectric transducer 102 and converted from an electrical signal to an ultrasonic wave. This ultrasonic wave is transmitted to the acoustic lens 1 to which the piezoelectric transducer 102 is attached.
03, the beam is focused into a minute spot, and is incident on a sample 104 placed near the focal point. The space between the sample 104 and the acoustic lens 103 is filled with water 105 for transmitting ultrasonic waves. The ultrasonic pulse incident on sample 104
04 reflects and transmits.

Affected by scattering, absorption, etc.

The ultrasonic waves reflected by the sample 104 pass through the acoustic lens 103 again.
and is converted into an electrical signal by the piezoelectric transducer 102. This electrical signal is amplified by a preamplifier 1.06. The amplified signal is input to a gate circuit 107 which is turned on and off by the $11 unit 100. Preamplifier 1
The signal output from the sample 106 includes unnecessary signals such as a directly transmitted pulse wave and an internally reflected wave from the acoustic lens 103,
Includes reflected waves from the front, inside, and back surfaces of 04.

Therefore, the gate circuit 107 is turned on.

By turning off, only necessary signals such as sample reflected waves are extracted and output to the detection section 108. The detection unit 108 detects the signal extracted by the gate circuit 107 and detects the signal strength. This detection signal is transmitted to the A/D converter 10
9, is sampled at extremely short intervals according to a control signal from a control unit 100, is converted into a digital signal, and is stored in an image memory 110.

The information obtained by the above operation is information in two directions at one point on the XY plane when the direction of incidence of the ultrasonic pulse is the Z axis. Therefore, by XY constant scanning 111, sample 1
04 and the acoustic lens 103 relative to each other, information in two directions at each point on the XY plane of the sample 104 is stored in the image memory 110. Image memory 110
After reading the information stored in the computer 112 and performing various image processing, it is returned to the image memory 110 again.
Further, by displaying the information on the display unit 113, it is possible to observe, for example, the situation inside the sample.

[Problem to be solved by the invention]

The ultrasonic microscope as described above captures the intensity (so-called spectrum) of the reflected wave reflected from the sample 104 as information. The signal reflected from the sample 104 and converted by the transducer 102 has a "frequency -
spectral characteristics. If the curve A shown in the same figure is the reflected wave from the sample surface, then the reflected wave from inside the sample is a curve in which the spectral intensity in the high frequency band attenuates more as the depth of the sample increases. It will look like B. In song 11A, the spectral intensity of the transmitted pulse wave generated from the pulse transmitter 101 is attenuated due to absorption due to differences in the frequency characteristics of the piezoelectric transducer 102 and the frequency characteristics of the water that serves as the coupler liquid, and reflection on the surface of the sample F4104. characteristics, the frequency characteristics of the acoustic lens, and even the transmission characteristics of electrical signals. Further, the curve B has a characteristic that is affected by attenuation R due to the absorption of ultrasonic waves inside the sample 104 in addition to the influence of each of the above-mentioned characteristics. Here, the sound intensity I is generally expressed as ■sting a e −a
It can be expressed as 4. Note that α is the amplitude absorption coefficient of a unit length in a certain substance, d is the propagation distance, and a is a constant. Also, the amplitude absorption coefficient α is affected by the frequency f, αoo
It shows the characteristics of f, αoo f2, etc. In other words, the absorption coefficient α increases as the frequency increases, and sample 1
The sound intensity I at a certain depth d at 04 also becomes smaller. Also,
The longer the propagation distance Md is (the deeper the position within the sample), the greater the attenuation. Therefore, the eighth
As shown in the figure, the reflected wave from the inside of the sample or from the back surface has a spectral value that becomes smaller as the frequency increases, as shown by curve B, in a high frequency band of, for example, several MHz to several hundred MHz.

Since the conventional ultrasonic microscope has the above-mentioned characteristics, when obtaining an internal image of the sample 104,
The spectrum value of the high frequency band differs depending on the depth position of the acoustic lens 103, and the center of the peak of the spectrum moves to the low frequency region as the depth increases.
There is a problem in that the frequency band in which the device operates is a low frequency band, and the azimuth resolution of the sample 104 in the X and Y directions deteriorates.

