Patent Publication Number: US-7721697-B2

Title: Plasma generating ignition system and associated method

Description:
TECHNICAL FIELD 
     The present invention relates generally to systems, devices, and methods for using a coaxial cavity resonator in producing radio frequency (RF) energy for generating a corona discharge plasma, and using the corona discharge plasma as an ignition means in combustion engines and processes. 
     BACKGROUND OF THE INVENTION 
     Prior art methods and apparatuses describe using plasma as an ignition means for combustion engines. One method of generating plasma involves using a radio frequency (RF) source and a coaxial cavity resonator to generate corona discharge plasma. The prior art uses a radio frequency (RF) oscillator and amplifier to generate the required RF power at a desired frequency. RF oscillators and amplifiers can be either semiconductor or electron tube based, and are well known in the art. The RF oscillator and amplifier are coupled to the coaxial cavity resonator, which in turn develops a standing RF wave in the cavity at the frequency determined by the RF oscillator. By electrically shorting the input end of the coaxial cavity resonator and leaving the other end electrically open, the RF energy is resonantly stepped-up in the cavity to produce a corona discharge plasma at the open end of the coaxial cavity resonator. The corona discharge plasma can function generally as an ignition means for combustible materials and specifically in a combustion chamber of a combustion engine. 
     A coaxial cavity resonator is designed to have an electrical length that is approximately one-quarter of the radio frequency delivered from the RF oscillator and amplifier, although cavities that are multiples of one-quarter of the radio frequency will also work. The electrical length of the coaxial cavity resonator depends upon the physical geometry of the cavity, the temperature, pressure and environment at the open end of the cavity, as well was whether one or more dielectrics are used to plug or seal the end of the cavity. Energy consumption is minimized and the corona discharge is maximized when the coaxial cavity resonator and radio frequency are appropriately matched. However, the cavity still generates a corona discharge plasma for a range of frequencies around the optimal frequency as well as at higher harmonics of the optimal frequency, although the unmatched coaxial cavity resonator generally results in lower efficiencies and less power being delivered to the coaxial cavity resonator and therefore potentially less corona discharge plasma. When the corona discharge plasma is used as an ignition source for a combustion chamber, a reduction in the amount or strength of the corona discharge plasma is undesirable as it could result in non-ignition of combustible materials in the combustion chamber. Therefore, it is best to closely match the generated radio frequency to the coaxial cavity resonator to maximize energy efficiency and maximize corona discharge plasma generation. 
     However, in practice, the resonant frequency of a coaxial cavity resonator may not be optimally matched with the RF oscillator and amplifier. This can occur for any number of reasons, including improper selection of frequency in the RF oscillator, mechanical fatigue and wearing of the coaxial cavity resonator or dielectric, or even transient changes in the resonant frequency of the coaxial cavity resonator due to, for example, the formation of the corona discharge plasma itself or other changes in the environment near the region of the cavity. Therefore, it is desired that the RF oscillation be dynamically generated and modulated in such a way that it is closer to the resonant frequency of the coaxial cavity resonator in order to attain the optimal frequency for corona discharge plasma generation. 
     Also, the prior art systems and apparatuses that describe systems, devices, and methods for using plasma as an ignition means in a combustion engine generally require redesign of electronic ignition control systems, the fuel injection systems, or even the combustion chambers of the engines themselves to function. Therefore, there exists a need for a corona discharge plasma ignition device that can function as a replacement for a spark plug in an internal combustion engine without requiring substantial modification to the engine, ignition control system or associated connections and circuitry. 
     SUMMARY OF THE INVENTION 
     The present invention meets the above and other needs. An apparatus that uses the coaxial cavity resonator as the frequency determining element in producing radio frequency (RF) energy comprises a coaxial cavity resonator operably coupled with an energy shaping means such that a sustained RF oscillation is generated closer to or at the resonant frequency of the coaxial cavity resonator for optimal corona discharge plasma generation. The apparatus can have a body adapted to mate with the combustion chamber of a combustion engine and a connection means for accepting an ignition stimulus from an ignition control system. 
