Patent Publication Number: US-10309386-B2

Title: Solid state pump using electro-rheological fluid

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The application claims the benefit of U.S. Provisional Application 62/243,377, titled “S OLID  S TATE  P UMP  U SING  E LECTRO -R HEOLOGICAL  F LUID ,” filed on Oct. 19, 2015. The entire disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     GOVERNMENT INTERESTS 
     This invention was made with the government support under Contract No. W31P4Q-13-1-0013 awarded by the U.S. Army. The government has certain rights in this invention. 
    
    
     BACKGROUND 
     As is known in the art, micropumps have rapidly expanded micro-hydraulic systems into a wider range of applications, such as drug delivery, chemical analysis and biological sensing. Empirical research has shown that micropumps suffer most from their extremely low efficiency. 
     In terms of actuation principles, the mechanical methods include piezoelectric, bimetallic, thermo-pneumatic, electrostatic, electromagnetic actuation and shape memory alloy (SMA). The non-mechanical methods include magneto-hydrodynamic (MHD), electro-hydrodynamic (EHD), and electro-osmotic actuation. 
     Piezoelectric actuation has been commonly used in reciprocating micropumps. This actuation concept is based upon the piezoelectric effect which correlates mechanical deformation and electrical polarization. Due to the fast response and precise dosage, piezoelectric micropumps are often used to maintain therapeutic efficacy, such as drug delivery. However, the drawbacks for the piezoelectric micropumps are considered to be the high actuation voltage and the mounting procedure. 
     Thermo-pneumatic micropumps are designed by a periodic change in the volume of the chamber expanded and compressed by a pair of heater and cooler. Micromachining, either for the heater and cooler or the diaphragm; contributes to the realization of this principle. The crucial disadvantages for thermo-pneumatic micropumps is the long thermal relaxation time constant of the cooling process which will limit the bandwidth of the actuation, and the driving power which is required to be maintained at a specified-constant level. 
     Shape memory alloy (SMA) micropumps generally refer to those applying the shape memory effect (SME) of an SMA (e.g., Titanium/Nickel (TiNi)), resulting in large pumping rates and high operating pressures. The main disadvantages of this approach are the relatively high power consumption indicating a low efficiency and the uncontrollable deformation of SMA due to its temperature sensitivity. 
     In an embodiment, considering the efficiency of micro-hydraulic systems, all types of pumps described above suffer from a low efficiency. Typically, the overall efficiency of a micro-pump is determined by the product of four components: volumetric efficiency, hydraulic efficiency, mechanical efficiency and electrical efficiency. Volumetric losses and hydraulic losses dominate at small scales, although an acceptable efficiency for macro-pumps has already been achieved. As the size of the system decreases, the volumetric efficiency is dramatically affected since the same dimensional and geometric tolerance result in a larger dimension fraction. In terms of hydraulic efficiency, a Reynolds number also decreases as the characteristic length scales decreases, leading to larger viscous losses. Especially at low pressure, the efficiency of all types of micro-pumps is quite low. 
     SUMMARY 
     The systems and methods described herein provide a method for pumping fluid in a hydraulic system, such as a solid state pump, which utilizes electro-rheological (ER) fluid as the hydraulic fluid. In an embodiment, a pumping system may include one or more plates. For example, in some embodiments, a middle plate can be disposed between an upper plate and a lower plate. The plates may be provided from a dielectric material or other non-conducting material. For example, in one embodiment, the plates may be provided as transparent acrylic plates. 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. The middle plate may include a channel through which the ER fluid may flow. In an embodiment, along the channel in the middle plate, two circuits, acting as electrodes, may be wrapped through the channel and around one or more surfaces of the middle plate. In response to an applied voltage, the circuits generate an electric field across the channel. 
     In response to the applied voltage (and resultant electronic field), ER fluid within the channel can be turned into chains of solid particles. By varying the applied voltage, the formed chains of particles may move along the channel, for example, from an inlet to an outlet. As a result, the ER fluid can be moved by the force of the electric field, dipole-dipole interaction, and drag, such that ER fluid is pumped from the inlet to outlet. 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. An edge of the middle plate may be used to couple the circuits, and thus the pumping system, to an independent power source. The lower plate may serve as a base of the pumping system. 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. The circuits may include electrodes which may be spaced long an edge of the middle plate based on a desired magnitude of a voltage to be applied to the channel. In some embodiments, the electrodes may be equally distributed along an edge of the middle plate. However, it should be appreciated, that a width and spacing of the electrodes can be varied according to the requirements of specific maximum pressure differential and a desired flow rate of the fluid through the channel. 
     For example, the electrodes may have a generally radial pattern to balance the limitation of the spacing along the channel and a requirement of the edge of the middle plate for connecting to a power supply to ensure insulation. It should be appreciated that the quantity of the electrodes can vary and be modified accordingly as the required nominal pressure differential varies. 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. The plates may be secured together by various coupling means. For example, in some embodiments, screws and locknuts may be distributed along the channel to couple the plates together. In an embodiment, an adhesive layer may be disposed between the plates to secure the plates together and to also provide a seal to prevent fluid from moving to undesired areas (e.g. to prevent leaks between the plates). 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. The system may include two pairs of pitot tubes and graduated scales to measure a pressure differential of the solid state pump. The pressure differential can be indicated by a difference between the heights of the fluid surfaces in the pitot tubes. In some embodiments, two components with a stair step cross-section can be included to mount the pitot tubes and graduated scales on the upper plate. 
     In an embodiment, ER fluids may include suspended non-conducting particles, up to 100 micrometers, in an insulating fluid. The operational mode for ER fluid can be categorized as flow mode, shear mode and squeeze mode. Typical applications for ER fluids can be used in applications such as valves, clutches, absorbers, and engine mounts. There are a wide range of application benefits from the characteristics of ER fluids, including fast dynamic response, facile mechanical interface connection and accurate controllability. 
