1. A method for fabricating a millimetre wave frequency selective surface slot array on a substrate using an aerosol jet printing process, wherein the method comprises: preparing a nanoparticle silver ink by diluting to an appropriate viscosity and degassing to remove air bubbles; preparing the substrate by cleaning and drying to remove contaminants; loading the substrate onto a printing stage of an aerosol jet printer; depositing the nanoparticle silver ink onto the substrate by controlling printing parameters including nozzle size, flow rate, and substrate temperature, to form a slot array with specified dimensions and pattern geometry; and sintering the deposited nanoparticle silver ink at a temperature suitable for the substrate material to achieve a conductive frequency selective surface structure.

2. The method as recited in claim 1, wherein the substrate comprises a polyimide material characterized by high-temperature resistance and flexibility.

3. The method as recited in claim 1, wherein the substrate comprises a glass-like material characterized by mechanical strength and transparency.

4. The method as recited in claim 1, wherein the nanoparticle silver ink comprises silver nanoparticles having an average particle size of less than 50 nanometers to ensure fine feature resolution.

5. The method as recited in claim 1, wherein the aerosol jet printing process involves adjusting the size of the printing nozzle to control the thickness of the deposited ink stream.

6. The method as recited in claim 1, wherein the sheath gas pressure is varied during printing to optimize the deposition quality and to achieve consistent slot dimensions.

7. The method as recited in claim 1, wherein the sintering temperature for the deposited nanoparticle silver ink is maintained in the range of 150 to 200 degrees Celsius for polyimide substrates.

8. The method as recited in claim 1, wherein the sintering temperature for the deposited nanoparticle silver ink is increased above 200 degrees Celsius for glass-like substrates to enhance conductivity.

9. The method as recited in claim 1, wherein the toolpath for depositing the nanoparticle silver ink is segmented into horizontal and vertical tracks, with gaps left between tracks to form slot heights and edges.

10. The method as recited in claim 1, wherein the method includes inspecting the printed frequency selective surface slot array using optical microscopy or scanning electron microscopy to verify the integrity and precision of the slots. METHOD FOR FABRICATING A MILLIMETRE WAVE FREQUENCY SELECTIVE SURFACE SLOT ARRAY USING AEROSOL JET PRINTING PROCESS Abstract The present disclosure discloses a method for fabricating a millimetre wave frequency selective surface slot array on a substrate using an aerosol jet printing process. The method comprises preparing a nanoparticle silver ink by diluting to an appropriate viscosity and degassing to remove air bubbles. The method further includes preparing the substrate by cleaning and drying to remove contaminants, loading the substrate onto a printing stage of an aerosol jet printer, depositing the nanoparticle silver ink onto the substrate by controlling printing parameters including nozzle size, flow rate, and substrate temperature, to form a slot array with specified dimensions and pattern geometry, and sintering the deposited nanoparticle silver ink at a temperature suitable for the substrate material to achieve a conductive frequency selective surface structure. Fig. 1 , Claims:Claims :

1. A method for fabricating a millimetre wave frequency selective surface slot array on a substrate using an aerosol jet printing process, wherein the method comprises: preparing a nanoparticle silver ink by diluting to an appropriate viscosity and degassing to remove air bubbles; preparing the substrate by cleaning and drying to remove contaminants; loading the substrate onto a printing stage of an aerosol jet printer; depositing the nanoparticle silver ink onto the substrate by controlling printing parameters including nozzle size, flow rate, and substrate temperature, to form a slot array with specified dimensions and pattern geometry; and sintering the deposited nanoparticle silver ink at a temperature suitable for the substrate material to achieve a conductive frequency selective surface structure.

2. The method as recited in claim 1, wherein the substrate comprises a polyimide material characterized by high-temperature resistance and flexibility.

3. The method as recited in claim 1, wherein the substrate comprises a glass-like material characterized by mechanical strength and transparency.

4. The method as recited in claim 1, wherein the nanoparticle silver ink comprises silver nanoparticles having an average particle size of less than 50 nanometers to ensure fine feature resolution.

5. The method as recited in claim 1, wherein the aerosol jet printing process involves adjusting the size of the printing nozzle to control the thickness of the deposited ink stream.

6. The method as recited in claim 1, wherein the sheath gas pressure is varied during printing to optimize the deposition quality and to achieve consistent slot dimensions.

7. The method as recited in claim 1, wherein the sintering temperature for the deposited nanoparticle silver ink is maintained in the range of 150 to 200 degrees Celsius for polyimide substrates.

8. The method as recited in claim 1, wherein the sintering temperature for the deposited nanoparticle silver ink is increased above 200 degrees Celsius for glass-like substrates to enhance conductivity.

9. The method as recited in claim 1, wherein the toolpath for depositing the nanoparticle silver ink is segmented into horizontal and vertical tracks, with gaps left between tracks to form slot heights and edges.

10. The method as recited in claim 1, wherein the method includes inspecting the printed frequency selective surface slot array using optical microscopy or scanning electron microscopy to verify the integrity and precision of the slots.

