Patent Publication Number: US-2022213737-A1

Title: Mcei trough for inductive coupler

Description:
RELATED APPLICATIONS 
     This application presents a modification of U.S. Pat. No. 7,511,598, to Hall et al., entitled Elements For Use In An Inductive Coupler For Downhole Components, issued Mar. 31, 2009. Said Patent is incorporated herein by this reference. 
     U.S. patent application No. 17/543,655, to Fox, entitled Inductive Data Transmission System for Drill Pipe, filed Dec. 6, 2021, is incorporated herein by this reference. 
     U.S. patent application No. 17/559,619, to Fox, entitled Inductive Coupler For Downhole Transmission Line, filed Dec. 22, 2021, is incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The following background is taken from the &#39;598 reference and applies to this disclosure except when modified by this disclosure. This invention relates to elements for use in inductive couplers for down-hole components, more specifically this invention relates to elements comprising segments of magnetically conductive material. 
     U.S. Pat. No. 6,670,880, which is herein incorporated by reference, discloses a downhole transmission system through a string of downhole components. A first transmission element is located in one end of each downhole component, which element includes a first magnetically conducting, electrically-insulating trough, and a first electrically conductive coil lying there in. A second data transmission element is located in the other end, with a similar arrangement comprising a second magnetically conducting, electrically-insulating trough and a second electrically conductive coil. The transmission system further comprises an electrical conductor in electrical communication with and running between each first and second coil in the downhole component. The string of downhole components is cooperatively arranged such that the elements are in magnetic communication with each other to thereby transmit signals through induction. 
     U.S. Pat. No. 6,670,880 discloses that the magnetically conductive troughs are preferably easily magnetized and demagnetized. Examples of magnetically conductive materials were given including soft iron, ferrite, nickel iron alloys, silicon iron alloys, cobalt iron alloys and mu-metals. One example of a nickel/iron alloy has a trade name of Permalloy, which is a compound that comprises about 20% iron and 80% nickel. A preferred magnetically conductive material is ferrite. 
     Rectangular segments are used as a substitute for a solid ring in the &#39;880 patent. Naturally, a circular trough comprising rectangular segments creates gaps between its segments. Rectangles by definition are not curved and do not conform to the curve created by the circumferences of the circular trough. Thus, interruptions including generally triangular or trapezoidal shaped gaps in the trough result from using the rectangular segments. Because the gaps in the magnetically conducting circular trough do not contribute to magnifying the magnetic field, it is now believed that these gaps may adversely affect the magnetic field generated by the magnetically conductive, electrically insulating trough. 
     SUMMARY OF THE INVENTION 
     In reference to  FIGS. 1-5 , this application presents an annular magnetically conductive electrically insulating (MCEI) trough or channel that may be used for data transmission in an inductive coupler system for drillstring tools, including in the drill pipe and the bottom hole assembly. The MCEI trough may comprise a ferrite material comprising oxygen, iron, and manganese elements in such quantities and sizes that may promote inductive coupling. The MCEI trough may comprise an axial interior channel comprising an axial opening intermediate its inner diameter and outer diameter top surfaces. The interior open channel may comprise an interior surface comprising an interior side wall joining an interior bottom wall. An exterior diameter side wall may be radially spaced apart from the interior diameter side wall. The respective spaced apart interior diameter side wall and exterior diameter side wall side walls may form the respective top surfaces. The top surfaces may be planar. The interior surface may comprise one or more interior axial flutes. The interior axial flutes may comprise axial flute ridges and interior flute furrows. 
     The exterior diameter side wall and the interior diameter side wall may also join an exterior bottom wall. The exterior diameter side wall surface may comprise one or more exterior axial flutes. The exterior axial flutes may comprise axial exterior flute ridges and exterior flute furrows. The respective interior and exterior flutes may promote stability of the MCEI trough when installed in a drill pipe or other downhole tool. 
     The annular MCEI trough may form a single piece ring, or the annular trough may comprise a plurality of MCEI annular trough segments arranged intimately in a ring. The trough segments may comprise axially spaced apart terminal surfaces intersecting the one or more axial flutes. The terminal surfaces may be nonparallel surfaces. The terminal surfaces may interlock with adjacent terminal surfaces in the ring configuration. 
