Abstract:
Systems and methods for producing electromagnetic devices are provided. The systems and methods allow for an electromagnetic device having both a substrate (e.g., polymer) and conductive material (e.g., metal) to be manufactured without using masks or other outside objects disposed over a surface (e.g., the substrate) onto which the conductive material is deposited. In one exemplary embodiment, the method includes performing additive manufacturing using a polymer to produce a device having a plurality of interconnected walls and a plurality of frequency selective surface elements, and then coating portions of the device with a conductive material. A plurality of shadowing features are formed as part of one or more of the walls to protect the frequency selective surface elements from being coated by the conductive material. Other methods, and a variety of systems that can result from the disclosed methods, are also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to and the benefit of U.S. Provisional Application No. 62/309,510, filed on Mar. 17, 2016, and titled “Process for the Selective Coating of a Substrate,” the content of which is incorporated herein by reference in its entirety. 
     
    
     GOVERNMENT RIGHTS 
       [0002]    This invention was made with Government support under Grant No. FA8650-14-D1714 awarded by the Air Force Research Laboratory. The Government has certain rights in the invention. 
     
    
     FIELD 
       [0003]    The present application relates to systems and methods for fabricating substrates, and more specifically to selectively coating fabricated substrates using shadowing features fabricated thereon. 
       BACKGROUND 
       [0004]    Efforts are underway to utilize the rapid prototyping capabilities of additive manufacturing for the fabrication of electromagnetic devices, including in the radio frequency (RF) and microwave domains, where interests can be found in uses for military, space, and aeronautics, among other industries. For example, antennas and other associated components of a radar or communication system can benefit from being rapidly built. Methods for producing components such as antennas and the like are often evaluated based on competing interests of size, weight, performance for a particular application, and expense. Current technology is often incredibly expensive. Additive manufacturing, however, has the flexibility to make an impact on all four of the aforementioned factors by enabling previously inconceivable designs that can ultimately reduce the size and weight of RF devices while improving performance and lowering the cost of development. 
         [0005]    There are many challenges, however, associated with trying to apply additive manufacturing techniques to the fabrication of electromagnetic devices. For example, there are many material limitations inherent to most additive manufacturing processes. This is because most additive manufacturing processes are designed to handle either substrates (e.g., polymers) or conductive materials (e.g., metals), but are not capable of constructing a part that comprises both a substrate and a conductive material. This means the electrical properties of a part are either conductive or those of a dielectric, but not both. This leaves most electromagnetic fabrication problems to be solved through printed circuit board processes. Attempts have been made to optimize the combination of conductive and dielectric properties into a single board. Printed circuit board processes, however, do not easily translate to the fabrication of electromagnetic devices. Further, there are drawbacks to the printed circuit board processes, including but not limited to the possibility of electrical shorts occurring because traces are undesirably electrically connected. 
         [0006]    In some instances, additive manufacturing that requires both a substrate and one or more conductive material is performed using a mask or other outside object or structure disposed over a surface onto which the conductive material is deposited (e.g., the substrate) to control a location of the conductive material. For example, first the substrate is deposited, then a mask or other outside object or structure is placed on the substrate, and then the conductive material is deposited onto the substrate, around the mask. However, as the design of the desired electromagnetic devices becomes more complex and/or intricate, the complexity as it applies to masks and the like is at least two-fold. First, it can be difficult to design and produce a mask having a more intricate or complex design due to the complex geometrical features involved. Second, it can be difficult for the mask to maintain its desired shape as complex geometrical features may not provide as much support for portions of the mask, thus causing the mask to move, shift, and/or collapse. This results in difficulties controlling where conductive metal particles ultimately settle—just as if no mask was involved at all. 
         [0007]    Accordingly, there is a need for systems and methods that allow a substrate to be coated with a conductive material without using masks or other outside objects or structures disposed over the substrate onto which the conductive material is to be deposited. 
       SUMMARY 
       [0008]    The present disclosure generally provides for systems and methods for producing electromagnetic devices. Many different electromagnetic devices can be formed in view of the present disclosures, including but not limited to circuit boards. The disclosed systems and methods allow for both a substrate (e.g., polymer) and conductive material (e.g., metal) to be used in the manufacturing of electromagnetic devices without using outside objects or structures (e.g., masks) to help control the deposition of the conductive material with respect to the substrate. As described in greater detail below, shadowing features are incorporated directly into the substrate as it is manufactured, and the shadowing features are then used as a way to control the deposition of the conductive material. Although the systems and methods described herein are primarily described in conjunction with additive manufacturing techniques, a person skilled in the art will recognize the present disclosures can be adapted for use with other manufacturing techniques without departing from the spirit of the present disclosure. 
