Method for manufacturing a hollow waveguide device and hollow waveguide device

Abstract

A method for manufacturing a hollow waveguide device (1) for transmission of radio frequency electromagnetic waves comprises a support body manufacturing step including the manufacture of a support body (2) made from a support body material (3). Afterwards, a coating step including coating at least a region of a surface (5, 10) of the support body (2) with an waveguide coating (6) made from an electrically conductive material. A thickness of the waveguide coating (6) is less than 0.5 mm. The method further comprises a support body removal step including the removal of the support body (2) from the remaining waveguide coating (6) and a stability enhancement step including the addition of a supporting structure (11) onto at least a region of a surface of the waveguide coating (6).

Description

Technical Field

[0001] The invention relates to a method for manufacturing a hollow waveguide device comprising a support body manufacturing step including the manufacture of a support body, further comprising a coating step including coating at least a region of a surface of the support body with a waveguide coating made from an electrically conductive material. The invention also relates to a hollow waveguide device for radio frequency electromagnetic waves with a cavity that extends in one direction of propagation of the electromagnetic waves.State of the Art

[0002] In the field of radio frequency signal transmission, the manufacturing of hollow waveguide units with a low net weight can be challenging. Usually, common manufacturing techniques involve extrusion, CNC machining and injection moulding. With the exception of straight line hollow waveguide sections, such manufacturing methods typically necessitate dividing the waveguide block into a minimum of two parts to facilitate the manufacturing process.

[0003] It is well known in prior art to manufacture a channel body with at least one channel recess that extends in a direction of propagation as one-piece made of metal, to manufacture a lid body by the same or similar manufacturing methods, and to mount the lid body onto the channel body in a manner that prevents any gap along a contact line between the channel body and the lid body that surrounds a channel recess, as any gap between the metal bodies allows for unwanted leakage of radio frequency electromagnetic waves, resulting in a significant weakening of the electromagnetic wave signal that is transmitted along the hollow waveguide device.

[0004] In high microwave frequencies, particularly for wavelengths of electromagnetic waves in the range of millimetres, effectively managing and minimizing leakage of electromagnetic waves through gaps within metallic inner walls or other openings is considered critical, but challenging. Achieving radio frequency transmission without power leakage usually necessitates securing the split parts tightly, e.g. with welding also known as dip brazing, or with screws, i.e. mounting and fixing the lid body onto the channel body by a number of screws that are arranged along a contact line around the channel recess that forms the cavity. The quantity of screws that is needed depends on the flatness of the surfaces, the operating frequency, and the location of the separation plane. The use of screw mount clamping is a widely recognized and economical technique for assembling waveguides comprising two or multiple parts.

[0005] Mounting split parts with screw fasteners imposes significant constraints on the design, usually necessitating a bulky structure, dedicated space for the arrangement of screws around each channel recess, and specific wall thicknesses of the channel body and the lid body along the contact line to be able to absorb the forces for the required contact pressure that is exerted by the screw connection. This limitation not only hampers design flexibility but also adds significant weight to the hollow waveguides, rendering them more expensive.

[0006] In order to reduce the weight of such hollow waveguide devices, it is known in prior art to make use of suitable polymer materials to manufacture such hollow waveguide devices. Usually, a trough-shaped channel body and a lid body are formed from a dielectric polymer material and subsequently coated with a metallic coating. Even though the density of many suitable polymer materials is usually smaller than the density of metallic materials, this change of material usually results in a weight reduction of approx. 50% or 60%, but requires an additional manufacturing step of adding a suitable coating of a metallic material to the channel body and the lid body that are formed from polymer material. A further reduction of weight is desirable, in particular for enabling extensive use of such hollow waveguide devices for applications in the aerospace industry.

[0007] Thus, there is a need for a hollow waveguide device with low weight and small size that does not exhibit significant radio frequency leakage, but is cost-effective to manufacture.Summary of the Invention

[0008] The present disclosure relates to a method for manufacturing a hollow waveguide device as described above, characterized in that a thickness of the waveguide coating is less than 0.5 mm, further comprising a support body removal step including the removal of the support body from the remaining waveguide coating, and further comprising a stability enhancement step including the addition of a supporting structure onto at least a region of a surface of the waveguide coating. Radio frequency electromagnetic waves do not penetrate deeply into a metallic material. The penetration depth can be determined and indicated, for example, via the skin depth. For radio frequency electromagnetic waves with a frequency of 1 MHz the skin depth is approx. 0.065 mm. For most applications a waveguide coating with a thickness of 3 to 5 times the skin depth is considered advantageous and sufficient for practical use. Thus, a waveguide coating with a thickness of 0.5 mm will be sufficient to act as hollow waveguide device as any radio frequency electromagnetic wave that is transmitted within the hollow waveguide device, i.e. inside of the waveguide coating, will not be able to penetrate through the waveguide coating and will be transmitted in the same manner, i.e. with the same transmission losses as within a hollow waveguide device that comprises metallic side walls with a thickness of several millimeters.