Furthermore, as shown in FIGS. 9(a) and 9(b), the time width Δti of the pulse wave portion of the reflected wave <b> from inside the sample is equal to the time width Δti of the pulse wave portion of the reflected wave (a) from the sample surface. Width Δts
It will be longer than As shown in Figure 8, this is because the sample 1
The spectrum of the reflected wave from inside sample 104 has a lower center frequency and a narrower frequency band. Therefore, as the reflection position inside sample 104 becomes deeper and the time width of the pulse portion of the reflected wave becomes longer, Since the reflected waves from different depth positions overlap, there is a problem that the depth resolution in the depth direction of the sample 104 deteriorates.

The present invention has been made in view of these circumstances, and provides an ultrasonic microscope that can improve lateral resolution and depth resolution, obtain high-resolution images, and accurately measure quantitative physical properties of a sample. The purpose is to provide

[Means to solve the problem]

In order to solve the above problems, the present invention injects a focused ultrasonic pulse into a sample, receives a repulsive wave from the sample, converts it into an electrical signal, and processes this electrical signal to convert it into desired data. In the ultrasonic microscope, the electric signal is amplified, and the frequency characteristic of the amplification is such that the higher the gain becomes from the middle to the high range, the higher the gain becomes. The structure includes means for synchronizing the gain in the region with the reflected wave from the sample and increasing it as the time passes.

[Effect]

By taking the above-mentioned measures, the present invention can reduce the spectral intensity of the reflected wave from inside the sample by using the high-frequency band correction means, whereas the deeper the sample is, the higher the attenuation in the high-frequency band. Since the gain from the middle range to the high range is amplified more as the range gets higher, attenuation in the high frequency band can be effectively corrected. Moreover, the reflected waves that are reflected from a deeper position in the sample and received with a time delay are amplified with a larger gain from the mid-range to the high-frequency range, effectively compensating for the attenuation in the high-frequency range. It's a big thing.

〔Example〕

Examples of the present invention will be described below.

FIG. 1 is a diagram showing the configuration of an ultrasound microscope according to a first embodiment of the present invention. Note that the same parts as those in the ultrasonic microscope shown in FIG. 7 are given the same reference numerals.

In this embodiment, a gate circuit 1 of an ultrasonic microscope shown in FIG.
07 and the detection unit 108, a variable high frequency band correction circuit 10 is provided that corrects the gain of the high frequency band of the human signal by changing the bias voltage applied from the outside. The configuration is such that the voltage generated by the circuit 11 is supplied as a bias voltage.

The variable high frequency band correction circuit 10 includes a wide band operational amplifier 11 that amplifies the output of the gate circuit 107 and this operational amplifier 1.
Variable capacitance element 12 constituting the feedback circuit of 1. Capacitor 13. It consists of resistors R1 to R3, and the output of the waveform generation circuit 20 is supplied between the variable capacitance element 12 and the capacitor 13. The waveform generation circuit 20 includes the variable high frequency band correction circuit 1
Waveform data ROM2 that stores waveform data (data related to gain correction) indicating changes in the bias voltage supplied to
1 and the waveform data stored in this ROM21 as D.
A D/A converter 22 that performs /A conversion, and this D/A converter 2
2. The σ-bus filter 23 smoothes the output waveform of the second output waveform.

Data for making the output waveform of the waveform generating circuit 20 into a desired waveform is preset and stored in each address of the waveform data ROM 21.

Here, the gain G of the variable high frequency band correction circuit 10 can be expressed as follows, where C is the combined capacitance of the capacitor 13 and the variable capacitance element 12. Note that it is ω-2πX (frequency).

As shown in FIG. 2, the frequency characteristic regarding the gain G of this variable high frequency band correction circuit 10 is, for example, 100 MHz.
The gain peaks in the front and rear high frequencies, and the high frequency characteristics change as the composite capacitance C changes. Variable capacity jiX:
The capacitance of the element 12 becomes smaller as the bias voltage applied from the waveform generating circuit 20 becomes larger, and the combined capacitance C also becomes smaller accordingly. Therefore, in the frequency characteristics of the variable high frequency band correction circuit 10, the higher the bias voltage is, the higher the peak frequency moves to a higher range, and the lower the gain from the middle range to the higher range.

Next, the operation of this embodiment will be explained.

The operation up to the point where the reflected wave from the sample 104 is extracted by the gate circuit 107 is similar to that of the ultrasonic microscope described in the [Prior Art] section.

