Abstract:
A microelectromechanical system (MEMS) device is used to transfer power from a source generator to a power generator that delivers electrical power to a load, while maintaining electrical isolation between the source generator and power generator for size critical applications where transformers or coupling capacitors would not be practical, but where electrical isolation is desired.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
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   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
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   BACKGROUND OF THE INVENTION 
   The present invention relates to microelectromechanical systems (MEMS) and in particular to MEMS for transferring electrical power from a source to an output while maintaining electrical isolation between the points of transfer. 
   MEMS are extremely small machines fabricated using integrated circuit techniques or the like. The small size of MEMS makes possible the mass production of high speed, low power, and high reliability mechanisms that could not be realized on a larger scale. 
   Often in electrical circuits, it is desirable to transfer power between two points while maintaining electrical isolation between those points. Isolation, in this context, means that there is no direct current (dc) path between the points of transfer. Isolation may also imply a degree of power limiting that prevents faults on one side of the isolation from affecting circuitry on the other side of the isolation. 
   Conventional techniques of power transfer with electrical isolation include the use of transformers or capacitors such as may provide alternating current (ac) power transfer while eliminating a direct dc path. Additional circuitry used to implement these conventional techniques can add considerable expense. Furthermore, the large size of the capacitor or transformer may preclude its use in certain applications where many independently isolated circuits must be placed in close proximity, or where isolation is required on a very small mechanical scale, for example, on an integrated circuit. 
   It is therefore desirable to provide an integrated circuit-level power converter that is less expensive and smaller than that achieved using conventional techniques. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with one aspect of the invention, an electrically isolated power transfer MEMS device is provided for delivering electric power to a load. The MEMS device includes a source generator including a movable member. The source generator converts an electrical input signal to a displacement of the movable member. An insulated power transfer structure defines an input end in communication with the movable member that receives the displacement. The power transfer structure further defines an output end opposite the input end that communicates the displacement. An electrical generator is disposed at a second end of the device and receives the displacement from the output end of the power transfer structure. The electrical generator, in response to the displacement, generates electrical power that is delivered to the load. 
   These and other aspects of the invention are not intended to define the scope of the invention for which purpose claims are provided. In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, and not limitation, preferred embodiments of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in more detail below on the basis of the accompanying drawings, in which: 
       FIG. 1  is a simplified top plan view of a MEMS-based power converter constructed in accordance with a preferred embodiment of the invention; 
       FIG. 2  is a simplified top plan view of a MEMS-based power converter having constructed in accordance with an alternate embodiment of the invention; 
       FIG. 3  is a simplified top plan view of a MEMS-based power converter constructed in accordance with another alternate embodiment of the invention; 
       FIG. 4  is a simplified top plan view of a force/displacement generator of the MEMS device illustrated in  FIG. 1  constructed in accordance with a preferred embodiment of the present invention; 
       FIG. 5  is a simplified top plan view of a force/displacement generator of the MEMS device illustrated in  FIG. 1  constructed in accordance with an alternate embodiment of the invention; 
       FIG. 6  is a sectional side elevation view taken along line  6 - 6  of  FIG. 5 ; 
       FIG. 7  is a top plan view of the force/displacement generator of the MEMS device illustrated in  FIG. 1  constructed in accordance with an alternate embodiment of the invention; 
       FIG. 8  is a sectional side elevation view taken along line  8 - 8  of  FIG. 1 ; 
       FIG. 9  is a sectional side elevation view of a MEMS device incorporating a plurality of loops connected in parallel in accordance with an alternate embodiment of the invention; 
       FIG. 10  is a simplified top plan view of a MEMS-based power converter similar to that illustrated in  FIG. 1 , but with a power transfer structure constructed in accordance with an alternate embodiment of the invention; 
       FIG. 11  is a simplified top plan view of an array of MEMS-based power converters connected to a single source in accordance with an alternate embodiment; and 
       FIG. 12  is a simplified top plan view of a MEMS device constructed in accordance with an alternate embodiment that includes an actuator enabling real-time adjustment to oscillate the movable beam at resonant frequency. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring initially to  FIG. 1 , a MEMS device  10  is supported by an underlying substrate  14 . Device  10  includes an insulated power transfer structure  21  that is interposed between a source generator  20  and an electrical generator  22 . Generator  20  can either receive or generate an electrical input signal and convert the signal to a force F that produces a mechanical displacement. Alternatively, generator  20  can produce the displacement from a mechanical or thermal source. Generator  20  can thus be interpreted broadly as an electrical power-to-force-to-displacement generator, whose force can either be received or generated locally from an input electrical signal. 
