PRIORITY CLAIM TO OTHER APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Patent Application No. 61/623, 327, filed April 12, 2012 (Attorney Docket No. 2911-03800); which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This disclosure relates, but is not limited to the methods of design and fabrication of different types of low-visibility antennas, for radiating or receiving electromagnetic signals, which can be adjusted individually to suit different frequencies or channels by means of high- definition conductive micro electrodes that might be printed on a transparent, thin flexible substrate by means of a roll to roll manufacturing process.

BACKGROUND

[0003] Conventionally, low-visibility antennas may be manufactured by screen printing a thick film with a conductive paste of copper/silver, or photolithography of copper. If an antenna is manufactured by screen-printing, a thick film paste such as a silver-loaded polymer is printed and cured in an oven. If photolithography is used, a copper foil is laminated to a flexible film and patterned with photo lithography. Antennas for wireless mobile devices may be optimized for various communication frequencies such as frequencies characteristic to GPS (Global Positioning System), Bluetooth, radio and television broadcasting. In addition, multiple antennas may be used to enable functions such as telephone internet communication.

SUMMARY

[0004] In an embodiment, a radio frequency antenna, comprises: a substrate; and a first antenna loop array disposed on a first side of the substrate, wherein the first antenna loop array is formed by flexographic printing, wherein the first antenna loop array comprises at least one line plated with a conductive material, and wherein the at least one line is 1 micron - 25 microns wide.

[0005] In an embodiment, a method of manufacturing an antenna structure, comprises: printing a first antenna loop array on a first side of a substrate, using an ink comprising a plating catalyst, wherein the first antenna loop array comprises a line from 1 micron - 25 microns thick; printing a second antenna loop array on a second side of the substrate, using an ink comprising a plating catalyst, wherein the second pattern comprises a plurality of lines from 1 micron - 25 microns thick; curing the first antenna loop array and the second antenna loop array; plating the first antenna loop array and the second antenna loop array with a conductive material; and disposing a coating on the first antenna loop array and the second antenna loop array.

[0006] In an alternate embodiment, a radio frequency antenna, comprises: a first antenna loop array disposed on a first side of a substrate, wherein the first pattern is disposed by flexographic printing, wherein the first antenna loop array comprises a first plurality of electrode formations, wherein each electrode formation of the first plurality of electrode formations comprises a base line, a tail line, and a spiral line, wherein a first end of the tail line is connected to the spiral line, and wherein a second end of the tail is connected to the base line, and wherein the tail, the base line, and the spiral line are 1 micron - 25 microns wide; and wherein the first pattern is plated with a conductive material subsequent to flexographic printing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A complete understanding of the optimized design and fabrication methods of the present disclosure and its various features, object and advantages may be obtained from the illustrations of the following drawings:

[0008] FIG. 1 is an illustration of an embodiment of a top view of a planar dipole low-visibility RF single loop antenna structure.

[0009] FIG. 2 is an illustration of an embodiment of a cross-sectional view of a planar dipole low-visibility RF single loop antenna structure.

[0010] FIG. 3 is an illustration of an embodiment of a top view of a planar dipole low-visibility RF multi-loop antenna structure.

[0011] FIG. 4 is an illustration of an embodiment of a cross-sectional view of a planar dipole low-visibility RF multi-loop antenna structure.

[0012] FIG. 5 is an illustration of an embodiment of a top view of a low-visibility double-sided RFID antenna structure. [0013] FIG. 6 is an illustration of an embodiment of a cross-sectional view of a low-visibility double-sided RFID antenna structure.

[0014] FIG. 7 is an illustration of an embodiment of a top view a low-visibility RFID antenna array structure.

[0015] FIG. 8 is an illustration of an embodiment of a cross-sectional view a low-visibility RFID antenna array structure.

[0016] FIG. 9 is an illustration of an embodiment of a system for manufacturing low-visibility by means of a roll to roll flexographic printing process.

DETAILED DESCRIPTION

[0022] The present disclosure relates, but is not limited to, optimizing the method of design, and fabrication of low-visibility antenna structures and to increasing the range of applications of low-visibility antenna structure. These antenna structures, which may also be referred to as antenna arrays, may comprise patterns disposed flexible substrate, the substrate may comprise glass or transparent polyester, polycarbonate flexible film, and a high-definition conductive material circuitry. The flexible substrate may be printed on one or both sides by means of a roll to roll manufacturing process. In some embodiments, each side of the substrate is printed separately, and in other embodiments both sides of the flexible substrate are printed at the same time which may improve efficiency and cost depending upon the volume of manufacturing. The methods and systems discussed herein may increase the range of application for RFID and RF low-visibility antennas, or antennas with array configurations. The high-definition conductive electrodes of the low-visibility antenna circuitry might be designed in any pattern geometry, or in any array of antenna patterns, that may be adjusted individually to suit different frequencies or channels to receive or transmit terrestrial broadcasting as well as satellite broadcasting and radio signals as appropriate for wireless communication such as cellular phones handset.