On the other hand, the control section 1 outputs a read signal and an address designation signal from the ROM 21 to the waveform data ROM 21. FIG. 3(a) shows changes in the LSB of the addressing signal. Addressed by the addressing signal, the waveform data R
The data read from OM21 is transferred to D/A converter 22.
It is converted into an analog signal and passed through a low-pass filter 23.
After smoothing the waveform, the variable high frequency band correction circuit 10
is output as a bias voltage. In addition, the waveform data R
The data stored in the OM 21 is set so that the output of the D/A converter 22 has the waveform shown in FIG. 3(b). That is, in the variable high frequency band correction circuit 0, the bias voltage changes from a large positive voltage to a small positive voltage as time passes.

Then, the control unit 1 outputs an address signal immediately before the reflected wave from the surface of the sample 104 enters the gate circuit 107, and operates in synchronization with the timing at which the reflected wave from the sample 104 is received. Therefore, in the variable high frequency band correction circuit 10 to which the bias voltage shown in FIG. 3(b) is applied, the peak frequency is in the high range at the start of operation, and the gain is small in the middle to high ranges. Then, as time passes, the gain in the middle to high range increases, and just before the end of the operation, the gain in the middle to high range becomes the largest.

As a result, a reflected wave reflected from a deeper position of the sample 104 and extracted later in time has a spectral value in a high frequency band amplified to a greater extent than a reflected wave from a shallower position of the sample 104.

Therefore, the attenuation of the spectral value in the high frequency band of the reflected wave from a deeper position of the sample 104 is corrected.

The signal whose attenuation in the high frequency band has been corrected in this way is detected by the detection circuit 108, and after being A/D converted by the A/D converter 109 at the timing specified by the control unit 1,
The image is stored in image memory 110. And image memory 1
The data stored in the computer 10 is read out by the computer 112, subjected to image processing, and displayed on the display section 113.

The information obtained by the above operation is information in the Z direction at one point on the XY plane when the direction of incidence of the ultrasonic pulse is the Z axis. Therefore, by XY constant scanning 111, sample 1
04 and the acoustic lens 103 relative to each other, information in two directions at each point on the XY plane of the sample 104 is stored in the image memory 110, which is read into the computer 112 and subjected to various image processing. After that, by returning the image to the image memory 110 and displaying it on the display unit 113, an accurately restored sample internal image can be displayed.

According to the first embodiment, the waveform generation circuit 20 generates the bias voltage shown in FIG. 3(b), and this bias voltage is applied to the variable high frequency band correction circuit 10. The high frequency band of the reflected wave reflected from a deeper position and received at a later time is amplified to a greater extent, and the attenuation of the spectral intensity in the high frequency band can be corrected. Therefore, the azimuth resolution of the internal image of the sample 104 can be improved, and the depth resolution when a three-dimensional image is also improved, making it possible to obtain an extremely high-resolution image.

Furthermore, since it is possible to obtain data corrected for attenuation within the sample, extremely accurate measurements can be made by outputting this data to the device 114 for quantitative measurement of physical properties of the sample and performing quantitative measurement of physical properties. .

In the above embodiment, the configuration in which the variable high frequency band correction circuit 10 has one stage is shown, but it may be configured in multiple stages, and by such a configuration, the correction characteristic can be made steep. Furthermore, the high frequency characteristics of each of the variable high frequency band correction circuits 10 may be changed. Further, the configuration of the variable high frequency band correction circuit 10 is not limited to that shown in FIG. 1, and other configurations may be used as long as the gain characteristics in the high frequency band change as described above by varying the input voltage. . Further, a greater effect can be obtained by changing the data stored in the waveform data ROM 21 of the waveform generating circuit 20 according to the absorption characteristics of the sample 104 so that the water loss is exactly canceled as a result of correction. In addition,
If the high frequency band is emphasized beyond the level at which flat characteristics can be obtained through cancellation, noise will increase and the S/N ratio will deteriorate, which is undesirable. Further, instead of the waveform generation circuit 20, a sawtooth wave generation circuit of an analog circuit can be used.

FIG. 4 is a diagram showing a second embodiment. In this example, the seventh
Gate circuit 107 and detection unit 10 of the ultrasound microscope shown in the figure
8, there is a switching high frequency band correction circuit (hereinafter referred to as "switching correction circuit") that controls the high frequency characteristics of the input signal frequency by using an external circuit connection switching signal.
40 is provided, and its switching is controlled by a switch control section 50.

