JP2913031B1 - Non-contact micromanipulation method and apparatus using two sound sources - Google Patents

Abstract

A small object in a liquid medium is captured and moved to a predetermined position in a non-contact manner. SOLUTION: A pair of ultrasonic vibrators 12a and 12b are arranged in a liquid medium 13 in which a minute object 14 is dispersed at a predetermined angle so as to be inclined at the same angle so that their sound axes intersect at one point, The pair of ultrasonic vibrators are driven by a predetermined electric signal, and a minute object is captured and supplied at a node of a sound pressure of a standing wave sound field generated in an intersection area of the two radiated ultrasonic waves 15a and 15b. The captured minute object is moved by changing the electric signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for capturing a minute object in a liquid medium and arbitrarily moving on a line parallel to a line connecting the centers of ultrasonic transducers. The present invention relates to a contact micromanipulation method and apparatus.

[0002]

2. Description of the Related Art Hitherto, micromanipulation methods for handling minute objects have been strongly demanded in fields such as biotechnology, material development, and micromachines, and various methods have been proposed. For example, a scale-down mechanism for handling an object on a conventional scale, a mechanism using static electricity, a mechanism using radiation pressure of a laser beam, and the like can be used.

[0003] However, in the minute object region, solid friction and the viscosity of the liquid exert a large effect. In addition, minute dust, which can be ignored in the conventional scale, becomes a large obstacle in the minute object region. It is necessary to work, and it is not possible to handle accurately with a scale-down conventional mechanism.

[0004] In addition, handling of a minute object using static electricity has a problem that the operating distance is short and that the electrodes are electrolyzed. 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 handling 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 reflects the sound waves. If it absorbs, a force by acoustic radiation pressure acts. By forming a standing wave sound field, a force can be applied only to a small region on the order of the wavelength. Further, an ultrasonic generator is less expensive than a laser or the like. Further, regarding the safety to the human body, if an air layer exists between the liquid medium and the human body, the ultrasonic waves are blocked, and 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 No. 2700058). In addition, 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 (Patent No. 2).
No. 723182). Furthermore, a method of moving a minute object two-dimensionally by dividing a back electrode of a curved vibrator into a plurality of strips has been proposed (Japanese Patent Application No. 9-287953).
issue).

It has long been known that in a standing wave sound field, an object sufficiently smaller than the wavelength (hereinafter, referred to as a minute object) receives a force from the antinode of the sound pressure toward a 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. Also,
With respect to the vertical plane in the direction of sound propagation, the range of action of the force is distributed over a relatively large area, and a small object in the sound field is drawn to a local maximum value of the force.

More specifically, as shown in FIG. 8, the ultrasonic vibrator 1 and the reflector 2 are set in parallel in water, and a voltage is applied between the ultrasonic vibrator 1 and the reflector to thereby provide a gap between the ultrasonic vibrator and the reflector. , A standing wave sound field is generated. The generated standing wave sound field is limited to a small area surrounded by the vibrator and the reflector. In the standing wave sound field, as shown in FIG. The antinode 3 and the node 4 alternately exist, and the minute object 5 floating in the sound field receives a force from the antinode of the sound pressure toward the node, and is captured by the node of the sound pressure existing at a half wavelength interval.

When the frequency of the ultrasonic wave is changed, FIG.
As shown in (1), the node of sound pressure can be moved on the sound axis (the direction of propagation of sound waves). However, since the distance of movement of the node of sound pressure increases with distance from the reflector, position control is possible. The control is limited to the vicinity of the reflector, and the above control is limited to a region surrounded by the vibrator and the reflector.

[0011]

Therefore, the problem to be solved by the present invention is not limited to the region surrounded by the ultrasonic vibrator and the reflector, but generates a standing wave sound field at an arbitrary position, A non-contact micromanipulation method and apparatus for capturing a small object at a pressure node and controlling the frequency near the resonance frequency of the vibrator to move the small object captured at the sound pressure node over a wide range. To provide.