     In one aspect, a solid state pumping system is provided having a first plate having first and second opposing surfaces and a second plate having first and second opposing surfaces. The second plate can be disposed under the second surface of the first plate. The second plate may include a channel formed within the second plate, having a first end and a second end. The second plate may further include a first circuit coupled to a first side of the channel and a second circuit coupled to a second side of the channel. In an embodiment, in response to a voltage applied thereto, the first and second circuits can provide an electric field voltage across the channel such that in response to the electric field voltage an electro-rheological (ER) fluid moves from the first end to the second end of the channel. The solid state pump system may further include a third plate having first and second opposing surfaces. The third plate can be disposed under the second surface of the second plate. 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. A plurality of electrodes can be coupled to each of the first and second circuits. A spacing of the plurality of electrodes along a length of the first and second circuits respectively can determine a magnitude of the electric field voltage applied across the channel. In some embodiments, a flow rate of the electro-rheological fluid through the channel is based, at least in part, on dimensions of the channel and the magnitude of the electric field voltage. 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. In an embodiment, a first fluid path (e.g. a tube) can be coupled to an inlet formed through a first portion of at least one of the first plate or the third plate and coupled to the first end of the channel. The first tube may provide the ER fluid to the first end of the channel. A second fluid path (e.g. a tube) may be coupled to an outlet formed through a second portion of at least one of the first plate or the third plate and coupled to the second end of the channel. The second tube can receive the ER fluid. 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. The second plate may comprise a recessed region on each of the first and second surfaces. The recessed region having a shape and dimension selected to accommodate the first and second circuits such that the surfaces of first and second circuits are substantially flush with the non-recessed portions of the first and second surfaces of the second plate. 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. The solid state pump may include a means for coupling the first and second circuits to the recessed region on the first surface of the second plate and the first and second circuits to the recessed region on the second surface of the second plate. A depth of the recessed regions on the first surface of the second plate may correspond to a thickness of the means for coupling and a depth of the recessed regions on the second surface of the second plate may correspond to a thickness of the means for coupling. 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. The second surface of the first plate can have a first recessed region. The first recessed region can have a shape and dimension selected to accommodate the first and second circuits such that the surfaces of first and second circuits are substantially flush with the non-recessed portions of the second surface of the first plate. The first surface of the third plate can have a second recessed region. The second recessed region having a shape and dimension selected to accommodate the first and second circuits such that the surfaces of first and second circuits are substantially flush with the non-recessed portions of the first surface of the third plate. A depth of the first recessed region on the second surface of the first plate can correspond to a thickness of the means for coupling and a depth of the second recessed region on the first surface of the third plate can correspond to a thickness of the means for coupling. 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. The first circuit can be wrapped through the channel and coupled to the first and second surfaces of the second plate and the second circuit can be wrapped through the channel and coupled to the first and second surfaces of the second plate. 
     In an embodiment, the first circuit may include a plurality of cathodes and the second circuit may include a plurality of anodes to form dipole-dipole interaction across the channel to move the electro-rheological fluid from the first end to the second end of the channel. 
     In some embodiments, the above pumping system can include one or more of the following aspects in any combination. Each of the first, second and third plates may include transparent acrylic plates. In an embodiment, the channel may be a first one of a plurality of channels formed within the second plate, wherein the electric field voltage is applied across each of the plurality of channels. 
     In another aspect, a method for solid state pumping is provided. The method includes introducing an ER fluid into a channel formed within a second plate. The second plate may be disposed under a second surface of a first plate. A first end of the channel can be coupled to an inlet and a second end of the channel can be coupled to an outlet. The method may further include applying an electric field voltage across the channel using a first circuit coupled to a first side of the channel and a second circuit coupled to second side of the channel. The electric field voltage can change a property of the electro-rheological fluid to move the electro-rheological fluid from the first end of the channel to the second end of the channel. 
     In some embodiments, the above method for solid state pumping can include one or more of the following aspects in any combination. The method can include receiving the ER fluid at the outlet formed through a portion of at least one of the first plate or a third plate. The third plate may be disposed under a second surface of second plate. A flow rate of the ER fluid through the channel can be based, at least in part, on dimensions of the channel and a magnitude of the applied electric field voltage. 
     In some embodiments, the above method for solid state pumping can include one or more of the following aspects in any combination. The electric field voltage can be varied at one or more points along the channel to move the electro-rheological fluid from the first end to the second end. The electro-rheological fluid can be pumped from the inlet to the outlet based on the applied electric field, dipole-dipole interaction and a drag factor. 
     In some embodiments, the above method for solid state pumping can include one or more of the following aspects in any combination. The first circuit can be wrapped through the channel and coupled to the first and second surfaces of the second plate and the second circuit can be wrapped through the channel and coupled to the first and second surfaces of the second plate to generate a horizontal electric field voltage across the channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing concepts and features may be more fully understood from the following description of the drawings. The drawings aid in explaining and understanding the disclosed technology. Since it is often impractical or impossible to illustrate and describe every possible embodiment, the provided figures depict one or more illustrative embodiments. Accordingly, the figures are not intended to limit the scope of the concepts, systems and techniques described herein. Like numbers in the figures denote like elements. 
