WO1995011541A1

WO1995011541A1 - Apparatus and method for reducing electromagnetic fields near electrical power lines

Info

Publication number: WO1995011541A1
Application number: PCT/US1994/012065
Authority: WO
Inventors: David R. Jensen; Billy Dan Jones
Original assignee: Norad Corporation
Priority date: 1993-10-22
Filing date: 1994-10-20
Publication date: 1995-04-27
Also published as: AU8123094A

Abstract

An apparatus and method is provided for reducing the strength of the magnetic field in a region near electric power lines (24, 26, 28) or other devices which generate ELF magnetic fields. The field strength is reduced by creating a second, canceling field by running a current through an appropriately configured canceling conductor (12). An alternative embodiment of the invention relates to the use of various shielding materials (148) which help to shape the field to be canceled through the use of a canceling conductor arrangement.

Description

APPARATUS AND METHOD FOR REDUCING ELECTROMAGNETIC FIELDS

NEAR ELECTRICAL POWER LINES

BACKGROUND OF THE INVENTION

1. -Field of the Invention

5 The present invention relates to an apparatus and method for reducing the magnitude

(strength) of an electromagnetic field (specifically, the magnetic field) in a designated region near electrical power lines, or any other object or device which generates ELF magnetic fields.

10 2. Description of Related Art

In the United States and throughout the world there has been a rising concern by scientists, and an increasing awareness by the general population, of the potential health hazards of magnetic fields like those created by some electrical power lines.

While the inventors are not aware of conclusive evidence that magnetic fields 15 adversely affect living cells, the inventors are aware of a significant public concern of the possibility that such fields can cause cell damage. This concern has had serious affects on the value of property and businesses located near strong power lines or other devices which generate magnetic fields. As a result, there is a need for an effective method and apparatus which will reduce the magnetic field strength in regions near power lines or magnetic field 20 generating devices, thereby alleviating fears regarding the potential effects of such fields on living cells.

The standard power lines which generate significant magnetic fields are high current lines which have significant spatial separation between the wires. Because the lines are spatially separated, there exists a resultant magnetic field in the region surrounding the lines

• 25 whose strength depends upon the relative position of the wires and the location of the point at which the measurement is being made.

Various methods and devices for reducing the magnetic field strength in a given region have been proposed. For example, U.S. Patent No. 5,153,378 (issued Oct. 6, 1992) describes an apparatus for shielding a personal occupancy space (e.g., a small room with a

30 bed) from electromagnetic and geopathic fields. The shields are made of ferrous, wire mesh screening and are erected so as to traverse all three soatial directions. Such an annaratus. however, would not likely be practical for protecting an entire dwelling, office building or other inhabitable structure due to its need to cover the floor and two adjacent walls of the protected region. In addition, the apparatus described in that patent could not shield low frequency magnetic fields. U.S. Patent Nos. 5,002,068 (issued March 26, 1991) and 5, 197,492 (issued Mar. 30,

1993) describe a method for shielding humans and inanimate objects from magnetic fields generated by magnetic resonance imaging devices and the like. The method includes interposing between the subjects and the magnetic field a permanent magnet to create a second magnetic field which cancels or at least partially neutralizes the strength of the first magnetic field in a given region. These patents, however, fail to disclose an apparatus or method which could be used effectively to cancel the magnetic fields generated by an alternating and varying flow of current like that found in power lines.

U.S. Patent No. 5,098,735 (issued Mar. 24, 1992) describes a process which shields occupants of any dwelling from EMF radiation. The process involves coating the dwelling with an organic based composition which absorbs EMF radiation within a certain frequency range. The disadvantages of this process include: (1) the coating cannot be placed on windows, (2) placing the coating on the dwelling is costly and time consuming, and (3) it cannot be used to shield against low frequency magnetic fields.

Finally, Monitor Industries, of Boulder, Colorado has advertised an AC Magnetic Field Cancellation System which cancels AC magnetic fields from power-frequency sources. This system suffers from a number of drawbacks.

More particularly, the Monitor system involves the use of a driven coil which is laid out around the area to be treated, in a plane perpendicular to the dominant field direction. While the driven coil need not be any particular shape, it is usually taped to the walls of a room or placed in a circle or rectangle about the area to be treated.

The magnetic field generated by the driven coil is potentially harmful in the region near the turns of wire which make up the coil. In general, the magnetic field generated by the driven coil is weakest at the center of the coil and strongest close to the wires making up the coil. Accordingly, if the turns of wire are taped to the wall of the room, then the areas near the walls will have substantial magnetic fields. Alternatively, if the driven coil has dimensions which are greater than the treated area, then there will be a region of high magnetic field strength near the turns of wire which must be crossed to get to the treated area. Further, when the driven coil is taped to the walls of a room and oriented to match the dominant field direction, doors and windows of the dwelling inevitably cross the path.

