Surface wave generator for igniting liquid monopropellant media with microwave power

Abstract

Embodiments relate to a surface-wave-generating device. The surface-wave-generating device includes an outer chamber. The outer chamber includes a first end a second end and four walls extending from the first end to the second end. The outer chamber defines an inner resonant cavity extending from the first end to the second end, from the first wall to the second wall, and from the third wall to the fourth wall. The surface-wave-generating device also includes an inner conductive chamber disposed within the inner resonant cavity and extending from the first end toward the second end. The inner conductive chamber defines an electric-field-producing gap intermediate the inner conductive chamber and the second end. The surface-wave-generating device also includes a media flow chamber disposed within the inner conductive chamber and extending from the first end to the second end and passes through the electric-field-producing gap.

Description

Atty. Ref. No. 0073605-000957 Surface Wave Generator For Igniting Liquid Monopropellant Media With Microwave Power CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is related to and claims the benefit of priority to U.S. provisional patent application no. 63 / 558,796, filed on February 28, 2024, the entire contents of which is incorporated by reference. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under Contract No. FA8251-22-P-0001 awarded by the United States Air Force. The Government has certain rights in the invention. FIELD OF THE INVENTION

[0003] Embodiments can relate to a surface-wave-generating device that can excite (e.g., ignite, smelt, etc.) various types of media, including liquid monopropellants, using microwave power by generating an electric field within a resonant cavity and passing said media through said electric field. Embodiments can further relate to a process for exciting various types of media via exposure to microwave-generated electric fields. BACKGROUND OF THE INVENTION

[0004] In some types of propulsion and / or power generating applications, propellant media (e.g., a liquid monopropellant) can be excited (e.g., ignited) to form a plasma that is expelled through a nozzle to generate thrust and / or to produce an exhaust gas that powers a generator. Some propellant media can be difficult to ignite and can require specialized ignition schemes (e.g., catalytic ignition) that require bulky equipment and significant energy to execute ignition of the propellant media. This can lead to the utilization of more toxic and less efficient propellant media (e.g., hydrazine) due to its ability to ignite more easily than more stable, more efficient, and safer propellant media (e.g., a green monopropellant). SUMMARY OF THE INVENTIONAtty. Ref. No. 0073605-000957

[0005] We determined that a surface wave generator having a resonant internal structure can utilize microwave power to generate an electric field within the surface wave generator internal structure that is powerful enough to ignite propellant media as it passes through the electric field. Such a surface wave generator utilizing microwave power can provide a more compact and efficient ignition scheme that can be utilized in numerous types of propulsion and / or power generating applications. We also determined that the electric field generated within the internal resonant structure can be utilized to excite (e.g., ignite, smelt, etc.) some types of gaseous media and / or solid media.

[0006] An exemplary embodiment can relate to a surface-wave-generating device. The surface- wave-generating device can include an outer chamber having a first end and a second end opposite the first end, a first wall extending from the first end to the second end, a second wall extending from the first end to the second end and opposite the first wall, a third wall extending from the first end to the second end and intermediate the first wall and the second wall, and a fourth wall extending from the first end to the second end and opposite the third wall. The outer chamber can define an inner resonant cavity extending from the first end to the second end, from the first wall to the second wall, and from the third wall to the fourth wall. The surface-wave- generating device can include an inner conductive chamber disposed within the inner resonant cavity and extending from the first end toward the second end. The inner conductive chamber can define an electric-field-producing gap intermediate the inner conductive chamber and the second end. The surface-wave-generating device can include a media flow chamber disposed within the inner conductive chamber and extending from the first end to the second end such that a portion of the media flow chamber adjacent the second end passes through the electric-field- producing gap.

[0007] In some embodiments, the outer chamber can include a first faceplate removably attachable to the first end and a second faceplate removably attachable to the second end. The first faceplate can define a first aperture adjacent the inner conductive chamber such that the media flow chamber extends through the first aperture. The second faceplate can define a second aperture adjacent the electric-field-producing gap such that the media flow chamber extends through the second aperture.

[0008] In some embodiments, the outer chamber can include a power input port disposed on an exterior surface of the outer chamber and extending into the inner resonant cavity.Atty. Ref. No. 0073605-000957

[0009] In some embodiments, the surface-wave-generating device can include a power input antenna disposed within the power input port and extending into the inner resonant cavity.

[0010] In some embodiments, the power input antenna can be an N-type candlestick antenna having a conductive disk disposed within the inner resonant cavity and adjacent the electric- field-producing gap.

[0011] In some embodiments, each of the first, second, third, and fourth walls can have a first, second, third, and fourth curvature, respectively, such that the outer chamber can be a cylinder, and the inner conductive chamber and the media flow chamber can each be cylinders.

[0012] In some embodiments, the outer chamber and the inner conductive chamber can be stainless steel.

[0013] In some embodiments, the media flow chamber can be quartz.

[0014] In some embodiments, the inner resonant cavity can have a length of approximately 78 millimeters (mm) and a diameter of approximately 40.8 mm, the inner conductive chamber can have an outer diameter of approximately 6.35 mm, and the media flow chamber can have an outer diameter of approximately 5 mm.

[0015] In some embodiments, the electric-field-producing gap can have a gap distance within a range of approximately 0.5 to 1.5 mm.

[0016] Another exemplary embodiment can relate to a process for exciting media via exposure to a microwave-excited electric field. The process can include depositing media into a media flow chamber that can be disposed within an inner conductive chamber. The inner conductive chamber can be disposed within an inner resonant cavity defined by an outer chamber having a first end and a second end opposite the first end, and the inner conductive chamber can extend from the first end toward the second end such that the inner conductive chamber defines an electric-field-producing gap intermediate the inner conductive chamber and the second end. The media can be deposited into the media flow chamber such that the media flows from the first end toward the second end and can pass through the electric-field-producing gap. The process can further include supplying microwave power at a predetermined frequency to a power input port of the outer chamber, and the power input port can extend into the inner resonant cavity. The microwave power can create an electric field in the electric-field-producing gap.

[0017] In some embodiments, the outer chamber can include a first faceplate removably attachable to the first end and a second faceplate removably attachable to the second end. TheAtty. Ref. No. 0073605-000957 first faceplate can define a first aperture adjacent the inner conductive chamber such that the media flow chamber can extend through the first aperture and the second faceplate can define a second aperture adjacent the electric-field-producing gap such that the media flow chamber can extend through the second aperture.

[0018] In some embodiments, the power input port can be an N-type “candlestick” antenna having a conductive disk disposed within the inner resonant cavity and adjacent the electric- field-producing gap.

[0019] In some embodiments, the outer chamber, the inner conductive chamber, and the media flow chamber can each be cylinders.

[0020] In some embodiments, the outer chamber and the inner conductive chamber can be stainless steel.

[0021] In some embodiments, the media flow chamber can be quartz.

[0022] In some embodiments, the inner resonant cavity can have a length of approximately 78 millimeters (mm) and a diameter of approximately 40.8 mm, the inner conductive chamber can have an outer diameter of approximately 6.35 mm, and the media flow chamber can have an outer diameter of approximately 5 mm.

[0023] In some embodiments, the electric-field-producing gap can have a gap distance within a range of approximately 0.7 to 1 mm.

[0024] In some embodiments, the predetermined frequency can be approximately 2.45 gigahertz (GHz).

[0025] Further features, aspects, objects, advantages, and possible applications of the present invention will become apparent from a study of the exemplary embodiments and examples described below, in combination with the FIGS., and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other objects, aspects, features, advantages and possible applications of the present innovation will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings. Like reference numbers used in the drawings may identify like components.

[0027] FIG. 1 shows an exemplary embodiment of the surface-wave-generating device.

[0028] FIG. 2 shows a cross-sectional view of the exemplary embodiment of the surface-wave- generating device in FIG. 1.Atty. Ref. No. 0073605-000957

[0029] FIGS. 3A and 3B show an exemplary embodiment of the surface-wave-generating device.

[0030] FIG. 4 shows a cross-sectional view of the exemplary embodiment of the surface-wave- generating device in FIG. 3A.

[0031] FIG. 5 illustrates a cross-sectional view of an exemplary embodiment of the surface- wave-generating device.

[0032] FIG. 6 illustrates an exemplary process of igniting media via exposure to a microwave field.

[0033] FIG. 7 shows an image of a simulation of an exemplary electric field strength within an exemplary embodiment of the surface-wave-generating device.