Description:METHOD FOR FABRICATING A MILLIMETRE WAVE FREQUENCY SELECTIVE SURFACE SLOT ARRAY USING AEROSOL JET PRINTING PROCESS
Field of the Invention
[0001] The present disclosure generally relates to 3D printing technologies. Further, the present disclosure particularly relates to a method for fabricating a millimetre wave frequency selective surface slot array on a substrate using an aerosol jet printing process.
Background
[0002] The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Frequency Selective Surfaces (FSS) are widely utilized in electromagnetic applications including antennas, radomes, and filters. Conventional fabrication methods for FSS arrays typically involve processes such as photolithography, etching, and sputtering. Such methods demand extensive time, are expensive, and require sophisticated equipment, presenting challenges in terms of cost-efficiency and production scalability.
[0004] Further, one of the traditional methods employed is photolithography, where light is used to transfer a geometric pattern from a photomask to a light-sensitive photoresist on a substrate. Photolithography, while capable of producing intricate patterns, necessitates a controlled environment, multiple processing steps, and specialized equipment. The requirement for cleanroom conditions and the complexity of steps such as exposure, development, and etching make photolithography both time-intensive and costly.
[0005] Moreover, etching is another method commonly used in FSS fabrication, involving the removal of material from the surface to create a desired pattern. Wet etching, using liquid chemicals, and dry etching, utilizing gases or plasmas, are both employed based on the material and application. However, controlling the etching process to achieve consistent pattern definition can be challenging, and the chemical handling involved adds to the complexity and cost of production.
[0006] Furthermore, sputtering techniques are used to deposit thin layers of material onto substrates in the creation of FSS arrays. Sputtering involves the ejection of material from a target source by energetic particle bombardment, leading to deposition on the substrate. Sputtering is valued for producing uniform thin films, but the required equipment and controlled conditions add to the operational costs and complexity. Moreover, achieving consistent deposition over large areas remains a challenge, further limiting the scalability of such methods.
[0007] Additionally, advancements in 3D printing technologies have introduced alternative approaches for the fabrication of FSS arrays. Specifically, the development of nanoparticle silver inks enables the deposition of conductive materials with high resolution through non-contact methods. Such advancements allow for the use of 3D printing techniques like Aerosol Jet Printing (AJP), which is adaptable to various substrates, including both flexible and rigid materials. The non-contact nature and high-resolution capabilities of AJP make it a promising alternative for efficient and scalable FSS array production.
[0008] In light of the above discussion, there exists an urgent need for solutions that overcome the problems associated with conventional systems and/or techniques for the fabrication of frequency selective surface (FSS) slot arrays.
Summary
[0009] The following presents a simplified summary of various aspects of this disclosure in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements nor delineate the scope of such aspects. Its purpose is to present some concepts of this disclosure in a simplified form as a prelude to the more detailed description that is presented later.
[00010] The following paragraphs provide additional support for the claims of the subject application.
[00011] The disclosure pertains to a system for
[00012] .
Brief Description of the Drawings
[00013] The features and advantages of the present disclosure would be more clearly understood from the following description taken in conjunction with the accompanying drawings in which:
[00014] FIG. 1 illustrates a method for fabricating a millimetre wave frequency selective surface slot array on a substrate using an aerosol jet printing process, in accordance with the embodiments of the present disclosure.
[00015] FIG. 2 illustrates a sequence diagram for fabricating a millimetre wave frequency selective surface (FSS) slot array, in accordance with the embodiments of the present disclosure.
[00016] FIG. 3 illustrates a tabular representation of fabrication parameters for creating the novel toolpath, in accordance with the embodiments of the present disclosure.
[00017] FIG. 4 (a to c) illustrates an experimentation process with the aerosol stream size and ink dispersions, in accordance with the embodiments of the present disclosure.
Detailed Description
[00018] In the following detailed description of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to claim those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims and equivalents thereof.
[00019] The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
[00020] Pursuant to the "Detailed Description" section herein, whenever an element is explicitly associated with a specific numeral for the first time, such association shall be deemed consistent and applicable throughout the entirety of the "Detailed Description" section, unless otherwise expressly stated or contradicted by the context.
[00021] As used herein, the term "fabricating" refers to the process of constructing, creating, or manufacturing a component, structure, or system from raw materials or semi-finished products. Fabricating involves various steps such as designing, material preparation, assembly, and finishing, and may include the use of techniques such as cutting, molding, printing, or sintering. The term "fabricating" as used herein encompasses processes applied in both traditional manufacturing settings and advanced technologies such as 3D printing and additive manufacturing. Said process may be used to produce a wide range of items, from simple components to complex systems, including those used in industrial, commercial, and research applications. Additionally, the process of fabricating may involve the use of specialized tools, equipment, and methods tailored to the specific requirements of the material and design being worked on. It is understood that fabricating is essential in the creation of products and systems in various fields, including electronics, automotive, aerospace, and consumer goods, among others.
[00022] As used herein, the term "millimetre wave" refers to the range of electromagnetic waves with frequencies typically between 30 GHz and 300 GHz, corresponding to wavelengths ranging from 1 millimetre to 10 millimetres. Such waves are characterized by their ability to support high data transmission rates and are widely utilized in applications such as telecommunications, radar systems, and imaging technologies. The term "millimetre wave" as used herein includes frequencies in both the lower and upper ends of this spectrum, encompassing applications in both sub-100 GHz and sub-300 GHz ranges. Said waves are capable of supporting advanced communication systems, including those employed in 5G and 6G networks, due to their high frequency and ability to carry large amounts of data. Additionally, millimetre wave technology is instrumental in the development of high-resolution imaging systems and is used in scientific research for studying materials and phenomena at small scales.
[00023] As used herein, the term "Frequency Selective Surface" (FSS) refers to a structure that is designed to selectively transmit or reflect electromagnetic waves based on their frequency. Such structures typically consist of periodic arrays of elements, such as slots, patches, or dipoles, which interact with incoming electromagnetic waves to filter specific frequency bands while allowing others to pass through or be reflected. The term "Frequency Selective Surface" as used herein includes surfaces used in a variety of applications, including antennas, radomes, filters, and electromagnetic shielding. Said surfaces are critical in controlling the propagation of electromagnetic waves in systems that require precise filtering of specific frequencies. Additionally, FSS structures can be tailored to operate over a wide range of frequencies, from microwave to millimetre wave, and can be integrated into various materials and substrates, including flexible and rigid surfaces, for use in communication, defense, and commercial technologies.
[00024] As used herein, the term "slot array" refers to a patterned arrangement of slots, or openings, within a surface, typically used to control the passage of electromagnetic waves. Such arrays are characterized by their ability to filter or transmit specific frequencies of electromagnetic radiation, depending on the geometry, spacing, and arrangement of the slots. The term "slot array" as used herein includes arrays that are designed for use in applications such as antennas, frequency filters, and waveguides, where the precise control of electromagnetic wave propagation is required. Said arrays are often fabricated using techniques that allow for high-resolution patterning, enabling the creation of slots with dimensions tailored to specific frequency ranges. Additionally, the design of a slot array may involve the use of materials and processes that ensure durability and stability in various environmental conditions, making them suitable for use in both commercial and military applications.
