RF absorbing structures

Abstract

RF absorbing structures include a dielectric layer, such as polycarbonate, and one or more layers of a carbon resistive material, such as carbon ink. The RF absorbing structures can further include one or more layers of a conductive material, such as silver ink.

Description

TECHNICAL FIELD

The invention relates to structures for radio frequency (RF) absorption with films of resistive carbon and/or conductive silver applied to dielectric substrates, methods of manufacturing these RF absorption structures, and RF apparatuses that include these RF absorption structures.

BACKGROUND

RF absorptive structures are desirable in many RF applications, including millimeter wave (mmW) applications, to improve the performance of RF apertures and RF cavities. For example, RF apertures may need to be surrounded by or lined with RF absorptive structures to improve the radiation patterns of the RF apertures and/or to prevent surface waves from propagating along structural features adjacent to the RF apertures. For an apparatus such as an RF repeater that includes an RF transmit aperture within proximity to an RF receive aperture, RF absorptive structures may be arranged between the RF transmit aperture and the RF receive aperture to increase isolation between the proximate apertures.

As another example, RF cavities may need to have enclosures that include RF absorptive structures to prevent RF energy from escaping the cavities. For a cavity that is provided by mating two or more conducting structures together, e.g., joining a ground plane to a metal plate that has been milled or molded to include a recessed cavity volume, RF absorptive structures can be included in the gasket between the mated conducting structures to prevent RF energy from escaping through the joint between the mated conducting structures.

Existing RF absorbing materials such as CUMING MICROWAVE C-RAM MT and WAVEXORB are cost-prohibitive for some applications. Further, existing RF absorbing materials may be too bulky for some applications, or not sufficiently absorptive at frequencies or polarizations of interest for certain applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example of a carbon/polycarbonate/carbon/pressure-sensitive-adhesive (PSA) laminate.

FIG. 2 depicts an example of a multilayer laminate using PSA between successive layers.

FIG. 3 depicts an example of a multilayer laminate using liquid adhesive between layers.

FIG. 4 depicts illustrative patterns for deposition of carbon ink.

FIG. 5 depicts illustrative patterns for deposition of carbon ink interleaved or interspersed with depositions of a conductive material.

DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, which form a part hereof, and which show, by way of illustration, specific embodiments by which the invention may be practiced. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Among other things, the present invention may be embodied as methods or devices. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. The following detailed description is, therefore, not to be taken in a limiting sense.

Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrase “in one embodiment” as used herein does not necessarily refer to the same embodiment, though it may. Similarly, the phrase “in another embodiment” as used herein does not necessarily refer to a different embodiment, though it may. As used herein, the term “or” is an inclusive “or” operator, and is equivalent to the term “and/or,” unless the context clearly dictates otherwise. The term “based on” is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of “a,” “an,” and “the” include plural references. The meaning of “in” includes “in” and “on.”

In some approaches the invention provides a low-cost laminate material with RF absorbing properties. The core laminate can be, for example, a polycarbonate sheet that is coated with electrically conductive carbon ink on one or both sides. A Pressure Sensitive Adhesive (PSA) can be applied to one side of the sheet for installation or lamination purposes.

The core laminate can be used as a single layer by, for example, cutting the material to the needed shape and adhering it to the surface of the product where RF absorption is required. In other applications two or more layers can be laminated together to achieve the desired RF performance.

Some approaches provide an RF absorbing structure that includes a first dielectric layer of a dielectric material; and a first upper film of a resistive carbon material disposed on an upper surface of the first dielectric layer. In some approaches, the resistive carbon material can be patterned, e.g., as zigzags, lines, circles, line segments, or the like, with a feature size that is substantially less than a free-space wavelength corresponding to an intended frequency range for the RF absorptive properties of the structure. The first upper film may also include a conductive material such as copper, silver, or gold ink, and that conductive material can also be similarly patterned, with the pattern of the resistive carbon material being interleaved or interspersed with the pattern of the conductive material. The patterning of the resistive carbon material and/or the conductive material can be selected to increase an impedance match between the RF absorbing structure and free space for the intended frequency range, to better admit RF energy into the structure for absorption and attenuation.

The RF absorbing structure can optionally include a first lower film of the resistive carbon material disposed on a lower surface of the first dielectric layer. In some approaches, the resistive carbon material can be patterned, e.g., as zigzags, lines, circles, line segments, or the like, with a feature size that is substantially less than a free-space wavelength corresponding to an intended frequency range for the RF absorptive properties of the structure. The first lower film may also include a conductive material such as copper, silver, or gold ink, and that conductive material can also be similarly patterned, with the pattern of the resistive carbon material being interleaved or interspersed with the pattern of the conductive material. The patterning of the resistive carbon material and/or the conductive material can be selected to increase an impedance match between the RF absorbing structure and free space for the intended frequency range, to better admit RF energy into the structure for absorption and attenuation. For approaches that included patterned films on both the upper and lower surfaces of the dielectric layer, the patterns on the upper or lower surfaces can be offset or rotated relative to each other (e.g., rotated 90 degrees relative to each other) to improve the free space impedance match and/or RF absorptive properties of the structure.