   Substrate  14  may be conductive or insulating, and may comprise glass, high resistivity silicon, crystalline sapphire, crystalline silicon, polycrystalline silicon, silicon carbide, or ceramic such as alumina, aluminum nitride, and the like, or gallium arsenide. Substrate  14  may alternatively comprise any suitable material capable of supporting MEMS device  10 . The MEMS device  10  is described herein as having components that enable the device  10  to be electrically isolated from substrate  14 , it being appreciated that isolation between the device  10  and the substrate  14  would not be necessary when the substrate  14  comprises an insulating material. 
   Power transfer structure  21  includes a movable elongated beam  12  that extends along a longitudinal axis L-L and is suspended above the substrate  14 . Beam  12  defines a leftmost longitudinal end  16  that defines an input end of the power transfer structure  21  that interfaces with source generator  20  such that displacement output by generator  20  is imparted onto input end  16 . Beam  12  further defines a rightmost longitudinal end  18  that defines the output end of the power transfer structure  21  and interfaces with electrical generator  22 . Displacement of beam  12  is thus imparted onto generator  22  which, in turn, generates power that is subsequently delivered to a load  32  as will be described in more detail below. As defined herein, end  16  is disposed “longitudinally inwardly” of end  18 . 
   Beam  12  includes at least a section  13  disposed between generators  20  and  22  that is formed from an electrically insulating material, such as SiO 2  in accordance with the preferred embodiment to provide electrical isolation between generators  20  and  22 . It should be appreciated, however, that beam  12  could, as a whole, comprise any suitable insulating material, such as Si 3 N 4 . Beam  12  could alternatively comprise any suitable material so long as the beam includes an insulating portion that is disposed between generators  20  and  22  to prevent electrical communication therebetween. It should further be appreciated that if the substrate  14  comprises an insulating material, the electrical isolation between generators  20  and  22  would be enhanced. 
   The beam  12  is connected proximal its left longitudinal end  16  to a pair of support structures  23  that are, in turn, attached to the substrate  14 . Each support structure  23  includes an outer frame  35  that is connected to a transverse arm  38  via wrist structures  40  that are disposed at the outer end of each transverse arm  38 . Arms  38  are aligned longitudinally, and extend transversely outwardly from beam  12  to the corresponding wrist structure  40 . Wrist structures  40  are compliant so as to support motion of arms  38 , and the beam  12 , in the direction of longitudinal axis L-L. 
   Arms  38  and wrist structures  40  are all suspended above the substrate  14  and are preferably coplanar with beam  12 . Outer frames  35 , including outer ends  41 , are connected to insulating pylons  42  that extend upwardly from the substrate  14 . Pylons  42 , and all pylons disclosed herein, may either be members separate from the substrate  14 , or could be integral with the substrate. 
   For instance, referring now to  FIG. 8 , pylons  42  (and preferably all pylons) are constructed to provide electrical isolation between substrate  14  and MEMS device  10 . Pylon  42  includes a layer  68  of wafer material, such as silicon, that extends outwardly from substrate  14  and is connected at its outer end to a layer  62  of insulating material, such as SiO 2  or Si 3 N 4 . The insulating layer  62  ensures that any electricity originating at, or input to, source  20  does not conduct into the MEMS device  10 . Alternatively, substrate  14  can be insulating, in which case pylons  42  would not need to provide electrical isolation but would only need to support MEMS device  10  above the substrate  14 . Wrist structure  40  is connected to the outer surface of layer  62  or, if an insulating layer is not needed, to the outer surface of layer  68 . 
   Because support structures  23  are electrically isolated from the substrate via pylons  42 , and because beam  12  is an insulator, as described above, the arms  38 , frames  35 , and wrist structures  40  may be insulating or conductive and preferably comprise Si in accordance with the preferred embodiment due to ease of fabrication. It should be appreciated that any suitable material, such as SiC, may be used as appreciated by one having ordinary skill in the art. 
   While support structures  23  enable longitudinal beam movement in accordance with the preferred embodiment, it should be appreciated that any structure supporting beam  12 , and enabling the beam to translate along the axis L-L can be implemented in accordance with the present invention. 