         [0009]    In one exemplary embodiment of a method for producing an electromagnetic device, the method includes performing additive manufacturing using a polymer to produce a device having a plurality of interconnected walls and a plurality of frequency selective surface (FSS) elements, and coating portions of the device with a conductive material. Each FSS element of the plurality of FSS elements has a first terminal end and a second terminal end, with the first terminal end of each FSS element being coupled to a wall of the plurality of interconnected walls and the second terminal end of each FSS element being coupled to a wall of the plurality of interconnected walls. The wall can be the same wall, although they do not have to be the same walls. A plurality of shadowing features are formed as part of one or more walls of the plurality of interconnected walls. The shadowing features are configured to protect a portion of the FSS element disposed in the respective feature and/or a portion of the wall to which the FSS element is coupled from being coated by the conductive material during the coating step. The term protecting may mean that no conductive material is deposited on at least some of the protected portion, or it may mean that inconsequential amounts of conductive material are deposited on at least some of the protected portion. An inconsequential amount can be an amount that is not significant enough so as to create a completed conductive path because the shadowing feature is designed to provide a break in contact between conductive portions or portions that may become conductive, for instance through deposition of a conductive material onto the substrate. A person skilled in the art will understand what an inconsequential amount is in view of the present disclosures. It is at least an amount that is less than the amount deposited onto the substrate that is intended to be conductive. 
         [0010]    The step of coating portions of the device with a conductive material can be performed without the use of a mask or other object or structure disposed over a surface onto which the conductive material is deposited to control a location of the conductive material. The surface can be, for example, the surface that results from the use of the polymer, which can form a substrate. In some embodiments, the plurality of interconnected walls and the plurality of FSS elements can be produced simultaneously during a single manufacturing pass. 
         [0011]    The plurality of shadowing features can be formed as part of one or more walls of the plurality of interconnected walls during the time the step of performing additive manufacturing using a polymer to produce a device having a plurality of interconnected walls is performed. In some embodiments, a base of the plurality of interconnected walls can be non-planar. 
         [0012]    An exemplary embodiment of an electromagnetic device includes a plurality of interconnected walls, a plurality of shadowing features, and a plurality of frequency selective surface (FSS) elements. The shadowing features are formed in the plurality of interconnected walls such that one or more shadowing features are formed in at least one wall of the plurality of interconnected walls. They can be formed in multiple walls. Each FSS element has a first terminal end and a second terminal end. The first terminal end of each FSS element is coupled to a wall of the plurality of interconnected walls, and the second terminal end of each FSS element is coupled to a wall of the plurality of interconnected walls. The walls can be the same wall, although they do not have to be the same wall. The first terminal end of at least one FSS element is disposed in a first shadowing feature of the plurality of shadowing features and the second terminal end of the same FSS element is disposed in a second shadowing feature of the plurality of shadowing features. 
         [0013]    In some embodiments, the plurality of interconnected walls can include four walls that form a rectangular shape, the plurality of shadowing features can include eight shadowing features with two shadowing features being formed in each of the four walls, and the plurality of FSS elements can include four FSS elements with the terminal ends of each of the elements being disposed in a separate shadowing feature of the eight shadowing features. 
         [0014]    One or more additional electromagnetic devices can be provided to form an array of electromagnetic devices. Each device of the one or more electromagnetic devices can be similarly configured to the earlier described electromagnetic device, or they can have different configurations. Thus, in some embodiments, each electromagnetic device of the one or more electromagnetic devices can include a plurality of interconnected walls, a plurality of shadowing features, and a plurality of FSS elements. The shadowing features can be formed in the plurality of interconnected walls such that one or more shadowing features are formed in at least one wall of the plurality of interconnected walls. They can be formed in multiple walls. Each FSS element can have a first terminal end and a second terminal end, with the first terminal end of each FSS element being coupled to a wall of the plurality of interconnected walls, and the second terminal end of each FSS element being coupled to a wall of the plurality of interconnected walls. The walls can be the same wall, although they do not have to be the same wall. The first terminal end of at least one FSS element can be disposed in a first shadowing feature of the plurality of shadowing features and the second terminal end of the same FSS element can be disposed in a second shadowing feature of the plurality of shadowing features. The one or more additional electromagnetic devices can share at least one wall of the plurality of interconnected walls in common. 
         [0015]    A thickness of at least one of the shadowing features of the plurality of shadowing features can be greater than a thickness of the wall in which the shadowing feature is formed. In some embodiments, the shadowing feature can include a block having opposed first and second block walls. The first block wall can have a bore formed in it through which the FSS element disposed in the shadowing feature passes through, and the second block wall can be the wall to which the first or second terminal end of the FSS element is coupled. In some embodiments, the shadowing feature can include one or more ledges formed in it. The ledges can be configured to protect a portion of the FSS element disposed in the shadowing feature and/or a portion of the wall to which the FSS element is coupled from a coating when a coating is applied to the electromagnetic device. The one or more ledges can further include stepped ledges that provide for multiple ledges having different configurations (e.g., shapes, sizes, etc.) formed in the shadowing feature. 
