Orientation sensor arrangement and method for use in a system for monitoring the orientation of an underground boring tool

• US 6,756,784 B2
• Filed: 12/19/2002
• Issued: 06/29/2004
• Est. Priority Date: 03/01/1991
• Status: Expired due to Fees

• Current Assignee: Merlin Technologies Incorporated
• Original Assignee: Merlin Technologies Incorporated
• Inventors: Mercer, John E.
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US10/324,804
• Publication Number:
  US 20030076106A1
• Time in Patent Office: 558 Days
• Field of Search: 324/326, 324/338, 324/339, 324/225, 175/45
• US Class Current: 324/326
• CPC Class Codes: E21B 47/0228 using electromagnetic energy or detectors therefor
• CPC Class Codes: E21B 47/0232 at least one of the energy sources or one of the detectors being located on or above the ground surface
• CPC Class Codes: E21B 47/024 of devices in the borehole determining slope or direction of the borehole E21B47/022
• CPC Class Codes: G01C 9/06 Electric or photoelectric indication or reading means
• CPC Class Codes: G01C 9/20 the indication being based on the inclination of the surface of a liquid relative to its container
• CPC Class Codes: G01V 3/165 operating with magnetic or electric fields produced or modified by the object or by the detecting device with electromagnetic waves G01V3/17

Abstract

The present invention provides a locator/monitor capable of locating a boring tool and monitoring the progress of the tool for control purposes. The locator/monitor may be used in expedited locating methodology and straightforward calibration techniques of the present invention. A durable and cost effective pitch sensor is also provided by the present invention. In addition, the present invention provides a slotted transmitter housing formed of an electrically conductive material, where the magnetic field generated by the transmitter is capable of penetrating to the surface.

Claims

1. In producing an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, a method comprising the steps of:

providing an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends;

positioning a transmitter in said interior chamber for originating said locating signal such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signal; and

forming a number of elongated slots in said wall arrangement including at least two elongated slots which are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field and said number of said slots is formed based, at least in part, on said locating signal exhibiting a signal strength that is substantially independent of roll orientation of the boring tool.

2. The method of claim 1 wherein each of said slots includes an overall elongated length and wherein said current path is broken entirely along said overall elongated length of each slot.

3. The method of claim 1 wherein each of said slots includes an overall elongated length and wherein said width is substantially constant along said elongated length of each slot.

4. The method of claim 1 further comprising the steps of protecting said transmitter by filling said slots with a filler material.

5. The method of claim 4 including the step of choosing the filler material to contribute to torsional rigidity and strength of said elongated electrically conductive wall arrangement.

6. The method of claim 5 wherein said slots are filled with a ceramic material.

7. The method of claim 5 wherein said slots are filled with a composite material.

8. The method of claim 4 wherein said slots are filled with an elastic material.

9. The method of claim 4 wherein said slots are filled with a rigid material.

10. In producing an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, a method comprising the steps of:

providing an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends;

positioning a transmitter in said interior chamber for originating said locating signal such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signal; and

forming at least two elongated slots in said wall arrangement which are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field and at least one of said slots is formed having a width of approximately 0.125 inches.

11. In producing an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, a method comprising the steps of:

providing an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends;

positioning a transmitter in said interior chamber for originating said locating signal such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signal; and

forming at least four of said slots spaced apart about said elongated electrically conductive wall arrangement which slots are arranged at least generally in said elongation direction, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field.

12. In producing an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, a method comprising the steps of:

providing an elongated electrically conductive wall arrangements, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends;

positioning a transmitter in said interior chamber for originating said locating signal such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signal; and

forming at least four of said slots in said elongated electrically conductive wall arrangement such that approximately no variation in signal strength is exhibited by the locating signal surrounding the boring tool and said slots are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field.

13. In producing an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, a method comprising the steps of:

providing an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends;

positioning a transmitter in said interior chamber for originating said locating signal such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signal; and

forming at least two elongated slots in said wall arrangement which are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field and each slot includes a length and at least one slot is formed having a ratio of length to width of approximately 1/36.

