Abstract:
A method and apparatus for providing multiple functions using nanotube threads comprising: a first nanotube thread and a second nanotube thread, the first nanotube thread and the second nanotube thread arranged to form a mesh, wherein the first nanotube thread further comprises a measurable invariant property and the second nanotube thread comprises a measurable variant property.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. provisional patent application Ser. No. 61/641,1468, filed May 2, 2012 which is herein incorporated by reference. 
     
    
     GOVERNMENT INTEREST 
       [0002]    Governmental Interest—The invention described herein may be manufactured, used and licensed by or for the U.S. Government. 
     
    
     FIELD OF INVENTION 
       [0003]    Embodiments of the present disclosure generally relate to wireless signal communications and, more specifically, to a method and apparatus for providing a multifunctional meshed nanotube sensor. 
       BACKGROUND OF THE INVENTION 
       [0004]    The capability to provide multiple functions for a single device provides convenient savings in physical space and costs. One traditionally single-tasked device is an antenna. Antennas used in the communication of electromagnetic signals have been developed with a concern for size reduction while providing high fidelity information during transmission and/or reception. Patch antennas have been a preferred choice of radio frequency (RF) front end design for their reliability and low profile topology. Such a profile makes them ideal for wireless systems where physical space on a wireless device is limited. Patch antennas are also lightweight and enable mounting onto various surfaces that are not suitable for dipole, wire loop, or multi-element antennas. The patch antenna has proven to be quite effective for a variety of applications, including terrestrial and satellite communications systems and various electromagnetic scanning arrays due to its low-profile, planar structure, reasonable bandwidth, and excellent gain. 
         [0005]    Antenna material composition is crucial in ensuring the efficient and accurate transmission and/or reception of wireless signals. The conductivity of these materials plays a critical role in riot contributing to attenuation or distortion of signals already degraded by environmental factors experienced during propagation. Traditional patch antennas are constructed from conductive metals such as copper. 
         [0006]      FIG. 1  is a schematic illustration of a traditional microstrip patch antenna.  FIG. 1  depicts a patch antenna  100  mounted on a substrate  115 . An electromagnetic wave is transmitted and/or received according to a radiating edge or slots (shown as  125 ,  130 ) of the patch antenna  100  given its length  105  and width  110 . Radiating slots  125  and  130  produce a broadside radiation pattern  145 . When the substrate thickness  140  is small, radiation is approximated by horizontal magnetic currents circulating the perimeter of the patch antenna  100  over a ground plane  135 . Communication of signals received or to be transmitted by the patch antenna  100  is achieved using an impedance matched microstrip feed line  120 . 
         [0007]    Military personnel and first responders carry various equipment to communicate with others and provide environmental information about their surroundings. For example, personnel may carry a wireless communications device as well as an environmental condition detector (e.g. temperature, pressure, gas, and the like). Carrying numerous devices decreases mobility, agility, and effectiveness of the user. 
         [0008]    Thus, there is a need in the art for a method and apparatus that can provide a multifunction sensor (e.g. both wireless communication as well as gas detection) in a compact lightweight form factor. 
       SUMMARY 
       [0009]    Embodiments of the present method and apparatus generally relate to a multifunction meshed patch sensor capable of simultaneous wireless communication and gas detection/sensing. The patch sensor comprising a first nanotube thread and a second nanotube thread, the first nanotube thread and the second nanotube thread alternately crossing each other substantially orthogonally to define a mesh element, wherein the first nanotube thread further comprises a measurable invariant property and the second nanotube thread comprises a measurable variant property. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    So that the manner in which the above recited features of the present disclosure car be understood in detail, a more particular description of the embodiment, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments in this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
           [0011]      FIG. 1  is a schematic illustration of a traditional microstrip patch antenna. 
           [0012]      FIG. 2  is a perspective view of a first type of nanotube material used in an embodiment of the present invention. 
           [0013]      FIG. 3  is a perspective view of a second type of nanotube material used in an embodiment of the present invention. 
           [0014]      FIG. 4  illustrates the formation of nanotube thread used in an exemplary embodiment of the present invention. 
           [0015]      FIGS. 5A and 5B  illustrate an exemplary mesh construction used in an embodiment of the present invention. 
           [0016]      FIG. 6  is an illustration showing of the meshed patch configuration in accordance with an embodiment of the present invention. 
           [0017]      FIG. 7  is a bottom view of the meshed patch of an embodiment of the present invention from  FIG. 6 . 