In some approaches, the dielectric material is a sheet-formed material or a rollable material. The dielectric material can be a low-dielectric constant material, e.g., having a dielectric constant less than about 1.5, or less than about 2.0, or less than about 3.0 The dielectric material can be a plastic material, such as polycarbonate, polyethylene, polyester, silicone, or RF prepreg. The dielectric material can be a ceramic or composite material. The dielectric layer can have a thickness of, for example, about 5, 10, or 20 mils, depending on the desired range of operating wavelengths for the RF application.

The resistive carbon material can be a carbon ink or paint, or a carbon film material, or a carbon paper or fabric material.

In some approaches, the RF absorbing structure includes an adhesive layer disposed on a lower surface of the first dielectric layer, or on a lower surface of the first lower film of the resistive carbon material. The adhesive layer can be a pressure sensitive adhesive layer.

In some multilayer embodiments of the RF absorbing structure, the first dielectric layer is one of a plurality of dielectric layers; the first upper film is one of a plurality of upper films; the first adhesive layer is one of a plurality of adhesive layers; and the pluralities are arranged as a laminate structure with repeating layers of film, dielectric, and adhesive, in that order. In other multilayer embodiments of the RF absorbing structure, the first dielectric layer is one of a plurality of dielectric layers; the first upper film is one of a plurality of upper films; the first lower film is one of a plurality of lower films; the first adhesive layer is one of a plurality of adhesive layers; and the pluralities are arranged as a laminate structure with repeating layers of upper film, dielectric, lower film, and adhesive, in that order. The adhesive layers can include one or more pressure sensitive adhesive layers and/or one or more liquid adhesive layers.

In some approaches, an RF apparatus includes an RF absorbing structure such as the various structures described above. For example, the RF apparatus can include an RF cavity that is loaded with the RF absorbing structure to improve isolation of the RF cavity. As another example, the RF apparatus can include an antenna aperture and the RF absorbing structure can be arranged on or around the antenna aperture to improve performance characteristics of the antenna aperture such as sidelobe characteristics. As another example, the RF apparatus can include two or more antenna apertures and the RF absorbing structure can be arranged or disposed on a surface between pairs of the two or more antenna apertures to attenuate surface waves that might otherwise propagate along the surface between the pairs of the two or more antenna apertures. For example, the RF apparatus can be a RF repeater apparatus with one or more receive antennas and one or more transmit antennas, and the RF absorbing structure can be arranged or disposed to attenuate surface waves that might otherwise propagate from a transmit antenna to a receive antenna or vice versa, thus to improve front-to-back isolation of the RF repeater apparatus.

Some approaches provide a method of manufacture (e.g., of the various RF absorbing structures described above) that includes applying an upper film of a resistive carbon material and/or conductive material to an upper surface of a dielectric layer of a dielectric material. The method can further include applying a lower film of the resistive carbon material and/or conductive material to a lower surface of the dielectric layer. The dielectric material, the resistive carbon material, and the conductive material can be selected from the various materials described above.

In some approaches, the method of manufacture is a roll-to-roll process. For example, the roll-to-roll process can include unrolling a roll of the dielectric material to present the dielectric layer for the applying of the upper film; and rolling a second roll of the dielectric material with the applied upper film.

The applying of the upper film can include coating the upper surface of the dielectric layer with the resistive carbon material. For example, the coating of the upper surface can be a spray or roller coating of the upper surface. Alternatively, the coating of the upper surface can be an applying of the resistive carbon material with precut sponges. In some approaches, the coating of the upper surface can be a patterned or stenciled coating of the upper service, e.g., using a silkscreen or similar process. For approaches in which the lower surface is also coated, these same coating approaches are applicable for the lower surface.

As an alternative to the roll-to-roll process, the method of manufacture can be a printed circuit board (PCB) process, e.g., where the dielectric layer is an RF prepreg material and the resistive carbon material is applied using a PCB printing process.

In some approaches, the method of manufacture is a multilayer process. For example, one multilayer process includes cutting the dielectric layer with the applied upper film to provide a set of sheets or patches with a selected shape and then stacking the set of sheets or patches to provide a laminar RF absorbing structure, with an adhesive material (e.g., liquid adhesive or pressure-sensitive adhesive) between adjacent layers of the stack. Another multilayer process can be a multilayer roll-to-roll process, e.g., where multiple layers are unrolled and brought together in a multilayer structure.

