Abstract:
A variable capacitor based electrical generator is described, using a detached conformal electrode that substantially conforms to surface irregularities of the exposed side of the dielectric. The conformal electrode increases the capacitance difference between a contacting state and non-contacting state. Consequently, by displacing the conformal electrode or dielectric, the capacitance can be significantly varied. By pre-charging the electrodes and by providing a displacement power source (wind, vibration, etc), power can be generated and converted into an electrical form. By networking or arranging a plurality of varactors, a significant power generator can be obtained. This system can be operated even at very low frequencies as compared to conventional magnetic generators.

Description:
FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT 
     This invention is assigned to the United States Government. Licensing inquiries may be directed to Office of Research and Technical Applications, Space and Naval Warfare Systems Center, Pacific, Code 72120, San Diego, Calif., 92152; telephone 619-553-2778; email: T2@spawar.navy.mil. Reference Navy Case No. 100708. 
    
    
     BACKGROUND 
     This disclosure relates generally to the field of energy harvesting. More particularly, this disclosure relates to energy harvesting utilizing a mechanical to electrical generator based on a variable capacitor. 
     SUMMARY 
     The following presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview, and is not intended to identify key/critical elements or to delineate the scope of the claimed subject matter. Its purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later. 
     In one aspect of the disclosed embodiments, a variable capacitor (varactor) is provided, comprising: a solid dielectric having two opposing sides, with an integrally attached electrode on one side of the dielectric; a conformal electrode formed in an initial fluid or molten state on an exposed other side of the dielectric, substantially conforming to surface irregularities of the exposed side of the dielectric, and removably displaceable from the dielectric; at least one guide between the conformal electrode and the dielectric, providing substantially perpendicular alignment of the conformal electrode with the other side surface of the dielectric during movement; pre-charging the conformal electrode and integrally attached electrode; and a displacement mechanism coupled to either the conformal electrode or to at least one of the dielectric and attached electrode, providing displacement substantially perpendicular to a junction of the conformal electrode and dielectric surface, wherein a capacitance is varied by displacing the conformal electrode from a surface of the exposed side of the dielectric. 
     In another aspect of the disclosed embodiments, a varactor-based electrical power generator is provided, comprising: a solid dielectric having two opposing sides, with an integrally attached electrode on one side of the dielectric; a conformal electrode formed in an initial fluid or molten state on an exposed other side of the dielectric, substantially conforming to surface irregularities of the exposed side of the dielectric, and removably displaceable from the dielectric; at least one guide between the conformal electrode and the dielectric, providing substantially perpendicular alignment of the conformal electrode with the other side surface of the dielectric during movement; pre-charging the conformal electrode and the integrally attached electrode, providing a voltage across the conformal electrode and the integrally attached electrode; a displacement mechanism coupled to either the conformal electrode or to at least one of the dielectric and the attached electrode, providing repeating displacement substantially perpendicular to a junction of the conformal electrode and dielectric surface, wherein a capacitance is varied by varying a displacement between the conformal electrode and a surface of the exposed side of the dielectric, and a power storage device coupled in series to either the conformal electrode or the attached electrode, storing generated power. 
     In another aspect of the disclosed embodiments, a varactor-based method for generating electrical power is provided, comprising: forming an electrode in an initial fluid or molten state on an exposed side of a solid dielectric having an integrally attached electrode on a non-exposed side of the dielectric; allowing the fluid or molten electrode to conform to surface irregularities of the exposed side of the dielectric to form a conformal electrode; allowing the fluid or molten electrode to harden; separating the conformal electrode from the dielectric; positioning at least one guide between the conformal electrode and the dielectric, the guide providing substantially perpendicular alignment of the conformal electrode with the dielectric during movement; charging the conformal electrode and the integrally attached electrode; displacing either the conformal electrode or at least one of the dielectric and attached electrode in a repeated manner that is substantially perpendicular to a junction of the conformal electrode and dielectric surface, wherein the conformal electrode contacts the dielectric surface during cycles of the repeated displacement; and tapping generated energy from either the conformal electrode or the attached electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a related art metal-to-dielectric interface. 
         FIG. 2  is an illustration of an exemplary metal-to-dielectric interface. 
         FIG. 3  is an illustration of an exemplary energy harvesting engine. 
         FIG. 4  is an illustration of an exemplary electrical generator/energy harvesting configuration. 
