CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/566,603, filed Dec. 3, 2011 and herein incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to mechanical energy harvesting and, more particularly to a method and apparatus for energy harvesting that utilizes magnetic and microfluidic elements to create electrical energy from otherwise “wasted” mechanical movements. 
       BACKGROUND OF THE INVENTION 
       [0003]    Currently, the majority of autonomous and mobile electronic systems are powered by electrochemical batteries. Although the quality of these batteries has substantially improved over the last two decades, their energy density has not greatly increased. At present, limitations such as cost, weight, limited service time and waste disposal problems intrinsic to the materials used to form electrochemical batteries are impeding the advance of many areas of electronics. The problem is particularly acute in the area of mobile electronic devices, where rapidly-growing performance and sophistication of these devices leads to ever-increasing power demands—demands that cannot easily be met by traditional electrochemical batteries. 
         [0004]    One of the technologies that holds great promise to substantially alleviate the current reliance on electrochemical batteries is high-power energy harvesting. The concept of energy harvesting works toward developing self-powered devices that do not require replaceable power supplies. In cases where device mobility is required, and high power consumption is anticipated, harvesters that convert mechanical energy into electrical energy are particularly promising as they can tap into a variety of high-power-density sources, including mechanical vibrations. 
         [0005]    High power harvesting of mechanical energy is a long-recognized concept that has not been significantly commercialized to date, based on the lack of a viable energy harvesting technology. Existing methods of mechanical-to-electrical energy conversion such as, for example, electromagnetic, piezoelectric or electrostatic do not allow for effective direct coupling to the majority of high power environmental mechanical energy sources. In particular, bulky and expensive mechanical or hydraulic transducers are required by each of these existing methods to convert the broad range of aperiodic forces and displacements typically encountered in nature into a form useable for conversion to electricity. 
         [0006]    An alternative approach to energy harvesting has recently been proposed that substantially alleviates the above-mentioned problems, the new approach being the use of a microfluidics-based energy harvester. In particular, an exemplary high power microfluidics-based energy harvester is disclosed in U.S. Pat. No. 7,898 issued to T. N. Krupenkin on Mar. 2, 2011, as well as U.S. Pat. No. 8,053,914 issued to T. N Krupenkin on Nov. 8, 2011, both of which are herein incorporated by reference. An exemplary embodiment of an energy harvester as described in the above-referenced patents generates electrical energy through the interaction of thousands of microscopic liquid droplets with a network of thin-film electrodes. A typical configuration of the Krupenkin energy harvester is capable of generating several watts of power. 
         [0007]    An exemplary embodiment of this energy harvester is shown in  FIG. 1 , which illustrates a train of energy-producing conductive droplets  1  located along a microscopically-thin channel  2 , where droplets  1  are suspended within a liquid dielectric medium  3  and are hydraulically actuated by applying a pressure differential between the ends of channel  2 . Pluralities of separate electrodes  4 - 1  and  4 - 2  are disposed along either side of channel  2 , which interact with droplets  1  as they move back and forth within channel  2  during changes in pressure. As conductive droplets  1  move along channel  2 , they create arrays of capacitors with electrodes  4 - 1  and  4 - 2 , the capacitors changing in stored charge as the droplets move back and forth, generating an electrical current flow along conductors  5 - 1  and  5 - 2 . This type of hydraulic activation method provides an important advantage as it allows for efficient direct coupling with a wide range of high power environmental mechanical energy sources, including human locomotion. 
         [0008]    While considered a significant advance in the field of energy harvesting, the arrangement as shown in  FIG. 1  requires the use of an external source of bias voltage to generate the charges at electrodes  4 - 1  and  4 - 2 . This bias voltage can be provided by sources such as electrochemical batteries or electrical capacitors. The output power density provided by the harvester device increases rapidly with larger bias voltages. Indeed, certain power density requirements may necessitate relatively high bias voltages (e.g., on the order of tens or even hundreds of voltages). The need to provide a bias voltage source may introduce unwanted complications in the design of the harvesting device and adversely affect its reliability. 
         [0009]    Thus, a need remains in the art for an arrangement that provides the advantages of the microfluidic energy harvesting configuration as developed by Krupenkin without requiring the use of an external bias voltage source. 