The switching correction circuit 40 includes a distributor 41 that divides the output signal of the gate circuit 107 into a large number of parts;
1) Each distributed signal is input (n+1)
bypass filters 43-1 to 43-n provided on the output side of each of the amplifiers 42 except for one, and bypass filters 43-1 provided on the output side of each of the bypass filters 43. It is comprised of switches S1 to Sn which are controlled on and off by a switch control section 50, and an adder 44 to which the outputs of each amplifier 42 are added. Each amplifier 42 is a wideband amplifier. Also,
Bypass filters 43-1 to 43, -〇 is capacitor C
and a resistor R, and each bypass filter 43-1 to 43-4
The frequency characteristics of the signal passing through 3-n are shown in Fig. 5(b) to (
As shown in d), each capacitance and resistance value of the bypass filter 43 are set so that its cut-off frequency gradually becomes a lower frequency.

In the second embodiment configured in this way, the signal extracted from the gate circuit 107 in the same manner as in the first embodiment is distributed by the distributor 41 and inputted to each amplifier 4 as well. Amplifier 4
The signal amplified by amplifier 2-1 is directly input to the adder 44, and the signal amplified by amplifiers 42-2 to 42-(n+1) is
They pass through corresponding bypass filters 43-1 to 43-n and reach switches 81 to Sn. Then, the switch control section 50 selectively connects the switches 81 to Sn to input the signal to the adder 44 .

Here, as the selection order of the switches 81 to Sn, all switches are turned off, only switch S1 is turned on, switch S1 and switch S2 are turned on, etc. By turning on switches 81 to Sn, the adder 44 is turned on. The output has the frequency characteristics shown in FIG.

That is, by switching the switches 81 to Sn in the order described above, similar to the frequency characteristics of the first embodiment, at the start of operation there is a slight gain increase characteristic in the high range, and as time passes, the gain increases from the middle range to The gain in the high range becomes large. With such frequency characteristics, the control section 60 operates in synchronization with the timing of receiving the reflected wave from the sample 104. Then, an image is displayed on the display section 113 in the same manner as in the first embodiment.

According to the second embodiment, the reflected wave reflected at a deeper position in the sample 104 and received at a later time is
Since it can be amplified more in the high frequency band, the attenuation of the spectral characteristics of the reflected wave in the high frequency band is corrected.
The same effects as in the first embodiment can be obtained.

Furthermore, since the signal output from the gate circuit 107 is input to each amplifier 42 via the distributor 41, it is possible to effectively prevent the signal input to the switching correction circuit 40 from being reflected, making it more accurate. data can be obtained.

In addition, in the second embodiment, the bypass filter 43 has C.
Although an R filter is used, it can also be configured with inductance and capacitance, and depending on the case, it can also be configured to have a characteristic that the phase does not change significantly. Further, the synthesized frequency characteristic is not limited to a smooth rise as shown in FIG. 6, but may be a step-by-step rise.

Furthermore, the configuration includes time gain control,
Attenuation at all frequencies may be corrected depending on the depth inside the sample 104.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to improve the lateral resolution and the depth resolution, and to provide an ultrasound microscope that can obtain high-resolution images. Further, when performing quantitative measurement of physical properties of a sample, accurate measurement can be performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the first embodiment of the present invention, FIG. 2 is a diagram showing the frequency characteristics of a variable high frequency band correction circuit, and No. 3-s'' (a) is a diagram showing changes in the LSB of the addressing signal. FIG. 3(b) is a diagram showing the output waveform of the waveform generation circuit, FIG. 4 is a configuration diagram of the second embodiment, and FIG. 5(a) to (d)
) is a diagram for explaining the synthesis of the frequency characteristics of the switching high frequency band correction circuit, FIG. 6 is a diagram showing the frequency characteristics of the switching high frequency band correction circuit, FIG. 7 is a block diagram of a conventional ultrasound microscope, Figure 8 is a diagram to explain the frequency characteristics of a conventional ultrasonic microscope, Figure 9 (a) is a diagram showing reflected waves from the sample surface, and Figure 9 (b) is a diagram showing reflected waves from inside the sample. FIG. 1.60...Control unit, 10...Variable high frequency band correction circuit, 20...Waveform generation circuit, 40...Switching high frequency band correction circuit, 50...Switch control unit.

Claims (1)

[Claims] In an ultrasonic microscope that injects a focused ultrasonic pulse into a sample, receives a reflected wave from the sample and converts it into an electrical signal, and processes this electrical signal to convert it into desired data. , a high frequency band correction means for amplifying the electrical signal, and the frequency characteristic of this amplification is such that the higher the frequency characteristic is from the middle range to the high range, the higher the gain; An ultrasonic microscope characterized by comprising: a means for increasing the height over time in synchronization with a reflected wave from a sample;