         [0016]    The plurality of interconnected walls can include a polymer coated in a metal. The plurality of shadowing features can include a polymer having portions of it coated in a metal with at least some portions not coated in a metal, or at least coated in less metal that other portions of the associated interconnected wall. The plurality of FSS elements can include a metal. 
         [0017]    In one exemplary method for producing a printed circuit board, the method includes performing additive manufacturing to produce a substrate having a plurality of channels formed in it that extend through a portion of a thickness of the substrate such that a depth of the channel is less than a thickness of the portion of the substrate in which the respective channel is formed. At least one channel of the plurality of channels has a first width at a top surface of the substrate and a second width at a location disposed below the top surface. The second width is greater than the first width such that the at least one channel includes a shadowing feature. The method further includes coating portions of the substrate with a conductive material to form a plurality of traces in conjunction with the channels. The portions of the channel associated with the shadowing feature receives less conductive material than other portions of the channel. 
         [0018]    A base of the substrate can be non-planar (i.e., curved). In some embodiments, the step of performing additive manufacturing to produce a substrate is performed using silicon. The conductive material can include a metal. 
         [0019]    One exemplary embodiment of a printed circuit board includes a substrate, a plurality of traces formed on a top surface of the substrate, and a plurality of shadowing features disposed below the top surface of the substrate. The shadowing features are configured such that a portion of the substrate is less accessible to receive material deposited onto the substrate than portions of the substrate not associated with the shadowing features. Although the traces are described as being formed on a top surface of the substrate, a person skilled in the art, in view of the present disclosures, will understand that at least a portion of the traces may be disposed below the top surface. 
         [0020]    In some embodiments, the printed circuit board can include a plurality of channels formed in the substrate. The channels can extend through a portion of a thickness of the substrate such that at depth of the channel is less than a thickness of the portion of the substrate in which the respective channel is formed. At least two channels of the plurality of channels can have a first width at the top surface of the substrate and a second width at a location disposed below the top surface. The second width can be greater than the first width such that each channel of the at least two channels includes a shadowing feature of the plurality of shadowing features. The plurality of traces can be associated with the plurality of channels. At least a portion of the traces may extend into a portion of the respective channels. In some embodiments, a base of the substrate can be non-planar. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]    The present application will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0022]      FIG. 1  is a perspective view of one exemplary embodiment of a three-dimensional FSS cell; 
           [0023]      FIG. 2A  is a perspective view of another exemplary embodiment of an FSS cell having shadowing features; 
           [0024]      FIG. 2B  is a perspective view of one exemplary embodiment of an array of the FSS cells of  FIG. 2A ; 
           [0025]      FIG. 3A  is a perspective view of one exemplary embodiment of an array of shadowing features; 
           [0026]      FIG. 3B  is a cross-sectional view of the array of  FIG. 3A  taken along the line L-L; 
           [0027]      FIG. 4A  is a perspective view of another exemplary embodiment of an FSS cell having shadowing features; 
           [0028]      FIG. 4B  is a perspective view of an array of the FSS cells of  FIG. 4A ; 
           [0029]      FIG. 4C  is a cross-sectional view of the FSS cell of  FIG. 4A  taken along the line T-T; 
           [0030]      FIG. 5A  is an exemplary embodiment of a printed circuit board; 
           [0031]      FIG. 5B  is another exemplary embodiment of a printed circuit board (PCB); 
           [0032]      FIG. 6A  is a perspective view of an exemplary embodiment of a three-dimensional PCB; 
           [0033]      FIG. 6B  is another perspective view of the PCB of  FIG. 6A ; 
           [0034]      FIG. 6C  is a magnified perspective view of the PCB of  FIG. 6A ; and 
           [0035]      FIG. 6D  is another magnified perspective view of the PCB of  FIG. 6A . 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the systems and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the systems and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present disclosure is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure. Further, in the present disclosure, like-numbered components of various embodiments generally have similar features when those components are of a similar nature and/or serve a similar purpose. 
         [0037]    The present disclosure includes some illustrations and descriptions that include prototypes or bench models. A person skilled in the art will recognize how to rely upon the present disclosure to integrate the techniques, systems, and methods provided for into a product, such as a consumer-ready, factory-ready, or lab-ready three-dimensional printer for fabricating substrates. 
