JPH0461306B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an automatic focus adjustment device for an ultrasound microscope. [Technical background of the invention and its problems] 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 electric signal, which is supplied to a piezoelectric transducer 3 via a circulator 2, where the electric signal is converted into an ultrasonic 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 detected signal corresponding to the intensity of the reflected wave, and this detected signal is used as a luminance signal to be sent to the scan controller 6 by the scan converter 10.
The ultrasonic image is displayed on the cathode tube 11 in synchronization with the scanning of the sample stage 7 by. In addition,
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 approaches the sample 8 from a sufficiently distant position, the signal processing circuit 9 outputs the first, The distance (Z) at which the intensity distribution of the detected signal, so-called the so-called V(z) curve, is obtained and the detected signal is obtained, with the second and third sequential maximum values, and
is determined by the frequency of the ultrasonic waves used, the structure of the acoustic lens 4, the five types of liquid, etc. In FIG. 2, the second maximum value point f where V(z) is maximum is obtained when the ultrasonic acoustic lens 4 is in a converged state with respect to the sample 8, and the points d before and after this point f are and the first and third appearing in h
The maximum value of is caused by interference between the surface wave and the reflected wave in the sample 8. 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 transverse wave 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, while observing the level of the reflected wave detection signal, determines, for example, the first to third maximum values of points d, f, and h in FIG. 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 focus adjustment is extremely difficult, differences in image contrast occur when a large number of samples are observed, making it extremely difficult to compare the samples. [Object of the Invention] An object of the present invention is to provide an automatic focus adjustment device that automatically performs focus adjustment that was conventionally performed manually. This can prevent damage to both the acoustic lens and the sample due to contact. [Summary of the Invention] The present invention is based on focus adjustment information obtained from the amplitude of an interference wave between a wave reflected at the interface between an acoustic lens and a liquid and a wave reflected at the sample surface.
The focus is automatically adjusted. [Embodiment of the Invention] An embodiment of the present invention will be described using FIGS. 3 to 7. Components used in common with those shown in FIG. 1 are designated by the same numbers. FIG. 3 shows a transducer section 12 consisting of a cylindrical acoustic lens used in the microscope apparatus of this embodiment, with a piezoelectric transducer 3 and an opening 14 provided approximately at the center of its upper and lower surfaces, respectively.
Then, the reflected waves at the interface between the lower surface of the acoustic lens 13 and the liquid 5 and the reflected waves from the surface of the sample 8 are
A sub-piezoelectric transducer 15 is provided in the same plane as the piezoelectric transducer 3 of the transducer section 12 so as to approximately form a plane wave. Here, the principle of the automatic focus adjustment device according to the present invention will be explained. As shown in FIG. 4, the opening diameter of the opening 14 is r
Then, the focal length f is, assuming that the liquid 5 is water,
When the material of the acoustic lens 13 is sapphire f
= 1.15r. Therefore, if the aperture angle of the aperture is θ, the distance l between the lower surface of the acoustic lens 13 and the surface of the sample 8 at the time of focusing is l=f−r+rcosθ=r(0.15+
cosθ). For example, if r = 0.5 mm and θ = 60°, l = 0.325 mm. Now, the ultrasonic wave i emitted from the sub-piezoelectric transducer 15 into the acoustic lens 13 is caused by interference between the reflected wave j at the interface between the lower surface of the acoustic lens 13 and the liquid 5 and the reflected wave k from the surface of the sample 8. It is returned to the sub piezoelectric transducer 15 again in a vine shape. Here, by appropriately determining the wavelength of the ultrasonic waves to be used, it is possible to maximize the wave cancellation in the interference between the reflected waves j and k in the focused state. That is, λ
=4l/2n+1 (where n is o or a positive integer), the amplitude of the interference wave becomes minimum at the time of focusing, that is, when the distance between the lower surface of the acoustic lens 13 and the surface of the sample 8 is l. On the other hand, when the image is out of focus, the interference effect weakens, so the amplitude conversely increases.
