Abstract:
A power supply includes a rotor having an undulated surface ( 658, 858, 958, 10, 58 ) and a magnetostrictive material disposed adjacent to the undulated surface. The undulated surface alternatingly compresses the magnetostrictive material as the rotor rotates, inducing an electric current in a conductor coupled to the magnetostrictive material.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/451,264, which was filed Mar. 10, 2011, and is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally wellbore operations and, more particularly, to magnetostrictive power supplies for bottom hole assemblies with rotation-resistant housings. 
         [0003]    Power for use in a downhole environment generally has been either stored in a device, such as a battery, and conveyed downhole, or it has been transmitted via conductors, such as a wireline, from another remote location. More common as of late is the use of vane turbines in the mud flow which use magnets and stator windings to generator power. 
         [0004]    As is well known, batteries have the capability of storing only a finite amount of power and have environmental limits, such as temperature, on their use. Additionally, batteries are not readily recharged downhole. And vane turbines are subject to wear and lock up in the event of unfavorable debris in the flow. 
         [0005]    Electrical conductors, such as those in a conventional steering tools where a cable is run on the outside of the drill pipe and enters the bottom hole assembly through a side wall port to power the down hole equipment, provide a practically unlimited amount of power, but require special facilities at the surface for deployment and typically have depth limitations and the drill string can not be rotated etc. while the conductors are in the flowpath. 
         [0006]    In wellbore operations, a wide variety of mechanical devices are used that convert electrical power to mechanical energy in order to perform work downhole. Those mechanical devices may be subject to a variety of forces, and much of the mechanical energy may be directed to the performance of that work, while some of the energy may be released in secondary ways. What is needed is a method of harvesting mechanical energy downhole and generating electrical power therefrom. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features. 
           [0008]      FIGS. 1-4  are diagrams of exemplary rotary steerable bottom hole assemblies, in accordance with certain embodiments of the present disclosure. 
           [0009]      FIG. 5A  is a longitudinal cross-sectional view of an example rotary steerable tool with a magnetostrictive power supply, in accordance with certain embodiments of the present disclosure. 
           [0010]      FIG. 5B  is a close-up view of the example rotary steerable tool with the magnetostrictive power supply of  FIG. 5A . 
           [0011]      FIGS. 6A ,  6 B and  6 C are latitudinal cross-sectional views illustrating an exemplary assembly  600 , in accordance with certain embodiments of the present disclosure.  FIG. 7  shows an example of a full wave rectifier fed by two sets of windings, in accordance with certain embodiments of the present disclosure. 
           [0012]      FIGS. 8A and 8B  show an axial magnetostrictive rod compression assembly, in accordance with certain embodiments of the present disclosure. 
           [0013]      FIG. 9  shows an axial magnetostrictive rod compression assembly, in accordance with certain embodiments of the present disclosure. 
           [0014]      FIGS. 10A and 10B  are cross-sectional views of an example tool with a magnetostrictive power rotor rotatably coupled to a shaft, in accordance with certain embodiments of the present disclosure. 
           [0015]      FIG. 11  is a cross-sectional view of an example assembly using a positive displacement motor to generate power, in accordance with certain embodiments of the present disclosure. 
       
    
    
       [0016]    While embodiments of this disclosure have been depicted and described and are defined by reference to exemplary embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure. 
       DETAILED DESCRIPTION 
       [0017]    The present disclosure relates generally wellbore operations and, more particularly, to magnetostrictive power supplies for bottom hole assemblies with rotation-resistant housings. 
         [0018]    Illustrative embodiments of the present invention are described in detail herein. In the interest of clarity, not all features of an actual implementation may be described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation specific decisions must be made to achieve the specific implementation goals, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of the present disclosure. 
         [0019]    To facilitate a better understanding of the present invention, the following examples of certain embodiments are given. In no way should the following examples be read to limit, or define, the scope of the invention. Embodiments of the present disclosure may be applicable to horizontal, vertical, deviated, or otherwise nonlinear wellbores in any type of subterranean formation. Embodiments may be applicable to injection wells as well as production wells, including hydrocarbon wells. Devices and methods in accordance with certain embodiments may be used in one or more of wireline, measurement-while-drilling (MWD), logging-while-drilling (LWD) and completions operations. 
