Levitation is the process by which an object is suspended by a physical force against gravity, in a stable position without solid physical contact. A number of different technique have been developed to levitate matter including aerodynamic, magnetic, electromagnetic, gas film, casimir force, buoyant levitation and optical levitation.[1]
Aims
The aim of this project planning document was to investigate the principle and methods of object levitation and also need to design and develop a laboratory system. The system enable let the object float and steadily without anything of support. It will no an object assist in levitation, on the same level of elevation as the levitating object. The control system and circuit must be investigated and recommend to improve the designed system. It also needs to identify the applications of levitating system in the modern technology.
Chapter 2: Literature Survey
For levitation on Earth:
(a)A force is required directed vertically upwards and equal to the gravitational force. [3]
(b) For any small displacement of the levitating object, a returning force should appear to stabilize it. The stable levitation can be naturally achieved by magnetic or forces. [3]
Levitation system can use in physics research. It also using in the high-temperature melt property studies because they eliminate the problem of reactions with containers and allow deep under cooling of melts. The container have less conditions maybe obtained by opposing gravity with a levitation force, or by allowing an entire experiment to freefall. [3]
Levitation methods
(A)Casimir force
The casimir force is an electric force, but its origin is different from that of ordinary electric forces. It is a purely quantum-mechanical effect arising from the zero-point energy of the harmonic oscillators that are the normal modes of the electromagnetic field. The electromagnetic field must satisfy certain boundary conditions at the surfaces of our conducting plates, and these boundary conditions rule out some of the modes (oscillators) that would otherwise exist in unbounded space. Since there are fewer oscillators between the plates, there is less zero-point energy in this region. If the plates are brought closer together, this volume of smaller energy density is decreased, while the volume of normal zero-point energy density is increased. Since the results in an overall gain of energy to the universe, a force pressing the plates together is the result. [2]
For Example, the region between the plates was at a lower pressure than outside, so that it possessed less pV energy. If E = pAx, where p is the difference in pressure, A the area of a plate, and x the separation, then the force, by the usual rule, is F = -dE/dx = -pA, as it expect. This is just 'nature abhors a vacuum,' as they used to say. [2]
The force can also be explained as the difference in attraction of the fluctuating zero-point fields between the plates and outside them for the electric charges induced in the plates by the zero-point fields. These zero- point fields are just those necessary to account for the zero-point energy. [2]
It using a way of levitating ultra small objects by manipulating the casimir force, which normally causes objects to stick together due to forces predicated by quantum filed theory. However, it just use for micro-objects only. [3]
(B)Buoyant levitation
Gases at the high pressure can have a density exceeding that of some solids. Thus they can be used to levitate solid objects through buoyancy. Noble gases are preferred for non-reactivity. Xenon is the densest noble gas at 5.894 g/L. Xenon has been used to levitate polyethylene; at a pressure of 154atm.[1]
(C)Gas Film levitation
The technique enables the levitation of an object against gravitational force by floating on a thin gas film formed by gas flow through a porous membrane. [5]
Advantages are no limitation on the type of material, and samples of fairly large mass can be routinely levitated. Disadvantages are just using to study thermo physical properties. [4]
(D) Acoustic levitation
It is a method for suspending matter in a medium by using acoustic radiation pressure from intense sound waves in the medium. It is possible because of the non-linear effects of intense sound waves. [6]
It can Some methods can levitate objects without creating sound heard by the human ear such as the one demonstrated at Osaka Lab, while others produce some audible sound. There are many ways of creating this effect, from creating a wave underneath the object and reflecting it back to its source, to using an acrylic glass tank to create a large acoustic field. [6]
Acoustic levitation is usually used for containerless processing which has become more important of late due to the small size and resistance of microchips and other such things in industry. Containerless processing may also be used for applications requiring very-high-purity materials or chemical reactions too rigorous to happen in a container. This method is harder to control than other methods of containerless processing such as electromagnetic levitation but has the advantage of being able to levitate nonHYPERLINK "http://en.wikipedia.org/wiki/Electrical_conductor"-conducting materials. [6]
There is no known theoretical limit to what acoustic levitation can lift given enough vibratory sound, but in practice current technology limits the amount that can be lifted by this force to at most a few kilograms. Acoustic levitators are used mostly in industry and for researchers of anti-gravity effects such as NASA; however some are commercially available to the public. [6]