     An electrically conductive wire coil may be disposed or laid within the open channel of the MCEI trough. The wire coil may comprise one or more exterior axial corrugations comprising corrugation grooves and corrugation crests. The ridges and furrows of the interior axial flutes may couple with the crests and grooves of the axial corrugations of the wire coil. The coupling of the wire coil with the interior axial flutes may aid in the positioning and retention of the wire coil in the channel of the MCEI trough. 
     The respective interior and exterior axial flute ridges may at least partially protrude from the MCEI trough wall surfaces. The ridges may protrude inward from the exterior wall surfaces and of the MCEI trough. The respective axial flute furrows and may at least partially extend inward from the respective wall surfaces. The coil wire may be captured within the channel by the one or more axial flutes protruding from the interior surface. The coil wire may comprise a single electrically conductive wire or a plurality of electrically wires. The coil wire may comprise a plurality of conductive wire strands. The fluted channel may aid in securing the wire strands  305  within the channel. 
     A polymeric filler material may encapsulate the wire coil within the fluted channel. The filler material may be nonelectrically conducting. 
     The wire coil and coil strands may comprise a circular or noncircular cross section. The noncircular cross section may be for example an oval, a square, or a hexagon. The noncircular cross section of the wire coil and coil strands may promote packing within the channel and among the flutes. The conductive coil wire and strands may at least be partially captured within the channel by the axial flutes. 
     The annular MCEI trough and may be molded within an annular polymeric block. See the &#39;619 reference. The annular polymeric block may comprise a substantial volume of ferrite particles and fibers. The annular trough may comprise perforations in the channel&#39;s bottom wall. See the &#39;655 reference. The perforations may provide for a gapless MCEI circular trough, contrary to what is show in (Prior Art)  FIG. 15 , since the ends of the wire coil may pass though the perforations connecting the ends of the coil to ground and to a cable within the downhole tool. 
     The following portion of the summary is taken from the &#39;598 reference. The following summary applies to this disclosure except when modified by this disclosure. 
     An element for use in an inductive coupler for downhole components comprises an annular housing having a generally circular recess. The element further comprises a plurality of generally linear, magnetically conductive segments. Each segment includes a bottom portion, an inner wall portion, and an outer wall portion. The portions together define a generally linear trough from a first end to a second end of each segment. The segments are arranged adjacent to each other within the housing recess so as to form a generally circular trough. The ends of the segments are shaped such that the first end of each segment is complementary to the second end of an adjacent segment. 
     The shaped ends are preferably selected from the group consisting of a concave shape, a convex shape, a V-shape, and a zigzagged shape. 
     In another aspect of the present invention, the first and second ends of the segments are generally planar and the first ends are angled to be parallel to the second end of the adjacent segment. In one embodiment, all of the ends are angled. Preferably, the first ends of the segments are angled with the same angle and the second ends of the segments are angled with the complementary angle. 
     In one aspect of the present invention, all of the ends are angled so that the included angle between the outer wall portion and each end in each segment is calculated as 90.degree.-180.degree./n, where n is the number of segments. In another aspect of the invention, every other segment arranged in the recess has two ends with an included angle between the outer wall portion and the two ends equal to 90.degree. The remaining segments have two ends with an included angle between the outer wall portion and the two ends calculated as 90.degree.-360.degree./n, where n is the total number of segments. 
     Preferably, the annular housing is a metal ring. More preferably, the annular housing is a steel ring. In other embodiments the annular housing is a stainless steel ring. Preferably, the annular housing is disposed in a groove formed in the end of a downhole component. In one aspect of the present invention, the element comprises an electrically insulating filler material. Preferably, the filler material is a polymer selected from a group consisting of epoxy, natural rubber, fiberglass, carbon fiber composite, polyurethane, silicon, a fluorinated polymer, grease, polytetrafluoroethylene and perfluoroalkoxy, or a combination thereof. 