         [0020]    In certain embodiments according to the present disclosure, magnetostrictive technology may be capable of generating electrical power during the process of drilling a borehole by using the mechanical energy generated in a bottom hole assembly. Magnetostrictive materials have the ability to convert kinetic/elastic energy into magnetic energy that may be used to generate electrical power. Magnetostrictive materials have the property that, when strain is induced in the material, the change in linear dimensions produces a corresponding change in magnetic field about the material. In other words, mechanical loads can deform the material and thereby rotate magnetic domains. The change of the magnetic flux can be used to generate electrical power. A suitable material for the magnetostrictive material may be Terfenol-D, available from Etrema Products, Inc. Various materials, e.g., iron and iron alloys such as Terfenol, may provide suitable magnetostrictive and giant magnetostrictive responses. These materials normally respond to a force applied to their mechanical connection by creating a magnetic field which can be detected, for example, by a surrounding coil. 
         [0021]    Certain embodiments of systems and methods disclosed herein may be useful in rotary steerable tools which have non-rotating housings or rotation-resistant housings (such as those used for sensor platforms, communication nodes, repeater nodes, or telemetry nodes, etc.) in a work string or drill string. Certain embodiments of systems and methods disclosed herein may be used to supply electrical power to components downhole, such as actuators, sensors, electronics and steering systems, using a power supply located in a non-rotating or rotation-resistant housing. A power supply comprising a magnetostrictive rod cam rotor and winding modules may be positioned within a non-rotating or rotation-resistant housing. The magnetostrictive rod cam may be rotatably coupled to the drive shaft that runs through the housing. The drive shaft may be rotatably coupled to a surface or down hole rotating motor. Suitable surface rotating motors may include a top drive or rotary table. Suitable downhole rotating motors may include a mud motor or turbine motor. The rotating motor may provide rotational energy to the shaft that is converted into electrical energy by the magnetostrictive power supply. 
         [0022]    For simplicity, various elements may be generally referenced herein as a stator due to remaining stationary relative to a rotor. And, various elements may be generally referenced herein as the rotor due to corresponding movement. However, it should be understood that motion is relative and, thus, the convention of which is the rotor or stator may be interchangeable. 
         [0023]      FIGS. 1 ,  2 , and  3  show various exemplary rotary steerable borehole assemblies, in accordance with certain embodiments of the present disclosure.  FIG. 1  shows a general layout of an exemplary bottom hole assembly  100  with a drill bit  105 , a rotary steerable tool  110  utilizing a rotation-resistant housing  115 , a drive sub  120 , a measuring-while-drilling (MWD) and/or logging-while-drilling (LWD) section  125 , and a telemetry sub  130  to communicate with the surface. The rotation-resistant housing  115  may be prevented from freely rotating by one or more spring-loaded carriages  116 . One or more wheels  117  resting in a spring-loaded carriage  116  may be pressed against a borehole wall (not shown) to brace the housing  115  against the borehole wall. 
         [0024]    A series of inside shafts (not shown) may run the length of the borehole assembly  100 . At the top of the rotation-resistant housing  115 , the shaft inside the housing may be connected to the shaft inside the drive sub  120 . At the bottom of the rotation-resistant housing  115 , the shaft inside the housing may be connected to the shaft inside drill bit  105 . Mud may flow inside one or more shafts. Mud may also flow between a shaft and a housing at various points along the length of the inside shaft if so desired. 
         [0025]      FIG. 2  shows a general layout of a rotary steerable borehole assembly  200  with a drill bit  205 , a rotary steerable tool  210  utilizing a rotation-resistant housing  215 , an adjustable joint  218 , a drive sub  220 , a MWD and/or LWD section  225 , and a telemetry sub  230  to communicate with the surface. The rotation-resistant housing  210  may be prevented from freely rotating by one or more adjustable pads  216 . Adjustable pads  216  may be arranged around the outer surface of the rotation-resistant housing  215 . 