           [0018]      FIG. 8  is a block diagram for an embodiment of the invention. 
           [0019]      FIG. 9  depicts a flow diagram of a method of operation of an embodiment of the present invention. 
           [0020]      FIG. 10  depicts a graph of the frequency shift anticipated by the mesh structure of an embodiment of the present invention compared to a traditional copper patch antenna. 
           [0021]      FIG. 11  depicts a graph of a radiation pattern of an embodiment of the present invention. 
           [0022]      FIG. 12  depicts a graph of frequency shifts in detected signal based on the amount of gas present achieved by an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    An embodiment of the present invention provides a multifunction sensor (e.g. an antenna and gas detector) integrated into a single device. in one embodiment, mesh construction of interwoven semiconductive and conductive nanotube threads capable of transceiving signals as well as changing properties when exposed to particular gases. 
         [0024]      FIG. 2  is a perspective view of a first type of nanotube material used in an embodiment of the present invention. Carbon nanotube (CNTs) structures to be used in embodiments of the invention are allotropes of carbon with a cylindrical nanostructure and may be single walled nanotubes (SWNTs) or multiwall nanotubes (MWNTs). Both SWNTs and MWNTs may be applied in embodiments of the invention.  FIG. 2  depicts a perspective view of SWNT comprised of a single monatomic layer of carbon rolled up into a hollow cylindrical tube  200 . The particular length (arrow  205 ) of the tube  200  can vary in size but is typically very small, for example, 0.2-5 μm. The tube  200  may have a width (arrow  210 ) of approximately 1-2 nm. One of the more recently researched properties of MWNTs is their wave absorption characteristics, specifically microwave absorption, which indicate that they are a viable material in the formation of antennas. 
         [0025]      FIG. 3  is a perspective view of a second type of nanotube material used in an embodiment of the present invention. The nanotube material may be MWNT, which may consist of two or more concentric cylinders of monatomic carbon layers. As an example, two layers are separated by a small gap  310  and can be as small as 0.36 nm with a combined width  305  of about 2-25 nm. The absorption characteristics may be altered by how certain metals fill, surround, or layer with respect to MWNT  300 . The filling of MWNT with certain metals, such as iron for example, changes complex permeability (μ r ) and complex permitivity (ε r ) of the material. In antenna applications, altering permeability and permittivity in a controlled manner can result in improvements in maximum absorption and bandwidth. 
         [0026]      FIG. 4  illustrates the formation of nanotube thread used in an exemplary embodiment of the present invention, Nanotubes may be formed into CNT threads  435  through a pulling technique  400 . The method begins with individual CNT  405  in a CNT forest  412  that is grown on a substrate  430 . Individual is nanotubes  405  naturally align themselves into intertwined “bundles”  435  held together by Van Der Waals forces ( 415  and  420 ), and more specifically, pi-stacking. The technique  400  forms the carbon nanotube thread by a pulling force (shown as  410  and  425 ) which may be supplied by a collection spool (not shown) or other pulling device. The composition of the thread  435  may include SWNT, MWNT, or a combination thereof. The interwoven CNT thread  435  can be used to construct a mesh structure with the beneficial physical properties of CNTs, including light weight and high tensile strength. 
         [0027]      FIGS. 5A and 5B  illustrate an exemplary mesh construction used in an embodiment of the present invention.  FIG. 5A  depicts one embodiment that includes the interwoven CNT threads  505  in a CNT meshed patch  500 . The manipulation of threads provides physical flexibility to the patch  500  as well as allows for ease of integration with other materials such as textile threads. In one embodiment, threads are spaced about λ/67 apart to visually be close to typical textile thread space, however alternative spaces may be realized. Additionally, other weaving patterns or shapes may be realized besides those shown in  FIG. 5 . A knitting machine could be used to create plaited fabrics. Layers of the weaving is limited only to the application of the mesh patch and substrate materials. 
         [0028]      FIG. 5A  also depicts a basket weave  505  wherein threads  510  alternate above and below threads  515 . The respective threads are interwoven such that alternating columns of one type of thread line  510  sits atop a row of another type of thread line  515  and vice versa. A basket weave  505  construction is disclosed but it will be appreciated by one skilled in the art that alternative patterns may also be realized.  FIG. 5B  depicts a cross-sectional view of the embodiment in which the basket weave  500  threads are formed as a patch  500  over a substrate  520 . This embodiment uses an aperture  530  to expose and couple the patch to a microstrip feedline  530 . The feedline  530  ultimately communicates signals to and from the patch  500  for operation with accompanying electronics, as detailed below. 