With reference now to FIG. 1, an illustrative example of an RF absorbing structure is depicted. View 101 depicts a top view of the structure. In this non-limiting example, the structure has a rectangular shape with small diagonal cutouts at each corner of the rectangle. View 102 depicts a cross section of the structure, showing a dielectric layer 110 having an upper film 111 and a lower film 112, with an adhesive layer 113 below the lower film 112. As discussed above, the dielectric layer can be, for example, a plastic material such as polycarbonate, polyethylene, polyester, silicone, or RF prepreg. The dielectric layer can have a thickness of, for example, about 5, 10, or 20 mils, depending on the desired range of operating wavelengths for the RF application. In some approaches, the dielectric layer can have a thickness substantially less than an operating wavelength for the RF application. For example, the dielectric layer thickness can be less than about one-fifth of an operating wavelength, or less then about one-tenth of an operating wavelength. As a specific example, for an RF device that operates at 28 GHz, a dielectric layer thickness of 10 mils corresponds to about one fortieth of the 28 GHz wavelength. The upper film 111 and lower film 112 can be films of resistive carbon, or films that includes both resistive carbon and a conductive material such as copper, silver, or gold ink. As discussed above, the films can include patterns of the resistive carbon and/or the conductive material, e.g., as zigzags, lines, dots, circles, etc.

With reference now to FIG. 2, illustrative examples of multilayer laminates using PSA between successive layers are depicted. Configuration 210 depicts a two-stack configuration 211 wherein two layers 201, each having an upper film 201a, a dielectric layer 201b, and a lower film 201c, are joined together with a pressure sensitive adhesive 202. A second pressure sensitive adhesive layer is positioned at the bottom of the stack for adhesion to an RF device for a desired RF application. Configuration 220 depicts a three-stack configuration 221 wherein three layers 201, each having an upper film 201a, a dielectric layer 201b, and a lower film 201c, are joined together with a pressure sensitive adhesive 202. A third pressure sensitive layer is positioned at the bottom of the stack for adhesion to an RF device for a desired RF application. While each layer is depicted as having both upper and lower films 201a and 201b, in some applications, only one film is applied to each layer.

With reference now to FIG. 3, illustrative examples of multilayer laminates using liquid adhesive between successive layers are depicted. Configuration 310 depicts a two-stack configuration 311 wherein two layers 301, each having an upper film 301a, a dielectric layer 301b, and a lower film 301c, are joined together with a liquid adhesive 302. A pressure sensitive adhesive layer 303 is positioned at the bottom of the stack for adhesion to an RF device for a desired RF application. Configuration 320 depicts a three-stack configuration 321 wherein three layers 301, each having an upper film 301a, a dielectric layer 301b, and a lower film 301c, are joined together with a liquid adhesive 302. A pressure sensitive adhesive layer 303 is positioned at the bottom of the stack for adhesion to an RF device for a desired RF application. While each layer is depicted as having both upper and lower films 301a and 301b, in some applications, only one film is applied to each layer.

With reference now to FIG. 4, illustrative examples for patterning of the resistive carbon material are depicted. While the resistive carbon material can be deposited in a solid layer, it can alternatively be deposited as, for example, a series of horizontal zigzags 401, a series of vertical zigzags 402, a series of horizontal lines 403, a series of vertical lines 404, a series of diagonal lines 405, an array of dots 406, an array of circles 407, an array of line segments 408, a random or pseudorandom arrangement of dots 409, or a random or pseudorandom arrangement of line segments 410. Feature sizes for these patterns can be substantially less than a wavelength corresponding to an intended frequency range for the RF absorbing structure. For example, feature sizes can be less than or equal to about one-fifth or one-tenth of a free-space wavelength corresponding to the intended frequency range. The particular pattern and/or feature size can be selected to enhance an impedance match between the RF absorbing structure and free space for the intended frequency range, to better channel RF energy into the RF absorbing structure for attenuation.

With reference now to FIG. 5, illustrative examples are depicted that interleave or intersperse patterns of resistive carbon material with patterns of a conductive material such as copper, silver, or gold ink. In 501, the resistive carbon material (solid lines) and the conductive material (dashed lines) are arranged as alternating horizontal zigzags. In 502, the resistive carbon material (solid lines) and the conductive material (dashed lines) are arranged as alternating vertical zigzags. In 503, the resistive carbon material (solid lines) and the conductive material (dashed lines) are arranged as alternating horizontal lines. In 504, the resistive carbon material (solid lines) and the conductive material (dashed lines) are arranged as alternating vertical lines. In 505, the resistive carbon material (solid lines) and the conductive material (dashed lines) are arranged as alternating diagonal lines. In 506, the resistive carbon material (solid dots) and the conductive material (hollow dots) are arranged in an alternating array of dots. In 507, the resistive carbon material (solid circles) and the conductive material (dashed circles) are arranged in an alternating array of circles. In 508, the resistive carbon material (solid line segments) and the conductive material (dashed line segments) are arranged in an alternating array of line segments. In 509, the resistive carbon material (solid dots) and the conductive material (hollow dots) are arranged in a random or pseudorandom arrangement of dots. In 510, the resistive carbon material (solid line segments) and the conductive material (dashed line segments) are arranged in a random or pseudorandom arrangement of line segments. While several of these illustrative examples depict alternating arrangements of the resistive carbon material and the conductive material, other arrangements are contemplated, e.g., having multiple resistive carbon material features interspersed with an occasional conductive material feature, or vice versa.