         [0026]    In certain embodiments, the adjustable pads  216  may extend outward and away from the housing to engage the wall of the wellbore. In certain embodiments, the adjustable pads  216  include a piston that extends outward to engage the wall of the wellbore. In certain embodiments, the adjustable pads  216  may include ribs that pivot or rotate to engage the wall of the wellbore. In other exemplary embodiments, the rotation-resistant housing may be prevented from rotating by a knuckle joint with one or more deflecting ramps. 
         [0027]    A series of inside shafts (not shown) may run the length of the bottom hole assembly  200 . At the top of the rotation-resistant housing  215 , the shaft inside the housing may be connected to the shaft inside the drive sub  220 . One or more shafts inside the housing  215  may be connected to the shaft inside drill bit  105  via the adjustable joint  218 . As described previously, mud may flow inside one or more shafts and/or between a shaft and a housing. 
         [0028]      FIG. 3  shows a layout of a bottom hole assembly  300  similar to the bottom hole assemblies  100  and  200 , but with carriages/pads  316  at the lower end of a rotary steerable tool  310  utilizing a rotation-resistant housing  315 .  FIG. 4  shows a layout of a rotary steerable bottom hole assembly  400  that may include a drill bit  405 , a rotary steerable tool  410 , a shaft coupling  421 , a drive sub  420 , MWD/LWD sensors  425 , and a telemetry module  430  to communicate with the surface. In the bottom hole assembly  400 , rotational drive may be provided via a motor in the drive sub  420  above the rotary steerable section  410 . In certain example embodiments, the rotary steerable is driven by one or more of a mud motor (e.g., a positive displacement motor), a turbine or vane motor, and an electric motor; and rotational energy may be provided, for example, by the surface drilling rig with the top drive or rotary table. By way of example without limitation, a hydraulic motor may be used to drive the shaft running through the rotation-resistant housing. When fluid flows through the mud motor or turbine, the rotor inside, which may be connected to the output shaft of the mud motor, may rotate. Accordingly, any suitable hydraulic or electric motor positioned above the shaft in the drill string may provide rotational energy to the magnetostrictive power supply mounted in the housing. 
         [0029]    It should be understood that the examples of  FIGS. 1-4  are not limiting. Embodiments of the present disclosure may have other rotary steerable tool configurations. And each of various configurations may include a magnetostrictive electrical power supply, in accordance with certain embodiments of the present disclosure. In certain embodiments, power may be supplied to a steering control system with a magnetostrictive power supply. 
         [0030]    A magnetostrictive electrical power supply may be disposed in a housing at any suitable location. The magnetostrictive power supply may be placed inside the rotation-resistant housing between the inside shaft and the outside of the housing. The power supply may be placed in a portion of the housing that is not easily prone to bending as a result of the bowing, flexing or pivoting of the shaft at the lower end of the assembly. Such bowing, flexing, or pivoting at the lower end of the shaft at the lower end of the assembly allows for the steering direction of the assembly to change in a desired direction. 
         [0031]      FIG. 5A  shows a longitudinal cross-sectional view of an example rotary steerable tool  510  with a magnetostrictive power supply  535 , in accordance with certain embodiments of the present disclosure. The magnetostrictive power supply  535  may implement a magnetostrictive rod array  540  to provide a housing power supply. A drive sub  520  may be threaded to an internal shaft  522  that may run the rest of the length of the tool. The outer housing  515  may be sealed on each end, e.g., with seals  519 , and may be configured such that drilling mud or other fluid may be kept away from the moving surfaces, e.g., in the actuator area. And the housing  515  may be filled with a lubricant. In other embodiments, the outer housing  515  may not sealed and drilling mud or other fluid may be allowed to flow or be stationary in the actuator area. 
         [0032]    A thrust bearing  545  may transfer axial loads from the housing  515  to the drive shaft  522 . A radial bearing  550  may support the shaft  522  and drive sub  520 . In this embodiment, the anti-rotation device  516  may include a spring-loaded cartridge with wheels  517  that are configured to engage a wellbore wall to create rotational friction. The rotational friction may reduce the tendency of the housing  515  to rotate with the shaft  522 . The anti-rotation housing  515  may thread into the steering housing. Other example embodiments may employ one or more other anti-rotational devices. 