   Generator  22  includes a deflectable transverse arm  24  connected at its midsection to the rightmost longitudinal outer end  18  of beam  12 . Arm  24  comprises a flexible conductive material so as to bow outwardly and inwardly during operation, as indicated by arrows +A and −A, respectively, in response to longitudinal translation of beam  12 . Arm  24  defines transverse outer ends  25  that are connected to longitudinal electrically conducting sections  28  that extend longitudinally outwardly (away from beam  12 ) and terminate at the transverse outer ends  27  of a transverse electrically conducting stationary trace  26  that extends generally parallel to arm  24 . 
   Traces  26  are connected to substrate  14  at their transverse outer ends  27  via insulating pylons  36  that extend upwardly from the substrate  14 . Pylons  36  are constructed in a manner similar to that illustrated and described above with reference to  FIG. 8 , and provide structural support for the generator  22  and beam  12 . Electrical sections  28  are preferably sufficiently rigid to prevent twisting about pylons  36  to ensure that the movement of beam  12  results in the deflection of transverse arm  24  rather than deformation of trace  26 , which would prevent a change in loop area. It should be appreciated that arm  24  may further be connected to substrate  14  via pylons at its outer ends  25  if additional structural support is desired. Traces  26  are further connected via longitudinal electrically conducting traces  34  to a load  32  that may be located remotely from MEMS device  10 . 
   An electrical loop  29  is thus formed including arm  24 , sections  28 , traces  26  and  34 , and load  32 . The area of the loop  29  thus varies in response to movement of arm  24 . It should thus be appreciated that an electrical circuit is also thereby formed by arm  24 , sections  28 , and traces  26  and  34  to deliver power to load  32  upon generation of an electrical current. Loop  29  is disposed in a magnetic field  39  such that, as the area of the loop varies, electrical current is generated and delivered to load  32 . 
   Components of the electrical circuit, and other electrically conductive elements of MEMS device  10 , may be formed of any suitably conductive material, such as aluminum, gold, nickel, and copper. Aluminum is used in accordance with the preferred embodiment because of ease of deposition during fabrication. 
   During operation, source generator  20  provides an output displacement that is imparted onto beam  12 . The beam receives the displacement at its leftmost end  16 , which provides an input for the power transfer structure  21 , and translates along the longitudinal axis L-L in response to the input displacement. As beam  12  is translated along the longitudinal axis L-L, the rightmost end  18  of beam  12  imparts the displacement onto arm  24 . Arm  24  thus provides an input for the electrical generator  22 , and is deflected in the +A direction when the displacement is positive, and in the −A direction when displacement is negative, it being appreciated that force F can cause displacement in either longitudinal direction; i.e., either a push or a pull. Force F can both push beam  12  for +A deflection and pull beam  12  for −A deflection, or it can apply one or the other and allow the spring action of section  24  to return the beam to the rest position. As arm  24  is deflected, the area of loop  29  is altered in the presence of magnetic field  39 . 
   As a result of the change of loop area, the magnetic flux (from the nearby magnet) enclosed within the loop changes which induces an EMF within the loop. The value of the EMF induced by the generator  22  is given in accordance with the following well-known equation:
 
 EMF=dΦ/dt   (1)
 
where EMF is induced by the generator  22  and Φ is the magnetic flux enclosed within loop  29 . Φ, in turn, equals B*A (where B is the magnetic field, and A is the area of the loop  29 ). Electrical power is thereby induced in the loop  29 , and is output along electrical traces  34  to be delivered to load  32 .
 
   It is preferable that source generator  20  produces a displacement that varies so as to continuously move the beam  12  back and forth in the longitudinal direction with both positive and negative displacements to continuously generate power at generator  22 , whereas a single direction displacement would only bias the beam  12  towards a predetermined direction as an isolated occurrence, thereby deflecting transverse arm  24  only once. The present invention further contemplates that it is typically desirable to transfer power from source generator  20  to produce an isolated ac output at electrical generator  22 . However, generator  22  could alternatively produce a dc output from an ac input using a standard filter and rectifier as is known by one having ordinary skill in the art. 