         FIG. 1  is an isometric view of a solid state pump system; 
         FIG. 1A  is an isometric view of a solid state pump system of  FIG. 1  having fluid paths coupled to an inlet and outlet; 
         FIG. 1B  is an exploded view of the solid state pump system of  FIG. 1A  having tubes coupled to an inlet and outlet; 
         FIG. 2  is an exploded view of the solid state pump system of  FIG. 1 ; 
         FIG. 3  is a top view of a surface of a middle plate of the solid state pump system of  FIG. 1 ; 
         FIG. 3A  is a side view of the middle plate of  FIG. 3 ; 
         FIG. 3B  is a top view of a surface of a middle plate of the solid state pump system of  FIG. 1  having a plurality of channels; 
         FIG. 3C  is a top view of a surface of a middle plate of the solid state pump system of  FIG. 1  having a channel with a varying width; 
         FIG. 3D  is a top view of a surface of a middle plate of the solid state pump system of  FIG. 1  having a channel with an alternate shape; 
         FIG. 4  is a top view of an unfolded circuit; 
         FIG. 5  is a perspective view of two folded circuits; 
         FIG. 6  is an isometric view of a solid state pump system with pitot tubes and graduated scales; and 
         FIG. 7  is a flow diagram of a method for pumping fluid using a solid state pump system. 
     
    
    
     DETAILED DESCRIPTION 
     Now referring to  FIGS. 1-2 , in which like designations represent like elements, a solid state pump  10  includes a first plate  16  (e.g., top plate), a second plate  14  (e.g., middle plate) and a third plate  18  (e.g., bottom plate). The second plate  14  includes a channel  12 , electrode circuits  42  and electrodes  50   a ,  50   b . The second plate may be disposed or otherwise positioned between the first and third plates  16 ,  18 . 
     In an embodiment, solid state pump  10  may be used to control a flow rate of an electro-rheological (ER) fluid through the channel  12  by applying a varying voltage gradient via electrodes  50   a ,  50   b , which may be formed as anodes  50   a  and cathodes  50   b.    
     In an embodiment, channel  12  may be formed within second plate  12 . For example, in some embodiments, channel  12  may be provided as a slot, aperture, bone, duct, or file passage or any void formed or otherwise provided in the second plate. Thus, in an embodiment, first and third plates  16 ,  18  may form a top surface and a bottom surface, respectively, of the channel  12  when the first, second and third plates  16 ,  14 ,  18  are coupled together. 
     Channel  12  may be formed in a variety of different portions of second plate  14 . For example, in one embodiment, channel  12  may be formed within a middle portion of second plate  14 . In other embodiments, channel  12  may be offset from a middle portion of second plate  12 . The positioning of channel  12  may be selected based at least in part on a particular application of solid state pump  10 . In some embodiments, multiple channels  12  may be formed. For example, two or more channels may be formed in at least one of first, second and third plates  16 ,  14 ,  18 . In other embodiments, one channel  12  may be formed in two or more plates (e.g., first, second and third plates  16 ,  14 ,  18 ). In still other embodiments, solid state pump  10  may include multiple second plates  14 . For example, second plate  14  may include multiple layers and a channel  12  may be formed in each of the layers. In an embodiment, the multiple layers of second plate  14  may be stacked together and thus disposed between first and third plate  16 ,  18 . The channel  12  will described in greater detail below with respect to  FIGS. 3-3D  below. 
     In an embodiment, electrodes  50   a ,  50   b  may be disposed along a first and second opposing edges  14   c ,  14   d  of second plate  14 . The electrodes  50   a ,  50   b  may be coupled to electrode circuits  42  to provide an electric field voltage across channel  12 . For example, the electrode circuits  42  may electrically couple electrodes  50   a ,  50   b  to a portion of channel  12 . Thus, electrode  50   a ,  50   b  may form one end of an electrode circuit  42  and the portion of the channel may form a second end of the electrode circuit  42 . For example, in one embodiment, a first group of electrodes  50   a  may be disposed along the first edge  14   c  and be coupled to a first circuit  40   a  to form an anode portion. A second group of electrodes  50   b  may be disposed along the second edge  14   d  and be coupled to a second electrode circuit  42   b  to form a cathode portion. Thus, first and second group of electrodes  50   a ,  50   b  may provide a varying voltage gradient across the channel  12  via the first and second electrode circuits  42   a ,  42   b . In an embodiment, the electrode circuits  42  may include flexible printed circuit boards. 
     In an embodiment, a flow rate of the ER fluid in and/or through channel  12  can be controlled by applying a varying voltage gradient to the first and second group of electrodes  50   a ,  50   b  (e.g., anodes and cathodes  50   a ,  50   b ). In response to the voltages applied to the electrodes, an electric field is established across channel  12 . In the presence of such an applied electric field voltage, chains of solid particles within the ER fluid can be aligned within channel  12  between the electrodes  50   a ,  50   b  on each side of the channel  12 . As the applied electric field voltage varies, the formed chains of particles can move along a length of channel  12 . Thus, the ER fluid can be moved by the force of applied electric field voltage, dipole-dipole interaction, and drag, such that the ER fluid moves from a first end of channel  12  to a second end of channel  12  and can be circulated from an inlet (not shown) of solid state pump  10  to an outlet (not shown) of solid state pump  10 . 
     In an embodiment, an inlet may be formed in at least one of the first, second or third plates  16 ,  14 ,  18 . For example, the inlet may be formed in a top surface or a side surface of first plate  16 . The inlet may be formed in a side surface of second plate  14 . In some embodiments, the inlet may be formed in a bottom surface or a side surface of third plate  18 . The inlet may be fluidly coupled to a first end of channel  12 , for example, to provide ER fluid to channel  12 . 
     In an embodiment, an outlet may be formed in at least one of the first, second or third plates  16 ,  14 ,  18 . For example, the outlet may be formed in a top surface or a side surface of first plate  16 . The outlet may be formed in a side surface of second plate  14 . In some embodiments, the outlet may be formed in a bottom surface or a side surface of third plate  18 . The outlet may be fluidly coupled to a second end of channel  12 , for example, to receive ER fluid to channel  12  being discharged from channel  12 . 
     In some embodiments, a means for coupling  28   a ,  28   b  may be disposed between the first, second and/or third plates  16 ,  14 ,  18  to couple one or more of first, second and/or third plates  16 ,  14 ,  18  together. For example, in one embodiment, a first means for coupling  28   a  may be disposed between first plate  16  and second plate  14  and a second means for coupling  28   b  may be disposed between second plate  14  and third plate  18 . In some embodiment, a means for coupling  28   a ,  28   b  may be used to couple at least one of electrode circuit  42  to a first and/or second surface of second plate  14 , which will be discussed in greater detail below with respect to  FIG. 3 . 
     In an embodiment, the means for coupling  28   a ,  28   b  may be used to seal a junction between two surfaces (e.g., between two surfaces of first, second, and/or third plates  16 ,  14 ,  18  and/or channel  12 ). In some embodiments, the means for coupling may be used to adhere two surfaces together (e.g., between two surfaces of first, second and/or third plates  16 ,  14 ,  18 ). For example, in one embodiment, each of the first, second and third plates  16 ,  14 ,  18  may include one or more threaded holes such that a screw may be inserted through the one or more threaded holes to couple the first, second and third plate  16 ,  14 ,  18  together. The one or more threaded holes may be formed through any surface and/or side edge of the first, second and/or third plates  16 ,  14 ,  18 . 
     The means for coupling  28   a ,  28   b  may include but is not limited to various types of gaskets, (e.g., a solid gasket or a liquid gasket), mechanical couplings, fasteners (e.g., nuts, bolts, screws, threaded holes, etc.), adhesive material (e.g., double sided tape) or adhesive liquid. In some embodiments, solid state pump  10  may use two or more different types of means for coupling. For example, in one embodiment, a first type of means for coupling may be used to secure the first, second and/or third plates  16 ,  14 ,  18  together and a second type of a means for coupling may be used to adhere the first and second electrode circuits  42   a ,  42   b  to one or more surfaces of the second plate  14 . 
     It should be appreciated that although in the example of  FIG. 1 , solid state pump  10  is illustrated as having three plates in other embodiments, solid state pump  10  may include a varying number of plates (e.g., one plate, two plates, etc.) For example, in one embodiment, solid state pump  10  may be a single unit (e.g., one plate or one module). In such an embodiment, a channel may be formed within a portion of the single unit solid state pump and be configured to provide an electric field across the channel to move ER fluid from an inlet to an outlet of the single unit solid state pump. One or more circuits may electrically couple electrodes formed at one end of the circuits to the channel. For example, the circuits and/or electrodes may be formed or otherwise disposed within the plate via injection molding. In other embodiments, the circuits and/or electrodes may be formed within the plate using techniques such as three-dimensional (3D) printing. Thus, in each of the different embodiments, solid state pump may operate substantially similar to solid state pump  10  as described herein. 
     In some embodiments, the solid state pump  10  may include two plates. In such an embodiment, a channel may be formed within a portion of one of plates or into a portion of both plates and be configured to provide an electric field across the channel to move ER fluid from an inlet to an outlet of the single unit solid state pump. Electrodes may be formed or printed along edges of one or both of the plates to the provide the voltage. In other embodiments, the solid state pump  10  may include a plurality of plates. The channel  12  may be formed within one of the plates or within a portion of two or more plates. Further, multiple channels  12  may be formed in on or more of the plurality of plates. In each of the different embodiments, solid state pump may operate substantially similar to solid state pump  10  as described herein. 
     In some embodiments, a first and second tube  24   a ,  24   b  may be coupled to the top surface  16   a  of first plate  16  to provide and receive the ER fluid being pumped through channel  12 . For example, and briefly referring to  FIGS. 1A-1B , first tube  24   a  may be coupled to the top surface  16   a  of first plate  16  and second tube  24   b  may be coupled to the top surface  16   a  of first plate  16 . In an embodiment, the first tube  24   a  can be fluidly coupled to a first end of channel  12  through a first opening  26   a  formed in the top surface  16   a  to provide ER fluid to channel  12 . Second tube  24   b  may be fluidly coupled to a second end of channel  12  through a second opening  26   b  formed in the top surface  16   a  to receive ER fluid from channel  12 . 
     In some embodiments, the first and second openings  26   a ,  26   b  may be threaded holes formed through a respective surface of first, second and/or third plates  16 ,  14 ,  18 , such that tube fittings can be screwed to the respective plate. Other techniques, may of course also be used to mount or otherwise couple tubes to ones of the plates. 
     In an embodiment, a means for coupling may be used to couple the first and second tubes  24   a ,  24   b  to the top surface  16   a  of the first plate  16 . For example, in one embodiment, the means for coupling may include instant-bonding adhesive that can be applied to a surface of first and second tubes  24   a ,  24   b  as well as to an inner surface of first and second openings  26   a ,  26   b  to ensure a liquid tight seal. 
     In some embodiments, a means for coupling  76  may be used to couple the first, second and third plates  16 ,  14 ,  18  together. For example, a plurality of openings  27  may be formed in each of first, second and third plates  16 ,  14 ,  18 . A first type of means for coupling  74  (e.g., screw) may be inserted through each of the openings  27  and fastened with a second type of means for coupling  76  (e.g., nut) to secure the first, second and third plates  16 ,  14 ,  18  together. 
     In an embodiment, at least portions of first, second and third plates  16 ,  14 ,  18  may be provided form a dielectric material or other non-conducting material. In one embodiment, each or portions of first, second and third plates  16 , 14 ,  18  may include transparent acrylic sheets. The first, second and third plates  16 , 14 ,  18  may include the same materials. In other embodiments, one or more of first, second and third plates  16 , 14 ,  18  may include different materials. 
