Patent Publication Number: US-9429488-B2

Title: System and method of magnetic shielding for sensors

Description:
BACKGROUND 
     The subject matter disclosed herein relates generally to sensors, and more particularly to magnetic shields for magnetostrictive sensors. 
     Sensors are used in a variety of industries to sense vibration, torque, speed, force, position, and other parameters. In certain applications, the performance of the sensor may decrease due to electrical and/or magnetic interference. Furthermore, some sensors may depend on magnetic principles for their operation, and thus a leakage magnetic flux may result in performance degradation. 
     BRIEF DESCRIPTION 
     Certain embodiments commensurate in scope with the present disclosure are summarized below. These embodiments are not intended to limit the scope of the claims, but rather these embodiments are intended only to provide a brief summary of certain embodiments. Indeed, embodiments of the present disclosure may encompass a variety of forms that may be similar to or different from the embodiments set forth below. 
     In a first embodiment, a system includes a magnetostrictive sensor. The magnetostrictive sensor includes a driving coil configured to receive a first driving current and to emit a first magnetic flux portion through a target and a second magnetic flux portion. The magnetostrictive sensor also includes a first sensing coil configured to receive the first magnetic flux portion and to transmit a signal based at least in part on the received first magnetic flux portion. The received first magnetic flux portion is based at least in part on a force on the target. The magnetostrictive sensor further includes a magnetic shield disposed between the driving coil and the first sensing coil. The magnetic shield is configured to reduce the second magnetic flux portion received by the first sensing coil. 
     In a second embodiment, a system includes a magnetostrictive sensor. The magnetostrictive sensor includes a driving coil configured to receive a first driving current and to emit a first magnetic flux portion through a target and a second magnetic flux portion. The magnetostrictive sensor also includes a first sensing coil configured to receive the first magnetic flux portion and to transmit a signal to a controller based at least in part on the received first magnetic flux portion. The magnetostrictive sensor further includes a magnetic shield comprising a flexible circuit. The magnetic shield is disposed between the driving coil and the first sensing coil and the magnetic shield is configured to reduce the second magnetic flux portion received by the first sensing coil. The system also includes the controller configured to determine a force applied to the target based at least in part on the signal. 
     In a third embodiment, a method includes supplying a first current to a driving coil of a magnetostrictive sensor. The method also includes emitting a first magnetic flux portion from the driving coil through a target. Furthermore, the method includes emitting a second magnetic flux portion from the driving coil. Moreover, the method includes sensing the first magnetic flux portion with a sensing coil of the magnetostrictive sensor. Still, the method includes reducing the second magnetic flux portion received by the sensing coil based at least in part on a magnetic shield of the magnetostrictive sensor disposed between the driving coil and the sensing coil. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will be better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a side view of an embodiment of a magnetostrictive sensing system with a magnetic shield in accordance with the present disclosure; 
         FIG. 2  is a side view of an embodiment of a magnetostrictive sensing system with a magnetic shield in accordance with the present disclosure; 
         FIG. 3  is a perspective view of an embodiment of a magnetic shield in accordance with the present disclosure; 
         FIG. 4  is a perspective view of an embodiment of a magnetic shield in accordance with the present disclosure; 
         FIG. 5  is a perspective view of an embodiment of a magnetic shield in accordance with the present disclosure; 
         FIG. 6  is a top view of the external side of the magnetic shield in  FIG. 5 ; 
         FIG. 7  is a top view of the internal side of the magnetic shield in  FIG. 5 ; 
         FIG. 8  is a side view of an embodiment of a magnetostrictive sensing system with a magnetic shield in accordance with the present disclosure; 
         FIG. 9  is a top view of a magnetostrictive sensing system having an outer magnetic shield; 
         FIG. 10  is a perspective view of an embodiment of the sensor head of the magnetostrictive sensing system as illustrated in  FIG. 1 ; and 
         FIG. 11  is a top view of the embodiment of the sensor head in  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     Ferromagnetic materials have a magnetostrictive property that causes the materials to change shape in the presence of an applied magnetic field. Conversely, when a force is applied to a ferromagnetic material to cause the shape to change, the magnetic properties (e.g., magnetic permeability) of the material also change. Therefore, ferromagnetic materials can convert magnetic energy into potential energy, or potential energy into magnetic energy. Accordingly, ferromagnetic materials may be used for sensors such as force sensors, position sensors, and torque sensors. A magnetostrictive sensor may generate a magnetic flux to pass through a ferromagnetic material. 