As a result, the coil must deviate around such doors and windows. These deviations tend to reduce the symmetry of the driven coil (and therefore the symmetry of the canceling field). This tends to lead to a reduced effectiveness of the coil.

SUMMARY OF THE DISCLOSURE

The present invention relates to an apparatus and method for reducing the strength of the magnetic field in a region near electrical power lines or any other such source of magnetic fields. According to embodiments of the present invention, the magnetic field of the power lines or the like is canceled or significantly reduced by creating a second, 'canceling' field. The canceling field is created by passing a continuously varying amount of appropriate current through a canceling conductor. The canceling conductor may be designed so that the amount of canceling current which needs to be generated is small in comparison to the amount of current running through the power lines.

In one preferred embodiment of the invention, the canceling conductor is part of a multi-wire current loop which uses a small amount of current (in comparison to the current in the power lines) to generate the canceling field.

In another preferred embodiment, the current in the canceling conductor is varied so as to reduce toward zero the magnetic field reading on a magnetic sensor contained in the region to be shielded from magnetic field.

In another preferred embodiment, passive shielding is used in conjunction with the canceling conductor to further reduce the strength of the magnetic field in a region.

In yet another preferred embodiment, a plurality of canceling conductors are positioned appropriately to achieve a desired level of magnetic field cancellation.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description will be made with reference to the accompanying drawings, wherein like numerals designate corresponding parts in the figures. Figure 1 is a perspective view of an apparatus for reducing the strength of the magnetic field in a region near standard power lines according to an embodiment of the present invention.

Figure 2 is a cross-section view of the canceling conductor shown in Fig. 1. Figure 3 is a cross-section view of an apparatus for reducing the strength of the magnetic field in a region near standard power lines according to an embodiment of the present invention.

Figure 4 is a cross-section of an apparatus for reducing the strength of the magnetic field in a region near standard power lines according to another embodiment of the present invention.

Figure 5 is a perspective view of an apparatus for reducing the strength of the magnetic field in a region near standard power lines according to another embodiment of the present invention. Figure 6 is a perspective view of an apparatus for reducing the strength of the magnetic field in a region near standard power lines according to another embodiment of the present invention.

Figure 7 is a cross-section view of an apparatus for reducing the strength of the magnetic field in a region near standard power lines according to another embodiment of the present invention.

Figure 8a is a plot of the strength of the canceling magnetic field versus the distance along the canceling conductor at a fixed distance from the canceling conductor when a canceling loop like that shown in Figure 1 is used.

Figure 8b is a plot of the strength of the canceling magnetic field versus the distance along the canceling conductor at a fixed distance from the canceling conductor when a canceling loop like that shown in Figure 9 is used.

Figure 9 is a perspective view of an apparatus for reducing the strength of the magnetic field in a region near standard power lines according to another embodiment of the present invention.

Figure 10 is a perspective view of an apparatus for reducing the strength of the magnetic field in a region near standard power lines according to another embodiment of the present invention.

Figure 11 is a perspective view of a room with a circuit panel which generates significant magnetic fields in such room.

Figure 12 is a plot of the magnetic field strength of the field generated by the circuit panel in Figure 11 at a fixed distance from the wall versus the distance away from the edge of the wall (along the line XI). Figure 13 is a perspective view of an apparatus for reducing the strength of the magnetic field in a region near a circuit panel or transformer according to an embodiment of the present invention.

Figure 14 is a cross-section view of a middle layer of the apparatus shown in Figure 13.

Figure 15 is a plot of the strength of the magnetic field generated by the canceling conductor in Figure 14 along the line XV.

Figure 16 is a perspective view of another embodiment of an apparatus for reducing the strength of the magnetic field near a circuit panel or transformer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description is of the presently contemplated mode of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of embodiments of the invention. The scope of the invention is best defined by the appended claims.

Theoretically, placing separate wires, one next to each power line, and each carrying current equal in amplitude and frequency, but 180° out of phase (opposing current) with the line it is placed beside, would nullify the magnetic fields generated by the power lines. Such an approach, however, may not be practical because the magnitude of the current in the canceling wires would have to be on the order of the power line currents.