         [0038]    Exemplary embodiments of the present disclosure provide for manufacturing of substrates for electromagnetic (EM) devices. In some exemplary embodiments, the EM devices described are frequency selective surface (FSS) with a three dimensional unit cell (referred to herein as “FSS cell”). 
         [0039]    Exemplary embodiments of the present disclosure provide for fabricating and coating substrates for electromagnetic (EM) devices. In some exemplary embodiments, the EM devices described are Frequency Selective Surface (FSS) with a three dimensional unit cell (referred to herein as “FSS cell”), or printed circuit boards (PCBs). 
         [0040]    Electromagnetic Devices with Shadowing Features 
         [0041]    Frequency Selective Surface Cells 
         [0042]      FIG. 1  is a perspective view of one exemplary embodiment of a three-dimensional FSS cell  100 . As will be described in further detail below, the FSS cell  100  includes shadowing features that are used to shadow (e.g., protect, cover, shield) portions of the FSS cell  100  from being coated (or fully coated) during a coating procedure. It should be understood that the FSS cell  100  illustrated in  FIG. 1  is one example of an electromagnetic device that can be designed, fabricated and used in accordance with the embodiments described herein, although other electromagnetic devices are contemplated. 
         [0043]    The FSS cell  100  can be fabricated using various techniques known by those skilled in the art, including, for example, additive manufacturing (AM) technologies such as three-dimensional printing, rapid prototyping, direct digital manufacturing, layered manufacturing and additive fabrication. The additively manufactured FSS cell  100  is a substrate made up of a non-conductive material such as plastic, fiberglass or other polymers known by those skilled in the art. The FSS cell  100  including its interconnected walls  102  and other parts (and/or an array of FSS cells such as  220  or  420  illustrated below in  FIGS. 2B and 4B ) can be printed in a single additive manufacturing or three-dimensional printing session and/or as a single printed unit. 
         [0044]    In turn, the fabricated FSS cell  100  is coated with one or more conductive materials. One example of a conductive material is metal. Non-exhaustive examples of suitable metals for coating the FSS cell  100  include a thin metal film of copper, gold, silver, nickel (or other conductive metals known by those of skill in the art) to add conductive or electromagnetic properties thereto. Coating of the FSS cell  100  refers to the deposition of the conductive material (e.g., metal) onto the substrate FSS cell using various techniques known by those of skill in the art, including sputtering, physical vapor deposition, electron beam deposition, thermal evaporation based metal deposition, spraying, splattering, splashing, spray painting and the like. The shadowing features of the FSS cell  100  allow for portions of the FSS cell  100  to not be coated (or to be coated less than other portions or areas of the FSS cell) such that the electrical conductivity between portions of the FSS cell  100  can be separated or discontinued relative to the fully or normally coated areas. Notably, the shadowing features reduce or eliminate the need for stencils or masks to be used to control the deposition of metal onto the generated FSS cell. In some embodiments, the shadowing features can be referred to as embedded masks—indicating that the FSS cell or other structure itself has geometric features that provide selective coating (e.g., controlled coating of a desired or target location). 
         [0045]    More specifically, the FSS cell  100  includes walls  102 , shadowing features  104  and FSS elements  106 . The walls  102  function as a low frequency filter of the FSS cell, the FSS elements  106  (e.g., portions thereof) function as high frequency filters, and the shadow features  106  protect parts—e.g., ends—of the FSS elements  106  from being fully or normally coated. The walls  102  can be interconnected with one another. 
         [0046]    Each of the walls  102  includes an inner surface  102   i  and an outer surface  102   o . Together, the walls  102  can form a geometric structure such as a rectangle, as shown in  FIG. 1 . When an FSS cell is printed as part of an array, the outer surface of a wall of the FSS cell can be adjacent to or touching the outer surface of a wall of another FSS cell, or can be exposed if the FSS cell is the edge or border of the array. The inner surfaces  102   i  of each wall  102  of the FSS cell  100  are positioned such that they face each other and in the direction of the FSS elements  106 . 
         [0047]    It should be understood that the height (measured in a direction along the Z axis), width (measured along the X or Y axes), and thickness of each of the walls (measured from the inner surface to the outer surface of a wall, along the X or Y axes) of an FSS cell can vary within a single wall, or relative to walls in the same or different FSS cells. The dimensions of the walls themselves and their dimensions relative to the rest of the FSS element have an effect on the mechanical and electrical properties of the FSS, such as the mechanical strength, and the upper frequency, lower frequency and bandwidth of the FSS elements that make up an FSS filter. Thus, these dimensions can be selected to achieve desired properties (e.g., mechanical strength, and the upper frequency, lower frequency and bandwidth) of the FSS cell. In some embodiments, outer surfaces of the walls  102 , and/or their inferior or superior surfaces can for a planar or non-planar surface. That is, the base or inferior surface of a plurality of walls of FSS cells can be fabricated to form a curved or cone structure, such that the set of FSS calls can be attached to or disposed on an structure having a curved surface of inverse geometry. 
