Patent Publication Number: US-2015069133-A1

Title: Nanotube patterns for chipless rfid tags and methods of making the same

Description:
Provisional Patent Application No.: 61/698,657 filed on Sep. 9, 2012 
    
    
     FIELD OF THE INVENTION 
     The present invention is related to chipless RFID tags with use of nanotube antenna resonators and patterns and the methods of making same. 
     BACKGROUND OF THE INVENTION 
     Radio Frequency Identification (RFID) has been widely used for automatic identification, asset tracking, supply chain management, counterfeiting of brand products, etc. Most of these RFID tags or transponders include a chip for storing the item information and a radio antenna for wireless communication or data transmission between the reader or the interrogator and the tag. Prior art of such tags can be illustrated in  FIG. 1 , from typical patents, for instance, U.S. Pat. No. 7,551,141 [1] and U.S. Pat. No. 6,265,977 [2]. The typical RFID tag  100  includes antenna elements  111 , a semiconductor IC chip  112  of the resonant circuit with memory, and a substrate  113 . There are various methods to attach the chip  112  to the antenna  111 . The resonant antenna circuit can be formed either capacitively [1] or conductively [3]. 
     The cost of the IC chip is high, comparing with traditional barcodes used billions each year. The chipped tag cost limits its huge applications and the replacement of the barcode. The optical barcode is usually printed on the paper substrate. It can carry multiple bits by ink strips and is extremely low cost. The limitations of optical barcodes are the line-of-sight, easy to be damaged, the short reading distance, and inaccurate, etc. On the other hand, two dimensional optical codes can be generated by an optical marking tag based on multiple diffraction gratings, for instance, U.S. Pat. No. 4,011,435 [4]. They also share the same limitations of the one-dimensional optical barcodes as described. The chipless tag is new category in the RFID family. The tag usually consists of multi-resonators [3] only without the IC chip. The tag responds wirelessly to an electromagnetic exciting radiation from the reader by transmitting, reflecting, or scattering mechanisms when the resonant conditions are satisfied. Fundamental principle of the wireless resonant or antenna is that the antenna element dimension is inversely proportional to its exciting wave length. For instance, the UHF (Ultra High Frequency) RFID tag works at the frequency band of 900 MHz. Its basic antenna length, i.e., half-wavelength, is 6 inches about 15 cm. In order to accommodate sufficient bits for item unique information, these tags with multiple resonators made from metal elements such as copper strips are very large in size. Therefore, only a few antenna elements are disclosed in the U.S. Pat. No. 6,997,388 [5] with traditional shapes and configurations. Specially, the fully-passive chipless tag working in microwave frequency bands has typical size from tens to hundreds of centimeters with only a few bits. It is not be satisfied for wide applications where the assets or items are small in volume or area. Therefore, current chipless RFID tags found very limited applications due to their limited bits or/and large size. 
     On the other hand, the dimension of antenna elements is bulky and still in macro-scale, typically, centimeter length and millimeter thickness. The fabrication methods are based on so-called top-down approach, for example, stamping from the metal foil. The thickness of antenna elements is limited by so-called skin depth due to RF loss requirements. The skin-depth is decreased by increasing the radio frequency, especially at millimeter wave frequency band (30˜300 GHz) and above. The skin effect becomes more of an issue and results in the loss of RF efficiency for these conventional solid and bulky antenna elements. It is desirable to provide novel materials such as nanotubes that can be almost no skin effect and extra RF loss when used as antennas or resonant elements without skin-depth limitation for applications in millimeter wave frequency bands and even Terahertz frequency bands. 
     As a result, there is also a strong demand and practical requirement for the RFID antennas or resonators that have much smaller dimensions for drug and food safety, jewelry and high brand products for anti-counterfeiting solutions. It is highly desirable that the antenna element or resonant works at much high radio frequencies such as millimeter frequency bands. The huge consumer market calls for the chipless tags that are capable of accommodating sufficient data bits with small size for item-level RFID applications. Finally, it needs to be manufactured by low cost technologies. 
