Abstract:
An improved magnetic levitation device has a first base magnet with a partially demagnetized central region over which a second dipole magnet is spun or rotated so as to levitate above the first magnet. The levitation device may be calibrated for stability and height of levitation of the second magnet by selected demagnetization of portions of the first magnet.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 08/413,949, filed on Mar. 30, 1995, now abandoned, which is a continuation-in-part of U.S. patent application Ser. No. 08/197,845 filed Feb. 17, 1994, now U.S. Pat. No. 5,404,062. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to levitation devices and methods and more particularly to the levitation or suspension of a permanent magnet in a magnetic field produced by another magnet (either permanent or electromagnetic) using no mechanical restraints or supports. 
     BACKGROUND OF THE INVENTION 
     Magnets, both permanent magnets and electromagnets, find a wide variety of uses, both practical and as entertainment devices. The poles of magnets have been named the north pole and the south pole, the north pole being the one that points northward in the Earth&#39;s magnetic field, i.e., the magnetic north-seeking pole. It is, of course, well known that like poles, i.e., two north poles, repel one another and unlike poles, i.e., a north pole and a south pole, attract one another. 
     This phenomenon has been used to levitate one magnet above another and offers the possibility of substantially reduced friction. Magnetic levitation of trains, for example, is one practical application of the phenomenon. However, in such a levitation application, highly sophisticated control devices are required for controlling the magnetic fields of electromagnets to overcome the inherent instabilities of the repulsion forces of two like magnetic poles. In a simple levitation system wherein one pole of a first permanent magnet is attempted to be suspended above a like pole of a second permanent magnet, the inherent instability of such a system results in the flipping over of the first magnet so that the unlike poles attract and are brought together into a stable configuration. 
     A number of simple levitation systems have been devised which employ specially configured permanent magnet arrangements intended to minimize the instability associated with magnetic levitation. In U.S. Pat. No. 2,323,837 to Neal, for example, there is disclosed a magnetic system having a base magnet comprising a circular disk in which a first plurality of cylindrical magnets is disposed in a circular array about the axis of the circular disk. An upper magnet member comprises a spherical segment in which a second plurality of cylindrical magnets is disposed in a circular array of smaller diameter than the diameter of the circular array of the base magnet. The first plurality of magnets is disposed with like (north) poles and longitudinal axes directed vertically upwardly or inclined slightly toward the axis of the circular disk. The second plurality of magnets is disposed with like (north) poles and longitudinal axes directed vertically downwardly or inclined at the same inclination as the first plurality of magnets. This arrangement of the base magnet is said to produce an inverted magnetic field cone which embraces the smaller diameter magnet field of like polarity of the upper magnet and thereby is said to stabilize the levitation system. 
     U.S. Pat. No. 4,382,245 to Harrigan discloses another simple magnetic levitation system which utilizes a dish-shaped lower magnet to magnetically support or levitate a magnetic top spinning coaxially above the lower magnet. The dish-shaped or concave surface of the lower magnet is said to produce radially inwardly directed lines of magnetization which, together with the gyroscopic effect of rotation of the magnetic top, provide stabilization ,of the levitation system. The Harrigan patent discloses another embodiment in which stabilization is said to be provided by a combination of the concave lower magnet surface and a pendulum effect resulting from a non-magnetic mass supported below the lower magnet on an arm extending from the upper magnet through a central bore in the lower magnet. Other embodiments are disclosed in which the lower field is not provided by a dish-shaped magnet but is provided by a plurality of cylindrical magnets arranged similarly to the arrangement of the aforementioned Neal patent. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a magnetic levitation device and method that accomplishes stable, unrestrained levitation of one magnet above another magnet by utilizing a previously unrecognized characteristic of the magnetic field above a magnetized surface and by incorporation of a rotational motion of the levitated magnet. Although the magnetic levitation device of the present invention may have other applications not specifically described herein, it is intended to provide an educational or amusement device that may be readily manufactured at low cost and operated simply, reliably and reproducibly with minimal instruction. 