         [0048]    The FSS elements  106  are filters for electromagnetic waves. The FSS elements  106  are configured to function as a band pass filter with a wide bandwidth and sharp cutoffs above and below the pass band. 
         [0049]    The FSS cell  100  also includes shadowing features  104 . While the FSS cell  100 , including its walls  102  and shadowing features  104 , are printed as a single unit, it should be understood that the shadowing features  104  can be identified or referred to separately from their respective walls  102 , as shown in exemplary  FIG. 1 . This is useful, for example, when the thickness of the shadowing features  104  is different than the thickness of the walls  102 , as in  FIG. 1 . The shadowing features  104  and the respective walls  102  can be referred to or identified together, for example, in embodiments in which the walls and shadowing features have a substantially similar thickness. It should be understood that in some embodiments the walls may have or correspond to a plurality of shadowing features, such as one, two, four, eight, or more shadowing features per wall. 
         [0050]    The shadowing features  104  of the FSS cell  100  include an inner surface  104   i  and an outer surface  104   o . As shown in  FIG. 1 , the thickness of the shadowing features  104  (which is measured as the distance between the inner surface  104   i  and outer surface  104   o  of a shadowing feature) can differ from the thickness of their respective walls. That is, in  FIG. 1 , the shadowing features  104  are thicker than the walls  102 . It should be understood that the height, width and thickness of the shadowing features can vary within a single shadowing feature, or relative to other shadowing features in the same or different FSS cells. 
         [0051]    Each of the shadowing features  104  includes a region—also referred to herein as the “shadowing region”—that is disposed or fabricated on or relative to the inner surfaces  104   i  of the shadowing features  104 . The shadowing regions are designed and fabricated in a manner that enable the shadowing (e.g., protecting, shielding) of at least a portion of a respective FSS element  106 , such that the shadowed portion (e.g., terminal end) of the FSS element is coated differently (e.g., less) than another portion (e.g., a substantially adjacent portion) of the same FSS element  106 . It should be understood that the shadowed portion or terminal end of the FSS element refers to a region of different sizes and locations. That is, the terminal end can refer to an area of the FSS element where conductivity is discontinued, rather than merely an end-point of the FSS element structure. In some embodiments, an FSS element can includes one, two, or more terminal ends. Further, in some embodiments, the shadowing features can also shadow, protect, or shield portions of the walls of the FSS cell. 
         [0052]    As shown in  FIG. 1 , the exemplary shadowing features  104  include a rectangular hollow portion—i.e., a concave or void area extending from the inner surface  104   i  in a direction towards the outer surface  104   o —of the shadowing features  104 . The dimension, shape and positioning of the shadowing regions on the shadowing features  104  can vary, and can be fabricated based on factors such as the type of coating process and material to be used, the angle or angles or the coating, the dimensions of the FSS elements, the type of substrate, environmental factors, and other factors understood by those of skill in the art. 
         [0053]    For instance, in some embodiments, the shadowing regions of shadowing features need not be hollow or concave relative to the inner surface of the shadowing features, as shown in exemplary  FIG. 1 . Instead (or additionally) the shadowing region can be or have a convex portion—i.e., extending from the inner surface of a shadowing feature in a direction extending away from the outer surface of the shadowing feature. Moreover, in some embodiments, the shadowing region can be circular, triangular, or other shapes. Further, in some embodiments such as those in which the shadowing region is a convex portion, the shadowing region need not form a closed geometry such as a full circle or rectangle. Instead, the shadowing region can be a semi-circle, arc, plane, bracket shape, or the like, that is optimally positioned relative to the corresponding FSS element in an area where the coating of the FSS element can best be forecasted and/or controlled. 
         [0054]    Still with reference to the shadowing features  104  of the FSS cell  100 , it should be understood that although not shown in  FIG. 1 , the FSS elements  106  are connected to, attached to or formed on the shadowing features  104 . That is, the FSS cell  100  is fabricated such that ends of the FSS elements  106  touch and connect to their respective shadowing features  104  (or, to the walls  102 , for instance, in embodiments in which the walls are said or interpreted to include or have incorporated therein the shadowing features  104 ) at a supplemental surface of their respective shadowing regions. For instance, in an embodiment such as that illustrated in  FIG. 1  in which the shadowing region of a shadowing feature  104  is concave, the supplemental surface of the shadowing feature refers to the surface of the shadowing region that is parallel (or substantially parallel, or most parallel among surfaces of the shadowing region) to the inner and outer surfaces of the shadowing feature  104 . In other embodiments such as those in which the shadowing region is convex, the supplemental surface can be the inner surface  104   i  of the shadowing feature  104 . 
