WO2012076994A1 - Passive components for millimeter, submillimeter and terahertz electromagnetic waves made by piling up successive layers of material - Google Patents

Abstract

The passive component for the transmission and manipulation of electromagnetic signals having frequencies from 30 GHz to 100 THz, comprises a corrugated or smooth wall unit alone or an assembly of at least one corrugated or smooth wall unit in a hollow guiding rod. The external shape of said unit(s) corresponds to the internal shape of the hollow guiding rod, and said units or the entire assembly may be metal plated to form the component. The manufacturing method of such components includes building units or sub units by piling up successive layers of material using 3D printing, 3D microfabrication based on 2-photon photopolymerisation, stereolithography, selective laser sintering (SLS), electron beam melting (EBM). The units or sub units are later possibly metal plated on selective or all surfaces.

Description

PASSIVE COMPONENTS FOR MILLIMETER, SUBMILLIMETER AND TERAHERTZ ELECTROMAGNETIC WAVES MADE BY PILING UP SUCCESSIVE LAYERS OF MATERIAL CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims the benefit of U.S. Provisional Application Number 61/421 ,293, filed December 9, 2010, the entire disclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a new approach to manufacture passive components for the transmission of electromagnetic waves with frequencies up to 100 THz permitting to overtake conventional machining techniques.

More specifically, the present invention concerns the fabrication of circular, rectangular, or any suitable shape corrugated waveguides, corrugated down or up-tapers, corrugated horn antennas, corrugated cavities, corrugated mirrors, interference gratings, phase control mirrors, directional couplers and in general components needing an internal corrugation or periodicity. But the invention also concerns smooth wall passive components such as waveguides, up and down tapers, horn antennas, cavities and mirrors and photonic band like structures.

Moreover this new approach permits the manufacturing of corrugated transmission line bends, conventional miter bend and innovative miter bend based on photonic band like structures. BACKGROUND OF THE INVENTION AND PRIOR ART

Due to low absorption, low dispersion, efficient coupling, and wave confinement, corrugated components (Fig. 1 ) apt for millimeter, submillimeter, THz (MMW . THz) waves are crucial in the signal transmission for experimental set-ups, while smooth wall passive components can be advantageous depending on the setup requirements. Both categories of passive components (corrugated and smooth wall) are crucial in the following applications:

- Physics applications such as fundamental studies of nanostructures and Quantum coherence and control experiments, as transmission lines for plasma additional heating techniques in plasma reactors based on magnetic confinement (e.g. Tokamaks, Stellarators)

- Chemistry studies on gas phase spectra and dynamics, membranes, Langumir-Blodget (LB) films, self-assembled monolayers (SAMs), phonon modes of inorganic and organic crystal, electron spin resonance (ESR), Dynamic Nuclear Polarization enhanced Nuclear Magnetic Resonance (DNP- NMR), Dissolution DNP-NMR techniques, high resolution Electron Paramagnetic Resonance (EPR), high resolution FerroMagnetic Resonance (FMR)

- Medical THz imaging or spectroscopy where endoscopic techniques are required for environments that are otherwise difficult to access

- Terahertz sensing and imaging for security applications such as for explosive detection. Moreover corrugated waveguides could be a crucial element for new method for drilling and fracturing subsurface formations and more particularly for method and system using millimeter- wave radiation energy. In fact drilling at depths beyond 7000 meters is increasingly difficult and costly using present rotary drilling methods.

The millimeter, submillimeter and THz (MMW-THz) wave region up to 100 THz in the electromagnetic spectrum is a frontier area for research in physics, chemistry, biology, material science and medicine. Sources for high quality radiation in this area have been scarce, but this gap has recently begun to be filled by a wide range of new technologies. Terahertz radiation is now available in both continuous wave (CW) and pulsed form. New sources have led to new scientific applications in many areas, as scientists are becoming aware of the opportunities for research progress using MMW-THz waves.

MMW-THz waves lie above the frequency range of traditional electronics, but below the range of optics. The fact that the THz frequency range lies in the transition region between photonics and electronics has led to unprecedented creativity in source and transmission components development.