(E)Optical levitation
Optical levitation is a method developed by Arthur Ashkin where by a material is levitated against the downward force of gravity by an upward force stemming from photon momentum transfer. Typically photon radiation pressure of a vertical upwardly directed and focused laser beam of enough intensity counters the downward force of gravity to allow for a stable optical trap capable of holding small particles in suspension. [7]
Micrometer transparent dielectric spheres such as fused silica spheres, oil or water droplets, are used in this type of experiment. The laser radiation can fixed in wavelength such as that of argon ion laser or that of a tunable dye laser. Laser power required is of the order of 1 watt focused to a spot size of several tens of micrometers. Phenomena related to morphology- dependent resonances in a spherical optical cavity have been studied by several research groups. [7]
For a shiny object, such as a metallic micro-sphere, stable optical levitation hasn't been achieved. [7]
A force diagram showing how vertical and lateral stabilization occurs in a vertically oriented optical trap. [7]
[F]Aerodynamic levitation
Aerodynamic levitation is the use of gas pressure to levitate materials so that they are no longer in physical contact with any container. In scientific experiments this removes contamination and nucleation issues associated with physical contact with a container. It just use on large object only. [8]
The term aerodynamic levitation could be applied to many objects that use gas pressure to counter force of gravity and allow stable levitation. Helicopters and air hockey pucks are 2 good examples of object that are aerodynamically levitated. However, more recently this term has also been associated with a scientific technique which uses a cone- shaped nozzle allowing stable levitation of 1-3mm diameter spherical samples without the need for active control mechanisms. [8]
These systems allow spherical samples to be levitated by passing gas up through a diverging conical nozzle. Combining this with >200W continuous COHYPERLINK "http://en.wikipedia.org/wiki/Carbon_dioxide_laser"2HYPERLINK "http://en.wikipedia.org/wiki/Carbon_dioxide_laser" laser heating allows sample temperatures in excess of 3000 degrees Celsius to be achieved. [8]
When heating materials to these extremely high temperatures levitation in general provides two key advantages over traditional furnaces. First, contamination that would otherwise occur from a solid container is eliminated. Second, the sample can be undercooled. [8]
Undercooling, or supercooling, is the cooling of a liquid below its equilibrium freezing temperature while it remains a liquid. This can occur wherever crystal nucleation is suppressed. In levitated samples, heterogeneous nucleation is suppressed due to lack of contact with a solid surface. Levitation techniques typically allow samples to be cooled several hundred degrees Celsius below their equilibrium freezing temperatures. [8]
Since crystal nucleation is suppressed by levitation, and since it is not limited by sample conductivity (unlike electromagnetic levitation), aerodynamic levitation can be used to make glassy materials that cannot be made by any other method. Several silica-free, aluminum oxide based glasses have been made. [8]
(G) Electrostatic levitation
Electrostatic levitation is the process of using an electric field to levitate a charged object and counteract the effects of gravity. [9]
Due to Earnshaw's theorem no static arrangement of classical electrostatic fields can be used to stably levitate a point charge. There is a point where the two fields cancel, but it is unstable. By providing feedback it is possible to adjust the charges to achieve a quasi static levitation. [9]
Earnshaw's theorem holds that a charged particle suspended in an electrostatic field is unstable, because the forces of attraction and repulsion vary at an equal rate that is proportional to the inverse square law and remain in balance wherever a particle moves. Since the forces remain in balance, there is no inequality to provide a restoring force; and the particle remains unstable and can freely move without restriction. [9]
(H) Electromagnetic levitation
The technique enables the levitation of an object using electromagnetic radiation. A typical EML coil has reversed winding of upper and lower sections energized by a Radio frequency power supply. [10]
(I) Magnetic levitation
Magnetic levitation is a method by which an object is suspended with no support other than magnetic fields. Magnetic pressure is used to counteract the effects of the gravitational and any other accelerations. [11]
Earnshaw's theorem proves that using only static ferromagnetism it is impossible to stably levitate against gravity, but servomechanisms, the use of diamagnetic materials, super conduction, or system involving eddy currents permit this to occur. [11]
In some cases the lifting force is provided by magnetic levitation, but there is a mechanical support bearing little load that provides stability. This is termed pseudo- levitation. [11]
Magnetic levitation is used for maglev trains, magnetic bearings and for product display purposes. [11]