         [0055]    As described above, the shadowing features protect or shield a portion of the FSS elements from being coated, for example, with a metal (or other conductive) coating material. In this way, although the FSS elements  106  are fabricated such that they are physically connected to the other portions of the FSS cell  100  (e.g., walls  102 , shadowing features  104 ), when the FSS cell  100  is coated, conductivity is severed or avoided by the non-coated or less coated portions of the FSS elements. 
         [0056]    In some embodiments, the shadowing features include a block having opposed first and second block walls. The first block wall has a bore formed therein through which the frequency selective surface element disposed in the shadowing feature passes through. The second block wall is the wall to which the first or second terminal end of the frequency selective surface element is coupled. The shadowing features may each include one or more ledges formed therein. The ledges are configured to protect at least one of a portion of the frequency selective surface element disposed in the shadowing feature and/or a portion of the wall to which the frequency selective surface element is coupled from a coating when a coating is applied to the electromagnetic device. As illustrated below in further detail in connection with  FIG. 3B , the ledges may be stepped ledges providing for multiple ledges having different configurations formed in the shadowing feature. In other words, stepped ledges can refer to walls or surfaces of the shadowing features having varying geometries such as increasing or decreasing widths and/or thicknesses analogous to stairs or steps. 
         [0057]      FIG. 2A  is a perspective view of another exemplary embodiment of an FSS cell  200  having shadowing features. As shown, the FSS cell  200  includes walls  202 , shadowing features  204 , and FSS elements  206 . As described above in connection with  FIG. 1 , the walls  202  and shadowing features  204  include interior and outer surfaces relative to the FSS elements  206 . In  FIG. 2A , the shadowing features  204  are designed such that they are seamlessly incorporated into the walls  202 . It can be said thus that the walls  202  and the shadowing features  204  have a same (or substantially the same) thickness and/or width. The shadowing features  204  include shadowing regions configured to shield, protect or shadow terminal ends of the FSS elements  206  during a metal coating of the FSS cell  200 . 
         [0058]      FIG. 2B  is a perspective view of one exemplary embodiment of an array  220  of FSS cells  200 . The array  220  is made up of twenty five FSS cells  200 . The entire array  220  can be printed during a single three-dimensional printing session, and can be fabricated as a single, interconnected structure. 
         [0059]    Each of the FSS cells  200  in the array  220  includes walls  202 , shadowing features  204  and FSS elements  206 . Adjacent FSS cells  200  can have walls  202  that are adjacent to one another. In other embodiments, a wall  202  can be a shared or common wall that forms a part of two adjacent FSS cells  202 . In such embodiments, the thickness of the shared wall  202  can be increased to allow for concave shadowing regions of respective shadowing features to be fabricated such that (1) they are thick or deep enough to provide adequate protection or shielding of the FSS elements  206 , and (2) they do not penetrate through the wall to form a hole from one interior surface to another. 
         [0060]      FIG. 3A  is a perspective view of one exemplary embodiment of an array  320  of shadowing features  304 . Although not visible in  FIG. 3A , each of the shadowing features  304  has a respective element attached to and/or fabricated such that it extends in a direction away from and substantially perpendicular to a supplemental surface of the shadowing feature. The shadowing features  304  are thus configured to protect or shield corresponding elements during a coating process. 
         [0061]      FIG. 3B  is a cross-sectional view of the array  320  taken along the line L-L. As shown, elements  306  are connected to respective supplemental surfaces  304   s  of the shadowing features  304 . The elements  306  may be, for example, FSS elements of an FSS cell. However, other types of elements  306  are contemplated including high frequency filters of electromagnetic devices. It should be understood that, in  FIG. 3B , only portions of the elements  306  are shown to illustrate the protective or shielding aspects of the shadowing features  304  on the terminal ends  306   t  of the elements  306 . 
         [0062]    As also shown in  FIG. 3B , the shadowing region of the shadowing features  304  can vary in shape. That is, surfaces  30411  and  30412  of the shadowing region of the shadowing feature  304  can vary in dimensions, thereby creating a geometry of the shadowing region that can be configured to achieve desired (1) amounts of desired protection of the corresponding FSS element from being coated during a metal coating procedure, and (2) properties such as resonance and filtering properties of the resulting FSS cell. 
         [0063]      FIG. 4A  is a perspective view of another exemplary embodiment of an FSS cell  400  having shadowing features. The FSS cell  400  includes walls  402 , shadowing features  404  and FSS elements  406 . As shown, the walls  402  and the shadowing features of the FSS cell  400  are of different dimensions, such that desired mechanical and electrical properties of the FSS cell, such as the mechanical strength, upper frequency, lower frequency and bandwidth of the FSS elements that make up an FSS filter can be achieved. 
         [0064]      FIG. 4B  is a perspective view of an array  420  of FSS cells  400 . The array  420  of FSS cells  400  can be fabricated a single structure using additive manufacturing techniques. In some embodiments, fabricating the array  420  of FSS cells  400  provides benefits such as enabling a large number of cells to be handled, transported and manipulated jointly, thereby also allowing for a more uniform coating of the FSS cells, resulting in FSS cells  400  having substantially matching mechanical and electrical properties. 
         [0065]      FIG. 4C  is a cross-sectional view of the FSS cell  400  taken along the line T-T. As shown, the FSS elements  406  extend into and connect to the shadowing features  404  at supplemental surfaces of the shadowing regions that are disposed between the internal surface and the outer surface of the shadowing features  404 . In doing so, a distal or end portion or region of each of the FSS elements  406  is shadowed or protected by the shadowing regions, such that metal is not or is less coated thereon. 
         [0066]    Printed Circuit Board 
         [0067]    In some embodiments, the shadowing features described herein can be fabricated on a printed circuit board (PCB) to protect areas of the PCB from being coated with metal, thereby discontinuing the conductivity between two regions of the PCB. As known by a person having skill in the art, electronic components such as microprocessors and controllers are provided on the board, and are connected to one another using lines or paths of metal (e.g., copper) provided on the board, via which electricity can be conducted. These lines or paths of metal such as copper are referred to as traces. 
         [0068]      FIGS. 5A and 5B  illustrate exemplary embodiments of PCBs  510 A and  510 B, each of which includes various traces, including traces  512 A- 1  and  512 A- 2  on PCB  510 A and traces  512 B- 1  and  512 B- 2  on PCB  510 B. In  FIG. 5B , the substrate of the PCB  510 A is illustrated only as extending to a portion of the traces, though it should be understood that a completed and ready-to-use PCB would include all of the traces disposed on or in the substrate. In some embodiments, chips and other components can be placed or positioned on the PCB at ends of traces, as known by a person skilled in the art. 
         [0069]      FIG. 6A  is a perspective view of an exemplary embodiment of a three-dimensional PCB  610  fabricated with channels  612 - 1  to  612 - 4 , and shadowing features such that the PCB  610  can be coated with metal while allowing for portions of the board to not be electrically connected. It should be understood that channels  612 - 1  to  612 - 4  are exemplary channels from among a larger set of channels that can be printed on a PCB, such as the channels (corresponding to traces) illustrated in  FIG. 5B . 
         [0070]      FIG. 6B  illustrates another perspective view of the PCB  610 . The PCB  610  includes a top or superior surface  614   s  and a bottom or inferior surface  614   i . In some embodiments, coating of the PCB  610  is performed in a top-down direction, such that metal is deposited onto the superior surface  614   s . In some embodiments, the coating is performed in a direction substantially perpendicular to the superior surface  614   s  of the PCB  610 , using coating techniques such as sputtering, physical vapor deposition, electron beam deposition, thermal evaporation based metal deposition, spraying, splattering, splashing, spray painting and the like. 
         [0071]    To ensure that conductivity can be discontinued between multiple areas or portions of the PCB  610 , regions between those areas should not be coated. To this end, the PCB  610  is fabricated with shadowing features. 
         [0072]      FIG. 6C  is a magnified view of the channels  612 - 3  and  612 - 4  along a side or lateral edge of the PCB  610 . The channels  612 - 3  and  612 - 4  include respective shadowing features  604 - 3  and  604 - 4 . The shadowing features  604 - 3  and  604 - 4  protect surfaces within the channel from being coated with metal during a metal coating process, as is described in more detail with reference to  FIG. 6D  below. It should be understood that the shadowing features  604 - 3  and  604 - 4  are exemplary, and shadowing features of different geometries, and different placements and orientations can be fabricated onto or with the PCB  610 , so long as a surface or a portion of a surface within the channels  612 - 3  and  612 - 4  can be protected from deposited metal to discontinue electrical conductivity. 
         [0073]      FIG. 6D  is another perspective view of the channels  612 - 3  and  612 - 4  along a side or lateral edge of the PCB  610 . More specifically,  FIG. 6D  is an upside-down view of  FIG. 6C . While in  FIG. 6C  the superior surface  614   s  of the PCB  610  is visible, in  FIG. 6D , the inferior surface is visible. As shown, channels  612 - 3  and  612 - 4  include shadowing features  604 - 3  and  604 - 4 , respectively. Moreover, the channels  612 - 3  and  612 - 4  include surfaces (e.g., walls) therein, namely surfaces  613 - 1  to  613 - 5  (collectively “surfaces” and/or “ 614 ”). 