     The method of the invention involves using the coaxial cavity resonator in producing radio frequency (RF) energy for generating a corona discharge plasma, wherein the coaxial cavity resonator can be in a body adapted for engagement with the combustion chamber of a combustion engine and attachment to an ignition control system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying figures depict multiple embodiments of the plasma generating corona discharge system. A brief description of each figure is provided below. Elements with the same reference numbers in each figure indicate identical or functionally similar elements. Additionally, as a convenience, the left-most digit(s) of a reference number identifies the drawings in which the reference number first appears. 
         FIG. 1  is a schematic diagram of a prior art ignition system using a spark plug as an ignition source. 
         FIG. 2  is a schematic diagram of a prior art ignition system using a coaxial cavity resonator as an ignition source. 
         FIG. 3  is a schematic diagram of an embodiment of the invention where the coaxial cavity resonator is used as a frequency determining element. 
         FIG. 4  is a schematic diagram of an alternative embodiment of the invention where the coaxial cavity resonator is used as a frequency determining element and where a power supply delivers additional power to the power shaping means. 
         FIG. 5  is a cross-sectional view of one embodiment of the coaxial cavity resonator where the power shaping means comprises a negative resistance device that is integrated into the center conductor of the coaxial cavity resonator. 
         FIG. 6  is a cross-sectional view of an alternate embodiment of the coaxial cavity resonator where the power shaping means comprises a spark gap that is integrated into the center conductor of the coaxial cavity resonator. 
         FIG. 7  is a cross-sectional view of an alternate embodiment of the coaxial cavity resonator where the power shaping means comprises a spark gap that is near the top of the center conductor of the coaxial cavity resonator. 
         FIG. 8  is a cross-sectional view of an alternate embodiment of the coaxial cavity resonator where the power shaping means comprises a spark gap near the base of the center conductor of the coaxial cavity resonator. 
         FIG. 9  is a cross-sectional view of an alternate embodiment of the coaxial cavity resonator with a simple probe providing an electrical feedback sense. 
         FIG. 10  is a cross-sectional view of an alternate embodiment of the coaxial cavity resonator with a loop pickup providing an electrical feedback sense. 
         FIG. 11  is a cross-sectional view of an alternate embodiment of the coaxial cavity resonator with separate waveguides providing power and an electrical feedback sense. 
         FIG. 12  is a cross-sectional view of an alternate embodiment of the coaxial cavity resonator with a common waveguide providing power and an electrical feedback sense. 
         FIG. 13  is a cross-sectional view of an alternate embodiment of the coaxial cavity resonator with a power connection entering through the base of the cavity and an electrical feedback sense. 
         FIG. 14  illustrates cutaway views of embodiments of the coaxial cavity resonator having an empty cavity, a filled or partially filled cavity, and a sealed cavity. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  and  FIG. 2  detail the prior art ignition systems. Exemplary embodiments of the present invention are detailed in  FIGS. 3-14 . 
     Prior Art Ignition System with a Spark Plug 
     Referring now to the schematic diagram of a prior art ignition system  100  depicted in  FIG. 1 , a battery  102  connects to an electronic ignition control system  104  which is connected by a spark plug wire to the terminal end of a spark plug  106 . 
     In a typical prior art ignition system  100 , like that found in an automobile, a battery  102  provides electrical power to an electronic ignition control system  104 . The electronic ignition control system  104  determines the proper timing for triggering an ignition event, and at the appropriate time sends a high voltage pulse via a spark plug wire to the terminal end of a spark plug  106 . The high voltage pulse causes a spark to discharge at the tip of the spark plug  106  that is displaced inside of a combustion chamber (not shown). The spark ignites combustible material, such as gasoline vapor, that is inside the combustion chamber of a combustion engine, completing the ignition sequence. 
     Prior Art Ignition System with a Stand-Alone Coaxial Cavity Resonator 
     Referring now to the schematic diagram of a prior art coaxial cavity resonator ignition system  200  depicted in  FIG. 2 , a power supply  202  connects to a radio frequency (RF) oscillator  204  that is connected through an electronic ignition control system  104  to an amplifier  206  that is connected to a stand-alone coaxial cavity resonator  208 . An exemplary system using a stand-alone coaxial cavity resonator  208  is described in U.S. Pat. No. 5,361,737 to Smith et al. herein incorporated by reference. 