     In the preferred embodiment the magnetically conductive segments comprise an easily magnetized and easily de-magnetized material selected from the group consisting of soft iron, ferrite, a nickel iron alloy, a silicon iron alloy, a cobalt iron alloy, and a mumetal. Ferrite is the preferred material. 
     In another aspect of the present invention, the segments comprise a planar surface comprising both the inner wall portion and the outer wall portion which forms a chamfered edge with at least one of the ends. 
     The present invention provides the advantage that the parallel ends of the magnetically conductive segments may reduce gaps within the annular housing and thereby strengthen the magnetic field. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectioned diagram of the MCEI annular trough of the present invention. 
         FIG. 2  is a diagram of the MCEI annular trough segment of the present invention. 
         FIG. 3  is a sectioned diagram of a coil wire in the MCEI trough of the present invention. 
         FIG. 4  is a sectioned diagram of a coil wire comprising corrugations of the present invention. 
         FIG. 5  is a sectioned diagram of a coil wire comprising wire strands of the present invention. 
       (Prior Art)  FIG. 6  is a cross sectional view of an embodiment of a downhole tool string. 
       (Prior Art)  FIG. 7  is a perspective cross sectional view of an embodiment of the invention in downhole components. 
       (Prior Art)  FIG. 8  is a perspective view of an embodiment of an inductive coupler. 
       (Prior Art)  FIG. 9  is a cross-sectional view of an embodiment of a magnetic transmission circuit. 
       (Prior Art)  FIG. 10  is an orthogonal view of an element (prior art). 
       (Prior Art)  FIG. 11  is a detailed view of a section of  FIG. 5  (prior art). 
       (Prior Art)  FIG. 12  is an orthogonal view of an embodiment of an element. 
       (Prior Art)  FIG. 13  is a detailed view of a section of  FIG. 7 . 
       (Prior Art)  FIG. 14  is an orthogonal view of an embodiment of an element. 
       (Prior Art)  FIG. 15  is an orthogonal view of an embodiment of an element. 
       (Prior Art)  FIG. 16  is a detailed view of a section of  FIG. 10 . 
       (Prior Art)  FIG. 17  is a partial perspective view of an embodiment of an element. 
       (Prior Art)  FIG. 18  is a partial perspective view of an embodiment of an element. 
       (Prior Art)  FIG. 19  is a partial perspective view of an embodiment of an element. 
       (Prior Art)  FIG. 20  is a partial orthogonal view of an embodiment of an element. 
       (Prior Art)  FIG. 21  is a partial orthogonal view of an embodiment of an element. 
       (Prior Art)  FIG. 22  is a partial orthogonal view of an embodiment of an element. 
       (Prior Art)  FIG. 23  is a partial orthogonal view of an embodiment of an element. 
       (Prior Art)  FIG. 24  is a partial orthogonal view of an embodiment of an element. 
       (Prior Art)  FIG. 24  is a partial orthogonal view of an embodiment of an element. 
       (Prior Art)  FIG. 25  is a partial orthogonal view of an embodiment of an element. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In Reference to  FIGS. 1-5 , this application presents an annular magnetically conductive electrically insulating (MCEI) trough or channel  205  that may be used for data transmission in an inductive coupler system for drillstring tools, including in the drill pipe and the bottom hole assembly. The MCEI trough  205  may comprise a ferrite material comprising oxygen, iron, and manganese elements in such quantities and sizes that may promote inductive coupling. The MCEI trough  205  may comprise an axial interior channel  255  comprising an axial opening intermediate its inner diameter  225  and outer diameter  210  top surfaces. The interior open channel  255  may comprise an interior surface  230  comprising an interior side wall  250  joining an interior bottom wall  245 . An exterior diameter side wall  240  may be radially spaced apart from the interior diameter side wall  220 . The respective spaced apart interior diameter side wall  220  and exterior diameter side wall  240  side walls may form the respective top surfaces  210 ,  225 . The top surfaces  210 ,  225  may be planar. The interior surface  230  may comprise one or more interior axial flutes  235 . The interior axial flutes  235  may comprise axial flute ridges  235 A and interior flute furrows  235 B. 