[0034] FIG. 8 illustrates a graphical representation of the dependence relationship between and operating frequency of the surface-wave-generating device and the gap length and cavity length of the surface-wave-generating device.

[0035] FIG. 9 illustrates the relationship between field strength of an electric field in the electric- field-producing gap and the gap length.

[0036] FIG. 10 shows an experimental set up of the surface-wave-generating device.

[0037] FIGS. 11A-C show optical images of an exemplary embodiment of the surface-wave- generating device.

[0038] FIGS. 12A-C show optical images of exemplary solid media smelted in an exemplary embodiment of the surface-wave-generating device.

[0039] FIG. 13 illustrates a graphical representation of power output compression.

[0040] FIG. 14 illustrates a graphical representation of the non-linear relationship between input power in decibels and output power in watts. DETAILED DESCRIPTION OF THE INVENTION

[0041] The following description is of exemplary embodiments that are presently contemplated for carrying out the present invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles and features of the present invention. The scope of the present invention is not limited by this description.

[0042] Referring to FIG. 1 through FIG. 4, embodiments can relate to a surface-wave-generating device 100. The surface-wave-generating device 100 can include an outer chamber 102. The outer chamber 102 can include a first end 104 and a second end 106 opposite the first end 104, aAtty. Ref. No. 0073605-000957 first wall 108, a second wall 110 opposite the first wall 108, a third wall 112 intermediate the first wall 108 and the second wall 110, and a fourth wall 114 opposite the third wall 112. The first wall 108, the second wall 110, the third wall 112, and the fourth wall 114 can each extend from the first end 104 to the second end 106 such that the inner resonant cavity 116 can extend from the first end 104 to the second end 106, from the first wall 108 to the second wall 110, and from the third wall 112 to the fourth wall 114. The outer chamber 102 can be a conductive material, such as copper, brass, aluminum, stainless steel, etc.

[0043] The surface-wave-generating device 100 can include an inner resonant cavity 116 defined by the outer chamber 102. The outer chamber 102 can be shaped and / or sized such that the inner resonant cavity 116 defined by the outer chamber 102 is suitable for generating a standing electromagnetic wave within the inner resonant cavity 116. A standing electromagnetic wave can be generated within the inner cavity 116 by transmitting electromagnetic energy (e.g., microwave power) into the inner resonant cavity 116, which can reflect off of the conductive surfaces of the inner resonant cavity 116 to generate a standing electromagnetic wave and facilitate resonance within the inner resonant cavity 116.

[0044] In some embodiments, the inner resonant cavity 116 can be pressurized such that the inner resonant cavity 116 can have an internal pressure within the inner resonant cavity 116. The internal pressure can range from approximately as low as a high-vacuum pressure (e.g., approximately 100 nanopascals to 100 millipascals) to as high of an internal pressure as the structural integrity of the outer chamber 102 (e.g., approximately 10–30 atmospheres), which defines the inner resonant cavity 116, will permit without compromising said structural integrity. The internal pressure of the inner resonant cavity can be any internal pressure that is suitable for establishing a standing-wave with microwave energy about the inner resonant cavity 116. Creating a pressurized atmosphere within the inner resonant cavity 116 can aid the operation of the surface-wave-generating device 100. For example, a pressurized atmosphere within the inner resonant cavity 116 can aid in the prevention of electrical arcing, the preservation of internal materials (e.g., dielectric materials), temperature control, and loss minimalization (e.g., dielectric losses), etc.

[0045] In some embodiments, the inner resonant cavity 116 can have an internal atmosphere that is made up of one or more gases such as oxygen, inert gases (argon, sulfur hexafluoride, etc.), noble gases (xenon, neon, etc.), or any other gas suitable for suitable for establishing a standing-Atty. Ref. No. 0073605-000957 wave with microwave energy about the inner resonant cavity 116. In some embodiments, the internal atmosphere of the inner resonant cavity 116 can be a single gas or a combination of gases.

[0046] In some embodiments, the inner resonant cavity 116 can have dielectric solid materials (e.g., alumina ceramic, polytetrafluoroethylene, etc.) disposed within the inner resonant cavity 116. For example, the inner resonant cavity 116 can have dielectric materials, such as rods, disks, coatings, removable plugs or inserts, etc., disposed within the inner cavity 116 and / or affixed / attached / applied to an inner surface of the outer chamber 102 that defines the inner cavity 116. In some embodiments, the materials of the outer chamber 102 can include dielectric materials.

[0047] The surface-wave-generating device 100 can include an inner conductive chamber 118. The inner conductive chamber 118 can be disposed within the outer chamber 102 such that the inner conductor 118 and the outer chamber 102 form a coaxial inner resonant cavity 116. The inner conductive chamber 118 can aid in the propagation, and / or focusing of a standing electromagnetic wave within the inner resonant cavity 116. For example, the inner conductive chamber 118 can be disposed within the outer chamber 102 such that the inner conductive chamber 118 extends from the first end 104 toward the second end 106 and defines a gap intermediate the inner conductive chamber 118 and the second end 106. The gap defined by the inner conductive chamber 118 and the second end 106 can be an electric-field-producing gap 122. The electric-field-producing gap 122 can influence electric field distribution within the inner resonant cavity 116. For example, surface waves can form along the inner conductive chamber 118, and the presence of the electric-field-producing gap 122 in the area of the surface waves (e.g., the end of the inner conductive chamber 118 adjacent the second end 106) can cause an electric field to be concentrated intermediate the inner conductive chamber 118 and the second end 106.

[0048] The inner conductive chamber 118 can be any conductive material suitable for suitable for establishing a standing-wave with electromagnetic waves within the inner cavity 116, such as copper, brass, aluminum, stainless steel, etc. In some embodiments, the outer chamber 102 and the inner conductive chamber 118 can be the same conductive material. In some embodiments, the outer chamber 102 and the inner conductive chamber 118 can be different conductive materials.Atty. Ref. No. 0073605-000957

[0049] The surface-wave-generating device 100 can include a media flow chamber 120 that can facilitate the flow of media through the surface-wave-generating device 100 to expose the media to an electric field generated within the inner resonant cavity 116. For example, the media flow chamber 120 can be disposed within the inner conductive chamber 118 and can extend from the first end 104 through the second end 106 such that the media flow chamber 120 extends through the electric-field-producing gap 122. It is understood that the media flow chamber 120 extending from the first end 104 through the second end 106 is merely exemplary, and that the media flow chamber 120 can be any suitable length, so long as the media flow chamber 120 extends through the electric-field-producing gap 122. For example, the media flow chamber 120 can extend from or through the first end 104 to or through the second end 106, from within the inner conductive chamber 118 to or through the second end 106, etc. In some embodiments, the media flow chamber 120 can have an outer diameter that is less than, or approximately equal to, the inner diameter of the inner conductive chamber 118, and can be securely positioned within the inner conductive chamber 118 by any means suitable for affixing the outer surface of the media flow chamber 120 to the inner surface of the inner conductive chamber 118, for example, with epoxy. In some embodiments, the media flow chamber 120 can have an outer diameter approximately equal to the outer diameter of the inner conductive chamber 118, and can extend from the end of the inner conductive chamber 118 adjacent the electric-field-producing gap 122. For example, a first end of the media flow chamber 120 can be affixed (e.g., epoxied, potentially explosive bonded, etc.) to the end of the inner conductive chamber 118 adjacent the electric- field-producing gap 122 and the second end of the media flow chamber 120 can extend to, into, or through the second end 106.

[0050] Media can be deposited into an end of the media flow chamber 120 adjacent to the first end 104 and can flow toward the second end 106 such that the media flowing through the media flow chamber 120 can be passed through the electric field contained within the electric-field- producing gap 122, which can excite (e.g., ignite, smelt, etc.) the media. As described above, the media flow chamber 120 can be any suitable length that extends through the electric-field- inducing gap 122. As such, in embodiments where the media flow chamber 120 does not extend from or through the first end 104, e.g., the end of the media flow chamber 120 into which media is deposited is disposed within the inner conductive chamber 118, media can be deposited into the inner conductive chamber 118.Atty. Ref. No. 0073605-000957

[0051] In some embodiments, the media flow chamber 120 can extend beyond the second end 106 of the outer chamber 102 such that the media can be excited as it passes through the electric- field-producing gap 122 without the media coming into contact with the inner surface of the outer chamber 102 and / or the inner surface of the inner conductive chamber 118. In some embodiments, the media flow chamber 120 can be a dielectric material. For example, the media flow chamber 120 can be a dielectric material such as quartz, polytetrafluoroethylene (PTFE), silicon dioxide (SiO2), alumina ceramic, sapphire, etc. In some embodiments, the media flow chamber can be any suitable material (e.g., dielectric material, stainless steel, titanium, ceramic, etc.) and can have a dielectric coating on the outer surface of the media flow chamber 120.