     In the prior art coaxial cavity resonator ignition system  200 , the power supply  202  provides electrical power to an RF oscillator  204 . The RF oscillator  204  generates an RF signal at a frequency chosen to approximate the resonant frequency of the stand-alone coaxial cavity resonator  208 . The RF oscillator  204  delivers the RF signal to an electronic ignition control system  104  that determines the proper timing for triggering an ignition event, and at the appropriate time forwards the RF signal to the amplifier  206  for amplification. The amplifier  206  amplifies the RF signal to the proper power to create sufficiently energetic corona discharge plasma  210  at the discharge tip of the stand-alone coaxial cavity resonator  208  to ignite a combustible material in the combustion chamber of a combustion engine. 
     Self-Oscillating Coaxial Cavity Resonator Ignition System 
     Referring now to an embodiment of the present disclosure depicted in  FIG. 3 , a battery  102  connects to an electronic ignition control system  104  which is connected to a power shaping means  302 . The power shaping means  302  is operably connected to a coaxial cavity resonator  304  such that the power shaping means  302  and the coaxial cavity resonator  304  are in a feedback loop with one another to form a self-oscillating coaxial cavity resonator ignition system  300 . 
     In the embodiment of  FIG. 3 , the battery  102  is a standard battery such as that found in an automobile or any other convenient power source as would be understood in the art, including but not limited to an alternator, a generator, a solar cell, or fuel cell. The battery  102  powers the electronic ignition control system  104 . The electronic ignition control system  104  outputs an impulse, e.g., a high voltage pulse, at the appropriate time to trigger ignition. The power shaping means  302  accepts the impulse, e.g., the high voltage pulse through a spark plug wire, from the electronic ignition control system  104 . Parasitically using only the power supplied in the impulse from the electronic ignition control system  104 , the power shaping means  302  regulates, amplifies, or generates the necessary electrical voltage, amplitude, and time-varying characteristics of the electrical waveform output to the coaxial cavity resonator  304 . The term waveform in the various embodiments disclosed herein is meant to encompass any suitable electrical or electromagnetic power whose time varying characteristics help create the RF oscillations as would be understood by one of ordinary skill in the art, including but not limited to, one or more high-voltage DC electrical pulses, an amplified AC signal, or RF energy delivered by waveguide. 
     Together, the power shaping means  302  and the coaxial cavity resonator  304  form a self-oscillating coaxial cavity resonator ignition system  300  and develop a sustained RF oscillation, or time limited RF oscillation such as an RF pulse, that is close to or at the resonant frequency of the coaxial cavity resonator  304  which results in optimal corona discharge plasma  210  generation. In one embodiment, the duration of the sustained RF oscillation is a short period ignition pulse as would be used for internal combustion engines such as those used in automobiles. In another embodiment, the duration of the sustained RF oscillation is approximately continuous, generating corona discharge plasma  210  during the period of engine operation, as in the case of a jet engine. 
     The power shaping means  302  is any electrical circuitry capable of creating an RF oscillation in conjunction with the coaxial cavity resonator  304 , without requiring a separate RF oscillator, to generate corona discharge plasma  210 . In different embodiments, the power shaping means  302  comprises various combinations of electron tubes or electron drift tubes, examples of which are traveling wave tubes or Magnetrons, Amplitrons, semiconductors including negative resistance devices, inductive or capacitive elements, or spark gaps. As is known in the art, various devices and circuit designs are capable of triggering, amplifying, and maintaining RF oscillations indefinitely or for a limited time period. By using the coaxial cavity resonator  304  as part of a frequency determining circuitry, the frequency of the oscillation is made to more closely approximate the resonant frequency of the coaxial cavity resonator  304 . 
     In an exemplary embodiment, the RF oscillations are between about 750 MHz and 7.5 GHz. A coaxial cavity resonator  304  measuring between 1 to 10 cm long approximately corresponds to an operating frequency in the range of 750 Mhz to 7.5 Ghz. The advantage of generating frequencies in this range is that it allows the geometry of a body containing the coaxial cavity resonator  304  to be dimensioned approximately the size of the prior art spark plug  106 . 
