Abstract:
A system and a method are described herein for demagnetizing a region of a magnetic structure. In one embodiment, the system comprises: (a) a pulsed magnetizer; and (b) at least one magnetizing coil that receives a sequence of discrete current with continually decreasing current values from the pulsed magnetizer and outputs a sequence of discrete magnetizing fields with continually decreasing field strengths to overwrite and at least partly demagnetize the region of the magnetic structure. The at least one magnetizing coil is located adjacent to the region of the magnetic structure.

Description:
CLAIM OF PRIORITY 
     This application claims the benefit U.S. Provisional Application Ser. No. 61/795,352 filed on Oct. 15, 2012. The contents of this document are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a system and method for demagnetization of a magnetic structure region. More particularly, the present invention relates to demagnetization of a magnetic structure region by magnetically overwriting alternating polarity maxels having decreasing field strengths. 
     BACKGROUND OF THE INVENTION 
     The demagnetization or removal of a magnetic field may be accomplished in several ways as described at http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/Demagnetization.htm, on Oct. 12, 2012, which is incorporated by reference herein. One demagnetization approach is to heat a material above its Curie temperature to produce a random orientation of the magnetic domains, which demagnetizes the material. Another demagnetization approach is to subject the material to a reversing and decreasing magnetic field produced by driving a (de)magnetizer with a decreasing alternating current. This AC demagnetization process, shown in  FIG. 1  (PRIOR ART), can be accomplished by pulling a component out and away from a coil with AC passing through it. The same can also be accomplished using an electromagnetic yoke with AC selected. Also, many stationary magnetic particle inspection units come with a demagnetization feature that slowly reduces the AC in a coil in which the component is placed. As can be seen in  FIG. 1  (PRIOR ART), which depicts a demagnetization hysteresis curve  102 , the current passing through a magnetizing coil decreases in accordance with an alternating current having a current curve  104 . The demagnetizing field of the magnetizing coil corresponds to a flux curve  106  that corresponds to the current curve  104 , where the alternating polarity H field that is produced by the coil results in a smaller and smaller B field being present in the material inside the coil. An alternative demagnetization approach is the subject of the present invention. 
     SUMMARY 
     A system and method for demagnetizing a region of a magnetic structure are described in the independent claims of the present application. Advantageous embodiments of the system and method have been described in the dependent claims of the present application. 
     In one aspect, the present invention provides a system for demagnetizing a region of a magnetic structure. The system comprises a pulsed magnetizer and at least one magnetizing coil. The at least one magnetizing coil receives a sequence of discrete currents with continually decreasing current values from the pulsed magnetizer and outputs a sequence of discrete magnetizing fields with continually decreasing field strengths to overwrite and at least partly demagnetize the region of the magnetic structure. The at least one magnetizing coil is located adjacent to the region of the magnetic structure. 
     In another aspect, the present invention provides a method for demagnetizing a region of a magnetic structure. The method comprises: (a) generating, by a pulsed magnetizer, a sequence of discrete currents with continually decreasing current values; (b) receiving, by at least one magnetizing coil, the sequence of discrete currents with continually decreasing current values; and (3) outputting, by the at least one magnetizing coil, a sequence of discrete magnetizing fields with continually decreasing field strengths to overwrite and at least partly demagnetize the region of the magnetic structure. The at least one magnetizing coil is located adjacent to the region of the magnetic structure. 
     Additional aspects of the invention will be set forth, in part, in the detailed description, figures and any claims which follow, and in part will be derived from the detailed description, or can be learned by practice of the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention may be obtained by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  (PRIOR ART) is a graph used to help explain a traditional AC demagnetization process for demagnetizing a magnetic structure; 
         FIG. 2  is a graph used to help explain a new demagnetization process for demagnetizing a magnetic structure in accordance with an embodiment of the present invention; 
         FIGS. 3A-3D  illustrate an exemplary demagnetization process for demagnetizing a region (i.e., outer edge or outer perimeter) on a magnetic structure in accordance with an embodiment of the present invention; 
         FIG. 4  is a flowchart illustrating an exemplary demagnetization method in accordance with an embodiment of the present invention; 
         FIG. 5  is a flowchart illustrating another exemplary demagnetization method in accordance with an embodiment of the present invention; and 
         FIG. 6  is a flowchart illustrating yet another exemplary demagnetization method in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully in detail with reference to the accompanying drawings, in which the preferred embodiments of the invention are shown. This invention should not, however, be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. 