[0009] For many fields of use, the mechanical stability of the waveguide coating with such a small thickness is too low for the usual requirements or the usual applications. Thus, a supporting structure is required. However, the supporting structure does not have to be made of metal, but can be made of any material with sufficient mechanical strength. There are many materials known in prior art that will provide sufficient mechanical strength but are very light in weight and, in particular, significantly lighter than metal.

[0010] According to a favorable aspect of the invention, the thickness of the waveguide coating can be less than 0.1 mm and preferably less than 0.05 mm. For most applications and in particular for radio frequency electromagnetic waves with a high frequency of more than e.g. 100 MHz, a metallic waveguide coating with such a small thickness provides for a hollow waveguide device with excellent transmission characteristics and low losses during transmission of the radio frequency electromagnetic waves, but are very lightweight though. A combination of a waveguide coating with such a small thickness and a supporting structure made of a lightweight material like e.g. a polymer foam material provides for hollow waveguide devices with similar transmission characteristics compared to prior art devices, but a weight that is less than one-tenth of the weight of said prior art device.

[0011] It is considered very advantageous that the support body is made from a material which can be removed from the waveguide coating by mechanical removal, chemical removal or thermal removal. There are many material removal techniques known in prior art that can be used for the removal of the support body. Mechanical removal of the support body material can be performed by milling. However, chemical removal including e.g. dissolving the support body material with help of solvents or stripper solutions or thermal removal including e.g. heating the support body with the waveguide coating up to a high temperature that results in melting away the support body material are considered less demanding for the waveguide coating. The support body removal step is preferably performed fully automatic and without any manual interaction or manual control.

[0012] According to a very favorable embodiment of the invention, during the coating step an outer surface of the support body is coated with the waveguide coating in such a manner as to provide a waveguide coating that forms a hollow waveguide. Coating surfaces of a support body can be performed by many different methods known in prior art, e.g. by electroplating or electroless plating, by chemical or physical vapor deposition, by vacuum metallizing or by different spraying methods. Providing a coating to outer surfaces allows for rapid coating of large surfaces. Furthermore, coating outer surfaces is usually less demanding and facilitates the manufacturing of very even coatings. In addition, as the coating is applied onto the outer surface of the support body, any variation on thickness or uniformity of the coating will affect the outside of the coating and thus will not interfere with the inner surface of the coating which is defined by the outer surface of the support body. Therefore, any variation of thickness or non-uniformity of the waveguide coating does not impact the inner surfaces of the waveguide coating that encloses the cavity of the hollow waveguide device in which electromagnetic waves can propagate.

[0013] According to yet another aspect of the invention, the stability enhancement step is performed before the support body removal step is performed. Thus, the support body removal step that removes the support body does not does not cause the thin waveguide coating to remain free-standing, but the waveguide coating is supported and stabilized by a support structure made of a suitable stability enhancing material, preferably surrounding and embedding the waveguide coating.

[0014] According to an alternative embodiment of the invention, during the coating step an inner surface of a cavity formed within the support body is coated with the waveguide coating in such a manner as to provide a waveguide coating that forms a hollow waveguide. Then, the support body removal step is performed before the stability enhancement step is performed. For some applications the desired design of the hollow waveguide device allows for the arrangement of the support body at the outside of the waveguide coating that is then added onto the inner surfaces of a cavity formed within the support body. The support body can be composed of multiple parts that have been manufactured separately and that have been assembled afterwards to form the support body with the cavity. For many applications, it is considered advantageous to manufacture the support body with a cavity inside e.g. with extrusion processes.

[0015] In yet another aspect of the invention, the stability enhancement step includes the deposition of an electrically non-conductive stability enhancement material at the outer surfaces of the waveguide coating. Such a stability enhancement material may be selected from any suitable lightweight material that provides sufficiently mechanical stability and support, but does not interfere with the transmission of electromagnetic waves along the hollow waveguide device. A suitable stability enhancement material can be deposited onto the outer surfaces of the waveguide coating by well-known methods like e.g. injection molding or resin potting. It is also possible to deposite a suitable electrically non-conductive stability enhancement material with additive manufacturing methods like e.g. 3D printing or by adding several layers of a stability enhancement material one after another.