This relationship is shown in FIG. Therefore, by measuring the amplitude of the interference wave while changing the distance between the acoustic lens and the sample, it is possible to obtain in-focus/out-of-focus information. , the drive mechanism of the sample stage), the focus can be adjusted automatically. The wavelength input condition for Oki is that if the frequency fc is used, then fc
=V/4l(2n+1) [Hz] (where, v is the speed of sound in the liquid 5, and n is 0 or a positive integer). For example, for the previous example (l=0.325mm), fc=
It becomes 1.154(2n+1)MHz. Now, in the present invention, the basic configuration of the ultrasonic microscope is the same as the conventional one. For example, the one shown in FIG. 1 may be used. Therefore, FIG. 6 shows only the newly added focus adjustment mechanism. The transducer section 12 faces the sample 8 on the sample stage 7 with the liquid 5 interposed therebetween. Sub piezoelectric transducer 15 of transducer section 12
are the movable terminals 18 and 19 of the first diode switch 16 and the second diode switch 17 , respectively.
is connected to. First diode switch 1
A continuous wave generated by a CW oscillator 21 and having a lower frequency than that used in the piezoelectric transducer 3 for a microscope is outputted to the fixed terminal 20 of 6.
Fixed terminal 22 of second diode switch 17
is connected to the input section of the detection amplification section 23.
The output of this detection amplification section 23 is branched and applied to sample and hold circuits 24 and 25, and then input to two input sections of a comparator 26, respectively. The pulse control section 27 generates pulses for controlling the opening and closing of the first and second diode switches 16 and 17 , and also generates an alternating pulse generator via a delayed pulse generator 28 that receives the pulses and generates delayed pulses. 29. The alternating pulse generator 29 alternately outputs delayed pulses to the sample and hold circuits 24 and 25, and the output section is connected to the Z direction drive control section 3 via the delay circuit 30.
It is also connected to 1. The Z-direction drive control section 31 controls the operation of the Z-direction drive mechanism 32 that drives the transducer section 12 in the vertical direction (Z direction), and the output of the comparator 26 is applied to an input section. The operation of the embodiment of the present invention configured as described above will be explained with reference to the waveform diagram shown in FIG. The opening and closing of the first and second diode switches 16 and 17 are controlled by pulses q and s (see FIG. 7) applied by a pulse control section 27. As can be seen from this waveform, when one of the second diode switches 16 and 17 is closed,
The other side is controlled so that it always opens. Therefore, the continuous wave p generated by the CW oscillator 21
is the first diode switch 16 at time t ₀
(waveform i) to the sub-piezoelectric transducer 15 (waveform i), where it is converted from an electrical signal to an ultrasonic signal i. First diode switch 16
The closing period is set to 2L/Vs, which is the time required for the first incident ultrasonic wave to return to the sub-piezoelectric transducer 15 (L is The thickness of the acoustic lens 13, Vs, is set to be slightly shorter than the sound velocity (velocity of sound in the acoustic lens 13). The incident wave is reflected at the interface between the lower surface of the acoustic lens 13 and the liquid 5, enters the acoustic lens 13 again, and is converted from an ultrasonic wave to an electric signal, resulting in a waveform as shown in FIG. 7j. Further, the ultrasonic waves that pass through the liquid 5 and are reflected on the surface of the sample 8 are similarly acoustic-electrically converted and have a waveform as shown in FIG. 7k. Waveform k has a longer wave path than waveform j, so it is delayed by a time of 2l/v. These reflected waves j and k interfere with each other and return to the sub-piezoelectric transducer 15, but during the period of their return, the first diode switch 16
is in an open state, and the second diode switch 17 is in a closed state. The pulse that has passed through the second diode switch 17 is amplified and detected through the amplification/detection section 23 and becomes a pulse shown by v in FIG. On the other hand, the pulse q output from the pulse control section 27 is delayed by a time tw so as to overlap with the pulse v by the delayed pulse generator 28, and is converted into a narrow pulse train. This pulse train is alternately selected every other pulse by the alternating pulse generator 29, and is used as pulses w1 and w2 as sampling pulses for the sampling and hold circuits 24 and 25. The pulse v obtained from the sub-piezoelectric transducer 15 through the amplification/inspection wave section 23 is sampled at the timing of the sampling pulses w1 and w2 in the sampling and hold circuits 24 and 25, and the value is held and the value shown in FIG. The signals become α and β. The voltages Vα and Vβ of the signals α and β are respectively input to the + terminal and the − terminal of the comparator 26, and their magnitudes are compared. The comparator 26 has Vα>