14. In producing an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, a method comprising the steps of:

providing an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends;

positioning a transmitter in said interior chamber for originating said locating signal such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signal; and

forming at least two elongated slots in said wall arrangement which are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field and each slot includes a length and at least one slot is formed having a ratio of length to width of approximately 1/44.

15. In the fabrication of a drill head for supporting a transmitter as part of an underground boring tool configured for allowing the transmission of a ground penetrating locating signal, a method comprising the steps of:

providing an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends;

forming a first elongated slot in said wall arrangement which is arranged at least generally in said elongation direction, said first elongated slot having a width that is just wide enough to disrupt a current flow in said housing induced by said transmitter when transmitting from within the housing so as to reduce a counter magnetic field that is induced in said wall arrangement by said current;

forming a second elongated slot in said wall arrangement which is arranged at least generally in said elongation direction and spaced apart from said first elongated slot about said wall arrangement, said first elongated slot having said width that is just wide enough to disrupt said current flow in said housing induced by said transmitter so as to further reduce said counter magnetic field;

forming an additional slot in said elongated electrically conductive wall arrangement having said width to additionally disrupt the current flow to additionally reduce variation in the signal strength of the locating signal surrounding the boring tool; and

forming further additional slots until approximately no variation is exhibited in the locating signal surrounding the boring tool.

16. The method of claim 15 wherein each of said slots includes an overall elongated length and wherein said current path is broken entirely along said overall elongated length of each slot.

17. The method of claim 15 wherein each of said slots includes an overall elongated length and wherein said width is substantially constant along said elongated length of each slot.

18. In the fabrication of a drill head for supporting a transmitter as part of an underground boring tool configured for allowing the transmission of a ground penetrating locating signal, a method comprising the steps of:

providing an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends;

forming a first elongated slot in said wall arrangement which is arranged at least generally in said elongation direction, said first elongated slot having a width that is just wide enough to disrupt a current flow in said housings induced by said transmitter when transmitting from within the housing so as to reduce a counter magnetic field that is induced in said wall arrangement by said current;

forming a second elongated slot in said wall arrangement which is arranged at least generally in said elongation direction and spaced apart from said first elongated slot about said wall arrangement, said first elongated slot having said width that is just wide enough to disrupt said current flow in said housing induced by said transmitter so as to further reduce said counter magnetic field;

forming an additional slot in said elongated electrically conductive wall arrangement having said width to additionally disrupt the current flow to additionally reduce variation in the signal strength of the locating signal surrounding the boring tool; and

forming further additional slots based, at least in part, on configuring said locating signal to exhibit a signal strength that is substantially independent of roll orientation of the boring tool.

19. In the fabrication of a drill head for supporting a transmitter as part of an underground boring tool configured for allowing the transmission of a ground penetrating locating signal, a method comprising the steps of:

providing an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends;

forming a first elongated slot in said wall arrangement which is arranged at least generally in said elongation direction, said first elongated slot having a width that is just wide enough to disrupt a current flow in said housing induced by said transmitter when transmitting from within the housing so as to reduce a counter magnetic field that is induced in said wall arrangement by said current;

forming a second elongated slot in said wall arrangement which is arranged at least generally in said elongation direction and spaced apart from said first elongated slot about said wall arrangement, said first elongated slot having said width that is just wide enough to disrupt said current flow in said housing induced by said transmitter so as to further reduce said counter magnetic field;

forming an additional slot in said elongated electrically conductive wall arrangement having said width to additionally disrupt the current flow to additionally reduce variation in the signal strength of the locating signal surrounding the boring tool; and

forming further additional slots until the locating signal surrounding the boring tool is approximately axisymmetric.