[0012]

In the non-contact micromanipulation method according to the present invention, a predetermined distance is maintained between a pair of ultrasonic vibrators in a liquid medium in which minute objects are dispersed such that their sound axes intersect at one point. Arranged in an inclined manner, the pair of ultrasonic transducers are driven by a predetermined electric signal, and the minute object in the medium in the standing wave sound field generated near the intersection area of the emitted ultrasonic waves is It is characterized in that it is captured at the node of the sound pressure in the sound field. Further, the non-contact micromanipulation device according to the present invention is arranged such that the sound axis thereof is inclined at the same angle in the liquid medium so as to intersect at a single point, while maintaining a predetermined interval in the liquid medium in which the minute object is dispersed. And a means for supplying an electric signal to the pair of vibrators, and a medium of the medium at the node of the sound pressure of the standing wave sound field generated near the intersection of the radiated ultrasonic waves. It is characterized by capturing a minute object inside.

[0013] The inclination angle formed by the sound axis of the vibrator with respect to the horizontal is preferably in the range of 5 ° to 30 °. As described above, by arranging the pair of ultrasonic transducers at a predetermined angle with respect to each other, the intersection area of the two ultrasonic waves is also outside the area surrounded by the conventional ultrasonic transducer and the reflector. Thus, it is possible to capture and move a minute object in a wide area. Also, by changing the phase of the electric signal supplied to the two vibrators or by giving a difference in frequency, the sound field of the ultrasonic wave can be electrically controlled, and the position of the node of the sound pressure can be controlled. .

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 shows a principle diagram of a non-contact micromanipulation method using two sound sources according to the present invention. A pair of ultrasonic vibrators 11a and 11b are placed in a liquid medium 13 in which a large number of minute objects 14 are dispersed and float. In the liquid medium, the axes 12a and 12b are arranged at a predetermined angle while being inclined at the same angle θ so that they intersect at one point.

When a predetermined electric signal is supplied to the pair of ultrasonic vibrators 11a and 11b, ultrasonic waves 15a and 15b are oscillated from the two vibrators, and a constant wave is generated in the vicinity of the intersection of the two ultrasonic waves. A standing wave sound field 16 is formed. FIG.
Is an enlarged explanatory view of the sound field 16 of a standing wave, in which two ultrasonic waves 15a and 15b intersect at an interval of λ / (2 cos θ) to form a sound pressure node 16 ′ (where λ is The wavelength of the sound wave) and captures the minute object 14 in the medium. As the ultrasonic transducers 11a and 11b, flat circular ultrasonic transducers can be used.

When the inclination angle θ of the sound axes 12a and 12b of the ultrasonic transducer with respect to the horizontal is in the range of about 5 to 30 °,
Capturing and movement of minute objects can be performed effectively. When the inclination angle θ exceeds 30 °, a small object can be captured. . If the inclination angle θ is 5 ° or less, the ultrasonic waves radiated from the ultrasonic vibrator are reflected by the other vibrators, and the ultrasonic wave returns to the radiated vibrator again, and the whole system resonates. become. In order to stably change the sound field 16 of the standing wave that is being formed, it is necessary to maintain a non-resonant state. For this purpose, the inclination angle θ of the sound axis of the vibrator is 5 ° or more. Is preferred.

If the same signal is supplied as an electric signal for driving the pair of ultrasonic transducers, as shown in FIG. 2, the sound field of a standing wave formed near the intersection of the two ultrasonic waves. A small object will be captured at the node. Further, when the phase of the applied voltage is changed, the node of the sound pressure can be moved on a line parallel to the line connecting the two vibrators, and the captured minute object also moves at the same time. Furthermore, if the frequency of the applied voltage has a slight difference, the phase of the applied voltage can be continuously changed at a constant speed. For example, one of the vibrators has a frequency of 1.750000 MHz.
And a voltage of 1.750001 MH is applied to the other vibrator.
When a voltage of z is applied, the frequency difference is 1.0 Hz, so that the phase is continuously changed at a rate of one cycle per second. At this time, the minute object captured at the node of the sound pressure also moves at a constant speed of the interval of the node of the sound pressure of the standing wave / second.