     The present invention pertains to a system and method for demagnetization of a magnetic structure region. Certain described embodiments may relate, by way of example but not limitation, to systems and/or apparatuses comprising magnetic structures, methods for using magnetic structures, magnetic structures produced via magnetic printing, magnetic structures comprising arrays of discrete magnetic elements, combinations thereof, and so forth. Example realizations for such embodiments may be facilitated, at least in part, by the use of an emerging, revolutionary technology that may be termed correlated magnetics. This revolutionary technology referred to herein as correlated magnetics was first fully described and enabled in the co-assigned U.S. Pat. No. 7,800,471 issued on Sep. 21, 2010, and entitled “A Field Emission System and Method”. The contents of this document are hereby incorporated herein by reference. A second generation of a correlated magnetic technology is described and enabled in the co-assigned U.S. Pat. No. 7,868,721 issued on Jan. 11, 2011, and entitled “A Field Emission System and Method”. The contents of this document are hereby incorporated herein by reference. A third generation of a correlated magnetic technology is described and enabled in the co-assigned U.S. patent application Ser. No. 12/476,952 filed on Jun. 2, 2009, and entitled “A Field Emission System and Method”. The contents of this document are hereby incorporated herein by reference. Another technology known as correlated inductance, which is related to correlated magnetics, has been described and enabled in the co-assigned U.S. Pat. No. 8,115,581 issued on Feb. 14, 2012, and entitled “A System and Method for Producing an Electric Pulse”. The contents of this document are hereby incorporated by reference. 
     Material presented herein may relate to and/or be implemented in conjunction with multilevel correlated magnetic systems and methods for producing a multilevel correlated magnetic system such as described in U.S. Pat. No. 7,982,568 issued Jul. 19, 2011 which is all incorporated herein by reference in its entirety. Material presented herein may relate to and/or be implemented in conjunction with energy generation systems and methods such as described in U.S. patent application Ser. No. 12/895,589 filed Sep. 30, 2010, which is all incorporated herein by reference in its entirety. Such systems and methods described in U.S. Pat. No. 7,681,256 issued Mar. 23, 2010, U.S. Pat. No. 7,750,781 issued Jul. 6, 2010, U.S. Pat. No. 7,755,462 issued Jul. 13, 2010, U.S. Pat. No. 7,812,698 issued Oct. 12, 2010, U.S. Pat. Nos. 7,817,002, 7,817,003, 7,817,004, 7,817,005, and 7,817,006 issued Oct. 19, 2010, U.S. Pat. No. 7,821,367 issued Oct. 26, 2010, U.S. Pat. Nos. 7,823,300 and 7,824,083 issued Nov. 2, 2011, U.S. Pat. No. 7,834,729 issued Nov. 16, 2011, U.S. Pat. No. 7,839,247 issued Nov. 23, 2010, U.S. Pat. Nos. 7,843,295, 7,843,296, and 7,843,297 issued Nov. 30, 2010, U.S. Pat. No. 7,893,803 issued Feb. 22, 2011, U.S. Pat. Nos. 7,956,711 and 7,956,712 issued Jun. 7, 2011, U.S. Pat. Nos. 7,958,575, 7,961,068 and 7,961,069 issued Jun. 14, 2011, U.S. Pat. No. 7,963,818 issued Jun. 21, 2011, and U.S. Pat. Nos. 8,015,752 and 8,016,330 issued Sep. 13, 2011, and U.S. Pat. No. 8,035,260 issued Oct. 11, 2011 are all incorporated by reference herein in their entirety. 
     Various methods for printing maxels are described in U.S. Parent application Ser. No. 13/240,355, field Sep. 22, 2011 and titled Magnetic Structure Production, which is incorporated by reference herein it its entirety. 
     In accordance with the present invention, a region of a magnetic structure is demagnetized (or erased) by successive overwriting of the region with magnetic sources having alternating polarities and decreasing field strengths. More specifically, the magnetic field sources, which are often called maxels, are produced using a pulsed magnetizer where a very short current pulse is passed through a magnetizing coil located adjacent to a location on the surface of a magnetizable material. Each maxel has a size, shape, depth, polarity, field strength, angle relative to the magnetization surface, and various other maxel characteristics that are in accordance with material characteristics such as material type (e.g., NIB), grade, thickness, shape (e.g., flat), etc., magnetizing coil characteristics such as metal type, layer thickness, number of turns, aperture width, coil width, coil shape, aperture shape, etc., and magnetizing characteristics such as the amount of current passed through the coil, and the direction of the current through the coil, distance between the coil and the surface, angle of the coil relative to the surface, etc., where one skilled in the art will understand that any of these magnetizing coil characteristics and/or magnetizing characteristics can be varied to effect demagnetization in accordance with the invention. As such, one or more magnetizer coils having the same or different magnetizing coil characteristics can be used with the same or different magnetizing characteristics to overwrite and demagnetize one or more regions on one or more magnetic structures. 