         FIG. 5  is an illustration of another exemplary electrical generator/energy harvesting configuration. 
     
    
    
     DETAILED DESCRIPTION 
     Variable capacitors are often referred to as varactors (or varicap, tuning diode, etc.), the typical varactor being a semiconductor diode-based device that varies its capacitance based on the impressed voltage across its terminals. The impressed voltage affects the charge density in the depletion zone, thereby affecting the capacitance the varactor exhibits. However, typical varactors are suitable for only low voltage and their capacitance value is usually very small, ranging in the picoFarads. 
     In view of the above, a new approach to a varactor is described having higher capacitance and range values, as well as systems and methods for harvesting energy by use of the exemplary varactor. 
     Referring to first principles, capacitance C is defined as C=q/V, where q is the charge distribution and V is the resulting voltage. Rearranging the above expression in terms of V results in V=q/C (Eq. 1). It can be seen that if q is held constant and if C decreases, the net result is that V increases. Therefore, if the capacitance C can be reduced, then the voltage V can be increased, and vice versa. 
     For a fixed symmetrical charge distribution q on an infinitely planar metal-to-dielectric-to-metal interface (i.e., planar capacitor), it is known that the expression for capacitance C can be reduced to the physical parameters as C=∈A/d (Eq. 2), where ∈ is the permittivity of the dielectric, A is the surface area, and d is the distance between the metal surfaces bounding the dielectric medium. If A is held constant and c is held constant, then C will inversely vary with the distance d. Therefore, by modulating the distance d, the capacitance C can increase or decrease proportionally. Correspondingly, the voltage V in Eq. 1 can be modulated with C for power generation. 
     A significant factor in Eq. 1 is the permittivity c, which is approximately 8.8542×10 −12  (C 2 ·N −1 ·m −2 ) for an air-based dielectric, where C is Columbs, N is Newtons and m is meters. To increase the capacitance, the dielectric can be replaced from being air to a high permittivity material, such as ceramic or anything other higher dielectric material. It is noted that high permittivity ceramics often have thousands of times the permittivity of air. Maximal capacitance is obtained when high dielectric material completely fills the volume between the metal plates (in a metal-dielectric-metal planar capacitor). That is, there is no “air” or gap between the plates, as air has a low permittivity and presents a degradation of the overall permittivity between the metal plates. This degradation is evident in typical planar varactors, as demonstrated in  FIG. 1 . 
       FIG. 1  is an illustration of a related art parallel plate capacitor  100 , formed with mechanical means, with a dielectric medium  110  between charged metal surfaces  120  and  150 . For the purposes of this explanation, it is presumed that the dielectric  110  is a high permittivity material. A blowup of the boundary between the upper metal surface  120  and the dielectric  110  is shown, illustrating that due to the molecularly coarse nature of the metal surface  120  and dielectric  110 , there will be an intrinsic air gap  125 . This air gap  125  and ensuing low permittivity prevents this related art parallel plate capacitor  100  from obtaining its maximal capacitance value. Therefore, if the upper metal surface  120  is raised and lowered (affecting the distance d—see Eq. 2), the maximal variation in capacitance will be compromised by the air gap&#39;s  125  low permittivity. 
       FIG. 2  is an illustration of an exemplary varactor  200 . Instead of mechanically attaching or affixing an upper metal plate/surface  220  to dielectric  210  (bounded on opposite side by metal surface  215 ), metal surface  220  can be formed by melting it to the exposed surface of dielectric  210 . A melting procedure or liquefying procedure will allow metal surface  220  to conform its molecular boundary to match the molecular boundary of dielectric  210 . Therefore, any surface roughness or irregularities can be overcome to provide a “matched” upper metal surface  220  to dielectric  210  boundary. Since liquid metal (e.g., solder) may have molecular structures that, even when flexible, cannot “match” every dimension of the dielectric&#39;s surface, it is understood that the conforming dimensions are typically less than 10 μm. Principally, by melting the metal or liquefying it, any air gap that may normally fill the mismatched surfaces is removed. 
     Upper blowup shows practically no air gap at the closed metal-to-dielectric interface  225   a . Lower blowup shows air gap  225   b  when the upper metal surface  220  is lifted from the dielectric  210 . The practical absence of an air gap, when the upper metal surface  220  is touching the dielectric  210 , significantly affects the capacitance value, enabling the exemplary varactor  200  to have a maximum capacitance value that is within 90% or more the capacitance value of an integrally formed metal plate. Since metal does not bond very well to dielectrics, only a modest amount of effort is needed to detach the cooled metal surface  220  from the surface of dielectric  210 . 