20. In the fabrication of a drill head for supporting a transmitter as part of an underground boring tool configured for allowing the transmission of a ground penetrating locating signal, a method comprising the steps of:

providing an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends;

forming a first elongated slot in said wall arrangement which is arranged at least generally in said elongation direction, said first elongated slot having a width that is just wide enough to disrupt a current flow in said housing induced by said transmitter when transmitting from within the housing so as to reduce a counter magnetic field that is induced in said wall arrangement by said current; and

forming a second elongated slot in said wall arrangement which is arranged at least generally in said elongation direction and spaced apart from said first elongated slot about said wall arrangement, said first elongated slot having said width that is just wide enough to disrupt said current flow in said housing induced by said transmitter so as to further reduce said counter magnetic field and forming two additional slots such that four of said slots are formed spaced apart about said elongated electrically conductive wall arrangement.

21. In the fabrication of a drill head housing, as part of an underground boring tool configured for allowing transmission of a ground penetrating locating signal from a transmitter, a method comprising the steps of:

providing an elongated drill head housing member for direct contact with the ground, serving as at least one part of said drill head housing, and defining an interior between opposing ends of the housing member for receiving said transmitter to isolate the transmitter from ground contact during drilling;

forming a first elongated slot in the wall of said elongated drill head housing, said slot having a width that is just wide enough to disrupt a current flow in said elongated housing induced by said transmitter when transmitting from within the housing which thereby reduces a counter magnetic field in the housing;

forming a second elongated slot having said width to further disrupt the current flow induced in said housing such that a radiated signal strength from said transmitter around said drill head is substantially independent of boring tool roll orientation;

forming an additional slot in said drill head housing member having said width to disrupt the current flow in the housing member to further reduce variation in the signal strength of the locating signal surrounding the boring tool; and

forming further additional slots until approximately no variation is exhibited in the locating signal surrounding the boring tool.

22. The method of claim 21 wherein each of said slots includes an overall elongated length and wherein said current path is broken entirely along said overall elongated length of each slot.

23. The method of claim 21 wherein each of said slots includes an overall elongated length and wherein said width is substantially constant along said elongated length of each slot.

24. In the fabrication of a drill head housing, as part of an underground boring tool configured for allowing transmission of a ground penetrating locating signal from a transmitter, a method comprising the steps of:

providing an elongated drill head housing member for direct contact with the ground, serving as at least one part of said drill head housing, and defining an interior between opposing ends of the housing member for receiving said transmitter to isolate the transmitter from ground contact during drilling;

forming a first elongated slot in the wall of said elongated drill head housing, said slot having a width that is just wide enough to disrupt a current flow in said elongated housing induced by said transmitter when transmitting from within the housing which thereby reduces a counter magnetic field in the housing;

forming a second elongated slot having said width to further disrupt the current flow induced in said housing;

forming an additional slot in said drill head housing member having said width to disrupt the current flow in the housing member to further reduce variation in the signal strength of the locating signal surrounding the boring tool; and

forming further additional slots based, at least in part, on said locating signal exhibiting a signal strength that is substantially independent of roll orientation of the boring tool.

25. In an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, an assembly comprising:

a transmitter for originating said locating signal; and

an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends and said transmitter being positioned in said interior chamber such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signal, said electrically conductive wall arrangement defining a number of elongated slots including at least two elongated slots which are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field and said number of slots is formed based, at least in part, on said locating signal exhibiting a signal strength that is substantially independent of roll orientation of the boring tool.

26. The assembly of claim 25 wherein each of said slots includes an overall elongated length and wherein said current path is broken entirely along said overall elongated length of each slot.

27. The assembly of claim 25 wherein each of said slots includes an overall elongated length and wherein said width is substantially constant along said elongated length of each slot.

28. The assembly of claim 25 wherein said slot is filled with a filler material to protect said transmitter and the width of each elongated slot is sufficiently narrow to protect the filler material disposed in the slot from abrasion during boring.

29. The assembly of claim 28 wherein said filler material contributes to torsional rigidity and strength of said housing.