[0023] The following US Patents are referred to herein as they may contain material that is peripherally relevant to the present disclosure: US 7973997 B2: Transparent structures; US 6,245,249: Micro-structure and manufacturing method and apparatus; US 6,632,342: Methods of fabricating a micro structure array; US 7,233,296 B2: Transparent Thin Film Antenna; US 5,709,832: Method of Manufacturing Printed Antennas; US 6,753,825 B2: Printed Antenna and Applications Thereof; US 5,355,144: Transparent window antenna; US 5,528,314: Transparent vehicle window antenna; US 6,388,621 B1 : Optically Transparent Phase Array Antennas; US 7,821,469: Printed Antenna; and US 7,656,357 B2: Transparent antenna for vehicle and vehicle glass with antenna.

[0024] The increasing demand for bandwidth in wireless communication led to a corresponding demand for multidirectional signal antennas in order to achieve reasonable ranges. Traditionally, multiple elements antenna with different frequencies has been used to increase the efficiency of the conventional single antenna channels, and to achieve a high antenna gain. In certain configurations the apparatus comprises various types of low-visibility antennas, planar, dipole, designed for exceptional broadband performance, with a nickel- plated copper conductor circuitry which is printed one on top side, and another on the bottom side of a thin, transparent, flexible, substrate that can be a polymer film, suitable for many applications. The present disclosure relates to a method of design and fabrication of flexible, shatter-proof, thin, conformable, roll-able in a process/feed-able through a process, RFID and RF low-visibility antennas for a plurality of applications. The term "low visibility" may be used to refer to structures that may comprise a plurality of lines or features that are less than 30 microns of width and cannot be easily detected by the naked eye. The antennas may be manufactured by means of an optimized fabrication method consisting in the roll to roll manufacturing process that does not use chemical etching. Low-visibility antennas may be suitable for multiple applications, including window mounted applications, which is a desirable alternative for motor vehicles and aircraft with mast, or other types of outside antennas, where these low-visibility antennas might be deployed as transmitter or receiver antennas. Accordingly, the fabrication process may be more cost-effective than conventional methods as a result of a high-definition printing of low-visibility, anti-corrosive, conductive, electrode material on a thin, transparent, flexible, substrate, by means of the roll to roll manufacturing process because, in part, this process does not use chemical etching.

[0025] Flexography is a form of a rotary web letterpress where relief plates are mounted on to a printing cylinder, for example, with double-sided adhesive. These relief plates, which may also be referred to as a master plate or a flexoplate, may be used in conjunction with fast drying, low viscosity solvent, and ink fed from anilox or other two roller inking system. The anilox roll may be a cylinder used to provide a measured amount of ink to a printing plate. The ink may be, for example, water-based or ultraviolet (UV)-curable inks. In one example, a first roller transfers ink from an ink pan or a metering system to a meter roller or anilox roll. The ink is metered to a uniform thickness when it is transferred from the anilox roller to a plate cylinder in order to have a uniform distribution when the ink is ultimately transferred to the substrate. When the substrate moves through the roll-to-roll handling system from the plate cylinder to the impression cylinder, the impression cylinder applies pressure to the plate cylinder which transfers the image on to the relief plate to the substrate. In some embodiments, there may be a fountain roller instead of the plate cylinder and a doctor blade may be used to improve the distribution of ink across the roller.

[0026] Flexographic plates may be made from, for example, plastic, rubber, or a photopolymer which may also be referred to as a UV-sensitive polymer. The plates may be made by laser engraving, photomechanical, or photochemical methods. The plates may be purchased or made in accordance with any known method. The preferred flexographic process may be set up as a stack type where one or more stacks of printing stations are arranged vertically on each side of the press frame and each stack has its own plate cylinder which prints using one type of ink and the setup may allow for printing on one or both sides of a substrate. In another embodiment, a central impression cylinder may be used which uses a single impression cylinder mounted in the press frame. As the substrate enters the press, it is in contact with the impression cylinder and the appropriate pattern is printed. Alternatively, an inline flexographic printing process may be utilized in which the printing stations are arranged in a horizontal line and are driven by a common line shaft. In this example, the printing stations may be coupled to curing stations, cutters, folders, or other post-printing processing equipment. Other configurations of the flexographic process may be utilized as well.

[0027] In an embodiment, flexoplate sleeves may be used, for example, in an in-the-round (ITR) imaging process. In an ITR process, the photopolymer plate material is processed on a sleeve that will be loaded on to the press, in contrast with the method discussed above where a flat plate may be mounted to a printing cylinder, which may also be referred to as a conventional plate cylinder. The flexosleeve may be a continuous sleeve of a photopolymer with a laser ablation mask coating disposed on a surface. In another example, individual pieces of photopolymer may be mounted on a base sleeve with tape and then imaged and processed in the same manner as the sleeve with the laser ablation mask discussed above. Flexosleeves may be used in several ways, for example, as carrier rolls for imaged, flat, plates mounted on the surface of the carrier rolls, or as sleeve surfaces that have been directly engraved (in-the-round) with an image. In the example where a sleeve acts solely as a carrier role, printing plates with engraved images may be mounted to the sleeves, which are then installed into the print stations on cylinders. These pre-mounted plates may reduce changeover time since the sleeves can be stored with the plates already mounted to the sleeves. Sleeves are made from various materials, including thermoplastic composites, thermoset composites, and nickel, and may or may not be reinforced with fiber to resist cracking and splitting. Long-run, reusable sleeves that incorporate a foam or cushion base are used for very high-quality printing. In some embodiments, disposable "thin" sleeves, without foam or cushioning, may be used. Flexographic printing processes may use anilox rolls for ink transfer as a means of metering the ink so that the ink prints the desired pattern with clear, uniform features free of clumping or smearing.