         [0033]    An inductive communications link or slip ring (not shown) may be positioned between the shaft  522 , which is rotatably connected with the drill string and bottom hole assembly, and the housing  515  to relay communications. Instructions may be passed to the housing electronics and data can be retrieved from the housing and transmitted to the surface by the downhole telemetry system. Information may be transmitted to the surface by, for example, one or more of a telemetry system such as mud pulse, wired drill pipe, pipe in pipe electrical communication, acoustic, or EM-MWD (electromagnetic-MWD). 
         [0034]      FIG. 5B  shows a close-up view of the rotary steerable tool  510  with the magnetostrictive power supply  535 , as an example of the power supply and electronics for use with an example rotary steerable sub in accordance with certain embodiments of the present disclosure. The rotor of the rotary steerable tool  510  may include a cam rotor  555  and the shaft  522 . The cam rotor  555  may be fixed to the shaft  522  with a compressed wedge C-ring pair  556  to lock the cam rotor  555  in place with a spacer and spring assembly  557 . The cam rotor  555  may rotate with the drive shaft  522  and may be engaged to the drive shaft  522  through the use of a spline arrangement on the shaft  522 . This may allow the cam rotor  555  to stay axially positioned using two radial bearings that engage with a stator  560 . The stator  560  may be fixed with the housing  515 . The outer face  558  of the cam rotor  555  may engage magnetostrictive rods  536  of the stator  560 . The face  558  may be undulated with at least one cyclical eccentricity to create variable compression on the magnetostrictive rods  536  as the shaft  522  rotates. As the shaft  552  rotates, the magnetostrictive rods  536  may be alternately compressed and allowed to decompress as the cam passes by the magnetostrictive rods  536 . This compression and decompression, in turn, induces a time-varying magnetic field in and around the magnetostrictive rods  536 . As depicted, the outer face  558  of the cam rotor  555  may have an undulated symmetric pattern. In certain alternative embodiments, the pattern may be skewed so that the rising and falling slopes of an undulation are not symmetrical. 
         [0035]    In certain embodiments, certain magnetostrictive materials may be soft and/or brittle such that the materials wear, fracture and/or deform due to contact with the cam. Accordingly, certain embodiments of automotive engine lifters (not shown) may be necessary. In certain embodiments, each magnetostrictive rod  536  may be coupled to a hardened contact and/or include friction reducing-coatings. Certain embodiments including hardened contacts and/or friction reducing-coatings may change the material properties of a given rod so that the heat-affected zone is no longer magnetostrictive. The contact area of a given rod may be plated and/or capped with any suitable hard and/or friction-reducing material. Certain embodiments may include roller lifters where a roller bearing rides on the cam. 
         [0036]    In certain embodiments, the magnetostrictive rods  536  may be spring-loaded and/or hydraulically or pneumatically cushioned to provide compliance for pressure and/or temperature changes and/or to dampen the impulse stress from impactt. Thus, a hydraulic/pneumatic element and/or a spring action may account for differential material expansion rates and may dampen the impact load when the lifter and/or magnetostrictive material impacts the cam. In certain embodiments with shorter rods, there may be no room for a separate spring or lifter, and hard face and/or anti-friction coatings may be suitable. In certain embodiments with longer rods, lateral supports for the rods may be provided. 
         [0037]    Wire may be wound around one or more of the magnetostrictive rods. In certain example embodiments, there is a winding  537  around each rod  536 . In other example embodiments, windings may group two or more rods. For example, one or more rods  536  that experience the same compression load timing with the rotation of the shaft may be grouped for a winding. In certain embodiments, the shape of the rod  536  can be made in longitudinal plates that align with the same compression cycle from the cam. 
         [0038]    In certain example embodiments, each end of the coil winding  537  may be wired together with windings that correspond to magnetostrictive rods  536  that experience the same phase of the cam. In certain example implementations, the wires that are wound around the magnetostrictive rods  536  may be coupled to power conditioning electronics  538 , which may be located in an electronics housing  539 . In certain example implementations, the electronics housing  539  may further include one or more of tool control electronics, sensors, memory including one or more of executable instructions and data, and one or more processors. The power generated by the power supply  535  may be used to supply electrical energy to other devices throughout the tool such as actuators for steering, survey sensors such as magnetometers, accelerometers and gyroscopes, formation evaluation sensors such as resistivity, gamma ray, density, porosity, acoustic fluid shear and drilling environment sensors such as weight on bit, bending, shaft torque, mud viscosity and density, temperature, vibration, whirl and shaft RPM and actuators such as fluid sampling equipment, steering pads and electric motors and electric clutches used in steering bias mechanisms, etc. 
         [0039]    In certain example implementations, a radial bearing may be positioned below the electronics housing  539  to straighten the shaft  522  over the interval of the cam rotor  555 . This radial bearing may also serve to cause the rotation of the shaft  522  more concentric over the power generator interval. In other example implementations, the radial bearing below the electronics housing  539  is omitted. 
         [0040]    In certain example implementations, below the radial bearing (if present) is a biasing unit. Certain biasing units may include a pair of nested eccentric rings. The nested eccentric rings may be rotated by the rotating shaft  522  through, for example, a clutch or brake mechanism, and further through a step down speed transmission, such as a harmonic drive gear box. In certain example implementations, each eccentric ring may be paired with a clutch and a harmonic drive gear box. Below the bias unit may be a spherical bearing that allows the shaft  522  to pivot about the bearing. In certain example implementations, a flexible seal may be positioned below the biasing unit to keep the oil contained in the housing while the bit box tilts. 
         [0041]      FIGS. 6A ,  6 B and  6 C are latitudinal cross-sectional views illustrating an exemplary assembly  600 , in accordance with certain embodiments of the present disclosure. While only one assembly  600  is depicted, it should be understood that certain embodiments may have a plurality of assemblies  600 . In certain embodiments, the plurality of assemblies  600  may be positioned axially in parallel. In certain embodiments, the plurality of assemblies  600  may be coupled electrically either in parallel or in series. 
         [0042]    A rotor of the assembly  600  may include a cam rotor  655  splined to a shaft  622 . The example depicted may be a two-phase stator and  28 -pole rotor, for example. In the example illustration, the cam undulations on the outer surface  658  of the cam rotor  655  have been exaggerated to exemplify the variation in diameter of the cam rotor  655 . In certain example implementations, the variance in the rotor diameter may depend on the Young&#39;s modulus of the magnetostrictive rod to ascertain how much compression the rod can bear without breaking. By way of example without limitation, actual magnetostrictive rod compression may vary from 0.0001″ to 0.030″ or more depending on the configuration, rod length relative to the compression / expansion axis and material selection. In the example of  FIG. 6A , the spines  656  may be designed to allow the cam rotor  655  to float over the drive shaft  622  while rotational energy is transferred via the spines  656 . 
         [0043]    In certain example implementations, separating the cam rotor  655  from the shaft  622  may allow for control of the diameter variations while rotating the shaft  622 . The shaft  622  may be exposed to forces, such as bending and twisting, which could cause the shaft  622  to flex off of the centerline of the housing. In such situations, separate rotor and shaft configurations may avoid or mitigate the possibility of the magnetostrictive rods being subjected to uneven compression cycles, which may even damage the rods. Other example implementations of rotor-shaft coupling are possible, including, for example, machining the rotor cam undulations on the shaft material itself to integrate the rotor into the shaft body directly. 
         [0044]      FIG. 6B  shows an example of magnetostrictive rods  636  of the stator positioned around the cam rotor  655 . The cam rotor  655  may rotate while the magnetostrictive rods  636  remain fixed with the housing of the stator. As a result, the magnetostrictive rods  636  may experience cyclical compression as the shaft  622  rotates. As depicted, a winding  637  may be around each rod  636 . 
         [0045]    In certain example implementations, the wire wound around the magnetostrictive material may be a magnetic wire. One example magnetic wire may be coated with, for example, a polyimide coating. Other example magnetic wires may feature coatings which are thinner, such as Gore&#39;s high strength toughened fluorocarbon (HSTF). A thinner insulator may allow more terfenol material and thus more power output. 
         [0046]    While the rods  636  are depicted as rectangular rods or groups of square or rectangular rods surrounded by one winding, it should be understood that the magnetostrictive material may have any other suitable form (e.g., trapezoidal rods to better fill the space around the rotor with magnetic field generating material). In the example shown in  FIG. 6B , the phase of the cam and the rods may be designed so that each rod is approximately 180 degrees out of phase with the rod beside it. In other example implementations, the compression phase difference between rods may vary. 
         [0047]      FIG. 6C  shows an exemplary two-phase coil wiring arrangement  637 ′, in accordance with certain embodiments of the present disclosure. In one example implementation, there may be two phases and two sets of winding pairs. The rods that are in phase 0° or Phase A may be wired together in parallel, and the extended rods may be likewise in phase 180° or Phase B may be wired in parallel together as depicted. In this manner, the electric power generated by each phase may work in unison to provide compression or expansion for each phase. In certain example implementations, the output of each phase may be a sinusoidal waveform at a frequency that corresponds to the rotational speed of the of the shaft times the number of lobes on the cam, which in this example is 28 lobes. If the drive shaft were rotating at 120 RPM, then the electrical output frequency of the coils may be (120 RPM/60 s/min)*28=56 Hz. 
         [0048]    In certain example implementations, the system may be designed to maximize the speed of compression and relaxation of the magnetostrictive rods to, in turn, increase the power extracted from the windings. In certain implementations, a limiting factor may be the propagation speed of the compression wave through the magnetostrictive rod. Another limitation may be the electrical inductance of the system, which resists changes to the magnetic field. In some instances, it may be desirable to increase the cyclical frequency of compression and relaxation of the magnetostrictive rods to extract more energy. In these cases, various means may be used to increase the rotation speed of the rotor and optimize the rod and winding size. By, for example, shortening the length of the rod, the propagation time of the compressive and relaxing stress wave through the magnetostrictive rod may decrease, and the magnetostrictive rod may tolerate a higher frequency and still stay relatively in phase with the rotation speed of the cam. 
         [0049]    In certain example implementations, one or more in-phase wirings may be wired in series to, for example, increase the voltage and reduce the current delivered from the windings. While such an arrangement may increase the series resistance of the group of windings, it may generate a higher voltage which may be converted to direct current by using, for example, through a full wave bridge rectifier. Alternatively, a step-up or step-down transformer can be used just before the rectifiers to adjust the voltage being applied to the rectifiers. 
         [0050]      FIG. 7  shows an example of a full wave rectifier  700  fed by two sets of windings. In general, the rectifier may convert alternating current (AC) from the windings to direct current. In certain example implementations, after the energy is converted to direct current, a smoothing capacitor is used to reduce the ripple of the output voltage. In certain example implementations, a zener diode may be included to limit the output voltage to, for example, prevent voltage surges from propagating past the power supply to other electronics in the housing. In example implementations, the output of the rectifier may be fed to circuits to use or the current may be subjected to further conditioning through the use of voltage regulators, DC-to-DC converters. In some example implementations, the output may power one or more electrical circuits, actuators, or sensors. 
         [0051]    In certain example implementations, the rotational energy may be supplied by the rotational motion of the drive shaft. This may limit the speed of the cam to the speed of the shaft. In other example implementations, the speed of the rotor relative to the shaft may be increased through the use of gears. Some example systems feature a harmonic drive gear. The harmonic drive gear may be mounted to the shaft and may output a high multiple of rotation for example 1:180. This may boost the 120 RPM example to a generator frequency of 10080 Hz. In other example implementations, the undulations of the cam may be increased, and the size of each magnetostrictive rod and winding module may be reduced to increase the frequency of the generated signal. In another example, the rotor can be connected to a vane that creates rotation from flowing mud through the tool. 
         [0052]    It should be understood that the exemplary rotor-stator configurations disclosed herein are not limiting.  FIGS. 8A and 8B  show an axial magnetostrictive rod compression assembly  800 , in accordance with certain embodiments of the present disclosure. In the view of  FIG. 8 , the housing of the stator is not shown. The magnetostrictive rods  836  may be disposed lengthwise along an axis of the tool instead of being disposed radially. The magnetostrictive rods  836  may be supported in a support carriage  835 ″ of the stator that may be coupled to the tool housing (not shown) and does not rotate with a shaft  822 . A cam assembly  855  may be rotatably coupled to the shaft  822  and may be disposed in an axial orientation to compress and relax the magnetostrictive rods  836 , similar to the compression and relaxation discussed above. Thus, the rotor may include the cam assembly  855  that compresses both ends of the magnetostrictive rods  836 . 
         [0053]    As depicted, in certain embodiments, the cam assembly  855  may have two ends with faces  858  undulating in synchronization. Again, the undulations as depicted should not be seen as limiting. In certain embodiments, the undulation may be less pronounced than that which is depicted. In certain alternative embodiments, the faces  858  of the cam assembly  855  may rotate in opposite directions, or one face  858  may rotate while the other face  858  remains stationary. 
         [0054]      FIG. 8B  is a cross-section of the stator  835  of the assembly  800 . The stator  835  may include housing  835 ′ at may be coupled to the tool housing (not shown). In certain embodiments, the magnetostrictive rods  836  may be supported by the support carriage  835 ″ at least in part with a flexible potting compound, which may include elastomeric material, such as rubber to hold the rods  836  in position while the cam assembly  855  rotates. In certain embodiments, the wiring of the stator may be essentially identical to previous examples, since for exemplary purposes the stator is a two-phase generator. However, the number of phases should not be seen as limiting, as embodiments according to the present disclosure may be implemented with any suitable number of phases. 
         [0055]    In certain alternative embodiments, a flat-faced member may be disposed generally opposite an undulating cam to vary the compressive load on the magnetostrictive rods.  FIG. 9  shows another axial magnetostrictive rod compression assembly  900 , in accordance with certain embodiments of the present disclosure. In assembly  900 , only one end of each magnetostrictive rod may receive compressive forces from the cam rotor  955 . Opposite the undulated face  958  of the cam rotor  955  may be a flat-faced member  959 . The assembly  900  may provide an advantage of propagation speed of stress waves requiring less time needed to completely compress the rods or let them expand. Again, a harmonic drive transmission may be employed to boost the speed of the cam rotor  955 . 
         [0056]    Referring again to radial magnetostrictive rod compression systems,  FIGS. 10A and 10B  are cross-sectional views of an example tool  1010  with a magnetostrictive power rotor  1035  rotatably coupled to a shaft  1022 , in accordance with certain embodiments of the present disclosure.  FIG. 10B  is a close-up view of a portion of  FIG. 10A . The tool  1010  may include a rotation-resistant housing  1015  having a stabilizer  1015 ′. The rotation-resistant housing  1015  may have a stator  1055  with undulated face  1058  coupled to the body of the stabilizer  1015 ′. By way of non-limiting example, the stator  1055  may be splined and locked to the body of the stabilizer  1015 ′. The magnetostrictive power rotor  1035 , with a magnetostrictive rod array  1040 , windings  1037 , and electronics  1038 , may be mounted on the shaft  1022  to rotate with the shaft  1022 . This configuration may be implemented with other tool elements disclosed herein. In this particular configuration, power may be distributed to other tool elements that may be connected to a box or pin of the drill string. Hence, power may be transferred via wires, connectors, and/or any suitable conductors  1065  along the shaft  1022  to the connectors on each end of the tool  1010 . The tool  1010  may include seals to keep the area filled with oil and bearings, such as ball or roller bearings to provide mechanical loading support through the tool  1010 . Additionally, the configuration may be implemented to operate in mud so that seals would not be necessary. The stator  1055  may be supported such that it is splined and floats on the housing  1015 . 
         [0057]    In reference to the more detailed view of  FIG. 10B , when the stabilizer blades  1015 ′ contact the wellbore wall, the blades  1015 ′ and outer housing  1015  may stop rotating relative to the bore, while the shaft  1022  with the magnetostrictive rods  1036  rotates, thereby causing cyclical compression of the magnetostrictive rods  1036 . The electronics  1038  may be keyed to the shaft  1022 , and the magnetostrictive rod carrier of the rotor  1035  may be keyed and electrically connected to the electronics carrier  1039  so it all rotates with the shaft  1022 . 
         [0058]    The stabilizer  1015 ′ may be of any suitable form, and the upper and lower ends of stabilizer  1015 ′ may be connected to the drill string. In the above example, integral straight blades  1015 ′ are shown. However, the stabilizer blades may be of any suitable form, including integral blades (such as a spiral integral stabilizer), welded (straight or spiraled), or stabilizers threaded onto the housing, for example. The stabilizer may be modified to permit the installation of various components inside of it. The stabilizer blades may have gaps or flow paths between the blades to allow for drilling fluid and cuttings to pass by the blades. 