Embodiments of the present invention relate to a practical apparatus and method for reducing or canceling the magnetic field generated by power lines or the like which is based upon certain physical principles behind such a theoretical approach. Fig. 1 shows one preferred embodiment of the invention, wherein the magnetic field reducing system includes a canceling conductor 12. The canceling conductor 12 is used to generate a second magnetic field to reduce or cancel the magnetic field in a specified region (the "shielded region") near power lines, like those shown in Fig. 1 as 24, 26, and 28. In general, the magnetic field generated by the canceling conductor 12 is oppositely directed to the field created by the power lines and results from running a current through canceling conductor 12. Such current can be varied to correctly reduce or cancel the field generated by the power lines in the shielded region.

A return conductor 14 is included in the preferred embodiment of Fig. 1 as a return path for current flow. It should be noted that while a return conductor is discussed in this preferred embodiment, it is not essential to the present invention, i.e., other returns, including the ground could be used. The canceling conductor 12 and return conductor 14 are electrically coupled to connecting conductor 34a or 34b (depending on whether an above surface or below ground route is used to power the canceling conductor). The connecting conductor 34a (or 34b) electrically couples the canceling and return conductors to a variable power source 36. The variable power source 36 is used to provide an appropriate canceling current in the canceling conductor 12 for reducing or canceling the magnetic field produced by the power lines, as discussed above. The canceling conductor 12, return conductor 14 and connecting conductor 34a (or 34b) together form a closed current loop through which the canceling current flows.

In one preferred embodiment, the variable power source 36 plugs into a standard electrical power outlet in the house or building 38 to be protected from magnetic fields. In further embodiments, the variable power source may be located outside of the region to be shielded. The variable power source 36 is connected to a sensing mechanism 40 and adjusts the amount of current in the canceling conductor 12 so that the magnetic field in the house or building 38 is eliminated or significantly reduced. The sensing coil or other sensing mechanism 40 (e.g., a pickup coil) can be placed inside or outside the house or building to determine the strength of the magnetic field in the region to be shielded. To eliminate or reduce the magnetic field, the power source (i.e., the current in the canceling conductor) should be adjusted to bring the sensor readings toward or to zero. Such an adjustment is preferably made automatically by suitable current regulating circuitry, although it may be performed manually.

Like the canceling conductor 12, the return conductor 14 generates its own magnetic field whenever a current is run therethrough. While the magnetic field generated by the return conductor 14 tends to negate the field generated by the canceling conductor 12, its affect may be reduced by placing it a suitable distance away from both the shielded region and the canceling conductor 12. In most, but not all instances, the distance between the canceling conductor 12 and return conductor 14 should preferably be as large as practical.

The size of the shielded region is dependent, in part, on the distance between the canceling conductor 12 and the power lines 24, 26, and 28; i.e., the closer the canceling conductor 12 is to the power lines, the larger the shielded region. In the Fig. 1 embodiment of the invention, the canceling and return conductors are suspended above the ground by a pair of suspension masts, 16 and 18. As shown in Fig. 1, the suspension masts are placed a distance "x" from the suspension masts, 20 and 22, which hold up the three power lines, 24, 26, and 28. The distance "x" can be any practical distance, but depends in large measure on the height of the power lines, the distance between the power lines and the house or building to be protected, and the strength of the field to be canceled. In a preferred arrangement the distance "x" may be about ten (10) feet.

The suspension masts 16 and 18 each have a cross bar, 30 and 32, respectively, from which the canceling conductor 12 and return conductor 14 hang. The cross bars 30 and 32 are located a distance "y" above the ground. As with the distance "x", the distance "y" depends on a number of variables, but preferably should be at least fifteen (15) feet for a standard arrangement. Note also that the cross bars may be tiltable to allow the canceling conductor to be positioned so as to achieve maximum field cancellation or reduction.

While the description above refers to only two suspension masts, the invention should not be viewed as being so limited. The canceling and return conductors may be hung from a series of masts, e.g., arranged about part of the periphery of the protected region (see, e.g., mast 42 in Fig. 1). Such an arrangement of suspension masts allows less current to be used to cancel the magnetic field generated by the power lines because the canceling fields created by each section of canceling conductor (i.e., the portion of the canceling conductor which is suspended between consecutive masts) add together to form the net canceling field.

As mentioned above, it may be undesirable and impractical to provide a large current flow (perhaps on the order of 200 Amperes) through the current loop created by the canceling conductor 12, return conductor 14, and connecting conductor 34a (or 34b). In preferred embodiments of the present invention, the amount of current required from the power source 36 is greatly reduced by using a multi-wire current loop. Such a design takes advantage of the fact that the magnetic field generated by two wires, with the same magnitude and direction of current flow as a single wire, is twice as strong as the magnetic field generated by the single wire. Thus, if in a given situation it would take 200 Amperes of current in a single canceling wire to nullify the magnetic field generated by a set of power lines, then a twenty (20) turn bundle of canceling wires carrying ten (10) Amperes per wire would generate the same canceling field.

