Abstract:
A device and a method for its use to attenuate electromagnetic noise, such as that caused in power supply line current by back-emf from devices being powered, in order to provide cleaner, or more regular alternating current and voltage waveforms. A permanently magnetized magnet is held close to a conductor cable for an alternating current, in a case, which may also hold a permeable material extending from the magnet and at least partly surrounding the cable. Multiple magnets may be included, arranged parallel with each other and with like poles adjacent or facing each other, forming a tubular arrangement about the cable.

Description:
This application claims the benefit of U.S. provisional application Ser. No. 60/114,956, filed Jan. 5, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the attenuation of common mode electromagnetic noise in the vicinity of electrical power, audio signal, and video signal cables, especially noise frequencies below 1 MHz, and in particular relates to attenuation of such noise in consumer and professional audio and video electronics cables. 
     Although electrical power utility companies attempt to provide a reasonably pure alternating current power supply to their customers, ordinary electrical power circuit wiring acts as an antenna and commercial line power thus is affected by electromagnetic noise originating from many sources. Much of such noise found in electrical power lines is related to the line frequency and its related harmonics and sub-harmonics, and some of such noise is caused by transient currents resulting from power source phase variations brought on by changing loads imposed by motors, etc. Imbalances in the utility transformer circuit of the power line can cause transient direct currents superimposed on the alternating current. All of the above can result in noise in the power line and affect the ideal sine wave form of the alternating current in the power line. 
     Noise may also be conducted into a power line from consumer electronics or electrically-powered devices. Changing power source loads imposed by power supplies in computers, digital audio electronics, video circuits, amateur radio devices, citizens, band transceivers, and household appliances all can contribute to changing electromagnetic flux fields whose lines of force are cut by a power cable located in the vicinity of such a device, and transient voltages can be fed back into the power source directly from electrical and electronic devices. 
     The performance of electronic devices can be noticeably affected by the presence of variations in the voltage wave form in the line power supply. In particular, the output of audio and video reproduction devices can be noticeably degraded by noisy power line voltage wave forms. Ferrite materials are commonly used to attenuate common mode circuit noise, as mentioned in Matsui U.S. Pat. No. 4,873,505, Fujioka U.S. Pat. Nos. 4,882,561 and 4,972,167, and Nakano U.S. Pat. No. 4,885,559. It is thus known to place a quantity of magnetizable material in the form of powdered ferrite carried in a matrix of an elastomeric material in the vicinity of a power cable, as mentioned in those patents. A problem with such use of ferrite materials is that the permeability of the material works well only in the higher frequency ranges of 10 MHz to 100 MHz. The ferrite material performs poorly at frequencies between 0 and 1 MHz with respect to attenuating common mode noise in an electrical conductor cable. 
     It is well known to provide shields of electrically conductive material and layers of ferro-magnetic material surrounding electrical conductor cables located in the vicinity of transient voltages, as disclosed, for instance, in Rogers, U.S. Pat. No. 5,349,133, Baigrie, et al., U.S. Pat. No. 4,816,614, and Palmer U.S. Pat. No. 5,548,082. Such shielding, however, is somewhat costly and is not particularly convenient to use, and it has not been particularly effective in the frequency range from 0 to 1 MHz. 
     While it is also known to use sophisticated and expensive electronic circuits in the power supply circuits of audio and video electronic devices to eject harmonics and other signals to arrive at a clean internal power supply output, what is desired is a device and a method for its use at a relatively low cost to provide noticeable improvement in the performance of electronic devices by attenuating the effects of electromagnetic noise on power cables, audio signal cables, and video signal cables. 
     SUMMARY OF THE INVENTION 
     The present invention provides an answer to the aforementioned need for a method and a device of relatively low cost for attenuating noise caused by incidental electromagnetic fields and stray or transient currents in alternating current cables and audio or video signal cables, through placement of a permanently magnetized magnet, preferably of relatively high field strength, in close proximity to an electrical conductor cable in which it is intended to attenuate electromagnetic noise from a desired signal. Use of the method and apparatus of the invention results in noticeable improvement in the audio and video output performance of electronic devices. 
     According to the present invention a permanent magnet may preferably be placed and retained as closely practical alongside an electrical conductor cable, with an axis extending between the poles of the magnet oriented generally parallel with the length of the cable. 