When Vβ, H (High) level output is set to Vα≦
When Vβ, an L (Lou) level output is output to the Z direction drive control unit 31, and the timing of the pulse γ, which is obtained by delaying the sampling pulse w2 by a predetermined time tr by the delay circuit 30, that is, both the signals α and β are in a hold state. If the timing is H level,
The Z-direction drive mechanism 32 is driven in a direction that increases the distance between the acoustic lens 13 and the sample 8, and is stopped when the distance is at L level. Here, if the operation is started from a place where the distance between the acoustic lens 13 and the sample 8 is as narrow as possible, Vα−
As can be seen from FIG. 5, Vβ has become a positive value, and the distance between the acoustic lens 13 and the sample 8 increases, but when this distance exceeds the distance l at the time of focusing, Vα−Vβ approaches zero value,
Since the output of the comparator 26 becomes L level, the Z-direction drive mechanism 32 is stopped and brought into focus. In the above embodiments, in order to focus more accurately, it is sufficient to increase the accuracy of comparison between Vα and Vβ and to increase the sampling frequency. Further, after the distance between the acoustic lens and the sample exceeds the distance l, if the Z-direction drive mechanism 32 is driven in a direction that decreases the distance, accurate focusing can be achieved. Furthermore, in the above embodiments, the focus is adjusted by changing the relative distance between the acoustic lens and the sample, but the present invention can also be applied to a microscope device that adjusts the focus while keeping the relative distance between the two constant. Applicable. For example, some systems use several concentrically arranged transducers and adjust the focus by changing which transducers are operated. In this case, the sub-piezoelectric transducers may also be concentric, and the selected transducer may be changed depending on the output of the comparator. [Effects of the Invention] As described above, according to the present invention, focus adjustment, which was conventionally performed manually by an observer, can be automatically performed quickly and with high precision. Moreover, when the distance between the acoustic lens and the sample approaches beyond the focusing position, the driving mechanism of the lens (or sample stage) either stops or is driven in the direction of increasing the distance. Damage to both can be prevented. In addition, since 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, which makes comparisons between samples easy and accurate. can be done.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of the configuration of a conventional ultrasound microscope, Fig. 2 is a graph showing the intensity distribution of the detected signal called the V(z) curve, and Fig. 3 is a graph showing the intensity distribution of the detected signal called the V(z) curve.
The figure is a perspective view of a transducer section according to an embodiment of the present invention, FIG. 4 is a front view and partially enlarged view of the transducer section, and FIG. 5 is a lens-sample distance and interference wave amplitude. FIG. 6 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 7 is a waveform diagram for explaining the operation of the same embodiment. 3...Piezoelectric transducer, 12 ...Transducer section, 13...Acoustic lens, 14...Aperture, 15...Sub piezoelectric transducer, 16
...first diode switch, 17 ...second diode switch.

Claims (1)

[Scope of Claims] 1. A sub-piezoelectric transducer for focus adjustment provided in the same plane as the piezoelectric transducer on the upper surface of a cylindrical acoustic lens, and a power supply section for driving the sub-piezoelectric transducer. , the ultrasonic waves generated by this sub-piezoelectric transducer are reflected by the surface of the sample facing the acoustic lens, the ultrasonic waves are reflected by the liquid interposed between the acoustic lens and the sample, and the acoustic lens. means for comparing the amplitudes of voltages obtained by electroacoustic exchange in the sub-piezoelectric transducer at different timings after the waves interfere with the reflected waves reflected at the interface of the sub-piezoelectric transducer and are incident on the sub-piezoelectric transducer; An automatic focus adjustment device for an ultrasound microscope, comprising: focus adjustment means for adjusting the focus of the ultrasound transducer section based on the output of the means.