JPH0136585B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an ultrasonic microscope in which, when an ultrasonic acoustic lens focuses on a sample, a detected signal of a reflected wave from the sample is equal to the detected signal when the ultrasonic acoustic lens is not focused. The distance between the ultrasonic acoustic lens and the sample is determined by the configuration of the ultrasonic acoustic lens. Sample and hold the detection signal obtained by focusing (focus detection signal) at a timing determined by the configuration of the reference ultrasonic acoustic lens, etc., and compare it with a predetermined threshold. and focus,
The present invention relates to an automatic focus adjustment device for an ultrasound microscope that determines out-of-focus.

Ultrasonic microscopes with various configurations have been proposed in the past. An example of its configuration is shown in FIG. In the illustrated ultrasound microscope, a high-frequency pulse generator 1 oscillates an ultra-high frequency burst wave electrical signal and supplies it to a piezoelectric transducer 3 via a circulator 2, where the electrical signal is converted into an ultrasound wave. The beam is projected onto a sample 8 placed on a sample stage 7 which moves two-dimensionally in the X and Y directions by a scanning controller 6 via an ultrasonic acoustic lens 4 and a liquid 5 in the form of a spot. In addition, the reflected waves from the sample 8 are collected by the ultrasonic acoustic lens 4, converted into electrical signals by the piezoelectric transducer 3, and supplied to the signal processing circuit 9 via the circulator 2, where unnecessary signals are removed. At the same time, only the signal corresponding to the necessary reflected wave is amplified and detected to obtain a detection signal corresponding to the intensity of the reflected wave, and this detection signal is used as a luminance signal to be used by the scan converter 10 to control the sample stage 7 by the scanning control device 6. The ultrasonic image is displayed on the cathode tube 11 in synchronization with the scanning. Note that the acoustic lens 4 can be displaced in the Z direction perpendicular to the sample stage 7.

In the ultrasonic microscope as described above, when the ultrasonic acoustic lens 4 is displaced in the Z direction and brought close to the sample 8 from a sufficiently distant position, the signal processing circuit 9 outputs the first, first and second signals as shown in FIG. The intensity distribution of the detected signal called the so-called V _(Z) curve having the second and third sequential maximum values and It is determined by the structure of liquid 4, the type of liquid 5, etc. In Figure 2, the second local maximum point f where V _(Z) is maximum
is obtained when the ultrasonic acoustic lens 4 is in focus on the sample 8, and the first and third maximum values appearing at points d and h before and after this point f are the surface waves in the sample 8. This occurs due to interference with reflected waves, etc.

Therefore, conventionally, the output of the signal processing circuit 9 is monitored with a measuring instrument such as an oscilloscope, and while visually observing this, the ultrasonic acoustic lens 4 is manually displaced in the Z direction to locate the position where the detected signal level is maximum ( The focus of the ultrasonic acoustic lens 4 on the sample 8 was adjusted by searching for point f) in FIG. 2 and aligning the acoustic lens 4 with this position.

However, in such manual focus adjustment, the operator memorizes, for example, the first to third maximum values of points d, f, and h in FIG. 2 while observing the level of the reflected wave detection signal. Since it is necessary to search for the maximum reflected wave point (focal point position) f while comparing these, adjustment is extremely difficult and time consuming. This is because the higher the frequency of the ultrasonic waves, the greater the attenuation of the ultrasonic waves in the liquid 5, and in order to suppress this, it is necessary to further shorten the distance between the ultrasonic acoustic lens 4 and the sample 8. Therefore, it becomes more difficult to find the point of maximum reflection based on minute changes in distance. Furthermore, since the operator operates the ultrasonic acoustic lens 4 while looking at the monitor, there is a risk that the ultrasonic acoustic lens 4 and the sample 8 will come into contact and be damaged. Furthermore, since focusing is extremely difficult,
When observing a large number of samples, differences in image contrast occur, making it extremely difficult to compare samples.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic focus adjustment device that automatically adjusts focus in order to eliminate the various problems described above.