   While generator  22  relies on beam displacement to cause a change of area of loop  29  in the presence of magnetic field  39  to induce electrical power, it should be appreciated that arm  24  of generator  22  could alternatively comprise a piezoelectric material. The piezoelectric material would receive the displacement output by source generator  20  via beam  12  and, in response to deformation of the piezoelectric material, generate a voltage that is delivered to load  32 . This embodiment would eliminate the need for magnetic field  39 . It should thus be appreciated in both embodiments that the output of source generator  20  causes beam  12  to translate, which, depending on the type of generator  22 , displaces arm  24 , thereby causing generator  22  to produce electrical power. 
   Referring now to  FIG. 10 , transfer structure  21  is illustrated in accordance with an alternate embodiment. In particular, structure  21  includes a lever  70  that extends substantially transversely, and is hinged connected to substrate  14  at joint  72 . Lever  70  defines a first end  74  proximal joint  72  and a second end  76  opposite the first end  74 . It should be appreciated that lever can be pivoted about joint  72  which will cause second end  76  to deflect longitudinally a significant distance greater than first end  74 . A first beam  12  extends longitudinally from source, as described above, and is connected at its outermost end to first end  74  of joint  72 . A second beam  12  extending longitudinally inwardly from generator  22  is connected to the second end of lever  70 . Both beams  12  preferably include an insulating member  13  to provide electrical isolation, as described above. During operation, deflection of first beam  12  acts against the first end  74  of the lever  70  and causes the lever to pivot about joint  72 . The deflection of first beam  12  is thus magnified at the second end  76 , which causes translation of second beam  12 . The increased beam translation causes greater deflection of movable arm  24 . Accordingly, transfer structure  21  illustrated in  FIG. 10  amplifies the source input and causes a higher power output from generator  22 . 
   Referring now to  FIG. 11 , it should be appreciated that an array of power converters  10  can be connected to a single source  20 . Source  20  can include a transverse beam  71  that is connected to the source output at one end, and connected to the left end  16  of beams  12  of a plurality of MEMS devices  10  at another end. Accordingly, source  20  can cause each beam  12  of a plurality of MEMS power converters  10  to deflect and induce power in the corresponding generators  22 . 
   While the induced EMF depends on, to some extent, the strength of force F output from source generator  20  driving the displacement, it may nonetheless be desirable to control the EMF by providing electrical generator  22  with multiple movable loop portions  29 ′,  29 ″, and  29 ′″ as illustrated in  FIG. 2 . This geometry serves to increase the amount of area change for a given displacement of beam  12 . While three such loop portions are illustrated, it should be appreciated that a greater or lesser number of loop portions may be implemented in generator  22  depending on the desired power output. Loop portions  29 ′,  29 ″, and  29 ′″ are defined herein as having a movable arm  24  and stationary trace  26 , respectively, that are electrically connected in series to an adjacent loop portion via sections  28 , it being appreciated that the last loop portion  29 ′″ in the series and the first loop portion  29 ′ in the series are considered to be adjacent to each other for the purposes of this description. For the purposes of clarity and convenience, loop portions  29 ′,  29 ″, and  29 ′″ are identified collectively as a loop portion  29  throughout this disclosure. 
   In order to accommodate loop portions  29  in the generator  22  of MEMS device  10 , the insulating beam  12  is further elongated and extends partially into generator  22 . A plurality of recesses  31  are formed in the upper surface of beam  12  so as to define a corresponding plurality of mounting platforms  33  disposed adjacent recesses  31 . Each recess  31  is thus correspondingly interposed between adjacent platforms  33 . The generator  22  includes a plurality of movable transverse arms  24  having a first transverse outer end  37  and a second transverse outer end  43 . Generator  22  further includes a plurality of stationary traces  26  having a first transverse outer end  45  and a second transverse outer end  47 . The first transverse outer ends  37  and  45  of the movable arm  24  and stationary trace  26 , respectively, as well as the second transverse outer ends  43  and  47  of the movable arms  24  and stationary traces  26 , respectively, are substantially transversely aligned with each other. 
   Each loop portion  29  includes a movable transverse arm  24  whose midsection is mounted onto beam  12  at a unique platform  33  along with a stationary electrical trace  26  that is mounted onto substrate  14  at its transverse outer ends  45  and  47  via insulating pylons  36 . Stationary traces  26  are positioned so as to extend transversely over recess  31 . First transverse outer ends  37  and  45  of adjacent movable arms  24  and stationary traces  26 , respectively, in a given loop are electrically connected to each other via electrical sections  28 . In particular, adjacent loop portions  29  are electrically connected via electrical sections  28  that extend from the second transverse outer end  47  of stationary trace  26  to the second transverse outer end  43  of movable arm  24 . 