[0016] It is considered a very favorable embodiment of the invention that the waveguide coating is embedded within an enclosing supporting structure made of a polymer foam material. A rigid polymer foam made from a suitable polymer material provides for very high mechanical strength in combination with a very low weight. Even more so a microcellular foam or nanocellular foam provides for high strength with very small cells, which is well-known for use in lightweight structural applications. By selecting a suitable polymer material, the manufacturing of a supporting structure made of a polymer foam material can be easily performed at very low costs. Furthermore, there are many suitable polymer materials which are insensitive to environmental conditions and can be used in outer space as well.

[0017] Preferably, the stability enhancement material is a dielectric material with a density less than 800 kg / m 3< , more preferably with a density less than 250 kg / m 3< . Suitable stability enhancement materials can be foams made from polymer materials like e.g. polystyrene foam, expanded polystyrene or extruded polystyrene foam. Many other materials like e.g. silica aerogels, carbon nanotube aerogels, metallic foams, other polymeric foams or metallic microlattices can also be considered as suitable stability enhancement materials with favorable characteristics. In particular lightweight or ultralight materials that have been developed for and that are used within aircraft and aerospace applications. Some of these ultralight materials are solids with a density of less than 100 kg / m 3< down to approx. 10 kg / m 3< or less and are also considered as suitable stability enhancement materials.

[0018] According to yet another favorable aspect, during the stability enhancement step the waveguide coating is arranged within an outer casing and that a free space between the outer surface of the waveguide coating and the outer casing is filled by a polymer foam material. There a many different methods known in prior art for generating the polymer foam within such a free space like e.g. gas injection, reaction injection molding, extrusion foaming or spray foaming. The design of the outer casing can be adapted to define the outer shape of the supporting structure. Thus, no additional manufacturing step is required to work out and finalize the outer shape of the supporting structure.

[0019] The invention also relates to a hollow waveguide device for radio frequency electromagnetic waves with a cavity that extends in one direction of propagation of the electromagnetic waves. Such hollow waveguide devices are usually manufactured from a single block of metal using machining processes that remove material in order to generate one body or several parts of the hollow waveguide device that must be assembled to form the closed cavity hollow waveguide device. However, such hollow waveguide devices made from metallic parts usually have a high dead weight.

[0020] It is considered a further object of this invention to provide for a hollow waveguide device with a very low weight that do not exhibit significant radio frequency leakage and are cost-effective to manufacture.

[0021] Thus, the present disclosure also relates to a hollow waveguide device as described above, characterized in that the hollow waveguide device comprises a waveguide coating made from an electrically conductive material that encloses the cavity in which electromagnetic waves can propagate, whereby a thickness of the waveguide coating is less than 0.5 mm, and whereby an electrically non-conductive stability enhancement material is arranged at the outer surfaces of the waveguide coating for providing mechanical stability to the waveguide coating. The electrically conducting surfaces that are required for transmission of radio frequency electromagnetic waves and for forming a hollow waveguide device are provided by a very thin waveguide coating that do not add significant weight to the hollow waveguide device, but are sufficient to prevent substantial leakage of the electromagnetic waves from the cavity that is surrounded by the thin waveguide coating. The mechanical stability of the hollow waveguide device is provided by the stability enhancement material that is arranged at the outer surfaces of the waveguide coating. The stability enhancement material can be any material that provides for mechanical stability like, e.g. a suitable polymer material with a specific weight that is significant less than the specific weight of the electrically conductive material that is used for the manufacture of the waveguide coating, e.g. a metallic material.

[0022] It is considered a favorable aspect of the invention that the thickness of the waveguide coating can be less than 0.1 mm, preferably less than 0.05 mm. A waveguide coating of this thickness provides good transmission characteristics of the hollow waveguide device with respect to radio frequency electromagnetic waves, but does not contribute significantly to the overall weight of the hollow waveguide device.