Although any electromagnetic force could be used to counteract gravity, magnetic levitation is the most common. Diamagnetic materials are commonly used for demonstration purposes. In this case the returning force appears from the interaction with the screening currents. For example, a superconducting sample, which can be considered either as a perfect diamagnetic or an ideally hard superconductor, easily levitates an ambient external magnetic field. In very strong magnetic field, by means of diamagnetic levitation even small live animals have been levitated. [11]
A magnetically levitated (maglev) train departing Pudong International Airport on the first commercial high-speed maglev line in the world. [11]
Magnetic levitation is in development for use for transportation systems. For example the Maglev transportation includes trains that are levitated by a very large number of magnets and, due to the lack of friction on guide rails, they are potentially faster, quieter and smoother than wheeled mass transit systems. [11]
Chapter 3: Methodology
Project specification
(A)Low cost magnetic levitation kits
[12]
A rewound solenoid around a soft steel bolt serves as the electromagnet. A hall- effect sensor mounted at the base of the solenoid senses the proximity of a permanent magnet attached to the levitation object. The power electronics and analog control will provide output voltage of the sensor drives the input of the fan-management chip which produces a pulse- width modulated (PWM). The PWM drive adjusts average circuit in the solenoid, which controls the magnetic fields. [12]
Damping is provided by some washers attached to the levitated object. Losses and eddy currents in the ferrous material help to dampen the vertical wobble of the object. The basic system exhibits unreasonable sensitivity to initial conditions and requires an extremely steady hand. Of course, the measurement of the magnetic field from the levitated object is corrupted by the field from the solenoid, so this measurement of position is far from ideal. However, for the basic system, the Hall-effect sensor is an inexpensive and adequate solution.[12]
Hall- effect sensor is a transducer that varies its output voltage in response to change in magnetic fields. It use for proximity switching, positioning, speed detection and current sensing applications. [13]
(B) Barry's maglev
[13]
The general principle is straight forward: An electromagnet pulls a ball upward while a light beam measures the exact position of the ball's top edge. The magnet's lifting force is adjusted according to position.
As less light is detected, the circuit reduces the electromagnet's current. With less current, the lifting effect is weaker and the ball can move downward until the light beam is less blocked. Voila! The ball stays centered on the detector! It is a small distance across the photodetector, perhaps a millimeter or two, but this is sufficient to measure small changes in position. Of course, if the ball is removed the coil runs at full power. And conversely, if the light beam is blocked the coil is turned completely off.
This device uses two photodetectors: the "signal" detector looks for an interruption in the light beam, and the "reference" detector measures the background light. The circuit subtracts one signal from the other to determine the ball's position. The use of two detectors is my small contribution to advance the art of levitation. This design automatically compensates for changes in ambient light, and eliminates a manually adjusted potentiometer.
(C) Electromagnetic Levitator
[16]
Magnetism and a closed-loop control system are the secrets to the stunning presentation produced by this electromagnetic levitator.
An electromagnet creates a magnetic field that attracts a hollow steel globe or similar object upward. The globe doesn't crash against the magnet, however. Instead, as it draws near, the magnet's intensity weakens, letting the globe drop slightly. As it drops, the magnet's intensity again increases, pulling the globe up again. The process is so smooth, however, that the globe appears to float, held in space by invisible forces.
An infrared emitter and detector mounted across from each other create an invisible beam that passes slightly below the coil. As the object rises towards the electromagnet, it begins to block the beam. When the beam becomes blocked, the output of the detector is reduced which in turn reduces the current in the electromagnet's coil. The reduced current weakens the magnetic field, the object begins to drop and the detector once again sees more of the beam. This causes the circuit to increase the magnetic field and the cycle repeats as the object is attracted upwards again.
The circuit is designed so that eventually equilibrium is reached where the magnetic attraction exactly balances the force of gravity pulling on the object. The object then remains perfectly suspended in the infrared beam's path with no visible means of support!
List of the Component and the schematic diagram
(A)Low cost magnetic levitation kits
This is the schematic diagram
List of the component
Number
Qty
U1 LM7805 voltage regulator
1
U2 MIC502 fan-management IC
1
U3 LMD18201 motor H-bridge IC
1
U4 SS495A Hall-effect sensor
1
C1 470 μF electrolytic capacitor
1
C2 1 μF ceramic capacitor
1
C3 0.1 μF ceramic capacitor
1
C4 0.01 μF ceramic capacitor
1
prewound solenoid
1
soft-steel carriage bolt
1
neodymium magnets
2
heat sink for LMD18201
1
[12]
(B) Barry's magnetic levitation
Schematic diagram
[16]
Part list
Resistors
Resistors listed in order by value are 1/4-watt, 5% unless otherwise indicated.