     Now referring to  FIG. 3 , a top surface  14   a  (e.g., first surface) of second plate  14  includes channel  12  having an inlet  34   a  formed at a first end and outlet  34   b  formed at a second end. The top surface  14   a  further includes two recessed regions  38   a ,  38   b  and two non-recessed regions  38   c ,  38   d . In an embodiment, recessed regions  38   a ,  38   b  may be formed into a surface (e.g., top surface and/or bottom surface) of second plate  14  to accommodate a circuit, such as electrode circuit  42  of  FIG. 1 , such that after the circuit has been disposed on the surface, a surface of the circuit is substantially flush with a surface of the non-recessed regions  38   c ,  38   d.    
     For example, and referring briefly to  FIG. 3A , a side view of second plate  14  illustrates recessed regions  38   a ,  38   b  and non-recessed regions  38   c ,  38   d  formed or otherwise provided on both a top surface  14   a  and a bottom surface  14   b  of second plate  14 . It should be appreciated that recessed regions  38   a ,  38   b  can be formed on the top surface  14   a , bottom surface  14   b  or both the top and bottom surfaces  14   a ,  14   b  of second plate  14  to accommodate electrode circuits that may be disposed on, wrapped around, or otherwise formed on each of the respective surfaces. In some embodiments, recessed regions  38   a ,  38   b  may be etched on the both sides of second plate  14  for the flexible circuit to wrap around. 
     A means for coupling may be used to couple the recessed regions  38   a ,  38   b  to both sides of second plate  14 . For example, in one embodiment, the means for coupling may include double sided tape that can be used to ensure the contact (e.g., mechanical contact, electrical contact) of electrode circuit  42  to both sides of second plate  14 . The means for coupling may be resistant to oil, for example, when ER fluid is the hydraulic fluid. 
     A depth of the recessed regions  38   a ,  38   b  may vary. For example, the depth of recessed regions  38   a ,  38   b  may be selected based at least in part on the dimensions (e.g., thickness of a circuit) and/or the dimensions of second plate  14 . In some embodiments, a depth of the recessed regions  38   a ,  38   b  may be selected based, at least in part on, a thickness of the means for coupling. In some embodiments, first and third plates  16 ,  18  may include one or more recessed regions and one or more non-recessed regions. The depth of recessed regions  38   a ,  38   b  on the first and/or third plate  16 ,  18  may be selected based at least in part on the dimensions (e.g., thickness of a circuit), dimensions of respective plate (e.g., first or third plate  16 ,  18 ) and/or a thickness of the means for coupling. 
     It should be appreciated, that in some embodiments, circuits may be formed within a surface of or otherwise printed directly on a surface of the second plate  14 , thus second plate  14  may not have recessed regions  38   a ,  38   b  and instead the top surface  14   a , bottom surface  14   b  or both the top and bottom surfaces  14   a ,  14   b  of second plate  14  may be flat or substantially flat across the entire respective surface. 
     Referring back to  FIG. 3 , in an embodiment, one or more teeth  36   a - 36   n  may optionally be formed along a first and second edge  14   c ,  14   d  of second plate  14 . In some embodiments, the one or more teeth  36   a - 36   n  may be formed along an edge of recessed regions  38   a ,  38   b . Each of the one or more teeth  36   a - 36   n  may be formed to couple to an electrode to the respective side of second plate  14 . The electrodes can be coupled to an independent power source to provide a voltage to the respective circuit deposed on or otherwise formed on a surface of second plate  14 . In an embodiment, arc region  70   a - 70   n  may be formed between each of the teeth  36   a - 36   n.    
     In some embodiments, a spacing between each of the teeth  36   a - 36   n  may be equal. In other embodiments, the spacing between one or more teeth  36   a - 36   n  may be different. The number of teeth formed along the first and/or second edge  14   c ,  14   d  may vary based at least in part on a particular application of solid state pump  10 , dimensions of solid state pump and/or second plate  14 . In some embodiments, the number of teeth formed along the first and/or second edge  14   c ,  14   d  may be selected to equal a number of electrodes to be coupled to second plate  14 . 
     In the illustrative embodiment of  FIG. 3 , channel  12  can be formed in a middle portion of second plate  14 . However, it should be appreciated that channel  12  may formed in any portion of second plate  14 . For example, in some embodiments, channel  12  may be formed such that it is offset with respect to a middle portion of second plate  14 . In some embodiments, second plate  12  may include multiple channels  12 . 
     For example, and referring to  FIG. 3B , a plurality of channels  12   a - 12   n  may be formed in second plate  14 . In an embodiment, each of channels  12   a - 12   n  may include a circuit coupled to at least two opposing sides of the respective channel to provide an electric field voltage across the respective channel to move ER fluid from the first end to the second end of the respective channel. Each of the channels  12   a - 12   n  may include and inlet  34   a - 34   n  formed at a first end and an outlet  35   a - 35   n  formed at a second end. In some embodiments, the channels  12   a - 12   n  may be equally spaced apart from each other. In other embodiments, the spacing between one or more channels  12   a - 12   n  may vary. 
     In some embodiments, each of the channels  12   a - 12   n  may have the same dimensions (e.g., length, width) and/or shape (e.g., straight, curved, etc.). In other embodiments, the dimensions (e.g., length, width) and/or shape (e.g., straight, curved, etc.) may vary from one channel to a next. 
     For example, and referring to  FIG. 3C , in some embodiments, a width of channel  12  may vary from a first end to a second end. For example, and as illustrated in  FIG. 3C , channel  12  may have a first width, W 1 , at the first end that is greater than a second width, W 2 , at the second end (e.g., W 1 &gt;W 2 ). Thus, the width may decrease along a length of channel  12 . In other embodiments, the first width, W 1 , at the first end may be less than the second width, W 2 , at the second end (e.g., W 1 &lt;W 2 ). Thus, the width may increase along a length of channel  12 . With such an approach a constant voltage applied to electrodes results in varied electric field along the channel. That is for the same applied voltage, the electric field magnitude across a narrow portion of the channel will be greater than an electric field magnitude at a wide portion of the channel. 
     Channel  12  may be formed in a variety of different shapes. For example, and referring to  FIG. 3 , channel  12  can be formed having a substantially straight shape. However, and now referring to  FIG. 3D , in some embodiments, channel  12  may have a curved shape. It should be appreciated that a shape of channel  12  (e.g., straight, curved, etc.) may be selected based at least in part on the shape of second plate  14  and/or a particular application of solid state pump  10 . 
     In some embodiments, a fillet  32  can be used connect channel  12  and the inlet  34  and outlet  35  to reduce the pressure loss to a minimum. In an embodiment, the flow rate of solid state pump  10  can be determined based, at least in part, on the dimensions of second plate  14 , channel  12  and a magnitude of the electric field voltage applied across channel  12 . For example, a thickness of second plate  14  may impact the flow rate of ER fluid through channel  12 . Further, a width of channel  12  may be selected (e.g., limited) based on the magnitude of applied electric field voltage. In some embodiments, an edge of second plate  14  may be modified (e.g., dented) to aid in sealing channel  12  and provide better insulation. 
     In an embodiment, a stair-step  40  may be used at the first and/or second end of channel  12  (e.g., next to inlet  34  and/or outlet  35 , respectively) to provide a uniform width of channel  12  after wrapping the electrode circuit  42  through the channel and around second plate  14 . 
     Now referring to  FIG. 4 , electrode circuit  42  includes one or more electrodes  44   a - 44   n  formed on a surface  43  of the electrode circuit  42 . In one embodiment, electrode circuit  42  may be a printed circuit board and include conducting materials, such as conductive tracks, pads and other features etched from conductive material and disposed onto a non-conductive substrate. Each of the electrodes  44   a - 44   n  may include an electrode end  50   a - 50   n  to couple to a power source. In some embodiments, a spacing between each of the electrodes  44   a - 44   n  may be equal. In other embodiments, the spacing between one or more of the electrodes  44   a - 44   n  may be different. In an embodiment, the spacing of the one or more of the electrodes  44   a - 44   n  may be selected based at least in part on a desired magnitude of an electric field voltage to be generated and applied across channel  12 . For example, to lower the electric field voltage, the spacing between electrodes  44   a - 44   n  can be decreased or minimized and to increase the electric field voltage, the spacing between electrodes  44   a - 44   n  can be increased or maximized. 
     In an embodiment, the number of electrodes  44   a - 44   n  formed on the surface  43  of electrode circuit  42  may vary based at least in part on dimensions of electrode circuit  42  and/or dimensions of a plate that electrode circuit  42  is to be coupled to. In some embodiments, the number of electrodes  44   a - 44   n  formed on the surface  43  of electrode circuit  42  may be selected based at least in part on the desired magnitude of an electric field voltage to be generated and applied across channel  12 . For example, the number of electrodes  44   a - 44   n  can be increased to increase the maximum pressure differential requirement across the channel and decreased to decrease the maximum pressure differential requirement across the channel  12 . 
     In an embodiment, a pattern of the electrodes  44   a - 44   n  may vary based at least in part on a spacing requirement between each of the electrodes  44   a - 44 . The electrodes  44   a - 44   n  may formed in a symmetric pattern or an asymmetric pattern. For example, and as illustrated in  FIG. 4 , electrode portions  44   a - 44   n  may have a radial pattern  55  to provide desired spacing for the electrodes pads  50   a - 50   n  (e.g. to facilitate electrical connection between pads  50   a - 50   n  and other circuitry (e.g. a voltage source)). In other embodiments, the electrode portions  44   a - 44   n  may be formed in a straight line pattern  54 . Those of ordinary skill in the art will appreciate how to select a pattern in which to provide electrode portions  44   a - 44   n  to meet the needs of a particular application. 
     In some embodiments, a width of each of the electrode ends  50   a - 50   n  may vary depending on dimensions of a power supply to be coupled to the electrode ends  50   a - 50   n . For example, the widths of each of the electrode ends  50   a - 50   n  may be increased or decreased based at least in part on the dimensions of a power supply and/or to ensure a stronger connection to the power supply. In some embodiments, the width of each of the electrode ends  50   a - 50   n  may be the same. In other embodiments, the width of one or more of the electrode ends  50   a - 50   n  may be different. 
     In some embodiments, an edge of electrode circuit  42  may be indented to ensure a better insulation (e.g., better coupling) between at least two of the electrodes  44   a - 44   n . For example, an edge of electrode circuit  42  may be indented or otherwise grooved or shaped to receive the electrodes  44   a - 44   n.    
     In some embodiments, arcs  52   a - 52   n  may be formed between each of the electrode ends  50   a - 50   b . The arcs  52   a - 52   n  may be by a means for coupling to couple first, second and/or third plates  16 ,  14 ,  18  together. For example, in one embodiment, a screw and/or nut may be used to couple first, second and/or third plates  16 ,  14 ,  18  together and the screw may be disposed through each of the arcs  52   a - 52   n  and through second plate  14 . 