[00025] As used herein, the term "substrate" refers to the underlying material or surface on which processes such as printing, deposition, or fabrication are performed. Such substrates serve as the foundation for building or applying other materials, and may include a wide range of materials such as polymers, metals, ceramics, and glass. The term "substrate" as used herein includes both rigid and flexible materials, and may be used in various applications such as electronics, photonics, and materials science. Said substrates are chosen based on their mechanical, thermal, and chemical properties, which must be compatible with the processes being applied. Additionally, substrates may undergo preparation steps, such as cleaning or surface treatment, to ensure proper adhesion and performance of the materials deposited or fabricated on them. The choice of substrate plays a critical role in determining the final properties and performance of the fabricated device or structure.
[00026] As used herein, the term "aerosol jet printing process" refers to a technique for depositing fine lines or patterns of material onto a substrate using a focused stream of aerosolized ink or material. Such a process is capable of producing high-resolution features with dimensions as small as a few micrometres, and is commonly used in applications requiring precise patterning of conductive, dielectric, or biological materials. The term "aerosol jet printing process" as used herein includes processes that utilize various types of inks, including nanoparticle-based inks, and can be applied to a wide range of substrates, including flexible and rigid materials. Said process is particularly suitable for creating complex patterns and structures in electronics, sensors, and biomedical devices. Additionally, the aerosol jet printing process allows for the non-contact deposition of materials, which is advantageous for working with delicate or uneven surfaces, and can be adapted to various manufacturing environments, from prototyping to large-scale production.
[00027] As used herein, the term "nanoparticle silver ink" refers to a colloidal suspension of silver nanoparticles, typically with particle sizes on the order of nanometres, used for printing or depositing conductive patterns on substrates. Such inks are characterized by their ability to form highly conductive traces after deposition and sintering, making them ideal for applications in printed electronics, sensors, and antennas. The term "nanoparticle silver ink" as used herein includes inks that are formulated with various stabilizers, solvents, and additives to achieve the desired viscosity, adhesion, and drying properties for specific printing processes. Said inks are typically prepared by dispersing silver nanoparticles in a solvent, followed by processes such as dilution, degassing, and filtering to ensure uniformity and performance. Additionally, nanoparticle silver inks can be used in various printing techniques, including inkjet, screen printing, and aerosol jet printing, and are sintered at temperatures suitable for the substrate to achieve optimal conductivity and durability.
[00028] As used herein, the term "printing parameters" refers to the set of variables and conditions that are controlled during a printing process to achieve the desired output. Such parameters may include factors such as nozzle size, flow rate, substrate temperature, printing speed, and layer thickness, all of which influence the quality and accuracy of the printed pattern or structure. The term "printing parameters" as used herein includes those specific to techniques such as aerosol jet printing, where precise control over the deposition process is required to produce high-resolution features. Said parameters are adjusted based on the material properties, substrate characteristics, and design specifications of the item being printed. Additionally, the optimization of printing parameters is critical for ensuring the repeatability and reliability of the printed components, and may involve iterative testing and calibration to achieve the desired results in various applications, from electronics manufacturing to biomedical device fabrication.
[00029] As used herein, the term "sintering" refers to the process of heating a material, typically in powder or particulate form, to a temperature below its melting point to induce bonding and densification. Such a process is commonly used to increase the strength, conductivity, and overall integrity of materials that have been printed or deposited in a loose or semi-solid state. The term "sintering" as used herein includes processes that are applied to materials such as metals, ceramics, and polymers, where the goal is to fuse particles together to create a solid, cohesive structure. Said process may be conducted in various environments, including in air, vacuum, or inert atmospheres, and may involve the application of pressure or other external forces to enhance the densification. Additionally, the sintering process is critical in applications such as printed electronics, where achieving the required electrical conductivity and mechanical stability is essential for the performance and longevity of the final product.
[00030] FIG. 1 illustrates a method for fabricating a millimetre wave frequency selective surface slot array on a substrate using an aerosol jet printing process, in accordance with the embodiments of the present disclosure. The method begins with preparing a nanoparticle silver ink. This preparation involves diluting the nanoparticle silver ink to achieve an appropriate viscosity suitable for the aerosol jet printing process. The viscosity must be carefully controlled to enable the precise deposition of the ink on the substrate. The nanoparticle silver ink is composed of silver nanoparticles, typically with a particle size in the nanometre range, dispersed in a solvent. To prepare the ink, a measured quantity of the nanoparticle ink is diluted using a suitable solvent to reach the desired viscosity, which is determined by the requirements of the aerosol jet printing process and the characteristics of the substrate. After achieving the correct viscosity, the ink is subjected to a degassing process to remove any trapped air bubbles. Air bubbles in the ink could disrupt the uniform deposition of the ink on the substrate, leading to defects in the printed slot array. The degassing process involves placing the diluted ink in a vacuum chamber or using other degassing techniques such as ultrasonic agitation. The removal of air bubbles is critical to ensure the continuous and uninterrupted flow of ink during the printing process. The nanoparticle silver ink, once properly diluted and degassed, is then ready for the subsequent steps in the method, where it will be deposited onto the substrate to form the desired frequency selective surface slot array.
[00031] The next step in the method involves preparing the substrate onto which the nanoparticle silver ink will be deposited. The substrate preparation process is essential for ensuring that the ink adheres properly and that the final frequency selective surface slot array exhibits the desired electrical and physical properties. The substrate, which may be composed of materials such as polyimide, glass, or other suitable materials, must be thoroughly cleaned to remove any contaminants that could interfere with the ink deposition process. The cleaning process typically begins with an ultrasonic bath in a solvent such as isopropyl alcohol, which helps to dislodge and remove particles, oils, and other impurities from the surface of the substrate. Following the ultrasonic cleaning, the substrate is rinsed with deionized water to remove any residual solvent and then dried to eliminate any remaining moisture. Drying can be performed using a nitrogen gas stream, a vacuum drying oven, or other drying methods that ensure the substrate is completely dry before printing. The cleanliness of the substrate is vital for achieving uniform ink deposition and preventing defects such as poor adhesion or uneven surface coverage. Once the substrate has been cleaned and dried, it is ready to be placed on the printing stage of the aerosol jet printer for the next step in the fabrication process.
[00032] The prepared substrate is then loaded onto the printing stage of an aerosol jet printer. The loading process involves carefully placing the cleaned and dried substrate onto the stage to ensure accurate alignment and stability during the printing process. The printing stage is typically designed to securely hold the substrate in place and may include features such as vacuum suction or mechanical clamps to prevent any movement during printing. Once the substrate is properly positioned, the stage is adjusted to the correct height and orientation relative to the printing nozzle. The alignment of the substrate with the nozzle is critical for achieving precise deposition of the nanoparticle silver ink. The aerosol jet printer uses a focused stream of aerosolized ink, which is directed onto the substrate to create the desired slot array pattern. The loading process may also involve setting up the printing parameters specific to the substrate being used, such as adjusting the stage temperature if the substrate requires heating to improve ink adhesion. The precise positioning and stabilization of the substrate are crucial for ensuring that the printed slot array is accurately aligned with the design specifications. Once the substrate is securely loaded and aligned, the aerosol jet printing