FIG. 3 is a block diagram showing an embodiment of the non-contact micromanipulation device according to the present invention. The two ultrasonic transducers 11a and 11b are connected to the liquid medium 1
The center axes (sound axes) of each oscillator in the water tank 17 containing 3
The sine-wave AC voltage from the function generator 19 is amplified by a power amplifier and applied to both vibrators to emit ultrasonic waves to the liquid medium 13. Ultrasonic waves 15a and 15b having the same wavelength are radiated from both vibrators, and a standing wave sound field 16 is formed near the intersection of the sound axes.

FIG. 4 shows that a sine wave alternating current having a frequency of 1.75 MHz is generated using a function generator, amplified by a power amplifier, supplied to an ultrasonic vibrator, and the formed standing wave sound field is formed using the Schlieren method. It is the explanatory drawing which was visualized. Brightness and darkness of vertical stripes are observed near the intersection of the sound axes above the center between the two vibrators, and it can be seen that a standing wave sound field is formed. The contrast of the Schlieren image corresponds to the nodes and belly of the sound pressure. Assuming that the angle between the sound axis of the vibrator and the horizontal axis is θ, the relationship between the sound pressure node intervals λ ′ and the wavelength λ of the sound wave radiated from the vibrator is λ ′ = λ / (2 cos θ). .

When a suspension of polystyrene particles having an average diameter of 0.5 mm was injected into the standing wave sound field using a pipette, the polystyrene particles were trapped at nodes of sound pressure. There are multiple sound pressure nodes at intervals of λ 'on a line parallel to the line connecting the two vibrators. By changing the phase of the voltage applied to the two vibrators, the sound pressure nodes It can move on a line parallel to the line connecting the two oscillators, and the captured particles also move at the same time.

FIG. 5 shows that 1.75 MHz (λ =
0.857 mm) in a sound field where the angle θ at which the sound axis is horizontal with the horizontal axis is 15 °, and the phase is 0 ° to + 36 °.
It is a photograph in which the movement of the particles when continuously changing to 0 ° is photographed every 90 °. In equation (1), λ ′ = 0.44 mm, and it can be seen that the robot has moved a distance corresponding to λ ′. Continuously changing the phase is equivalent to providing a difference in frequency. Therefore, in order to perform long-distance movement at a constant speed, an experiment was conducted in which the frequencies applied to the two vibrators were slightly different.

FIG. 6 shows that the two vibrators have 1.750000.
It is a multiple exposure photograph in which the movement of particles when signals of MHz and 1.750002 MHz are applied is photographed at one second intervals. Since the frequency difference is 2 Hz, there is a phase change of two cycles per second, and a movement of about 0.44 mm / sec is observed.

FIG. 7 shows that one of the two vibrators is fixed at a frequency of 1.750000 MHz and the other vibrator has a frequency of 1.7500005 MHz and 1.750001 MHz.
z, 1.750002 MHz, 1.750005 MHz
When the frequency difference between the two vibrators is 0.5H
It is a graph which shows the position of the particle which moves with time at z, 1 Hz, 2 Hz, and 5 Hz. In each case, the particles move at a constant speed with time, and it can be seen that the speed (slope of the graph) is proportional to the difference in frequency.

When the inclination θ of the vibrator and the horizontal is θ = 15 °, and the distance L from the center of the vibrator to the intersection of the sound axis is L = 30 mm,
The intersection of the sound axes is about 7.76 mm from the line connecting the centers of the transducers
is seperated. Although this distance varies depending on θ and L, it indicates that a sound field can be generated at a position away from the vibrator, particles can be captured, and position control can be performed.

By arranging an ultrasonic vibrator outside a water tank surrounded by a substance transmitting ultrasonic waves such as a glass plate, a minute object in the water tank is captured and moved by ultrasonic irradiation from outside the water tank. It becomes possible.