[0028] Low-visibility antennas are self-contained structures that allow the high-definition printing of conductive, electrode circuitry of a single antenna, or antenna arrays on one side or both sides of a flexible substrate. These antenna arrays may work simultaneously in different frequency bands due to the physical disposition of the elements permitting adjustments of radiation efficiency, orientation, frequency band, and impedance matching, which may have an effect on performance of wireless communication devices such as mobile phone handsets. Low-visibility antennas may also be used windshields of vehicles for electronic toll collection where the antenna is laminated, or to boost cellphone reception between cell towers, as well as for satellite and terrestrial telecommunication, the flexible design capability of low-visibility antennas permit to receive or transmit electromagnetic signals in a range from 125 KHz to 20 GHz. Conventionally, the standard in the industry is 13.56 MHz, making these low-visibility antennas suitable to be laminated on windows of high rise buildings and thus the building itself becomes a tower in order to replace some of the existing expensive telecommunication towers. Another application of low-visibility antennas is the wireless integration of low-visibility antennas with a car's proximity sensor system, to alert drivers when they are getting close to another car or to a side of a building, in order to warn of an imminent collision. Other applications for RFID antennas may include for Wi-Fi, WiMax, 3G, and 4G, micro base stations, as well as satellite communications, , or similar electronic devices that require an excellent wireless communication system. Low-visibility antennas may also be used in retail and attached to garments for Radio Frequency Identification (RFID) to replace large security tags used to prevent shoplifting in stores. In addition, the antennas may be used to monitor health conditions of the elderly, pregnant women, or anyone else requiring monitoring of health conditions. In another example, the antenna may be used in some embodiments for tracking military troop's movements, vital signs, access to public transportation turnstiles, electronic payment systems, and the like.

[0029] In order to integrate these antennas into a wireless mobile device such as a mobile phone handset, the antenna may need to fit in the allocated space or withstand environmental conditions. In some applications, the space allocated for the antenna may be small and/or in an unprotected area that may be subject to mechanical deformation, for example, from customers picking up and/or trying on items in a store that have security tags. As such, the antenna design is preferably a thin, flexible, shatter proof, conformable low-visibility antenna that can be printed on one side or both sides of a thin transparent flexible substrate to create different antenna circuitries. These various configurations, or arrays, of antennas might be integrated into the front surface of a wireless communication device such as mobile phone handset, instead of the back of the mobile devices. It is appreciated that the substrate discussed herein is an insulating material used as a base to print integrated circuits. In some embodiments, the antenna design may comprise loops, the number of which may determine the frequency at which data is transmitted or received.

[0030] A low-visibility antenna circuit may be manufactured using a roll-to-roll process to print conductive micro-structural patterns on one or both sides of a flexible substrate. This process may include: (1 ) cleaning the flexible substrate using, for example, a high-electric field ozone cleaner and a web cleaner; (2) printing high-resolution, low-visibility antenna patterns on one or two (both) sides of the flexible substrate by a flexographic printing process using UV curable ink that comprises a plating catalyst; (3) curing the substrate (e.g., ultra-violet (UV) curing); (4) electrolessly plating the substrate to cover the low-visibility antenna patterns with a conductive material; (5) washing the plated and printed low-visibility antenna electrodes; and (6) drying the plated and printed low-visibility antenna electrodes. The conductive plating material used in the electroless plating process may comprise nickel (Ni), tin (Sn), gold (Au), zinc (Zn), aluminum (Al), palladium (Pd), copper (Cu), silver (Ag), or combinations thereof to provide corrosion resistance. The conductive material used in the plating process for the antenna circuit may plate antenna patterns wherein each line is from 1 micron - 30 microns thick prior to plating. The plated pattern may also achieve light transmission greater than 85% to attain low-visibility in a particular area of interest. It is appreciated that a substrate that undergoes an electroless plating process may not use chemical etching. The methods and systems disclosed herein may reduce or eliminate a low-visibility deficiency that may be seen in conventionally-manufactured methods by means of an optimized, cost-effective method of design and manufacturing low-visibility antennas. Thus, in certain applications a thin, low-visibility, printed, an antenna circuit might be integrated in the front surface of a wireless communication device such as a cell phone handset or other portable electronic device.