         [0059]    The tool  1010  may be positioned in the bottom hole assembly to power down hole devices such as MWD/LWD and steering assemblies. It also may be placed throughout the drill string to power communications repeaters, sensors and actuators like fluid sampling and sensing devices in a distributed manner. Such repeaters may be wired pipe repeaters, such as in a wired drill pipe system, electro-magnetic telemetry repeaters, acoustic repeaters, mud pulse repeaters or other forms of telemetry repeaters. A slip ring or transformer may be used to jump electrical energy and/or communications signal between the motor housing and the shaft if electrical power is desired on the other side of the motor stator/rotor pair. 
         [0060]    Additionally, a hydraulic or electric motor may be integral to a power supply rather than being separate entities.  FIG. 11  illustrates an assembly  1100  using a positive displacement motor  1170  to generate power, in accordance with certain embodiments of the present disclosure. A magnetostrictive power supply  1135  according to embodiments disclosed herein may be positioned above, below or interstitially between stages of the positive displacement motor  1170 . Depending on needs for routing power, the magnetostrictive rods may be mounted on the drive shaft  1122  so power can be extracted to elements rotatably connected to the drive shaft  1122 . Or, the rods may be mounted in an inverted arrangement on the motor housing to provide power to elements connected to the motor housing, such as the MWD above the motor, for example. 
         [0061]    A MWD/LWD or telemetry sub may be fitted with actuators and electronics that require power. The electronics carrier may connect through a connector across the tool joint to the power supply electronics in the upper power sub. The drive shaft  1122  may be supported with radial bearings and may have a through path for mud to flow down its center. Mounted onto the drive upper drive shaft  1122  may be a cam rotor  1155  which engages a stator that is connected to the power housing. The stator  1160  may be rotationally fixed with the collar which is the power housing  1115 . Below the power generator may be another radial bearing. The two radial bearings may be used to allow for concentric rotation of the rotor shaft in the generator area. 
         [0062]    The rotor cam  1155  may be splined or fixed to the rotor shaft  1122 , or integrated into its parent material. The mud may exit the drive shaft  1122  and flow around the shaft  1122  via a flow diverter  1171  and enters the positive displacement motor  1170 . The positive displacement motor  1170  may create rotational energy from mud flow and hydraulic force. In certain embodiments, another flex shaft  1172  may be connected below the hydraulic motor in a reverse manner to supply power to devices below the power section. In addition, a thrust bearing may be included in this lower assembly to support the rotor rotation, but this bearing could easily be positioned in the upper section as well. It should be understood that the lower drive shaft  1172  can be extended downward to a bit box and optionally through a bent housing to provide drilling rotational power to a drill bit. The positive displacement motor  1170  may also be any suitable type of hydraulic motor supply of rotational energy including a vane or turbine motor. 
         [0063]    Accordingly, certain embodiments of the present disclosure allow for a magnetostrictive power supply for a bottom hole assembly. Although certain non-limiting examples are disclosed herein, it should be understood that embodiments according to the present disclosure may be implemented with any suitable rotary steerable tool that utilizes a rotation-resistant housing. Further, in addition to rotary steerable applications, a magnetostrictive power supply in accordance with the present disclosure may be used in a straight shaft in a rotation-resistant housing used for mounting various FEWD (Formation Evaluation While Drilling) or other sensors or actuators. 
         [0064]    And even though the figures depict embodiments of the present disclosure in a vertical orientation, it should be understood by those skilled in the art that embodiments of the present disclosure are well suited for use in a variety of orientations. Accordingly, it should be understood by those skilled in the art that the use of directional terms such as above, below, upper, lower, upward, downward and the like are used in relation to the illustrative embodiments as they are depicted in the figures, the upward direction being toward the top of the corresponding figure and the downward direction being toward the bottom of the corresponding figure. 
         [0065]    Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. The indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that the particular article introduces; and subsequent use of the definite article “the” is not intended to negate that meaning.