   Transverse outer end  45  of stationary trace  26  of longitudinally outermost loop portion  29 ′″ is connected to load  32  via trace  34 . The load  32  is further connected via trace  34  to transverse outer end  47  of trace  26  of loop portion  29 ′″. Transverse outer end  37  is, in turn, connected to transverse outer end  43  of movable arm  24  of the longitudinally innermost loop portion  29 ′ to complete the electrical circuit and connect all loop portions  29 ′″ and  29 ′ in series with the load  32 . A magnetic field  39  is disposed adjacent each movable beam  24  of each loop to generate power upon deflection of the beam  24 , as described above. 
   During operation, source generator  20  imparts a displacement onto the leftmost end  16  of beam  12 . Beam  12  is translated along the longitudinal axis L-L, which correspondingly deflects movable transverse arms  24  of loop portions  29  in the directions of +A and −A, depending on the direction of force F. Recesses  31  prevent stationary traces  26  from interfering with the beam  12  as it translates. Alternatively, traces  26  could be suspended higher above substrate  14  than arm  24 , thereby avoiding any potential interference between traces  26  and beam  12  without the need to form recesses  31 . However it is preferable that arms  24  and traces  26  be coplanar for ease of fabrication. 
   As arms  24  are deflected in the longitudinal direction, the area of corresponding loop portions  29  also changes in the presence of magnetic field  39 , thereby inducing electrical power that is delivered to load  32  as a function of the aggregate change in area of the loop portions  29 . Because loop portions  29  are connected in series, generator  22  produces an increased area change and thus an increased EMF as compared to the single movable arm embodiment illustrated in  FIG. 1 . It should further be appreciated that the insulating portion of power transfer structure  21  enables the source generator  20  to be electrically isolated from the electrical generator  22 . It should be appreciated that there are geometric arrangements other than the one illustrated in  FIG. 2  where there are multiple portions of the loop that move and so enhance the total area change and therfore the induced EMF. 
   It should be appreciated that arms  24  can alternatively comprise a piezoelectric material that deforms to generate a voltage as described above. If arms  24  are piezoelectric, they would not be connected to stationary transverse traces  26 , but rather connected to beam  12  and to substrate  14  at pylons  36 , such that beam displacement would cause a deformation of arms  24 . It should thus be appreciated that no need would exist to form recesses  31  in beam  12  in accordance with this embodiment. Arms  24  would be connected in series to generate an increased voltage (compared to the embodiment illustrated in  FIG. 1 ) that is applied to load  32 . 
   Alternatively, referring now to  FIG. 3 , it should be appreciated that the current level output to load  32  could be increased by connecting a plurality of loops  29  in parallel. In particular, the structure of beam  12  extends into generator  22  as described above, but does not include either the stationary arms  26  or the recesses  31  illustrated in  FIG. 2 . Electrically conductive arms  24  extend laterally across beam  12 , and are connected to beam  12  at their midsection. Adjacent lateral outer ends  37  are connected to each other via electrical traces  28 , and laterally outer ends  43  are also connected to each other via electrical sections  28 . Longitudinally outer arm ends  37  and  43  are connected to load  32  via traces  26  and  34 . Accordingly, adjacent loops  29  are connected in parallel with load  32  to increase the current level output to the load. 
   During operation, beam  12  is displaced which, in turn, causes each arm  24  to displace laterally in the direction of +A and −A, as described above. Each arm  24  forms a loop  29  with stationary traces  26  and  34  in the presence of a magnetic field  39 . Accordingly, arm  24  displacement causes a change in loop area which induces an electrical output, as described above. As illustrated in  FIG. 3 , the area of each loop  29  will undergo the same change in area and so the EMF produced in each loop will be the same. Alternatively, each arm  24  could be connected at its transverse outer ends  37  and  43  to a stationary electrical trace via sections  28 , as illustrated and described above with reference to  FIGS. 1 and 2 . It should further be appreciated that the number of movable members  24  can be varied depending on the desired electrical output. 