[0023] Preferably, the waveguide coating is at least partially surrounded by a polymer foam material. The surrounding polymer foam material is designed to provide for a supporting structure with high mechanical stability. In case that the waveguide coating is fully embedded into the polymer foam material, the surrounding polymer foam material also provides for protection against mechanical wear and tear of the thin waveguide coating that defines the propagation of the radio frequency electromagnetic waves.Brief description of the drawings

[0024] The present invention will be more fully understood, and further features will become apparent, when reference is made to the following detailed description and the accompanying drawings. The drawings are merely representative and are not intended to limit the scope of the claims. In fact, those of ordinary skill in the art may appreciate upon reading the following specification and viewing the present drawings that various modifications and variations can be made thereto without deviating from the innovative concepts of the invention. Like parts depicted in the drawings are referred to by the same reference numerals. Figs. 1 to 5 schematically illustrate consecutive steps of a method for manufacturing a hollow waveguide device, and Figs. 6 to 9 schematically illustrate consecutive steps of another embodiment of a method for manufacturing a hollow waveguide device.

[0025] An exemplary embodiment of a method for manufacturing a hollow waveguide device 1 which is shown in Fig. 5 is schematically illustrated in Figs. 1 to 5, whereby each Fig. illustrates the result of a step that is performed during the execution of this manufacturing method.

[0026] In order to manufacture the hollow waveguide device 1, a support body manufacturing step is performed, whereby a support body 2 is made from a support body material 3 that can be easily removed later on. The support body 2 comprises a cavity 4 that is surrounded by support body material 3. Inner surfaces 5 surround the cavity 4 and determine its shape. Such a support body 2 is shown in Fig. 1. A suitable support body material 3 can be e.g. a dielectric polymer material.

[0027] Fig. 2 illustrates the result of a coating step that is performed after the body manufacturing step. During the coating step all inner surfaces 5 defining the cavity 4 within the support body 2 are coated with a waveguide coating 6 made from an electrically conductive material, e.g. a metal with favorable electric conductivity characteristics. The thickness of the waveguide coating 6 is preset to e.g. 0.1 mm. The shape of the waveguide coating 6 defines the shape of a radio frequency electromagnetic wave transmitting cavity 7 of the hollow waveguide device 1 as shown in Fig. 5. For illustrative purposes, the dimensions of the waveguide coating 6 are not to scale, as the thickness of the waveguide coating 6 is e.g. 0.1 mm, whereas the characteristic dimensions of a cross-section of the support body 2 are e.g. centimeters.

[0028] Fig. 3 illustrates the result of a body material removal step that is performed after the coating step. The body material removal step includes the complete removal of the support body 2 i.e. of all dielectric support body material 3 without affecting the waveguide coating 6.

[0029] Afterwards, the waveguide coating 6 is arranged within an outer casing 8 for performing a stability enhancement step that includes the deposition of a stability enhancement material 9 within a free space between an outer surface 10 of the waveguide coating 6 and the surrounding outer casing 8. According to a favorable embodiment as shown in Fig. 4, the free space is completely filled by a polymer foam material that provides for a supporting structure 11 that completely surrounds the waveguide coating 6. Thus, the waveguide coating 6 is embedded within the polymer foam that is used as stability enhancement material 9. The stability enhancement material 9 can be a polymer foam material with a density of less than 800 kg / m 3< , preferably with a density less than 250 kg / m 3< and most preferably less than 100 kg / m 3< .

[0030] Fig. 5 illustrates the hollow waveguide device 1 after the removal of the outer casing 8. The hollow waveguide device 1 comprises the waveguide coating 6 that is embedded within a supporting structure 11 made from the stability enhancement material 9. By surrounding the thin waveguide coating 6 with the stability enhancement material 9, the mechanical stability of the waveguide coating 6 will be significantly enhanced and allows for the use of the hollow waveguide device 1 comprising the waveguide coating 6 and the surrounding supporting structure 11 made from the stability enhancement material 9 for applications with expected high mechanical stress during the intended service life.

[0031] An alternative method for manufacturing the hollow waveguide device 1 is exemplarily illustrated in Figs. 6 to 9. In order to manufacture the hollow waveguide device 1 as shown in Fig. 9, a support body manufacturing step is performed, whereby the support body 2 is made from the support body material 3 that can be easily removed later on. Outer surfaces 12 of the support body 2 determine the shape of the waveguide coating 6 and thus the electrically conductive surfaces of the hollow waveguide device 1. As before, a suitable support body material 3 can be e.g. a dielectric polymer material. The support body 2 is shown in Fig. 6.

[0032] Afterwards, a coating step is performed. During the coating step all outer surfaces 12 of the support body 2 are coated with the waveguide coating 6 made from an electrically conductive material, e.g. a metal with favorable electric conductivity characteristics. The thickness of the waveguide coating 6 is preset to e.g. 0.05 mm. The shape of the waveguide coating 6 defines the shape of a radio frequency electromagnetic wave transmitting cavity 7 of the hollow waveguide device 1. The support body 2 with the surrounding waveguide coating 6 is shown in Fig. 7.