Low-visibility RFID Single-Sided Antenna

[0031] Figures 1-4 are illustrations of embodiments of various antenna configurations printed on a single side of a substrate. FIG. 1 is an illustration of an embodiment of a top view of a planar dipole low-visibility RF antenna structure printed on one side of a substrate. This low- visibility RF antenna structure 100 may be designed for radiating or receiving wireless electromagnetic signals, as in telecommunication applications. In an embodiment, the RF antenna structure 100 comprises a planar, dipole low-visibility single loop rectangular electrode pattern 102 which may be referred to as an antenna loop array or a first antenna loop array. Pattern 102 comprises a single line in rectangular loop geometry. It is appreciated that antenna geometry is not limited to a rectangular loop and may comprise geometries such as a square, triangle, circle, spiral, polygon, or combinations thereof. Section A-A is shown on FIG. 1 and is shown and described in FIG. 2. The low-visibility single loop rectangular electrode pattern 102 used in the antenna design has a width 106 that may vary from 1 micron to 30 microns, preferably 5 microns - 10 microns. This range may produce a low-visibility effect to the naked eye depending to the distance from the user. This electrode pattern 102 is a conductive pattern that may have been printed and plated in a flexographic printing and electroless plating process. The printed electrodes in the low- visibility single loop rectangular electrode pattern 102 may exhibit a light transmission efficiency of greater than 85%. The conductive electrodes might be constructed of gold plated copper, silver plated copper, or nickel plated copper, to provide passivation for corrosion resistance of copper that does not use chemical etching. Alternatively, the conductive material used is a metallic material such as aluminum, palladium, nickel, zinc, or combinations thereof that contain electrons, which are movable electric-charged particles.

[0032] In some embodiments, the resistivity of the printed electrode in the low-visibility single loop rectangular electrode pattern 102 may range from 0.005 micro Ohms to 500 Ohms per square. The length 108 of the printed electrode may vary from 0.01 m - 1 m, depending on the frequency range which may also vary from 125 MHz to 25 GHz. In some embodiments, the low-visibility RF antenna structure 100 may exhibit an omnidirectional radiation pattern according to the desired application. The impedance for RF antennas may be given by the shape of the antenna, the type of material used, and changes in the environment.

[0033] The transparent flexible substrate 104 may be polyethylene terephthalate (PET) film, polycarbonates, and other polymers. In some embodiments, the transparent flexible substrate 104 may include the DuPont/Teijin Melinex 454 and DuPont Teijin Melinex ST505, the latter being a heat stabilized film specially designed for processes where heat treatment is involved. The flexible substrate 104 may exhibit a thickness between 5 and 500 microns, with a preferred thickness between 100 microns and 200 microns. A detailed method of manufacturing low-visibility antenna circuits using roll to roll process is depicted in FIG. 9 to print conductive micro structural patterns on one or both sides of the transparent flexible substrate 104. While a rectangular geometry is represented in FIG. 1 , the low-visibility RF antenna structure 100 might be designed in any pattern geometry, or array of antenna patterns, such as squares, circles, half circles, trapezoids, hexagons, pentagons, or other shapes and combinations of shapes that can be adjusted to suit different frequencies or channels to receive or transmit terrestrial broadcasting as well as satellite broadcasting and radio signals which may be used for telecommunication application. The low-visibility RF antenna structure 100 may be used along with reflective elements (not pictured) to increase the directivity of the radiation pattern.

[0034] Figure 2 is an illustration of an embodiment of a cross-sectional view of a single loop antenna. FIG. 2 is a view of cross-section "A-A" of the low-visibility RF antenna structure 100 depicted in FIG. 1. Section A-A comprises the high-definition circuitry of a printed dipole low- visibility single loop rectangular electrode pattern 102 printed on the top surface of the previously defined transparent flexible substrate 104. Each part, or line, of pattern 102 may have a width 204 from 1 micron - 50 microns. It is appreciated that, while the cross section indicates that electrode pattern 102 which is rectangular on its surface as discussed with respect to FIG. 1 also has lines with a rectangular cross section, the cross sectional geometry could include geometries such as a semi-circle, trapezoid, square, polygon, circle, triangle, or combinations thereof. In some embodiments, the height 202 of the printed conductive lines in both the low-visibility single loop rectangular electrode pattern 102 and the plurality of low- visibility loops rectangular electrode pattern 302 may vary from 200nm - 100 microns thick, preferably from 5-10 microns, while the distance between conductive lines might vary from 10 microns to 5 mm.

[0035] Figure 3 is an illustration of a top view of an embodiment of a low-visibility RFID antenna structure. RFID antenna may be double or single-sided depending on the application for which the antenna will ultimately be used. In an embodiment, the structure 300 is designed for RFID applications and comprises a plurality of low-visibility planar, dipole loops rectangular electrode pattern 302 printed on the top surface of a transparent flexible substrate 104. The width 304 of the printed antenna electrodes in the plurality of loops rectangular electrode pattern 302 may vary from 1 micron to 30 microns, a dimension range that may produce a low-visibility effect to the naked eye depending to the distance from the user. The width 306 of each line of the plurality of lines in the pattern 302 is from 1 micron - 50 microns. It is appreciated that the width 306 of each loop of the plurality of loops in the pattern 302 may be equidistant from the other loops in the pattern 302. In one example, the width 306 may be 10 microns; the same for all of the lines in the pattern 302, and the spacing 308 between the lines is 10 microns. In another example, the width 306 may be 5 microns, and the spacing 308 may be 10 microns.