     The exterior diameter side wall  240  and the interior diameter side wall  220  may also join an exterior bottom wall  240 A. The exterior diameter side wall surface  240  may comprise one or more exterior axial flutes  295 . The exterior axial flutes  295  may comprise axial exterior flute ridges  285 A and exterior flute furrows  295 B. The respective interior and exterior flutes may promote stability of the MCEI trough when installed in a drill pipe or other downhole tool. 
     The annular MCEI trough may form a single piece ring, or the annular trough may comprise a plurality of MCEI annular trough segments  260  arranged intimately in a ring. The trough segments may comprise axially spaced apart terminal surfaces  265  intersecting the one or more axial flutes  235 . The terminal surfaces  265  may be nonparallel surfaces. The terminal surfaces  265  may interlock with adjacent terminal surfaces  265  in the ring configuration. 
     An electrically conductive wire coil  275  may be disposed or laid within the open channel  255  of the MCEI trough  270 . The wire coil  275  may comprise one or more exterior axial corrugations  280  comprising corrugation grooves  280  and corrugation crests  285 . The ridges  235 A and furrows  235 B of the interior axial flutes  235  may couple with the crests  285  and grooves  280  of the axial corrugations  280  of the wire coil  275 . The coupling of the wire coil  275  with the interior axial flutes  235  may aid in the positioning and retention of the wire coil  275  in the channel  255  of the MCEI trough  270 . 
     The respective interior  235 A and exterior  295 A axial flute ridges may at least partially protrude from the MCEI trough  300  wall surfaces. The ridges  290  may protrude inward from the exterior wall surfaces  240  and  220  of the MCEI trough  300 . The respective axial flute furrows  235 B and  295 B may at least partially extend inward from the respective wall surfaces. The coil wire  275  may be captured within the channel  255  by the one or more axial flutes  235  protruding from the interior surface  230 . The coil wire  275  may comprise a single electrically conductive wire or a plurality of electrically wires. The coil wire  275  may comprise a plurality of conductive wire strands  305 . The fluted channel may aid in securing the wire strands  305  within the channel  255 . 
     A polymeric filler material may encapsulate the wire coil  275  within the fluted channel  255 . The filler material may be nonelectrically conducting. 
     The wire coil  275  and coil strands  305  may comprise a circular or noncircular cross section. The noncircular cross section may be for example an oval, a square, or a hexagon. The noncircular cross section of the wire coil  275  and coil strands  305  may promote packing within the channel  255  and among the flutes  235 . The conductive coil wire  275  and strands  305  may at least be partially captured within the channel  255  by the axial flutes  235 . 
     The annular MCEI trough  205 ,  260 , and  270  and may be molded within an annular polymeric block. See the &#39;619 reference. The annular polymeric block may comprise a substantial volume of ferrite particles and fibers. The annular trough may comprise perforations in the channel&#39;s bottom wall  245 . See the &#39;655 reference. The perforations may provide for a gapless MCEI circular trough since the ends of the wire coil may pass though the perforations connecting the ends of the coil to ground and to a cable within the downhole tool. 
     The following portion of the detailed description is taken from the &#39;598 reference and applies to this disclosure except when modified by this disclosure. 
     The disclosed description is meant to illustrate the present invention and not limit its scope. Other embodiments of the present invention are possible within the scope and spirit of the claims. 
     (Prior Art)  FIG. 6  shows an embodiment of a downhole tool string  31  suspended in a well bore by a derrick  32 . Surface equipment  33 , such as a computer, connects to a data swivel  34 . The data swivel  34  is adapted to transmit data to and from an integrated transmission network while the downhole tool string  31  is rotating. The integrated transmission network comprises the transmission systems of the individual components  35 ,  36 ,  57  of the downhole tool string  31 . Preferably the downhole component is a tool  35 . 
     Preferably the downhole component is a pipe  36 ,  57 . Tools  35  may be located in the bottom hole assembly  37  or along the length of the downhole tool string  31 . Examples of tools  35  on a bottom hole assembly  37  comprise sensors, drill bits, motors, hammers, and steering elements. Examples of tools  35  located along the downhole tool string  31  are links, jars, seismic sources, seismic receivers, sensors, and other tools that aid in the operations of the downhole tool string  31 . Different sensors are useful downhole such as pressure sensors, temperature sensors, inclinometers, thermocouplers, accelerometers, and imaging devices. Preferably the downhole tool string  31  is a drill string. In other embodiments the downhole tool string  31  is part of a production well. 