Fig. 2 shows a cross-section view of one embodiment of the canceling conductor 12 shown in Fig. 1. The canceling conductor 12 is designed as a multi-wire bundle. As shown in Fig. 2, a multi-wire bundle 43 may be supported by a small support cable 44. The multi- wire bundle of Fig. 2 is formed of twenty (20) insulated copper wires 46 supported by cable 44, all within an outer sheath 45. Preferably, the number of wires in the bundle 43 is chosen so that the voltages and canceling currents involved will be relatively low. For example, the number of wires in the bundle 43 may be chosen such that the canceling current is no more than about ten (10) Amperes per wire maximum.

When the embodiments of the invention described herein are used in a specific setting, two factors should be considered:

(1) the proximity of the canceling conductor to the power lines, and

(2) the proximity of the canceling conductor to its own return conductor. By arranging the canceling conductor closer to the power lines, a greater area of magnetic field cancellation can be achieved. Likewise, the greater the distance between the canceling conductor and the return conductor, the lower the canceling current needed to provide an appropriate canceling field. By adjusting these two factors, a desired amount of field reduction or cancellation may be provided. In practice, there may be physical or legal barriers which prevent a user from placing the canceling conductor close enough to the power lines (or other source of magnetic field) so as to achieve the desired canceling effect in a specified region to be protected from magnetic fields. In such a case, other preferred embodiments of the invention may be employed (see, e.g, Figure 4) in which a series of canceling conductors generate an appropriate canceling field.

Figure 3 depicts an arrangement in which a single canceling conductor 52 and return conductor 54 create a magnetic field, Bj, which is used to cancel the magnetic field, B„ created by the power lines (indicated generally by 68). In such an arrangement, magnetic fields Bj (shown with clockwise direction) and Bj (shown with counter-clockwise direction), have approximately opposite directions in the region between lines L_t and L₂ (shown in Fig. 3). By appropriately adjusting the strength of magnetic field, B₂, a sizable region of significant field cancellation(or substantial reduction) can be created between the lines L_t and Lj, so long as the distance "w" between the power lines and the edge of a region to be protected is large compared to the distance "x" between suspension masts 56 and 60. When the distance "x" cannot be made small compared to the distance " w" , a plurality of properly placed canceling conductors may be used to achieve the desired amount of field cancellation in a specified region. Figure 4 depicts an embodiment in which three (3) canceling conductors 90, 91, and 92 are used to cancel the field generated by the power lines. Because the distance "x" between the suspension masts 76 and 80 is not small compared to the distance "w" between the power lines and the edge of a region to be protected, a single canceling conductor can only effectively cancel the field generated by the power lines in a small region. As can be seen in Figure 4, if only the canceling conductor 92 is used, the region of significant magnetic field cancellation or reduction (the region between lines L_x and Lj) would be very narrow.

If, however, a plurality of canceling conductors are used and optimally positioned, the magnetic fields of the canceling conductors work together to cancel or reduce the magnetic field of the power lines. In Figure 4, the magnetic fields B__>, B-j, and B₄ generated by canceling conductors 92, 91, and 90 combine to effectively cancel or reduce the magnetic field, B_1} of the power lines in the region between I---, and ₃ (for ease of discussion the effect of the magnetic field generated by the return conductor 94 is neglected). While the figure illustrates the use of three canceling conductors, the invention should not be so limited. Nor should the invention be limited to a positioning of the canceling conductors in a straight line as shown. Instead the choice of the number and positioning of the canceling conductors should be made to achieve maximum field cancellation or reduction in a specified region by taking into consideration the practical, physical, and geometrical constraints of the particular environment.

Figures 5 and 6 illustrate further embodiments of a suspension system for a multi- canceling conductor apparatus. Referring to Figure 5, a suspension system is shown having suspension masts 102 and 104. Cross bars 106 and 108 are operatively coupled to suspension masts 102 and 104, respectively, in a manner which allows the cross bars to be rotated about pivot joints 101 and 103 to an appropriate angle relative to the power lines. Cross bars 106 and 108 support canceling conductors 121a-f. Also shown in Figure 5 are cross bars 110 and 112. These cross bars are operatively coupled to cross bars 106 and 108, respectively, in a manner which allows the cross bars to be rotated about pivot joints 109 and 111 to an appropriate angle relative to the such cross bars. Cross bars 110 and 112 support return conductor 124.

