JPS6018755A - Automatic focus adjusting apparatus of ultrasonic microscope - Google Patents

Abstract

PURPOSE:To automatically perform focus adjustment with high accuracy, by detecting the reflected wave from a specimen of an ultrasonic wave emitted from an ultrasonic acoustic lens, and variably controlling the relative position of the acoustic lens and the specimen on the basis of the phase difference signal of the receiving signal and a reference signal. CONSTITUTION:The reflected wave from a specimen 8 of an ultrasonic wave emitted from the ultrasonic acoustic lens 4 of an ultrasonic microscope is received by a piezoelectric transducer 3 through the lens 4. The output thereof is inputted to a phase detector 18 through a diode switch 14, an amplifier 16 and a phase shifter 17, which are electrically connected, by opposite polarity control signals (p), (s) from a coaxial change-over device 12 and a pulse control part 13. The receiving signal (j) inputted to the detector 18 is compared with the continuous wave (reference) signal from a continuous wave oscillator 15 and the phase difference signal of the outputs thereof is sent to a sample hold device 19 while the relative distance Z of the lens 4 and the specimen 8 is variably controlled through a Z-direction driving control part 20 and a Z-direction drive mechanism 21 by the focus error signal Vn of the output thereof and focus adjustment is performed with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus adjustment device for an ultrasonic microscope with high focus adjustment accuracy, and in particular to an automatic focus adjustment device for an ultrasonic microscope that has high focus adjustment accuracy, and in particular, an ultrasonic focus adjustment device that changes in accordance with the time it takes for emitted ultrasonic waves to be reflected by a sample. The present invention relates to an automatic focus adjustment device for an ultrasound microscope that obtains focus information from the phase amount of a received sound wave signal.

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 ultrahigh-frequency burst wave electric signal, which is supplied to a piezoelectric transducer 1-3 via a circulator 2, where the electric signal is converted into an ultrasonic wave. The beam is projected in the form of a spot through the ultrasonic acoustic lens 4 and the liquid 5 onto a sample 8 placed on a sample stage 7 that moves two-dimensionally in the X and Y directions by a scanning controller 6. Further, the reflected waves from the sample 8 are collected by the ultrasonic acoustic lens 4, received by the piezoelectric transducer 3, and converted into electrical signals.

This received signal is supplied to the signal processing circuit 9 via the circulator 2, where unnecessary signals are removed, and only the signal corresponding to the necessary reflected wave is amplified and detected, resulting in a detected signal corresponding to the intensity of the reflected wave. get.

The scan converter 10 uses this detection signal as a luminance signal.
Accordingly, the ultrasonic image is displayed on the cathode tube 11-F in synchronization with the scanning of the sample stage 7 by the scanning control device 6. Note that the ultrasonic acoustic lens 4 can be displaced in seven directions perpendicular to the sample stage 7.

In the ultrasonic microscope as described above, when the ultrasonic acoustic lens 4 is moved in seven directions and brought close to the sample 8 from a sufficiently distant position, the signal processing circuit 9 sends a signal to the sample 8 as shown in FIG. The intensity distribution of the detected signal V(7), the so-called V(Z) curve, with second and third sequential maximum values I, If and It is determined by the frequency of the ultrasonic waves, the structure of the ultrasonic acoustic lens 4, the type of liquid 5, etc.

In Figure 2, the second local maximum value I at which ■(7) is the maximum
The point "f" is obtained when the ultrasonic acoustic lens 4 is in focus on the sample 8, and the first and third maximum values ■ and ■ appearing at points d and h before and after this point [
Ha, try 'F! This is caused by interference between the surface wave and the reflected wave at 48.

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

However, in such manual focus adjustment, the operator observes the level of the reflected wave detection signal and determines, for example, the first to third maximum values of points d, f, and h in FIG.
Keep in mind ■, observe the monitor while displacing it in the Z direction, and compare these to determine the maximum reflected wave point (focal position).
Since it is necessary to find t, not only is the adjustment not easy, but it also takes a long time. In this focus adjustment work, the higher the frequency of the ultrasonic waves, the greater the attenuation of the ultrasonic waves in the liquid 5. In order to suppress this, the distance between the ultrasonic acoustic lens 4 and the sample 8 is further increased. Since it is necessary to shorten the distance, it becomes extremely difficult to find the maximum reflection point f from minute changes in distance. In addition, because the operator operates the ultrasonic acoustic lens 4 while looking at the 3-monitor, he may not notice that the ultrasonic acoustic lens 4 and the sample 8 are in contact with each other. There is a risk of damaging it. Furthermore, due to the difficulty in accurately adjusting the focus, when observing a large number of samples, the focus adjustment tends to be inconsistent, resulting in differences in image contrast, making comparisons between samples extremely difficult. It may happen.