The barriers to perform experiments using MMW-THz radiation are considerable because of the need not only of a THz source, but also a chain of elements for the signal transmission, manipulation and receiving.

Circular, rectangular, or any suitable shape corrugated waveguides, corrugated down or up-tapers, corrugated horn antennas, corrugated cavities, corrugated mirrors, interference gratings, phase control mirrors, directional couplers and in general components needing an internal corrugation or periodicity, but also smooth wall passive components such as waveguides, up and down tapers, horn antennas, cavities and mirrors and photonic band like structures are very difficult or impossible to manufacture when increasing frequency toward the THz range. In fact, for the exemplified corrugation, the corrugation period, width and depth (fig.1 ) are related to the wavelength λ. In corrugated waveguides, for instance, the period has to be less than λ/2 (p < λ/2) of the lowest suited frequency (e.g. to transmit more than 1 THz, period has to be less than λ/2 =0.15 mm), while width (w, as wide as possible) and depth (d ~ λ/4) can be used to tune the bandwidth. Finally, in the case of a cylindrical component, the diameter should be bigger than the wavelength (D » λ).

The use of corrugations implies very low losses in transmission. Power losses are on the order of 0.05dB per 100m (about 0.01 % per meter) for the frequency for which corrugation has been designed and anyway well below 0.5dB per 100m (about 0.12% per meter) for ten times the nominal frequency.

Prior art publications include the following documents: US 4,408,208, WO 2004/032278, WO 03/096379, US, 4,492,020, GB 1 586 585, JP 52044140, US 3,914,861 , US 3,845,422, WO 99/59222, JP 2004282294, US 3,01 1 ,085, WO 2008/073605.

US 4,408,208 for example concerns corrugated feed horns for circularly polarized antennas including super high frequency and extra high frequency parabolic antennas operating in the 12-100 GHz range. In this prior art, the feed horn is made by dip brazing a plurality of laminations providing alternate fins and grooves in an inner conical configuration. An assembly of laminations is built with pins which align in registry the stacked laminations. Braze metal wires are added into a set of apertures provided on the assembly. The assembly is then dipped in a molten salt solution heated above the melting point of the braze metal wires but below the melting point of the laminations. Each braze metal wire melts in the solution and creeps or wicks by capillary action along the interfaces between the laminations. The wires are thin enough that there is not enough material to creep into the grooves between the fins along the inner conical surface of the horn. This wicking inward from the outside thus facilitates prevention of braze material build-up in the grooves. Finally, the outer surface of the assembly is then machined to a conical periphery down to base to provide a horn.

GB 1 586 585 discloses radio horns and in particular radio horns whose internal shapes render difficult their manufacture by machining from the solid wherein the horn is a corrugated elliptical horn antenna. According to GB 1 586 585 an elliptical radio horn is formed of a stack of plates each of which individually has an elliptical aperture which defines the inner shape of the horn over the length thereof formed by the thickness of said individual plate, said plates being normally held together by nuts and bolts or studs passing therethrough. SUMMARY OF THE INVENTION

An aim of the present invention is to improve the known devices and methods.

A further aim of the present invention is to provide corrugated components or smooth wall components used in the field of transmission and manipulation of MMW-THz waves. The present invention enables the manufacturing of passive components for electromagnetic waves with frequency up to 100 terahertz overtaking conventional machining techniques.

According to an aspect of the present invention, an idea is to create these components from one or a plurality of passive components formed by pilling up successive layers of material to be used as such or possibly stacked together in a hollow guiding rod. Depending on the material used for the passive components, a metal plating can be necessary to maintain the necessary surface reflection properties. In the case of sub-units piled up ion a hollow guiding rod, the outer edge of the sub-units could be shaped with indentations or other equivalent means in order to reduce friction against the internal wall of the hollow guiding rod.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be better understood from a detailed description of several embodiments and from the drawings which show

Figure 1 illustrates the principle of possible corrugations for hollow components in the present invention;

Figures 2(a) - 2(b) illustrate an example of basic corrugated units to form a corrugated component made by stacking subunits in a guiding hollow guiding pipe or rod.; Figures 3(a) to 3(c) illustrate an exploded view of all elements needed to form two segments of circular corrugated waveguide according to the present invention, with a auto-aligning connection system guaranteeing the continuity of corrugation at the interface between two hollow guiding pipes.