     In our prior copending application U.S. patent application Ser. No. 08/197,845 filed Feb. 17, 1994, now U.S. Pat. No. 5,404,062, the complete disclosure of which is incorporated herein by reference, we disclosed a magnetic levitation device and method. The levitation device comprises a uniformly magnetized flat or substantially planar magnetic base above which is caused to levitate a spinning magnetic top made of a flat ring magnet, a nonmagnetic spindle and one or more nonmagnetic weights for adjusting the mass and therefore the height of levitation of the spinning magnetic top. For a substantially uniformly magnetized base or shell it was explained in our prior application that the outer periphery of the base or shell affects the stability of a levitation system incorporating the shell. In particular, a shell having a polygonal shaped periphery has a region a few centimeters above the surface of the shell and along the diagonals thereof where the magnetic field gradients are such as to provide both lifting and centering forces on a magnetic dipole (the spinning top) in that region. It was observed that non-polygonal peripheral shapes, such as circular and elliptical shapes, of a uniformly magnetized shell did not appear to provide the aforementioned region where both lifting and centering forces exist. 
     As was explained in our aforementioned prior application, now U.S. Pat. No. 5,404,062, the height at which the dipole magnet levitates can be increased by weakening the magnetic field at the geometric center of a polygonal (square) shell or base magnet. Such weakening can be accomplished by cutting a hole in the center of the shell magnet or by mounting a magnetic disk of opposite polarity over the geometric center of the base magnet. 
     It has now been found according to the present invention, that the outer periphery of the shell or base magnet need not be polygonal in shape if the magnetic field of the base magnet is made non-uniform by partial demagnetization in a central region of the base magnet. In other words, the outer periphery of the flat base magnet can be any shape, e.g., circular, elliptical, polygonal, if the magnetic field of the base magnet is partially demagnetized or weakened to some extent at or near a central region of the base magnet, preferably at or near the geometric center of the base magnet. 
     The magnetic field may be weakened by cutting a central hole in the base magnet or by mounting a smaller magnet such as a disk magnet of opposite polarity in a central region of the base magnet. It is preferred, however, to weaken the magnetic field of the base magnet by applying a strong magnet field of opposite polarity, e.g., with an electromagnet or permanent magnet, to a central region of the base magnet to permanently weaken or partially demagnetize a portion of the central region. 
     In addition to making possible the use of a base magnet having virtually any peripheral shape, the present invention also causes the levitated spinning dipole (top) to float or levitate at a greater height than for a uniformly magnetized base. 
     Furthermore, it has been found that the top is more easily spun when the magnetic field of the base is weakened. 
     A further feature of the method of the invention is the use of controlled partial demagnetization or weakening of the magnetic field in the central region of the base magnet to “calibrate” the levitation device by making the spinning top more stable. This feature, together with the adjustment of the weight of the spinning top, can be used to achieve an easily spun top which levitates in a relatively stable position for several minutes. 
     Still another feature of the invention is the use of small wedges or shims to adjust the position of the magnetic field of the base magnet with respect to the local vertical. This position adjustment helps to stabilize the levitation of the spinning magnet above the base magnet. 
    
    
     With the foregoing and other advantages and features of the invention that will become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several views illustrated in the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1-4 are a perspective views of one embodiment of the improved magnetic levitation device of the invention showing the method of operating the device of the invention; and 
     FIG. 5 is a perspective view of the base magnet shown in FIGS. 1-4 illustrating the weakened magnetic field in the central region thereof. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of the invention is shown in FIG. 1. A first or base ceramic magnet  10  having a circular periphery of about 10 cm in diameter and a thickness of about 0.7 cm is disposed horizontally on a level surface T. Magnet  10  is magnetized normal to its large surface area with (for description purposes) its north (+) pole oriented upwardly. As described hereinafter, a central region of the magnet  10  has been demagnetized to an extent sufficient to weaken the magnetic field in that region. A non-magnetic lifter plate  12 , such as a transparent plastic sheet, rests on the base magnet  10  with an edge or handle  11  extending beyond the base magnet  10 . On the lifter plate  12  a top  13  is held by the hand H of a user for operation in the manner described hereinafter. Top  13  comprises a second magnet, such as a ceramic ring magnet  14 , with (for description purposes) its north (+) pole oriented downwardly toward the like north pole of the first or base magnet  10 . A spindle  18 , preferably made of a non-magnetic material, is fitted tightly into the central hole or ring magnet  14  for manually imparting spin to the ring magnet  14 . One or more non-magnetic washers  16  are placed over the spindle  18  and fits snugly on the spindle  18  in the manner shown in FIG.  1 . Washers  16  are used for weight adjustment of the magnetic top  13  as described in more detail hereinafter. Top  13  is held against the lifter plate  12  above the geometric center G of base magnet  10  and is spun, either by hand or by any appropriate mechanism, such as a cord. 
