JP2899691B2 - Non-contact micromanipulation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-dimensional system using ultrasonic waves, which captures minute objects in a liquid medium at half-wavelength intervals and can move arbitrarily in the direction of sound wave propagation and in the direction parallel to the vibrator. The present invention relates to a non-contact micromanipulation method.

[0002]

2. Description of the Related Art Actuator techniques for handling minute objects include those using a scale-down mechanism for handling an object on a conventional scale, those using static electricity, those using the radiation pressure of laser light, and the like. .

Further, in a minute area, solid friction and a viscosity of a liquid greatly act, and minute dust, which can be ignored in a conventional scale, also acts as a large obstacle in a minute area, so that a force acts in a non-contact manner. It is necessary, and downsizing of the conventional mechanism is inconvenient.

Devices using static electricity have a short operating distance and have problems such as electrolysis at the electrodes. In addition, the target object and atmosphere are limited with respect to conductivity.

[0005] Handling of a minute object by laser light requires that the object optically transmit and refract light. Further, since the acting force is weak, the target object is limited to an extremely small one. Furthermore, there are various problems, such as the need for expensive equipment and the consideration of safety for the human body.

[0006] In contrast to these techniques, those using ultrasonic waves can be used in a medium that propagates sound waves. The target object has an acoustic impedance acoustically different from that of the medium, and reflects or absorbs the sound waves. If it does, a force due to acoustic radiation pressure acts. By forming a standing wave or a sound field, the force can be applied only to a small region on the order of the wavelength. Also, the device is less expensive than a laser or the like. Further, regarding the safety for the human body, if an air layer exists between the liquid medium and the human body, the ultrasonic waves are blocked, so that it is easy to consider the leakage of the ultrasonic waves.

[0007] The inventors of the present invention have proposed a technique in which a microscopic wave trapped at a node of a sound pressure by changing a frequency in a standing wave sound field generated by installing a reflector at a focal position using a concave vibrator. A method for moving an object one-dimensionally on a sound axis has been proposed (Japanese Patent Application Laid-Open No. 9-193055). Furthermore, a method has been proposed in which a back electrode of a rectangular vibrator is divided into a plurality of strips to control and move a minute object in a direction perpendicular to a sound axis (Japanese Patent Application No. 8-281497). However, since the vibrators used in both methods have greatly different shapes, two-dimensional movement cannot be easily realized simply by combining these methods.

[0008]

An object (hereinafter, referred to as a minute object) that is sufficiently small in comparison with the wavelength in the standing wave sound field,
It has been known for a long time to receive the force from the belly of the sound pressure toward the node. Since the nodes and antinodes of the sound pressure are alternately present at quarter-wavelength intervals in the direction of sound wave propagation, the mechanically stable point at which a minute object is captured in the direction of sound propagation is limited to a very small area. Further, with respect to the vertical plane in the direction of sound propagation, the range of action of the force is distributed over a relatively wide area, and the minute object in the sound field is drawn to the local maximum value of the force.

[0009] By changing the frequency of the ultrasonic wave, the node of the sound pressure can be moved on the sound axis (in the direction of propagation of the sound wave). To spread over a wide area equivalent to the transducer surface between the transducer and the reflector,
It is difficult to identify the particle capture position.

Further, it is considered that the entire sound field can be moved in a state of capturing a minute object by arranging a plurality of transducers side by side and switching the driven transducers.

Accordingly, the problem to be solved by the present invention is to generate a standing wave in a liquid medium, capture a minute object in a limited specific region (node of sound pressure), and apply it to a single vibrator. A means for performing a two-dimensional movement operation of a minute object captured by a node of sound pressure by smoothly moving a node of sound pressure in a sound axis direction and a direction orthogonal to the sound axis by controlling an electric signal. Is to develop.

[0012]

A standing wave sound field is generated between the ultrasonic vibrator and the reflector by placing the ultrasonic vibrator and the reflector parallel in water and applying a voltage. In the standing-wave sound field, antinodes and nodes of sound pressure alternate at quarter-wavelength intervals, and a small object floating in the sound field receives a force from the antinode of sound pressure toward the node, and becomes a half-wavelength interval. Captured by existing sound pressure nodes.