     In one embodiment of the self-oscillating coaxial cavity resonator ignition system  300  in  FIG. 3 , and in other embodiments described later in  FIGS. 4-13 , the power shaping means  302  and the coaxial cavity resonator  304  are contained in a body dimensioned approximately the size of the prior art spark plug  106  and adapted to mate with the combustion chamber of a combustion engine (not shown). In another embodiment, the body is a modified prior art spark plug  106  body comprised of steel or other metals. A connection terminal (not shown) on the body approximating that of the prior art spark plug  106  accepts a spark plug wire from the ignition control system  104 . In the embodiment of the invention of  FIG. 3 , the system  300  is powered solely by the impulse delivered from the ignition control system  104  and therefore can be used as a replacement spark plug  106  without requiring substantial modifications to the engine, ignition system, or associated connections and circuitry. In another embodiment, the coaxial cavity resonator  304  is contained in the body adapted for mating with the combustion chamber and the power shaping means  302  resides outside the body. 
     Powered Self-Oscillating Coaxial Cavity Resonator Ignition System 
     Referring now to the embodiment depicted in  FIG. 4 , a power supply  202  connects to both an electronic ignition control system  104  and the power shaping means  302 . The electronic ignition control system  104  is connected to a power shaping means  302 . The power shaping means  302  is operably connected to a coaxial cavity resonator  304  such that the power shaping means  302  and the coaxial cavity resonator  304  are in a feedback loop with one another to form a powered self-oscillating coaxial cavity resonator ignition system  400 . 
       FIG. 4  is similar to  FIG. 3  but has a power supply  202  that replaces the battery  102  of  FIG. 3 , and the power supply is electrically connected to the power shaping means  302 . Because the power supply  202  provides regulated power to the power shaping means  302 , the power shaping means  302  does not have to run parasitically solely from the impulse energy delivered from the electronic ignition control system  104  as in one embodiment detailed in  FIG. 3 . In a powered self-oscillating coaxial cavity resonator ignition system  400 , the regulated power may be used in various embodiments to power negative resistance devices  502  (shown on  FIG. 5 ) or electron tubes. As is generally known in the art, one category of semiconductor devices called negative resistance devices  502 , including Gunn diodes, IMPATT diodes, or TRAPATT diodes, can be used to turn direct current (DC) impulses into RF energy. Gunn diodes may also be referred to as a type of transferred electron device (TED). A small offset voltage, or bias, puts the negative resistance device  502  into the proper operating range for having the characteristic negative resistance necessary for generating RF waveforms. When a negative resistance device or electron tube is matched to a resonator, for example a coaxial cavity resonator  304 , and given an additional pulsed electrical stimulus, the negative resistance device  502  or electron tube and coaxial cavity resonator  304  together generate the desired RF waveform, thus forming a powered self-oscillating coaxial cavity resonator ignition system  400 . 
     In the embodiment of  FIG. 4 , feedback from the power shaping means  302  and coaxial cavity resonator  304  is coupled back to the electronic ignition control system  104  for on-board diagnostics as well as control of other engine functions such as fuel flow, ignition advance, emission control and other systems as would be obvious to one having ordinary skill in the art. 
     In an alternative embodiment of a powered self-oscillating coaxial cavity resonator ignition system  400 , the regulated power powers an RF amplifier in the power shaping means  302  for generating more energetic corona discharge plasma  210 . For example, a suitable field effect transistor (FET), HEMT, MMIC or other semiconductor amplifier capable of operating in the RF spectrum is used along with a simple probe  902  or pickup loop  1002  as a feedback mechanism in making an RF oscillator. More energetic corona discharge plasma  210  allows easier ignition of a wider range of combustible materials. In yet another embodiment, the regulated power supports a power shaping means  302  with additional circuitry to allow the electronic ignition control system  104  to utilize low voltage signals or even data transmissions to initiate an ignition sequence, instead of the standard high voltage impulses used in most ignition systems today. 
     Coaxial Cavity Resonator with Negative Resistance Device 
     Referring now to the embodiment of the coaxial cavity resonator  304  depicted in  FIG. 5 , a power feed wire  512  enters the coaxial cavity resonator  304  through an insulated guide  510 , and attaches to the suspended center conductor  504 . The insulated guide  510  prevents contact between the power feed wire  512  and the coaxial cavity resonator  304 . The insulated guide  510  terminates at the wall of the coaxial cavity resonator  304  near the base  516 . In alternate embodiments, the insulated guide  510  extends into the coaxial cavity resonator  304 . In alternate embodiments, the power feed wire  512  enters into the coaxial cavity resonator  304  through the base  516 . In an alternate embodiment, the power feed wire  512  extends into the coaxial cavity resonator  304  without an insulated guide  510 . 