An object of the present invention is to develop an ultrasonic microscope that can detect focus information with high accuracy, in order to free an ultrasonic microscope from the burden of manual focus adjustment and eliminate the various problems described above. The present invention attempts to provide an automatic focusing device.

The automatic focus adjustment device of the ultrasound microscope of the present invention provides a relative distance between the ultrasound acoustic lens and the sample in the ultrasound projection direction.
In an ultrasonic microscope configured to adjust the focus by displacing the ultrasonic acoustic lens, the phase of the received signal and the phase of the reference signal 4- are determined by receiving the reflected wave from the sample of the ultrasonic wave projected from the ultrasonic acoustic lens. The present invention is characterized by comprising: a phase detecting means for detecting a difference between the two positions; and a focus adjusting means configured to variably control the relative position based on a detection signal obtained from the phase detecting means.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 3 is a block diagram showing the configuration of an example of an embodiment of the present invention. This example shows the case where it is implemented in the conventionally configured ultrasonic microscope shown in FIG. It operates as an ultrasound microscope. In addition,
The configuration within the range indicated by the dashed-dotted line is as described above, and therefore illustrations other than those necessary for explaining this embodiment are omitted.

The contacts of the coaxial switch 12 are connected to a diode switch 14 which is controlled by control pulses q and S from a pulse control section 13. That is, the diode switch 14 is composed of two switch elements that are made conductive by two switch control signals q and S of opposite polarity from the pulse control section 13, and one of the switch elements 14a is made conductive. At that time, the output 1) of the continuous wave oscillator 15 is applied to the piezoelectric transducer 3 as a burst pulse signal 1, and at other times, the other switch cable 1411 is conductive and receives the reflected wave from the sample 8. It is inserted between the coaxial switch 12, the continuous wave oscillator 15, and the amplifier 16 so that the signal J is guided to the amplifier 16. The continuous wave oscillator 15 is set to oscillate at a lower frequency than the oscillation frequency of the high frequency pulse generator 1 which is supplied to the piezoelectric 1 to the lance gycoser 3 in order to obtain an ultrasonic image. Details of the decision will be provided later.

The received signal 1 amplified by the amplifier 16 is guided to the phase detector 18 via the phase shifter 17, where a detection signal vk corresponding to the phase difference with the reference signal is obtained. In this embodiment, the continuous wave signal derived from the continuous wave oscillator 15 is used as a reference signal, and the received signal @
J is configured to obtain a detection signal corresponding to which phase difference, and the received signal input to the phase detector 18 has a phase difference of j with respect to the phase of the reference signal, i
is the reflected wave from the focal plane of the ultrasonic acoustic lens 4, so that the phase shifter 17 eliminates the influence of the delay time of the received signal due to the path length, line length, etc. inside the ultrasonic acoustic lens 4 The phase is adjusted to compensate for the 19
is a sample hold device that sequentially samples and holds the output detection signal Vk of the phase detector 18 using the sampling pulse m supplied from the pulse control section 13, and the output Vn of the sample bold device 19 controls the seven-direction drive control section. 20 is activated to automatically control a Z-direction drive mechanism 21 configured to be able to vary the relative position of the ultrasonic acoustic lens 4 and the sample stage 7 in the ultrasonic projection direction Z by the ultrasonic acoustic lens 4. There is.

In the above configuration, first, the oscillation frequency of the continuous wave oscillator 15 is determined as follows.

As shown in FIG. 4, when the radius of curvature of the open lower part spherical surface 4a of the ultrasonic acoustic lens 4 is set to r and the material of the lens is sapphire, when water is used as the liquid 5 which is the ultrasonic transmission medium. , the focal length f is fzl,15r, and for example, if it is r-0,5, then it becomes [=0.575°.

Therefore, when changing the distance in seven directions between the ultrasonic acoustic lens 4 and the sample 8 with respect to the phase of the continuous wave signal derived from the continuous wave oscillator 15 as a reference signal, the reflected wave from the sample In order to effectively detect the change in the phase of
In the liquid 5 interposed between the aperture 4a and the sample F18 of the ultrasonic acoustic lens 4, the focal length f is approximately 1/4 of the wavelength of the continuous wave signal or 〒X(211+1) of that wavelength.
) times (n: integer).