     In accordance with the method of the present invention a permanently magnetized magnet may be so located and held in proximity to a cable providing main power to an electronic device, a cable carrying alternating current power between a power panel and an electronic device, or an analog or digital signal conductor cable, to produce improvement in the perceived output quality of audio equipment such as CD players and phonographs, or of DVD playback equipment and other video reproduction electronic equipment. 
     In a device that is one embodiment of the invention a pair of permanently magnetized magnets may be similarly oriented magnetically and kept in place on opposite sides of a conductor cable, with quantities of magnetically permeable magnetic material, such as an appropriately formed sheet of iron, extending around the magnets and the cable to shape a magnetic field surrounding the cable. 
     Preferably a permanently magnetized magnet and such a piece of magnetic material is contained in each part of a two-part case, which is held together around a cable by suitable fasteners. 
     In a device that is one embodiment of the invention permanently magnetized material of one or more permanent magnet elements may itself be of a shape to enclose and surround a portion of the length of a cable of two or more electrical conductors, with axes of polarity of such permanent magnet elements extending generally parallel with the portion of the conductor cable along which the permanently magnetized material is located. 
     In another embodiment of the invention one or more permanent magnets may be located in proximity to a cable, with the poles of the magnet located in such a manner that the lines of force extend predominantly transversely with respect to a longitudinal axis of the cable, but this orientation apparently is less effective than having the axes of polarity parallel with the longitudinal axis of the cable. 
     While it is not fully understood how the method and apparatus of the present invention provide the desired attenuation of spurious and transient signals imposed on an electronic signal of a predetermined desired wave form and frequency, it appears that the performance of the invention is improved when the field strength of the permanent magnet is greater, and particularly when the field strength in the vicinity of the cable with which such a device according to the present invention is used is at least 1000 Gauss. 
     It has been found that the present invention is apparently effective with respect to use of a device incorporating the invention on conductor cables including parallel pairs of conductors carrying alternating current, parallel pairs associated with a parallel ground conductor, twisted pairs of conductors, and shielded coaxial pairs of conductors. 
     The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a perspective view of an electronic noise attenuator device embodying the present invention. 
     FIG. 2 is a top plan view of the noise attenuator device shown if FIG.  1 . 
     FIG. 3 is a right end view of the electromagnetic noise attenuator device shown in FIGS. 1 and 2, the left end view being a mirror image thereof. 
     FIG. 4 is a partially cutaway side elevational view of the device shown in FIGS. 1-3. 
     FIG. 5 is a section view of the device shown in FIG. 1 taken along line  5 — 5  thereof. 
     FIG. 6 is a simplified end view of the arrangement of the magnets and shields included in the device shown in FIG. 1, shown together with a length of an electrical conductor cable, the case shown in FIGS. 1-5 being omitted for the sake of clarity. 
     FIG. 7 is a right side view of the arrangement of magnets and shields shown in FIG. 6, together with a length of electrical conductor cable. 
     FIG. 8 is a simplified end view of an arrangement of a pair of magnets in accordance with the method of the present invention, together with a length of electrical conductor cable, a case to hold the magnets in place with respect to the cable being omitted for the sake of clarity. 
     FIG. 9 is a right side view of the arrangement of magnets and length of cable shown in FIG.  8 . 
     FIG. 10 is a simplified end view of a single magnet and a length of electrical conductor cable arranged in accordance with the method of the present invention. 
     FIG. 11 is a right side view of the length of cable and magnet shown in FIG.  10 . 
     FIG. 12 is an end view of a pair of permanent magnets each defining a semi-cylindrical cavity, arranged in accordance with the method of the present invention, together with a length of electrical conductor cable. 
     FIG. 13 is a right side view of the magnets and length of cable shown in FIG.  12 . 
     FIG. 14 is a simplified view of an electric power service panel showing the locations of several electromagnetic noise attenuators according to the invention in place on branch electrical power distribution cables in accordance with the method of the invention. 
     FIG. 15 is a simplified pictorial view of an electromagnetic noise attenuator device according to the present invention in place on a detachable AC power cord for an electronic device. 
     FIG. 16 is a simplified pictorial view of an electromagnetic noise attenuator device according to the present invention in place on an AC power extension cord equipped with multiple power outlet sockets. 
     FIG. 17 is a simplified pictorial view of an electromagnetic noise attenuator device according to the present invention in place on the AC power cord of a radio receiver. 
     FIG. 18 is a simplified pictorial view of an electromagnetic noise attenuator device according to the present invention in place on the AC power cord of a phonograph turntable. 