     The downhole tool string  31  is made up of components, as shown in (Prior Art)  FIG. 7 . Preferably the components are pipes  36 ,  57  or some of the above mentioned tools  35 . The components comprise inductive couplers  85  (shown in (Prior Art)  FIG. 8 ) located in the secondary shoulder  39  of the pin end  40  and the secondary shoulder  41  of the box end  42  of the component  36 ,  57 . Preferably, the inductive couplers  85  comprise an element  38 ,  47  comprising an annular housing  43  (shown in (Prior Art)  FIG. 8 ) having a generally shaped recess  86  (shown in (Prior Art)  FIG. 17 ). The element  38 ,  47  further comprises a plurality of generally linear, magnetically conductive segments  68 , each of which segments  68  includes a bottom portion  88 , an inner wall portion  80 , and an outer wall portion  79  (shown in (Prior Art)  FIG. 17 ). The portions  79 ,  80 ,  88  together define a generally linear trough  89  (shown in (Prior Art)  FIG. 8 ) from one end to the other end of each segment. The segments  68  are arranged within the housing recess  86  so as to form a generally circular trough  55 . At least half of the ends  77 ,  78  (shown in (Prior Art)  FIG. 13 ) of the segments  68  are angled such that the ends  77 ,  78  of adjacent segments  68  are substantially parallel. 
     Preferably the element  38 ,  47  is disposed in an annular groove  62  (shown in (Prior Art)  FIG. 9 ) formed in the secondary shoulders  39 ,  41 . Preferably the annular housing  43  is a metal ring. More preferably, the annular housing  43  is a steel ring. The elements  38 ,  47 , in a single downhole component, are connected by an electrical conductor  44 . Preferably the electrical conductor  44  is a coaxial cable. 
     Preferably the circular trough  55  houses an electrically conductive coil  45  embedded in the magnetically conductive segments  68 . Preferably, the magnetically conductive segments  68  comprise an easily magnetized and de-magnetized material selected from the group consisting of soft iron, ferrite, a nickel iron alloy, a silicon iron alloy, a cobalt iron alloy and a mu-metal. More preferably the magnetically conductive segments  68  are made of ferrite. Preferably the coil  45  comprises at least two loops of insulated wire. More preferably, the coil  45  comprises one loop of insulated wire. The coil  45  may comprise two or more loops of insulated wire. More preferably the coil  45  comprises one loop of insulated wire. Preferably, the wire is made of copper and is insulated with an insulating layer  73  (shown in (Prior Art)  FIG. 17 ) of a varnish, enamel, or a polymer. When the components  36 ,  57  of the downhole tool string  31  up are made, the elements  38 ,  47  line up adjacent each other and allow data transmission between the components  36 ,  57 . A threaded portion  48  located between the primary shoulder  49  and secondary shoulder  39  of the pin end  40  and a threaded portion  50  located between the primary shoulder  51  and secondary shoulder  41  of the box end  42  provide a means of attachment for the downhole components  36 ,  57 . 
     (Prior Art)  FIG. 8  shows an embodiment of a connection between the electrical conductor  44  and the electrical conducting coil  45 . In the preferred embodiment, a signal travels along the electrical conductor  44  of a downhole component  36 . The signal passes from the electrical conductor  44  to a lead wire  52  of the coil  45 . The inductive coupler  85  comprises an anti-rotation device  53 , which keeps the annular housing  43  from rotating about the axis of the lead wire  52 . In the preferred embodiment the lead wire  52  may enter the annular housing  43  through a hole  75  (shown in (Prior Art)  FIG. 10 ) in the annular housing  43 , where there is a void  54  of magnetically conductive material. The coil  45  is housed within the circular trough  55  of magnetically conductive material and is grounded to the annular housing  43  in the void  54  of the magnetically conductive material. 