     The suspended center conductor  504  is suspended above the base  516  of the coaxial cavity resonator  304  by physical contact with a negative resistance device  502 , by filling the internal cavity of the coaxial cavity resonator  304  with a supporting dielectric (not shown), or by any other supporting means as known in the art. At one end, the proximal end, the suspended center conductor  504  is electrically connected to the negative resistance device  502  near the base  516 . At the other end, the distal end, the suspended center conductor  504  has a discharge electrode  506  where the corona discharge plasma  210  is generated. The negative resistance device  502  is electrically connected to the base  516  of the coaxial cavity resonator  304 . An electrical return path  514  attaches directly to the coaxial cavity resonator  304 . In an alternative embodiment, the negative resistance device  502  is physically raised from the base  516  of the coaxial cavity resonator  304  on a bottom stub of the center conductor  504 . In alternate embodiments, the negative resistance device  504  is positioned anywhere along length of the center conductor  504  between the base  516  and the discharge electrode  506 . In alternate embodiments, the negative resistance device  502  is electrically connected to the wall of the coaxial cavity resonator  304  instead of the base  516 . In an alternate embodiment, the negative resistance device  502  is electrically connected to the electrical return path  514 . 
     The power feed wire  512  delivers both a small direct current (DC) bias and an electrical impulse to the suspended center conductor  504 . The power feed wire  512  is insulated from the rest of the coaxial cavity resonator  304  by the insulated guide  510 . The DC bias delivered by the power feed wire  512  is conducted through the suspended center conductor  504  to the negative resistance device  502 . The DC bias puts the negative resistance device  502  in the proper operating range for having the characteristic negative resistance necessary for generating RF waveforms. The electrical return path  514  completes the DC electrical circuit, allowing proper DC biasing of the negative resistance device  502 . The electrical impulse, also delivered on the power feed wire  512 , then starts the RF oscillation between the negative resistance device  502  and coaxial cavity resonator  304 . The RF oscillation creates a standing wave in the coaxial cavity resonator  304 , resulting in corona discharge plasma  210  being generated at the discharge electrode  506 . The discharge electrode  506  is formed from or coated with a metal or semi-metallic conductor, for example stainless steel, that can withstand the temperature conditions near the corona discharge plasma  210  without deformation, oxidation, or loss. 
     Coaxial Cavity Resonator with Spark Gap 
     Referring now to the embodiment of the coaxial cavity resonator  304  depicted in  FIG. 6 , a power feed wire  512  enters the coaxial cavity resonator  304  through an extended insulated guide  610 , and attaches to the suspended center conductor  504 . The extended insulated guide  610  prevents contact between the power feed wire  512  and the coaxial cavity resonator  304  The suspended center conductor  504  is suspended above the base  516  of the coaxial cavity resonator  304  by physical contact with the extended insulated guide  610 . In alternative embodiments, the suspended center conductor  504  is suspended by filling the internal cavity of the coaxial cavity resonator  304  with a supporting dielectric (not shown), or by any other supporting means as known in the art. In alternate embodiments, the extended insulated guide  610  is an insulated guide  510  and does not extend into the coaxial cavity resonator  304 . In alternate embodiments, the extended insulated guide  610  contacts the suspended center conductor  504  anywhere along the length of the suspended center conductor  504  up to the discharge tip  506 . In alternate embodiments, the power feed wire  512  enters into the coaxial cavity resonator  304  through the base  516 . 
     At one end, the proximal end, the suspended center conductor  504  has an electrically open spark gap  602  near the base  516 . At the other end, the distal end, the suspended center conductor  504  has a discharge electrode  506  where the corona discharge plasma  210  is generated. On the base  516  side of the spark gap  602  is a slightly raised bottom stub center conductor  604 . An electrical return path  514  also attaches to the coaxial cavity resonator  304 . In an alternate embodiment, the spark gap  602  is positioned anywhere along the length of the center conductor  504  between the base  516  and the discharge electrode  506 . In an alternative embodiment, the spark gap  602  is between the suspended center conductor  504  and the base  516 . 