That is, the automatic focus adjustment device for an ultrasound microscope of the present invention is applicable to an ultrasound microscope having a focus adjustment mechanism configured to adjust the focus by displacing the relative position of an ultrasound acoustic lens and a sample in the ultrasound projection direction. , sampling and holding a detection signal obtained by receiving the reflected wave from the sample of the ultrasonic wave projected from the ultrasonic acoustic lens at a predetermined timing determined by the configuration of the ultrasonic acoustic lens, etc. and comparing means configured to compare the output voltage from the sample and hold means with a predetermined threshold value to obtain a stop pulse signal, The invention is characterized in that the focus adjustment mechanism is configured to stop the operation of the focus adjustment mechanism.

The present invention also provides an ultrasonic microscope having a focus adjustment mechanism configured to adjust the focus by displacing the relative positions of an ultrasonic acoustic lens and a sample in an ultrasonic projection direction, wherein The detection signal obtained by receiving the reflected wave of the ultrasonic wave from the sample was sampled at two points: a predetermined timing determined by the configuration of the ultrasonic acoustic lens, and a timing in the vicinity thereof. sample-and-hold means for holding two values separately; a comparator that compares these two values and outputs an output when the sample-and-hold value at the predetermined timing is larger than the sample-and-hold value at the neighboring timing; Comparing means includes a comparator for comparing one of the binary values with a predetermined threshold value, and an AND circuit for extracting the AND output of the outputs from both of the comparators as a stop pulse signal. That is.

The present invention will be described in detail below with reference to the drawings.

FIG. 3 shows a first example of the configuration of an embodiment of the present invention.
This is a block diagram showing a case where the present invention is applied to the conventional ultrasonic microscope shown in the figure.
Further, the same parts as those shown in FIG. 1 are denoted by the same reference numerals, but since these parts have been explained earlier, the explanation will be omitted here.

In the figure, 12 indicates the ultrasonic acoustic lens 4 at Z
This is a Z-direction drive mechanism, that is, a focus adjustment mechanism, including a drive device for intermittently displacing the Z-direction.
Reference numeral 13 denotes a Z-direction drive control device for controlling the Z-direction drive mechanism 12, and is configured to stop the operation of the Z-direction drive mechanism 12 when a stop pulse signal is supplied. Further, 14 is a control pulse generator for controlling the start/stop of the high-frequency pulse generator 1, and 15 is a control pulse generator for sampling and holding the reflected wave detection signal obtained from the signal processing circuit 9 using the pulse signal from the control pulse generator 14. A sample-and-hold device configured to hold the pulse signal for only the time necessary to match the timing of the detection signal at the time of focusing, which has a timing determined by the configuration of the ultrasonic acoustic lens 4, etc. The signal is delayed by a delay pulse generator 16 and applied to the sample/hold device as a sampling pulse.

That is, the pulse output from the control pulse generator 14 is divided into two parts, one of which drives the high-frequency pulse generator to generate a high-frequency pulse signal, and the piezoelectric transducer 3 is thereby driven. A detected signal of the reflected wave from the sample 8 such as
6, the pulse signal is generated with a timing that matches the timing of the detection signal at the time of focusing corresponding to the second maximum value shown in FIG. 2, and this pulse signal causes the signal processing circuit to Since the detection signal from 9 is sampled and held, the Z of ultrasonic acoustic lens 4 and sample 8
When the ultrasonic acoustic lens 4 is displaced from a position far away from the sample 8 to closer to the sample 8 so that the distance in the direction changes, the detected wave is sampled and held by the sample and holder 15. The position of the ultrasonic acoustic lens 4 when the output voltage of the signal shows the maximum value exactly corresponds to the in-focus position. 17 is a comparator for separating the output voltage from the sample-and-hold device 15 from signals such as noise, and it compares the voltage V _f captured by the sample-and-hold device 15 with the voltage V _r of the threshold reference voltage setting device 18. It is configured to output when V _f > V _r .

Therefore, in the V _(Z) curve shown in Figure 2,
Threshold reference voltage setting device 1 so that only the second maximum value, which is the detection signal during focusing, exceeds the threshold value.
If the voltage _Vr of 8 is set, a pulse signal is generated from the comparator 17 when the position of the ultrasonic acoustic lens in the Z direction reaches the focused point. In this embodiment, the pulse signal is supplied to the Z-direction drive control device 13 as a stop pulse signal.

As explained earlier, the Z-direction drive control device 13 is configured to control the Z-direction drive mechanism 12 to stop using a stop pulse. The sonic acoustic lens stops at the time when the stop pulse is generated from the comparator 17, that is, at the focus position where the detection signal at the time of focus is obtained.