   Electrical sections  28  connected to transverse outer ends  37  and  43  of longitudinally outermost arm  24  are supported by substrate  14  via insulating pylons  36  as described above. Pylons  36  provide support for stationary traces  26  and  34 , and further support all arms  24 , which are suspended over substrate  14 . Beam  12  also provides support for arms  24 . 
   Referring now to  FIG. 9 , an alternate embodiment is illustrated, whereby a plurality of loops  29  are stacked vertically on top of each other, and electrically separated by loops  53  of an insulating material, for example SiO 2 , that are interposed between adjacent loops  29 . In particular, each loop  29  includes a movable arm  24  that is connected to a stationary trace  26  via electrical sections  28  as described above with reference to  FIG. 1 . Insulating material is disposed between adjacent arms  24 , traces  26  and sections  28 , thereby electrically isolating adjacent loops  29 . Arm  24  of the lowermost loop  29 ′ is directly connected to longitudinal end  18  of beam  12 . Arms  24  of the upper loops  29 ″ and  29 ′″ are in mechanical communication with (and preferably mechanically connected to) arm  24  of loop  29 ′, and deflect in response to beam movement as described above. Accordingly, all arms  24  will deflect in response to beam movement, thereby changing the area of all loops  29  in the presence of magnetic field  39 . 
   An electrical trace  55  connects the stationary traces  26  of adjacent loops  29 . Trace  55  is further connected to sections  28  that connect to load  32  via traces  34  in the manner described above. Accordingly, each loop  29  is connected to the load in parallel while conserving space as compared to the embodiment illustrated in  FIG. 3 . Vertically stacked loops  29  and  53  are furthermore easier to fabricate using a selective etching process with respect to the embodiment illustrated in  FIG. 2 . It should be appreciated that any number of loops  29  can be included (and separated by an insulating layer) until generator  22  produces the desired electrical output in response to beam deflection. 
   With reference again to  FIGS. 1-3 , it should be appreciated that a source generator  20  can include a plurality of displacement causing members connected together that collectively act against left end  16  of beam. Accordingly, both generators  20  and  22  can include any and all power generator technologies described herein in any combination. It may further be desirable to encapsulate MEMS power converter  10  in a cap of the type described in U.S. patent application Ser. No. 09/842,975, the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein. The cap can define an enclosure that houses a dielectric fluid that would permit the device  10  to operate at higher voltages while minimizing the likelihood of an arc being created across adjacent MEMS components. The cap can alternatively define an enclosure for a vacuum that would limit losses of the device  10  due to air resistance. The cap can also enclose any gas, such as argon, nitrogen, or other, and at any pressure, above or below atmospheric pressure, to control the mechanical damping of MEMS structure. 
   The present invention further recognizes that displacement of beam  12  will be maximized when the power transfer structure  21  is caused to oscillate at its resonant frequency. Beam oscillation at the resonance frequency can be achieved in one of several ways. First, the displacement caused by the source generator  20  can be adjusted to oscillate beam  12  at the resonance frequency. However, given that the electrical power supplied to source  20  is typically standard and not easily adjustable, the mass of the beam  12  and/or arm  24  can be increased or decreased during fabrication to cause the beam  12  to oscillate at the resonant frequency given a known source generator output. Alternatively, if the electrical power supplied to source generator  20  has adjustable frequency, the frequency can be set to a value that causes beam  12  to oscillate at the resonant frequency. 
   The present invention further contemplates that, even in circumstances where the electrical input to source generator  20  is fixed, thermal and other changes during operation can effect the frequency of beam oscillation. Accordingly, it may be desirable to adjust the resonant frequency of power transfer structure  21  in real time during operation of the device. Referring in particular to  FIG. 12 , one method of accomplishing the real-time adjustment of the resonant frequency includes connecting one of the pylons  42  to a movable arm  80 . Accordingly, pylon  42  is no longer connected to substrate  14  as illustrated in  FIG. 8 , but rather is supported by arm  80 . Arm  80  is, in turn, connected to the output end of an actuator  82 . Actuator  82  is connected to substrate  14 . Actuator  82  can comprise any actuators of the type described herein including a Lorentz force actuator and an electrostatic actuator. Accordingly, during operation, a voltage or current is supplied to actuator  82 , which causes arm  80  to extend or retract transversely against beam  12  as indicated by Arrow G. Accordingly, the position or arm  80  can be adjusted by adjusting the electrical input to actuator  82 , thereby changing the oscillation of beam  12  during operation. Advantageously, arm  80  can be set at a position that causes beam  12  to oscillate at its resonant frequency. 