       FIG. 2  depicts exemplary discreet current values  202  of current used to drive a magnetizer coil in order to produce (or write) overwrite alternating polarity maxels at a given location on a material, where each discreet current value  202  has a corresponding discreet flux value  204  of magnetic flux produced by the magnetizer coil. As shown, the current values  202  used to drive the magnetizer coil change polarity and decrease with each printed maxel to produce a sequence of alternating polarity maxels with decreased field strength in order to demagnetize the location on the material. The discrete current values  202  and flux values  204 , for example, correspond to the peak current and peak flux values of the current and flux curves  104  and  106  of  FIG. 1 . However, the discrete current values  202  can decrease in accordance with some other desired decrement pattern such as a uniform decrement pattern. Generally, the starting discrete current value  202  of a demagnetization process can be selected based on the field strength of the region of the magnetic structure as determined prior to demagnetization. For example, a measurement of the field to be erased could be made, and a current value  202  could be selected such that the starting demagnetizing magnetic field would be of opposite polarity of the field being erased and somewhat lower in field strength. However, an alternate approach would be to select a starting current value  202  based on material characteristics that will result in a near saturating field. However, if only partial demagnetization is desired, the starting demagnetizing field may be selected that is substantially lower than the field strength of the region of the magnetic structure prior to demagnetization. 
     Because the printing of each maxel is substantially a discreet event as opposed to demagnetization using a continuous alternating current, all sorts of combinations are possible for demagnetizing a region on a magnetic structure including use of multiple print heads to demagnetize one or more regions on one or more magnetic structures, where characteristics of a given print head and the use of such print head can be controlled to control the demagnetization process. For example, one or more print heads can be used to demagnetize a region on a magnetic structure, where the location of at least one print head is fixed. Alternatively, one or more movable print heads may be used. Combinations of different print head sizes (e.g., aperture diameters), maxel shapes, maxel depths, and the like can be used. Many patterning choices are available such as maxel print order, the amount of overlapping of maxels (or spatial density), the spacing between maxels, etc. Moreover, instead of alternating polarity with each overwriting maxel, multiple maxels of the same polarity may overwrite successively. In other words, a region may be overwritten one or more times with a magnetizing field having the same polarity before being overwritten one or more times with a magnetizing field having the opposite polarity. Generally, one skilled in the art will recognize that all sorts of variations of the invention are possible. 
       FIGS. 3A through 3D  are provided to illustrate an exemplary demagnetization process for demagnetizing a region  306  on a magnetic structure  303  corresponding to its outer boundary (i.e., outer edge or outer perimeter). Referring to  FIG. 3A , a first maxel pattern  300   a  of first polarity maxels  302   a  and second polarity maxels  304   a  have been printed onto a magnetizable material  303  having an outer boundary  306 . The maxels  302   a  and  304   a  have been printed in columns from the bottom of the magnetizable material  303  to the top of the magnetizable material  303  and from the left side to the right. As such, the first maxel printed is in the lower left corner and the last maxel printed is in the upper right corner. A field scan  308   a  shows the resulting magnetic field, where the outer boundary  306  of the magnetizable material  303  is shown.  FIG. 3B  shows a second maxel pattern  300   b  comprising overlapping first polarity maxels  302   b  having a first field strength that are printed by magnetizing coils  305  (and a pulsed magnetizer  307 ) along the outer boundary  306 , which corresponds to a demagnetization region  310  on the magnetizable material  303 . The resulting field scan  308   b  shows the outer boundary  306  and demagnetization region  310  of the magnetizable material  303 . In  FIG. 3C , a third maxel pattern  300   c  comprising overlapping second polarity maxels  304   c  having a second field strength less than the first field strength that are printed by magnetizing coils  305  (and a pulsed magnetizer  307 ) along the outer boundary  306 , which corresponds to a demagnetization region  310   c  on the magnetizable material  303 . As seen in the field scan  308   c  of  FIG. 3C , the demagnetization region  310   c  is becoming more and more demagnetized on the magnetizable material  303 . In  FIG. 3D , a fourth maxel pattern  300   d  comprising overlapping first polarity maxels  302   d  having a third field strength that are printed by magnetizing coils  305  (and a pulsed magnetizer  307 ) along the outer boundary  306 , which corresponds to a demagnetization region  310   c  on the magnetizable material  303 . As seen in the field scan  308   d  of  FIG. 3D , the demagnetization region  310  is substantially demagnetized on the magnetizable material  303 . 