[0036] The resistivity of the printed electrodes in the plurality of low-visibility loops rectangular electrode pattern 302 may range from 0.005 micro Ohms per square to 500 Ohms per square. In this example, the loops are concentric and are comprised of a single, continuous line. In some embodiments, the width 304 of the smallest loop 310 may vary from 0.01 m to 1 m. The number of loops may be from about 1 loop to about 1000 loops respectively, depending on the frequency range which may also change from 125 MHz to 25 GHz. The spacing between the loops may be determined in part by the width of the loops. The low- visibility RFID antenna structure 300 may exhibit an omnidirectional or directional radiation pattern according to the desired application. The impedance for RFID antennas may be determined by, for example, the shape of the antenna, the type of material used, and changes on the environment. FIG. 3 also comprises section C-C, discussed in detail in FIG. 4.

[0037] FIG. 4 is an illustration of a cross sectional view of the low-visibility RFID antenna structure in FIG. 3. FIG. 3 shows section "C-C" comprising the previously defined flexible substrate 104, and a high-definition electrode circuit comprising a plurality of low-visibility loops rectangular electrode pattern 302, to be employed for RFID applications, which is printed on the top side of the transparent flexible substrate 104 by means of a roll to roll manufacturing process described on FIG. 9, that have the option of printing any circuitry of low-visibility electrode antennas, or arrays of antennas on one side or both sides of the transparent flexible substrate 104 at the same time, ensuring high efficiency and cost effective manufacturing. Each loop of the plurality of loops in the pattern 302 comprises a height 404 and a width 306 as well as a spacing 406. In some embodiments, the height 404, thickness 306, and spacing 406 may not be uniform, depending upon the desired frequencies. This is discussed in more detail with respect to Figure 6 below. Preferably, the spacing 406 between loops as well as the height 404 and thickness 306 may be uniform amongst and between each loop of the plurality of loops.

Low-visibility Double-Sided RFID Antenna [0038] In addition to the embodiments disclosed in FIGS. 1-4, an antenna structure may be double sided, that is, a single substrate may contain a least one antenna loop array on both sides of the substrate. Figure 5 is an illustration of an embodiment of a top view of a low- visibility double-sided RFID antenna structure. Turning to FIGS. 1-4 as well as FIG. 5, double-sided antenna 500, comprises the previously described plurality of low-visibility loops rectangular electrode pattern 302 circuits printed on the top surface of the flexible substrate 104 and a low-visibility single loop rectangular electrode pattern 102 circuits printed on the bottom side of the flexible substrate 104, as discussed above with respect to FIGS. 1-4. This type of double-sided antenna configuration may be used, for example, in order to optimize the RFID applications of such an antenna structure where there is a space limitation for the antenna.

[0039] The resistivity of the foregoing planar, dipole low-visibility single loop rectangular electrode pattern 102 printed on the bottom surface of the flexible substrate 104, and the plurality of low-visibility loops rectangular electrode pattern 302 printed on top surfaces of the flexible substrate 104 may range from 0.005 micro Ohms per square to 500 Ohms per square. In an embodiment, the length and the number of loops of the printed electrodes in the plurality of low-visibility loops rectangular electrode pattern 302 may vary from 0.01 m to 1m and from about 1 loop to about 1000 loops respectively, depending on the frequency range which may also vary from 125 MHz to 25 GHz. The low-visibility double-side RFID antenna structure 500 with printed antenna patterns on both sides may exhibit an omnidirectional or directional radiation pattern according to the desired application, while its impedance may be given by the shape of the antenna, the type of material used, and changes on the environment. Both the single loop rectangular electrode pattern 102 and the plurality of low-visibility loops rectangular electrode pattern 302 may be printed on either side of the flexible substrate 104 and may operate at different frequencies. In addition, each pattern may exhibit different radiation patterns that can be adjusted individually to suit the requirements for receiving or transmitting wireless communication simultaneously.

[0040] FIG. 6 illustrates a cross sectional view "B-B" of the low-visibility double-side RFID antenna structure 500 illustrated in FIG. 5, comprising the previously defined flexible substrate 104, located at the center of the low-visibility double-side RFID antenna structure 500. The flexible substrate 104 has a high-definition circuit of a plurality of low-visibility rectangular loops comprising electrode pattern 302 on a first (top) side, and on the bottom side a circuit of a low-visibility single loop rectangular electrode pattern 102 is printed and plated. It is appreciated that the pattern 102 and the pattern 302 as shown in FIG. 6 are different widths. While this is only shown as an example, it is appreciated that in an embodiment such as in FIG. 6 where two patterns are disposed on opposite sides of one substrate the two patterns may have varying widths, heights, and thicknesses depending upon the frequency or frequencies desired for the end application. Further, it is appreciated that each pattern may be printed using a plurality of flexomasters and different inks depending upon the desired dimensions for the particular feature.