process can commence, where the nanoparticle silver ink will be deposited in a controlled manner to form the frequency selective surface slot array.
[00033] The deposition of the nanoparticle silver ink onto the substrate is carried out by controlling various printing parameters, including nozzle size, flow rate, and substrate temperature. These parameters must be precisely managed to form a slot array with specified dimensions and pattern geometry. The nozzle size of the aerosol jet printer is selected based on the desired feature size of the slot array. Smaller nozzles enable finer details and higher resolution in the printed pattern, while larger nozzles may be used for broader coverage. The flow rate of the ink is controlled by adjusting the pressure of the aerosol stream and the rate at which the ink is supplied to the nozzle. A consistent flow rate is necessary to ensure that the ink is deposited uniformly across the substrate without gaps or overlaps. The substrate temperature is another critical parameter that influences the adhesion and drying rate of the ink. Depending on the material of the substrate, the temperature may be adjusted to enhance the wetting properties of the ink, allowing it to spread evenly and adhere to the substrate surface. The pattern geometry of the slot array is defined by the movement of the printing stage and the nozzle, which are precisely coordinated to follow the design path. The aerosol jet printer may use a combination of horizontal and vertical track alignments to create the slots and define the edges of the array. The control of printing parameters is essential for producing a slot array that meets the desired specifications in terms of both electrical performance and physical dimensions. The precise deposition of the nanoparticle silver ink onto the substrate forms the foundation for the final frequency selective surface structure.
[00034] Following the deposition of the nanoparticle silver ink, the final step in the method is sintering the deposited ink at a temperature suitable for the substrate material to achieve a conductive frequency selective surface structure. Sintering is the process of heating the deposited ink to a temperature below its melting point, causing the silver nanoparticles to bond together and form a continuous, conductive film. The sintering temperature must be carefully controlled to ensure that the silver nanoparticles fuse properly without damaging the underlying substrate. For substrates made of polyimide, the sintering temperature is typically maintained in the range of 150 to 200 degrees Celsius, while higher temperatures may be used for glass or other heat-resistant substrates. The sintering process may be conducted in an oven, a hot plate, or using a focused heat source, depending on the specific requirements of the substrate and the design. During sintering, the silver nanoparticles undergo a transformation that enhances their electrical conductivity, creating a robust and stable frequency selective surface slot array. The duration of the sintering process is also a key factor, as it must be long enough to ensure complete bonding of the nanoparticles, but not so long as to cause degradation of the substrate. The successful sintering of the nanoparticle silver ink results in a conductive slot array that can be used in various electromagnetic applications, such as antennas, filters, and shielding devices. The method, therefore, concludes with the formation of a high-quality frequency selective surface slot array, ready for integration into the desired application.
[00035] In an embodiment, the substrate comprises a polyimide material characterized by high-temperature resistance and flexibility. Polyimide is a polymer known for its excellent thermal stability, making it suitable for applications that require exposure to high temperatures. The high-temperature resistance of polyimide allows the substrate to withstand the thermal conditions during processes such as sintering, without degrading or losing its structural integrity. Flexibility is another key characteristic of polyimide, enabling the substrate to be used in applications where conformability to non-flat surfaces is required. The combination of high-temperature resistance and flexibility makes polyimide an ideal substrate material for the fabrication of frequency selective surface slot arrays, particularly in applications involving flexible electronics or environments with fluctuating thermal conditions. The use of polyimide as a substrate allows for the deposition of nanoparticle silver ink using aerosol jet printing, followed by sintering, without compromising the mechanical or electrical properties of the final structure. Polyimide’s inherent properties ensure that the substrate remains intact and functional throughout the fabrication process, contributing to the overall performance and durability of the frequency selective surface slot array.
[00036] In an embodiment, the substrate comprises a glass-like material characterized by mechanical strength and transparency. Glass-like materials, such as borosilicate glass, offer robust mechanical properties, making them suitable for applications where structural integrity is paramount. The mechanical strength of such materials allows the substrate to resist deformation, cracking, or breaking during the fabrication process and in subsequent use. Transparency is another significant feature of glass-like materials, enabling their use in optical applications or scenarios where visual inspection of underlying components is necessary. The combination of mechanical strength and transparency makes glass-like substrates ideal for the fabrication of frequency selective surface slot arrays, particularly in applications requiring both durability and visual access to the substrate or the underlying layers. The use of a glass-like substrate allows for the precise deposition of nanoparticle silver ink using aerosol jet printing, followed by a controlled sintering process, without affecting the optical or mechanical properties of the final structure. Such substrates maintain their structural and optical characteristics throughout the fabrication process, ensuring the integrity and performance of the frequency selective surface slot array in various applications.
[00037] In an embodiment, the nanoparticle silver ink comprises silver nanoparticles having an average particle size of less than 50 nanometers to ensure fine feature resolution. Silver nanoparticles are used in conductive inks due to their excellent electrical conductivity and ability to form continuous conductive pathways when deposited and sintered. The particle size of the silver nanoparticles is a critical factor in determining the resolution of the printed features. Nanoparticles with an average size of less than 50 nanometers enable the deposition of finer lines and smaller features, which is essential for creating high-resolution frequency selective surface slot arrays. The small particle size allows the ink to be deposited in a controlled manner, resulting in sharp edges and well-defined patterns that meet the design specifications. Additionally, smaller nanoparticles sinter more effectively at lower temperatures, forming a dense and continuous conductive layer. The use of silver nanoparticles with an average particle size of less than 50 nanometers ensures that the printed slot array exhibits the required electrical and structural properties, making the nanoparticle silver ink suitable for high-performance applications in electronics and communication systems.
[00038] In an embodiment, the aerosol jet printing process involves adjusting the size of the printing nozzle to control the thickness of the deposited ink stream. The nozzle size directly influences the resolution and thickness of the printed features, with smaller nozzles producing finer lines and thinner layers, and larger nozzles allowing for broader coverage and thicker deposits. The ability to adjust the nozzle size provides flexibility in the printing process, enabling the creation of slot arrays with varying feature sizes and thicknesses as required by the design. By selecting the appropriate nozzle size, the thickness of the deposited ink stream can be precisely controlled, ensuring uniform coverage and consistent feature dimensions across the substrate. This control is particularly important when printing frequency selective surface slot arrays, where the accuracy of the printed features is critical to the performance of the final structure. The adjustment of the nozzle size during the aerosol jet printing process allows for the customization of the slot array’s physical characteristics, ensuring that the printed pattern meets the desired specifications for its intended application.
[00039] In an embodiment, the sheath gas pressure is varied during printing to optimize the deposition quality and to achieve consistent slot dimensions. The sheath gas, which surrounds the aerosolized ink stream, plays a critical role in focusing the ink as it is deposited onto the substrate. By adjusting the pressure of the sheath gas, the width and uniformity of the deposited ink stream can be controlled, allowing for precise manipulation of the printed features. Variations in sheath gas pressure can be used to refine the edges of the slots, control the ink’s spreading behavior, and ensure that the printed features maintain the intended dimensions. During the printing of frequency selective surface slot arrays, maintaining consistent slot dimensions is essential for achieving the desired electromagnetic properties. Therefore, the ability to vary the sheath gas pressure provides a valuable tool for optimizing the quality of the printed slots, ensuring that the final array meets the stringent requirements for its application. The controlled adjustment of sheath gas pressure during the aerosol jet printing process enables the production of high-quality slot arrays with consistent and accurate features.