     The power feed wire  512  delivers an electrical impulse to the suspended center conductor  504 . The power feed wire  512  is insulated from the rest of the coaxial cavity resonator  304  by the extended insulated guide  610  that extends into the cavity of the coaxial cavity resonator  304 . The electrical impulses necessary for the generation of RF waveforms require short pulses with sharp rise-times, and the center conductor  504  and the stub center conductor  604  on either side of the spark gap  602  are constructed to withstand the possible erosion due to these sparks. The electrical impulses trigger sparks to arc across the spark gap  602 , ringing the coaxial cavity resonator  304  and triggering RF oscillations which then form standing waves in the coaxial cavity resonator  304 . The resonating standing waves in the coaxial cavity resonator  304  result in corona discharge plasma  210  being generated at the discharge electrode  506 . 
     Referring now to the embodiments of the coaxial cavity resonator  304  depicted in  FIGS. 7 and 8 , a spark wire  712  enters the coaxial cavity resonator  304  through an insulated guide  510 , and creates an electrically open wire spark gap  702  with the center conductor  704 . The center conductor  704  is attached to the base  516  of the coaxial cavity resonator  304 . The center conductor  704  has a discharge electrode  506  at the distal end of the coaxial cavity resonator  304 . An electrical return path  514  also attaches to the coaxial cavity resonator  304 . 
       FIGS. 7 and 8  differ only in the location of the spark wire  712  and insulated guide  510 , and function similarly to embodiment depicted in  FIG. 6 . The spark wire  712  allows an electrical impulse to arc across the wire spark gap  702  to the center conductor  704 . The spark wire  712  is insulated from the rest of the coaxial cavity resonator  304  by the insulated guide  510  that also may extend into the cavity of the coaxial cavity resonator  304  similar to the extended insulated guide  610  of  FIG. 6  (not shown). 
     In alternate embodiments, the internal cavity  1404  of the coaxial cavity resonator  304  is filled with a dielectric (shown in  FIG. 14   b  and  FIG. 14   c ) that does not prevent a spark from bridging the spark gap  602  or wire spark gap  702 . In an alternate embodiment, the spark gap  602  is between the suspended center conductor  504  and the wall of the coaxial cavity resonator  304 . In an alternate embodiment, the wire spark gap  702  is between the suspended center conductor  504  and the electrical return path  514 . Various other locations and arrangements for the spark gap  602  and wire spark gap  702  are possible and would be obvious to one having skill in the art. The above figures and descriptions represent merely exemplary embodiments of the invention. 
     Coaxial Cavity Resonator with Feedback Sense 
     Referring now to the embodiments of the coaxial cavity resonator  304  depicted in  FIGS. 9 and 10 , a power feed wire  512  enters the coaxial cavity resonator  304  through an extended insulated guide  610 , and attaches to the center conductor  704 . The center conductor  704  is attached to the base  516  of the coaxial cavity resonator  304  and the internal cavity of the coaxial cavity resonator  304  may be filled with a dielectric (not shown). The center conductor  704  has a discharge electrode  506  at the open end of the coaxial cavity resonator  304 . An electrical return path  514  also attaches to the coaxial cavity resonator  304 .  FIG. 9  depicts a simple probe  912  with an insulated probe guide  910  that extends into the coaxial cavity resonator  304  and has an open ended probe tip  902  that extends through the insulated probe guide  910  further into the coaxial cavity resonator  304 .  FIG. 10  depicts a pickup loop  1012  with an insulated loop guide  1010  that allows a wire loop  1002  to extend into the coaxial cavity resonator  304  and attach to an inner surface of the coaxial cavity resonator  304 . In an alternate embodiment, a probe  902  is used as a power feed instead of the directly connected power feed wire  512 . In an alternate embodiment, a wire loop  1002  is used as a power feed instead of the directly connected power feed wire  512 . 
     Referring now to the embodiment of the coaxial cavity resonator  304  depicted in  FIG. 11 , an input waveguide  1102  is coupled to the coaxial cavity resonator  304 . The input waveguide  1102  couples an electron tube device such as a magnetron, amplitron, traveling wave tube, or other RF amplifier to the coaxial cavity resonation  304 . A feedback waveguide  1104  provides feedback to the magnetron, traveling wave tube, or other RF amplifier. Referring now to the embodiment of the coaxial cavity resonator  304  depicted in  FIG. 12 , a waveguide  1202  is coupled to the coaxial cavity resonator  304 , similar to  FIG. 11 , but utilizing the waveguide  1202  for both transferring power to the coaxial cavity resonator  304  and providing a feedback signal. 