Low-visibility Antenna Array

[0041] There are different types of low-visibility antenna arrays, including linear arrays. When the low-visibility antenna array is arranged in a straight line this is called a linear array, arranged in parallel lines on one plane has a plane array in two dimensions. The gain of a low-visibility antenna array is typically proportional to the number of individual antennas, but may be limited to how accurately the antennas can be positioned together. It is appreciated that the electrical characteristics of the low-visibility RFID antenna array structure 700 may be determined according to the application of the antenna design. FIG. 7 is an illustration of an embodiment of the top view a low-visibility RFID antenna array structure. The array structure 700 comprises a low-visibility planar antenna array 702 circuitry that may be flexographically printed on the top surface of the transparent flexible substrate 104 by means of a roll to roll manufacturing process. The array structure 700 comprises a plurality of electrodes 708 disposed on a plurality of conductive lines 706. In one example, there may be four lines 706 wherein four electrodes, which may also be referred to as swirls or lollipops, 708 extend uni- directionally from each of the four lines 706. Each electrode has a tail 710 attached to the line 706 and a swirl design 712. FIG. 7 depicts what may be referred to as a lollipop array. Each line that forms the tail 710 and swirl 712 of the printed antenna electrodes in the low-visibility planar antenna array 702 may vary from 1 micron to 30 microns wide, which is a dimension range that may, depending upon the distance of the antenna structure from the user, produce a low-visibility effect to the naked eye. In some embodiments, the plated thickness 802 of each line is from 200 nm - 100 microns thick, and may be preferably from 5-10 microns. It is appreciated that the plated thickness 802 is illustrative and refers to the thickness of the plating on the printed array structure 700 and not the height or thickness of the printed array structure 700. This array structure 700 is designed to work in applications such as those discussed above where space is at a premium, this configuration may also optimize the RFID and RF applications.

[0042] The gain of a low-visibility antenna array may be proportional to the number of individual antennas, but is limited to how accurately they can be positioned together. It is appreciated that the electrical characteristics of the low-visibility RFID antenna array structure 700 may be determined according to the application of the antenna design.

[0043] FIG. 8 is an illustration of a cross sectional view of the low-visibility RFID antenna array structure. FIG. 8 is a cross section of section D-D of the array in FIG. 7. While a single-sided cross section is depicted in FIG. 8, the array may be printed in the same double-sided manner as discussed above with respect to the loop configuration in FIGS. 5 - 6. Cross sectional view "D-D" 700 comprises the previously defined flexible substrate 104, and a high-definition circuit of a low-visibility planar antenna array 700 from FIG. 7 that is printed on the top surface of the transparent flexible substrate 104. The lines 706 are visible as well as the lines of the swirl 712 and the outline of the tail 710. It is appreciated, as discussed above with respect to FIGS. 5-6, that this type of lollipop array may also be printed in a double-sided configuration. Roll-to-Roll Manufacturing Process

[0044] Figure 9 is an illustration of an embodiment of a system for manufacturing low-visibility by means of a roll to roll flexographic printing process. Figure 14 is a flow chart of an embodiment of a method of manufacturing low-visibility antenna. Specifically, FIG. 9 is an example whereby a roll-to-roll handling system 900 is used to manufacture various single and double-sided embodiments of low-visibility antenna configurations. The thickness of flexible substrate 104 may be chosen so that it is thin enough to avoid excessive stress during flexing. For some applications, a thickness of the transparent flexible substrate 104 between 100 microns to 200 microns is preferred. A positioning cable at an alignment station 908 may be used to maintain the right alignment of the features during the printing and plating processes. To initiate the roll to roll manufacturing process, the transparent flexible substrate 104 is transferred via any known roll to roll handling method from an unwind roll at unwind station 904 to a first cleaning station 906. In some instances, cleaning the substrate at block 1402 comprises a first cleaning station 906 wherein the first cleaning station 906 comprises a high electric field ozone generator used to remove impurities, like oils or grease, from the flexible substrate 104. In some embodiments, cleaning the substrate as indicated at block 1402 comprises more than one cleaning process and the flexible substrate 104 moves through a second cleaning at second cleaning station 910, which may comprise a web cleaner.

[0045] After cleaning at block 1402 using at least one of cleaning stations 906 and 910, the transparent flexible substrate 104 may be printed 1404 in a flexographic process wherein at least a first pattern is printed at block 1406. Printing station 912 may use a flexomaster disposed on a roller 912a (not pictured) as illustrated and discussed in Figure 10 below, prints a microscopic antenna pattern is printed on top side of flexible substrate 104 using a flexographic printing process and an ink comprising a plating catalyst which may also comprise other polymers, binders, and photo-initiators. The antenna pattern, which may also be referred to as an antenna loop array, may comprise a single or multi-loop pattern as discussed in FIGS. 1-6, or may comprise an array as discussed in FIGS. 7-8. The microscopic antenna pattern is imprinted by first master plate at the first printing station 912 using UV curable ink that may have a viscosity between 200 and 2000 cps. The amount of ink transferred from the first master plate at first printing station 912 to the flexible substrate 104 may be regulated by a high precision metering system. The amount (volume) of ink transferred may also depend on the speed of the process, ink composition, patterns shape and dimension. In some embodiments, the speed of the machine may vary from 20 feet/min to 750 ft/m. Preferably, the speed of the machine may be 50 ft/m to 200ft/m. The first printing at first printing station 912 may be followed by curing at block 1410. The curing at block 1410 may comprise ultraviolet light curing at a first curing station 914 with target intensity from about 0.5mW/cm ² to about 50 mW/cm ² and wave length from about 280 nm to about 480 nm, in addition it may comprise an oven heating at a second curing station 916 that applies heat within a temperature range of about 20°C to about 85°C. In an embodiment, a double-sided antenna may be manufactured by printing a second pattern 1408 on the side of the substrate opposite where the first pattern was printed 1406 second low-visibility antenna, for example, a single-loop, multi-loop, or array pattern. This second pattern is printed 1408 on the bottom side of the flexible substrate 104 and the bottom side of flexible substrate 104 may pass through a second printing process at a second printing station 918. When a second microscopic antenna pattern is printed on the bottom side of flexible substrate 104, the second microscopic pattern is imprinted by a second master plate using UV curable ink. The amount of ink transferred from a second master plate to the bottom side of flexible substrate 104 may be regulated by a high precision metering system that transfers enough ink to uniformly print the pattern but not so much ink as to result in clumping, smearing, or other printing complications. Printing the second pattern at block 1408 may be followed by curing the second pattern at block 1410. Curing the pattern man comprise an ultraviolet light curing at curing station 920 with target intensity from about 0.5 mW/cm ² to about 50 mW/cm ² and wavelength from about 280 nm to about 480 nm, in addition it may comprise a second curing station 922 that may be oven heating. Second curing station 922 applies heat within a temperature range of about 20 ⁰ C to about 85 ⁰ C. After the second curing step, the low- visibility single loop rectangular electrode pattern 102 is formed on the bottom side of the flexible substrate 104. In an embodiment, the first and the second patterns are printed either simultaneously or in series so that the substrate is cured when both the patterns have been printed.