According to the present invention, an ultrasonic vibrator for forming a standing wave sound field is formed into a curved shape having a predetermined curvature in one direction, so that sound waves are focused and sound is generated when the frequency is changed. It is possible to move the node of pressure on the sound axis. Then, in the direction having no curvature, the back electrode of the vibrator is divided into a plurality of parts and arranged, and by selecting an electrode to which a voltage is applied,
It electrically controls the sound field of the ultrasonic wave and controls the range and position of the sound field.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a line-focusing type multi-electrode ultrasonic transducer used in the non-contact micromanipulation method of the present invention and a coordinate system for the following description. The ultrasonic transducer 16 is straight in the longitudinal direction (x direction), but is curved at a predetermined curvature in the short direction (y direction).

FIGS. 2A and 2B show the shape of the ultrasonic vibrator 16 of the present embodiment. FIG. 2B is a rear view, and FIG.
(C) is a BB cross-sectional view of (b).

As shown in FIG. 2, the ultrasonic vibrator 16 includes a vibrator 30 that is curved in one direction, such as a piezoelectric ceramic,
It comprises a surface electrode 32 provided on the entire inner peripheral surface of the diaphragm 30 and a plurality of back electrodes 34 divided in the longitudinal direction (x direction) on the outer peripheral surface of the diaphragm 30. In this embodiment, the ultrasonic vibrator 16 is a rectangle of about 40 × 20 mm and the thickness is about 1 mm.
mm and a radius of curvature of about 40 mm in the short direction (y direction).
It is curved. Fifteen back electrodes 34 are arranged in the longitudinal direction, and lead wires 38 'are attached to each of them. The size of the back electrode 34 is about 2 × 20 mm, and the interval between the electrodes is about 0.5 mm. A part of the front electrode 32 is folded back to the rear surface, and a lead wire 38 whose end is connected to the ground of the electric device is attached to the rear surface. Therefore, by applying a voltage to any back electrode 34,
The vibrator at the portion where the back electrode 34 to which the voltage is applied is provided vibrates. The back surface of the vibrator 16 is waterproofed and fixed by filling the acrylic pipe with silicone rubber (not shown). The resonance frequency of the ultrasonic vibrator 16 used in this embodiment is about 2.1 MHz.

FIG. 3 is a block diagram showing an embodiment of the present invention. A sine wave alternating current having a frequency of 2.1 MHz is generated using the function generator 24 and amplified by the power amplifier 22.

The ultrasonic vibrator 16 is fixed in a water tank 14 containing the liquid medium 12 so that the surface electrode side faces upward, and a sine-wave AC voltage from a power amplifier 24 is applied to the ultrasonic vibrator 16 in the water. Radiate. A reflector 18 made of ceramics (alumina) is installed at a position about 40 mm above the vibrator in parallel with the vibrator 16 to generate a standing wave sound field between the vibrator 16 and the reflector 18. Each back electrode 34 of the vibrator 16 is connected to the switch 20 via a lead wire 38 ', and only when the switch 20 is turned on, a voltage is applied to the electrode 34 to emit ultrasonic waves.

The switch 20 is a personal computer 2
6, the sound field can be changed by a program. Although the rated value of the gain of the power amplifier 22 is 50 dB, it changes depending on the load (the number of electrodes to which a voltage is applied). In order to maintain the voltage at a constant value, the voltage applied to the vibrator 16 is measured by a digital oscilloscope 28, and the output voltage of the function generator 24 is adjusted to a set value.

When a suspension of alumina particles having an average diameter of 16 μm was injected into the standing wave sound field using a pipette, the alumina particles were moved above the driving portion of the vibrator 16 (near the reflector) in the direction of the sound axis (z). Direction) at half-wavelength intervals. The shape is a linear shape extending in the x direction, and agglomerates at one point in the y and z directions, but the dimension in the x direction changes according to the size of the drive electrode (because the length differs depending on the voltage or the like, , But not necessarily proportional to the size of the electrodes).

FIG. 4 is a conceptual diagram showing particles supplemented in a node of sound pressure when driving three electrodes (7 × 20 mm). The particle capturing position in the x direction is substantially at the center of the entire driving electrode, and the captured particles move in the x direction by switching the driving electrode. In the case of driving with the same number of electrodes, the width of the electrodes becomes the resolution of movement. However, the resolution of movement can be reduced to half of the electrode width by using the case where the number of drive electrodes is odd and the case where the number of drive electrodes is even.

As shown in FIG. 5, the wavelength changes by gradually changing the frequency, and the minute object captured by the sound pressure node moves on the sound axis. The resolution of the movement differs depending on the amount of change in the frequency and the distance from the reflector 18, and by reducing the amount of change in the frequency, high-resolution movement becomes possible.

Since the distance between the nodes of each sound pressure changes by a change amount of a half wavelength, an arbitrary captured minute object can be moved by the distance between the nodes of the sound pressure. Since the change amount is integrated, the longer the distance from the reflector, the longer the distance. Therefore, when the frequency is changed in a stepwise manner, the distance of the particles separated from the reflector from the reflector becomes longer than a half (波長 wavelength) of the interval between the nodes of the sound pressure.

In this case, the adjacent sound pressure node in the opposite direction is closer to the corresponding sound pressure node than in the corresponding sound pressure node, and moves in the opposite direction. Particles). At that time, when the frequency is increased, the particles are separated, and when the frequency is reduced, the particles are united. Using this technique, it is possible to separate and coalesce particles that are aligned at half-wavelength intervals.

Changing the frequency means moving away from the resonance frequency of the vibrator, which lowers the electro-acoustic conversion efficiency. Therefore, a method of moving a long distance while keeping the change width of the frequency small was invented. As described above, when the frequency greatly changes, the particles move to a nearby node of the sound pressure. Therefore, the frequency gradually changes to more than half (1/1 /
If the frequency is returned to the initial value instantaneously at the time of moving (4 wavelengths or more), only the particles can be moved with the frequency being the same as the initial value (FIG. 6). By repeating this operation, particles can be moved over a long distance.

As described above, the lateral movement of the particles is realized by switching the electrodes, but the resolution of this movement is １ ／ of the width of the electrodes. A method for further reducing the resolution will be described. By shifting the phase of the voltage applied between two adjacent electrodes, it is possible to control the positions of the parts where the sound waves strengthen and cancel each other in the sound field.

FIG. 7 is a conceptual diagram optically visualizing the sound field when the phase is changed in this manner. Numerical values indicate the phase difference values of the AC signals applied to the two electrodes, and FIG. It is a graph which shows the movement at the time of throwing particles into such a sound field, and it turns out that the movement in a stepless manner is realized.

By combining the movement on the sound axis due to the change in the frequency with the movement in the direction perpendicular to the sound axis due to the electrode switching and the phase change between the electrodes, the particle as shown in FIG. Dimensional movement is now possible. Since the sound wave is attenuated in the medium during propagation and the reflectivity of the reflector is 1 or less, the sound wave traveling from the vibrator to the reflector and the sound wave traveling from the reflector to the vibrator are different in their acoustic radiation pressure. Occurs. As a result, a flow of the medium from the vibrator to the reflector occurs (acoustic streaming).

At the time of particle manipulation, this phenomenon is very disturbing, but the tone burst wave (FIG. 10)
By using, it is possible to suppress the energy of the acoustic stream (proportional to the time average of the square of the sound pressure amplitude) while maintaining the force for capturing the fine particles (proportional to the square of the sound pressure amplitude). It became.

[0030]

As described above, in short, in the non-contact micromanipulation method of the present invention, fine particles can be captured and moved two-dimensionally, and fine particles can be freely operated using a microcomputer. The entire device can be reduced in size, and the device can be supplied at a low price.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a line focusing type multi-electrode vibrator according to the present invention.

FIGS. 2A and 2B are views showing the shape of a line focusing type multi-electrode vibrator according to the present invention, wherein FIG. 2B is a rear view, FIG. 2A is a cross-sectional view along AA, and FIG. is there.

FIG. 3 is a block diagram showing an experimental apparatus of an ultrasonic micromanipulator using a line focusing type multi-electrode transducer in one embodiment of the present invention.

FIG. 4 is a conceptual diagram showing that alumina particles are trapped at nodes of sound pressure in a standing wave sound field generated between a vibrator and a reflector in one embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a node of sound pressure and a movement of particles supplemented by the node of sound pressure when a frequency changes in an embodiment of the present invention.

FIG. 6 is an explanatory diagram showing movement at the time of frequency change in one embodiment of the present invention, and is a conceptual diagram showing that long-distance movement is possible by changing the frequency change width to be small.

FIG. 7 is a Schlieren image at the time of a phase change in one embodiment of the present invention.

FIG. 8 is a characteristic diagram showing stepless movement of particles during a phase change in one embodiment of the present invention.

FIG. 9 is a conceptual diagram illustrating two-dimensional movement according to an embodiment of the present invention.

FIG. 10 is a timing chart showing a tone burst wave in one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ultrasonic micromanipulator 12 Liquid medium 14 Water tank 16 Ultrasonic oscillator 18 Reflector 20 Switch 22 Power amplifier 24 Function generator 26 Personal computer 28 Digital oscilloscope 30 Ultrasonic oscillator 32 Front electrode 34 Back electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B25J 7/00

Claims (10)

(57) [Claims] 1. A vibrating plate curved at a predetermined curvature in one direction in a liquid medium in which a minute object is dispersed and present, a surface electrode provided on the entire inner peripheral surface of the vibrating plate, and an outer periphery of the vibrating plate A line-focusing type ultrasonic transducer composed of a plurality of strip-shaped back electrodes provided along a direction having a curvature on the surface is installed, and a voltage is applied to a predetermined electrode among the plurality of back electrodes to generate ultrasonic waves. In the standing wave sound field generated between the reflector placed in parallel with the vibrator at the focal position of the vibrator, the minute object in the medium is radiated and the sound pressure in the sound field in front of the drive electrode is radiated. A non-contact micromanipulation method characterized in that the nodes are arranged at half-wavelength intervals in the direction of the sound axis in the direction of the sound axis, and are aggregated and captured in a one-dimensional shape in a direction without the curvature of the vibrator. 2. The apparatus according to claim 1, wherein the captured minute object can be moved in a sound field between the vibrator and the reflector by changing the frequency of an ultrasonic wave. Non-contact micromanipulation method. 3. When moving the captured minute object,
2. The method according to claim 1, wherein a moving direction of the minute object is selected by changing a frequency in a stepwise manner and an amount of the change is selected, and the minute objects captured at half wavelength intervals are separated and united. Or the non-contact micromanipulation method according to any one of 2. 4. When the minute object is moved, the frequency is gradually changed from an initial value, and after sufficiently moving the captured minute object, the frequency is returned to the initial value instantaneously. The non-contact micromanipulation method according to claim 2 or 3, wherein the captured small object can be moved over a long distance. 5. A method according to claim 1, wherein a voltage is applied to any one of a plurality of continuous electrodes of said line-focusing type ultrasonic transducer to drive an arbitrary part of said line-focusing type ultrasonic transducer.
The non-contact micromanipulation method according to any one of claims 1 to 4, wherein a capturing range of the minute object is selectable. 6. A one-dimensional one-dimensional structure for the minute object by applying a voltage to a plurality of continuous electrodes of the line focusing ultrasonic transducer and driving an arbitrary portion of the line focusing ultrasonic transducer. The non-contact micromanipulation method according to claim 5, wherein the size of the aggregate shape can be selected. 7. A micro object captured in the sound field is increased or decreased by one drive electrode of the line focusing type ultrasonic vibrator for each pole, so that the width of the electrode is reduced in a direction perpendicular to the sound axis. The non-contact micromanipulation method according to claim 5, wherein the non-contact micromanipulation method is movable at a resolution of half of the resolution. 8. An AC voltage applied to two electrodes when a voltage is applied to two adjacent electrodes of the line focusing type ultrasonic transducer to generate a standing wave sound field and a minute object is captured at a node of sound pressure. 8. The method according to claim 1, wherein a capturing position of the object can be steplessly moved between the two electrodes by changing a phase of the signal.
The non-contact micromanipulation method according to any one of the above. 9. A two-dimensional movement of a captured small object is possible by combining a movement in a sound axis direction connecting the line focusing ultrasonic transducer and the reflector and a movement in a direction perpendicular to the sound axis. The non-contact micromanipulation method according to any one of claims 1 to 8, wherein 10. A standing wave sound field is generated by applying a voltage to said line-focusing type ultrasonic transducer, and a voltage applied to said electrode is applied to a tone burst when a minute object is captured and moved at a node of sound pressure. By using waves, the maximum value of the sound pressure amplitude is kept large, the time average value of the sound pressure amplitude is reduced, and it is possible to capture and move an object while suppressing the generation of acoustic streaming, which is the flow of the medium The non-contact micromanipulation method according to claim 1, wherein: