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Levitation

About: Levitation is a research topic. Over the lifetime, 6750 publications have been published within this topic receiving 68392 citations. The topic is also known as: levitation (scientific).


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Journal ArticleDOI
TL;DR: In this article, a single vertically directed focused TEM00-mode cw laser beam of ∼250 mW is sufficient to support stably a ∼20μ glass sphere.
Abstract: The stable levitation of small transparent glass spheres by the forces of radiation pressure has been demonstrated experimentally in air and vacuum down to pressures ∼1 Torr. A single vertically directed focused TEM00‐mode cw laser beam of ∼250 mW is sufficient to support stably a ∼20‐μ glass sphere. The restoring forces acting on a particle trapped in an optical potential well were probed optically by a second laser beam. At low pressures, effects arising from residual radiometric forces were seen. Possible applications are mentioned.

780 citations

Journal ArticleDOI
TL;DR: The phases used to drive an ultrasonic phased array are optimized and it is shown that acoustic levitation can be employed to translate, rotate and manipulate particles using even a single-sided emitter.
Abstract: Sound can levitate objects of different sizes and materials through air, water and tissue. This allows us to manipulate cells, liquids, compounds or living things without touching or contaminating them. However, acoustic levitation has required the targets to be enclosed with acoustic elements or had limited manoeuvrability. Here we optimize the phases used to drive an ultrasonic phased array and show that acoustic levitation can be employed to translate, rotate and manipulate particles using even a single-sided emitter. Furthermore, we introduce the holographic acoustic elements framework that permits the rapid generation of traps and provides a bridge between optical and acoustical trapping. Acoustic structures shaped as tweezers, twisters or bottles emerge as the optimum mechanisms for tractor beams or containerless transportation. Single-beam levitation could manipulate particles inside our body for applications in targeted drug delivery or acoustically controlled micro-machines that do not interfere with magnetic resonance imaging.

602 citations

Journal ArticleDOI
08 Jan 2009-Nature
TL;DR: It is shown experimentally that the sign of the force can be changed from attractive to repulsive by suitable choice of interacting materials immersed in a fluid, and the measured repulsive interaction is found to be weaker than the attractive.
Abstract: Space is not completely empty; the vacuum teems with quantum mechanical energy fluctuations able to generate an attractive force between objects that are very close to each other. This 'Casimir–Lifshitz' force can cause static friction or 'stiction' in nanomachines, which must be strongly reduced. Until now only attractive interactions have been reported but in theory, if vacuum is replaced by certain media, Casimir–Lifshitz forces should become repulsive. This has now been confirmed experimentally. Repulsion, weaker than the attractive force, was measured in a carefully chosen system of interacting materials immersed in fluid. The magnitude of both forces increases as separation decreases. The repulsive forces could conceivably allow quantum levitation of objects in a fluid and lead to new types of switchable nanoscale devices with ultra-low static friction. Levitation depends only on the dielectric properties of the various materials. The cover illustrates repulsion between a tiny gold sphere and a silica substrate (left). Replace the silica with gold (right), and the force becomes attractive. In a vacuum, the Casimir–Lifshitz force causes friction effects that either hinder or may be exploited in nanomechanical device applications. So far, only attractive interactions have been measured, but theory predicts that when vacuum is replaced with certain media, the Casimir–Lifshitz force can also be repulsive. This effect is now experimentally confirmed in this study, which carefully chooses a system of interacting materials immersed in a fluid. The measured repulsive interaction is found to be weaker than the attractive force whereas in both cases the magnitude of the force increases with decreasing surface separation. Quantum fluctuations create intermolecular forces that pervade macroscopic bodies1,2,3. At molecular separations of a few nanometres or less, these interactions are the familiar van der Waals forces4. However, as recognized in the theories of Casimir, Polder and Lifshitz5,6,7, at larger distances and between macroscopic condensed media they reveal retardation effects associated with the finite speed of light. Although these long-range forces exist within all matter, only attractive interactions have so far been measured between material bodies8,9,10,11. Here we show experimentally that, in accord with theoretical prediction12, the sign of the force can be changed from attractive to repulsive by suitable choice of interacting materials immersed in a fluid. The measured repulsive interaction is found to be weaker than the attractive. However, in both cases the magnitude of the force increases with decreasing surface separation. Repulsive Casimir–Lifshitz forces could allow quantum levitation of objects in a fluid and lead to a new class of switchable nanoscale devices with ultra-low static friction13,14,15.

516 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that stable zones always exist on the axis of a field with rotational symmetry, and include the inflection point of the magnitude of the field.
Abstract: Diamagnetic objects are repelled by magnetic fields. If the fields are strong enough, this repulsion can balance gravity, and objects levitated in this way can be held in stable equilibrium, apparently violating Earnshaw's theorem. In fact Earnshaw's theorem does not apply to induced magnetism, and it is possible for the total energy (gravitational+magnetic) to possess a minimum. General stability conditions are derived, and it is shown that stable zones always exist on the axis of a field with rotational symmetry, and include the inflection point of the magnitude of the field. For the field inside a solenoid, the zone is calculated in detail; if the solenoid is long, the zone is centred on the top end, and its vertical extent is about half the radius of the solenoid. The theory explains recent experiments by Geimet al, in which a variety of objects (one of which was a living frog) was levitated in a field of about 16 T. Similar ideas explain the stability of a spinning magnet (Levitron TM ) above a magnetized base plate. Stable levitation

435 citations

Journal ArticleDOI
TL;DR: The first man-loading high temperature superconducting Maglev test vehicle in the world is reported in this paper, where the onboard superconductors are melt-textured YBaCuO bulks.
Abstract: The first man-loading high temperature superconducting Maglev test vehicle in the world is reported. This vehicle was first tested successfully on December 31, 2000 in the Applied Superconductivity Laboratory, Southwest Jiaotong University, China. Heretofore over 17,000 passengers took the vehicle, and it operates very well from beginning to now. The function of suspension is separated from one of propulsion. The high temperature superconducting Maglev provides inherent stable forces both in the levitation and in the guidance direction. The vehicle is 3.5 m long, 1.2 m wide, and 0.8 m high. When five people stand on vehicle and the total weight is 530 kg, the net levitation gap is more than 20 mm. The whole vehicle system includes three parts, vehicle body, guideway and controlling system. The high temperature superconducting Maglev equipment on board is the most important for the system. The onboard superconductors are melt-textured YBaCuO bulks. The superconductors are fixed on the bottom of liquid nitrogen vessels and cooled by liquid nitrogen. The guideway consists of two parallel permanent magnetic tracks, whose surface concentrating magnetic field is up to 1.2 T. The guideway is 15.5 m long.

434 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20241
2023288
2022539
2021254
2020311
2019314