The operation of the configuration of the embodiment of the present invention described above is as follows:
This will be explained in more detail with reference to the timing chart shown in FIG.

The Z-direction drive control device 13 operates the Z-direction drive mechanism 12 to drive the ultrasonic acoustic lens 4 and the sample 8 closer to or farther apart in the Z direction. On the other hand, a high frequency pulse generator 1 generates repetitive high frequency pulses for driving the piezoelectric transducer, and the generation is controlled by a pulse signal from a control pulse generator 14. In Fig. 4, if the wave generated by the high-frequency pulse generator 1 is an incident wave P and its timing is set at _t1 , the wave is converted into an ultrasonic wave by the piezoelectric transducer 3, and the ultrasonic acoustic lens 4
and hits the surface of the sample 8 via the liquid 5,
The reflected wave passes through the reverse path and is extracted from the signal processing circuit 9 as an output detection signal. When the surface of the sample 8 is at the focus of the ultrasonic acoustic lens 4, there is the largest reflection as explained earlier, the reflected wave at that time is R _f , and the delay time from the incident wave P is t _f
shall be. Let R ₁ be the reflected wave when the focus of the ultrasonic acoustic lens 4 is slightly away from the surface of the sample 8 and the reflected wave when it is close to the surface of the sample 8 is R ₂ , then the timing relationship between them is as follows. The result will be as shown in FIG. Therefore, in order to extract the reflected wave detection signal corresponding to the largest reflected wave R _f from the reflected wave detection signals from the signal processing circuit 9, the pulse signal from the control pulse generator 14 is transferred to the delayed pulse generator 1.
₆ , the reflected wave detection signal is sampled by _the sample/hold circuit 15, and the voltage value at that time is held. and supplies it to the comparator 17.

Therefore, the output of the sample-and-hold unit 15 supplied to the comparator 17 includes an unfocused detection signal during the process until the ultrasonic acoustic lens 4 focuses on the surface of the sample 8. However, comparator 17
is set in advance by the threshold reference voltage setting device 18 so that V _f >V _r with respect to the threshold value V _r is output only when the detected signal V _f of the largest reflected wave R _f is input. Since the predetermined threshold value V _r is set, when the surface of the sample 8 is located at the focal point of the ultrasonic acoustic lens 4, that is, the detected signal V _f corresponding to the maximum reflected wave R _f is detected by the sample and hold device. A Z-direction drive control device 13 outputs a pulse signal from the comparator 17 only when the sample is sampled and held, and stops the displacement of the ultrasonic acoustic lens 4 in the Z direction by the Z-direction drive mechanism 12.
control. As a result, the displacement of the ultrasonic acoustic lens 4 in the Z direction is stopped, and the ultrasonic acoustic lens 4 automatically focuses on the surface of the sample 8.

FIG. 5 is a block diagram showing a part of the configuration of another embodiment of the present invention, and shows only the part surrounded by the dashed line in FIG. Since the configuration is the same as that in the figure, illustration is omitted.

In this embodiment, automatic focus adjustment can be performed with higher precision than in the previous embodiment, and the sample and hold means consist of two sample and hold devices 19 and 20.
On the one hand, the timing of the pulse signal from the control pulse generator shown at 1 in FIG. 3 is changed to t _f shown in FIG. The detected signal from the signal processing circuit shown at 9 in FIG. 3, which is applied from the detected signal input terminal 23, is sampled by the delayed pulse signal delayed by the first delayed pulse generator 22 for time delaying. It is configured to be held in place.

Further, the other sample-and-hold device 20 transmits the delayed pulse signal delayed by the first delayed pulse generator 22 to the second delayed pulse generator 24.
The detection signal from the signal processing circuit 9 is sampled and held using a delayed pulse signal obtained by delaying the signal by a minute time Δt.