     FIG. 19 is a simplified pictorial view showing the location of multiple electromagnetic noise attenuators according to the present invention in place on the AC power cord, input signal cables, and output signal cables of an amplifier. 
     FIG. 20 is a simplified pictorial view of several electromagnetic noise attenuator devices according to the present invention in use in accordance with the method of the present invention on AC power cords, a digital signal cable, and analog signal output cables of a sound reproduction system including a CD player and a digital-to-analog converter. 
     FIG. 21 is a simplified pictorial view of several electromagnetic noise attenuator devices according to the present invention in use in accordance with the method of the present invention on the AC power cords of a video monitor and an electronic device providing video output signals, as well as on analog and digital signal cable connected therewith. 
     FIG. 22 is a simplified view of an electronic device including a power transformer and circuitry driven by the output from the power transformer secondary side, with electromagnetic noise attenuator devices according to the present invention within the chassis of the electronic device. 
     FIG. 23 is a perspective view of a pair of permanent magnets arranged to cooperatively form a cylindrical tube of permanently magnetized material for use in accordance with the present invention. 
     FIG. 24 is a perspective view of a tubular magnet for use in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings which form a part of the disclosure herein, and in particular referring to FIGS. 1-5, an electronic noise attenuator  22  includes a case  24  having an upper half  26  and a lower half  28  normally held together by suitable fasteners such as a pair of screws  30  extending through appropriate bores in the upper half  26  into threaded bores  32  in the lower half  28 . The upper and lower halves  26 ,  28  are further kept aligned with each other by suitable pins such as brass pins  34  fitting in corresponding holes in the upper and lower halves  26 ,  28 . The screws  30  and pins  34  should be of non-magnetic material, and the case  24  should similarly be of non-magnetic material. For example, the upper and lower halves  26 ,  28  of the case may be of a suitable injection-molded synthetic plastic resin. 
     The case  24  is generally elongate and has a pair of aesthetically rounded opposite ends  38  and  40 , resulting in a length  42 , which may in one preferred embodiment of the invention be about four inches. A slightly depressed flat surface  43  may be provided on each half of the case  24  as a location for a label. The upper and lower halves  26  and  28  of the case  24  define respective halves of a cylindrical cable-receiving passageway  44  extending along a central longitudinal axis of the case  24 . The cable-receiving passageway  44  may have a diameter  46  of, for example, about 0.625 inch, in order to accommodate a power cable of ample size for a powerful audio amplifier. The attenuator  22  can thus be assembled with a cable (not shown in FIGS. 1-5) extending through the case within the cylindrical cable-receiving passageway  44  by attaching the upper half  26  tightly to the lower half  28  and fastening the halves of the case  24  together with the screws  30 . 
     A permanent magnet  48  and a shield member  50  of magnetically permeable ferro-magnetic material, which is preferably electrically conductive, are fixedly located in the upper half  26 , as by being included in the molded plastic resin material of the upper half  26  during its manufacture, or by being potted in place within a partially manufactured upper half  26 , with the respective. portion of the cylindrical cable-receiving passageway  44  being formed along the magnet  48 . Similarly, a magnet  52  and a shield member  54  are fixedly located in the lower half  28  of the case  24 . 
     Preferably, the magnets  48  and  52  are located along, parallel with, and closely adjacent to the cylindrical cable-receiving passageway  44 , and the shield members  50  and  54  extend respectively along surfaces of the magnets  48  and  52  that face away from the cable-receiving passageway  44 . A thin layer of the material of the upper half  26  and lower half  28 , or potting material retaining the magnets  48  and  52  in place in those parts of the case  24 , is present between the surface of the cable-receiving passageway  44  and the surface of the magnet  48  or  52 . 
     The shield members  50  and  54  generally have the form of channels of extruded or folded sheet metal, thick enough not to be magnetically saturated by the flux of the respective magnet. For example, the shield members  50  and  54  may be of a suitable magnetic steel, such as cold rolled steel. Each has a pair of legs  56  extending beyond the respective magnet toward the mating faces of the upper half  26  and lower half  28 . Preferably, the shield members  50  and  54  are so located within the upper half  26  and lower half  28  that the margins of the legs  56  abut against each other or are separated by a minimum of space when the upper half  26  and lower half  28  are fastened together by the screws  30 . 
     The magnets  48  and  52  are preferably similar to each other, and for the sake of simplified manufacture they may be of generally rectangular bar magnet configuration. Their opposite north and south pole faces are located respectively near the ends  40  and  38  of the case  24 , so that linear axes  58  and  60 , extending between the respective pole faces of each magnet, are parallel with each other and with the central longitudinal axis of the case  24 , as may be seen in FIG.  4 . The magnets  48  and  52  are thus aligned parallel with each other and with like poles adjacent each other. That is, the north pole faces of both magnets  48  and  52  are located nearer to the left end  40  of the attenuator  22  as shown in FIG. 4, while the south pole faces of both of the magnets  48  and  52  are located adjacent, i.e., opposite, each other near the right end  38  of the attenuator  22  as shown in FIG.  4 . The screws  30  and threaded bores  32  thus must be adequate to overcome the mutual repulsion of the magnets  48  and  52 . 
     Preferably the magnets  48  and  52  are made of a material which is permanently magnetizable and resists being demagnetized, and which when magnetized produces a reasonably high magnetic flux, as it appears that the effectiveness of the attenuator  22  as used on power cables increases with the strength of the magnets utilized. While some improvement is perceptible in the performance of a sound reproduction system using magnets producing a field as small as 1000 Gauss surrounding a power cable, a stronger field is preferable. 
     To suitably enclose the magnets  48  and  52  and their associated shields  50  and  54 , the case  24  may have a height  62  of about 1.425 inch, for example, and to accommodate the threaded bores  32  and pin holes  36  the case  24  may have a width  64  of about 1.95 inch. 
     Preferably, the shield members  50  and  54  extend over at least the same length as the respective magnet  48  and  52  with which each is associated, so that with the margins of the legs  56  of the shields  50  and  54  abutting each other the combined shield members  50  and  54  substantially enclose the magnets  48  and  52 , except the portions thereof facing toward the ends  38  and  40  of the attenuator  22 . It will be appreciated that for different cable sizes it may be desired to have a cable receiving passageway  44  of different sizes and for the shield members to have leg portions of different sizes to have the magnets  48  and  52  be located close to the cable. 
     Referring next to FIGS. 6 and 7, the magnets  48  and  52  and shield members  50 ′ and  54 ′ are shown in their respective positions with respect to a cable  70 , with the case  24  omitted for the sake of clarity. It should be realized that the critical factor is the presence of a permanent magnet in close proximity with the cable  70 , preferably, but not necessarily, aligned so that an axis of polarity, extending directly between the opposite poles of the magnet, extends generally parallel with the length of the conductors of the cable in which it is desired to attenuate electromagnetic noise in accordance with the present invention. Accordingly, a case, as such, is not necessary to the practice of the invention, and other ways such as adhesives or fasteners acting directly to hold the magnets and any shields may be used. 
     Referring next to FIGS. 8 and 9, magnets  72  and  74  are located on opposite sides of a cable  70 , again with like poles of the magnets  72  and  74  adjacent each other on opposite sides of the cable  70  and with axes of polarity  76  and  78  of the magnets parallel with each other and with the longitudinal axis  71  of that portion of the cable. 
     While it is preferred to use at least a pair of magnets as shown in previously described figures, beneficial results can be obtained using a single magnet such as the magnet  82  in proximity with the cable  70  as shown in FIGS. 9 and 10. Again, it is preferable to have the axis of polarity  84  of the magnet  82  aligned parallel with the longitudinal axis  71  of that portion of the cable  70  with which the magnet  82  is associated. 
     It is not required for the magnets utilized in accordance with the method of the present invention to be bar magnets, and satisfactory results will also be obtained by using magnets of a shape including in the permanently magnetized material itself the shape of a cable-receiving passageway  90 . As shown in FIGS. 12 and 13, a pair of magnets  86  and  88  may be fashioned, for example, of an extrudable permanently magnetizable material such as a rare earth magnetic material or a magnetic material embedded in a matrix of a ceramic or synthetic plastic resin material, so that the two magnets  86  and  88  together define the cylindrical cable-receiving passageway  90  within which the cable  70  can be located. As with the previously described arrangements shown in FIGS. 1-9, the magnets  86  and  88  are aligned with each other with their axes of polarity  92  and  94  parallel with each other and with the longitudinal axis of the cable  70 . 
     There are numerous locations where electromagnetic noise attenuation devices may be advantageously used according to the invention. In FIG. 14 a service panel  98  receives line AC current through a supply cable  100  and provides distributed power through output cables  102  each connected to the supply cable  100  or disconnected therefrom by a respective on/off switch  104 . A respective electromagnetic noise attenuator  22  located on each of the output cables  102  attenuates noise in the respective one of the output cables  102 , in order to improve the output from electronic devices receiving power from the output cables  102 . 
     Electromagnetic noise attenuators  22  may also be useful on a detachable AC power cord  106 , shown in FIG. 15, for an electronic device. Similarly, a utility distribution AC power cord  108  with multiple output power sockets  110  is an appropriate location for usage of an electromagnetic noise attenuator device  22  according to the present invention, as shown in FIG.  16 . 
     An electromagnetic noise attenuator  22  is also appropriately used on the AC power cord  112  of a radio receiver such as an FM tuner/receiver  114 , as shown in FIG. 17, or on the AC power cord  116  of a phonograph turntable  118 , as shown in FIG.  18 . Because of the shielding provided around the magnets  48  and  52  in the electromagnetic noise attenuator  22 , the attenuator  22  does not cause any adverse effects on the performance of a phonograph pick-up cartridge  120 . 
     Not only is the electromagnetic noise attenuator  22  useful on power cords as previously shown, but such a device can also be useful on cables carrying audio signals, such as the coaxial input cable  122  and coaxial output cables  124  of an amplifier such as a power amplifier  126 , resulting in noticeable improvement in the output sound quality from a loudspeaker (not shown) driven by the amplifier  126 . 
     The electromagnetic noise attenuators  22  according to the present invention are also useful in connection with digital signal cables, such as the digital signal transmission cable  128  interconnecting a CD player  130  with a digital-to-analog converter  102 , and on the power supply cords  134  and  136  to the CD player  130  and the digital-to-analog converter  132  respectively, as well as on the analog signal output cables  138  of the digital-to-analog converter  132 , as shown in FIG.  20 . 
     The electromagnetic noise attenuator  22  is also useful in connection with video signals as carried by the video signal cable  140  interconnecting a video electronic device  142  such as a laser disc player, digital video disc player (DVD), or video cassette recorder/player (VCR), to provide output signals to a video monitor  144 , or in conjunction with signal cables  146  providing digital or analog audio or video signals to or from the electronic device  142 . Use of an electromagnetic noise attenuator  22  on the power cables  148  and  150  of the electronic device  142  and video monitor  144  can also provide noticeable improvement in the video display and in the output performance of the electronic device  142 . 
     While the electromagnetic noise attenuator  22  has been shown as applicable to power cables and signal cables externally located with respect to various electronic devices, it is also advantageous to use magnets in close proximity to electrical conductor cables within an electronic device in accordance with the invention. In this fashion, an electromagnetic noise attenuator  152  including permanently magnetized magnetic material is located in proximity to the input power cable  154  providing line AC current to the primary side of the power transformer  156  in the chassis enclosure of an electronic device  158 . Additionally, a second electromagnetic noise attenuator  160  is included in proximity to the output cable  162  from the secondary side of the power transformer  156 , between the power transformer  156  and other circuitry  164  of the electronic device  158 . 
     Additional forms of permanent magnets useful in accordance with the present invention are shown in FIGS. 23 and 24. In FIG. 23, a pair of similar permanently magnetized magnets  166  and  168  have the form of identical halves of a tube and are mated with each other along a plane bisecting the tube along a diameter thereof. The magnets  166  and  168  define a centrally located axially extending cable passageway  170  having a diameter  172  preferably fitting fairly snugly about a cable (not shown) with which it is intended to use the pair of magnets  166  and  168 . As shown, the magnets  166  and  168  are longitudinally polarized so that each has an axis of polarity parallel with the length  174  of the tube formed by the pair of magnets, with the south poles of both of the magnets  166  and  168  at one end of the pair of magnets, as shown in FIG. 23, and the north pole of each magnet being located at the opposite end. 
     In FIG. 24, a single tubular permanent magnet  178  defines an open tubular cable passageway  180  whose diameter  182  is preferably large enough to allow an electrical conductor cable (not shown) to be extended through the cable passageway  180  so that the cable fits snugly within the cable passageway  180  without excessive space between the exterior of the cable and the interior of the cable passageway  180 . This, of course, may require insertion of the cable through the magnet  178  before terminals are affixed to the cable. Preferably, the magnet  178  is magnetized with a south pole at one end and the north pole at the opposite end, to define an axis of polarity parallel with the length  184  of the magnet, as shown in FIG.  24 . 
     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.