Electro-less Plating

[0046] After printing the first pattern at block 1406 and second pattern at block 1408, the low- visibility antenna electrode patterns may be plated at block 1412 at an electroless plating station 924. Similarly, an array pattern printed on the substrate as discussed in FIGS. 7-8 may also be electrolessly plated. During plating, a layer of conductive material is deposited on the microscopic printed patterns that are also referred to as high resolution patterns or high resolution conductive patterns. Plating may be accomplished by submerging the substrate 104, comprising the top plurality of low-visibility loops rectangular electrode pattern 302 and the bottom low-visibility single loop rectangular electrode pattern 102 printed on the flexible substrate 104, or a single or double-sided array pattern, into an electroless plating tank. The plating tank at electroless plating station 924 may contain copper (Cu), silver (Ag), gold (Au), nickel (Ni), palladium (Pd), zinc (Zn), aluminum (Al), or combinations thereof in a liquid state at a temperature range between 20°C and 90°C. Preferably, the conductive material is copper held at about 80° C. In an embodiment, the deposition rate may be 10 nanometers per minute and the conductive material may be disposed on the pattern with a thickness of about 0.001 microns to about 100 microns, depending on the speed of the web and according to the application. Electroless plating at block 1412 at plating station 924 does not require the application of an electrical current and only plates the patterned areas containing plating catalysts that were previously activated by the exposition to UV radiation during the curing process. In an embodiment, the plating bath is copper and the copper plating bath may include powerful reducing agents, such as borohydride or hypophosphite. The plating thickness tends to be uniform compared to electroplating due to the absence of electric fields. The electroless plating at block 1412 may be well suited for parts with complex geometries and/or many fine features such as those exhibited by the printed low-visibility antenna patterns.

[0047] In some embodiments, the substrate 104 may be washed at block 1414 at wash station 926 subsequent to plating. After the electroless plating at block 1412, both the printed and plated plurality of low-visibility loops rectangular electrode pattern 302 and low-visibility single loop rectangular electrode pattern 102 (or an array as discussed in FIGS. 7 - 8) may be cleaned at block 1414 in a cleaning tank at the wash station 926 that may contain water at room temperature. The substrate 104 may then be dried at block 1416, for example, by the application of air at room temperature at a drying station (not pictured). In another embodiment, the substrate may be passivated at block 1418 after the drying at block 1416 at a passiviation station (not pictured) where a pattern spray may be applied to the pattern to prevent any dangerous or undesired chemical reaction between the conductive materials and water. In addition, and as discussed below with respect to figures 11-13, the substrate may be coated at block 1420, for example, with a scratch-resistant coating as discussed in Figures 11-13.

[0048] Figure 10 is an illustration of two embodiments of isometric views of top and bottom flexomaster patterns. FIG. 10 illustrates the single loop pattern 102 on a flexomaster 1002, which may be referred to as a bottom flexomaster in some embodiments, and the multi-loop pattern 302 on flexomaster 1004, which may in some embodiments be referred to as a top flexomaster. In an embodiment, a top flexomaster 102 is mounted on the roller 912a and used in conjunction with a printing system, for example a metered printing system, to print the transparent single loop antenna circuitry 102 on the top surface of a flexible substrate such as pictured in FIG 1. The top flexomaster 1004 is employed to print the transparent multiple loops antenna circuitry 302 comprising a plurality of loops on the bottom surface of the transparent flexible substrate. In an embodiment, flexomaster 1004 and flexomaster 1002 are separately patterned flexoblanks that are each disposed on a different roll. In this embodiment, the rollers such as roller 912a may be arranged in series wherein the first pattern created by 1004 is printed on the top surface and the second pattern created by 1002 is printed on the top surface adjacent to the first pattern 102. In an alternate embodiment, the rollers may be arranged such that the first pattern and the second pattern are printed by two different flexomasters on two different rolls and both patterns are printed on one substrate wherein the first pattern 102 is printed on the top (first) surface and the second pattern 302 is printed on the bottom (second) surface. This may occur simultaneously or in series as part of an in-line process. In another example, at least one of the top pattern or the bottom pattern is formed by a plurality of flexoplates disposed on a plurality of rolls. This may occur, for example, because the desired end pattern is designed with varying transitions, dimensions, and geometries that may make it appropriate to use more than one ink, which would then mean that more than one roll may be used. In another example, multiple rolls may be used to create one pattern because the pattern geometry, transitions, or dimensions are more uniformly printed in stages. In an embodiment, the thickness of the flexoblank used to create a master for the bottom flexomaster 1002 and the top flexomaster 1004 may range between 1 mm - 3 mm, preferably between 1.65 mm and 1.90 mm.