[0033] After the coating step, a stability enhancement step shown in Fig. 8 is performed that includes the addition of the supporting structure 11 onto at least a region of the outer surface 10 of the waveguide coating 6. The support body 2 with the surrounding waveguide coating 6 is inserted into the outer casing 8. Then the stability enhancement material 9 is inserted into the free space between the outer surface 10 of the waveguide coating 6 and the surrounding outer casing 8. Thus, the waveguide coating 6 is embedded within the polymer foam that is used as stability enhancement material 9.

[0034] Afterwards, the body material removal step is performed. The body material removal step includes the complete removal of the support body 2 i.e. of all dielectric support body material 3 without affecting the waveguide coating 6. Fig. 9 illustrates the hollow waveguide device 1 after the performance of the body material removal step and after the removal of the outer casing 8.

[0035] Both methods allow for the easy and cost-effective manufacture of a lightweight hollow waveguide device 1. Both methods can be fully automated and adapted to manufacture large amounts of hollow waveguide devices 1 with different shapes and sizes.

Claims

1. Method for manufacturing a hollow waveguide device (1) for transmission of radio frequency electromagnetic waves comprising a support body manufacturing step including the manufacture of a support body (2), further comprising a coating step including coating at least a region of a surface of the support body (2) with an waveguide coating (6) made from an electrically conductive material, characterized in that a thickness of the waveguide coating (6) is less than 0.5 mm, further comprising a support body removal step including the removal of the support body (2) from the remaining waveguide coating (6), and further comprising a stability enhancement step including the addition of a supporting structure (11) onto at least a region of a surface of the waveguide coating (6).

2. Method for manufacturing according to claim 1, characterized in that the thickness of the waveguide coating (6) is less than 0.1 mm and preferably less than 0.05 mm.

3. Method for manufacturing according to claim 1 or claim 2, characterized in that the support body (2) is made from a support body material (3) which can be removed from the waveguide coating (6) by mechanical removal, chemical removal or thermal removal.

4. Method for manufacturing according to any of the preceding claims, characterized in that during the coating step an outer surface (12) of the support body (2) is coated with the waveguide coating (6) in such a manner as to provide a waveguide coating (6) that defines a cavity (7) of the hollow waveguide device (1).

5. Method for manufacturing according to claim 4, characterized in that the stability enhancement step is performed before the support body removal step is performed.

6. Method for manufacturing according to any of the claims 1 to 3, characterized in that during the coating step an inner surface (5) of a cavity (4) formed within the support body (2) is coated with the waveguide coating (6) in such a manner as to provide a waveguide coating (6) that defines a cavity (7) of the hollow waveguide device (1).

7. Method for manufacturing according to claim 6, characterized in that the support body removal step is performed before the stability enhancement step is performed.

8. Method for manufacturing according to any of the preceding claims, characterized in that the stability enhancement step includes the deposition of an electrically non-conductive stability enhancement material (9) at the outer surfaces of the waveguide coating (6).

9. Method for manufacturing according to claim 8, characterized in that the waveguide coating (6) is embedded within an enclosing supporting structure (11) made of a polymer foam material.

10. Method for manufacturing according to claim 9, characterized in that during the stability enhancement step the waveguide coating (6) is arranged within an outer casing (8) and that a free space between the outer surface (10) of the waveguide coating (6) and the outer casing (8) is filled by a polymer foam material.

11. Hollow waveguide device (1) for radio frequency electromagnetic waves with a cavity (7) that extends in one direction of propagation of the electromagnetic waves, characterized in that the hollow waveguide device (1) comprises a waveguide coating (6) made from an electrically conductive material that encloses the cavity (7) in which electromagnetic waves can propagate, whereby a thickness of the waveguide coating (6) is less than 0.5 mm, and whereby an electrically non-conductive stability enhancement material (9) is arranged at the outer surfaces (10) of the waveguide coating (6) for providing mechanical stability to the waveguide coating (6).

12. Hollow waveguide device (1) according to claim 11, characterized in that the thickness of the waveguide coating (6) is less than 0.1 mm, preferably less than 0.05 mm.

13. Hollow waveguide device (1) according to claim 11 or claim 12, characterized in that the waveguide coating (6) is at least partially surrounded by a polymer foam material that is used as stability enhancement material (9) and forms a supporting structure (11).

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