[00040] In an embodiment, the sintering temperature for the deposited nanoparticle silver ink is maintained in the range of 150 to 200 degrees Celsius for polyimide substrates. Polyimide is known for its high-temperature resistance, but it is important to maintain the sintering temperature within a range that allows for effective bonding of the silver nanoparticles without damaging the substrate. The selected temperature range of 150 to 200 degrees Celsius is optimal for sintering silver nanoparticles while preserving the integrity of the polyimide substrate. At this temperature range, the silver nanoparticles begin to coalesce, forming a continuous conductive path, which is essential for the functionality of the frequency selective surface slot array. The sintering process at this temperature also minimizes the risk of thermal degradation of the polyimide, ensuring that the substrate retains its mechanical and electrical properties. By carefully controlling the sintering temperature, the method enables the production of a durable and highly conductive slot array on a polyimide substrate, suitable for use in various high-performance applications.
[00041] In an embodiment, the sintering temperature for the deposited nanoparticle silver ink is increased above 200 degrees Celsius for glass-like substrates to enhance conductivity. Glass-like materials, such as borosilicate glass, can withstand higher temperatures than polymer-based substrates like polyimide. Increasing the sintering temperature above 200 degrees Celsius allows the silver nanoparticles to bond more effectively, resulting in a denser and more conductive film. The elevated temperature promotes the complete sintering of the nanoparticles, reducing the resistivity of the printed slot array and improving its overall electrical performance. The ability to increase the sintering temperature is particularly advantageous when fabricating frequency selective surface slot arrays intended for high-frequency applications, where low electrical resistance is crucial. By utilizing a higher sintering temperature, the method enhances the conductivity of the nanoparticle silver ink on glass-like substrates, ensuring that the final slot array meets the required specifications for its intended use. The controlled application of heat during sintering allows for the production of high-quality conductive patterns on glass-like materials, suitable for advanced electromagnetic applications.
[00042] In an embodiment, the toolpath for depositing the nanoparticle silver ink is segmented into horizontal and vertical tracks, with gaps left between tracks to form slot heights and edges. The segmentation of the toolpath allows for precise control over the pattern geometry and dimensions of the slot array. By dividing the toolpath into horizontal and vertical tracks, the method ensures that each segment is accurately aligned with the design specifications, resulting in a consistent and well-defined slot array. The gaps left between the tracks are carefully calculated to form the desired slot heights and edges, which are critical for the performance of the Frequency Selective Surface. The controlled deposition of ink along the segmented toolpath allows for the creation of slots with sharp edges and uniform dimensions, minimizing variations that could affect the array's electromagnetic properties. This approach also facilitates the printing of complex patterns, where multiple layers or intersecting tracks are required. The segmentation of the toolpath is an important aspect of the printing process, ensuring that the final slot array exhibits the precision and accuracy necessary for high-performance applications.
[00043] In an embodiment, the method includes inspecting the printed frequency selective surface slot array using optical microscopy or scanning electron microscopy to verify the integrity and precision of the slots. Optical microscopy provides a non-destructive way to examine the surface features of the printed slot array, allowing for the detection of any defects, such as incomplete coverage, misalignment, or irregular edges. Scanning electron microscopy (SEM) offers a more detailed view, enabling the examination of the slot array at a higher magnification to assess the fine details of the printed pattern. The inspection process is critical for ensuring that the slot array meets the required specifications for its intended application. By using these microscopy techniques, the method allows for the identification and correction of any issues before the slot array is integrated into a final product. The thorough inspection of the printed slots ensures that the array exhibits the necessary electrical and mechanical properties, making it suitable for use in advanced electromagnetic applications. The inspection process is an essential step in the fabrication method, providing quality control and ensuring the reliability of the final frequency selective surface slot array.
[00044] In an embodiment, the method enables the fabrication of a millimetre wave frequency selective surface slot array by precisely preparing a nanoparticle silver ink with the correct viscosity and eliminating air bubbles through degassing. This process leads to uniform ink flow and consistent deposition, preventing defects that could disrupt the integrity of the printed slot array. Cleaning and drying the substrate before printing enhances the ink’s adhesion, reducing surface irregularities and ensuring a smooth deposition. By carefully controlling the printing parameters—such as nozzle size, flow rate, and substrate temperature—the method achieves accurate pattern geometry and dimensions, which are crucial for the electromagnetic performance of the slot array. Sintering the deposited nanoparticle silver ink at a suitable temperature for the substrate material solidifies the structure, promoting strong bonding between nanoparticles and resulting in a highly conductive and durable frequency selective surface slot array.
[00045] In an embodiment, the method incorporates the use of a polyimide substrate, which is characterized by its high-temperature resistance and flexibility. The selection of polyimide as the substrate material allows the method to withstand the elevated temperatures required during the sintering process without compromising the substrate’s structural integrity. Polyimide’s flexibility also supports applications where the substrate must conform to curved or non-flat surfaces, making it versatile for use in advanced electromagnetic systems. The ability to maintain both the mechanical and electrical properties of the polyimide substrate throughout the fabrication process enhances the reliability and performance of the resulting frequency selective surface slot array, particularly in environments subject to thermal variation or mechanical stress.
[00046] In an embodiment, the method employs a glass-like substrate that provides mechanical strength and transparency, making it suitable for applications where structural integrity and optical access are essential. The mechanical strength of the glass-like material ensures that the substrate remains stable during both the printing and sintering processes, preventing cracks or deformation that could otherwise affect the performance of the frequency selective surface slot array. Additionally, the transparency of the glass-like substrate is beneficial in applications where visual inspection or interaction with underlying components is required. This combination of durability and transparency supports the method’s applicability in high-performance optical and electromagnetic systems, where both physical robustness and clear visibility are necessary.
[00047] In an embodiment, the method involves the use of nanoparticle silver ink with silver nanoparticles having an average particle size of less than 50 nanometers. This small particle size allows for the deposition of fine features within the slot array, leading to higher resolution in the printed patterns. The reduced particle size enables more precise control over the printed features, ensuring sharp edges and well-defined slots, which are critical for achieving the desired frequency selectivity in the Frequency Selective Surface. The smaller nanoparticles also facilitate effective sintering at lower temperatures, forming a dense, continuous conductive film that enhances the electrical performance of the slot array, making it suitable for applications in high-frequency millimetre wave and terahertz systems.
[00048] In an embodiment, the method adjusts the size of the printing nozzle during the aerosol jet printing process to control the thickness of the deposited ink stream. This adjustment allows for fine-tuning of the printed features, enabling the creation of both thin and thick lines as required by the slot array’s design. By controlling the nozzle size, the method can achieve the desired feature resolution and ensure uniform coverage across the substrate. This flexibility in adjusting the nozzle size is crucial for meeting specific design requirements and maintaining the precision needed for the frequency selective surface slot array to function effectively in high-frequency applications.
[00049] In an embodiment, the method varies the sheath gas pressure during printing to optimize the deposition quality and achieve consistent slot dimensions. The sheath gas pressure influences the focus and stability of the aerosolized ink stream, which is essential for maintaining uniformity in the printed features. By adjusting the sheath gas pressure in response to the substrate’s properties or environmental conditions, the method can ensure that the slot array’s dimensions are accurate and consistent throughout the printing process. This control over the sheath gas pressure is vital for producing a reliable and high-quality frequency selective surface slot array, which requires precise feature dimensions to perform effectively in electromagnetic applications.
[00050] In an embodiment, the method involves maintaining the sintering temperature for the deposited nanoparticle silver ink within the range of 150 to 200 degrees Celsius when using a polyimide substrate. This temperature range is optimal for allowing the silver nanoparticles to bond effectively without causing thermal damage to the polyimide substrate. The controlled sintering process enhances the electrical conductivity of the slot array while preserving the flexibility and structural integrity of the polyimide. This careful balance between sintering temperature and substrate preservation is crucial for producing a durable and conductive frequency selective surface slot array that can withstand the operational demands of various high-frequency applications.