30. The assembly of claim 29 wherein said filler material is a ceramic material.

31. The assembly of claim 30 wherein said filler material is a composite material.

32. The assembly of claim 28 wherein said filler material is an elastic material.

33. The assembly of claim 28 wherein said filler material is a rigid material.

34. In an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, an assembly comprising:

a transmitter for originating said locating signal; and

an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends and said transmitter being positioned in said interior chamber such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signal, said electrically conductive wall arrangement defining at least two elongated slots which are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field and at least one slot includes a width of approximately 0.125 inches.

35. In an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, an assembly comprising:

a transmitter for originating said locating signal; and

an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends and said transmitter being positioned in said interior chamber such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signal, said electrically conductive wall arrangement defining four elongated slots which are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field.

36. In an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, an assembly comprising:

a transmitter for originating said locating signal; and

an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends and said transmitter being positioned in said interior chamber such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signal, said electrically conductive wall arrangement defining a number of elongated slots which are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field and said number of elongated slots includes at least four of said slots formed in said elongated electrically conductive wall arrangement such that approximately no variation in signal strength is exhibited by the locating signal surrounding the boring tool.

37. In an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, an assembly comprising:

a transmitter for originating said locating signal; and

an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends and said transmitter being positioned in said interior chamber such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signal, said electrically conductive wall arrangement defining at least two elongated slots which are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field and each slot includes a length and a ratio of length to width of approximately 1/36.

38. In an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, an assembly comprising:

a transmitter for originating said locating signal; and

an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends and said transmitter being positioned in said interior chamber such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangment, upon transmission of the locating signal, said electrically conductive wall arrangement defining at least two elongated slots which are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field and said slot includes a length and a ratio of length to width of approximately 1/44.

39. In an underground boring tool having a drill head configured for allowing the transmission of a ground penetrating locating signal, an assembly comprising:

a transmitter for originating said locating signal; and

an elongated electrically conductive wall arrangement, as part of said drill head for direct contact with the ground, including a pair of opposing ends to at least partially bound an interior chamber formed between said opposing ends, said wall arrangement further extending in an elongation direction between the opposing ends and said transmitter being positioned in said interior chamber such that transmission of the locating signal by the transmitter induces a current flow in said wall arrangement, resulting in a counter magnetic field originating from the wall arrangement, upon transmission of the locating signals, said electrically conductive wall arrangement defining at least two elongated slots which are arranged at least generally in said elongation direction and spaced apart about said wall arrangement, each slot having a width that is just wide enough to disrupt said current flow, thereby reducing the counter magnetic field and said elongated electrically conductive wall arrangement further defines an additional slot having said width to additionally disrupt the current flow in said housing to additionally reduce variation in the signal strength of the locating signal surrounding the boring tool.

40. The assembly of claim 39 wherein the elongated electrically conductive wall arrangement defines further additional slots until approximately no variation is exhibited in the locating signal surrounding the boring tool.

41. The assembly of claim 39 wherein a number of said additional slots are defined based, at least in part, on said locating signal exhibiting a signal strength that is substantially independent of roll orientation of the boring tool.

42. The assembly of claim 39 wherein the elongated electrically conductive wall arrangement defines further additional slots until the locating signal surrounding the boring tool is approximately axisymmetric.

43. The assembly of claim 39 wherein said elongated electrically conductive wall arrangement defines four of said slots.

44. In an underground boring tool configured for transmitting a ground penetrating locating signal, a method comprising the steps of:

providing an electrically conductive housing having an exterior surface for direct contact with the ground as part of an exterior outline of the boring tool, said housing defining an interior having an interior housing diameter;

positioning a transmitter, including an antenna coil having an antenna outer diameter and an antenna length, in said housing interior for emanating said locating signal such that a ratio of the interior housing diameter to the antenna outer diameter is approximately 2.5 or more; and

forming a number of elongated narrow slots in the housing proximate to said antenna coil based, at least in part, on structural integrity of said housing and having a minimum slot length of approximately 1.5 times the antenna length.