     It should be noted that while the descriptions herein recite “upper,” or “lower” or “raised,” or “lowered,” or “top,” or “bottom,” it is be understood that these terms are simply used to indicate a relative position or direction of action, and depending on the frame of reference of the desired result, the terms may be interchanged without any loss of specificity. For example, in  FIG. 2 , the dielectric  210  and “lower” metal surface  215  may be “lowered” from the “upper” metal surface  220 , rather than “upper” metal surface  220  being “raised.” 
     In various experiments conducted by the inventor, a high permittivity (∈ r  of approximately 1000) dielectric disc made of ceramic sourced from Dimat, Inc., having a barium strontium titanate composition, of approximately 1 inch in diameter and 0.1 inch thickness, was tested using the exemplary approach shown in  FIG. 2 . The ceramic disc was obtained with one side (“lower”) per-silvered (aka—lower electrode). The non-silvered side was covered with melted solder and cooled to form the “upper” metal surface (aka—upper electrode). The cooled solder was separated from the ceramic with only modest pressure. A test of the capacitance with the upper electrode contacting the ceramic revealed a value of approximately 9.8 nF. 
     The above approach was compared to a ceramic disc of the identical composition and size, but with a non-conforming upper electrode (formed from a metal sheet) contacting the ceramic surface; and also to a fully silvered ceramic disc (both sides are silvered from Dimat, Inc.) The former tested to show a capacitance value of 0.3 nF while the latter showed a capacitance value of 9.9 nF, demonstrating a loss of only 0.1 nF when compared to the inventor-fabricated model. This corresponds to only a 1% decrease over a factory-silvered upper electrode. It is noted that the “metal sheet” capacitor&#39;s 0.3 nF value is approximately thirty (30) times lower than the exemplary approach shown in  FIG. 2 . Therefore, by utilizing a conforming upper electrode, a significant increase in capacitance can be obtained. By pre-charging the electrodes and very slightly modulating the distance from the conforming upper electrode to the dielectric, a variable voltage source can be obtained and used for energy/power generation. 
     The energy producing capacity can be demonstrated by the following example. An exemplary embodiment can be constructed that has a closed gap, maximum capacitance C max  that is fifty (50) times larger than the open gap, minimum capacitance C min  (e.g., C min =  1 / 50 C max ). An open gap, precharging voltage of V 0 =100 V can be impressed across the electrodes from, for example, a voltage source and a high impedance series resistor to minimize charging current across the electrodes, resulting in the maximum voltage V max =50V 0 . Since energy is defined as E=½ CV 2 , then minimum energy E 0 =½ C min  V 0   2 , whereas maximum energy is E max =½ C max V max   2 =½·  1 / 50 C min  (50 V 0 ) 2 =50 E 0 . A fifty fold increase can be obtained, using this one example. If N multiple exemplary varactors are positioned together or networked, an N-fold increase in energy/power can be obtained. 
       FIG. 3  is an illustration of an exemplary energy harvesting engine  300  including an exemplary variable capacitor  200  of  FIG. 2 , with actuators  340  coupled via arms  335  to pre-charged conforming upper electrode  320 . Pre-charged lower electrode  315  is stabilized or affixed, for example, to ground  330  to prevent movement of the lower electrode  315  and dielectric  310 . The charge type (+ or −) is arbitrary and may be reversed, depending on the connection configuration which is denoted by contacts  305 . 
     Registration guides or precision guide rods  350  are shown “penetrating” through vias (not shown) in conforming upper electrode  320 , which stabilize and prevent lateral movement of conforming upper electrode  320  when being raised by actuators  340 . In the configuration shown in  FIG. 3 , the conforming upper electrode  320  “slides” through registration guides  350  and are understood to be non-conducting. Other forms of allowing registration guides  350  to keep the conforming upper electrode  320  in alignment with dielectric  310  may be utilized. For example, registration guides  350  may be situated outside of the conforming upper electrode  320 , going through vias in arms  335 . Accordingly, various modifications and changes to how the conforming upper electrode&#39;s  320  lateral position is maintained with respect to dielectric&#39;s  310  position may be made without departing from the spirit and scope of this disclosure. 