[00051] In an embodiment, the method increases the sintering temperature above 200 degrees Celsius when the substrate is made of glass-like material to enhance the conductivity of the slot array. The higher sintering temperature allows for more complete fusion of the silver nanoparticles, resulting in a denser and more conductive film. This improved conductivity is particularly important for applications involving high-frequency signals, where low resistance is critical for maintaining signal integrity. The glass-like substrate’s ability to withstand higher temperatures without deformation ensures that the sintering process does not compromise the structural stability of the slot array, making it suitable for use in advanced electromagnetic devices.
[00052] In an embodiment, the method segments the toolpath for depositing the nanoparticle silver ink into horizontal and vertical tracks, with gaps left between tracks to form the slot heights and edges. This segmentation allows for precise control over the printed pattern, ensuring that the slots have sharp edges and uniform dimensions. By carefully calculating the gaps between tracks, the method can produce a slot array with the exact geometrical characteristics required for optimal electromagnetic performance. The segmented toolpath approach is essential for maintaining the accuracy and consistency of the printed features, which are crucial for the slot array’s effectiveness in high-frequency applications such as communication and radar systems.
[00053] In an embodiment, the method includes inspecting the printed frequency selective surface slot array using optical microscopy or scanning electron microscopy to verify the integrity and precision of the slots. These inspection techniques allow for detailed examination of the printed features, ensuring that they meet the required specifications for size, shape, and alignment. Detecting and correcting any defects during the inspection process helps maintain the overall quality and performance of the slot array. The use of optical and electron microscopy ensures that the printed array is free from imperfections that could affect its electromagnetic properties, thereby supporting its application in high-performance electromagnetic systems.
[00054] FIG. 2 illustrates a sequence diagram for fabricating a millimetre wave frequency selective surface (FSS) slot array, in accordance with the embodiments of the present disclosure. The process begins with the operator preparing nanoparticle silver ink, which involves diluting the ink to an appropriate viscosity and degassing it to remove any air bubbles. Once the ink is prepared, the substrate undergoes preparation, which includes cleaning and drying to remove any contaminants that may affect the printing quality. After the substrate is ready, it is loaded onto the printing stage of an aerosol jet printer. The operator then controls the printing parameters, adjusting the nozzle size, flow rate, and substrate temperature to ensure precise deposition of the nanoparticle silver ink onto the substrate. The ink is deposited in a manner that forms a slot array with specified dimensions and pattern geometry. Following the deposition, the printed substrate undergoes a sintering process at a temperature suitable for the substrate material, solidifying the nanoparticle silver ink to achieve a conductive FSS structure. The sequence diagram effectively outlines each step and interaction in the method, ensuring that the process is carried out systematically to produce a high-quality FSS slot array.
[00055] FIG. 3 illustrates a tabular representation of fabrication parameters for creating the novel toolpath, in accordance with the embodiments of the present disclosure. The nozzle size is set at 150 µm, which optimizes the balance between resolution and deposition rate during printing. The sheath gas level is maintained at 20 cm³, which plays a crucial role in focusing the aerosolized ink stream for precise deposition. The impact exhauster operates within a range of 600-700 cm³ to regulate the flow of the aerosol stream, ensuring consistent ink delivery. The atomizer is set to 800 cm³, generating a fine mist of nanoparticle silver ink, which is essential for high-resolution printing. The speed of the toolpath during printing is controlled within the range of 4-6 mm/sec, while the speed at corners is reduced to 1 mm/sec to enhance accuracy in complex geometries. For rapid tool motion, a speed of 10 mm/sec is used, facilitating efficient movement between print areas.
[00056] FIG. 4 (a to c) illustrates an experimentation process with the aerosol stream size and ink dispersions, in accordance with the embodiments of the present disclosure. The experimentation involved adjusting the aerosol stream size and ink dispersions to achieve the desired deposition quality. Initial experiments revealed that the ink tracks failed to disperse properly and did not fuse together as intended, leading to discontinuities in the printed patterns. For the specific design, the impact exhauster volume was initially set at 700 cm³. However, the substrate properties, particularly when using Corning Eagle glass, presented challenges similar to those encountered with Kapton due to differences in surface characteristics. To address these issues, the impact exhauster volume was carefully monitored and adjusted within a range of 620 cm³ to 700 cm³, depending on the ink deposition and the instantaneous width of the tracks being printed. Additionally, variations in the sheath gas pressure were employed throughout the process, allowing for the fine-tuning of the deposition to achieve the correct slot shapes. Through iterative adjustments and close observation of the sheath gas pressure, the desired slot geometry was successfully obtained, as depicted in FIG. 4.
[00057] The millimetre wave (mm-wave) low-THz frequency selective surface (FSS) slot arrays fabricated using the described method are versatile and applicable across various advanced electromagnetic technologies. These slot arrays are particularly effective in electromagnetic shielding applications for mm-wave frequencies, where they can block or attenuate specific frequencies to protect sensitive electronic equipment from interference. Additionally, they are well-suited for use as frequency selective filters in 5G and 6G antennas, where precise control over the transmission and reflection of electromagnetic waves is required to optimize signal quality and bandwidth. The slot arrays are also valuable in advanced radome designs, where they enhance the performance of radar systems by selectively filtering frequencies while allowing the passage of desired signals. Furthermore, these FSS slot arrays are integral to the development of metamaterial-based devices, which manipulate electromagnetic waves in novel ways for 5G and 6G communications, improving signal control and efficiency. The method provides a robust solution for creating high-performance components essential for cutting-edge communication and shielding technologies.
[00058] The method describes 3D printing millimetre wave frequency selective surface (FSS) slot arrays on polyimide and glass-like substrates using nanoparticle silver ink with Aerosol Jet Printers. Said method allows direct fabrication of highly conductive slot arrays on various substrates without traditional photolithography or etching processes. The process is scalable, cost-effective, and suitable for creating high-resolution FSS structures for multiple electromagnetic applications. A toolpath specific to the design was laid out, requiring the design to be divided into several parts, allowing breaks in the printing process for cleaning the tube and deposition head. A 100 µm nozzle was used to fabricate two designs, with the FSS designs arranged in a 50 mm² square array on a 50-micron-thick Kapton polyimide sheet. Kapton's thin, smooth characteristics and high-temperature tolerance make said material ideal for frequency filters and electromagnetic shielding. The small square FSS lattice included arrays with varying sizes for sub-125 GHz and sub-300 GHz ranges. Unlike conventional methods, the arrays were divided into four subparts, with a strategic approach employed to maintain design quality. The design was broken down into smaller sections, with toolpaths planned using a combination of horizontal and vertical track alignments. The entire FSS structure was assumed to be fabricated as a grid of horizontal and vertical fine tracks, with horizontal tracks printed adjacent to each other and a 0.1 mm gap left after every four tracks to form the slots and define the slot heights. Vertical line tracks were used to create smooth slot edges and widths, with margins left to allow the ink to spread within design boundaries. The speed of the toolpath was also adjusted, determined through rigorous pre-planning and testing on inks of varying viscosities, as the design required an approach with no pre-established toolpath guidelines. The thickness of the ink stream from the Aerosol Jet printer was controlled by adjusting the size of the printing nozzle or by modifying the flow rate of the sheath gas.
[00059] Operations in accordance with a variety of aspects of the disclosure is described above would not have to be performed in the precise order described. Rather, various steps can be handled in reverse order or simultaneously or not at all.
[00060] While several implementations have been described and illustrated herein, a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein may be utilized, and each of such variations and/or modifications is deemed to be within the scope of the implementations described herein. More generally, all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific implementations described herein. It is, therefore, to be understood that the foregoing implementations are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, implementations may be practiced otherwise than as specifically described and claimed. Implementations of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present disclosure.