     In accordance with one method  400  shown in  FIG. 4 , a maxel can be demagnetized by successively printing maxels having reversing polarity and decreasing field strength at the same location. At step  402 , the demagnetizing process is started. At step  404 , establish first magnetizing polarity. At step  406 , establish first magnetizing field strength. At step  408 , move material and/or magnetizing coil to location coordinate for demagnetization. At step  410 , magnetize maxel with established magnetizing field having established magnetic field strength. At step  412 , determine if region has been demagnetized. If result of step  412  is no, then at step  414  reverse established magnetizing polarity and decrease established magnetizing field strength then return to step  410 . If result of step  412  is yes, then at step  416  stop the demagnetizing process. 
     In accordance with another demagnetizing method  500  shown in  FIG. 5 , the demagnetization of a region can involve magnetization of an entire region by printing a plurality of maxels of the same polarity and field strength over the region, rewriting the region with opposite polarity maxels having a lesser field strength, and repeating the previous two steps until the region is demagnetized. At step  502 , the demagnetizing process is started. At step  504 , establish first magnetizing polarity. At step  506 , establish first magnetizing field strength. At step  508 , move material and/or magnetizing coil to first location coordinate for demagnetization. At step  510 , magnetize maxel with established magnetizing polarity with magnetizing field having established magnetic field strength. At step  512 , determine if all locations have been demagnetized. If result of step  512  is no, then at step  514  move material and/or magnetizing coil to next location coordinate for demagnetization and then return to step  510 . If result of step  512  is yes, then at step  516  determine if region has been demagnetized. If result of step  516  is no, then at step  518  reverse established magnetizing polarity and decrease established magnetizing field strength then return to step  508 . If result of step  516  is yes, then at step  520  stop the demagnetizing process. 
     Yet another demagnetizing method  600  is shown in  FIG. 6 , this demagnetizing method  600  involves demagnetizing a region by demagnetizing each maxel location one at a time. At step  602 , the demagnetizing process is started. At step  604 , establish first magnetizing polarity. At step  606 , establish first magnetizing field strength. At step  608 , move material and/or magnetizing coil to first location coordinate for demagnetization. At step  610 , magnetize maxel with established magnetizing polarity with magnetizing field having established magnetic field strength. At step  612 , determine if region has been demagnetized. If result of step  612  is no, then at step  614  reverse established magnetizing polarity and decrease established magnetizing field strength then return to step  610 . If result of step  612  is yes, then at step  616  determine if all locations have been demagnetized. If result of step  616  is no, then at step  618  move material and/or magnetizing coil to next location coordinate for demagnetization and then return to step  604 . If result of step  616  is yes, then at step  620  stop the demagnetizing process. 
     In accordance with the invention, a material can be demagnetized on one side and then demagnetized on the other, or both sides may be demagnetized at the same time. Under another arrangement, only one side may be demagnetized. The depth of demagnetization may or may not correspond to the depth that a material was previously magnetized. Demagnetization can involve printing maxels of alternating polarity with a different magnetization direction then a material was originally magnetized. 
     In accordance with the invention, maxels of a given polarity may overwrite a given region a plurality of times before the polarity of the overwriting maxels is changed. The maxels of the given polarity may be printed by the same print head or multiple print heads as necessary to efficiently overwrite the region. 
     A region to be demagnetized may correspond to an outer boundary of a material such as depicted in  FIGS. 3A-3D , which might be done to limit side interaction between two magnetic structures in which case the width of the demagnetized region can be selected to achieve a desired minimum attractive force between the two structures. A region may be internal to the structure. 
     More generally, demagnetization of a region in accordance with the invention does not have to be complete demagnetization. Instead, the demagnetization process may be used to partially magnetize so as to lower the field strength of a given region. As such, the present invention enables a way of weakening a maxel or a group of maxels. 
     Demagnetization in accordance with the invention can enable conveyance of information, where a sensor can detect demagnetized regions, which can be in accordance with a predefined pattern corresponding to the information. 
     While particular embodiments of the invention have been described, it will be understood, however, that the invention is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings.