Abstract:
A magnetorheological fluid damping system includes a hydraulic cylinder, a piston head, a piston rod, and a porous valve. The hydraulic cylinder is configured for disposing magnetorheological fluid therein. The piston head is disposed within the hydraulic cylinder and has first and second sides defining first and second chambers within the hydraulic cylinder. The piston head is configured to be in sliding engagement with the hydraulic cylinder. The piston rod is connected to the piston head. The porous valve includes a magnetorheological fluid pathway, has first and second fluid connections, and is configured to dampen the flow of the magnetorheological fluid between the first and second fluid connections in accordance with a magnetic field. The first fluid connection is fluidly connected to the first chamber and the second fluid connection is fluidly connected to the second chamber. The magnetorheological fluid pathway at least partially directs magnetorheological fluid flow through a porous media.

Description:
PRIORITY CLAIM TO PROVISIONAL APPLICATION 
     This claims priority to and the benefit of U.S. Provisional Patent Application No. 60/804,979, filed in the U.S. Patent and Trademark Office on Jun. 16, 2006, entitled “Damper Exploiting Flow through a Magnetorheological Valve Filled with a Porous Media”, the entire contents thereof is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to magnetorheological fluid damping, and, in particular, to a system and method for magnetorheological-fluid damping utilizing porous media. 
     2. Description of Related Art 
     Generally, magnetorheological fluids (herein referred to as “MR” fluids) are a class of fluids that change in viscosity in the presence of a magnetic field. An MR fluid may have the viscosity of commercially available motor oil when no magnetic field is present and may behave similarly to a solid when a magnetic field is applied (e.g., it may become a viscoelastic solid). Therefore, they exhibit controllable yield strength. When no magnetic field is present, MR fluids may be sufficiently modeled as Newtonian liquids. These unique properties make the material ideal for mechanical vibration damping because of the ability to utilize a magnetic field to control the viscosity of the MR fluid. Additionally, some MR fluids have a response time of less than 10 milliseconds making it well suited for mechanical vibration damping systems. 
     MR fluid dampers are emerging as a promising technology for semi-active damping control. They have been widely applied to control and suppress unwanted mechanical vibrations and shock of various systems and structures because of their inherent advantages. Such advantages include its ability to assist in continuously controlling force, its fast response time, and its relatively small power consumption. Some mechanical vibration and shock mitigation systems that utilize MR fluid dampers include either a power supply and/or a current amplifier. 
     Many MR fluid damping systems include a hydraulic cylinder containing MR fluid, and a piston head adapted for movement within the housing. The piston head and/or hydraulic cylinder may be formed from one or more materials including ferrous metal. Additionally, the piston head may be designed to contain and/or connect to several windings of conductive wire forming a magnetic coil. For example, a magnetic coil may be embedded inside the piston head or wrapped around the piston head. Magnetic coils may be in the shape of a solenoid (sometimes referred to as “a solenoid” or “a coil”). The magnetic coil may generate a magnetic field in and around the piston to affect the MR fluid. Descriptions of various MR dampers can be found in U.S. Pat. No. 5,277,281 to J. D. Carlson et al., U.S. Pat. No. 6,279,700 to I. Lisenker et al., U.S. Pat. No. 6,311,810 to P. N. Hopkins et al., U.S. Pat. No. 6,694,856 to P. C. Chen and N. M. Wereley, and U.S. Pat. No. 6,953,108 to E. N. Anderfaas and D. Banks. In these MR damper configurations, the MR fluid pathways move with the piston (U.S. Pat. Nos. 5,277,281, 6,279,700, 6,311,810, and 6,953,108) or are fixed relative to the damper body (U.S. Pat. No. 6,694,856). The MR fluid pathways are straight or in rectilinear simple geometry shapes and are configured to be perpendicular to the magnetic field. 
     There has been a modern trend towards miniaturization of MR fluid valves. This trend has imposed some design constraints on the overall design of MR fluid damping systems. One MR fluid valve configuration uses tortuous channels that naturally exist in porous media, e.g., as described in the reference Shulman Z., Magnetorheological systems and their application, Magnetic Fluids and Applications Handbook (1996) pp. 188-229. This reference proposes spiral channels or packed beds of particles as flow channels placed inside a solenoid. Kuzhir et al. developed a hydraulic device for the investigation of MR fluid flow through porous media in the presence of a magnetic field parallel to the flow. (see Kuzhir P., Bossis G., Bashtovoi V. and Volkova O., Flow of magnetorheological fluid through porous media, Euro. J. Mech. B/Fluids 22 (2003) pp. 331-343) Their measurements demonstrated that a packed bed of magnetic grains had a higher controllable damping range than spiral channels. There is a continuing need for efficient and effective MR fluid damping systems utilizing MR fluid valves to control the flow of MR fluid. 
     SUMMARY 
     The present disclosure relates to magnetorheological fluid damping, and, in particular, to a system and method for magnetorheological-fluid damping utilizing porous media. 
     It is an aspect of the present disclosure to provide an active length of an MR fluid pathway in an MR fluid valve that may be increased without significant detriment to the overall performance of an MR fluid damping system. It is yet another aspect of the present disclosure to provide a valve that can be activated by a magnetic coil that is effective and efficient at dissipating the thermal energy generated by resistance of the MR fluid. It is yet another aspect of the present disclosure to provide an MR fluid damping system with effective and efficient mechanical vibration damping over a sufficient range of mechanical amplitudes and frequencies. Not all embodiments address all aspects and some embodiments may address none. Other aspects and/or advantages are made apparent by referencing the claims in light of the disclosure. 
     In one aspect thereof, the present disclosure includes a magnetorheological fluid damping system including a hydraulic cylinder, a piston head, a piston rod, and a porous valve. The hydraulic cylinder may have partially disposed magnetorheological fluid therein and includes first and second ends. A diaphragm may be disposed in the hydraulic cylinder forming an accumulator. 
     The piston head is disposed within the hydraulic cylinder and has first and second sides. The piston head defines first and second chambers within the hydraulic cylinder. The first chamber being adjacent to the first side of the piston head; the second chamber being adjacent to the second side of the piston head. And the piston head is configured to be in sliding engagement with the hydraulic cylinder. 
     The piston rod is at least partially disposed within the hydraulic cylinder through the first side of the hydraulic cylinder and is operatively connected to the piston head on the first side. 
     In another aspect thereof, the porous valve includes at least one magnetorheological fluid pathway and includes first and second fluid connections. Also, the porous value is configured to dampen the flow of the magnetorheological fluid between the first and second fluid connections in accordance with a magnetic field. The first fluid connection is fluidly connected to the first chamber and the second fluid connection is fluidly connected to the second chamber. The at least one magnetorheological fluid pathway is configured to at least partially direct the magnetorheological fluid flow through a porous media. The porous valve may be a bypass porous valve. 
     In another aspect thereof, the at least one magnetorheological fluid pathway may include a nonmagnetic tube configured for at least partially disposing the porous media therein. The porous media may include spherical beads, cylindrical columns, irregular cylinders, irregular columns, arrays of hollow cylinders, straight geometry arrays of hollow cylinders, circuitous geometry arrays of hollow cylinders, flakes, irregular shapes, flat plates with holes aligned perpendicular to the flow of the magnetorheological fluid, open cell foams, cellular structures, lattice structures, fibers, a columnar array, carbon nanofibers, carbon tubes, a shape memory alloy, and/or combination thereof. The porous media may be metallic and/or nonmetallic. A magnetic coil may be used to generate the magnetic field at least partially through the porous media. 
     In another aspect thereof, the hydraulic cylinder may include an inner wall and an outer wall. At least one magnetorheological fluid pathway may be at least partially disposed adjacent to the inner wall of the hydraulic cylinder. Additionally or alternatively, the at least one magnetorheological fluid pathway may be at least partially disposed within the piston head. 
     In another aspect thereof, a porous valve includes a magnetorheological fluid pathway, and a magnetic coil. The magnetorheological fluid pathway may include a tube with porous media partially disposed therein. The tube defines first and second ends. Also, the magnetic coil forms an approximate cylinder shape. The tube is at least partially disposed within the magnetic coil. 
     In another aspect thereof, the porous valve may include first and second fluid connections. The first fluid connection is operatively secured to a first end of a tube, and the second fluid connection is operatively secured to a second end of a tube. The first fluid connection may form an internally threaded region configured to house at least one nylon washer and a mesh. The at least one nylon washer can secure the mesh. And the first fluid connection may be further configured for receiving a hollow set hex screw. 
     Additionally or alternatively, the first fluid connection ma y be configured to receive a securing member and secure the porous media. Similarly, the second fluid connection may form an internally threaded region configured to house at least one nylon washer and a mesh. The at least one nylon washer can secure the mesh. The second fluid connection may be further configured for receiving a hollow set hex screw. Additionally or alternatively, the second fluid connection may be configured to receive a securing member and secure the porous media. 
     In another aspect thereof, a tube included in an MR fluid pathway may be a nonmagnetic tube and/or the porous media contained therein may include one or more nonmagnetic stainless steel spheres or magnetic steel spheres. Also, a magnetic coil may be included that is a copper magnetic coil configured to affect MR fluid. A current source may be connected to the magnet coil and may supply electric current to the magnetic coil to generate the magnetic field. 
     In another aspect thereof, a method for dampening mechanical vibrations is disclosed that include the steps of: (1) providing a magnetorheological fluid damping system, and (2) adjusting the magnetic field for dampening mechanical vibrations. The magnetorheological fluid damping system may be any one of the ones described herein. The step of adjusting the magnetic field for dampening mechanical vibrations may include varying a load-stroke profile of the magnetorheological fluid damping system, e.g., when the mechanical vibrations include a shock load and/or a short duration impulsive load 
     In another aspect thereof a method for controlling a porous valve is disclosed and may include the steps of (1) providing a porous valve, and (2) controlling a current source operatively connected to a magnetic coil in the porous valve. The current source supplies electric current to the magnetic coil to generate a magnetic field. The porous valve may be any porous value described herein. 
     In another aspect thereof, a magnetorheological fluid damping system is disclosed that includes a means for providing a hydraulic cylinder with a piston head disposed therein. The piston head defines first and second chambers. And the damping system further includes a means for directing the flow of magnetorheological fluid through a porous valve. The porous valve includes at least one magnetorheological fluid pathway. The porous valve includes first and second fluid connections. The first fluid connection is fluidly connected to the first chamber; and the second fluid connection is fluidly connected to the second chamber. The at least one magnetorheological fluid pathway is configured to at least partially direct the magnetorheological fluid flow through a porous media. The system also includes a means for controlling a magnetic field at least partially affecting the magnetorheological fluid flowing through the porous media. 
     In another aspect thereof, a porous valve is disclosed that includes a means for directing magnetorheological fluid through a porous media, and a means for generating a magnetic field to affect the magnetorheological fluid flowing through the porous media. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other advantages will become more apparent from the following detailed description of the various embodiments of the present disclosure with reference to the drawings wherein: 
         FIG. 1A  is a cross-sectional view of a prior art MR fluid damper using flow channels; 
         FIG. 1B  is a cross-sectional view of the piston head of the MR fluid damper of  FIG. 1A ; 
         FIG. 2  is a schematic of an MR fluid damping system that includes a bypass porous valve in accordance with the present disclosure; 
         FIG. 3A  is a three-dimensional graphic of a bypass porous valve in accordance with the present disclosure; 
         FIG. 3B  is a three-dimensional graphic of a portion of the porous valve of  FIG. 3A  in accordance with the present disclosure; 
         FIGS. 4A ,  4 B, and  4 C are cross-sectional graphics of several porous valves with differing porous media in accordance with the present disclosure; 
         FIG. 5  is a cross-sectional view of an MR fluid pathway with a tube with porous media disposed therein, in accordance with the present disclosure; 
         FIG. 6  is a cross-sectional view of an MR fluid damping system with a bypass porous valve, the piston head having piston rods connected to both sides, in accordance with the present disclosure; 
         FIG. 7  is a cross-sectional view of a bypass porous valve in accordance with the present disclosure; 
         FIG. 8  is a cross-sectional view of an MR fluid damping system with a bypass valve, the piston head having a piston rod connected to a first side, the hydraulic cylinder has a diaphragm which is included and forms an accumulator, in accordance with the present disclosure; 
         FIG. 9  is a cross-sectional view of an MR fluid damping system with a hydraulic cylinder, an MR fluid pathway is partially disposed on the inner wall of the hydraulic cylinder in accordance with the present disclosure; 
         FIG. 10  is a cross-sectional view of an MR fluid damping system with an MR fluid pathway disposed within a piston head in accordance with the present disclosure; 
         FIG. 11  is a cross-sectional view of an MR fluid damping system with an MR fluid pathway and a magnetic coil disposed within a piston head in accordance with the present disclosure; 
         FIG. 12  is a cross-sectional view of an MR fluid damping system with a hydraulic cylinder, an MR fluid pathway is partially disposed on the inner wall of the hydraulic cylinder and a magnetic coil is disposed around the hydraulic cylinder in accordance with the present disclosure; 
         FIG. 13  is cross-sectional view of an MR fluid damping system with a hydraulic cylinder, an MR fluid pathway is partially disposed within the piston head and a magnetic coil is disposed around the hydraulic cylinder, in accordance with the present disclosure; 
         FIG. 14  is a cross-sectional view of an MR fluid damping system with a hydraulic cylinder and a piston head, the MR fluid pathway and the magnetic coil are disposed within the piston head and the hydraulic cylinder has a diaphragm forming an accumulator, in accordance with the present disclosure; 
         FIG. 15  is a graphic of hysteresis cycles with respect to displacement demonstrated by the embodiment shown in  FIG. 6  with an applied electric current from approximately 0 to 1.5 Amps generating a magnetic field in accordance with the present disclosure; 
         FIG. 16  is a graphic of hysteresis cycles with respect to velocity demonstrated by the embodiment shown in  FIG. 6  with an applied electric current from approximately 0 to 1.5 Amps generating a magnetic field in accordance with the present disclosure; 
         FIG. 17  is a graphical view of controllable equivalent damping with respect to applied frequency (damper velocity) demonstrated by the embodiment shown in  FIG. 6 , in accordance with the present disclosure; and 
         FIG. 18  is a graphical view of controllable damping ratio with respect to different bead size demonstrated by the embodiment shown in  FIG. 6 , in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring simultaneously to drawings  FIGS. 1A and 1B ;  FIG. 1A  shows a cross-sectional view of a prior art MR fluid damper  100  and  FIG. 1B  shows an enlarged view of piston head  102  of  FIG. 1A . Damper  100  includes hydraulic cylinder  104 . Note that diaphragm  106  forms accumulator  108 . Accumulator  108  provides compensation for the movement of piston rod  110  as it slides through hydraulic cylinder  104 . Flow channels  112  are shown with magnetic coil  114  positioned in piston head  102 . Note that magnetic material  116  provides for a magnetic flux return. Additionally, magnetic coil  114  is immersed in MR fluid, which may wear on magnetic coil  114  if not properly designed. The thermal characteristics of damper  100  may provide sufficient heat dissipation from the heat generated therein, including the heat generated by magnetic coil  114 . Moreover, the aggregate volume of magnetic coil  114  may result in designs that have a reduced active length for fluid channels  112 , and impose additional constrains on the dimensions of fluid channels  112  and the magnetic material  116  so that specific criteria regarding the magnetic flux return has proper magnetic field saturation and precise return path width. 
     Referring to  FIG. 2 , schematic of MR fluid damping system  200  that includes bypass porous valve  202  that includes hydraulic cylinder  104  that has chambers  204  and  206  defined by piston head  102 . Piston rod  110  extends through hydraulic cylinder  104  and is attached to piston head  102 . Additionally or alternatively, piston rod  110  as shown in  FIG. 2  may be described as two separate piston rods each attached to a differing side of piston head  102 . Herein, the describing a single piston rod going through a piston head being attached to the piston head is considered equivalent to two piston rods being operatively attached to the two side of a piston head. The chamber  206  is fluidly connected to bypass porous valve  202  via fluid connection  208  while chamber  204  is fluidly connected to bypass porous valve  202  via fluid connection  210 . The bypass porous valve  202  includes MR fluid pathway  212 , magnetic coil  114  formed around a portion MR fluid pathway  212  and around tube  216 . Within tube  216  porous media  214  is contained therein which may include multiple spherical beads and/or other fillers are randomly or orderly packed inside an MR fluid pathway  212 . Magnetic coil  114  is wrapped around tube  216  and may include a steel tube that is stationary to hydraulic cylinder  104 . MR fluid connections  208  and  210  are used to connect bypass porous valve  202  to hydraulic cylinder  104 . 
     A feature of some embodiments of bypass porous valve  202  is that both MR fluid and porous media  214  are placed in the center magnetic coil  114  and may be designed to function as a magnetic flux guide. Natural tortuous fluid channels exist in porous media  214  thus allowing non-unidirectional flow of MR fluid through bypass porous valve  202  resulting in magnetic field with varying orientations relative to the velocity of the MR fluid. In such a configuration, mean values of the magnetic field applied to the MR fluid depend on material properties and geometry shape of porous media  214  resulting in flexible design requirements of bypass porous valve  202 . Comparatively, in some flow mode MR dampers, a fluid channel must be configured to convey MR fluid perpendicularly to a magnetic field, which places numerous geometry constraints on damper and magnetic coil design and also increases damper cost. 
     Additionally or alternatively, bypass porous valve  202  may improve damper efficiency and effectiveness because of the natural tortuous fluid channels existing in porous media  214 . This natural consequence allows for the aggregate fluid channel length to be easily increased by the curvedness found in porous media  214 . Also, yield and viscosity behavior of the MR fluid can be affected by the applied magnetic field as the consequence of the resulting capillary style of MR fluid pathway  212 . By using tortuous paths, the magnetic field and flow paths can be oriented at an angle thereby improving the activation efficiency of the MR fluid yield stress. 
     As piston rod  110  moves relative to hydraulic cylinder  104 , piston head  102  pushes the MR fluid from, for example, chamber  206  into fluid connection  208  of bypass porous valve  202  along MR fluid pathway  212  and at least partially through tube  216 . This pushes MR fluid through porous media  214  that may be affected by a magnetic field generated by magnetic coil  114 . The MR fluid then exits bypass porous valve  202  through fluid connection  210  and enters chamber  204 . As a result, when piston head  102  moves, the MR fluid must pass through bypass porous valve  202  where the yield stress and viscosity of the MR fluid therein may be controlled by a magnetic field generated by magnetic coil  114 . The result is that MR fluid system  200  is controllable by an electric current supplied by a current source (not shown). 
     Referring to  FIG. 3 , in a detailed 3-D perspective view of bypass porous valve  202 , the porous media  214  is depicted as spherical beads disposed in tube  216  which are constrained by screw and washer set  302  at fluid connections  208  and  210 . Instead of spherical beads, tube  216  may be filled with various filler media according to damper performance requirements. 
     Referring to  FIGS. 4A-4C , porous media  216  is shown within tube  216  that include multiple particles having varying geometries. Spherical beads are included in porous media  214  in  FIG. 4   a;  cylindrical columns are shown as included in porous media  214  in  FIG. 4   b ; and irregular cylinders are depicted to be included in porous media  214  in  FIG. 4   c . However, porous media  214  may be arrays of hollow cylinders of either straight or circuitous geometries, bundled such arrays with various degrees of packing, non-bundled such arrays, flakes or other irregular shapes and any mixture of these particles where the mixture is based on morphology (shape), scale (size). A porous media  214  may include one or more flat plates of arbitrary thickness aligned perpendicular to the flow each with one or more holes the holes in consecutive plates having varying degrees of overlap with arbitrary spacing between the consecutive plates. Porous media  214  may include metallic and/or nonmetallic particles in various additional geometrical arrangements/forms, including but not limited to open-cell foams, cellular structures such as what might be produced by sintering or lost foam casting, lattice structures, randomly or non-randomly oriented fiber or other columnar arrays (such as carbon nanofibers or tubes) that are sufficiently strong to not be compressed during damper operation. Also materials may be included in porous media  214  that can be deformed elastically during damper operation but sufficiently strong so as to not be permanently deformed, i.e. deformed plastically during damper operation. Porous media  214  can also be, at least in part, a shape memory alloy, the shape memory properties being utilized in either thermally or stress activated modes to effect controllable, and, depending on the arrangement, reversible changes in the geometry and arrangement of the filler material. The porosity of the porous media  214  varies according to a required viscous damping and/or controllable damping range. In addition, the magnetic property of the porous media  214  is dependent on the material, and may be magnetic or nonmagnetic. 
     As mentioned above, the flow of the MR fluid through porous valves disclosed herein is equivalent to MR flowing through multiple tortuous channels connecting the pores in the filler media. 
     Referring to  FIG. 5 , tube  216  is illustrated with a magnetic field parallel to the axis. At each point along tube  216 , the inclined angle between the axis and magnetic field direction is varied and stochastically the average angle of the channel relative to the magnetic field is a function of the tortuosity of porous media  214 . As the tortuosity increases, the active length of the tortuous channel increases leading to a larger controllable damping range of the damper. 
     Referring to  FIG. 6 , MR fluid damping system  600  is shown that includes piston rod  110  that is through hydraulic cylinder  104 . Additionally bypass porous valve  202  is shown. Consider a particular example where hydraulic cylinder  104  has a  2  inch bore and a  6  inch stroke which may compress the MR fluid contained therein. Piston head  102  in hydraulic cylinder  104  defines chambers  204  and  206 . Piston rod  110  goes wholly through hydraulic cylinder  104  thus mitigating the need to include a diaphragm forming an accumulator. Any necessary seals may be standard hydrocarbon fluid seals that are compatible with MR fluids. Bypass porous valve  202  is mounted to hydraulic cylinder  104  via fluid connections  208  and  210 . The connections from bypass porous valve may be done via stainless steel tubes  602 . When piston head  102  moves, the MR fluid is operatively forced through bypass porous valve  202 , where a magnetic field is generated by magnetic coil  114 , thus damping the MR fluid flow. 
     Referring to the drawings,  FIG. 7  shows a cross-sectional view of bypass porous valve  202 . Bypass porous valve  202  include tube  216  which may be made of non-magnetic stainless steel, fluid connections  208  and  210 , porous media  214 , magnetic coil  114 . Magnetic coil  114  may have 50 Ohms of resistance is disposed around the outside of the tube  216  that can generate a magnetic field parallel to the flow of an MR fluid. Additionally or alternatively, magnetic coil  114  may be made of copper. Tube  216  may be made of a non-magnetic material in order to encourage the magnetic field to be stronger within the MR fluid rather than tube  216  itself. Fluid connections  208  and  210  may be made of magnetic steel to reduce the reluctance to the MR fluid. Contained within tube  216  is porous media  214  that may include packed magnetic stainless steel spheres on the order of several millimeters in diameter. These spheres form the tortuous channels that the MR fluid may flow through. The narrowness of these channels, along with the variation in their orientation relative to the magnetic field direction, allows the bypass porous valve  202  to achieve a strong resistance to flow despite the fact that the magnetic field is oriented parallel to the overall MR fluid flow direction. The spheres are secured in tube  216  near fluid connection  208  by a steel mesh  700 . Fluid connection  208  may be configured receive hollow set hex screw to be tightened down onto steel mesh  700  via nylon washers  704  and  706 . Hollow set hex screw  702  may be hollowed in a hex shape, allowing MR fluid to pass through without restriction. 
     Referring to  FIG. 8 , MR fluid damping system  800  with a bypass porous valve  202  is shown. Note that piston rod  110  does not extend through piston head  102  out the other side of hydraulic cylinder  104 . Rather diaphragm  802  is included to form accumulator  804  which allows for volumetric compensation as piston rod  110  slides in and out of hydraulic cylinder  104 . Accumulator may contain a gas, a compressible fluid, a non-compressible fluid, necessary seals and gaskets, and/or some combination thereof. 
     Referring to drawings,  FIG. 9  shows cross-sectional view of an MR fluid damping system  900  with a hydraulic cylinder  104 , an MR fluid pathway is partially disposed on the inner wall of the hydraulic cylinder  104 . Porous media  214  is sandwiched between the inner wall of hydraulic cylinder  104  and tube  216  forming a porous valve. Note that system  900  does not include a bypass porous value as discussed supra. Also note that piston rod  110  passes through piston head  102 . U-cups  902  and  904  and are shown and may use standard hydrocarbon fluid seals, compatible with many MR fluids. Magnetic coil  114  is wrapped around outer wall of hydraulic cylinder  104  such that the sandwiched porous media  214  becomes a center magnetic flux path. Hydraulic cylinder  104  and tube  216  may be made of non-magnetic stainless steel to encourage most of the magnetic field through porous media  214  rather than through metal components. 
     Referring to drawings,  FIG. 10  is a cross-sectional view of an MR fluid damping system  1000  with an MR fluid pathway  1002  disposed within piston head  102 . Hydraulic cylinder  104  includes piston head  102  defines chambers  204  and  206 . Piston rod  110  goes through piston head  102  and is connected to it, thus mitigating the need for a diaphragm. U-cups  902  and  904  are shown and may be standard hydrocarbon fluid seals compatible with MR fluids. Piston head  102  may include a nonmagnetic center column to support cover plates and connect with piston rod  110 . Also piston head  102  may include piston cover plates to hold porous media  214 . Magnetic coil  114  is disposed around hydraulic cylinder  104  such that porous media  214  and piston rod  110  function as a center magnetic flux path. Hydraulic cylinder  104  may include non-magnetic stainless steel in order to encourage the magnetic field to be stronger in MR fluid pathway  1002  rather than in hydraulic cylinder  104 . 
     When piston head  102  moves relative to hydraulic cylinder  104 , piston head  102  pushes MR fluid through MR fluid pathway  1002 , e.g., when the MR fluid passes through porous media  214  the presence of a magnetic field affects the movement of piston head  102 . The MR fluid may flow between chamber  204  and  206  via MR fluid pathway  1002 . 
     Referring to the drawings,  FIG. 11  shows a cross-sectional view of MR fluid damping system  1100  with an MR fluid pathway and magnetic coil  114  disposed within a piston head. Piston rod  110  and/or piston head  102  may be non-magnetic to focus the magnetic field within MR fluid pathway  1002  and consequently porous media  214 . MR fluid damping system  1100  is similar to MR fluid damping system  1000  depicted in  FIG. 10 , however, the magnetic coil  114  is disposed within piston head  102  in MR fluid damping system  1100 . 
       FIG. 12  is a cross-sectional view of an MR fluid damping system  1200  with a hydraulic cylinder  104 . MR fluid pathway  1202  is partially disposed on the inner wall of the hydraulic cylinder  104 . Note that diaphragm  802  is shown and forms accumulator  804  because piston rod  110  only enters hydraulic cylinder on one side and is attached to piston head  102  though going through piston head  102 . Also, magnetic coil  114  is disposed around hydraulic cylinder  104 . 
     Referring to the drawings,  FIG. 13  shows cross-sectional view of an MR fluid damping system  1300  with a hydraulic cylinder  104  with MR fluid pathway  1302  within piston head  102 . Also, note that MR fluid pathway  1302  is disposed within piston head  102  and magnetic coil  114  is disposed around hydraulic cylinder  104 . Since piston rod  110  enter into one end of hydraulic cylinder  104  to attach to piston head  102 , diaphragm  802  is provided to form accumulator  804 . 
       FIG. 14  is a cross-sectional view of an MR fluid damping system  1400  with a hydraulic cylinder  104  and a piston head  102  disposed therein. MR fluid pathway  1402  is position through piston head  102 . Also, in this particular embodiment, diagram  802  forms accumulator  804  and may be needed because piston rod  110  is connected into piston head  102  on one side. Also note that magnetic coil  114  is disposed within piston head  102  as well. 