From this, the oscillation frequency F of the continuous wave oscillator 15 is F
It is appropriate to set it to ``'' -1f (2n +1 > (Hz) (v: sound speed in liquid 5).If you calculate this using the example given earlier and 1 = f = 0.575 mm, [
It can be seen that it is desirable to set the oscillator wave number F to a frequency around -652x (2n +1) KHz.

In FIG. 3, assuming that the oscillation frequency F of the continuous wave oscillator 15 is set as described above, its operation will be explained with reference to the waveform diagram in FIG.

The coaxial switch 12 switches to the contact side as shown in the figure only when adjusting the focus. The continuous wave oscillator 15 is configured to oscillate in conjunction with this.

FIG. 5(a) shows the oscillator @p. Mouth oscillation signal p
is one switch element 14 of the diode switch 14
As a burst pulse signal i corresponding to the timing and time width of the switch control signal q in FIG. 5(1)) supplied from the pulse control unit 13 via a,
It is guided at a suitable constant period to a piezoelectric transducer 3, where it is converted into an ultrasonic wave and projected onto the sample 8 through the liquid 5. FIG. 5(C) shows the piezoelectric transducer 3
2 shows a burst-like pulse signal Qi guided by. The reflected wave from the sample F18 is received by the piezoelectric transducer 3 through the reverse path and converted into an electrical signal.

As shown in FIG. 5(d), this received signal j is shown in FIG. There is a delay of at least a time 11 which is twice the time it takes to reach the sample 8 (round trip). This received signal j (Fig. 5 ((1)
) is FIG. 5(e) from the pulse control I-roll section 13.
The signal is input to the amplifier 16 through the switch wire 14b of the diode switch 14, which is turned on by the switch control signal S shown in FIG.

As explained earlier, the phase detector 18 receives a burst-like pulse signal (FIG. 5(C)) applied to the juice transducer 3 from the continuous wave oscillator 15 as a reference signal.
A continuous wave signal p is supplied which is in phase with . Also, the delay time 1. of the received signal j (FIG. 5(d)) applied to this phase detector 18. changes depending on the relative distance 1Illz between the ultrasonic acoustic lens 4 and the sample 8 in seven directions, and if Z is not long, 1. becomes longer, and conversely, if 2 becomes shorter, t,b becomes wider, and the phase of the received signal J lags or advances with respect to t at the time of focus. As explained earlier, the received signal j input to the phase detector 18 has been phase-adjusted in advance by the phase shifter 17 so that the phase of the received signal at the time of focusing is in phase with the phase of the reference signal. From the phase detector 18, as shown in FIG. 6, a detection signal Vk is obtained according to the difference between the phase θ after phase adjustment of the received signal 1 and the phase θβ of the continuous wave signal p used as the reference signal. . That is, when in focus, θ−θβ and Vk−
However, when Z is z>f, θ6 lags θβ and becomes 06−θβ>0°, and the output Vk of the phase detector 18
becomes negative polarity when vk>0. Conversely, when z<f, θ6 advances to θβ, and θα-θβ<Q', and vk becomes negative when vk <0. FIG. 5(f) shows an example of the detection signal Vk. The polarity varies depending on the focal position of the ultrasonic acoustic lens 4 on the sample 8, and its absolute value varies depending on the distance between the focus and the sample 8. Change.

This detection signal Vk is guided to the next sample and hold device 19 and sampled and held. The sampling pulse signal m supplied to the sample hold device 11-hold device 19 is ts as shown in FIG.
This is generated by the pulse control section 13 with a time delay. The time ts is the time at which a sampling pulse signal with a timing suitable for sampling the phase detector output (Fig. 5 (f)) in response to the received signal of the correct reflected wave from the sample shown in Fig. 5 (d) is obtained. is set to .

FIG. 5(h) shows a focus error signal Vn obtained from the sample and hold device 19 when the output of the phase detector 18 shown in FIG. 5(f) is sampled and held.

That is, the focus error signal vn obtained in this way is
It has a level corresponding to the focus error for each cycle of the sampling pulse m, and a polarity corresponding to the out-of-focus direction.