     A magnetostrictive sensor may include a driving coil to generate magnetic flux and a sensing pole to sense the magnetic flux passing through a ferromagnetic material (e.g., a target material). Because the changes in the measured magnetic flux depend partly on the changes in magnetic permeability of the ferromagnetic material, which in turn are related to the amount of force applied to the ferromagnetic material, measurement of the magnetic flux may be used to sense and/or calculate the value of the applied force. Unfortunately, a leakage magnetic flux from the driving coil to the sensing coil may occur in the magnetostrictive sensor. The leakage magnetic flux does not pass through the ferromagnetic material and, therefore, provides little information on the magnetic permeability of the ferromagnetic material. In addition, because the leakage magnetic flux also passes through the sensing coil, the leakage magnetic flux may be a noise relative to the measured magnetic flux that is from the driving coil to the sensing coil passing through the ferromagnetic material. Such noise may reduce the dynamic range of the magnetostrictive sensor. 
     The present disclosure provides a magnetostrictive sensor with a magnetic shield. As discussed in greater detail below, the magnetic shield may be disposed in the space between a driving pole and a sensing pole of the magnetostrictive sensor. The magnetic shield may also be disposed about the driving pole. The magnetic shield may reduce or eliminate the leakage flux between the driving pole and the sensing pole. Advantageously, the resulting magnetostrictive sensor may have an increased dynamic sensing range. In addition, the magnetic shield may improve the signal to noise ratio of the magnetostrictive sensor. Furthermore, by including the magnetic shield, the magnetostrictive sensor may use a simpler conditioning circuitry. 
       FIG. 1  is a side view of an embodiment of a magnetostrictive sensing system  10  with a magnetic shield  11  (e.g., a magnetic shield  12 ) in accordance with the present disclosure. The magnetostrictive sensing system  10  may be used for sensing a force applied to a target material  14  of a machine or equipment  15 , such as a turbomachine (e.g., a turbine engine, a compressor, a pump, or a combination thereof), a generator, a combustion engine, or a combination thereof. The target material  14  may be a ferromagnetic material including, but not limited to, iron, steel, nickel, cobalt, alloys of one or more of these materials, or any combination thereof. The magnetostrictive sensing system  10  includes a sensor head  16  positioned proximate to the target material  14 , thereby forming a gap  17  between the sensor head  16  and the target material  14 . The sensor head  16  may be coupled to a frame or fixture to maintain the sensor head  16  in the proper orientation and/or position. 
     The sensor head  16  has a core  18  that may be formed from a ferromagnetic material. The core  18  has at least two ends, such as a driving pole  20  and a sensing pole  22 . A driving coil  24  and a sensing coil  26  are disposed about (e.g., wrapped around) the driving pole  20  and the sensing pole  22 , respectively. A power source  28  (e.g., electrical outlet, electrical generator, battery, etc.) provides an AC current (e.g., first driving current) to the driving coil  24 . The first driving current passes through the driving coil  24  to induce a magnetic flux  30  that emanates from the driving coil  24 . A controller  32  electronically coupled to the power source  28  is configured to control characteristics of the first driving current delivered to the driving coil  24  by the power source  28 . For example, the controller  32  may control the frequency, amplitude, or the like, of the first driving current. The controller  32  may be coupled to the power source  28  by wired or wireless connections. Wireless communication devices such as radio transmitters may be integrated with the controller  32  to transmit the signals to a receiver integrated with the power source  28 . 
     The controller  32  may include a distributed control system (DCS) or any computer-based workstation that is fully or partially automated. For example, the controller  32  may be any device employing a general purpose or an application-specific processor  34 , both of which may generally include memory circuitry  36  for storing instructions related to frequencies, amplitudes of currents, for example. The processor  34  may include one or more processing devices, and the memory circuitry  36  may include one or more tangible, non-transitory, machine-readable media collectively storing instructions executable by the processor  34  to perform the methods and control actions described herein. 
     Such machine-readable media can be any available media other than signals that can be accessed by the processor or by any general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can include RAM, ROM, EPROM, EEPROM, CD-ROM, or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by the processor or by any general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium. Thus, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions includes, for example, instructions and data which cause the processor or any general purpose computer, special purpose computer, or special purpose processing machine to perform a certain function or group of functions. 