[0052] Surface waves generated within the inner resonant cavity 116 can propagate along the surface of the dielectric material extending through the electric-field producing gap, which can further enhance the electric field contained within the electric-field-producing gap 122. In some embodiments, the media flow chamber 120 can be a dielectric material and / or have a dielectric coating on the outer surface and can extend beyond the second end 106, as described above. In such embodiments, surface waves propagating along the dielectric material / coating disposed within the electric-field-producing gap 122 can continue to propagate along the portion of the media flow chamber 120 that extends beyond the second end 106, such that media can be excited by the propagating surface waves in the portion of the media flow chamber 120 that extends through / beyond the second end 106.

[0053] Examples of media can include, but are not limited to, gaseous media (e.g., helium), liquid media (e.g., liquid propellants, water, etc.), and / or solid media (e.g., ilmenite, metal particles). It is understood that, in some embodiments, multiple types of media can be deposited into the media flow chamber 120 simultaneously. For example, in some embodiments, liquid media, such as a liquid propellant, and gaseous media, such as a carrier gas, can be simultaneously deposited into the media flow chamber 120 such that the gaseous media can aid in the excitement of the liquid media as it passes through the electric field within the electric- field-producing gap 122. It is understood that any combination of liquid media, gaseous media, and / or solid media can be simultaneously deposited into the media flow chamber 120 and can be excited by the electric field within the electric-field-producing gap 122. Additionally, any gaseous or liquid media can be used to entrain particles of solid media into a stream as aAtty. Ref. No. 0073605-000957 mechanism for flowing solid particles through the electric field produced by the electric-field- producing gap.

[0054] In an exemplary use, it is contemplated that the surface-wave-generating device 100 can be operated to ignite liquid media, which can include liquid monopropellants, such as AF- M315E (ASCENT), a liquid monopropellant belonging to a class of green monopropellants. Such liquid monopropellants can be difficult to ignite and can require specialized ignition schemes, such as a catalytic ignition scheme, which can be inefficient and can require large amounts of physical space, power consumption, and / or time to achieve ignition. Thus, it is contemplated that an inventive aspect of the surface-wave-generating device 100 is to provide a more efficient device and / or a process for igniting liquid monopropellants that requires a smaller amount of physical space, less energy consumption, and / or less time to successfully achieve ignition.

[0055] In some embodiments, media can be deposited into an end of the media flow chamber 120 at a predetermined mass flow rate. For example, a liquid media can be deposited into the media flow chamber 120 at a flow rate within the flow rate range of approximately 0.5 milliliters per minute (mL / min) to 9.5 mL / min. It is understood that this flow rate range is merely exemplary, and that a value for the predetermined flow rate can be chosen based on the application in which the surface-wave-generating device 100 operates, operational parameters (e.g., available microwave energy, strength of the electric field in the electric-field-producing gap, etc.), the type of media, etc.

[0056] The surface-wave-generating device 100 can include a first faceplate 124 and a second faceplate 126. The first faceplate 124 and / or the second faceplate 126 can be removably attached to the first end 104 and / or the second end 106, respectively. The faceplates 124,126 can be removably attached by any suitable method of removeable attachment, such as fasteners, clips, etc. The faceplates 124 and 126 can enclose the inner resonant cavity 116 at the first end 104 and the second end 106, respectively. Enclosing the first end 104 and the second end 106 can confine electromagnetic energy input into the surface-wave-generating device 100 within the inner resonant cavity 116 such that resonance can be achieved within the inner resonant cavity 116.

[0057] In some embodiments, the first faceplate 124 and / or the second faceplate 126 can be attached to the outer chamber 102 such that the faceplates are not removable. For example, theAtty. Ref. No. 0073605-000957 first faceplate 124 and / or the second faceplate 126 can be adhered, welded, etc. to the ends of the outer chamber 102. In some embodiments, the outer chamber 102 and the first faceplate 124 and / or the second faceplate 126 can be one unified body of conductive material, such as a unified body of conductive material that is made via casting, machining, additive manufacturing, etc. In such an embodiment, the inner conductive chamber 118 can also be part of the unified body of conductive material. FIG. 5 depicts an exemplary embodiment of a surface wave generator having a unified body including first and second faceplates and an inner conductive chamber.

[0058] The first faceplate 124 can define a first aperture 128 and the second faceplate 126 can define a second aperture 130. In some embodiments, the first aperture 128 and the second aperture 130 can be defined within the first faceplate 124 and the second faceplate 126, respectively, such that they align with the inner conductive chamber 118 and / or the media flow chamber 120. For example, the first aperture 128 can be defined within the first faceplate 124 such that the first aperture 128 aligns with the inner diameter of the inner conductive chamber 118 or the media flow chamber 120. In some embodiments, the diameter of the first aperture 128 can be approximately equal to the inner diameter of the inner conductive chamber 118 or the media flow chamber 120.

[0059] Further to the above, the inner conductive chamber 118 can be affixed (e.g., welded, epoxied, etc.) to and extend from the inner surface of the first faceplate 124 about the first aperture 128 such that the first aperture 128 aligns with the inner diameter of the media flow chamber 120 or the inner diameter of the inner conductive chamber 118. In some embodiments, the inner conductive chamber 118 can be affixed (e.g., welded, epoxied, etc.) to and extend from the inner surface of the first faceplate 124 and the media flow chamber 120 can be disposed within the inner conductive chamber 118 such that the inner diameter of the media flow chamber 120 aligns with the first aperture 128.

[0060] In some embodiments, the first aperture 128 can be a diameter that is approximately equal to the outer diameter of the inner conductive chamber 118 or the outer diameter of the media flow chamber 120, and can be defined within the first faceplate 124 such that the inner conductive chamber 118 or the media flow chamber 120 can extend into and / or through the first aperture 128. For example, in some embodiments, the inner conductive chamber 118 can be affixed (e.g., welded, epoxied, etc.) to the inner surface of the first faceplate 124 and the media flow chamber 120 can be disposed within the inner conductive chamber 118 such that the outerAtty. Ref. No. 0073605-000957 diameter of the media flow chamber 120 aligns with the first aperture 128 and the media flow chamber 120 can extend into or through the first aperture 128. In some embodiments, the first faceplate 124 and the inner conductive chamber 118 can be one unified body that is made via casting, machining, additive manufacturing, etc.

[0061] Further to the above, in some embodiments, the inner conductive chamber 118 can be adjustably attached to the first faceplate 124 such that the length of the inner conductive chamber 118 within the inner resonant cavity 116, and thus, the length of the electric-field-producing gap 122, can be adjusted. For example, the first faceplate 124 can have an assembly for adjustably attaching the inner conductive chamber 118 disposed on the outer surface of the first faceplate 124 and about the first aperture 128. For example, in some embodiments, the first faceplate 124 can have an attachment assembly aligned with the first aperture 128 such that the inner conductive chamber 118 can extend through the first aperture 128 and into / through the attachment assembly. The interior of the attachment assembly and the outer surface of a portion of the inner conductive chamber 118 that extends beyond the outer surface of the first faceplate 124 can have mating (e.g., female and male threads) threads such that the inner conductive chamber 118 can be adjustably threaded into / through the attachment assembly.

[0062] In some embodiments, the attachment assembly can have one or more attachment members extending from the outer surface of the first faceplate 124 and positioned parallel to a portion of the inner conductive chamber 118 that extends beyond the outer surface of the first faceplate 124, and the inner conductive chamber 118 can be secured to the one or more attachment members, e.g., with a clamp, pin, fastener, etc., such that the length of the inner conductive chamber 118 within the inner resonant cavity 116 can be adjusted as desired. It is understood that the above attachment assemblies are merely exemplary, and that any suitable attachment assembly that provides adjustable attachment of the inner conductive chamber 118 to the first faceplate 124 can be used.