[0026]

As described above, the ultrasonic micromanipulation method and apparatus using two sound sources according to the present invention capture a small object in a liquid medium in a non-contact manner, and provide a difference in phase change and frequency. This enables movement. By tilting the vibrator at that position, a standing wave sound field is generated at a position away from the space between the vibrators, and operation can be performed at a place that is infinitely expanded in one direction. In the embodiment, the vibrator is tilted by 15 ° from the horizontal, and the distance between the center of the vibrator and the intersection of the sound axis is set to 30 mm, so that the distance from the center of the vibrator is 7 mm.
It was possible to generate a standing wave sound field at a distance as described above. The moving distance can be several centimeters in parallel with the transducers, and the resolution is 0.11 mm when the phase is changed every 90 °. These characteristics vary depending on the inclination of the oscillator, the distance between the intersection of the oscillator and the sound axis, etc.
By changing the frequency and the inclination of the vibrator, it becomes possible to capture and move a minute object with high resolution over a wider range.

[Brief description of the drawings]

FIG. 1 is a principle diagram of an ultrasonic micromanipulation method according to the present invention.

FIG. 2 is an explanatory diagram of a state in which a minute object is captured at a node of a sound pressure in a standing wave sound field.

FIG. 3 is an explanatory view showing an experimental apparatus of an ultrasonic micromanipulator using two sound sources.

FIG. 4 is an explanatory diagram in which a range of a sound field is optically visualized by a Schlieren method.

FIG. 5 is a photograph showing a moving state of a particle when a phase change of an applied signal is changed.

FIG. 6 is a multiple exposure photograph of moving particles taken at 1 second intervals when the frequency difference between applied signals is 2 Hz.

FIG. 7 is a graph showing a relationship between a frequency difference of an applied signal and a moving speed of a particle.

FIG. 8 is an explanatory diagram of a state in which a standing wave sound wave is generated by a conventional ultrasonic transducer and a reflector.

FIG. 9A is an explanatory diagram showing a state in which a minute object is captured by the generated standing wave sound waves. b is an explanatory diagram of a state in which the captured minute object is moved on the sound axis.

[Explanation of symbols]

 11a, 11b Ultrasonic vibrator 12a, 12b Sound axis 13 Liquid medium 14 Micro object 15a, 15b Ultrasonic 16 Sound field

Claims (6)

(57) [Claims] 1. A pair of ultrasonic vibrators are arranged in a liquid medium in which a minute object is dispersed at an equal angle while keeping a predetermined distance so that their sound axes intersect at one point in the liquid medium, Driving the pair of ultrasonic transducers with a predetermined electric signal, and capturing a minute object in the medium at a node of a sound pressure of a standing wave sound field generated near an intersection area of the two ultrasonic waves to be emitted. Non-contact micromanipulation method characterized by the above-mentioned. 2. A sound axis of the pair of vibrators is horizontal with respect to a horizontal axis.
The micromanipulation method according to claim 1, wherein the vibrator is arranged to be inclined so as to form an angle in a range of 5 to 30 °. 3. The micromanipulation method according to claim 1, wherein the pair of ultrasonic transducers are driven by supplying electric signals whose phases are displaced from each other. 4. The micromanipulation method according to claim 1, wherein the pair of ultrasonic transducers are driven by supplying electric signals having different frequencies to each other. 5. A pair of ultrasonic vibrations which are arranged at a predetermined interval in a liquid medium in which a minute object is dispersed and whose sound axes are inclined at the same angle so as to intersect at one point in the liquid medium. And a means for supplying an electric signal to the pair of transducers, and captures a node of a sound pressure of a standing wave sound field generated near an intersection area of the radiated ultrasonic waves and a minute object in the medium. Non-contact micromanipulation device characterized by performing. 6. The micromanipulation device according to claim 5, wherein the pair of ultrasonic transducers are arranged so as to be inclined such that the sound axes thereof are inclined within a range of 5 to 30 ° with respect to the horizontal.