Claims

1. An RF absorbing structure, comprising: a first dielectric layer of a dielectric material;a first upper film that includes a resistive carbon material disposed on an upper surface of the first dielectric layer; anda first lower film of the resistive carbon material disposed on a lower surface of the first dielectric layer.

2. The structure of claim 1, wherein the first upper film further includes a conductive material.

3. The structure of claim 1, wherein the first upper film is arranged in a first pattern.

4. The structure of claim 3, wherein the RF absorbing structure has a selected frequency range for RF absorption, and the first pattern is a periodic pattern having a feature size substantially less than a free-space wavelength corresponding to the selected frequency range.

5. The structure of claim 3, wherein the RF absorbing structure has a selected frequency range for RF absorption, and the first pattern is a random or pseudorandom pattern having a feature size substantially less than a free-space wavelength corresponding to the selected frequency range.

6. The structure of claim 1, wherein the first lower film is arranged in a second pattern.

7. The structure of claim 6, wherein the RF absorbing structure has a selected frequency range for RF absorption, and the second pattern is a periodic pattern having a feature size substantially less than a free-space wavelength corresponding to the selected frequency range.

8. The structure of claim 6, wherein the RF absorbing structure has a selected frequency range for RF absorption, and the second pattern is a random or pseudorandom pattern having a feature size substantially less than a free-space wavelength corresponding to the selected frequency range.

9. The structure of claim 1, further comprising: a first adhesive layer disposed on a lower surface of the first lower film.

10. The structure of claim 9, wherein: the first dielectric layer is one of a plurality of dielectric layers;the first upper film is one of a plurality of upper films;the first lower film is one of a plurality of lower films;the first adhesive layer is one of a plurality of adhesive layers; andthe pluralities are arranged as a laminate structure with repeating layers of upper film, dielectric, lower film, and adhesive, in that order.

11. An RF absorbing structure, comprising: a first dielectric layer of a dielectric material;a first upper film that includes a resistive carbon material disposed on an upper surface of the first dielectric layer; anda first adhesive layer disposed on a lower surface of the first dielectric layer.

12. The structure of claim 11, wherein: the first dielectric layer is one of a plurality of dielectric layers;the first upper film is one of a plurality of upper films;the first adhesive layer is one of a plurality of adhesive layers; andthe pluralities are arranged as a laminate structure with repeating layers of film, dielectric, and adhesive, in that order.

13. An apparatus, comprising: a first RF antenna aperture;a second RF antenna aperture; andan RF absorbing structure disposed on a surface between the first RF antenna aperture and the second RF antenna aperture, wherein the RF absorbing structure comprises a first dielectric layer of a dielectric material and a first upper film that includes a resistive carbon material disposed on an upper surface of the first dielectric layer.

14. The apparatus of claim 13, wherein the RF absorbing structure is arranged to at least partially improve sidelobe characteristics of the first RF antenna aperture or the second RF antenna aperture.

15. The apparatus of claim 13, wherein the RF absorbing structure is arranged to at least partially improve RF isolation between the first RF antenna aperture and the second RF antenna aperture.

16. A method, comprising: applying an upper film of a resistive carbon material to an upper surface of a dielectric layer of a dielectric material; andcutting the dielectric layer with the applied upper film to provide a set of sheets or patches with a selected shape.

17. The method of claim 16, wherein the first upper film includes a conductive material.

18. The method of claim 16, further comprising: applying a lower film of the resistive carbon material to a lower surface of the dielectric layer.

19. The method of claim 18, further comprising: applying an adhesive layer to a lower surface of the lower film.

20. The method of claim 16, wherein the dielectric material is a plastic material.

21. The method of claim 20, wherein the method is a roll-to-roll process.

22. The method of claim 21, wherein the roll-to-roll process includes: unrolling a roll of the dielectric material to present the dielectric layer for the applying of the upper film; androlling a second roll of the dielectric material with the applied upper film.

23. The method of claim 22, wherein the applying of the upper film includes: coating the upper surface of the dielectric layer with the resistive carbon material.

24. The method of claim 16, further comprising: applying an adhesive layer to a lower surface of the dielectric layer.

25. The method of claim 16, further comprising: stacking the set of sheets or patches to provide a laminar RF absorbing structure.