This focus error signal Vn is guided to the seven-direction drive control section 20. The Z-direction drive control section 20 outputs a focus error signal Vn
When V>0, the relative distance Z between the ultrasonic acoustic lens 4 and the sample 8 is shortened to 12-, and when Vn<0, the relative distance l is lengthened by 7. The Z-direction drive mechanism is automatically controlled so that the Z-direction drive mechanism is driven and stopped when Vn-0 is reached.

Therefore, when the ultrasonic acoustic lens 4 focuses on the sample 8, the output Vn of the sample holder 19 becomes zero, and the seven-direction drive mechanism 21 stops at that point, which automatically focuses the sample. state.

After automatically focusing in this way, if you switch the coaxial switch 12 to the lower contact point a and obtain an ultrasonic microscope image in the same way as before, you can accurately focus. Ultrasonic microscopy images with excellent resolution can be obtained.

In the above embodiment, the oscillation frequency of the continuous wave oscillator 15 was specifically illustrated, but this frequency may be a relatively low frequency, and the phase θα of the received signal of the wave reflected by the sample 8 and the continuous It should be taken into consideration that the phase of the received signal can be adjusted by the phase shifter 17 so that the difference in phase θβ of the continuous wave signal guided as a reference signal from the wave oscillator 15 becomes θα−θβ−0 at the time of focusing. For example, the oscillation frequency of the continuous wave oscillator 15 is not limited to 4T in the embodiment. In addition, when the frequency of ultrasound used to obtain ultrasound microscopic images is relatively low,
The oscillation mode of the high-frequency pulse generator (indicated by 1 in FIG. 1) for generating ultrasonic waves is switched to continuous wave oscillation only during automatic focus adjustment, and it is configured to replace the continuous wave oscillator 15 of the embodiment. is also possible.

In the above embodiment, the phase θα of the received signal obtained at the time of focusing is adjusted to the phase of the received signal in order to equalize the phase θβ of the reference signal, but the phase of the reference signal is adjusted. Of course, it is possible to make the phases of both signals coincide with each other during focusing, and in some cases, the phase shift adjuster can be omitted.

As explained in detail above, according to the present invention, focus adjustment, which conventionally had to be done manually by an observer, can be done automatically and quickly and with high precision prior to observing an ultrasonic microscope image of a sample. . Therefore, not only can the observer be freed from this type of work that conventionally required time and effort, but also it can effectively prevent damage accidents caused by contact between the ultrasonic acoustic lens and the sample, which tend to occur during manual operation. be able to.

Furthermore, according to the ultrasonic microscope embodying the present invention, uniform and highly accurate focus adjustment is automatically performed at all times, so when a large number of samples are sequentially observed using the same ultrasonic microscope,
This method has the advantage of being able to obtain an ultrasonic microscope image with a constant contrast for each sample, and therefore provides convenience for the observer, such as being able to easily and accurately compare the samples.

[Brief explanation of drawings]

Fig. 1 is a block diagram schematically showing an example of a general configuration of an ultrasound microscope, Fig. 2 is an explanatory diagram of a V(z) curve, and Fig. 3 is an embodiment of the present invention. A block diagram showing the configuration of an example; FIG. 4 is a diagram illustrating the focal length of the ultrasonic acoustic lens; FIG. 5 is a waveform diagram of each part to explain the operation of the embodiment shown in FIG. 3. , FIG. 6 is a curve diagram showing an example of the output characteristics of the phase detector. 1... High frequency pulse generator 2... Circulator 3... Piezoelectric transducer 4... Ultrasonic acoustic lens 5... Liquid 7... Sample stage 8... Sample 9... Signal processing circuit 12... Coaxial switch 13... Pulse control unit 14... Diode switch 14a, 14b... Switch element 15... Continuous wave oscillator 16... Amplifier 17... Phase shifter 18.
・・Phase detector 19・・Sample hold device 20・・Z direction drive control section 21・・Z direction drive mechanism 16 - Figure 2 Figure 3 Figure 5

Claims (1)

[Claims] 10. In an ultrasonic microscope configured to adjust the focus by displacing the relative position of an ultrasonic acoustic lens and a sample in an ultrasonic projection direction, receiving reflected waves from the sample of ultrasonic waves projected from the ultrasonic acoustic lens. phase detection means for detecting the difference between the phase of the received signal obtained by the above-described method and the phase of the reference signal; and a focus adjustment configured to variably control the relative position based on the detection signal obtained from the phase detection means. An automatic focus adjustment device for an ultrasound microscope, characterized in that it consists of means.