         [0074]    When a metal coating is applied to the superior surface  614   s  of the PCB  610 , the shadowing features  604 - 3  and  604 - 4  prevent the metal from being applied to at least some of the surfaces  613 . For instance, when a metal coating is applied to the PCB  610 , portions of the superior surface  614   s  are metal coated and thus gain conductive properties. Examples of these portions of the superior surface that are coated are labeled as  614   s - 1  and  614   s - 2  in  FIG. 6C . Likewise, during the metal coating, surfaces of the channels  612 - 3  and  612 - 4  are metal coated and thus gain conductive properties. Examples of the surfaces that are coated are labeled as  613 - 1 ,  613 - 2  and  613 - 5  in  FIGS. 6C and 6D . 
         [0075]    However, the shadowing features  604 - 3  and  604 - 4  prevent some surfaces from of the channels  612 - 3  and  612 - 4  from being metal coated—e.g., by ensuring that none or less metal is applied to those surfaces. Examples of the surfaces that are protected or shielded by the shadowing features and thus are not or are less metal coated are labeled as channel surfaces  613 - 3  and  613 - 4 . The non- or less coated channel surfaces  613 - 3  and  613 - 4  thus prevent PCB surface regions  614   s - 1  and  614   s - 2  from being electrically connected to one another. 
         [0076]    It should be understood that the systems and methods herein are described in connection with planar electromagnetic devices such as planar PCBs (e.g., PCB  610 ). However, the systems and methods described herein can be applied to fabricate and/or coat non-planar (e.g., curved, shaped) structures, or specific junctures in complex structures. Curved or non-planar structures means that at least one plane—e.g., formed by the base of a plurality of electromagnetic devices—is not planar. For instance, a base of the various printed structures (e.g., substrates) provided for herein can be non-planar. It should also be understood that the systems and methods described herein can be used to fabricate other types of devices known by those of skill in the art, including three-dimensional antennas (e.g., Vivaldi antennas) for radar and communications, coplanar waveguides, microwave structures that require a separation between a conductive surface and a ground plane to ensure proper conditions for the transmission and radiation of microwave energy, and/or three-dimensional metamaterials. 
         [0077]    Fabrication and Coating of Electromagnetic Devices with Shadowing Features 
         [0078]    In some example embodiments, the systems and methods described herein can be used to fabricate and coat an electromagnetic device. Initially, a three-dimensional model corresponding to a three-dimensional structure is generated using modeling software known by those skilled in the art. The three-dimensional structure that is modeled and is to be fabricated can be a single electromagnetic device such as an FSS unit cell, a printed circuit board or other electromagnetic devices known to those skilled in the art. In other embodiments, the modeled structure to be fabricated can include a plurality of electromagnetic devices arranged, for example, as an array. The three-dimensional model is designed to include shadowing features that protect, shield or shadow other portions of the structure during a coating process. It should be understood that in some embodiments, shadowing features can be referred to as embedded masks—meaning that the resulting structure is designed to include or have incorporated therein geometric features that can replace the need for a mask to provide the desired metal coating of the structure. 
         [0079]    In turn, the modeled three-dimensional structure is printed using additive manufacturing techniques such as three dimensional printing. In some embodiments, a three-dimensional structure that is printed can be a substrate for an electromagnetic device, made of a non-conductive material such as plastic, silicon, or fiberglass. The fabricated substrate can be rigid or flexible. In some embodiments, the fabricated substrate can be planar or non-planar. For instance, a non-planar or curved substrate. The fabricated substrate includes shadowing features that are designed to provide the desired amount of shadowing of another portion of the structure. In some embodiments, the amount of shadowing that is desired or optimal is a size or dimension that results in the other portion of the structure being not coated with metal or coated with metal less than other portions such that it can serve as a boundary that cuts off conductivity between two coated and conductive portions or regions of the structure. 
         [0080]    In turn, the structure is coated with a metal such as copper using a variety of coating techniques described herein. Coating can consist of depositing the metal onto a structure from a specific point or a bounded set of points that are taken into account when designing, modeling and fabricating the shadowing features of the structure. For instance, in embodiments in which metal coating is applied from a single point at the top-center portion of the structure, the shadowing features are disposed on top of the element or region of the structure to be shadowed, or at a point substantially along a line from the element or region to be shadowed and the point from which the coating is performed (e.g., a nozzle). In this way, at least a portion of the structure has less or no conductivity, thereby discontinuing the conductivity between two regions adjacent to the non-coated (or less-coated) portion of the structure. 
         [0081]    One skilled in the art will appreciate further features and advantages of the disclosure based on the above-described embodiments. Accordingly, the disclosure is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.