On the other hand, the comparison means also includes two comparators 25 and 26.
The outputs from both comparators 25 and 26 are led to an AND circuit 27, and the obtained AND output is taken out as a stop pulse signal, and one of the first
Similar to the previous embodiment, the comparator 25 separates the output voltage of the first sample-and-hold device 19 from signals such as noise to prevent malfunction. The output voltage is compared with a threshold value and is configured to be output only when the output voltage exceeds the threshold value. The other second comparator 26 is configured to take the difference between the output voltages from the sample-and-hold devices 19 and 20 obtained by sampling the reflected wave detection signal at a very short time difference Δt. It's connected. However,
The stop pulse signal from the AND circuit 27 is inputted from the stop pulse signal output terminal 29 to the Z-direction drive control device shown at 13 in FIG. 3, so that the same operation as in the previous embodiment is performed. The rest of the structure is the same as that shown in FIG. 3, so the operation of this embodiment will be explained below based on the timing charts shown in FIGS. 6 and 7, with reference also to the same figure.

Similarly to the first embodiment, when the ultrasonic acoustic lens 4 is gradually brought closer to the sample 8 from a position far from the sample 8 and the focal position of the ultrasonic acoustic lens 4 reaches near the surface of the sample 8, the signal processing The detection output obtained from the circuit 9 changes as shown in FIG.

If the detection output when the surface of the sample 8 is at the focal point of the ultrasonic acoustic lens 4 is B in the same figure, then when the ultrasonic acoustic lens 4 and the sample 8 are a little apart from each other by their focal distance, As shown in A, the detection output is lower than the detection output when the object is in focus, as shown in B of the same figure, and even when the object is a little closer, as shown in C of the same figure, the detected output is reduced. In order to detect this subtle difference in detection output level and determine the in-focus position, the pulse from the control pulse generator 14 is used as in the case of the previous embodiment. The signal has a time difference t _f between when a reflected wave detection signal is obtained at the time of focusing obtained by the incident wave from the ultrasonic acoustic lens 4 to the sample 8 due to the timing of the pulse signal. 1 delayed pulse signal is output from the first delayed pulse generator 22, and the reflected wave detection signal from the signal processing circuit 9 is sampled by the first sample/hold device 19 using the first delayed pulse signal. and obtain the output voltage _V1 .

Further, a second delayed pulse signal is obtained by delaying the first delayed pulse signal by a minute time Δt as shown in FIG. 7 by the second delayed pulse generator 24, and this second delayed pulse signal is According to the signal, the reflected wave detection signal from the signal processing circuit 9 is sampled in the second sample-and-hold device 20 to obtain an output voltage V ₂ . FIG. 7 shows these output voltages V ₁ ,
This shows the timing relationship of V ₂ .

The output voltage V ₁ of the first sample-and-hold device 19 is equal to the reference voltage set by the threshold reference voltage setter 28 in the first comparator 25.
Compared to V _r . The reference voltage V _r is set to be a threshold suitable for separating the output voltage from noise and obtaining a comparison output, so V ₁
>V _r , the first comparator outputs an output. That is, it is determined here that the surface of the sample 8 is near the focal point of the ultrasonic acoustic lens 4.

If B in the same figure is the detection output when it is in focus, when driving the ultrasonic acoustic lens 4 in the Z direction to bring it closer to the sample 8, from A to B in the figure,
The detection output level changes from B to C. Therefore, in order to distinguish the subtle level differences in the detection outputs shown in A, B, and C of FIG. Then, when the detection output is in the state of A in the figure with respect to the focal position, the output voltage from the first sample-and-hold device 19 is
V ₁ and the output voltage V ₂ from the second sample-and-hold device 20 become V ₁ <V ₂ , in which case V ₁ >V _r and the first comparator 25 outputs an ON state. Also, V 1 is applied to the input terminal and V ₂ is applied to the input terminal so that the second comparator 26 outputs only when V ₁ <V _{2 .}
is input, the second comparator 26 becomes
It is in the OFF state, and accordingly, the AND circuit 27 also remains in the OFF state.

Next, the ultrasonic acoustic lens 4 focuses on the surface of the sample 8, and the relationship between the focal position and the detection output reaches the state shown in Figure B, or in the state immediately before that.
The relationship between V ₁ and V ₂ becomes V ₁ > V ₂ , and the second comparator 2
6 is in the ON state and outputs. At this time, the first
Since the comparator 25 is in the ON state and outputting the output, the AND circuit 27 becomes the ON state at or just before the in-focus state shown in FIG. The signal is input to the Z-direction drive control device 13 and the operation of the Z-direction drive mechanism 12 is stopped. The driving of the ultrasonic acoustic lens 4 in the Z direction is thereby stopped, and its focus is now on the surface of the sample 8.

In the second embodiment described above, a case has been described in which the ultrasonic acoustic lens 4 is moved in the direction approaching the sample 8 and automatic focusing is performed, but the ultrasonic acoustic lens 4 is moved in the direction away from the sample 8. When automatic focusing is to be carried out using the above-described second embodiment, the same operation as in the second embodiment described above can be achieved by configuring the outputs of the sample-and-hold devices 19 and 20 to be connected in reverse.

As described above, according to the present invention, the distance between the ultrasonic acoustic lens and the sample is changed, and the detected signal of the reflected wave from the sample when the ultrasonic acoustic lens is focused on the sample surface is sampled and held. The ultrasonic acoustic lens is focused on the sample surface by stopping the driving of the ultrasonic acoustic lens based on the timing of the comparison output obtained by comparing this hold voltage with a predetermined threshold. Because of this, focus adjustment, which conventionally had to be done manually by the observer, can be done automatically and quickly and with high precision, and also effectively prevents damage caused by contact between the ultrasonic acoustic lens and the sample. can. In addition, because it is possible to always automatically adjust the focus with high precision, it is possible to obtain images with a constant contrast when observing a large number of samples, making comparisons between samples easy and accurate. can be done.

In particular, in the second embodiment, the driving of the ultrasonic acoustic lens can be stopped at the timing of the detection signal close to the peak point of the reflected wave during focusing, so even more precise automatic focusing is possible. becomes.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of an example of a conventional ultrasonic microscope, Figure 2 is an intensity distribution diagram of the reflected wave detection signal with respect to the distance between the acoustic lens and the sample.
FIG. 3 is a block diagram showing an example of an embodiment of the present invention when the device of the present invention is applied to the device of FIG.
4 is a timing chart for explaining the operation of the embodiment of FIG. 3, FIG. 5 is a block diagram showing a part of the configuration of another embodiment of the present invention, and FIGS. 6 and 7 is a timing chart to explain its operation. DESCRIPTION OF SYMBOLS 1... High frequency pulse generator, 2... Circulator, 3... Piezoelectric transducer, 4... Ultrasonic acoustic lens, 5... Liquid, 6... Scanning controller, 7... Sample stage, 8... Sample, 9...Signal processing circuit, 11...Cathode ray tube, 12...Z direction drive mechanism, 13...Z direction drive control circuit, 14...Control pulse generator, 15...Sample/hold device,
16...Delayed pulse generator, 17...Comparator, 1
8, 28... Threshold reference voltage setter, 19...
First sample and hold device, 20...Second sample and hold device, 21...Pulse signal input terminal, 22...First delay pulse generator, 23...
Detection signal input terminal, 24...second delay pulse generator, 25...first comparator, 26...second comparator, 27...AND circuit, 28...stop pulse signal output terminal.

Claims (1)

[Scope of Claims] 1. In an ultrasonic microscope having a focus adjustment mechanism configured to adjust the focus by displacing the relative positions of an ultrasonic acoustic lens and a sample in the ultrasonic projection direction, sample/hold means configured to sample and hold a detection signal obtained by receiving reflected waves of the ultrasonic wave from the sample at a predetermined timing determined by the configuration of the ultrasonic acoustic lens; ,
comparing means configured to compare the output voltage from the sample and hold means with a predetermined threshold value to obtain a stop pulse signal, and stop the operation of the focusing mechanism by the stop pulse signal. An automatic focus adjustment device for an ultrasound microscope, characterized in that it is configured as follows. 2. In an ultrasonic microscope having a focus adjustment mechanism configured to adjust the focus by displacing the relative positions of the ultrasonic acoustic lens and the sample in the ultrasonic projection direction, the ultrasonic sample projected from the ultrasonic acoustic lens The detection signal obtained by receiving the reflected wave from the ultrasonic acoustic lens is sampled at two points in time: a predetermined timing determined by the configuration of the ultrasonic acoustic lens, and a timing in the vicinity thereof, and the obtained binary values are separately obtained. sample/hold means for holding;
a comparator that compares these two values and outputs an output when the sample-and-hold value at the predetermined timing is larger than the sample-and-hold value at the neighboring timing; one of the two values and a predetermined threshold; 1. An automatic focusing device for an ultrasound microscope, comprising: a comparator for comparing the two comparators; and a comparing means having an AND circuit for extracting the AND output from both the comparators as a stop pulse signal.