     Referring now to the embodiment of the coaxial cavity resonator  304  depicted in  FIG. 13 , a simple probe  912  with an open ended probe tip  902  extends through the insulated probe guide  910  into the base  516  of the coaxial cavity resonator  304  as a feedback sense. An RF cable  1302  connects to the base  516  of the coaxial cavity resonator  304  and the RF cable center wire  1304  is electrically connected to the center conductor  704 . One or more loops  1308  used to energize the coaxial cavity resonator  304  are displaced further along the center conductor  704 , and loop back to the RF cable shield  1306  and the base  516  of the coaxial cavity resonator  304 . In alternate embodiments, the simple probe  912  and RF cable  1302  are placed at any convenient location on the coaxial cavity resonator  304  as would be understood by one of ordinary skill in the art. In alternate embodiments, various combinations of simple probes  912 , pickup loops  1012 , waveguides  1202 , and feedback waveguides  1104  and direct electrical coupling are used to energize the coaxial cavity resonator  304 , provide a feedback sense, or both, as would be understood by one of ordinary skill in the art. 
     A direct electrical coupling, a simple probe  912 , a pickup loop  1012 , a waveguide  1202 , or a feedback waveguide  1104  provide a feedback sense back to the power shaping means  302  (not shown) for sensing the electrical oscillations in the coaxial cavity resonator  304 . The power shaping means  302  uses this electrical feedback as input to frequency determining circuitry resulting in the frequency of the oscillations more closely approximating the resonant frequency of the coaxial cavity resonator  304 . Direct electrical couplings, simple probes  912 , pickup loops  1012 , waveguides  1202 , and feedback waveguides  1104  are well known in the art for use with RF cavity resonators, as are other suitable feedback devices that would be obvious to one having ordinary skill in the art. 
     Coaxial Cavity Resonator 
     Referring now to  FIGS. 14   a ,  14   b , and  14   c , in alternate embodiments the center conductor  704  and cavity wall  1402  of the coaxial cavity resonator  304  are each comprised of a material taken from the group of copper, brass, steel, platinum, silver, aluminum, or other good electrical conductors in order to provide high conductivity and low power absorption in the coaxial cavity resonator  304 . Referring to  FIG. 14   a , in one embodiment of the coaxial cavity resonator  304  the cavity wall  1402  defines a cavity  1404  having a hollow interior region. Referring to  FIG. 14   b , in another embodiment, the cavity  1404  of the coaxial cavity resonator  304  is filled or partially filled with one or more solid materials  1406  including, but not limited to, low electrical loss and non-porous ceramic dielectric materials, such as ones selected from the group consisting of: aluminum oxide, silicon oxide, glass-mica, magnesium oxide, calcium oxide, barium oxide, magnesium silicate, alumina silicate, and boron nitride, to create a solid plug in the cavity. The solid materials  1406  form a plug in the coaxial cavity resonator  304  thereby minimizing physical perturbation of the combustion chamber and also minimizing electrical perturbation of the coaxial cavity resonator  304  by materials from the combustion chamber. Referring to  FIG. 14   c , in another embodiment, the cavity  1404  of the coaxial cavity resonator  304  is filled with other suitable dielectric materials  1408  as would be known in the art including, but not limited to, a relatively unreactive gas such as nitrogen or argon. The cavity  1404  is then sealed, for example, with one of the aforementioned solid materials  1406 , to prevent interaction with the combustion chamber. 
     Conclusion 
     The numerous embodiments described above are applicable to a number of different applications. One particular application where the corona discharge ignition system is particularly applicable is in a combustible fuel powered internal combustion engines, such as those found in electrical generators, power tools, motorcycles, automobiles, airplane engines and marine engines. The technology for igniting combustible materials using corona discharge plasma is also applicable to aviation jet engines or even rocket motors. Using corona discharge plasma as an ignition source in lieu of more traditional spark plug technologies has many additional applications apparent to one of ordinary skill in the art. 
     The embodiments of the invention shown in the drawings and described above are exemplary of numerous embodiments that may be made within the scope of the appended claims. It is contemplated that numerous other configurations of the disclosed system, process, and device for igniting combustible materials in combustion chambers may be created taking advantage of the disclosed approach. It is the applicant&#39;s intention that the scope of the patent issuing herefrom will be limited only by the scope of the appended claims.