         [0029]      FIG. 6  is an illustration showing of the meshed patch configuration in accordance with an embodiment of the present invention.  FIG. 6  depicts a top plan view (i.e. a two dimensional view represented by arrows  640  and  645 ) of the specific weaving pattern for a mesh patch  600  on an exemplary substrate  635 . It will be appreciated that the respective threads of one type are interwoven with a second type in the meshed patch  000 . As a specific example, conductive MWNTs thread lines  605  run in first line axis  645  and semiconducting thread lines  610  comprised of nanotubes with significant added defects run in a second thread line axis  640 . The semiconducting thread lines  610  substantially orthogonal to the first thread line axis  645 . Threads depicted as an intersection  615  are formed in a basket weave pattern, as described above. Although the axes of specific materials may be switched in other embodiments.  FIG. 6  also depicts an embodiment wherein threads of the same type  620  are electrically connected when they cross above and/or below each other at their intersections  620  across at least two layers of the meshed patch  600 . 
         [0030]    One exemplary embodiment design consists of a 2.65×3.68 nm patch constructed from 50 μm diameter meshed CNT threads  605 ,  610  residing on a ground plane (not shown) separated by a dielectric substrate  635 . An exemplary construction of the substrate may include an RT/Duriod 6010 (ε r =10.2) feedline layer, RT/Durioud 5870(ε r =2.33) for a patch layer. The mesh patch  600  of  FIG. 6  connects to a microstrip feedline  625  through an aperture  630 , as further illustrated in  FIG. 7 . The microstrip feedline  625  connects through a connector  650  to additional electronics for processing as will be discussed further below. Positioning of the aperture  630  is dependent on the size of the meshed patch  600  and the operating frequency and length of the feedline  625 . 
         [0031]      FIG. 7  is a bottom view of the meshed patch of an embodiment of the present invention from  FIG. 6 .  FIG. 7  depicts the mesh patch  800  connected to a microstrip feedline  625  through an aperture  630 . Signals travel to and from the patch through the microstrip feedline  625  to through a connector  650 . Specifically, the aperture  630  allows for connection to the microstrip feedline  625 , ground plane  680 , substrate  635 , and ultimately a For Mobile Equipment (FME) connector  650 . However, alternative RF connectors and coupling techniques may also be realized. 
         [0032]      FIG. 8  is a block diagram of a system  800  that utilizes the mesh patch as a sensor in accordance with an embodiment of the invention. During operation, the system  800  may transmit and/or receive wireless communication signals  890  or other RF/microwave signals for use, for example in RADAR, via the patch  801 . The system comprises a patch sensor  801 , a coupler  815 , a transceiver  805 , a gas detector  810 , CPU/Memory  809 , and a user interface  813 . The system  800  may have alternate receiving and transmitting signals either physically, such as alternating lines or chronologically through time division utilizing a transceiver  805 . The system additionally may simultaneously, substantially simultaneously, or separately detect gases  810  in the surrounding environment. 
         [0033]    In one embodiment of the invention, defects are introduced into the semiconducting threads  880  of the patch  801 . The defects ensure that the threads exhibit lower conductivity than their conductive thread neighbors  875  and acting almost as a dielectric buffer. The defects also provide more locations for reactive gas molecules to donate or accept electrons, thus increasing the likelihood that a reactive gas will cause a noticeable change in the semiconducting thread  880  permittivity. The arrangement of semiconducting and conducting threads may be varied in other embodiments. Gas detection capability is realized when an oxidizing or reducing gas  885  changes the permittivity of the semiconducting thread such that a received electromagnetic or wireless signal  890  is distorted. The distortion may then can be compared to a predetermined expected baseline signal to determine the presence of a gas and its concentration. 