Claims
I/We Claim:
1. A method for fabricating a millimetre wave frequency selective surface slot array on a substrate using an aerosol jet printing process, wherein the method comprises:
preparing a nanoparticle silver ink by diluting to an appropriate viscosity and degassing to remove air bubbles;
preparing the substrate by cleaning and drying to remove contaminants;
loading the substrate onto a printing stage of an aerosol jet printer;
depositing the nanoparticle silver ink onto the substrate by controlling printing parameters including nozzle size, flow rate, and substrate temperature, to form a slot array with specified dimensions and pattern geometry; and
sintering the deposited nanoparticle silver ink at a temperature suitable for the substrate material to achieve a conductive frequency selective surface structure.
2. The method as recited in claim 1, wherein the substrate comprises a polyimide material characterized by high-temperature resistance and flexibility.
3. The method as recited in claim 1, wherein the substrate comprises a glass-like material characterized by mechanical strength and transparency.
4. The method as recited in claim 1, wherein the nanoparticle silver ink comprises silver nanoparticles having an average particle size of less than 50 nanometers to ensure fine feature resolution.
5. The method as recited in claim 1, wherein the aerosol jet printing process involves adjusting the size of the printing nozzle to control the thickness of the deposited ink stream.
6. The method as recited in claim 1, wherein the sheath gas pressure is varied during printing to optimize the deposition quality and to achieve consistent slot dimensions.
7. The method as recited in claim 1, wherein the sintering temperature for the deposited nanoparticle silver ink is maintained in the range of 150 to 200 degrees Celsius for polyimide substrates.
8. The method as recited in claim 1, wherein the sintering temperature for the deposited nanoparticle silver ink is increased above 200 degrees Celsius for glass-like substrates to enhance conductivity.
9. The method as recited in claim 1, wherein the toolpath for depositing the nanoparticle silver ink is segmented into horizontal and vertical tracks, with gaps left between tracks to form slot heights and edges.
10. The method as recited in claim 1, wherein the method includes inspecting the printed frequency selective surface slot array using optical microscopy or scanning electron microscopy to verify the integrity and precision of the slots.