     In an embodiment, double-dashed line  56  (i.e., fold line) represents a folding line of electrode circuit  42  where electrode circuit  42  can be folded to wrap through a channel and around second plate  14 . Thus, as illustrated in  FIG. 5  to be discussed below the electrode circuit  42  may be disposed on both, a top and bottom surface, of second plate  14 . 
     Now referring to  FIG. 5 , first and second electrode circuit  42   a ,  42   b  each include a plurality of electrodes  44   a - 44   n . It should be appreciated that first and second electrode circuits  42   a ,  42   b  are the same or substantially the same as electrode circuits  42  described above with respect to  FIG. 4 , however first and second electrode circuits  42   a ,  42   b  are illustrated in a folded position. For example, first and second electrode circuits  42   a ,  42   b  can be folded at each of their respective folding lines  56   a ,  56   b  ( FIG. 4 ). In an embodiment, folding lines  56   a ,  56   b  correspond to folding line  56  of electrode circuit  42  of  FIG. 4 . 
     In an embodiment, folding lines  56   a ,  56   b  are positioned on first and second electrode circuits  42   a ,  42   b  based at least in part on a geometry of the second plate  14  and a recessed region formed on the second plate  14 . For example, in a folded position, first and second electrode circuits  42   a ,  42   b  may each have a top portion  58   a ,  58   b , respectively and a bottom portion  60   a ,  60   b , respectively. 
     In some embodiments, a length of the first top portion  58   a  may be equal to a length of the recessed region formed on the first electrode circuit  42   a  and a length of the top portion  58   b  may be equal to a length of the recessed region formed on the second electrode circuit  42   a . A length of first and second bottom portions  60   a ,  60   b  may be less than the length of first and second top portions  58   a ,  58   b , respectively. For example, in some embodiments, a length of the first bottom portion  60   a  may be equal to a difference between the length of the first top portion  58   a  and a length to couple to a power supply and a length of the second bottom portion  60   b  may be equal to a difference between the length of the second top portion  58   b  and a length to couple to a power supply. For example, first and second top portions  58   a ,  58   b  may extend beyond first and second bottom portions  60   a ,  60   b , respectively, to enable a connection to the power supply. 
     Now referring to  FIG. 6 , a solid state pump  60  includes a first, second and third plates  86 ,  84 ,  88 , first and second scales  64   a ,  64   b  and first and second pressure measurement devices  62   a ,  62   b . In an embodiment, first, second and third plates  86 ,  84 ,  88  may the same or substantially similar to first, second and third plates  16 ,  14 ,  18  described above with respect to  FIGS. 1-5 . Further, solid state pump  60  may be the same or substantially similar to solid state pump  10  described above with respect to  FIGS. 1-5 , however, solid state pump  60  includes first and second pressure measurement devices  62   a ,  62   b  to measure a pressure differential between an inlet  74   a  and outlet  74   b.    
     In an embodiment, the first pressure measurement devices  62   a  may be coupled to inlet  74   a  using a base  66   a  and second pressure measurement devices  62   b  may be coupled to outlet  74   b  using a second base  66   b . First and second pressure measurement devices  62   a ,  62   b  may include any type of pressure measure device. For example, and as illustrated in  FIG. 6 , first and second pressure measurement devices  62   a ,  62   b  may include pitot tubes. In some embodiments, the first and second pressure measurement devices  62   a ,  62   b  may be used as a substitute for tube fittings to provide ER fluid to the solid state pump  60  via the inlet  74   a  and receive ER fluid from the solid state pump  60  via the outlet  74   b.    
     Solid state pump  60  may include first and second scales  64   a ,  64   b  to measure a height of first and second pressure measurement devices  62   a ,  62   b . For example, in one embodiment, first and second scales  64   a ,  64  may include graduated scales and can be aligned with first and second pressure measurement devices  62   a ,  62   b  in parallel to measure the height of the surface of ER fluid in the first and second pressure measurement devices  62   a ,  62   b . It should be appreciated that although  FIG. 6  illustrates first and second scales  64   a ,  64  as graduated scales, that other types of pressure measurement devices and scales may be used based on a particular application and/or design of solid state pump  60 . 
     In some embodiments, the height of the surface of ER fluid in the first and/or second pressure measurement devices  62   a ,  62   b  may change responsive to a voltage gradient being applied to a channel within solid state pump  60  that causes the ER fluid to flow from the inlet  74   a  to the outlet  74   b . The height of the first and second pressure measurement devices  62   a ,  62   b  and/or first and scales  64   a ,  64  can be determined by a specific varying voltage gradient applied to the electrodes disposed on or otherwise formed on at least one of first, second or third plates  86 ,  84 ,  88 . In an embodiment, a difference of the height of the fluid surfaces in first and second pressure measurement devices  62   a ,  62   b  indicates the pressure differential. 
     In the illustrative embodiment of  FIG. 6 , the first pressure measurement devices  62   a  may be coupled to inlet  74   a  formed on a top surface  86   a  of first plate  86  using the first base  66   a  and second pressure measurement devices  62   b  may be coupled to outlet  74   b  formed on the top surface  86   a  of first plate  86  using the second base  66   b . Further, first scale  64   a  may be coupled to the top surface  86   a  of first plate  86  using a first base  68   a  and second scale  64   b  may be coupled to the top surface  86   a  of first plate  86  using a second base  68   b . However, it should be appreciated that the inlet  74   a  and outlet  74   b  may be formed on any surface and/or side edge of the solid state pump  60  (e.g., any surface or side edge of first, second and third plates  86 ,  84 ,  88 ). For example, in one embodiment, inlet  74   a  may be formed on the top surface  86   a  of first plate  86  and the outlet  74   b  may be formed on a bottom surface  88   b  of third plate  88 . Thus, first and second pressure measurement devices  62   a ,  62   b  and first and second scales  64   a ,  64   b  may be formed on any surface and/or side edge of the solid state pump  60  (e.g., any surface or side edge of first, second and third plates  86 ,  84 ,  88 ). 