45. The method of claim 44 wherein transmission of the locating signal by the antenna coil within the housing induces a current flow in the housing and a resulting a counter magnetic field originating from the housing and wherein each slot is formed having a width that is just wide enough to disrupt said current flow in said housing.

46. The method of claim 45 wherein each of said slots includes an overall elongated length and wherein said current path is broken entirely along said overall elongated length of each slot.

47. The method of claim 45 wherein each of said slots includes an overall elongated length and wherein said width is substantially constant along said elongated length of each slot.

48. The method of claim 45 further comprising the steps of protecting said transmitter by filling each slot with a filler material.

49. The method of claim 48 including the step of choosing the filler material to contribute to torsional rigidity and strength of said housing.

50. The method of claim 49 wherein said slot is filled with a ceramic material.

51. The method of claim 49 wherein said slot is filled with a composite material.

52. The method of claim 48 wherein said slot is filled with an elastic material.

53. The method of claim 48 wherein said slot is filled with a rigid material.

54. The method of claim 48 wherein said slot is formed having a width of approximately 0.125 inches.

55. The method of claim 44 wherein at least two of said slots are formed circumferentially spaced apart about said housing.

56. The method of claim 44 wherein four of said slots are formed in the housing axisymmetrically spaced around said housing.

57. The method of claim 44 wherein the number of slots is selected based, at least in part, on said locating signal exhibiting approximately no variation in signal strength surrounding the boring tool.

58. The method of claim 44 wherein a number of said slots are formed based, at least in part, on said locating signal exhibiting a signal strength that is substantially independent of roll orientation of the boring tool.

59. In an underground boring tool configured for transmitting a ground penetrating locating signal, a drill head for transmitting said locating signal and for forming a borehole, said drill head comprising:

a transmitter including an antenna coil having an antenna outer diameter and an antenna length for emanating said locating signal;

an electrically conductive housing having an exterior surface for direct contact with the ground as part of an exterior outline of the boring tool, said housing defining an interior having an interior housing diameter for receiving said transmitter, said housing further defining a number of elongated narrow slots proximate to said antenna coil, when received in the housing, with the number of slots based, at least in part, on structural integrity of said housing and having a minimum slot length of approximately 1.5 times the antenna length and such that a ratio of the interior housing diameter to the antenna outer diameter is approximately 2.5 or more.

60. The drill head of claim 59 wherein transmission of the locating signal by the antenna coil within the housing induces a current flow in the housing and a resulting a counter magnetic field originating from the housing and wherein each slot includes a width that is just wide enough to disrupt said current flow in said housing.

61. The drill head of claim 60 wherein each of said slots includes an overall elongated length and wherein said current path is broken entirely along said overall elongated length of each slot.

62. The drill head of claim 60 wherein each of said slots includes an overall elongated length and wherein said current path is broken entirely along said overall elongated length of each slot.

63. The drill head of claim 59 wherein each slot is filled with a filler material.

64. The drill head of claim 59 wherein the filler material contributes to torsional rigidity and strength of said housing.

65. The drill head of claim 63 wherein each slot is filled with a ceramic material.

66. The drill head of claim 63 wherein each slot is filled with a composite material.

67. The drill head of claim 63 wherein each slot is filled with an elastic material.

68. The drill head of claim 63 wherein each slot is filled with a rigid material.

69. The drill head of claim 59 wherein said each slot is formed having a width of approximately 0.125 inches.

70. The drill head of claim 59 wherein at least two of said slots are formed circumferentially spaced apart about said housing.

71. The method of claim 59 wherein four of said slots are formed in the housing axisymmetrically spaced around said housing.

72. The drill head of claim 59 wherein four of said slots are formed in the housing.

73. The drill head of claim 59 wherein the number of slots is selected based, at least in part, on said locating signal exhibiting approximately no variation in signal strength surrounding the boring tool.

74. The drill head of claim 59 wherein the number of slots is selected based, at least in part, on said locating signal exhibiting a signal strength that is substantially independent of roll orientation of the boring tool.