     As illustrated, a first magnetic flux portion  38  permeates the target material  14 , passes through the sensing coil  26 , and returns to the driving coil  24  via the core  18 . The sensing coil  26  may be used to measure the first magnetic flux portion  38 . A force (e.g., compressive, tensile, torsional, etc.) applied to the target material  14  may change the permeability of the target material  14 , thereby causing the first magnetic flux portion  38  to change. The sensing coil  26  is configured to transmit a signal indicative of the changes in the first magnetic flux portion  38  to the controller  32 . The processor  34  of the controller  32  may process the signal received from the sensing coil  26  to calculate the force applied to the target material  14 . For example, the processor  34  may execute pre-stored and/or user-defined algorithms in the memory  36  to calculate the magnitude and/or direction of the force applied to the target material  14  based on the characteristics of the target material  14 , the sensor head  16 , and the first driving current. The signal from the sensing coil  26  may be communicated by wired or wireless connections to the controller  32 . In some embodiments, wireless communication devices, such as radio transmitters, may be integrated with the sensor head  16  (e.g., proximate to the sensing coil  26 ) to transmit the signals to a receiver integrated with the controller  32 . The signal received from the sensing coil  26  may also be processed with other electronic components, such as an amplifier, a filter, or the like, before or after being processing by the processor  34  of the controller  32 . 
     A second magnetic flux portion  40  emitted by the driving coil  24  may enter the sensing coil  26  without permeating the target material  14 , as illustrated in  FIG. 1 . The second magnetic flux portion  40  may also be referred to as the leakage magnetic flux  40 . As noted above, the leakage magnetic flux  40  provides little information on the magnetic characteristics (e.g., magnetic permeability) of the target material  14  because the leakage magnetic flux  40  does not permeate the target material  14 . Accordingly, the leakage magnetic flux  40  may be an undesirable noise signal sensed by the sensing coil  26  relative to the signal from the first magnetic flux portion  38 . The noise from the leakage magnetic flux  40  may be significant compared to the measured first magnetic flux portion  38 . As discussed below, the magnetic shield  12  may help to reduce or eliminate noise associated with the leakage magnetic flux  40  by substantially or entirely blocking the leakage magnetic flux  40 . Accordingly, the magnetic shield  12  may improve accuracy of sensor measurements, and thus enable better control of the machine or equipment, such as a turbomachine (e.g., a turbine engine, a compressor, a pump, or a combination thereof), a generator, a combustion engine, or a combination thereof. 
     In operation, the controller  32  may send a control signal to the power source  28  to deliver a desired AC current to the driving coil  24 . The driving coil  24  emits the first magnetic flux portion  38  that permeates the target material  14  and is detected by the sensing coil  26 . A change in the first magnetic flux portion  38  emitted from the driving coil  24  to the first magnetic flux portion  38  sensed by the sensing coil  26  due to a force applied to the target material  14  may be measured by the magnetostrictive sensing system  10 . A signal corresponding to such change may be transmitted to the controller  32 . The processor  34  of the controller  32  may process the signal received from the sensing coil  26  to obtain a measurement of the force applied to the target material  14 . In addition, the driving coil  24  may also emit the second (i.e., leakage) magnetic flux portion  40  that does not permeate the target material  14 . The corresponding signal from the leakage magnetic flux  40  sensed by the sensing coil  26  may constitute noise relative to the measured signal from the first magnetic flux portion  38 . 
     In order to reduce or eliminate the sensed leakage flux  40  present in the magnetostrictive sensing system  10 , the magnetic shield  12  in accordance with the present disclosure may be disposed between the driving pole and the sensing pole. As illustrated, the magnetic shield  12  is disposed in the space  42  between the driving pole  20  and the sensing pole  22 . As discussed in greater detail below, the magnetic shield  12  may be a split tube or annulus formed from a material with a high magnetic permeability. Additionally, or in the alternative, the magnetic shield  12  may be a flexible printed circuit board rolled up to a tube or annulus. Additionally, or in the alternative, the magnetic shield  12  may be a flexible printed circuit board rolled up to a tube or annulus that is provided with an additional driving current to emit a counter-active magnetic flux to the leakage magnetic flux  40 , thereby providing active magnetic shielding. As illustrated, the leakage magnetic flux  40  sensed by the sensing coil  26  may be reduced or eliminated by the magnetic shield  12  (e.g., an active and/or passive magnetic shield). Accordingly, the leakage magnetic flux  40  is illustrated with a dashed line. 
     The driving coil  24  has a length  44  along an axis  46  substantially perpendicular to the portion in the core  18  connecting the driving pole  20  and the sensing pole  22 , and the sensing coil  26  has a length  48  along the axis  46 . The magnetic shield  12  has a length  50  along an axis  47  parallel to the axis  46 . A longer length of the magnetic shield  12  may have less sensed leakage flux than a shorter length of the magnetic shield  12 , the length  50  of the magnetic shield  12  is substantially the same or greater than the length  44  of the driving coil  24  and the length  48  of the sensing coil  26 . Accordingly, the magnetic shield  12  may be disposed between the driving pole  20  and the sensing pole  22  such that the magnetic shield  12  substantially covers the full length of the driving coil  24  and/or the full length of the sensing coil  26 . 
     In some embodiments in accordance with the present disclosure, the magnetostrictive sensing system  10  may include more than one magnetic shield  12 . For example, more than one magnetic shield  12 , coupled with each other in any suitable manner (e.g., in series, in parallel, concentric, coaxial, telescopic, or any combination thereof), may be disposed in the space  42  between the driving pole  20  and the sensing pole  22 . 
       FIG. 2  illustrates an embodiment of a magnetostrictive sensing system  60  that includes a magnetic shield  11  (e.g., a magnetic shield  62 ) disposed about (e.g., wrapped around) the driving coil  24  of the driving pole  20 . Additionally, or in the alternative, the magnetic shield  62  may be disposed about (e.g., wrapped around) the sensing coil  26  of the sensing pole  22 . As discussed in greater detail below, the magnetic shield  62  may be a split tube or annulus formed from a material with a high magnetic permeability. Additionally, or in the alternative, the magnetic shield  62  may be a flexible printed circuit board rolled up to a tube or annulus. As illustrated, the leakage magnetic flux  40  sensed by the sensing coil  26  may be reduced or eliminated by the magnetic shield  62 . Accordingly, the leakage magnetic flux  40  is illustrated with a dashed line. 
     The magnetic shield  62  has a length  64  along the axis  46 . Similar to the embodiment discussed above with reference to  FIG. 1 , a longer length of the magnetic shield  62  may have less sensed leakage flux than a shorter length of the magnetic shield  62 . Accordingly, the length  64  of the magnetic shield  62  is substantially the same or greater than the length  44  of the driving coil  24  and the length  48  of the sensing coil  26 . The magnetic shield  62  may be disposed about the driving pole  20  such that the magnetic shield  62  substantially covers the full length of the driving coil  24 . Additionally, or in the alternative, the magnetic shield  62  may be disposed about the sensing pole  22  such that the magnetic shield  62  substantially covers the full length of the sensing coil  26 . 
     In some embodiments in accordance with the present disclosure, more than one magnetic shield  62 , coupled with each other in any suitable manner (e.g., in series, in parallel, concentric, coaxial, telescopic, or any combination thereof), may be disposed about (e.g., wrapped around) the driving coil  24  of the driving pole  20 . In some embodiments, one or more magnetic shields  62  may be disposed about the driving coil  24  of the driving pole  20  together with one or more magnetic shields  12  (as illustrated in  FIG. 1 ) disposed in the space  42  between the driving pole  20  and the sensing pole  22 . 
       FIG. 3  illustrates an embodiment of a magnetic shield  11  (e.g., a magnetic shield  70 ) in accordance with the present disclosure, which may be disposed in the space  42  between the driving pole  20  and the sensing pole  22  (e.g., as shown in  FIG. 1 ), or disposed about (e.g., wrapped around) the driving coil  24  of the driving pole  20  (e.g., as shown in  FIG. 2 ), or a combination thereof. An axial axis  72 , a radial axis  74 , and a circumferential axis  76  are utilized herein to describe the magnetic shield  70 . As illustrated, the magnetic shield  70  is a split cylindrical tube. The magnetic shield  70  has a length  78  along the axial axis  72 . The length  78  of the magnetic shield  70  may be substantially the same or greater than the length of the driving coil  24  and the sensing coil  26  in a magnetostrictive sensing system  10  (e.g., the length  44  of the driving coil  24  and the length  48  of the sensing coil  26  in  FIGS. 1 and 2 ). 
     The magnetic shield  70  includes a shell  80  (e.g., outer annular wall) that has a split  82  (e.g., an axial opening) along the axial axis  72 . The split  82  of the magnetic shield  70  is for breaking the induced current path around the circumferential axis  76 . The shell  80  encompasses a space  84  such that the driving pole  20  with the driving coil  24  may be fit into the space  84  without contacting the inside wall  86  of the shell  80 . The split  82  may have any suitable size  88  along the circumferential axis  76 , for example, less than half (e.g., approximately 3, 5, 10, 15, 20, 25, 30, 45, 60, 90, 120, 135, 175 degrees) of the circumference of the shell  80  along the circumferential axis  76 . The shell  80  may also have any suitable thickness  90 , including, but not limited to, between approximately 50 μm and 1000 μm, between approximately 100 μm and 750 μm, between approximately 150 μm and 500 μm, between approximately 200 μm and 400 μm, or between approximately 250 μm and 300 μm. The magnetic shield  70  may be oriented in the space  42  such that the split  82  is not disposed directly between the driving coil  24  and the sensing coil  26 . 
     The magnetic shield  70  may be fabricated from a material with a high magnetic permeability, such as a material with a relative permeability between approximately 100 and 100,000, such as between approximately 200 and 90,000, between approximately 300 and 70,000, between approximately 500 and 50,000, between approximately 1,000 and 30,000, between approximately 2,000 and 20,000, or between approximately 5,000 and 10,000. The high magnetic permeability material of the magnetic shield  70  may include iron, Mu-metal, cobalt-iron, permalloy, nanoperm, electrical steel, ferrite, carbon steel, nickel, or any combination thereof. In some embodiments, the magnetic shield  70  may be manufactured by any suitable methods (e.g., casting, machining, molding, manual, or any combination thereof) to roll up a sheet of high magnetic permeability material as discussed herein to the desirable shape (e.g., with a cross section of a split circle, square, rectangle, triangle, or oval). 
     As illustrated in  FIG. 3 , the magnetic shield  70  is substantially a cylindrical tube. In some embodiments, the magnetic shield  70  may have any suitable shape. For example, the cross section of magnetic shield  70  on the plane defined by the axes  74  and  76  may be substantially a square, a rectangle, a triangle, or an oval. In some embodiments, the magnetic shield  70  may also include a tapered portion at one or both of the two axial ends of the magnetic shield  70 . 
       FIG. 4  illustrates an embodiment of a magnetic shield  11  (e.g., a magnetic shield  92 ) with tapered portions  93 ,  94  at both axial ends. Each of the tapered portions  93 ,  94  is angled inward (e.g., toward the space  84 ) with an angle  95  with respect to the axial axis  72 . The angle  95  may be between approximately 1 degree and 90 degrees, such as between approximately 5 degrees and 80 degrees, between approximately 10 degrees and 75 degrees, between approximately 15 degrees and 70 degrees, between approximately 20 degrees and 65 degrees, between approximately 30 degrees and 60 degrees, or between approximately 40 degrees and 50 degrees. 
     Each of the tapered portions  93 ,  94  has a length  96  along the axial axis  72 . The length  96  may be any suitable length such that the driving pole  20  with the driving coil  24  may be fit into the space  84  without contacting an edge  97  of each of the tapered portions  93 ,  94 . Although the illustrated tapered portions  93 ,  94  have the same dimensions (e.g., the length  96  along the axial axis  72 , and the angle  95  with respect to the axial axis  72 ), in some embodiments the tapered portions  93 ,  94  may have different dimensions. 
       FIGS. 5, 6, and 7  are diagrams of an embodiment of a magnetic shield  11  (e.g., a magnetic shield  100 ) that may be disposed in the space  42  between the driving pole  20  and the sensing pole  22  (e.g., as shown in  FIG. 1 ), or disposed about (e.g., wrapped around) the driving coil  24  of the driving pole  20  (e.g., as shown in  FIG. 2 ), or a combination thereof. Similar to the magnetic shield  70 , the magnetic shield  100 , as illustrated in  FIG. 5 , is substantially a cylindrical tube. In some embodiments, the magnetic shield  100  may have any suitable shape. For example, the cross section of the magnetic shield  100  may be substantially a square, a rectangle, a triangle, or an oval. 
     As illustrated in  FIGS. 6 and 7 , the magnetic shield  100  is a substantially rectangular flexible printed circuit board  102  rolled up to a substantially cylindrical tube. The magnetic shield  100  has an external side  104  and an internal side  106 , which are illustrated in  FIGS. 6 and 7 , respectively. These two sides of the magnetic shield  100  may also be referred to herein as the front side  104  and the back side  106  of the printed circuit board  102 . 
       FIG. 6  illustrates an embodiment of the front side  104  of the printed circuit board  102 . As illustrated, the front side  104  of the printed circuit board  102  may include a substrate layer  108  and a printed pattern  110 . The substrate layer  108  may be fabricated from a flexible material such as FR4 (e.g., a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant), kapton, or polyamide, or any combination thereof. The substrate layer  108  may have a thickness between approximately 200 μm to 5 mm, 300 μm to 4 mm, 500 μm to 2 mm, 800 μm to 1.5 mm, or 1 mm to 1.2 mm. 
     The printed pattern  110  is printed or otherwise disposed onto the substrate layer  108 . The printed pattern  110  may be a spiral coil around the printed circuit board  102 . In some embodiments, the printed pattern  110  may be connected lines substantially parallel to either side  104 ,  106  of the printed circuit board  102 . The printed pattern  110  may substantially cover the front side  104  of the printed circuit board  102 . In other embodiments, the printed pattern  110  may substantially cover both the front side  104  and the back side  106 , for example, with the spiral coils on both sides  104 ,  106  around a same direction (e.g., counterclockwise or clockwise). A first end  112  of the printed pattern  110  is on the front side  104  of the printed circuit board  102 , and a second end  116  of the printed pattern  110  is on the back side  106  of the printed circuit board  102  through a hole (e.g., via)  118  on the substrate layer  108  of the printed circuit board  102 . The first end  112  of the printed pattern  110  may be coupled to a resistor  114 . The resistor is configured to properly dissipate the electrical energy generated from the leakage flux such it may have minimum back electromotive force to the driving coil  24 . An end  117  of the resistor  114  is electrically connected to the second end  116  of the printed pattern  110  through a hole (e.g., via)  119  on the substrate layer  108  of the printed circuit board  102 . 
     The printed pattern  110  may have a thickness (e.g., height arising on top of the substrate layer  108 ) of between approximately 10 μm to 1 mm, 20 μm to 800 μm, 30 μm to 500 μm, 40 μm to 300 μm, 50 μm to 200 μm, or 70 μm to 100 μm. The printed pattern  110  may be fabricated from a material with a high electrical conductivity, such as copper, silver, gold, aluminum, calcium, tungsten, zinc, nickel, lithium, iron, tin, platinum, carbon steel, or any combination thereof. 
     The magnetic shield  100  may be rolled or formed to the desirable shape (e.g., a cylindrical tube) with no split between two ends  122 ,  124  of the printed circuit board  102 . For example, the overlapping ends  122 ,  124  may form an overlapping region  120  when the printed circuit board  102  is rolled up to form the cylindrical shape. The purpose of overlapping region is to ensure a complete coverage of the leakage flux in radial directions. As discussed above, the magnetic shield  100  may reduce or eliminate the leakage magnetic flux  40  between the driving coil  24  and the sensing coil  26  of the magnetostrictive sensing system  10 . 
       FIG. 8  illustrates an embodiment of a magnetic shield  11  (e.g., an active magnetic shield  130 ) in accordance with the present disclosure. The magnetic shield  130  may be disposed in the space  42  between the driving pole  20  and the sensing pole  22  of a magnetostrictive sensing system  132  (e.g., as shown in  FIG. 1 ). The magnetic shield  130  may be generally the same as the magnetic shield  100  in a generally flat fashion as illustrated in  FIGS. 6, and 7  (e.g., without being rolled up to a substantially cylindrical tube). The front side  104  of the magnetic shield  130  may generally face either the driving pole  20  or the sensing pole  22 . In some embodiments, the magnetic shield  130  may exclude the resistor  114 . The magnetic shield  130  is provided with an AC current to emit additional magnetic flux, as described in greater detail below. Accordingly, the magnetic shield  130  may be referred to as an active magnetic shield. In contrast, the magnetic shield  100  is not provided with any current, thereby no additional magnetic flux is emitted by the magnetic shield  100 . Accordingly, the magnetic shield  100  may be referred to as a passive magnetic shield. 
     The two ends  112 ,  116  of the printed pattern  110  in the magnetic shield  130  are not connected with one another via the hole  119  but are electrically coupled to a power source  134 . The power source  134  may be the same or separate from the power source  28 . The power source  134  provides an AC current (e.g., a second driving current) to the printed pattern  110  of the active magnetic shield  130 . The second driving current through the printed pattern  110  induces a third magnetic flux portion  136  and a fourth magnetic flux portion  138 . As noted above, the controller  32  is electronically coupled to the power source  134 . The controller  32  is configured to control characteristics (e.g., frequency, amplitude) of the second driving current delivered to the printed pattern  110  by the power source  28 . In some embodiments, a combined power source (e.g., combining the power sources  28  and  134 ) may be used to provide power to the driving coil  24  and the magnetic shield  130 . 
     As illustrated, the third magnetic flux portion  136  permeates the target material  14 . The fourth magnetic flux portion  138  passes through the driving coil  24 , the sensing coil  26 , and the core  18  without permeating the target material  14 , similar to the leakage magnetic flux  40 . In accordance with the present disclosure, the second driving current has the same frequency as, but the opposite phase to, the first driving current. Accordingly, the fourth magnetic flux portion  138  has an opposite direction of the leakage magnetic flux  40  at a given time during operation. The magnitude of the fourth magnetic flux portion  138  may be tuned to be substantially the same as the magnitude of the leakage magnetic flux  40 . Through tuning the fourth magnetic flux portion  138 , the overall leakage magnetic flux (e.g., sum of the fourth magnetic flux portion  138  and the leakage magnetic flux  40 ) between the driving coil  24  and the sensing coil  26  may be reduced or eliminated. Because the active magnetic shield  130  is provided with a driving current (e.g., the second drive current) to actively emit a magnetic flux (e.g., the fourth magnetic flux portion  138 ) to negatively counteract the leakage magnetic flux  40 , the printed pattern  110  of the magnetic shield  130  may also be referred to herein as a compensation coil  110 . 
     As noted above, the magnitude of the fourth magnetic flux portion  138  may be tuned to be substantially the same as the magnitude of the leakage magnetic flux  40 . The magnitude of the fourth magnetic flux portion  138  depends, at least, on magnitude of the second driving current and the number of turns of the printed pattern  110 . Accordingly, by tuning the magnitude of the second driving current and/or the number of turns of the printed pattern  110 , the magnitude of the fourth magnetic flux portion  138  may be tuned. In some embodiments, the number of turns of the printed pattern  110  of the magnetic shield  130  is the same as the number of coils of the driving coil  24 . When in operation, the controller  32  may send a control signal to the power source  28  to deliver two driving currents to the driving coil  24  and the magnetic shield  130 , respectively, where the two driving currents have substantially the same magnitude but the opposite phase. Accordingly, the leakage magnetic flux  40  due to the first driving current may be substantially reduced or eliminated by the fourth (or compensation) magnetic flux portion  138  with substantially the same magnitude but the opposition direction due to the second driving current. 
     Regardless of the disposition of the magnetic shield  11  (e.g., as shown in  FIGS. 1 and 2 ), the number of the magnetic shield  11  (e.g., one or more), or the configurations and/or shapes of the magnetic shield (e.g., the magnetic shields  70 ,  92 ,  100 ,  130 ), the magnetostrictive sensing systems  10 ,  60 ,  132  may additionally include an outer magnetic shield enclosing the sensor head  16 . The outer magnetic shield may reduce external electromagnetic interference received by the driving coil and the sensing coil.  FIG. 9  illustrates a top view of an embodiment of a magnetostrictive sensing system  140  incorporating such an outer magnetic shield  142 . As discussed above, the magnetostrictive sensing system  140  includes the sensor head  16 . The sensor head  16  includes the core  18 , the driving pole  20 , and the sensing pole  22 . The driving coil  24  is disposed about the driving pole  20 , and the sensing coil  26  is disposed about the sensing pole  22 . As illustrated, the magnetostrictive sensing system  140  also includes a magnetic shield  11  (e.g., a magnetic shield  144 ) in accordance with the present disclosure (e.g., the magnetic shields  70 ,  92 ,  100 ). While the magnetic shield  144  illustrated in  FIG. 9  is disposed about the driving pole  20 , the magnetic shield  144 , as noted above, may be in any configuration, or disposed in any space between the driving pole  20  and the sensing pole  22 . For example, the magnetic shield  144  may be disposed in the space  42 . 
     As illustrated, the magnetostrictive sensing system  140  also includes the outer magnetic shield  142 . The outer magnetic shield  142  may include one or more layers for reducing the magnetic interference from an outside source. For example, in some embodiments, the outer magnetic shield  142  may include, but is not limited to, one or more layers of material with a high conductivity to reduce high frequency interference. Such high electrical conductivity material may include copper, silver, gold, aluminum, calcium, tungsten, zinc, nickel, lithium, iron, tin, platinum, carbon steel, or any combination thereof. 
     Alternatively or additionally, the outer magnetic shield  142  may include one or more layers of material with a high magnetic permeability to reduce low frequency interference. Such material has a relative permeability between approximately 100 to 100,000, 200 to 90,000, 300 to 70,000, 500 to 50,000, 1,000 to 30,000, 2,000 to 20,000, or 5,000 to 10,000. Such high magnetic permeability material may include, but is not limited to, iron, Mu-metal, cobalt-iron, permalloy, nanoperm, electrical steel, ferrite, carbon steel, nickel, or any combination thereof. 
     As illustrated in  FIG. 1 , the sensor head  16  includes a driving pole  20  and at least one sensing pole  22  with the corresponding driving coil  24  and at least one sensing coil  26  disposed thereabout, respectively. Some embodiments of the sensor head  16  may include one or more driving poles and one or more sensing poles.  FIG. 10  is a perspective view of an embodiment of a sensor head  150  with one driving pole  152  and four sensing poles  154 ,  156 ,  158 ,  160 .  FIG. 11  is a top view of the embodiment of the sensor head  150  of  FIG. 10 . 
     As illustrated in  FIGS. 10 and 11 , the sensor head  150  includes a core  162 . The core  162  may be fabricated from any ferromagnetic material (e.g., iron, steel, nickel, cobalt). The core  162  has a cross axis yoke  164  with a yoke portion  166 . Four members  168 ,  170 ,  172 ,  174  of the cross axis yoke  164  extend radially outward in a plane from the yoke portion  166 . The four members  168 ,  170 ,  172 ,  174  are substantially orthogonal to each other around the yoke portion  166 . Each of the four members  168 ,  170 ,  172 ,  174  may extend from the yoke portion  166  in any configuration and for any length that enables each member to operate as described herein. In some embodiments, the yoke  164  may have any number of members that enables the yoke  164  to operate as described herein. For example, the sensor head  150  may have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more members that extend radially from the yoke portion  166 . The one or more members may be angularly spaced apart by approximately 10, 20, 30, 40, 45, 60, 75, 90, 120, or 130 degrees, or any combination thereof. 
     As illustrated in  FIG. 10 , the driving pole  152  extends outward from the yoke portion  166  perpendicular to a planar surface defined by the yoke  164 . In addition, the four sensing poles  154 ,  156 ,  158 ,  160  extend outward from the yoke  164  substantially perpendicular to the planar surface defined by the yoke  164  and substantially parallel to driving pole  152 . The sensing pole  154  extends from the distal end of member  168 , the sensing pole  156  extends from the distal end of member  170 , the sensing pole  158  extends from the distal end of member  172 , and the sensing pole  160  extends from the distal end of member  174 . In some embodiments, the core  162  may have any number of poles (including driving poles and sensing poles) extending from the yoke  164  that enables the core  162  to operate as described herein. For example, the core may have one driving pole and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more sensing poles extending from the yoke  164 . Also, a driving coil  176  is disposed about (e.g., wrapped around) the driving pole  152 . Four detection coils  178 ,  180 ,  182 ,  184  are disposed about (e.g., wrapped around) each of the respective sensing poles  154 ,  156 ,  158 ,  160 . 
     In operation, an AC current is passed through the driving coil  176  to induce the first magnetic flux portion  38 . The first magnetic flux portion  38  flows from the driving pole  152 , through the target material  14 , to the four sensing poles  154 ,  156 ,  158 ,  160 , where the respective sensing coils  178 ,  180 ,  182 ,  184  detect the first magnetic flux portion  38 . As noted above, a change in the first magnetic flux portion  38  due to a force applied to the target material  14  may be measured by the sensing coils  178 ,  180 ,  182 ,  184 . In addition, the driving coil  176  may also emit leakage magnetic fluxes  40  that do not permeate the target material  14 . The signal from the leakage magnetic fluxes  40  detected by the sensing coils  178 ,  180 ,  182 ,  184  may constitute noise relative to the measured signal from the first magnetic flux portion  38 . 
     In accordance with the present disclosure, one or more magnetic shields  11  (e.g., the magnetic shield  12 ,  62 ,  70 ,  92 ,  100 ,  130 ,  144 ) may be disposed in the space between the driving pole  152  and each of the respective sensing poles  154 ,  156 ,  158 ,  160 , or one magnetic shield (e.g., the magnetic shield  62 ,  70 ,  92 ,  100 ,  144 ) may be disposed about (e.g., wrapped around) the driving coil  176  of the driving pole  152 , or any combination thereof. In some embodiments, more than one magnetic shield (e.g., the magnetic shield  70 ,  92 ,  100 ,  130 ), coupled with each other in any suitable manner (e.g., in series, in parallel, concentric, coaxial, telescopic, or any combination thereof), may be disposed in the space  42  between the driving pole  152  and each of the respective sensing poles  154 ,  156 ,  158 ,  160 , or disposed about (e.g., wrapped around) the driving coil  176  of the driving pole  152 . 
     Technical effects of the subject matter disclosed herein include, but are not limited to, disposing one or more magnetic shields in the magnetostrictive sensing system to reduce or eliminate the leakage flux between the driving pole and the sensing pole. Advantageously, the resulting magnetostrictive sensing system may have an increased dynamic sensing range. In addition, the magnetic shields may improve the signal to noise ratio of the magnetostrictive sensing system. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.