Figures 4(a) and 4(b) illustrate an exploded view of all elements needed to form a corrugated waveguide bend. Figures 5(a) and 5(b) illustrate a cut view and an image of a corrugated horn antenna, wherein the cut corrugated horn antenna is connected to a circular corrugated waveguide.

Figures 6(a) illustrates an example of corrugation on a flat mirror. Such mirrors could also have any periodic pattern different from the presented corrugation.

Figures 6(b) and 6(c) show images of two corrugated mirrors, one made by conventional machining and one made by piling up successive layers of material as described in this invention.

Figure 7(a) shows an example of smooth wall horn antenna.

Hence, the object of the present invention is to provide circular, rectangular, or any suitable shape corrugated waveguides, corrugated down or up-tapers, corrugated horn antennas, corrugated cavities, corrugated mirrors, interference gratings, phase control mirrors, directional couplers and in general components needing an internal corrugation or periodicity. But the invention also concerns smooth wall passive components such as waveguides, up and down tapers, horn antennas, cavities, mirrors, and photonic band like structures to transmit and manipulate signals with high frequency up to 100 THz. Moreover this new approach permits the manufacture of corrugated waveguide bend, conventional miter bend and innovative miter bend based on photonic band like structures. To achieve the above mentioned objects, the invention proposes to manufacture the waveguides from one or a plurality of passive components formed by pilling up successive layers of material to be used as such or possibly stacked together in a hollow guiding rod. Depending on the material used for the passive components, a metal plating may be necessary to maintain the necessary surface reflection properties. In the case of sub-units piled up in a hollow guiding rod, the outer edge of the sub-units could be shaped with indentations or other equivalent means in order to reduce friction against the internal wall of the hollow guiding rod while still providing aligning properties.

There are various techniques that can be used to build these basic corrugated units in various materials. Typical examples are the following:

- 3D printing, is a form of additive manufacturing technology where a three dimensional object is created by laying down successive layers of material. - Sub millimeter features may be made by 3D microfabrication technique based on of 2-photon photopolymerization. In this approach the desired 3D object is traced out in a block of gel by a focused laser. The gel is cured to a solid only in the places where the laser was focused, due to the nonlinear nature of photoexcitation, and then the remaining gel is washed away.

- Stereolithography is an additive manufacturing process using a vat of liquid UV-curable photopolymer "resin" and a UV laser to build parts a layer at a time. On each layer, the laser beam traces a part cross-section pattern on the surface of the liquid resin. Exposure to the UV laser light cures, or, solidifies the pattern traced on the resin and adheres it to the layer below. - Selective laser sintering (SLS) is an additive manufacturing technique that uses a high power laser (for example, a carbon dioxide laser) to fuse small particles of plastic, metal (Direct Metal Laser Sintering), ceramic, or glass powders into a mass that has a desired 3-dimensional shape. The laser selectively fuses powdered material by scanning cross-sections generated from a 3-D digital description of the part on the surface of a powder bed.

- Electron beam melting (EB ) is a type of additive manufacturing for metal parts. It is often classified as a rapid manufacturing method. The technology manufactures parts by melting metal powder layer per layer with an electron beam in a high vacuum. Unlike some metal sintering techniques, the parts are fully dense, void-free, and extremely strong.

This new approach using the above mentioned techniques or equivalent ones) permits to build passive components segments with length only limited by precision in the manufacturing of hollow guiding rods, in the case of an assembly of units. This means segments up to at least one meter for an inner diameter of the guiding rod on the order of centimeters to millimeters. In the case of assembled units, especially designed auto-aligning flanges link the different parts of the transmission line. They permit to employ the approach proposed with this invention without discontinuity also at the junction between two passive component segments avoiding imperfections on the internal wall pattern or shape (fig.3).