       SUMMARY OF THE INVENTION 
       [0010]    The needs remaining in the art are addressed by the present invention, which relates to mechanical energy harvesting and, more particularly to a method and apparatus for energy harvesting that utilizes a combination of magnetic and microfluidic elements to create electrical energy from otherwise wasted mechanical movements. 
         [0011]    In accordance with one embodiment of the present invention, an energy harvesting apparatus comprises a chain of energy-producing elements, alternating between a magnetic element and microfluidic droplets, the chain configured to laterally move within an energy-producing channel consisting of an alternating arrangement of coils (each coil having one or more turns) and dielectric-coated electrodes. The lateral movement is caused by a pressure differential between the opposite ends of the channel (for example, human locomotion). The presence of the magnetic elements moving within the turns of a coil produces the electromagnetic energy required to bias the electrodes of the capacitive structure created with the droplets, eliminating the need for an external bias voltage source. 
         [0012]    Indeed, an exemplary embodiment of the present invention comprises apparatus for converting mechanical energy into electrical energy comprising a channel formed as a tube and comprising a plurality of coils and a plurality of dielectric-coated electrodes disposed within the tube in an interleaved configuration such a single dielectric-coated electrode is disposed between a pair of adjacent individual coils and a chain formed of alternating regions of magnetic material and microfluidic conductive droplets, the chain disposed along a hollow longitudinal area within the tube and capable of lateral movement within the hollow longitudinal area such that the application of mechanical energy to the apparatus in the form of movement of the chain with respect to the channel creates multiple alternations of an area of overlap between the regions of magnetic material and turns of the coil to create electromagnetic energy, and multiple alternations of an area of overlap between the microfluidic conductive droplets and the dielectric-coated electrodes to create electrostatic energy, the electrostatic energy created in the presence of a bias voltage. 
         [0013]    Other and further embodiments of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Referring now to the drawings, where like numerals represent like parts in several views: 
           [0015]      FIG. 1  illustrates a prior art microfluidic-based energy harvesting arrangement; 
           [0016]      FIG. 2  is a cut-away side view of an exemplary electrostatic and electromagnetic energy harvesting arrangement formed in accordance with the present invention; 
           [0017]      FIG. 3  is an isometric view of a portion of the arrangement of  FIG. 2 ; 
           [0018]      FIG. 4  is an alternative illustration of the embodiment of  FIG. 2 , in this case showing the relative movement of the energy-producing chain with respect to the energy-producing channel; 
           [0019]      FIG. 5  is an exploded view of the embodiment of the present invention as shown in  FIG. 2 ; 
           [0020]      FIG. 6  is an enlarged view of a selected segment of the embodiment of  FIG. 2 , in this case illustrating the relationship between a single conductive microfluidic droplet and a pair of dielectric-coated electrodes as used to create electrostatic energy in accordance with the present invention; 
           [0021]      FIG. 7  illustrates an exemplary configuration for creating electromagnetic energy utilizing a moving magnet in accordance with Faraday&#39;s Law; 
           [0022]      FIG. 8  is an enlarged view of a selected segment of the embodiment of  FIG. 2 , in this case illustrating the relationship between a single magnetic element and surrounding turn of a coil as used to create electromagnetic energy in accordance with the present invention; 
           [0023]      FIG. 9  is an isometric view of a portion of an alternative embodiment of the present invention, in this case formed to create only electrostatic energy; 
           [0024]      FIG. 10  is a cut-away side view of the embodiment of  FIG. 9 ; 
           [0025]      FIG. 11  is an isometric view of a portion of yet another embodiment of the present invention, in this case formed to create only electromagnetic energy; and 
           [0026]      FIG. 12  is a cut-away side view of the embodiment of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    As described in detail below, an embodiment of the present invention comprises a synergistic combination of an electromagnetic energy generation arrangement and a microfluidic-based electrostatic energy generation arrangement, where the energy created by the electromagnetic portion of the system can be used to provide the bias voltage required for the electrostatic portion of the system. The incorporation of the electromagnetic elements allows for this embodiment of the energy harvesting system of the present invention to operate without the need for an external voltage bias source, as required in prior art arrangements. 