METHOD FOR FABRICATING A MILLIMETRE WAVE FREQUENCY SELECTIVE SURFACE SLOT ARRAY USING AEROSOL JET PRINTING PROCESS
Abstract
The present disclosure discloses a method for fabricating a millimetre wave frequency selective surface slot array on a substrate using an aerosol jet printing process. The method comprises preparing a nanoparticle silver ink by diluting to an appropriate viscosity and degassing to remove air bubbles. The method further includes preparing the substrate by cleaning and drying to remove contaminants, loading the substrate onto a printing stage of an aerosol jet printer, depositing the nanoparticle silver ink onto the substrate by controlling printing parameters including nozzle size, flow rate, and substrate temperature, to form a slot array with specified dimensions and pattern geometry, and sintering the deposited nanoparticle silver ink at a temperature suitable for the substrate material to achieve a conductive frequency selective surface structure.
Fig. 1 , Claims:Claims
I/We Claim:
1. A method for fabricating a millimetre wave frequency selective surface slot array on a substrate using an aerosol jet printing process, wherein the method comprises:
preparing a nanoparticle silver ink by diluting to an appropriate viscosity and degassing to remove air bubbles;
preparing the substrate by cleaning and drying to remove contaminants;
loading the substrate onto a printing stage of an aerosol jet printer;
depositing the nanoparticle silver ink onto the substrate by controlling printing parameters including nozzle size, flow rate, and substrate temperature, to form a slot array with specified dimensions and pattern geometry; and
sintering the deposited nanoparticle silver ink at a temperature suitable for the substrate material to achieve a conductive frequency selective surface structure.
2. The method as recited in claim 1, wherein the substrate comprises a polyimide material characterized by high-temperature resistance and flexibility.
3. The method as recited in claim 1, wherein the substrate comprises a glass-like material characterized by mechanical strength and transparency.
4. The method as recited in claim 1, wherein the nanoparticle silver ink comprises silver nanoparticles having an average particle size of less than 50 nanometers to ensure fine feature resolution.
5. The method as recited in claim 1, wherein the aerosol jet printing process involves adjusting the size of the printing nozzle to control the thickness of the deposited ink stream.
6. The method as recited in claim 1, wherein the sheath gas pressure is varied during printing to optimize the deposition quality and to achieve consistent slot dimensions.
7. The method as recited in claim 1, wherein the sintering temperature for the deposited nanoparticle silver ink is maintained in the range of 150 to 200 degrees Celsius for polyimide substrates.
8. The method as recited in claim 1, wherein the sintering temperature for the deposited nanoparticle silver ink is increased above 200 degrees Celsius for glass-like substrates to enhance conductivity.
9. The method as recited in claim 1, wherein the toolpath for depositing the nanoparticle silver ink is segmented into horizontal and vertical tracks, with gaps left between tracks to form slot heights and edges.
10. The method as recited in claim 1, wherein the method includes inspecting the printed frequency selective surface slot array using optical microscopy or scanning electron microscopy to verify the integrity and precision of the slots.