     Preferably, the grounded portion  56  of the coil  45  is brazed to the annular housing  43 . In some embodiments of the present invention, the coil  45  and magnetically conductive segments  68  are disposed in a groove  62  formed in the secondary shoulders  39 ,  41  of both the pin end  40  and also in the box end  42  of the down-hole component  36 . Preferably, the elements  38 ,  47  comprise an electrically insulating filler material  60  (shown in (Prior Art)  FIG. 17 ) which holds the segmented circular trough  55  in place. Preferably the filler material  60  is a polymer selected from the group consisting of epoxy, natural rubber, fiberglass, carbon fiber composite, polyurethane, silicon, a fluorinated polymer, grease, polytetrafluoroethylene and perfluoroalkoxy, fluorinated ethylene propylene copolymer (FEP), or a combination thereof. Polytetrafluoroethylene and perfluoroalkoxy are the more preferred filler materials  60 , with FEP grade 6100 the most preferred material. 
     It is important that the electrically-insulating filler material  60  withstand the elevated pressures and temperatures in downhole conditions. Consequently, it is preferred to treat the filler material  60  to make sure that it does not contain any air pockets. Preferably the filler material  60  is centrifuged to remove all bubbles that might be introduced during mixing. One such treatment method involves subjecting the filler material  60  in a centrifuge. A most preferred form of this method subjects the material  60  to a centrifuge at between 2500 to 5000 rpm for about 0.5 to 3 minutes. 
     (Prior Art)  FIG. 9  shows an embodiment of the magnetic transmission circuit  61  formed by cooperating magnetic fields. As the signal travels along the coil  45 , the magnetic field from the electrical current is concentrated by the magnetically conductive segments  68 . The concentrated magnetic field influences the magnetically conductive segments  68  in the adjacent element  47  in the adjacent downhole component  57 . The electrically conducting coils  45 ,  59  are arranged in a manner to allow the magnetic fields to generate a magnetic transmission circuit  61 . A magnetic transmission circuit  61  may be allowed by disposing one coil  45  in a clockwise direction in the segmented circular trough  55  and disposing an adjacent coil  59  in a counterclockwise direction in an adjacent segmented circular trough  76 . The coil  59  in the adjacent element  47  is influenced by the magnetic transmission circuit  61  to generate an electrical current and that signal is passed to the electrical conductor  58  in the adjacent downhole component  57 . 
     (Prior Art)  FIGS. 10 and 11  show the prior art using rectangular segments  67 . Rectangular segments  67  of magnetically conductive material necessarily leave gaps  65  in the circular trough  55 . It is believed that a MCEI trough formed with these gaps provide a magnetic field and allow transmission. 
     Angled ends  77 ,  78  (shown in (Prior Art)  FIG. 13 ) of the magnetically conductive segments  68 , may reduce the gaps  65  significantly as the ends are complementary. Elements  38 ,  47  with rectangular segments  67  lose a percentage of the signal strength passed between them. Repeaters, which are included throughout the downhole tool string  31 , are used to strengthen the diminished signals. It is believed that by reducing the size of the gaps  65  in the annular housing  43 , that a stronger magnetic field is generated, which results in passing a stronger signal between the elements  38 ,  47 . 
     (Prior Art)  FIG. 12  shows an embodiment of an element  38  wherein all of the ends  77 ,  78  are angled. (Prior Art)  FIG. 13  is a detailed view of a portion of (Prior Art)  FIG. 12 . In the preferred embodiment of the present invention, all of the one ends  77  of the segments  68  are angled with the same angle and all of the other ends  78  of the segment  68  are angled with the complementary angle. The magnetic transmission circuit  61  is represented coming out of the page by  69  and represented going into the page by  70 . Since the one end  77  in this embodiment is planar and generally parallel to the other end  78 , the segments  68  may be arranged in the annular housing  43  such that minimal gaps  71  are formed. As used herein a minimal gap refers to a gap of between about 0.050 and 0.0001 inches. It is believed that the minimal gaps  71  have a negligible adverse affect on the magnetic transmission circuit  61 . 
     In one aspect of the present invention, all of the ends  77 ,  78  are angled in a complementary fashion so that the included angle between the outer wall portion  79  and each end  77 ,  78  in each segment  68  is calculated as 90.degree.-180.degree./n, wherein n is the number of segments  68 . For example if the annular housing  43  comprised forty segments  68 , all with angled edges  77 ,  78  and are arranged to form minimal gaps  71  with no voids  54  in the annular housing  43 , then the included angle between the outer wall portion  79  and each end  77 ,  78  would be 85.5.degree. 
     In another aspect of the present invention is shown in (Prior Art)  FIG. 14 , every other segment  67  arranged in the recess  86  has two ends  84 ,  85  with an included angle between the outer wall portion  79  and the two ends  84 ,  85  equal to 90.degree, and wherein the remaining segments  68  have two ends  77 ,  78  arranged in a complementary manner with an included angle between the outer wall portion  79  and the two ends  77 ,  78  calculated as 90.degree.-360.degree./n, where n is the total number of segments  67 ,  68 . An embodiment is show in (Prior Art)  FIG. 14 . An example illustrates that if the annular housing  43  comprised forty segments  67 ,  68 , half of which were rectangular segments  67 , and all the segments  67 ,  68  are arranged such so as to form minimal gaps  71  and that there are no voids  54 , then the angle included between the outer wall portion  79  and the angled ends  77 ,  78  would be 81. degree. 
     (Prior Art)  FIG. 14  also illustrates a magnetic transmission circuit  61  running in an opposite direction as shown in (Prior Art)  FIG. 12 , due to the electrically conducting coil  45  running in a counterclockwise direction. 
     (Prior Art)  FIG. 15  shows an embodiment of generally linear shaped segments  72  comprising curved inner wall portions  81  and curved outer wall portions  82 . The first end  77  and the second ends  78  of the segments  72  are shaped such that the first end  77  of each segment  72  is complementary to the second end  78  of adjacent segments. Some small gaps may still be present between these annular housing  43  and the magnetically conductive segments  72 ; however, these gaps are believed to have less impact on the strength of the magnetic field, and are smaller than the gaps  65  created by the segments  68  with angled ends  77 ,  78  and the annular housing  43 . In order for the current in the electrically conducting coil  45  to influence the magnetically conductive segments  67 ,  68 ,  72  to generate a magnetic field, the electrically conducting coil  45  needs to be at least partially encapsulated in the magnetically conductive material. Other factors such as the number of loops in the electrically conducting coil  45 , the thickness of the electrically conducting coil  45 , and the length of the cross section of magnetically conductive circular trough  55 , all have positive direct relationships with the strength of the magnetic transmission circuit  61 . The gaps  65  that are present between the annular housing  43  and the segments  68  affect the strength of the magnetic field by decreasing the thickness of the cross section of the circular trough  55 , which is believed to be considerably less than the impact that the gaps  65  formed between the segments  68  and the annular housing  43  have on the magnetic field strength. (Prior Art)  FIG. 16  shows a detailed view of the (Prior Art)  FIG. 15 . (Prior Art)  FIG. 17  is a perspective view of an element. (Prior Art)  FIG. 18  is a perspective view of (Prior Art)  FIG. 15 . 
     (Prior Art)  FIG. 19  shows an embodiment of the present invention wherein the segments  74  comprise a planar surface  66  comprising both the inner wall portion  80  and the outer wall portion  79  which forms a chamfered edge  83  with at least one of the ends  77 ,  78 . When attaching the downhole components  36 ,  57  in a down-hole tool string  31 , the planar surfaces  66  slide together under some friction. Depending on the pitch and other factors dealing with the threaded portion  48  on the pipe, the planar surfaces  66  may slide against each other for 5 to 30 degrees. However, 5 to 10 degrees is more likely. The chamfered edge  83  prevents the ends  77 ,  78 ,  84 ,  85  of the segments  74  from catching while the planar surfaces  66  are sliding against each other. Ideally the surfaces  66  are coated with the filler material  60  and then grinded down to provide a smooth surface  66 , but if a segment  67 ,  68 ,  72  is popped out of the recess  86  a little bit, the planar surfaces  66  of one of the elements  38 ,  47  may be damaged. Popped up segments  67 ,  68 ,  72  may be destroyed or create a gap, such as a groove, scratch, or crack in one of the planar surfaces  66  which may adversely affect the magnetic transmission circuit  61 . When the planar surface  66  is being finished, it is important that the polishing procedures do not compromise the surface  66  in such a way as to interfere with the magnetic transmission circuit  61 . 
     It is believed that the electrical signal passed between the elements  38 ,  47  is stronger when the planar surfaces  66  are in physical contact with each other. It is believed, that the physical contact between the planar surfaces  66  increases the cross section of the magnetically conductive material, and this increases the magnetic field. Sometimes rocks or dirt keep the planar surfaces  66  from touching each other. The signal may still pass between the elements  38 ,  47 , even if the planar surfaces  66  aren&#39;t touching because the magnetic transmission circuit  61  may still be made, but the signal is weaker. It is believed that if a small space exists, then air&#39;s magnetic resistance adversely affects the magnetic fields. A rock or some other object may dislodge one or more of the segments  67 ,  68 ,  72 , but it is believed that segments  74  with chamfered edges  83  may reduce the frequency that it happens. 
     A method of forming an element  38 ,  47  of magnetically conductive segments  67 ,  68 ,  72 ,  74  begins with providing a mold having a trough conforming to the final dimensions of the circular trough  55 . A two-part, heat-curable epoxy formulation is mixed in a centrifuge cup, to which the individual magnetically conductive segments  67 ,  68 ,  72 ,  74  and a length of fiberglass rope are added. The parts are centrifuged for up to 30 minutes to cause all bubbles induced by mixing to rise out of the viscous liquid, and to cause the liquid to penetrate and seal any porosity in the magnetically conductive material. The fiberglass rope is then laid in the bottom of the mold, which is either made from a material, which does not bond to epoxy, such as polymerized tetrafluoroethane or which is coated with a mold release agent. The individual magnetically conductive segments  67 ,  68 ,  72 ,  74  are then placed on top of the fiberglass rope, to fill the circle. Any excess epoxy is wiped out of the groove. The planar surfaces  66  of the parts may be precisely aligned with each other by holding them in position with magnets placed around the circular trough in the mold. After the epoxy is cured, either at room temperature or in an oven, the circular tough  46  is removed from the mold. Other filler materials may be used in the place of epoxy such as the filler materials mentioned above. 
     (Prior Art)  FIG. 20  shows an embodiment of an element comprising diamond shaped segments  95 . Complementary ends  78  and  77  are arranged in the housing  43  to fit to form a minimal gap  71 , which is believed to not adversely affect the magnetic transmission circuit. (Prior Art)  FIG. 21  shows an embodiment comprising interlocking segments  96  having non-planar ends. Non-planar end  77  is inserted into complementary end  78  and is believed to produce a minimal gap  71  between the segments  96 . Zigzagged shaped non-planar segments  97  are shown in (Prior Art)  FIG. 22 . (Prior Art)  FIG. 23  shows an embodiment of a segment  91  with a concave shaped non-planar end  99  and a convex shaped non-planar end  98 . The concave shaped end  99  may be rotated in the complementary convex end  98  so that gaps  65  between the segment  91  and the annular housing  43  may be minimized and the gap between segments  91  may be minimal gaps  71 . (Prior Art)  FIG. 24  shows segments  92 ,  93  comprising V-shaped ends  100 ,  101 . Segment  92  comprising two out-ward V-shaped ends  100  and segment  93  comprising two complementary inward V-shaped ends  101 . In (Prior Art)  FIG. 25  an embodiment of a segment  94  comprising both an inward V-shaped end  101  and an outward V-shaped end  100  is shown. Also shown in (Prior Art)  FIG. 25  is a longitudinal axis  90  of one of the segments  94 . In some embodiments, the longitudinal axis  90  runs from one  77  end of the segment  94  to the other end  78 . The segments  68  may be arranged such that their longitudinal axes  90  intercept at a point  102  which is intermediate the two segments  68 . 
     Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.