Referring to Figure 6 a suspension system is shown having suspension masts 126 and 128. Cross bars 134 and 136 support canceling conductors 137a-c and may be rotated about pivot joints 135 and 139 to an appropriate angle relative to the power lines. Cross bars 130 and 132 support return conductor 138.

In the preferred embodiment illustrated in Figure 7, another canceling loop arrangement is shown for use when the canceling conductor cannot be placed near the power lines. In this embodiment, two canceling loops are used. The masts 176 and 178 are each part of separate canceling loops which may be similar to the loops described in connection with Figures 1, 5 or 6. The canceling loops associated with masts 176 and 178 are placed on opposite sides of the region to be shielded 180, with the canceling loop associated with mast 178 nearest the power lines. In this embodiment, the net canceling field results from a superposition of the fields generated by the loops associated with masts 176 and 178. By using a second current loop like that associated with mast 176, which produces a lower canceling field by using less current or less turns of wire in a multi-wire bundle, the resultant canceling field can be made to decrease in strength so as to effectively approximate the linear drop off of the field strength of the magnetic field created by the power lines. The second loop is used to address the problem of the first loop being unable to cancel the field of the power lines over any significant distance when the first loop cannot be placed near the power lines.

While the embodiments of the invention disclosed above all show the canceling conductor(s) running approximately parallel to the return conductor and the power lines, this need not always be the case. In other preferred embodiments, the canceling and return conductors may be positioned advantageously relative to each other and the power lines to achieve the desired cancellation in any given situation.

For example, in the Figure 1 embodiment, the canceling field strength near the end of the canceling loop drops off as shown in Figure 8a. If that area still needs to be canceled, small "shimming" loops 170 and 172 can be included in the canceling arrangement as shown in Figure 9.

Alternatively, a canceling arrangement as illustrated in the preferred embodiment of Figure 10 may be used to generate the proper canceling field, if this type of set up is more appropriate to the situation. In Figure 10, instead of having the canceling and return conductors run approximately parallel to the power lines, canceling loops are placed on opposites sides of the region to be shielded 200 with canceling conductors 192 and 194 running transverse to the power lines 190. The strength of the canceling field is made to decrease as the distance from the power lines increases by adjusting the spacing between (i) the return conductors 196 and 198 and the (ii) canceling conductors 194 and 192, respectively. The spacing between the respective return and canceling conductors is largest near the power lines and decreases as the distance from the power lines increases.

The net canceling field results from the superposition of the fields generated by each of the canceling and return conductor current loops. Since the field of a long wire drops of linearly, the superposition of the fields generated by these two loops results in a nearly constant strength field along any line running parallel to the power lines. Accordingly, by appropriately adjusting (i) the current in the canceling conductors 192 and 194 and (ii) the spacing between the return and canceling conductors, a resultant canceling field can be shaped to effectively cancel or reduce the magnetic field generated by the power lines. While the embodiments of the invention discussed above contemplate the use of a single return conductor and canceling conductors which carry equal amounts of current, the invention is not so limited. In other embodiments of the invention, it is possible to use a plurality of appropriately positioned return conductors to achieve a desired amount of magnetic field cancellation. Further, the current in any particular canceling or return conductor may adjusted relative to the current in any other conductor in order to shape a desirable canceling magnetic field.

A further preferred embodiment of the invention can be used to shield a building, or rooms therein, from magnetic fields generated by a transformer or a circuit panel which may be located in or behind a wall or floor of a building. Figure 11 shows a circuit panel 140, placed in a wall 142, which generates a magnetic field that is primarily directed normal to the wall.

Figure 12 is a plot of the magnetic field strength of the field generated by the circuit panel in Figure 11 at a fixed distance from the wall versus the distance away from the edge of the wall 145 (along the line VD). As can be seen from the solid line, the field is peaked in the region between the edges of the circuit panel 141 and 143.

Figure 13 shows an embodiment of an apparatus to reduce or cancel the field strength in the room. Figure 13 illustrates a three layer panel 146 which reduces the magnetic field strength near the circuit panel. The canceling panel 146 is preferably the size of the circuit panel 140. However, if the panel 146 cannot be placed adjacent to the circuit panel, then it may be slightly larger than such circuit panel. In normal operation, the panel 146 is placed against the wall 142. However, the panel 146 could also be placed behind the outer layer of the wall if there is room to fit the panel 146 between the circuit panel and the wall.