[0049] Figure 11 is an illustration of an embodiment of a cross sectional view of a planar, dipole low-visibility RFID antenna structure. Antenna structure 300 comprises a planar, dipole plurality of low-visibility loops rectangular electrode pattern 302 printed on the top surface of the flexible substrate 104. The type of materials employed, the width of the high-definition printed electrodes, and overall characteristics may be the same as the previous configurations described in FIG. 3. In this embodiment, the top surface of the low-visibility RFID antenna structure 300 might be protected with a layer of scratch resistant coating 1102, to protect the high-definition conductive antenna electrodes, causing this top surface to be durable, washable, scratch resistant, shatter resistant, chemical resistant, and finger print resistant. The selected scratch resistant coating 1102 might be composed of multifunctional acrylic monomer, and acrylic oligomers, that can be applied or deposit over the top outside surface of the low-visibility RFID antenna structure 300 by means of Slot Die, Gravure spray, Meier Rod or by standard protocols of dip coating application. In some embodiments, this coating may be applied after plating as described in FIG. 9 with respect to plating station 924. In alternate embodiments, the coating may be applied after passivation as discussed in FIG. 9, or as part of a subsequent, off-line process.

[0050] Figure 12 is an illustration of an embodiment of a cross-sectional view of a single loop dipole depicts a cross sectional view of a double-sided antenna structure with scratch- resistant coating. In this embodiment, another configuration of the planar, dipole low-visibility double-side RFID antenna structure 500 that comprises the plurality of low-visibility loops rectangular electrode pattern 302 circuits printed on the top surface of the flexible substrate 104, and a low-visibility single loop rectangular electrode pattern 102 circuits printed on the bottom side of the flexible substrate 104. In an embodiment, the antenna structure 500 may comprise rectangular loops as in FIG. 12, and in alternate embodiments the antenna structure 500 may comprise circular or multi-sided loops, or combinations thereof. The type of materials employed, the width of the high-definition printed electrodes, and overall characteristics may be the same as the previous configuration described in FIG. 5.

[0051] In an embodiment, depending on the application of the antenna structure 500, the top and/or bottom surfaces of the planar, dipole low-visibility double-side RFID antenna structure 500 may be protected with a layer of scratch resistant coating 1102. This coating 1102 may be applied to protect the low-visibility, high-definition conductive electrodes, printed on both sides, causing both surfaces to be durable, washable, scratch resistant, shatter resistant, chemical resistant, and finger print resistant. The selected scratch resistant coating 1102 might be composed of multifunctional acrylic monomer, and acrylic oligomers, that can be applied or deposit over the outside surface of the flexible substrate 104 on the side opposite to the low-visibility antenna, by means of Slot Die, Gravure spray, Meier Rod or by standard protocols of a dip coating application. The selected scratch resistant coating 1102 might have the same chemical composition previously described on FIG. 11 , employing the same coating application protocols, with the dip coating application being preferred.

[0052] Figure 13 is an illustration of an embodiment of a low-visibility RFID antenna array structure with scratch-resistant coating on the side of the substrate opposite to the printed pattern. FIG. 13 shows array 700 from FIG. 7 that comprises a low-visibility planar antenna array 702 circuitry that is printed on the top surface of the flexible substrate 104 by means of a roll to roll manufacturing process that have the option of printing any circuit of low-visibility antennas, or arrays of antennas on one side or both sides of the flexible substrate 104. The type of materials employed, the width of the high-definition printed electrodes, and overall characteristics are the same as the previous configuration described in FIG. 7. Depending on the application, the side opposite to the low-visibility planar antenna array 702 circuitry might be protected with a layer of scratch resistant coating 1102, to protect the surface of the transparent flexible substrate 104, causing this surface to be durable, washable, scratch resistant, shatter resistant, chemical resistant, and finger print resistant. Thus, the present disclosure comprises an optimized method of design and fabrication of RFID and RF transparent antennas comprising schematic diagrams illustrating the configuration of a high- definition printed antennas on one side or over both surfaces of a flexible substrate material, that can be glass or a thin, flexible transparent polymer such as a polyester, or polycarbonate film, and a high-definition, low-visibility conductive material circuitry, that is printed by means of an optimized roll to roll manufacturing process, that does not use chemical etching, and have the option of printing one side or both sides of the flexible substrate at the same time, thereby ensuring high efficiency and cost effective manufacturing.

[0053] While the preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described and the examples provided herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. To further illustrate various illustrative embodiments of the present invention, the following examples are provided.