     BRIEF SUMMARY OF THE INVENTION 
     Present invention provides a unique solution for chipless RFID tags by using nanotubes as the resonator elements with different length and patterns. The sufficient bits can be achieved by the plurality of nanotube antennas or resonators with very small size in two-dimensional patterns or even one-dimensional patterns just like traditional barcodes. The radio frequencies of these nanotubes can reach millimeter wave range or tens to hundreds GHz frequency bands with each resonator element length from millimeters down to microns. Furthermore, the nanotube resonators can be fabricated by low-cost manufacturing methods such as printing technologies. The special fabrication substrate with the nanotube dispersion method is also disclosed in the embodiment of this invention. When the very low density of the nanotube resonants is achieved with disclosed patterns, the chipless RFID tag is small, transparent, and even invisible, making extra safety for anti-counterfeiting purposes physically. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying figures, where are incorporated in and form part of the specifications, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention. The foregoing aspects and the others will be readily appreciated by the skilled artisans from the following descriptions. 
         FIG. 1  illustrates a typical chipped RFID tag  100  with a semiconductor IC chip  112  as the digital information storage. At least one antenna with traditional metal elements  111  is necessary to receive the power from the reader and active the chip with the stored data. The same antenna can transmit the data back to the reader for identification. The carrier structure of the RFID tag is the substrate  113 . 
         FIG. 2A  are the patterns of the one dimensional nanotube antennas or resonators for the chipless RFID tag as the first exemplary embodiment. These nanotube resonator elements have the same or very close length with the same or different space between individual nanotubes. 
         FIG. 2B  are another patterns of the one dimensional nanotube antennas or resonators for the chipless RFID tag as the second exemplary embodiment. The nanotube resonator elements have the different length patterns with the same or very close space between individual nanotubes. 
         FIG. 2C  are yet another patterns of one dimensional nanotube antennas or resonators for the chipless RFID tag as the third exemplary embodiment. These nanotube resonator elements have the different patterns of both different lengths and different spaces between them. 
         FIG. 2D  are yet other patterns of one dimensional nanotube antennas or resonators for the chipless RFID tag as the forth exemplary embodiment. These nanotube resonator elements have the any combined patterns disclosed in  FIGS. 2A ,  2 B, and  2 C. 
         FIG. 3A  are the nanotube patterns of two-dimensional nanotube antennas or resonator elements for the chipless RFID tag as the exemplary embodiment. The first group of nanotube resonator elements is perpendicular to the second group of nanotube resonators or antenna elements. Each group can have the patterns as illustrated in  FIGS. 2A ,  2 B, and  2 C with different nanotube length or/and different space between tubes. 
         FIG. 3B  are the another nanotube patterns of two-dimensional nanotube antennas or resonator elements for the chipless RFID tag as the exemplary embodiment. The first group of nanotube resonator elements is oriented in an angle to the second group of nanotube resonators or antenna elements. The angle is in a range from 0 to 180 degree. Each group can have the patterns as illustrated in  FIGS. 2A ,  2 B, and  2 C with different nanotube length or/and different space between tubes. 
         FIG. 3C  are yet other nanotube patterns of two-dimensional nanotube antennas or resonator elements for the chipless RFID tag as the exemplary embodiment. The first group of nanotube resonator elements is oriented and stacked or overlapped in an angle to the second group of nanotube resonators or antenna elements. The angle is in a range from 0 to 180 degree. Each group can have the patterns as illustrated in  FIGS. 2A ,  2 B, and  2 C with different nanotube length or/and different space between tubes. 
         FIG. 4A  are the nanotube patterns of two-dimensional nanotube antennas or resonator elements for the chipless RFID tag as the exemplary embodiment. The nanotubes are distributed randomly with the same or very close length. 
         FIG. 4B  are the another nanotube patterns of two-dimensional nanotube antennas or resonator elements for the chipless RFID tag as the exemplary embodiment. The nanotubes are distributed randomly with the different tube length. 
         FIG. 4C  are the other nanotube patterns of two-dimensional nanotube antennas or resonator elements for the chipless RFID tag as the exemplary embodiment. The nanotubes are distributed randomly by the different tube length and different orientations with a much dense tubes. 
         FIG. 5A  are the nanotube patterns of two-dimensional nanotube antennas or resonator elements for the chipless RFID tag as the exemplary embodiment. The nanotubes are distributed with some local orders. The distributions are generated by an applied electric field to the mixture of nanotubes and liquid crystal host with a special dielectric index. The electrical return path is in the middle of the tag. 
         FIG. 5B  are the another nanotube patterns of two-dimensional nanotube antennas or resonator elements for the chipless RFID tag as the exemplary embodiment. The nanotubes are distributed with the local orders. The distributions are generated by an applied electric field to the mixture of nanotubes and liquid crystal host with another dielectric index. 
         FIG. 5C  are the other nanotube patterns of two-dimensional nanotube antennas or resonator elements for the chipless RFID tag as the exemplary embodiment. The nanotubes are distributed with the different local orders. The distributions are generated by an applied electric field to the mixture of nanotubes and liquid crystal host with certain dielectric index. The electrical return point is located in the anywhere of the tag. Multiple electrical return points can be located in the anywhere of the tag as illustrated. 
         FIG. 6A  presents the dispersion method of the nanotube resonators into a liquid crystal solution randomly for the fabrication of one of chipless RFID tags as the exemplary embodiment. The liquid crystals serve as the carry media or host to separate the individual nanotube one from another effectively. The following curing step can be utilized to permanently frozen the nanotube patterns into a RFID tag, as described in  FIGS. 4A ,  4 B, and  4 C. The liquid crystal solution becomes a crystallized film as liquid crystal polymer that has been approved a high quality dielectric substrate for antennas with very low loss property [6]. This embodiment is the fabrication method of the nanotube resonators embedded into the liquid crystal polymer. Other similar media can be used for the fabrication process as long as the proper dielectric property is satisfied, which consists of yet another embodiment of present invention. 
         FIG. 6A  also presents the alignment method of the nanotube resonators into a liquid crystal host by an applied field for the fabrication of the one of chipless RFID tags as the another exemplary embodiment. The liquid serves as the carry media to separate the individual nanotube one from another effectively. When a static electrical or magnetic field is applied cross the nanotube liquid crystal mixture, the nanotubes can be oriented by the liquid crystal molecules since their orientation can be tuned by the applied field. The field can be also increased by applied voltage through the proper device. Furthermore, following curing step can be utilized to permanently frozen the ordered nanotube patterns as illustrated in  FIGS. 2A ,  2 B,  2 C, and  2 D. The applied electric field can be removed once the pattern has been frozen or fixed. The liquid crystal solution becomes the crystallized film as liquid crystal polymer that has been approved a high quality dielectric substrate for antennas with very low loss property [6]. This embodiment presents the fabrication method of ordered nanotube patterns of present invention. 
         FIG. 6B  presents the patterns of two-dimensional nanotube antennas or resonator elements for the fabrication of one of chipless RFID tags as the exemplary embodiment by combining or repeating the regions disclosed in  FIG. 6A . 
         FIG. 6C  presents the more complicated patterns of two-dimensional nanotube antennas or resonator elements for the fabrication of one of chipless RFID tags as the another exemplary embodiment by combining or repeating the multiple regions in two directions disclosed in  FIG. 6A . 
     
    
    
     Skilled artisans will appreciate that elements or nanotubes in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to actual scales. For instance, some of these nanotube elements in the figures may be exaggerated relatively to other elements to help to improve understanding of the embodiments of the present invention. 
     DETAILED DESCRIPTION OF THE INVENTION  
     Definitions 
     For the purpose of the disclosure and embodiments, the term “nanotube” in this invention is meant to include any high aspect ratio linear or curved nano-scaled structures, including single-walled, double-walled, and multi-walled nanotubes, semiconducting or conductive nanotubes, nanowires, nanotube bundles, nanotube yarns, nanowires, and nano-columns, and nano-beams which can be used as resonators or can be made to vibrate in an electrical or/and electromagnetic fields. These preferably have a length from 1 micron, to 1 millimeter, and to tens of centimeters, depending on the radio frequencies and the tag size requirements. The diameters have a width or diameter from 0.2 nm to 1 micron, and to tens of millimeters. Examples of the present nanotubes also include such metallic as Ni, Cu, Ag, and Au nanowires. Preferred carbon nanotubes have metallic or conducting properties with one, two, or multi-walls and directional or anisotropic conductivity. 
     For the purpose of present invention, the term “electromagnetic signal” is used to mean either electromagnetic waves moving through air or dielectric or electrons moving through wires or both in any a frequency or a frequency range. 
     For present disclosure, the term “radio” is used to mean the wireless transmission or communication through electromagnetic waves in any a frequency or a frequency range from 1 MHz to 1 GHz, and to 1 THz. Preferred millimeter waves are frequencies from 30 GHz to 300 GHz. 
     For present disclosure, the term “tag” is used to mean a layer of nanotube patterns and a substrate with any shape of an oval, a square, a rectangle, a triangle, a circle, or polygons, and any size from 1 micron to 1 millimeter, and to tens of centimeters. It can also be multi-layers with different nanotube patterns and substrate materials. 
       FIG. 2A  describes the embodiment of present invention of the patterns of one-dimensional nanotube antennas or resonator elements. The chipless tags  200  and  210  are formed in the substrates  202  and  212  respectively. In the first tag  200 , the nanotubes have the very close or the same length with the same space between the two elements. Therefore, under the incoming electromagnetic wave radiation, the nanotubes are excited and re-radiated in a certain frequency correlated to the nanotube length. A diffraction pattern from the nanotube pattern can be received by a remote receiver device. The pattern  211  is different from the pattern  201  by that the space between the two nanotubes can be changed and different from one to another. Therefore, different diffraction patterns are formed with the same frequency but different phase angles. The RF characteristics can be used for coding and decoding. We will disclose the coding and decoding methods based on nanotube patterns in another patent disclosure [7]. 
       FIG. 2B  describes the embodiment of present invention of the patterns of one-dimensional nanotube antennas or resonator elements. The chipless tags  220  and  230  are formed in the substrates  222  and  232  respectively. In the tags  220  and  230 , the nanotube patterns  221  and  231  have different length and shapes which can be formed by printing the nanotube ink or cutting or stamping the nanotube pattern  201 . The different length patterns will generate different diffraction patterns with different frequencies or a broadband spectrum under the incoming electromagnetic radiation. The broadband diffraction patterns from the nanotube patterns can be received by a remote receiver device and utilized for enhancing the codes or bits disclosed in another patent disclosure [7]. 
       FIG. 2C  describes the embodiment of present invention of the other patterns of one-dimensional nanotube antennas or resonator elements. The chipless tags  240  and  250  are formed in the substrates  242  and  252  respectively. In the tags  240  and  250 , the nanotube patterns  241  and  251  have different length, different spacing, and different shapes. These pattern features can be formed by printing the nanotube ink or cutting or stamping the nanotube pattern  211 . The tag  260  presents a plurality of nanotube patterns by any combinations of the previous patterns of  201 ,  211 ,  221 ,  231 ,  241 , and  251 . The plenty of various different diffraction patterns with broadband and a wide phase difference can be generated once the RFID reader radiates the electromagnetic radiation on the tags. A remote receiver device can utilize the information patterns for obtaining sufficient number of codes or bits for the RFID detection disclosed in another patent disclosure [7]. 
       FIG. 3A  describes another embodiment of present invention of patterns of the two dimensional nanotubes. The tag  310  presents a plurality of nanotube patterns by combinations of the previous  201  (now  312 ) and  211  (now  313 ) in a 90 degree angle on the substrate  311 , for instance.  FIG. 3B  discloses the two dimensional patterns by angling the group  322  and group  323  of nanotubes. In the  FIG. 3C , the two dimensional nanotube patterns are formed by stacking one pattern  333  on the pattern  332  in any angle from 0 to 180 degrees according to the embodiment of current invention. The advantages are such pattern fabrication is at least double of the frequency spectrum and much wider the phase difference. If the same bits are required, the tag size can be at least 4 times smaller, comparing with the patterns in  FIG. 3B . Again, a remote receiver device can utilize the diffraction information patterns for obtaining sufficient number of codes or bits and the small size of tags for the RFID detection disclosed in another patent disclosure [7]. 
     As such, nanotube elements  312 ,  322 , or  332  can be excited and resonating, provide a series of radio frequencies in responding to their excitation frequency spectrum in one direction. The second group of the nanotube elements  313 ,  323 , or  333  can provide another series of radio frequencies in responding to their excitation frequency spectrum in another direction. RF (Radio Frequency) responsiveness in principle from any nanotube element can be radiation, reflection, and scattering. The two groups of elements can be oriented by any combinations from an angle from 0 to 180 degrees. Therefore, a very complicated directional RF patterns can be formed. The RF receiver can collect these responsiveness properties with different patterns selectively or collectively. Large number of digital bits is formatted by coding and decoding technologies [7] based on their RF responsiveness properties that can be two-dimensional and even three dimensional patterns, as disclosed in present invention. 
       FIGS. 4A ,  4 B, and  4 C are the nanotube patterns of two-dimensional nanotube antennas or resonator elements for the chipless RFID tags where the nanotubes are distributed randomly with the same length  402 , different length  412 , and  422 . A very wide frequency spectrum can be generated with a broadband phase signature for the coding and decoding of the chipless RFID disclosed in another patent disclosure [7]. The fabrication method is also disclosed in present patent. The nanotubes are distributed randomly by the different tube length and different orientations with a tube volume percentage from as low as 0.01% to 10%. As such, millions of patterns and codes can be generated both physically and digitally for RFID tag security. Protected and unique software can be provided to customers for the secured identification of brand products to protect their high value products for counterfeiting purpose. 
       FIGS. 5A and 5B  present the dispersion method of the nanotube elements into a liquid crystal solution host. Liquid crystals have several basic phases, which are widely used for various display devices. A liquid crystal, e.g., nematic phase, has shown to be good host for carbon nanotubes&#39; dispersion effectively [6, 8, 9, 10]. The liquid crystal host  605  illustrated in  FIG. 6A  is made of elongated molecules with anisotropic properties. The liquid  605  serves as the carry media to separate the individual nanotube element  604  one from another. The nanotube tags  400 ,  410 , and  420  can be processed in two-steps basically. The first step is the mixing and dispersion of nanotube elements  402 ,  412 ,  422  with the liquid crystal host  605  with the certain ratio or percentage of the nanotube elements. The mixing percentage can be a range from 0.01 percent to 10 percent, depending on the complexity and bits level requirements. After the proper formation of the nanotube elements&#39; solution, the second step can be a thin coating, screen printing, or alternative printing techniques, followed by a curing process to fabricate the nanotube tag into the very thin liquid crystal polymer substrate  401 ,  411 , or  421 . It can be transparent and even invisible since a very thin liquid crystal polymer is formed and the nanotube is well dispersed in a very low percentage. This embodiment of the tag processing can fabricate the tags  400 ,  410 ,  420  etc. with unique codes, transparent and invisible film substrates as well as low-cost fabrication methods such as printing. Furthermore, the tags can be attached or embedded into the small products for RF identification with high security for preventing the tag replaced or/and faked by any third party. Alternative media or host liquids can be used for the same or similar fabrication processes as long as the proper dielectric property of the substrate made from the host liquid is satisfied for RFID purpose, which consists of yet another embodiment of present invention. 
     Another fundamental function, so-called Freederick transition of the liquid crystals needs to be utilized for the fabrication purpose. A collective reorientation of the liquid crystal directors can be achieved by applying an electric field  606  [8,9,10]. The strength of the applied electric field can be controlled by the device  603  and  606  using the electrical high voltage. It has been shown that the nanotube elements can be well-aligned and controlled by the applied electric field with the sufficient field strength [8,10] that is furthermore controlled by the device  603 . The nanotube element tags  500 ,  510 ,  520 , and  600  with specific orientation distribution of different orders inside local areas can be processed in four basic steps. The first step is the mixing and dispersion of nanotube elements with the liquid crystal host to form the mixture  502  or  512  with the certain ratio or percentage of the nanotube elements. The mixing percentage can be a range from 0.01 percent to 10 percent, depending on the requirements of the complexity and bits. After the proper formation of the nanotube elements&#39; solution can be coated, screen printed, or distributed uniformly in an area for fabricating the nanotube tags. The electric field is applied as the third step, which can be realized by immersing a conductive structure with one positive pole  601  and another negative pole  602  into the area. The final step is the curing process to fabricate the nanotube tags  500 ,  510 ,  520  and  600 . A very thin liquid crystal polymer substrate with the designed patterns of nanotube elements is fabricated by the described process steps. The fabrication of the tag  610  can be repeated from one area to another area. Multiple tags can be fabricated at the same time using a conductive structure pattern that is designed as the  FIG. 6(   c ) for tag  620 . The conductive structure is to be removed after the tag fabrication. There is no limitation for designing the innovative patterns disclosed in present invention. The embodiment should cover all these pattern variations in different shapes and sizes. The tags as fabricated in the embodiments can be transparent and even invisible since a very thin liquid crystal polymer is formed and the nanotube is well dispersed in a very low percentage and oriented in one or more designed patterns. These embodiments of the tag processing can fabricate the tags into unique codes, transparent, invisible with the low cost. Furthermore, the tags can be stamped into different shapes for encoding and attached or embedded into the products for RF identification with high security for preventing the tag replaced or/and faked by any third party. 
     REFERENCES 
     [1] U.S. Pat. No. 7,551,141, Hadley et al., RFID Strap Capacitively Coupled and Method of Making Same, Jun. 23, 2009 
     [2] U.S. Pat. No. 6,265,977, Vega et al., Radio Frequency Identification Tag Apparatus and Related Method, Jul. 24, 2001. 
     [3] U.S. Pat. No. 6,424,263, Lee et al., Radio Frequency Identification Tag On a Single Layer Substrate, Jul. 23, 2002. 
     [4] U.S. Pat. No. 4,011,435, Phelps et al., Optical Indicia Marking and Detection System, Mar. 8, 1977. 
     [5] U.S. Pat. No. 6,997,388, Yogev et al., Radio frequency data carrier and method and system for reading data stored in the data carrier, Feb. 14, 2006. 
     [6] Lapointe et al., Elastic Toque and the Levitation of Metal Wires by a Nematic Liquid Crystal, Science, Vol303, January 2004, pp. 652-655. 
     [7] Zhengfang Qian, Patent Application: Coding and Decoding Methods of Nanotube Chipless RFID Tags. 
     [8] Onuki A., Liquid Crystals in Electric Field, J Physical Society of Japan, Vol73, March 2004, pp. 511-514. 
     [9] Jeon et al., Dynamic Response of Carbon Nanotubes Dispersed in Nematic Liquid Crystal, NANO: Brief Reports &amp; Reviews, Vol2, 2007, pp. 41-49. 
     [10] Dierking I et al., Liquid Crystal-carbon nanotube dispersions, J Applied Physics, Vol. 97, 044309, 2005, pp. 1-5.