The layer 148, which is placed closest to the source of the magnetic field (i.e., the circuit panel), is a thin metal layer (perhaps 14 mils or thicker). It may be made of low carbon steel, or other high permeability metals, such as mu-metal or silicon steel. The purpose of this layer is to: (1) even out the field generated by the circuit panel and make it more uniform as it leaves the source of the field and (2) act as a shield reducing the strength of the field in the room. The fact that a thin metal layer can be used to even out the field lines and reduce the field strength follows directly from Maxwell's equations.

The dashed, approximately horizontal curve in Figure 12 shows the strength of the magnetic field generated by the circuit panel at a fixed distance from the wall versus the distance away from the edge of the wall 145, in a situation where a layer 148 is placed against the wall. As can be seen from the Figure, placing the layer 148 in front of the wall reduces the strength of the field and makes it more uniform. This is advantageous because a uniform field is more easily canceled than a field which varies significantly over a specified region.

The middle layer 150 of the panel 146 includes a canceling conductor 154, a sensing coil 156, and a filler material layer 158. As illustrated in Figure 14, the canceling conductor 154 and sensing coil 156 each form a loop and are placed near the perimeter of the panel on a plane parallel to the wall between the thin metal layer 148 and the electric circuit panel. It is also contemplated that the sensing coil could be smaller than the canceling conductor 154 and placed within the loop created by the canceling conductor or at some other location inside the room or in the area near or on the circuit panel itself. The sensing coil could be sensing either the magnetic fields generated by the electrical panel or, alternatively, could be designed to sense the electrical current which is the cause of the magnetic field.

In the case where the sensing coil and the canceling coil are in the same plane, and since the canceling conductor and sensing coil are not completely flat, a filler material layer 158, made of Masonite or other similar material (perhaps an eighth of an inch thick), is placed on the layer 148 in the region inside the loops created by the canceling conductor and the sensing coil. In a case where the sensing coil is substantially within the canceling coil, the sensing coil may be placed within the external boundary of the filler material.

A lead 160 runs from the canceling conductor 154 to a variable power source (not shown) so that an appropriate canceling current can be provided to cancel the field generated by the circuit panel 140. A lead 162 runs from the sensing coil 156 to a sensing mechanism (also not shown). The amount of current provided by the power source may be adjusted automatically by a suitable controller which is electronically coupled to both the sensing mechanism and the variable power source.

One of the advantages of having a sensing coil which runs around d e perimeter of the source of the field, instead of over a much smaller region, is that the coil senses the majority of the magnetic flux which enters the room rather than just a small isolated portion of such flux. The sensing coil shown in Figure 14 can be used to achieve a better average cancellation of field throughout the room than a smaller coil which (i) only senses the field over a limited region, and (ii) is used to adjust the canceling current to cancel the field sensed in this limited region.

Figure 15 depicts, generally, the strength of the magnetic field generated by the canceling conductor 154 inside the canceling conductor loop, along the line XV. As should be clear, if a small sensing coil is placed in the center of the canceling conductor loop, and if a canceling current is provided to cancel the field sensed by such sensing coil, there will exist a region near the canceling conductor where the field strength is high. As discussed above, the use of a sensing coil as shown in Figure 10, in combination with the magnetically permeable material which evens out the field, tends to avoid the problem of creating a region of strong magnetic field by having the coil sense the entire field. In this manner, when the canceling current is adjusted to bring the sensor readings toward or to zero, the average field is canceled or reduced rather than the field in a particular region.

In a preferred embodiment, a thin metal layer 152 is placed adjacent to the middle layer 150. The purpose of this layer is to spread out and reduce the strength of any magnetic field which is not completely canceled. Thus, if regions exist where the field strength is somewhat high, the field in this region will be further reduced and spread out more uniformly, leaving the room free from strong magnetic fields.

In further preferred embodiments as shown in Fig. 16, the layer 148', which is placed closest to the source of the magnetic field (for example, a circuit panel), includes the canceling coil and is mounted against and backed by one or more additional layers, 150', 152', which, in these further embodiments, comprise one or more layers of magnetic permeable metal (perhaps as thin as 14 mils). Layer 150' may be made of low carbon steel, or other high permeability metals, such as mu-metal or silicon steel, which functions to: (1) even out the field generated by the circuit panel and make it more uniform as it leaves the source of the field and (2) act as a shield reducing the strength of the field in the room. Layer 152' of panel 146' could be either another layer of magnetically permeable material or a layer of conductive shielding material (i.e. , aluminum or copper). If layer 152' is magnetically permeable, its purpose is to further smooth the fields remaining from layer 150' and to provide further shielding for the room. If layer 152' is a layer of conductive material, its purpose is to generate eddy currents from any residual fields penetrating through layer 148' and 150' and, by generating an apposing field, cancel these residual fields.