Since flanges are fixed to the hollow guiding rod with series of screws they also act as stopper and are used to mechanically compress stacked basic units. When needed, these flanges can be realized in polyimide-based plastics or similar materials in order to obtain thermal insulation between two waveguide elements, using the principle of the present invention.

Moreover this new approach permits an easier and more flexible manufacture of conventional miter bend and innovative miter bend as for example in figure 4.

The surfaces of the obtained passive components have to be metallic or metal plated with any suitable metal for the application. The plating may be carried out with any suitable technique known in the art. This plating can be made on independent units, or on units to be assembled before or after the assembly.

In one embodiment, the invention relates to a passive component for the transmission and manipulation of electromagnetic signals having frequencies from 30 GHz to 100 THz, wherein said component comprises a corrugated or smooth wall unit alone or an assembly of at least one corrugated or smooth wall unit in a hollow guiding rod, wherein the external shape of said unit(s) corresponds to the internal shape of the hollow guiding rod, wherein said units or the entire assembly is metal plated to form the component.

In one embodiment, the assembly comprises a plurality of corrugated or smooth wall units. In one embodiment, the corrugation is periodic and can take any possible shape.

In one embodiment, the rod is straight. In one embodiment, the rod is bent.

In one embodiment, the units are made of synthetic materials which are metal ized. In one embodiment, the component comprises at least a first flange connected to a first rod for connection to a second flange connected to a second rod, said flanges cooperating together to allow a connection of said rods together without discontinuity at the junction. In one embodiment, the invention relates to a method for manufacturing a corrugated, surface periodic or smooth wall component for the transmission and manipulation of electromagnetic signals having frequencies from 30 GHz to 100 THz by building units or sub units by piling up successive layers of material using one of the following techniques: 3D printing, 3D microfabrication based on 2-photon photopolymerisation, stereolithography, selective laser sintering (SLS), electron beam melting (EBM).

These units or sub units may be later possibly metal plated on selective or all surfaces.

In one embodiment, the invention relates to a photonic band gap like structure in 1 D, 2D or 3D made by a method as above wherein its surface is metalized if necessary.

Figure 1 illustrates an example of geometry for a circular corrugated waveguide with diameter, D, period, p, width, w, and depth, d with reference 1 identifying a slot and reference 2 identifying a ridge. The inner region where electromagnetic signal propagates is metallic or metal plated according to the principles of the present invention.

Figure 2a and 2b illustrates a perspective view and cut view of basic corrugated units 3 and a guiding hollow rod 5 needed for forming a segment of circular corrugated waveguide.

Rings 4, such as o-rings, may be employed with threaded connectors to fasten waveguide components. As an example, the O-rings may be employed with threaded connectors to fasten waveguide components together, said rings being attached to the outer surface of the rods. They thus allow the connection (i.e. coupling) of two rods one with another.

Figures 3a to 3c illustrate exploded views of all elements needed to compose two segments of circular corrugated waveguide, in particular the two flanges and the basic corrugated module at the junction.

The basic corrugated units 3 are as illustrated in figures 2a/2b and introduced in rods 5, for example hollow circular rods. Flanges 6 are designed to link two waveguide segments. In particular, flanges 6 act as unit-stopper and host a corrugated module referenced 7 and forming a special corrugated unit to maintain corrugation continuity at the junction of waveguide segments. Screws 8 are used to attach the flanges 6 to the rods 5 in order to determine the suited strength on stacked basic corrugated modules. Other equivalent means may of course be used to attach flanges 6 to the rod 5.

Typically, the flanges 6 of two rods to be connected together nest into each other to provide an aligned connection between rods. Inside the two nested flanges 6 there is the special corrugated unit 7 that allows continuity of corrugation in order to maintain the properties of the assembly of rods. This unit may be made in accordance with the techniques described herein.

