Classifying – separating – and assorting solids – Miscellaneous
Reexamination Certificate
1999-05-25
2001-08-14
Matecki, Katherine A. (Department: 3653)
Classifying, separating, and assorting solids
Miscellaneous
C209S005000, C209S155000, C209S208000
Reexamination Certificate
active
06273262
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a particle concentration device, and in particular to a particle concentration device suitable for concentrating sample particles in a solution, using ultrasound.
It has been known since the 19th century that particles in a fluid can be trapped without contact by irradiating the particles with ultrasound. Concerning acoustic radiation force that particles receive when the acoustic radiation force acts on the particles, for example, in Acoust. Soc. Am. 89(1991) pp. 2140-2143, J. Wu, J. reported that he succeeded in trapping polystyrene spheres of 270 &mgr;m diameter at the focal point of focal ultrasound. As regards the principle that particles are trapped by acoustic radiation force, in Acoustica 5 (1955) pp. 167-178, K. Yosioka and Y. Kawasima reported that they calculated the intensity, in an ideal fluid, of acoustic radiation force which particles receive in a standing wave and a traveling wave, and the acoustic radiation force which the particles levitated in the standing wave receive is in proportion to the volume of the particles and the frequency of the ultrasound forming the standing wave. Furthermore, Japanese Patent laid open No. 7-47259, proposed by the present inventors, discloses a manner of introducing ultrasound into a tube in which a fluid is allowed to flow so as to focus particles continuously within some area, or a method for collecting the focused particles.
It has been known heretofore that as the frequency of ultrasound used in a standing wave is gradually changed, the position of nodes of the standing wave changes accordingly and further particles also move accordingly. In J. Acoust. Soc. Am. 91(1992), pp. 3152-3156, T. L. Tolt et al., reported a means for moving and concentrating particles trapped in nodes of a standing wave actually by sweeping, upwards and downwards, the frequency of ultrasound introduced into a fluid wherein the particles are dispersed. Furthermore, U.S. Pat. No. 5,225,089 by E. Benes et al. discloses a means for concentrating particles by raising the frequency of ultrasound radiated from an ultrasound source arranged in a channel.
Moreover, it has also been known heretofore that the position of nodes of a generated standing wave can be controlled by controlling the phases of ultrasounds radiated from a pair of opposite ultrasound vibrators for generating a standing wave. U.S. Pat. No. 4,743,361 by C. J. Schram discloses a means of applying this technique actually to measure physical properties of particles by observing how much the particles follow the movement of the position of nodes of a standing wave. It has also been reported that when ultrasound having slightly different frequencies are radiated oppositely, the position of nodes of a generated standing wave advances by the slight difference between the frequencies.
Additionally, it has been known that the generation of cavitation which may damage a sample can be suppressed by raising the frequency of used ultrasound. It has also been known that when, for example, ultrasounds having the same density are introduced, the sound pressure peak p
c
of its cavitation threshold is in proportion to the frequency f of the incident ultrasounds. As reported in, for example, Acustica 24 (1971) pp. 191-196 by G. Iernetti, cavitation can be prevented only by raising the frequency of ultrasound. Actually, in the step of washing silicon wafers by irradiation with ultrasound in pure water in the process of producing semiconductors, the frequency of used ultrasound is within the MHz range in order to prevent the surfaces of the silicon wafers from being damaged by cavitation based on the ultrasound.
SUMMARY OF THE INVENTION
The above-mentioned conventional techniques are techniques of introducing ultrasound into a solution containing sample particles to be concentrated so as to generate a standing wave in the solution and concentrating the particles around pressure node or pressure loops of the standing wave generated in the solution. They have a problem that, in order to concentrate the particles in the solution between the adjacent pressure nodes or pressure loops of the generated standing wave, the wavelength of the ultrasound must be strictly adjusted so that the value (n+½)&lgr; becomes equal to the width of the inner wall of a chamber.
Besides, in the above-mentioned conventional techniques, to make concentration efficiency maximum in a chamber having a limited volume, the frequency of incident ultrasound is adjusted so that the value &lgr;/2 becomes equal to the width of the chamber. In this case, only one pressure node of a standing wave is generated at the center of the tube-like chamber so that particles in the chamber are concentrated around this pressure node. In this way, the concentration efficiency becomes maximum. However, the distribution of the particles has some width around the node. Thus, in the case that the concentration of the particles is high, even if the distribution of the particles reaches an equilibrium state, the particles cannot be sufficiently concentrated or separated.
Moreover, in the above-mentioned conventional techniques, when the width of the channel is made large, it is necessary to lower the frequency of the used ultrasound to make the channel width equal to the value (&lgr;/2). However, as the frequency is lowered, the cavitation originating from the ultrasound is liable to be generated. Thus, a means for suppressing the cavitation, such as a degass module, is necessary.
An object of the present invention is to provide a particle concentration method and a particle concentration device wherein it is unnecessary to adjust the frequency of used ultrasound strictly in accordance with changes in the width of a chamber and the sort of a solvent.
Another object of the present invention is to provide a particle concentration device which can exceed the limitation of the concentration efficiency based on any conventional distribution of the particles at the time of the equilibrium state of a standing wave.
The present invention is implemented by comprising a means for radiating ultrasound from one face of a chamber holding a sample solution containing particles to be concentrated, and a reflective face inclined to the face irradiated with the ultrasound, and further causing the frequency of the ultrasound to be changed periodically and asymmetrically with the passage of time.
REFERENCES:
patent: Re. 33524 (1991-01-01), Schram
patent: 4055491 (1977-10-01), Parath-Furedi
patent: 4523682 (1985-06-01), Barmatz et al.
patent: 4743361 (1988-05-01), Schram
patent: 4877516 (1989-10-01), Schram
patent: 4948497 (1990-08-01), Ohkawa
patent: 5006266 (1991-04-01), Schram
patent: 5164094 (1992-11-01), Stuckart
patent: 5225089 (1993-07-01), Benes et al.
patent: 5527460 (1996-06-01), Trampler et al.
patent: 5902489 (1999-05-01), Yasuda et al.
patent: 5947299 (1999-09-01), Vazquez et al.
patent: 7-47259 (1995-02-01), None
Journal of Acoustical Society of America, vol. 89, No. 5, May 1991, “Acoustical Tweezers”, J. Wu, pp. 2140-2143.
Acustica, vol. 5, 1955, “Acoustic Radiation Pressure on a Compressible Sphere”, K. Yosioka et al, pp. 167-178.
Journal of Acoustical Society of America, vol. 91, No. 6, Jun., 1992, “Separation devices based on forced coincidence response of fluid-filled pipes”, T. Tolt et al, pp. 3152-3156.
Acustica, vol. 24, 1971, Cavitation Threshold Dependence on Volume, G. Iernetti, pp. 191-196.
Sakamoto Takeshi
Yasuda Kenji
Hitachi , Ltd.
Matecki Katherine A.
Mattingly Stanger & Malur, P.C.
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