         [0028]      FIG. 2  is a cross-sectional view of an exemplary embodiment of the present invention, illustrating an energy harvesting system  10  utilizing a plurality of microfluidic conductive elements and a plurality of magnetic disks in an interdigitated arrangement that is capable of creating both microfluidic-based electrostatic energy and electromagnetic energy, respectively.  FIG. 3  is an isometric view of a portion of the arrangement of  FIG. 2 . 
         [0029]    As shown in this particular embodiment, energy harvesting system  10  includes a hollow tube  12 , with a plurality of dielectric-coated electrodes  14  and a plurality of coils  16  embedded within the material  13  forming tube  12 . It is an aspect of the present invention that electrodes  14  and coils  16  are disposed in an interleaved configuration within tube  12 , with a single electrode  14 - a  disposed between an adjacent pair of coils  16 -T 1  and  16 -T 2 . The pitch of the plurality of coils  16 , defined as the spacing d between the center of adjacent individual coils  16 -T 1  and  16 -T 2 , is essentially constant in this particular configuration. Similarly, the spacing x between adjacent electrodes  14 - a  and  14 - b  is essentially constant. As a result, a well-controlled, known amount of energy can be reproducibly created with system  10 . This combination of tube  12 , electrodes  14  and coils  16  is referred to at times herein as a “channel” portion  11  of energy harvesting system  10 . 
         [0030]    Continuing with the description of the embodiment of  FIG. 2 , energy harvesting system  10  further comprises a plurality of magnetic rings  18  and a plurality of energy-producing droplets  20  disposed in an alternating configuration within the hollow inner region  15  of tube  12 . Neighboring magnetic rings  18  are magnetized through their thickness in opposite polarities (as particularly shown by the arrows in  FIGS. 2 and 3 ). An alloy of neodymium, iron and boron (Nd 2 Fe 14 B) is one exemplary material that may be used for magnetic rings  18 . 
         [0031]    Energy-producing conductive droplets  20  used to provide energy as the electrostatic portion of system  10  are disposed between neighboring magnetic rings  18 , as shown in  FIGS. 2-5 . Examples of suitable electrically conductive liquids that may be used for droplets  20  include aqueous salt solutions and molten salts. Exemplary aqueous salt solutions include 0.01 molar solutions of salts such as CuSO.sub.4, LiCl, KNO.sub.3, or NaCl. Exemplary molten salts include 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, which are both commercially available. In other cases the conductive liquid can comprise liquid metals such as, gallium, indium or mercury, as well as their alloys. 
         [0032]    In order to maintain a desired, fixed spacing between adjacent magnetic rings  18 , a plurality of spacers  22  are included in system  10  as shown, where droplets  20  will fill the region surrounding spacers  22 . The use of spacers is considered to be optional. 
         [0033]    In accordance with this embodiment of the present invention, the plurality of magnetic rings  18 , spacers  22  and droplets  20  are connected by a single, centrally disposed flexible rod (e.g., “string”)  24 , to form what is referred to at times hereinafter as an energy-producing “chain”  25 . The various elements disposed along rod  24  are affixed thereto in a manner such that they are permitted to rotate about rod  24 , but not slide along rod  24 . As will be described in detail below, chain  25  is permitted to slide, as a single “fixed” unit, back and forth within channel  11 , as indicated by the double-ended arrows. In accordance with the present invention, this movement will cause the creation of energy as magnetic rings  18  move within the plurality of coil  16  (creating electromagnetic energy) and droplets  20  move to overlap dielectric-coated electrodes  14  (creating electrostatic energy).  FIG. 4  illustrates, in exaggerated form, the movement of chain  25  with respect to channel  11 . 
         [0034]      FIG. 5  is an exploded view of this embodiment of the present invention, showing the elements forming channel  11  as one grouping, and the elements forming chain  25  as a separate grouping. Channel  11  is particularly shown as comprising tube  12 , formed of a material  13  such as, polyvinyl chloride (PVC), polypropylene or similar plastics, preferably forming a flexible tube. As shown tube  12  includes a central opening  15  of a diameter sufficient to allow for chain  25  to freely move laterally as a differential hydraulic pressure is applied to the ends of tube  12 . Coils  16  and dielectric-coated electrodes  14  are shown as separate elements of the grouping forming channel  11  in this view. In a preferred embodiment, these elements are formed as embedded within material  13  of tube  12  (see  FIG. 3 ). Alternatively, coils  16  and dielectric-coated electrodes  14  may be disposed over the elements forming chain  25  (e.g., disposed in a separate sleeve element covering chain  25 ), with tube  12  then disposed over the combination of chain  25 , coils  16  and electrodes  14 . Regardless of the implementation, it is an important aspect of the present invention that coils  16  and electrodes  14  be interposed such that an electrode is positioned between adjacent individual coils of the plurality of coils  16  (i.e., an interleaved configuration). This is evident in the views shown in  FIGS. 2-4 . 
         [0035]    Continuing with the description of the exploded view of  FIG. 5 , the elements shown as forming chain  25  include the plurality of magnetic rings  18 , the plurality of conductive droplets  20  and the plurality of spacers  22 . The separate elements are disposed in an alternating arrangement, where it is to be understood that droplets  20  will fill the area outside of spacers  22  between adjacent magnetic rings  18  (as shown in  FIGS. 2-4 ). Flexible rod (string)  24  is also shown, and as described above, is used as a central support member to hold magnetic rings  18  and spacers  22  is a fixed arrangement, eliminating the possibility of translational movement of these elements. 
         [0036]    In order to understand the details of the present invention, it is considered important to also understanding of the underlying principles of electrostatic energy harvesting from the basic microfluidic structure, as well as the principles of electromagnetic energy harvesting from the basic magnetic structure. Microfluidics is a branch of micro-fabrication which is concerned with developing means of handling small volumes of liquids. An aspect of the present invention is to utilize fluidic structures consisting of a large number of microscopic volumes of liquids (e.g., volumes from picoliters to microliters) as a working element in a mechanical-to-electrical energy conversion system. The large number of these microscopic elements (on the order of hundreds or even thousands) yields a realistic amount of electrical energy that can be generated from a relatively small volume of mechanical motion. 
         [0037]    Indeed, the maximum electrical energy output that can be produced by the microfluidic-based portion of the energy harvesting system of the present invention is directly proportional to the variation of the electrostatic field energy during the change in size of contact area between the droplets within the chain and the overlying electrodes along the channel, as mentioned above. For the simplest case where the structure has a total capacitance of C and is maintained at a given electrical voltage differential V, the electrostatic field energy E 0  is expressed as E 0 =0.5CV 2 . Here, E 0  is the energy measured in Joules, V is measured in volts, and C is the capacitance measured in Farads. As will be described hereinbelow, the voltage differential is supplied in accordance with various embodiments of the present invention by the electromagnetic portion of the energy harvesting system. 
         [0038]    An operating principle of the microfluidic-based aspect of the present invention can be understood with reference to a simplified embodiment, as illustrated in  FIG. 6 , which presents a close-up cross-sectional view of a short segment  600  of system  10 , showing only a single conductive droplet  20 .  FIG. 6  also illustrates a pair of dielectric-coated electrodes  14 - 1  and  14 - 2  which, together with conductive droplet  20 , forms two substantially planar electrical capacitors C 1  and C 2 . In this embodiment, the dielectric coating portion  14 -D serves as the spacer in each capacitor structure between conductive droplet  20  and the inner conductive portion  14 -C of each electrode. The first capacitor C 1  is formed by droplet  20  and dielectric-coated electrode  14 - 1  (with dielectric  14 -D- 1  being the spacer). The second capacitor C 2  is formed by conductive droplet  20  and dielectric-coated electrode  14 - 2  (similarly, dielectric  14 -D- 2  forming the spacer between the conductive surfaces in the capacitor structure). 
         [0039]    As shown, charges accumulate at the conductive elements of capacitors C 1  and C 2  in the area of the interfaces with the interposed dielectric. Since droplet  20  is conductive, capacitors C 1  and C 2  are substantially equal and electrically connected in series. Hence, their total capacitance C tot  is one half of their respective individual capacitance. The actual value of capacitance C tot  associated with electrodes  14 - 1  and  14 - 2  depends on the relative position of droplet  20  with respect to electrodes  14 - 1  and  14 - 2 . In particular, when droplet  20  is aligned with electrodes  14 - 1  and  14 - 2  such as to maximize the area of overlap, the capacitance reaches its maximum value. When droplet  20  slides away from electrodes  14 - 1  and  14 - 2  and is positioned in between the neighboring electrodes (that is, positioned underneath coil  16  as chain  25  moves, as shown in  FIG. 4 ), no overlap is present and the capacitance approaches zero. 
         [0040]    Quite obviously, the same evolution of capacitance occurs at each pair of opposing dielectric-coated electrodes  14  within tube  12  (see  FIG. 2 ). Since all these pairs of electrodes are connected in parallel, one can treat the entire set of electrodes as electrically coupled between a pair of conductors  30  and  32  as one variable capacitor with the total capacitance C tot  equal to NC tot , where N is a number of electrode pairs embedded within tube  12 . The movement of droplets  20  through channel  11  causes multiple variations of the total capacitance C between zero and some maximum value C max . 
         [0041]    In contrast to prior art arrangements that utilized an external voltage source to provide a bias between conductors  30  and  32 , and transfer electrical current generated in response to multiple alternations in total electrical capacitance C tot  to a power consumption means (not shown), this embodiment of the present invention utilizes the electromagnetic portion of system  10  to supply this bias voltage. 
         [0042]    Advantageously, the interdigitated arrangement of the electromagnetic portion of system  10  with the microfluidic-based electrostatic portion will automatically move the bias voltage through the range of zero to V max  each time the total capacitance C tot  reaches its maximum value C max , i.e. when the plurality of conductive droplets  20  are aligned with their dielectric-coated electrodes  14  and magnetic rings  18  are aligned with coils  16 . The creation of this bias voltage, in association with the operation of Faraday&#39;s Law, is explained hereinbelow. For now, it is useful to understand that the bias voltage supplied by the electromagnetic portion of system  10  will increase as the total capacitance C tot  increases by virtue of the interdigitated arrangement of the energy-producing elements within system  10 . Thus, as the total capacitance C tot  starts to decrease again (i.e., as chain  25  continues to slide within channel  10 ), the bias voltage will move back to zero. 
         [0043]    The above-described microfluidic-based portion of energy harvesting system  10  can be configured to provide a very high level of tunability with respect to coupling to environmental motion characterized by various levels of force and displacement. For example, by increasing the length of tube  12 , while preserving the size of individual droplets  20 , one can adjust the amount of displacement that can be handled by system  10 , without affecting the force acting on the droplets. At the same time, by increasing the total area covered by electrodes, one can adjust the level of force that can be successfully coupled to system  10 , without affecting the level of possible displacements. 
         [0044]    It is also be understood that there are a number of methods that can be used to extract electrical energy from a variable capacitor with a periodically alternating capacitance value and that can be adapted for use with the present invention. Some of those methods are disclosed in U.S. Pat. Nos. 6,936,994; 4,127,804; 6,127,812; 3,094,653; 3,013,201; 4,054,826; 6,750,590; 4,897,592; 4,126,822; 2,567,373; 3,405,334; 6,255,758; 7,112,911; 4,595,852 and 4,814,657, all of which are incorporated by reference herein in their entirety. 
         [0045]    Similarly, it is important to understand the concepts behind the generation of energy from the electromagnetic portion of energy system  10  of the present invention as illustrated in the embodiment of  FIG. 2 .  FIG. 7  illustrates well-known principles of Faraday&#39;s Law as applied to this aspect of the present invention. In its most general form, Faraday&#39;s Law can be defined as follows: any change in the magnetic field distribution within a coil of wire will induce a current to flow through the wire, thus creating a bias voltage between the terminations of the coil.  FIG. 7  shows a simple magnet M approaching a wire coil C, with the magnetic field lines (flux) shown. The magnetic field lines that pass through the coil create this voltage, V=Md(BA)/dt, where B is defined as the magnetic flux density, A is the area of the coil, M is the number of turns in the coil, t is the parameter of time and d( )/dt denotes the derivative with respect to time. Thus, a moving magnet, as a function of time, will produce a voltage that changes as a function of time as well. 
         [0046]      FIG. 8  illustrates a small section of energy harvesting system  10 , showing a single magnetic ring  18  as it approaches a specific coil  16 - 1  of the plurality of coils  16 . As with the electrostatic aspect described above, as magnetic ring  18  approaches coil  16 - 1 , the coupling therebetween will increase, thus generating a positive voltage that is created by the plurality of coils  16 . Similarly, as magnetic ring  18  moves away from the plurality of coils  16  (and is instead passing through a pair of dielectric-coated electrodes  14 ), the field coupling will also decrease, generating a bias voltage of the opposite polarity. Thus, as the plurality of magnetic rings  18  slide back and forth within tube  12 , the cumulatively-created bias voltage will continuously alternative polarities between positive and negative values as the magnetic field coupling to the plurality of coils  16  changes. 
         [0047]    Applying these principles to the arrangement of  FIG. 2 , therefore, as chain  25  slides back and forth within channel  11 , an electrostatic energy harvesting arrangement is formed by the plurality of variable capacitors created from the combination of droplets  20  with dielectric-coated electrodes  14 , and an electromagnetic energy harvesting arrangement is formed by the plurality of variable voltage sources created from the combination of magnetic rings  18  with the plurality of coils  16 . These variable energy-producing elements are constantly changing in value, increasing and decreasing, creating electrical energy that may be used to drive a load (not shown). 
         [0048]    Inasmuch as the movement of chain  25  with respect to channel  11  can be provided by human locomotion or other types of conventional mechanical movements, the arrangement of  FIG. 2  can advantageously be used in specific circumstances to provide needed energy to mobile electronic devices by harvesting this otherwise wasted mechanical movement. The particular interdigitated arrangement as shown in  FIG. 2  results in a relatively compact configuration that exhibits synergistic properties in terms of the magnetic portion of the arrangement providing the bias voltage necessary for the microfluidic-based portion of the arrangement. Further each portion serves as a “spacer” element for the other portion, allowing for a plurality of separate segments to be formed along the lateral extent of the arrangement. 
         [0049]    It is to be understood that in an alternative configuration of the embodiment of  FIG. 2 , the energy produced by the electromagnetic portion of energy harvesting system  10  can be independently utilized (at least partially, or perhaps fully) to power an electric load (i.e., a device such as a mobile telephone or the like). In the case where the electromagnetic portion of energy harvesting system  10  is fully utilized to power an electric load, the bias voltage required for energy generation by the electrostatic portion of system  10  can be supplied by an external source, as used in prior art arrangements. The flexibility in configuring this hybrid arrangement of energy harvesting system  10  to include both an electromagnetic portion and an electrostatic portion thus allows the user to tailor the arrangement as best-suited for a particular purpose. 
         [0050]    Moreover, it is contemplated that the configuration as shown in  FIGS. 2-4  may be simplified to create either an electrostatic-only embodiment or an electromagnetic-only embodiment.  FIG. 9  illustrates an exemplary microfluidic energy harvesting system  50  formed in accordance with the present invention as an electrostatic-only arrangement. In this embodiment, system  50  comprises a tube  52 , with a plurality of dielectric-coated electrodes  54  embedded within the material  53  forming tube  52 , as shown. In order to minimize the spacing between the electrodes forming the capacitive structure, it is preferred to locate electrodes  54  as close to the inner surface  51  of tube  52  as possible. This combination may be defined as a “channel”  53  of the embodiment. 
         [0051]    As with the above-described embodiment, system  50  utilizes a plurality of conductive droplets  56  that will form pairs of parallel capacitors with the plurality of dielectric-coated electrodes  54 , creating an energy-producing variable capacitance as the overlap between droplets  56  and electrodes  54  changes. When a pressure differential is created on opposite ends of tube  52  (i.e., during mechanical movement of tube  52 ), the overlap between droplets  56  and electrodes  54  will change as droplets  56  slide back and forth (as a chain  55 ) within the opening of tube  52 . A plurality of spacer rings  58  are shown as used in this embodiment to provide physical separation between adjacent droplets  56 . Inasmuch as this is an electrostatic-only configuration, spacer rings  58  do not have to be magnetic; any material of suitable mechanical strength and rigidity can be used. 
         [0052]    System  50  further comprises a plurality of spherical spacers  60 , as shown, which are affixed to a flexible rod  62  in the same manner as the embodiment described above, with a spherical spacer  60  disposed between adjacent spacer rings  58 . Again, the fluid of droplet  56  will naturally fill the region surrounding spherical spacer  60 . Although not specifically shown in this illustration, it is to be understood that an external bias voltage source is necessary to charge the electrode portions (within the dielectric coating material) to form the capacitive energy storage ability of the arrangement. 
         [0053]      FIG. 10  is a cut-away side view of system  50  of  FIG. 9 , used as an electrostatic energy-only embodiment. As shown in this view, a separate voltage source  64  is used to provide a bias voltage across the plurality of electrodes  54  as disposed on opposing sides of conductive microfluidic droplets  56 . While the electrodes are shown as separate conductive plates in this particular view, it is to be understood that this is a function of this view and in actual formation the plurality of electrodes  54  are configured as shown in the exploded view of  FIG. 5 . Additionally, tube  52  is shown in this particular embodiment as being separated from electrodes  54 . However, this is for the purposes of illustration and it is to be understood that in a preferred embodiment, electrodes  54  are embedded within the material forming tube  52 . 
         [0054]    Indeed, if it a particular embodiment tube  52  is formed of a dielectric material, electrodes  54  may comprise a metal without any additional coating. In this case, it is advised that electrodes  54  be disposed as close as possible to the inner edge of tube  52 , in order to form as small a dielectric gap as possible (the smaller gap creating a larger charge). The relative positioning of spacer rings  58  and spherical spacers  60  is clearly shown in this view. 
         [0055]    A configuration of an electromagnetic-only energy harvesting system  70  is shown in  FIG. 11 , which utilizes the principles of Faraday&#39;s Law to create (induce) a voltage as a plurality of magnetic elements move through a coil. Referring to  FIG. 11 , system  70  is shown as comprising a tube  72  within which a plurality of coils  74  is embedded, where the plurality of coils  74  is defined as having a plurality of separate coils, each with one or more turns, with a spacing of d between the centers of adjacent coils, as shown. Thus structure thus forms a “channel”  71  of the system. 
         [0056]    A plurality of magnetic rings  78  is disposed to pass along the central opening of tube  72 , where rings  78  are inserted over a flexible rod  80  that is used to control the lateral motion of disks  78  back and forth within tube  72 , forming a chain  73  which is free to slide within channel  71 . As with the embodiments discussed above, magnetic rings are ordered such that adjacent elements are of opposite polarity (indicated by the arrows in  FIGS. 11 and 12 ). In order to maintain a consistent spacing between adjacent magnetic rings  78  (and thus control the generation of the voltage across the plurality of coils  74 ), a plurality of spherical spacers  82  are disposed between disks  78 , as shown. 
         [0057]      FIG. 12  is a cut-away side view of system  70 , clearly showing the positioning of spherical spacers  82  between adjacent magnetic rings  78 . The spacing d between adjacent coils of the plurality of coils  74  is also shown. While tube  72  is shown as separated from the plurality of coils  74 , this is again to be considered as for the purposes of clarity; in many arrangements, the plurality of coils  74  may be embedded within the material forming tube  72 . In operation of this embodiment, the act of imparting a hydraulic motion at either end termination of tube  72  will cause the plurality of magnetic rings  78  will slide through the center of coil  74 , creating a voltage in accordance with the principles of Faraday&#39;s Law as discussed above. 
         [0058]    Although the present invention has been described in detail, those of ordinary skill in the art should understand that they could make various changes, substitutions and alterations herein without departing from the scope of the invention.
An energy harvesting system for converting mechanical energy into electrical energy uses an electrostatic arrangement based upon the interaction between conductive microfluidic droplets and dielectric-coated electrodes in combination with an electromagnetic arrangement based upon the interaction between magnetic elements and coils, with the two arrangements disposed in an interleaved configuration that provides a degree of synergy to the overall system in the form of providing spacings between adjacent elements and providing a bias voltage source for the electrostatic arrangement from the energy created by the electromagnetic arrangement.