[0063] Adjusting the length of the electric-field-producing gap 122 can tune, strengthen, and / or weaken the electric field within the electric-field-producing gap. It is understood that the length of the electric-field-producing gap 122 can be adjusted based on desired electrical field within the gap, the type of media, operational parameters, etc.

[0064] In some embodiments, the second aperture 130 can have a diameter approximately equal to the inner diameter of the media flow chamber 120, and can be defined within the secondAtty. Ref. No. 0073605-000957 faceplate 126 such that the second aperture 130 aligns with the inner diameter of the media flow chamber 120. In some embodiments, the second aperture 130 can have a diameter that is less than the inner diameter of the media flow chamber 120. In some embodiments, the media flow chamber 120 can be affixed (e.g., epoxied, potentially explosive bonded, etc.) to the inner surface of the second faceplate 126 about the second aperture 130. In some embodiments, the second aperture 130 can have a diameter that is approximately equal to the outer diameter of the media flow chamber 120 and can be defined within the second faceplate 126 such that the media flow chamber 120 can extend into and / or through the second aperture 130.

[0065] In some embodiments, there can be a gap between the first and / or second aperture 128,130 and the inner conductive chamber 118 and / or media flow chamber 120. In such embodiments, the first and / or second aperture 128,130 can include shims and / or conductive tape within and / or about the first and / or second aperture 128,130 such that the inner resonant cavity 116 is sealed, and the electromagnetic energy within the resonant cavity 116 remains confined within the inner resonant cavity, e.g., the electromagnetic energy does not leak through the first and / or second aperture 128,130.

[0066] In some embodiments, the surface-wave-generating device can include a power input port 132. The power input port 132 can be disposed on an outer surface of the outer chamber 102. The power input port 132 can extend into the inner resonant cavity 116 such that electromagnetic energy (e.g., microwave power) can be transmitted into the inner resonant cavity 116. The power input port 132 can be physically connected (e.g., via a coaxial transmission cable, DIN power cable, etc.) with an electromagnetic power source, such as a magnetron, a solid-state power amplifier, etc.

[0067] In some embodiments, the power input port 132 can include a power input antenna 134. The power input antenna 134 can be any type of antenna suitable for transmitting electromagnetic energy, such as a coaxial probe antenna. For example, the power input antenna 134 can be an N-type candlestick probe antenna that can extend into the inner resonant cavity 116. The candlestick probe antenna can be any suitable conductive material, such as copper, titanium, tungsten, etc. In some embodiments, the power input antenna 134 can include a conductive disk 136. The conductive disk 136 can be disposed at the end of the power input antenna 134 that is disposed within the inner resonant cavity 116. The conductive disk 136 can aid in the conversion of electromagnetic energy to standing electromagnetic waves within theAtty. Ref. No. 0073605-000957 inner resonant cavity 116, and can be any suitable conductive material, such as copper, titanium, tungsten, etc.

[0068] Physical aspects and parameters of the exemplary embodiments of the surface-wave- generating device 100 described above and depicted in FIGS. 1–5 can be based on the desired application and / or desired operational and / or performance characteristics of the surface-wave- generating device 100. For example, the overall geometric design and / or physical specifications of the surface-wave-generating device 100 can be based on generating the maximum electric field strength in the electric-field-producing gap 122 at a predetermined operating frequency of the power transmitted into the surface-wave-generating device 100. The predetermined operating frequency can be based on applicational and / or operational parameters, such as spatial and / or size limitations of the surface-wave-generating device 100, the materials of which the surface-wave-generating device 100 is constructed, power source limitations, the desired strength of the electric field generated within the surface-wave-generating device 100, the media subjected to the electric field within the surface-wave-generating device 100, etc.

[0069] For instance, in the exemplary embodiment shown in FIGS. 3–4, each of the following physical parameters can be altered to achieve the maximum electric field strength in the electric- field-producing gap 122 at the predetermined operating frequency: (a) the cavity diameter (DC) of the inner resonant cavity 116; (b) the cavity length (LC) of the inner resonant cavity 116; (c) the outer diameter (DI) of the inner conductive chamber 118; (d) the distance (H) of the electric- field-inducing gap 122 between the inner conductive chamber 118 and the inner surface of the second faceplate 126; (e) the length (LA) of the power input antenna 134; (f) the diameter (DD) of the conductive disk 136; and the distance (LD) between the central longitudinal axis power input antenna 134 and / or conductive disk 136 and the inner surface of the second faceplate 126.

[0070] It is understood that each of the above physical parameters can have an effect on the tuning of the surface-wave-generating device 100 relevant to the predetermined frequency at which power is supplied to the surface-wave-generating device 100. Proper tuning of the surface-wave-generating device 100 relevant to the frequency of the power supplied to the surface-wave-generating device 100 can ensure that the surface-wave-generating device 100 is capable of forming a standing electromagnetic wave within the inner resonant cavity 116 at the predetermined frequency, and thus, that the majority of the power supplied is absorbed by the surface-wave-generating device 100. Without proper tuning of the surface-wave-generatingAtty. Ref. No. 0073605-000957 device 100, large amounts of supplied power can be reflected back to the power source, which can damage components of the device 100 and / or the power source supplying power, and can reduce the strength of the electric field generated within the electric-field-producing gap 122.

[0071] Further to the above, it is understood that any combination of the above physical parameters can be adjustable or can be fixed in exemplary embodiments of the surface-wave- generating device 100. For example, in some embodiments each of the physical parameters can be fixed based on a predetermined frequency such that the surface-wave-generating device is only operable at the predetermined frequency. In some embodiments, one or more of the physical parameters can be fixed, while one or more of the physical parameters can be adjustable, such that the surface-wave-generating device 100 can be adjustably tuned to operate at a range of predetermined frequencies. In some embodiments, each of the physical parameters can be adjustable such that the surface-wave-generating device 100 can be adjustably tuned to operate at the broadest possible range of predetermined frequencies. In other words, the above physical parameters can all be fixed, can be a combination of fixed and adjustable, or can all be adjustable.

[0072] In an exemplary embodiment, the predetermined operating frequency can be approximately 2.45 gigahertz (GHz). It is understood that 2.45 GHz is merely an exemplary operating frequency, and that the predetermined operating frequency can be any frequency within the microwave frequency range (e.g., 300 megahertz (MHz) to 300 GHz) that is suitable to generate an electric field within the surface wave device 100 that is strong enough to excite (e.g., ignite, smelt, etc.) the media being deposited into the surface-wave-generating device 100. For example, in some embodiments, the predetermined frequency can be a frequency within a range of approximately 2.3 GHz to 2.6 GHz.

[0073] In an exemplary embodiment with a predetermined operating frequency of approximately 2.45 GHz, the outer chamber 102 and the inner cavity 116 can have an annular or cylindrical geometric shape. The inner cavity 116 can have a cavity length of approximately 78 mm and a cavity diameter of approximately 40.8 mm. The inner conductive chamber 118 and the media flow chamber 120 can have an annular or cylindrical geometric shape. The inner conductive chamber 118 can have an outer diameter of approximately 6.35 mm and the media flow chamber 120 can have an outer diameter of approximately 5 mm and an inner diameter of approximately 4mm.Atty. Ref. No. 0073605-000957

[0074] In such an exemplary embodiment, the maximum electric field value in the electric-field- producing gap 122 can be approximately 1.56×106V / m, as depicted in FIG. 7. Further to the above, FIG. 9 illustrates the effect of altering the size of the electric-field-producing gap 122 on the electric field generated within the gap 122. The density of the lines depicted within the gap in FIG. 9 correlates with the strength of the electric field, with a larger density of lines, e.g., the larger number of lines closer together in the smaller gap, depicting a stronger electric field compared to the lesser density lines shown in the larger gap.

[0075] Referring now to FIG. 6, embodiments can relate to a process for exciting (e.g., igniting, smelting, etc.) media via exposure to a microwave electric field. The process 300 can include depositing media into a media flow chamber disposed within an inner conductive chamber, the inner conductive chamber can be disposed within an inner resonant cavity defined by an outer shell having a first end and a second end opposite the first end, the inner conductive chamber can extend from the first end toward the second end to define an electric-field-producing gap intermediate the inner conductive chamber and the second end, and the media flow chamber can extend through the second end such that the media flow tube passes through the electric-field- producing gap and such that the media being deposited into the media flow chamber flows from the first end toward the second end and passes through the electric-field-producing gap 302.

[0076] The process 300 can further include supplying microwave power at a predetermined frequency to a power input port of the outer chamber, the power input port can extend into the inner resonant cavity, and the electrical microwave power can generate an electric field in the electric-field-producing gap 304.

[0077] In an exemplary embodiment, the outer chamber can include a first faceplate removably attachable to the first end, and the first faceplate can define a first aperture adjacent the inner conductive chamber such that the media flow chamber can extend through the first aperture. The outer chamber can include a second faceplate removably attachable to the second end, and the second faceplate can define a second aperture adjacent the electric-field-producing gap such that the media flow chamber can extend through the second aperture.

[0078] In some embodiments, the power input port can include a power input antenna that can extend from the power input port into the inner resonant cavity. The power input antenna can be an N-type candlestick antenna and can include a conductive disk disposed within the inner resonant cavity and adjacent the electric-field-producing gap.Atty. Ref. No. 0073605-000957

[0079] In some embodiments, the outer chamber, the inner conductive chamber, and the media flow chamber can each be cylinders. The outer chamber and the inner conductive chamber can be stainless steel. The media flow chamber can be quartz.

[0080] In some embodiments, the inner resonant cavity can have a length of approximately 78 mm and a diameter of approximately 40.8 mm. The inner conductive chamber can have an outer diameter of approximately 6.35 mm. The media flow chamber can an outer diameter of approximately 5 mm. The electric-field-producing gap can have a gap distance within a range of approximately 0.7 to 1 mm. The predetermined frequency can be approximately 2.45 GHz.

[0081] In use, it is contemplated that the process 300 can be carried out with an exemplary device such as the surface-wave-generating device 100 described above. As such, it is understood that the variance of physical parameters, operational parameters, materials, media, geometric shapes, power supplies, etc. described above in relation to the surface-wave- generating device 100 can also apply to the process 300. For example, the process 300 can include any predetermined frequency within the microwave frequency range sufficient to excite the media deposited into the media flow chamber, and the parameters, materials, geometric shapes, etc. of the elements included in the process 300 can be altered to carry out the process 300 at the predetermined frequency.

[0082] The following disclosure discusses exemplary implementations, methods, and test data related to the same.

[0083] EXAMPLES

[0084] Example 1

[0085] Exemplary embodiments discussed in the EXAMPLES section relate to exciting (e.g., igniting, smelting, etc.) media with a surface-wave-generator (SWG) device.

[0086] Several experiments were performed to demonstrate the versatility of the SWG as a mechanism for subjecting media to concentrated electric fields. The experiments consisted of helium plasma formation, microwave ignition of ASCENT monopropellant, and ilmenite smelting.

[0087] Fabrication of the Surface Wave Generator (SWG)

[0088] The SWG body was fabricated out of 1.5″ schedule 40 stainless steel pipe, which has a nominal inner diameter of 40.89 mm. This pipe was chosen as it most closely matched the simulated inner diameter of 40 mm. Once the pipe was cut to 78 mm in length, a hole wasAtty. Ref. No. 0073605-000957 drilled 6.9 mm from the end of the pipe for the antenna. Holes in the top and bottom walls were drilled and tapped to be able to thread the front and rear stainless-steel plates to close the cavity (FIG. 11A).

[0089] The inner conductor was made from a 1 / 4″ stainless steel pipe. In order to fit the 5-mm-OD quartz tubing into the inner conductor, the 1 / 4″ pipe’s inner diameter first had to be increased. The quartz tube was inserted into the inner conductor and adhered with epoxy.

[0090] The antenna assembly (FIGS. 11A-C) contains an N-type candlestick antenna and a 1-cm-OD metallic disk. The disk was originally made from copper (FIG. 11B), but was transitioned to titanium (FIG. 11C).

[0091] Tuning of the SWG

[0092] Before the SWG can be used to subject media to strong electric fields, the cavity can first be tuned to absorb the appropriate frequency. Without proper tuning, no standing wave can form within the cavity at the desired frequency and a significant portion of the supplied power can be reflected back to the source. This large reflected power can damage components of the experimental setup, thus it is important that the SWG is properly tuned to the supplied frequency. More importantly, having a properly-tuned SWG can enable the cavity to form the strongest electric fields. Proper tuning allows for the maximum electric field strength for a given input power. The SWG can be tuned by adjusting one or several of the following parameters: gap length, cavity length, and antenna height. In this setup, the cavity length and antenna height were kept constant and the gap length was adjusted to achieve a maximum absorption of the 2.45-GHz signal.

[0093] A vector network analyzer (VNA) was used to determine the frequency that the SWG was tuned to at any given gap position, as well as the peak level of absorption at that frequency. The VNA was first calibrated using an SMA open–short–load (OSL) calibration kit. After calibration, the VNA should showed an S11absorption of –50 decibel (dB) at all measured frequencies. The range of frequencies that the VNA would display was then set at 2.4 to 2.5 GHz. The SWG was connected to “Port 1” of the VNA via a 3.5-mm-to-N-type coaxial adapter. The inner tube of the SWG was then slid in or out of the cavity until the peak absorption fell at 2.45 GHz. The absorption level (in dB) was noted at that time. The peak absorption ranged from −8 dB to −28 dB, with typical values being approximately −16 dB. For example, an absorption of −15 dB corresponds to 97% absorption of the input power.Atty. Ref. No. 0073605-000957

[0094] Experimental Setup with Magnetron Power Source

[0095] The magnetron power source setup consisted of the following components: a. High-voltage power supply: The high-voltage (HV) power supply is used to convert 60-Hz, 240-Vacpower to high-voltage DC power for the magnetron microwave source. b. Daihen magnetron microwave source: The microwave power source produces high amplitude microwaves at a frequency of 2.45 GHz. This source is capable of producing up to 1.5 kW at this frequency. c. Daihen microwave tuning unit: The tuning unit automatically adjusts a three-stud tuner that matches the source and load impedances in order to maximize the power transferred to the load. This reduces the amount of reflected power to the source, which minimizes the risk of damaging the magnetron. d. Control unit: The control unit is used to monitor the forward and reflected power and toggle between automatic and manual tuning. e. Waveguide to coaxial adapter: The output of the magnetron is a WR340 rectangular waveguide, which must be converted to a coaxial transmission line to connect to the SWG. The adapter allows for such conversion. f. A 7 / 16 DIN power cable: The 7 / 16 DIN power cable was fitted with a 7 / 16 DIN to N- type adapter to connect the SWG to the magnetron power source. g. Surface Wave Generator (SWG) h. Syringe pump: The pump contains a motor that pushes on the syringe at controlled rates. This allows the ASCENT to be dispensed at constant flow rates on the order of mL / min.

[0096] Once the SWG was tuned to 2.45 GHz, the magnetron was turned on to verify that the SWG was absorbing the output power and to test for microwave leakage. A microwave leakage detector determined that the leakage was insignificant (on the order of mW per square centimeter). This test was done to make sure the SWG was safe to use without a protective enclosure.

[0097] Production of Helium Plasma via SWG

[0098] Before ASCENT can be flowed through the SWG, it was important to verify that the SWG could produce the electric field necessary to produce a plasma in an inert gas. This stepAtty. Ref. No. 0073605-000957 helped simplify the experimental setup and avoid the added complications of using a liquid propellant like ASCENT. Helium was chosen as the propellant for this trial.

[0099] Surface-wave generator products used for atomic emission spectroscopy use spark starters to initiate the plasma. It was determined this step was necessary for starting the helium plasma after unsuccessful attempts were made to ignite it. A handheld spark generator (ETP BD-10A) was used as the sparking device. The tip of the spark generator was brought close to the exposed quartz tube. Once the spark reached the quartz tube, there was immediate plasma formation.

[0100] Experimental Setup with Solid-State Power Source The solid-state power source experimental setup, as depicted in FIG. 10, consisted of the following components: a. DC power supply: The power supply takes 60-Hz, 120-Vaccurrent and outputs a constant-voltage DC current for the SSPA. b. Solid-state power amplifier (SSPA): The SSPA amplifies an input signal of 2.45 GHz. This is far more compact than the magnetron power source; however, it needs an input signal from a separate signal generator. c. Signal generator: The signal generator provides the input signal to the SSPA. It controls the output power from the SSPA by supplying a varying input power. This input power is in the range of 0 to 12 dBm (decibel milliwatt). d. Surface Wave Generator (SWG) e. Heat sink and cooling fans: This provides thermal control to the SSPA, which can heat up significantly when operating. f. Step-up transformer for cooling fans: The cooling fans use 240-Vacpower, so the step- up transformer converts 120-Vacto 240-Vacfor use. g. Circulator: Whereas the SSPA contains an internal circulator, it was not initially known how much reflected power the SSPA would be subjected to. In order to protect the SSPA from larger amounts of reflected power than it could handle, an additional circulator was added to redirect the reflected power to a load. h. Dual directional coupler: The directional coupler is used to measure the forward and reflected power going to and coming from the SWG. The directional coupler “bleedsAtty. Ref. No. 0073605-000957 off” a small amount of power (–50 dB with respect to the actual forward and reflected power) to send to power sensors. i. Power sensor and power meter (2×): The power sensors and meters allow for the monitoring of the forward and reflected power. j. High power coaxial cable: This allows for the coaxial transfer of microwave power directly from the SSPA to the SWG. This 7 / 16 DIN cable is capable of transferring up to ~ 500 W of power between the source and load. k. 300-W coaxial load: The coaxial load acts as a sink for the reflected power coming from the SWG. This is connected to the circulator and dissipates the reflected power as heat. l. Syringe pump: The pump contains a motor that pushes on the syringe at controlled rates. This allows the ASCENT to be dispensed at constant flow rates on the order of mL / min.

[0101] The signal generator produces the 2.45-GHz signal and the solid-state power amplifier (SSPA) amplifies the signal by 43 dB. The connection between the signal generator and SSPA input can be coaxial (SMA), and the SSPA output can also be coaxial (N-type).

[0102] The signal generator provides an RF signal to the SSPA, which amplifies that signal. The signal travels through a circulator, which redirects any reflected power to the load. Transmitted power is passed through a directional coupler, which determines forward and reflected power with power sensors and meters.

[0103] The solid-state power amplifier had a maximum power delivery of 550 W at 50 V, 20 A (equating to an efficiency of 55%). However, there were several factors that limited the amount of forward power that was able to be delivered to the SWG. The bidirectional coupler had a maximum allowable forward power of 400 W. There are also losses throughout the system, including line loss in the 7 / 16 DIN power cable and attenuation in the circulator and N-type connectors and adapters. The input power is increased by increasing the power level on a signal generator that is outputting at 2.45 GHz.

[0104] The SSPA operates with a gain of 43 dB. However, it experiences compression as the output power approaches 550 W. FIG. 13 depicts the compression of the SSPA power output. Two signal generators were used to collect this data. The power levels from the first signal generator were controlled by hand and the power levels from the second signal generator wereAtty. Ref. No. 0073605-000957 controlled via software installed on a computer. The latter signal generator is used for remote testing applications.

[0105] This non-linear relationship between input signal strength and output power is important to characterize when remote control of the signal generator is required. Since this relationship is not linear, a curve was fitted to the plot in FIG. 14, which gave an equation that can be used to determine the input power level for a desired value of the output power. This is necessary if the power meters are removed from the experimental setup.

[0106] For the experimental solid-state power source setup, a 550-W (550 watt) SSPA was used. The 550-W SSPA was chosen due its implementation in aircraft emergency power units (EPUs), which is a contemplated use case for the SWG. The 550-W SSPA requires a turn-on signal of 5.6 VDC at 0.05 A. A data acquisition (DAQ) system can also be connected to the additional pins on the SSPA to monitor the forward power, reflected power, temperature, and attenuation. Thus, this SSPA can be monitored remotely, which is important for testing for the aircraft EPU application.

[0107] Reflected power was a concern for the SSPA. While there is a built-in circulator in the SSPA, it is unknown how much reflected power it can handle. This was not a concern in the magnetron setup, as the magnetron has automatic tuning and the ability to dissipate hundreds of watts of reflected power for short durations. Therefore, a circulator was implemented, as shown in FIG. 10. The circulator requires an N-type load with which to reject the power.

[0108] Proof-of-Concept of Liquid Monopropellant Ignition using the SWG

[0109] With the transition to solid-state power and demonstration of helium ignition, the experimental setup was altered to provide ASCENT to the inner conducting tube. A syringe pump was used to control the mass flow rate of the ASCENT. The syringe pump can pump liquid at mass flow rates on the order of mL / min, with a precision of 0.1 mL / min. Care is taken to relieve all components of air pockets, including the syringe, plastic tubing, and the inner conductor of the SWG. If air were to remain in the setup, this could cause instabilities in the decomposition of the monopropellant.

[0110] When preparing to ignite the monopropellant, the inner conductor is filled with ASCENT as previously mentioned. This is accomplished by running the syringe pump at ~ 1 mL / min until ASCENT is seen in the quartz tubing at the outlet of the SWG. This visual confirmation of the propellant in the quartz tube shows that the propellant line is filled withAtty. Ref. No. 0073605-000957 ASCENT and, thus, there will be no lag in the ignition once the power source is turned on. However, this also means that the quartz in the gap region of the SWG is flooded with propellant. In order to eliminate ASCENT from this region, a piece of tissue can be inserted into the quartz opening until the ASCENT has been absorbed and removed. Propellant in the gap region of the SWG cavity can be detrimental to the electric field due to the differing dielectric constants of air and ASCENT.

[0111] Smelting of Ilmenite Sand

[0112] While the SWG was designed and fabricated for the ignition of ASCENT, it was theorized that the cavity could also be used to smelt solids, such as components of lunar regolith in aerospace applications. If the SWG is able to smelt ilmenite, then it could theoretically be used as a method of continuously smelting ilmenite granules if the ilmenite were entrained in a carrier gas and sent through the SWG. As a preliminary step in the implementation of this idea, it was necessary to demonstrate that the SWG could smelt ilmenite that is stationary in the inner conductor.

[0113] For this experimental setup, the propellant line was removed and the inlet side of the inner conductor was capped. Ilmenite was funneled into the quartz opening of the outlet until there was complete coverage of the ilmenite in the gap region of the SWG, as depicted in FIG. 12A.

[0114] While ilmenite only represents a fraction of lunar regolith, it was assumed that the ilmenite could be isolated from the bulk of the regolith. Ilmenite was originally placed in a microwave oven where it subsequently melted, showing that it reacts with electric fields. This gave rise to the prospect of smelting ilmenite in the SWG.

[0115] For this test, the ilmenite was stationary in the dielectric tube. The objective was to observe how the ilmenite reacts inside the SWG, and therefore, the stationary ilmenite was sufficient for the proof-of-concept.

[0116] Results and Discussion

[0117] The results and discussion below detail the results of the experiments described above. The objective of this research was to describe the ignition characteristics of ASCENT using a SWG igniter. Therefore, the mass flow rate and forward input power were measured when applicable. The powers were obtained by observing the readings on the power meters.

[0118] Helium Gad Ignition CharacteristicsAtty. Ref. No. 0073605-000957

[0119] Helium gas was ignited with the SWG at a forward power of 200 W and a mass flow rate of 0.3 standard liters per minute (SLM). A spark generator was needed to start the ignition. The mass flow rate was decreased by intervals of 0.05 SLM until the mass flow rate was 0.1 SLM. No visual changes in the intensity of the helium plasma were observed as the mass flow rate was decreased. Then, the input power was decreased until the helium plasma extinguished at approximately 170 W. As the power decreased to the extinguishing point, the helium plasma began making a distinct shrieking noise. The presence of this noise as the power was being decreased was consistent among all of the helium tests. The helium plasma was purple in color.

[0120] Ignition Characteristics of ASCENT

[0121] Unlike with helium, ASCENT was able to self-ignite without the use of a spark generator. The ability to self-ignite is a substantial result, as this eliminated the need to develop a sparked ignition system for remote testing of the SWG. The lack of a sparked ignition system reduces the complexity of this device and eliminates a point of failure were the SWG to be further developed for specific applications. Ignition was achieved for as long as 99 seconds. This was the longest continuous test. Failure did not occur in this time frame, so this is the lower bound for the possible continuous burning duration.

[0122] Power

[0123] The purpose of this first set of tests with ASCENT was to characterize the dependence of ignition on the input power to the SWG. These tests were performed at a mass flow rate of 0.5 mL / min. Self-ignition was repeatably demonstrated at a power of 200 W.

[0124] It is noted that these tests were performed with the magnetron power source with automatic tuning enabled. Tests using the SSPA power source require a higher input power to the SWG as the reflected power is much greater than with the magnetron. With the SSPA, ignition occurred at forward power values ranging from 390 to 430 W (10.5 to 11 dBm on the signal generator) with measured reflected powers ranging from 225 to 250 W.

[0125] Mass Flow Rate

[0126] The purpose of this subsequent set of tests with ASCENT was to determine the maximum mass flow rate at which the SWG was capable of igniting ASCENT. This result is of interest for the aircraft EPU application, with a mass flow rate of 10 mL / min being desired. At an input power of 300 W, the mass flow rate was varied between 0.5 and 9.5 mL / min in steps of 1 mL / min.Atty. Ref. No. 0073605-000957

[0127] Ignition of ASCENT was immediate at 0.5 mL / min and ignition was sustained throughout the entirety of the test (through and including 9.5 mL / min). However, there was an increasing amount of unignited propellant that was expelled from the outlet of the SWG as the mass flow rate was increased. Therefore, while smoke was observed at 9.5 mL / min, the presence of liquid propellant being ejected from the outlet means that complete decomposition did not occur. Since the unignited propellant was ejected from the quartz tube as far as 12 inches, it was not possible to estimate the ratio of unignited and ignited propellant since the ejected propellant could not be recollected and measured.

[0128] Verification of Ignition with Flooded Cavity

[0129] When connected to a VNA, the SWG S11value decreases from –7 dB to –2 dB when air in the gap region of the SWG is replaced with ASCENT. In other words, the S11absorption peak is flattened out when the propellant is introduced into the quartz tube. This effect was known to be detrimental to the electric field that the SWG produces, but it was still of interest to determine whether a flooded quartz tube can still achieve ignition. This flooded condition may occur if the SWG needs to be extinguished and reignited, in which case there is nothing to remove the ASCENT from the quartz tube.

[0130] With propellant filling the quartz tube in the gap region of the SWG, ignition was still achieved at (0.5 mL / min and approximately 390 W), and the expansion of the exhaust gases of the ASCENT in the quartz tube ejected the downstream liquid propellant from the quartz tube. It took approximately 69 milliseconds (ms) to achieve ignition with a flooded cavity, which shows how quickly the flooded cavity condition is reverted to the nominal state. This proves that re- ignition is possible with the SWG.

[0131] Smelting of Ilmenite via SWG

[0132] The SWG was able to smelt ilmenite after exposed to the strong electric field for 30 seconds. Over this 30-second test, the power was gradually increased from 40 to 250 W. This proof-of-concept test resulted in a thin line of fused ilmenite that formed along the gap region of the SWG, which can be seen in FIGS. 12B-C. This thin line extended both forward and aft of the gap region, suggesting that the strong electric field propagates both forward and backward in and along the quartz tube. The ilmenite essentially acted as an analog electric field detector. Thus, the length of the region where the strong electric field exists was larger than anticipated. ItAtty. Ref. No. 0073605-000957 was initially thought that the strong electric field only existed in the length of the gap region; however, this test implies that the electric field extends beyond this region.

[0133] Challenges Encountered with the SWG Setup

[0134] There were several challenges that were encountered during the testing of the SWG with helium and ASCENT. The main challenge was the melting of the disc antennas due to arcing. The SWG needed to be cleaned and rebuilt with a new candlestick and disc antenna after a short period of ignition time (on the order of minutes). This poses a significant reliability challenge if the SWG needs to be on for extended durations. The arcing was caused by the disc’s proximity to the front plate of the SWG cavity (approximately 2 mm). This caused melting of the antenna, vaporization and deposition of Teflon from the candlestick antenna on the cavity walls and inner conductor, and pitting on the front stainless steel plate from arcing. The pitting did not result in any quantifiable changes in performance.

[0135] There were two iterations of the antenna assembly, the second necessary due to the aforementioned arcing. The first iteration consisted of a copper disc that was press-fit to the candlestick antenna and subsequently soldered in place. There were multiple problems with this configuration. The first was that copper has a relatively low melting point (1084 °C) compared to the temperature of the arc, which can exceed 3000 °C. Melting, and even vaporization, of the copper antenna occurred repeatedly. Another problem was with the solder connection between the candlestick antenna and the copper disk. If the copper was not fit tight enough to the candlestick, the solder would easily melt with the heat produced from arcing and the disk would fall off.

[0136] The second iteration of the antenna assembly consisted of a titanium disk that was screwed onto the candlestick antenna. Titanium was chosen for its higher melting point (1668 °C) and its relative ease of fabrication in comparison to tungsten. A hole punch was used to punch 1-cm-diameter disks out of a titanium sheet. The hole punch would leave the disks deformed, so each antenna was flattened in a vice between two aluminum plates. A hole that is slightly smaller than the diameter of the candlestick was drilled into the titanium disk. A jeweler’s tap and die set was used to create threads in the disk and on the candlestick, which would allow the disk to screw onto the candlestick. This mechanical connection proved to be a more reliable option and even allowed for disassembly of the antenna assembly between uses. Arcing still occurred between the titanium disk and the front plate and resulted in the melting ofAtty. Ref. No. 0073605-000957 the front of the titanium disk; however, this process was much slower and less pronounced than with the copper disks.

[0137] The final major challenge was the sensitivity of the tuning characteristics of the SWG. The SWG is only tuned via sliding the inner tube in and out to vary the gap length. Very small changes in the gap length (on the order of 0.1 mm) can change the tuned frequency enough to be completely out of the 2.45-GHz range. Additionally, twisting the inner tube with respect to the SWG body resulted in changes in the peak absorption value. This was due to imperfections in the inner conductor–quartz tube assembly resulting in axial-asymmetry. The inner conductor was fastened using a hose clamp. As the hose clamp was tightened, the tuned frequency would tend to shift. Therefore, the inner tube had to be shifted past the 2.45-GHz tuning point in order to account for the frequency change upon tightening. Once tightened, pressure on the inner tube or quartz tube could shift the peak absorption frequency. Care had to be taken to ensure there was no tension in the connection between the syringe pump and inner conductor.

[0138] Conclusions

[0139] Originally conceived for the replacement of hydrazine with liquid green monopropellants in the aircraft EPUs, the SWG has proven to be multifaceted in its possible applications. The SWG has subjected solids, liquids, and gases to a strong electric field without having the subjects come in contact the inside of the SWG cavity. Therefore, the SWG may be considered an effective device for subjecting many different media to strong electric fields, given that they can fit within the 3-mm ID quartz tube.

[0140] Summary

[0141] The surface wave generator was initially conceived in the 1970s, and for the last several decades it has aided in atomic emission spectroscopy as a means of producing columns of plasma. The SWG described herein has shed light on a variety of additional applications for the SWG nearly 50 years after its invention. To our knowledge, these experiments are the first examples of a SWG igniting a liquid.

[0142] The primary purpose of the SWG described herein was to ignite ASCENT using solid- state microwave power at a frequency of 2.45 GHz. The SWG was able to ignite the green monopropellant at flow rates varying from 0.5 to 9.5 mL / min and powers as low as 200 W for ignition start-up. At high flow rates and low powers, the ASCENT would not completely dissociate, leading unburned propellant to spray from the quartz tube. The ASCENT did notAtty. Ref. No. 0073605-000957 need to be ignited with a spark generator like the helium required. The ability to self-ignite reduces the complexity, as a spark-ignition system would needed to have been designed and integrated into the SWG system. Instead, igniting ASCENT in the SWG is as straightforward as turning on the power supply. Ignition is nearly instantaneous, and as long as there is ASCENT in the gapped region of the quartz tube, the ignition delay cannot be discerned with the naked eye.

[0143] The SWG has proven to be reliable and robust in its operation. Once properly tuned, the SWG repeatably ignited and re-ignited ASCENT at 200 W, leading to the conclusion that the SWG can operate in a pulsed mode. The SWG was even able to ignite ASCENT with a flooded gapped region, even though the VNA showed that the S11parameter was significantly reduced when ASCENT is present in the gap. While antenna degradation and melting was a reoccurring problem, the SWG was still able to ignite ASCENT with a significant portion of the antenna being melted off. This attributes to the robustness of the SWG. Additionally, antenna degradation and / or melting can be mitigated or remedied through a variety of techniques. For example, altering the distance between the antenna body and / or disk and the end wall of the SWG, evacuating the air from within the SWG cavity, and / or replacing the existing gas / air within the SWG cavity with an arc-quenching gas (e.g., sulfur hexafluoride, etc.).