     Referring now simultaneously to  FIGS. 15-18 , that show representative test data obtained from an example use of  FIG. 6 . Consider the following example of  FIG. 6 : Hydraulic cylinder  104  may be using commercially available hydraulic cylinder with a 50.8 mm (2 inch) bore and a 152.4 mm (6 inch) stroke. Bypass porous value  202  may be fabricated around tube  216  that is made of stainless steel tube with an inner diameter of 10 mm. Non-magnetic stainless steel may be used to encourage the field to be stronger in the MR fluid rather than in the walls of tube  216 . Tube  216  may be filled with magnetic media  216  that includes magnetic steel spheres of 3.5 mm diameter. Magnetic coil  114  may have 50 ohms of resistance and may be wrapped around the outside of tube  216 . The ends of the porous bypass valve  202  may be welded to hydraulic cylinder  104  via machined steel end parts forming fluid connections  208  and  210 . A ball valve may also be attached for filling system  600  with MR fluid. To evaluate the performance of the damper, measurements of damper response under steady-state sinusoidal displacements were taken using an 8 kN scotch yoke damper dynamometer and a 25 kN load frame with a servo-hydraulic actuator. The results are discussed infra. 
       FIG. 15  shows the force vs. piston displacement behavior of an exemplary MR fluid damping system  600 , and  FIG. 16  shows the force vs. piston velocity behavior of an exemplary MR fluid damping system  600 . The total energy dissipated by an exemplary damping system  600  is represented by the area within the hysteresis cycles on the force vs. displacement plot in  FIG. 15 . As a current is increased (and consequently the magnetic field increases as well), more energy is dissipated by an exemplary MR fluid damping system  600 . At a certain displacement and frequency, the dynamic force range of exemplary MR fluid damping system  600 , shown in  FIG. 16 , is about six, which is much higher than some prior art MR dampers. The detailed relationship between the controllable damping and the applied current is shown in  FIG. 17 , wherein the equivalent damping coefficient is obtained by equating the energy dissipated per cycle for the exemplary MR fluid damping system  600  to an equivalent viscous damper. As can be seen, the applied magnetic field changes (from 0 to 1.5 Amps of supplied electric current), so does the equivalent viscous damping coefficient of the exemplary MR fluid damping system  600  dramatically increase. Compared with the zero field case, the maximum increase of the equivalent damping coefficient is eight times as the excitation frequency is 0.1 Hz (corresponding to the maximum velocity 7.98 mm/s). As the frequency increases, the equivalent damping coefficient of the exemplary MR fluid damping system  600  decreases. The minimum increase of the damping is two times as the frequency is 1 Hz (corresponding to the maximum velocity 79.8 mm/s). Similar results can be shown as the displacement amplitude increases while the frequency is kept a constant. In other words, the damping control range is a function of the applied velocity. It is demonstrated that the performance of the MR damper behaves as a combination of viscous and friction damper. However, the distinction between an MR damper with a porous valve and the damper with a conventional flow mode valve is that not only the friction or yield force but the viscosity of the porous valve damper is a function of an applied field. Thus, when using an MR damper system with exemplary bypass porous valve  202 , the damping control range can be still kept in a required objective in a larger velocity range, which is favorable for a damper in high speed or shock resistance applications. 
       FIG. 18  is used to evaluate performance of the MR damping system  600  as a function of sphere bead size (2.0 mm, 3.5 mm, and 5.5 mm in diameter). Controllable damping range is a key performance metric for an MR damper, so that the non-dimensional damping coefficient (ratio of equivalent damping at 1.2 A to damping at 0 A) for three different bead sizes (2.0 mm, 3.5 mm and 5.5 mm ) is compared in  FIG. 18 . The peak velocity is the product of excitation amplitude and frequency for each testing case. To maximize the controllable damping range, on-state damping (Ceq at 1.2A) should be maximized, and off-state damping minimized (Ceq at 0A). The damping coefficient for the 3.5 mm case is largest because off-state damping for the 2 mm case is largest, which implies an optimized bead size for maximizing damping coefficient. In addition, the damping coefficient is a function of the peak velocity (dependent on amplitudes and frequencies), and the damping coefficient decreases as the peak velocity increases. 
     Accordingly, it will be understood that various modifications may be made to the embodiments disclosed herein, and that the above descriptions should not be construed as limiting, but merely as illustrative of various embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.