   Referring now to  FIGS. 4-7 , source generator  20  of MEMS device  12  is illustrated in accordance with various embodiments of the present invention, it being appreciated that the generators illustrated and described herein are not exhaustive, and that any source capable of generating a force to displace beam  12  in the longitudinal direction is contemplated by the present invention. Furthermore, it should be appreciated that the sources illustrated are compatible with MEMS devices  10  having one loop or multiple loops or multiple loop portions  29 , and may be implemented in one or more MEMS devices  10  whose output electrical traces  34  are connected together. 
   Referring to  FIG. 4  in particular, source generator  20  of one embodiment of the present invention relies on Lorentz forces to convert an input electrical current to a force and thus to translate beam  12  in the longitudinal direction under the generated forces F. In particular, a traditional ac current source  44  is connected via electrical traces  46  to a conductive transverse arm  48  that is suspended over the substrate  14  and is coplanar with beam  12 . Ac current source  44  may also be suspended above the substrate  14 , or could alternatively be mounted to the substrate  14 . An electrical circuit is thereby formed from source  44 , traces  46 , and transverse arm  48 . Transverse arm  48  defines transverse outer ends  49  that are connected to substrate  14  via insulating pylons  51  that extend upwardly from the substrate. Arm  48  extends perpendicular with respect to beam  12 , and is connected to the leftmost longitudinal end  16  of beam  12 . Transverse arm  48  is fabricated so as to be flexible with respect to bowing in the longitudinal direction, and is disposed in a magnetic field  50 . 
   During operation, ac source  44  outputs electrical current through traces  46  and transverse arm  48  which, in combination with magnetic field  50 , generates a Lorentz force F according to the right hand rule. The force F acts upon arm  48  and deflects the arm longitudinally forwards and backwards, depending on whether the output from source  44  is positive or negative. Because beam  12  is connected to arm  48 , the deflection of arm  48  translates beam  12  along the longitudinal axis L-L. Beam  12  is preferably connected to the middle portion of arm  48 , which experiences the greatest amount of deflection during use. The longitudinal movement of beam  12  drives electrical generator  22  to produce power that is delivered to load  32 , as described above. Because section  13  of beam  12  preferably comprises an insulating material, current flowing through transverse arm  48  is advantageously unable to conduct to the electrical generator  22 , thereby protecting the load  32  from power surges and the like. 
   While an ac source  44  is preferable to ensure that the beam  12  is constantly in motion, and the area of loop  29  is thereby constantly in flux, source  44  could also comprise a dc power source in accordance with the present invention. When electrical source  44  comprises a dc source, however, it will be desirable to include a switch in the circuitry of source generator  20  to deliver pulses of electricity from 0V to the dc level that is applied to transverse arm  48 . When the electrical pulse is high, transverse arm  48  will deflect longitudinally outwardly. When the pulse is at zero, arm  48  will revert to its original undeflected position, thereby translating the beam  12  back and forth in the longitudinal direction and constantly generating electrical power in generator  22 . 
   Alternatively still, source generator  20  could provide a power source  44  that does not draw from an electrical source, but rather whose power is provided by mechanical or thermal sources that respond to movement of the device  10  or fluctuations in temperature. For instance, the source  44  alternatively may comprise a piezoelectric crystal rather than an electrical source  44  that delivers current to transverse arm  48 , thereby causing deflection of arm  48 , upon deflection of the crystal due, for example, to vibration of the MEMS device  10  or underlying substrate  14 . Alternatively, source  44  could comprise a thermocouple that produces a voltage in response to fluctuations in temperature. The electrical output from the thermocouple or piezoelectric crystal would travel through electrical traces  46  and arm  48  in the presence of magnetic field  50  to generate force F, as described above. In addition, deflection due to the various thermal expansion coefficients of different materials such as provided by a suitably constructed bi-morph, as is well known in the art, could be utilized to provide the beam displacement. An applied ac field can be used to generate heat such as due to electrical resistance to alternatively head and cool the bi-metallic strip. 
   Referring now to  FIG. 5 , source generator  20  comprises an electrostatic actuator in accordance with an alternate embodiment of the invention. In particular, source generator  20  includes a power source  44 , which preferably provides an ac voltage, but could alternatively comprise a dc source as described above. Alternatively, source  44  could comprise a piezoelectric material or a thermocouple, as described above, to generate a deflection in beam  12 . Source generator  20  further includes a capacitor  54  having a first transverse capacitor plate  56  that is suspended above substrate  14  and coplanar with beam  12 . Plate  56  further extends perpendicular to beam  12  and is connected to the leftmost longitudinal end  16  of beam at the midsection of the plate  56 . Plate  56  is connected at one of its transverse outer ends  59  to power source  44  via an electrical trace  60 . The outer ends  59  of plate  56  can further be connected to wrist structures  40 , described above, that support plate  56  above substrate  14  while permitting longitudinal movement of plate  56 . It should be appreciated that electrical trace  60  is fabricated so as to be flexible to also enable longitudinal movement of plate  56  during operation. 
   A pair of second transverse capacitor plates  58  extends parallel to plate  56  at a location longitudinally outwardly from first capacitor plate  56 . Plates  58  define inner transverse ends  61  and outer transverse ends  63 . Inner transverse ends  61  terminate at a location adjacent the longitudinally extending edge of beam  12 , but do not contact the beam  12 . Outer transverse ends  63  are disposed laterally outwardly from the transverse outer ends  59  of plate  58 . Capacitor plate  56  and plates  58  are thus offset in the longitudinal direction such that their corresponding fingers are interdigitated, as understood by one having ordinary skill in the art. Outer transverse ends  63  are connected to source  20  via electrical traces  60 , and are further connected to the substrate  14  via insulating pylons  65  that extend the entire length of plate  58  to prevent the plate from moving relative to the substrate  14 , as illustrated in  FIG. 6 . 
   Referring now also  FIG. 6 , pylons  65  are constructed so as to electrically isolate the substrate  14  with respect to plates  58  and electrical traces  60 , but to enable electrical communication between the plates  58  and electrical traces  60 . In particular, a layer  68  of a wafer material, such as silicon, extends outwardly from substrate  14  and is connected at its outer end to a layer  62  of insulating material, such as SiO 2  or Si 3 N 4 . A layer  64  of electrically conductive material is connected to the outer end of the insulator  62 , and provides a connection between the capacitor plate  58  and electrical trace  60 . The insulating layer  62  ensures that any electricity traveling from ac source  44  to plate  58  does not conduct into the substrate  14 . Plates  58  are thus rigidly connected to the substrate  14  in an electrically isolated manner. Furthermore, beam  12  is insulated between the source  20  and generator  22 , as described above and, accordingly, source generator  20  is advantageously electrically isolated from the source  20 . 
   During operation, a voltage is applied to plates  56  and  58  to produce an electrostatic charge that draws the interdigitated fingers (and therefore the plates) closer together. Movable plate  56  is thus drawn towards plate  58  when voltage is applied and subsequently relaxes back when the applied voltage is decreased or removed, which correspondingly translates beam  12  back and forth in the longitudinal direction. The longitudinal beam movement enables electrical generator  22  to output power to load  32  in the manner described above. 
   Referring now to  FIG. 7 , the present invention recognizes that source generator  20  may comprise a mass  67  that is attached to the leftmost longitudinal end  16  of beam  12  and suspended above the substrate  14 . Mass  67  may comprise a conductive or insulating material, and preferably comprises a material that is sufficiently dense in order to minimize its size without reducing its functionality. In accordance with the preferred embodiment, mass  67  comprises Si, though it should be appreciated that SiO 2  may also be used. During operation, vibration of the MEMS device  10  (or underlying substrate  14 ) causes mass  67  to vibrate which, in turn, produces a force F that acts on beam  12  to translate the beam back and forth along the longitudinal axis L-L. Mass  67  thus preferably has a weight sufficient to produce a force F in response to vibration, wherein the force F overcomes the initial resistance of the beam  12  and movable transverse arm(s)  24  in the electrical generator  22  to bias beam  12  in the longitudinal direction. In this regard, it should be appreciated that mass  17  could be disposed anywhere on beam  12  that enables longitudinal movement of the beam  12  or uniformly along the length of the beam. 
   The invention has been described in connection with what are presently considered to be the most practical and preferred embodiments. However, the present invention has been presented by way of illustration and is not intended to be limited to the disclosed embodiments. In order to apprise the public of the scope of the present invention, the following claims are provided.