     Continuing with  FIG. 3 , optional springs or return mechanisms  355  are positioned around registrations guides  350 , secured by retainer  360 , to provide an automatic mechanism for forcing lifted conforming upper electrode  320  back to the surface of dielectric  310 . In some embodiments, gravity may provide sufficient force to cause conforming upper electrode  320  to return to a dielectric surface contacting position. Of course, any form of return mechanism may be utilized, according to design preference. 
     Actuators  340  may be formed from piezoelectric materials (for example, lead-zirconium-titanium (PZT)) and so forth. Any form of movement generating device or mechanism can be used, as applicable, for actuators  340  to cause the conforming upper electrode  320  to displace itself from the surface of dielectric  310 . In fact, depending on the type of motion generating source, springs may used as the actuators  340 , with the entire assembly being displaced, for example, by environmental movement or vibration—from an open air gap position to a closed (no air gap) position. 
       FIG. 4  is an illustration of an exemplary energy harvesting configuration  400  using a single registration guide  450  and single arm  435  attached to conforming upper electrode  420 . Movement of the conforming upper electrode  420  is achieved via eccentric cam  440  that is rotated/powered by power source  470 , which can be any one or more of motion generating systems, including but not limited to, solar powered motor, wind, vibration, tidal, heat, and so forth. The assembly formed by dielectric  410  and lower electrode  415  is secured via mount  430 , preventing the assembly from moving while conforming upper electrode  420  is moving. A tapped voltage output of the conforming upper electrode  420  (or, alternatively, the lower electrode  415 ) can be obtained by channeling the modulated voltage to rectifier  460  to charge storage unit/battery  465 . In this example, a DC generator is obtained by the rectified output. Based on the above examples, a system of networked power generators can be developed. 
       FIG. 5  is an illustration of another exemplary energy harvesting configuration  500  showing a stack of three (3) or more exemplary units A, B, C, and optional unit N. In this configuration, the exemplary units are vertically stacked (to minimize space requirements), and an actuating arm  540  that moves up and down is coupled via a coupler or connection  535  to the respective moving element in the units. Depending on design implementation, the stack could be horizontal or any combination of directions. For ease of description, electrical connections are not shown. 
     In this example, actuating arm  540 , via its movement, forces the upper electrode in unit A to move up and down, and similarly the dielectric/lower electrode assembly for unit B, and also for the reversed upper electrode for unit B. The non-moving elements of the units are fixed, indicated by element  530 . Depending on design implementation and alignment tolerances, actuating arm  540  can travel through the interior of the elements through a via (not shown), or may be external to the elements. If interior to the elements, actuating arm  540  can also operate as a registration guide. It is noted that in this example, unit C&#39;s arrangement of elements is reversed from that shown in the earlier embodiments. 
     In view of the above, it should be apparent than any arrangement of units that achieves the desired movement may be contemplated. For example, two (2) actuating arms may be used, one that moves one set of elements in one direction, while the other actuating arm moves the complementary set of elements in the opposite direction. That is, no element is stationary and movement of both the dielectric and upper electrode towards and away from each other may be developed. Accordingly, it is understood that various modifications and changes may be made to the embodiments without departing from the spirit and scope of this disclosure. 
     As opposed to variable capacitors that are available, the exemplary varactor described herein can handle higher applied power. Its variability is derived from changing the air gap of its conforming electrode to the dielectric insert. The gap can be changed from near zero to any desired gap thickness. As such, this new varactor can be used as a direct energy converter, converting mechanical energy to electrical energy at high efficiency with minimal motion. The exemplary embodiments are not dependent on frequency as is the case with magnetic generators. At very low frequencies a magnetic generator will not produce any significant output power, whereas the exemplary variable capacitor generator will continue to output power. The exemplary embodiments are also not dependent on the shape of the dielectric. That is, curved surface dielectrics or angled, or any variation that enables the top electrode to be “molded” thereto, can be used. In addition to energy harvesting uses, the exemplary varactor can be used in parametric amplifiers, parametric oscillators and voltage-controlled oscillators as part of phase-locked loops and frequency synthesizers. 
     In view of the above, it will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated to explain the nature of the disclosure, may be made by those skilled in the art within the principal and scope of the disclosure as expressed in the appended claims.