     Now referring to  FIG. 7 , a method  700  for pumping ER fluid through a solid state pump begins at block  702 , whereby ER fluid can be introduced into one or more channels formed within a solid state pump. 
     The ER fluid may be provided to an inlet coupled to a first end of the channel. Thus, the channel may have a first end fluidly coupled to an inlet of the solid state pump and a second end fluidly coupled to an outlet of the solid state pump. In some embodiments, a first tube may be coupled to the inlet and be fluidly coupled to the first end of the channel. The first tube may provide the ER fluid to the first end of the channel. Further, a second tube may be coupled to the outlet and be fluidly coupled to the second end of the channel. The second tube can receive the ER fluid after the ER fluid has been pumped through the solid state pump. 
     At block  704 , an electric voltage may be applied across the channel to move the electro-rheological fluid from the inlet to an outlet of the channel. In an embodiment, one or more circuits may electrically couple electrodes to a portion of the channel to provide a varying voltage to the channel. For example, in one embodiment, a spatially varying horizontal electric field may be applied across the channel. In other embodiments, a spatially varying vertical electric field may be applied across the channel. 
     The electric field voltage can change a property of the ER fluid to move the ER fluid from the first end of the channel to the second end of the channel and thus, from the inlet to the outlet of the solid state pump. 
     In an embodiment, the electric field voltage can be varied at one or more points along the channel to move the ER fluid from the first end to the second end. For example, the electric field voltage applied across the first end of the channel can be different (e.g., greater than, less than) than the electric field voltage applied across the second end of the channel. In some embodiments, during operation of the solid state pump, the electric field voltage can be continuously varied at different points to generate a wave like response to pump the ER fluid through the channel. A pattern of electric field distribution can be propagated down the channel by the applied voltage. In some embodiments, the electric field to be propagated may not uniform. 
     In some embodiments, the electric field voltage may be maintained at a constant level and the width of the channel may be varied from first end to the second end to generate a different pressure differential at the first end as compared with the second end of the channel. For example, the width of the channel at the first end may be greater than or less than the width of the channel at the second end. Thus, the electric field applied across the channel may vary based, at least in part on, a width of the respective portion of the channel. In other embodiments, the electric voltage received from an independent source via the circuits and electrodes may be varied and the width of the channel may be varied, thus the electric field voltage applied across the channel may be a result of the both the varied electric voltage and the differing widths of the channel. 
     In some embodiments, the shape of the channel may be varied (e.g., s-shape, curved shape, etc.), thus the electric field voltage can be varied at one or more points along the channel to move the ER fluid from the first end to the second end. 
     In an embodiment, the pumping of the ER fluid from the inlet to the outlet may be based at least in part on the applied electric field, dipole-dipole interaction and a drag factor. For example, a first circuit may include a plurality of cathodes and be electrically coupled to a first side of the channel and a second circuit may include a plurality of anodes and be electrically coupled to a second side of the channel. 
     In an embodiment, the cathodes, first circuit, anodes and second circuit may form a dipole-dipole interaction across the channel to move the ER fluid from the first end to the second end of the channel. In an embodiment, the drag factor may refer to a numerical rate at which the flow rate of the ER fluid is decreasing based at least in part on the dimensions and/or properties of the channel as the ER fluid flows from one end to a second end of the channel. Thus, a flow rate of the ER fluid through the channel can be based, at least in part, on dimensions of the channel (e.g., length, shape, width), properties (e.g., type of material) and a magnitude of the electric field voltage. 
     In some embodiments, a plurality of electrodes may be coupled to each of the first and second circuits. The plurality of electrodes may be coupled to a power source to provide a voltage to each of the first and second circuits. In an embodiment, a spacing of the plurality of electrodes along a length of the first and/or second circuits respectively can determine a magnitude of the electric field voltage applied across the channel. Thus, the electrodes may be spaced according to a desired electric field to be generated and/or dimensions of the first and second circuits. 
     At block  706 , the ER fluid may be received at the outlet of the channel. The flow rate of the ER fluid through the channel can be based, at least in part, on dimensions of the channel and the magnitude of the applied electric field voltage. 
     In some embodiments, the solid state pump may include pressure measuring devices to measure a pressure difference between the inlet and the outlet. For example, a first pressure device may be coupled to the inlet and a second pressure device may be coupled to the outlet. 
     In some embodiments, scales may be coupled to the solid state pump to measure the pressure difference between the inlet and the outlet. For example, in one embodiment, a first graduated scale may be coupled to the solid state pump and aligned with the first pressure measurement device and a second graduated scale may be coupled to the solid state pump and aligned with the second pressure measurement device. The first and second graduate scales can measure a height of the first pressure measurement device and the second pressure measurement device respectively to determine the pressure difference between the inlet and the outlet. 
     In some embodiments, the solid state pump may include a plurality of channels. Each of the plurality of channels may be formed and operate substantially similar to the channels described above (e.g., channel  12  of  FIGS. 1-3D ). For example, each of the plurality of channels may include circuits coupled to at least two opposing sides of the respective channel to apply an electric field voltage across them. In such an embodiment, the solid state pump may include a plurality of inlets and outlets. For example, the solid state pump may include at least one inlet and one outlet for each of the plurality of channels. 
     While the concepts, systems and techniques sought to be protected have been particularly shown and described with references to illustrated embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the concepts as defined by the appended claims. 
     Elements of different embodiments described herein may be combined to form other embodiments not specifically set forth above. Other embodiments not specifically described herein are also within the scope of the following claims.