The presently disclosed embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are, therefore, intended to be embraced therein.

Claims

WHAT TS ΓLATMFD TSΪ

1. An apparatus for reducing the strength of a magnetic field in a region in the vicinity of power lines or any other source of ELF magnetic fields comprising: a canceling conductor extending around less than the full perimeter of said region; and a variable current source for providing a variable flow of current through said canceling conductor.

2. An apparatus as recited in claim 1, additionally comprising a return conductor operatively coupled between the canceling conductor and the variable current source.

3. An apparatus as recited in claim 1, additionally comprising: a magnetic sensor located within the region to sense the magnetic field within the region, the magnetic sensor being operatively coupled to the variable current source to vary current in the canceling conductor dependent upon the strength of the magnetic field sensed in the region; and at least one support structure for supporting said canceling conductor and said return conductor in the vicinity of power lines or other source of ELF magnetic field.

4. An apparatus as recited in claim 2, additionally comprising at least one support structure for supporting said canceling conductor and said return conductor in the vicinity of power lines or other source of ELF magnetic field.

5. An apparatus as recited in claim 1 , wherein said canceling conductor comprises a plurality of wires bundled together.

6. An apparatus as recited in claim 2, wherein said canceling conductor and said return conductor each comprise a plurality of wires bundled together.

7. An apparatus for reducing the strength of a magnetic field in a region in the vicinity of power lines or any other source of ELF magnetic fields comprising: a canceling conductor extending around less than the full perimeter of said region; a variable current source for providing a variable flow of current through said canceling conductor; and a magnetic sensor located within the region to sense the magnetic field within the region, the magnetic sensor being operatively coupled to the variable current source to vary current in the canceling conductor dependent upon the strength of the magnetic field sensed in the region.

8. An apparatus as recited in claim 7, additionally comprising a return conductor operatively coupled between the canceling conductor and the variable current source.

9. An apparatus as recited in claim 8, additionally comprising a means for supporting said canceling conductor and said return conductor in the vicinity of power lines or other source of ELF magnetic field.

10. An apparatus as recited in claim 7, wherein said canceling conductor comprises a plurality of individually insulated wires bundled together.

11. A method for reducing the strength of a first magnetic field in a region in the vicinity of power lines or any other source of ELF magnetic field, the method comprising the steps of: placing a canceling conductor around less than the full perimeter of said region; and providing a flow of current in said canceling conductor of sufficient magnitude and direction so that a second magnetic field created by said flow of current cancels or significantly reduces the strength of the first magnetic field.

12. A method as recited in claim 11, the method comprising the additional step of placing a magnetic sensor in said region.

13. A method as recited in claim 11, the method comprising the additional step of providing said flow of current in a return conductor which is electrically coupled to said canceling conductor.

14. A method as recited in claim 13, the method comprising the additional step of supporting said canceling conductor and said return conductor in the vicinity of the power lines or other source of ELF magnetic field.

15. A method as recited in claim 13, wherein the step of providing said flow of current in said canceling conductor and said return wire includes providing said current flow in a plurality of wires bundled together to form said canceling conductor and said return conductor.

16. An electrical network comprising: a plurality of electrical power lines or other source of ELF magnetic field; a canceling conductor extending around less than the full perimeter of a region to be shielded from magnetic fields; and a variable current source for providing a variable flow of current through said canceling conductor.

17. An electrical network as recited in claim 16, additionally comprising a return conductor operatively coupled between the canceling conductor and the variable current source.

18. An electrical network as recited in claim 16, additionally comprising a magnetic sensor located within the region to sense the magnetic field within the region and operatively coupled to the variable current source to vary current in the canceling conductor dependent upon the strength of the magnetic field sensed in the region.

19. An electrical network as recited in claim 17, additionally comprising a means for supporting said canceling conductor in the vicinity of the power lines or other source of ELF magnetic field.

20. An apparatus as recited in claim 17, wherein said canceling conductor and said return conductor each comprise a plurality of wires bundled together.

21. An apparatus for reducing the strength of a magnetic field in a region near a circuit panel, a transformer, or other source of ELF magnetic field comprising: a canceling conductor which forms a current loop; a variable current source for providing a variable flow of current through said canceling conductor; and a first metal sheet placed adjacent to said canceling conductor.