Figures 4a to 4d illustrate perspective and cut views of all elements needed to build a possible design of corrugated waveguide bend. Reference 10 identifies a hollow circular rod that provides housing for the basic corrugated units 3. Special corrugated module 7, made for example using the technique disclosed herein, is used to maintain corrugation continuity at junctions of waveguide segments between rod 10 and bent shell 12. In this bent shell, there is a special corrugated module 1 1 to create waveguide bends without discontinuity of the corrugations. Flanges 6 designed to link two straight waveguide segments and/or waveguide bends are used as described previously, said flanges acting as ring-stopper and host a corrugated module described in previous figures. The shells 12 are attached together for example via screws 13.

Figures 5 (a) and (b), show a possible design for a corrugated horn antenna alone Figure 5 (a), or connected to a circular corrugated waveguide made by the assembly of sub-units into a hollow guiding rod as illustrated in figure 5(b). The corrugated horn antenna 14 is characterized by a varying aperture size along its axis, but also possibly a varying corrugation pattern, even with some smooth wall parts. It is linked to the circular waveguide assembly described above (3,4,5,6,7,8), for example in figures 3(a) to 3(c). Figure 6 (a) illustrates an example of geometry for grooved or corrugated mirrors, with period, p, width, w, and depth, d. The surface where the electromagnetic wave reflects is metallic or metal plated according to the principles of the present invention.

Figures 6 (b) and (c) show two corrugated mirrors, one made by conventional machining in aluminum 17 and one made by piling up successive layers of material 16 before being gold plated according to a concept of the invention. Flat, smooth wall, curved or mirrors with any pattern could be built according to the concept of the invention.

Figure 7 shows a possible example of smooth wall horn antenna 18, with a variable aperture size or shape along the axis of propagation of the waves.

All elements of the above mentioned invention can be made out of any material as long as all surfaces in contact with the region where electromagnetic waves reflect and propagate are metallic or metal plated with a sufficient thickness for them to be reflecting, this thickness depending on the propagated frequency. For example, such materials may include all metals such as, but not limited to, aluminum, stainless steel, titanium, copper or brass, but various plastics or polymers could be used such as, but not limited to PEEK, vespel, Kel-F, epoxy plastics, glass fibers, polyester, Plexiglas, PTFE or any other ceramic or composite materials

The invention is not limited to the embodiments described herein as non- limiting examples and other embodiments may be envisaged within the spirit and scope of the present invention. The different embodiments described herein may be combined together at will according to circumstances and depending on the product to be achieved and equivalent means may be used without departing from the spirit or scope of the present invention.

Claims

Claims

1. A passive component for the transmission and manipulation of electromagnetic signals having frequencies from 30 GHz to 100 THz, wherein said component comprises a corrugated or smooth wall unit alone or an assembly of at least one corrugated or smooth wall unit in a hollow guiding rod, wherein the external shape of said unit(s) corresponds to the internal shape of the hollow guiding rod, wherein said units or the entire assembly is metal plated to form the component.

2. The component as defined in claim 1 , wherein said assembly comprises a plurality of corrugated or smooth wall units.

3. The component defined in claim 1 , wherein the corrugation is periodic and can take any possible shape.

4. The component as defined in one of the preceding claims, wherein said rod is straight.

5. The component as defined in one of the preceding claims 1 to 3, wherein said rod is bent.

6. The component as defined in one of the preceding claims, wherein said units are made of synthetic materials.

7. The component as defined in one of the preceding claims, wherein it comprises at least a first flange connected to a first rod for connection to a second flange connected to a second rod, said flanges cooperating together to allow a connection of said rods together without discontinuity at the junction.

8. A method for manufacturing a corrugated, surface periodic or smooth wall component for the transmission and manipulation of electromagnetic signals having frequencies from 30 GHz to 100 THz by building units or sub units by piling up successive layers of material, using 3D printing, or 3D microfabrication based on 2-photon photopolymerisation, or stereolithography, or selective laser sintering (SLS), or electron beam melting (EBM), wherein said units or sub units are later possibly metal plated on selective or all surfaces.

9. A photonic band gap like structure in 1 D, 2D or 3D made by a method as defined in claim 8 wherein its surface is metalized if necessary.