300 ohms
R11
500 ohms
R2
1,000 ohms
R1, R12, R13, R14
1,500 ohms
R10
10,000 ohms
R4
11,000 ohms
R6
22,000 ohms
R8
56,000 ohms
R3
100,000 ohms
R5
150,000 ohms
R7
370,000 ohms
R9
50K linear taper
VR1 (and VR2 opt.)
Capacitors
C1,C2
47 uF electrolytic
C3
0.1 uF ceramic or tantalum (must not be electrolytic)
Semiconductors
Q1,Q2
OP505A infrared photo detector, or equivalent
Q3
2N3055 NPN power transistor
LED1,2,4
Red light-emitting diode
LED 3
Infrared LED emitter
IC1-4
LM741 op amp, Radio Shack 276-007
D1
1N4001 (or 1N4004) silicon diode, 50v (or more) peak inverse voltage
Miscellaneous
+/- 15 vdc power supply, 1 amp
9 vdc power supply, 1 amp
Breadboard wiring pad (or printed circuit board by Amadeus)
18-ga stranded wire for power
Solid hook-up wire
24-ga (or thicker) magnet wire for lifting coil
6-terminal barrier strip (2 ea.)
Wood for base and frame [17]
(C)Electromagnetic levitator
Schematic diagram
[20]
Parts List
Resistors
All resistors are 1/4-watt, 5% unless otherwise indicated
Other Components
R1 - 82 ohms
L1 - Electromagnet coil - relay coil, 6-volts (P&B: KUP11ED15 - see text)
R2, R3, R4, R5 - 1000 ohms
Adapter - 12-volts DC, 500 mA
R6 - 2000 ohms
S1 - SPST sub-miniature toggle switch
R7 - 2200 ohms
Miscellaneous
R8 - 3300 ohms
Etched printed-circuit board
R9 - 12,000 ohms
Heat sink for Q5 (TO-220)
R10, R11 - 100,000 ohms
Plastic enclosure (Pac Tec K-HPL)
R12 - 150,000 ohms
Hollow metal globe
R13 - 360,000 ohms
Aluminum bracket
R14 - 470,000 ohms
LED panel bezel mount (2 ea.)
R15 - 560 ohms, 1/2 watt
Plastic LED clip mount
R16 - 10,000 ohms, panel-mount potentiometer
Knob for potentiometer
Capacitors
No. 6-32 x 3/8 inch screw
C1 - 0.1 uF, ceramic disc
No. 6-32 x 1.0 inch screw (2 ea.)
C2 - 0.22 uF, 50 volts, polyester film
No. 6-32 x 1/4 inch screw (2 ea.)
C3 - 330 uF, 25 volts, electrolytic
No. 6 hex nut (2 ea.)
Semiconductors
No. 4-male/female, 1/4 inch standoff (4 ea.)
IC1 - LM78L09, 9-volt DC regulator (TO-92)
No. 4-40 x 1/4 inch screw (5 ea.)
IC2 - LM358N, dual op-amp
No. 4 hex nut (5 ea.)
Q1 - 2N2907 (or MPS2907) PNP transistor
Q2, Q3 - 2N3904 (or 2N4401) NPN transistors
Q4 - 2N3906 (or 2N4403) pnp transistor
Q5 - TIPr1A, NPN power transistor
Q6 - IRD500 infrared photo detector (Jameco No. 112168 or equiv.)
D1 - 1N4001 (or 1N4004) silicon diode
LED1 - Red light-emitting diode
IRLED - TLN110 infrared LED (Jameco No. 106425 or equiv.)
[21]
Chapter 5: Summary
Levitation system is the process by which an object is suspended by a physical force against gravity, in a stable position without solid physical contact. [1]
In the path of doing the laboratory levitating system can learn a lot of new stuff for the principles and methods of object levitation and the application of levitating system in the modern technology as well. This knowledge may be added advantages in the future as well when apply for jobs in the future.
Chapter 6: Reference