22. An apparatus as recited in claim 21, additionally comprising a magnetic sensor generally located within a plane defined by the current loop formed by said canceling conductor to sense the magnetic field entering the region and operatively coupled to the variable current source to vary current in the canceling conductor dependent upon the strength of the magnetic field sensed.

23. An apparatus as recited in claim 21, additionally comprising a second metal sheet placed on an opposite side of a plane defined by the current loop formed by said canceling conductor from the first metal sheet.

24. An apparatus as recited in claim 23, additionally comprising a filler material placed between the first and second metal layers in a region within the current loop formed by said canceling conductor.

25. A method for reducing the strength of a first magnetic field in a region near a circuit panel, a transformer, or other source of ELF magnetic field, the method comprising the steps of: placing a first metal sheet adjacent the circuit panel, transformer, or other source of ELF magnetic field; and providing a flow of current in a canceling conductor loop, situated adjacent to the first metal sheet, of sufficient magnitude and direction so that a second magnetic field created by said flow of current cancels or significantly reduces the strength of the first magnetic field.

26. A method as recited in claim 25, the method comprising the additional step of placing a magnetic sensor within a plane defined by the current loop formed by said canceling conductor to sense the magnetic field entering the region and operatively coupled to a variable current source to provide varied current in the canceling conductor dependent upon the strength of the magnetic field sensed.

27. A method as recited in claim 26, the method comprising the additional step of placing a second metal sheet on an opposite side of a plane defined by the current loop formed by said canceling conductor from the first metal sheet.

28. An apparatus for reducing the strength of a magnetic field in a region in the vicinity of power lines or any other source of ELF magnetic fields comprising: a plurality of appropriately positioned canceling conductors extending around less than the full perimeter of said region; and a variable current source for providing a variable flow of current through said plurality of canceling conductors.

29. An apparatus as recited in claim 28, additionally comprising at least one return conductor operatively coupled between said plurality of canceling conductors and the variable current source.

30. An apparatus as recited in claim 28, additionally comprising a magnetic sensor located within the region to sense the magnetic field within the region, the magnetic sensor being operatively coupled to the variable current source to vary current in said plurality of canceling conductors dependent upon the strength of the magnetic field sensed in the region.

31. An apparatus as recited in claim 29, additionally comprising means for supporting said plurality of canceling conductors in the vicinity of power lines or other source of ELF magnetic field.

32. An apparatus as recited in claim 30, additionally comprising means for supporting said plurality of canceling conductors in the vicinity of power lines or other source of ELF magnetic field.

33. An apparatus as recited in claim 28, wherein each of said plurality of canceling conductors comprises a plurality of wires bundled together.

34. An apparatus as recited in claim 29, wherein each of said plurality of canceling conductors and each of said at least one return conductor comprise a plurality of wires bundled together.

35. A method for reducing the strength of a first magnetic field in a region in the vicinity of power lines or any other source of ELF magnetic field, the method comprising the steps of: placing a plurality of appropriately positioned canceling conductors around less than the full perimeter of said region; and providing a flow of current in said plurality of canceling conductors of sufficient magnitude and direction so that a second magnetic field created by said flow of current cancels or significantly reduces the strength of the first magnetic field.

36. A method as recited in claim 35, the method comprising the additional step of placing a magnetic sensor in said region.

37. A method as recited in claim 35, the method comprising the additional step of providing said flow of current in at least one return conductor which is electrically coupled to said plurality of canceling conductors.

38. An apparatus as recited in claim 21, additionally comprising a magnetic sensor to sense the magnetic field entering the region or the electrical current which is causing the magnetic field and operatively coupled to the variable current source to vary current in the canceling conductor dependent upon the strength of the magnetic field or electrical current sensed.

39. An apparatus as recited in claim 21, additionally comprising a second metal sheet or sheets placed on an opposite side of a plane defined by the first metal sheet from the current loop formed by said canceling conductor.

40. An apparatus as recited in claim 39, additionally comprising a filler material placed between the ELF magnetic field source and the first metal layer in a region within the current loop formed by said canceling conductor.

41. A method as recited in claim 25, the method comprising the additional step of placing a magnetic sensor or electrical current sensor to sense the magnetic field entering the region or the current causing the magnetic field, and operatively coupled to a variable current source to provide varied current in the canceling conductor dependent upon the strength of the magnetic field or electrical current sensed.

42. A method as recited in claim 41 , the method comprising the additional step of placing a second metal sheet or sheets on an opposite side of a plane defined by the first metal sheet from the current loop formed by said canceling conductor.