     Referring now to FIG. 2 which shows top  13  spinning clockwise, the user grips handle  11  and raises lifter plate  12  vertically upwardly in the direction of arrow  20 . The user lifts the plate  12  slowly by hand until the spinning top  13  approaches the height of maximum negative gradient of the vertical component of the magnetic field. Now referring to FIG. 3, the top  13  has passed through the height of maximum negative gradient generally represented by dimension h 1 , which causes it to lift or levitate upwardly in the direction of arrow  22  off the surface of lifter plate  12  to a new height h 2 . As shown in FIG. 4, the lifter plate  12  may (but need not) be removed, e.g., in the direction shown by arrow  24 . The spinning top  13  will remain levitating or floating above the geometric center G of base magnet  10  as shown in FIG. 4 until the rotation rate of the top  13  drops below that which will maintain the system stable. 
     If the top  13  does not lift off the lifter plate  12  as shown in FIG. 3, it is too heavy and one or more washers  16  should be removed before the procedure is repeated. If the top  13  suddenly jumps off the lifter plate  12 , becomes unstable and falls, the top is too light and one or more washers  16  (FIG. 1) should be added to the spindle  18  before the procedure is repeated. When the top is correctly weighted, it will rise gently off the lifter plate  12  as the peak negative gradient is approached and levitate. In actual operation, the top  13  will levitate or float for several minutes during which time it precesses, nutates gently up-and-down and from side-to-side until it slows and falls onto the base magnet. 
     Also shown in FIG. 4 are a pair of wedge-shaped shims  17 ,  19  which are used to adjust the position of the plane of the upper surface  21  of the base magnet  10 . It is desirable that the surface T be substantially level so that the upper planar surface  21  of the base magnet  10  is also level, at least initially. It has been found, however, that even if the base magnet  10  is perfectly level, the spinning top  13  may quickly drift in one direction from its levitating position shown in FIG.  4  and fall. Should that occur, one of the shims  17 ,  19  is placed under the edge of the base magnet  10  along the direction the spinning top drifted so as to slightly raise the base magnet  10  at that point. The top  13  is again spun and levitated as shown in FIGS. 1-4 and if the top  13  still drifts in the same or a different direction, the shims  17 ,  19  are used to again slightly raise the edge of the base magnet along the direction of drift. By appropriate adjustment and positioning of the shims  17 ,  19  the spinning top can be made to levitate nearly directly above the geometric center G of the base magnet  10  for several minutes. 
     Referring now to FIG. 5, the base magnet  10  is shown with a central region R (shown in dashed lines) in which the magnetic field has been weakened in one of three ways. First, the weakened magnetic field in region R may be achieved by cutting a hole  26  in the geometric center G of the base magnet  10 . Secondly, a magnetic disk  28  of opposite polarity, i.e., with its south (−) pole oriented upwardly over the geometric center G of the base magnet  10 , may be mounted to region R by adhesive bonding or by any other suitable fixing means. Thirdly, a magnet, such as an electromagnet or permanent magnet (not shown), with a strong magnetic field may be positioned at region R and energized so that the magnetic field of the electromagnet or permanent magnet opposes that of base magnet  10  and effects a permanent partial demagnetization or weakening of the magnetic field in region R of magnet  10 . It should be understood that while the region R is depicted in FIG. 5 as a circular region in the center of base magnet  10 , the partial demagnetization is not necessarily centered in the base magnet and does not necessarily create a reduced field of circular shape. 
     This latter method is a preferred method since it involves no structural changes to the base magnet and is easily adjusted since the entire base magnet can be remagnetized over its entire surface and demagnetized in region R again and again. It is also possible to use this latter technique for adjusting or calibrating the magnetic field of the base magnet to achieve more stable levitation of the spinning top. Because of the inherent instability of opposed polarity magnetic systems, it is advantageous to adjust or calibrate the levitation device of the present invention to improve the ease of use of the device. While it is desirable that the use of the levitation device of the invention requires a certain degree of skill to achieve levitation, if the user becomes frustrated by an inability to operate the device, the marketability and success of the device can be adversely affected. 
     It has been found that by appropriate application of a demagnetized field in the central region of the base magnet, i.e., position of application and strength of the demagnetized field, both the height and stability of levitation can be increased. Because of the many variables involved, e.g., relative field strength of the magnets, mass of the spinning magnet, local magnetic fields, uniformity of magnetization, etc., calibration by partial demagnetization cannot be precisely controlled and calibration procedures are to some extent based on operator experience and empirical information. 
     Although certain presently preferred embodiments of the invention have been described herein, it will be apparent to those skilled in the art to which the invention pertains that variations and modifications of the described embodiment may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention be limited only to the extent required by the appended claims and the applicable rules of law.