[0144] It was found that the SWG was sensitive with regard to its tuning characteristics. Several adjustments to the inner conductor had to be made to limit its movement within the SWG cavity, where even slight adjustments (even slight rotations of the inner conductor) could push the peak absorption frequency out of the 2.45 GHz-range. Care was taken to make sure that no pressure was applied to the inlet end of the inner conductor, which would cause the tube to shift within the cavity. It is possible that this problem could be solved with tighter tolerances between the inner conductor and the upstream wall of the SWG. The SWG was tuned by changing the length of the gap between the front of the inner conductor and the downstream wall of the SWG. The gap needed to be adjusted by tenths of a millimeter. A deviation of that size from the tuned gap length resulted in the cavity being completely out of tune.

[0145] The SWG was able to smelt lunar regolith simulant with less than 250 W of power. Even though the regolith simulant was stationary in the quartz tube, this test still concluded that the ilmenite was able to react to the electric field produced by the SWG. This could be aAtty. Ref. No. 0073605-000957 significant development in the ability to produce usable ores from the lunar environment, aiding in the goal of broader lunar in-situ resource utilization.

[0146] Example 2

[0147] It was noticed early in the design process of the SWG system that it was being designed for a very specific application before its operation was generally understood. Through its development for the aircraft EPU application, it became apparent that the SWG had much broader uses as a device to subject nearly any medium to a strong electric field. After this was understood, several additional applications became known. The most obvious application could be its use as an in-space thruster for small-satellite orbit keeping and attitude control. Another application could be its use for self-pressurizing a propellant tank. Research should be conducted to determine how the SWG behaves in a vacuum. Several propellants could be used, including ASCENT, liquid, or vapor water and other gases like argon and nitrogen. A thrust stand would need to be developed to determine the thrust and Isp (specific impulse) of the SWG. Several propulsion tests could be performed, including long-duration thrusts, pulsed thrusts, and throttling capability. As the technology readiness level of a SWG thruster increases, efforts could be made to develop a compact system which integrates the components into a 3U or smaller module.

[0148] It should be understood that the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points. It should also be appreciated that some components, features, and / or configurations may be described in connection with only one particular embodiment, but these same components, features, and / or configurations can be applied or used with many other embodiments and should be considered applicable to the other embodiments, unless stated otherwise or unless such a component, feature, and / or configuration is technically impossible to use with the other embodiment. Thus, the components, features, and / or configurations of the various embodiments can be combined together in any manner and such combinations are expressly contemplated and disclosed by this statement.

[0149] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible considering the above teachings of the disclosure. The disclosed examples and embodiments are presented for purpose of illustration only. Other alternate embodiments may include some or all of the features disclosed herein.Atty. Ref. No. 0073605-000957 Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof.

[0150] It should be understood that modifications to the embodiments disclosed herein can be made to meet a particular set of design criteria. Therefore, while certain exemplary embodiments of the compositions, materials, apparatuses, and methods of using and making the same disclosed herein have been discussed and illustrated, it is to be distinctly understood that the invention is not limited thereto but may otherwise be variously embodied and practiced within the scope of the following claims.

Claims

Atty. Ref. No. 0073605-000957 WHAT IS CLAIMED IS:

1. A surface-wave-generating device comprising: an outer chamber comprising: a first end and a second end opposite the first end; a first wall extending from the first end to the second end; a second wall extending from the first end to the second end and opposite the first wall; a third wall extending from the first end to the second end and intermediate the first wall and the second wall; a fourth wall extending from the first end to the second end and opposite the third wall; wherein the outer chamber defines an inner resonant cavity extending from the first end to the second end, from the first wall to the second wall, and from the third wall to the fourth wall; an inner conductive chamber disposed within the inner resonant cavity and extending from the first end toward the second end, wherein the inner conductive chamber defines an electric-field-producing gap intermediate the inner conductive chamber and the second end; and a media flow chamber disposed within the inner conductive chamber and extending from the first end to the second end such that a portion of the media flow chamber adjacent the second end passes through the electric-field-producing gap.

2. The surface-wave-generating device of claim 1, wherein the outer chamber further comprises:Atty. Ref. No. 0073605-000957 a first faceplate removably attachable to the first end, wherein the first faceplate defines a first aperture adjacent the inner conductive chamber such that the media flow chamber extends through the first aperture; and a second faceplate removably attachable to the second end, wherein the second faceplate defines a second aperture adjacent the electric-field-producing gap such that the media flow chamber extends through the second aperture.

3. The surface-wave-generating device of claim 2, wherein the outer chamber further comprises a power input port disposed on an exterior surface of the outer chamber and extending into the inner resonant cavity.

4. The surface-wave-generating device of claim 3, further comprising a power input antenna disposed within the power input port and extending into the inner resonant cavity.

5. The surface-wave-generating device of claim 4, wherein the power input antenna comprises an n-type candlestick antenna having a conductive disk disposed within the inner resonant cavity and adjacent the electric-field-producing gap.

6. The surface-wave-generating device of claim 1, wherein each of the first, second, third, and fourth walls comprise a first, second, third, and fourth curvature, respectively, such that the outer chamber comprises a cylinder, and wherein the inner conductive chamber and the media flow chamber each comprise cylinders.

7. The surface-wave-generating device of claim 6, wherein the outer chamber and the inner conductive chamber comprise stainless steel.

8. The surface-wave-generating device of claim 6, wherein the media flow chamber comprises quartz.Atty. Ref. No. 0073605-000957 9. The surface-wave-generating device of claim 6, wherein the inner resonant cavity comprises a length of approximately 78 millimeters (mm) and a diameter of approximately 40.8 mm, wherein the inner conductive chamber comprises an outer diameter of approximately 6.35 mm, and wherein the media flow chamber comprises an outer diameter of approximately 5 mm.

10. The surface-wave-generating device of claim 1, wherein the electric-field-producing gap comprises a gap distance within a range of approximately 0.7 to 1 mm.

11. A process for exciting media via exposure to a microwave electric field comprising the steps of: depositing the media into a media flow chamber, wherein the media flow chamber is disposed within an inner conductive chamber, wherein the inner conductive chamber is disposed within an inner resonant cavity defined by an outer chamber having a first end and a second end opposite the first end, and wherein the inner conductive chamber extends from the first end toward the second end such that the inner conductive chamber defines an electric-field-producing gap intermediate the inner conductive chamber and the second end, wherein the media flow chamber extends through the second end such that the media flow chamber passes through the electric-field-producing gap, and wherein the media is deposited into the media flow chamber such that the media flows from the first end toward the second end and passes through the electric-field-producing gap; supplying electrical microwave power at a predetermined frequency to a power input port of the outer chamber, wherein the power input port extends into the inner resonant cavity, wherein the electrical microwave power generates an electric field in the electric-field-producing gap.

12. The process of claim 11, wherein the outer chamber further comprises:Atty. Ref. No. 0073605-000957 a first faceplate removably attachable to the first end, wherein the first faceplate defines a first aperture adjacent the inner conductive chamber such that the media flow chamber extends through the first aperture; and a second faceplate removably attachable to the second end, wherein the second faceplate defines a second aperture adjacent the electric-field-producing gap such that the media flow chamber extends through the second aperture.

13. The process of claim 11, wherein the power input port comprises a power input antenna, wherein the power input antenna extends from the power input port into the inner resonant cavity.

14. The process of claim 13, wherein the power input antenna comprises an n-type candlestick antenna having a conductive disk disposed within the inner resonant cavity and adjacent the electric-field-producing gap.

15. The process of claim 11, wherein the outer chamber, the inner conductive chamber, and the media flow chamber each comprise cylinders.

16. The process of claim 15, wherein the outer chamber and the inner conductive chamber comprise stainless steel.

17. The process of claim 16, wherein the media flow chamber comprises quartz.

18. The process of claim 15, wherein the inner resonant cavity comprises a length of approximately 78 millimeters (mm) and a diameter of approximately 40.8 mm, wherein the inner conductive chamber comprises an outer diameter of approximately 6.35 mm, and wherein the media flow chamber comprises an outer diameter of approximately 5 mm.

19. The process of claim 11, wherein the electric-field-producing gap comprises a gap distance within a range of approximately 0.7 to 1 mm.Atty. Ref. No. 0073605-000957 20. The process of claim 11, wherein the predetermined frequency comprises a frequency of approximately 2.45 Gigahertz (GHz).

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