         [0034]    The system  800  further processes a signal from a coupler  815  which is then processed by a transceiver portion  805  and/or a gas detector  810 . The transceiver  805  comprises a circulator/isolator  803 , a first amplifier  807 , a second amplifier  820 , a mixer  825 , a local oscillator  835 , a signal detector  830 , and a signal processor  840 . A coupler  815  connects the transceiver  805  to the patch sensor  801 . For communications signals, the patch sensor  801  operates as an antenna. The circulator/isolator  803  directionally couples the signal to/from the coupler  815  and to/from the transceiver&#39;s receiver and transmitter. In a transmitter mode, a user interface  813  sends commands to the CPU/Memory  809 , such that there is a signal input  852  to a first amplifier  807  which passes the signal to the circulator/isolator  803 , and ultimately to the patch  801  for transmission. In a receiver mode, the transceiver  805  receives a signal from the circulator/oscillator  803  via a second amplifier  820 . The signal  816  is then mixed with a local oscillator  835  within a mixer  825 . The local oscillator  835  is controlled (e.g. frequency and/or phase locked) to the received signal. A signal detector  830  processes the mixed signal to create the oscillator control signal as well as provide detected signal information (e.g., modulation) to the signal processor. The signal processor  840  produces an output  850  that is coupled to the CPU/Memory  809  and, ultimately, to the user interface  813 . In some embodiments, the user interface  813  may comprise a display, keyboard, mouse, and other peripheral devices. 
         [0035]    The gas detector  810  comprises an impedance detector  855 , comparator operational amplifier  860  and threshold generator  865 . The sensor  801  is coupled to an impedance detector  855 . The impedance detector  855  senses the impedance of the sensor  801  (e.g. a resonance impedance by applying an RF signal to the sensor  801 ). The impedance value is coupled to the comparator  860  and compared to a predetermined threshold level  865 . A change in the impedance will show as a difference value of the resulting signal  816  that forms the output. The result may be processed and/or stored in the CPU/Memory  809  and ultimately displayed to the user through the user interface  813 . The CPU/Memory  809  may also provide analog to digital conversions, digital to analog conversions, and various digital signal processing. An all digital solution may be used by implementing the transceiver  805  and gas detector  810  as software modules within the CPU/Memory  809 . As such, the signals from the path sensor  801  would be digitized and processed as described above. 
         [0036]    The multifunctional system  800  is implemented as a gas detector by taking advantage of newly discovered reactions of types of CNTs when introduced to particular oxidizing gases  885 . Thus, the mesh antenna patch comprises two measurable properties, invariant and variant. The first invariant property allows the transceiver to communicate through the conductive lines  875 . The second variable property interacts with the environment to provide a gas sensing capability through semiconductive lines  880 . The reactions of the invariant property have been exploited as an ambient gas sensor by incorporating semiconductive SWNT thread lines  880  with a high number of defects along as part of an electromagnetic wave resonator of the embodiment. Oxidizing and reducing gases such as He (helium), Ar (argon), N 2  (nitrogen), NH 3 (ammonia) and O 4  (oxygen) proximate to CNT threads temporarily affect the permittivity and conductivity of such CNTs in the semiconductive material. 
         [0037]    In some embodiments, wireless communication is to be continuously performed through the transmission or reception of electromagnetic waves on the conductive threads  875 . Simultaneously or nearly simultaneously, the semi-conductive threads  880  are performing gas sensing by detecting an impedance change. The radiating signals may originate from the patch  801  or in other embodiments may also be received from a separate source (not shown) which is distinct from the meshed patch antenna  801  structure in other embodiments. 
         [0038]    A multifunctional device is thus realized when the invariant conductive CNT threads  875  serve as the meshed patch antenna structure and the variant semiconducting CNT threads  880  serve as dielectric spacer material with variable permittivity. In one embodiment, the meshed CNT thread patch  800  may simultaneously serve as both the radiating antenna for a communications system  805  and as the dielectric loaded resonator for a gas detector  810 . 
         [0039]      FIG. 9  depicts a flow diagram of a method of operation of a routine executed by the CPU to detect specific gases in accordance with an embodiment of the present invention. The exemplary method  900  for determining the gas type comprises comparing detected results received at step  901  against a look up table (LUT)  939 . The method  900  begins by receiving gas detection results at step  901 . The results are then compared to a look-up-table (LUT) at step  930 . The LUT comprises predetermined impedance values of gases (e.g., difference values measured against a threshold value). Should it be determined that a gas is found at step  935  (i.e., a value compares favorably to the LUT values), the method outputs the gas type at step  940  and ends the comparison at step  955 . The method continues the comparison at step  945  as long as the end of the LUT has not been reached. However, if the comparison reaches the end of the table at step  945 , without outputting a correct gas type  950 , the process ends at step  955 , notifying the user that no match was found or there is a need for manual entry of the gas type if the type is known. 
         [0040]      FIG. 10  depicts a graph  1040  of the frequency shift anticipated by the mesh structure of an embodiment of the present invention compared to a traditional copper patch antenna.  FIG. 10  depicts the frequency response  1000  of the copper patch  1005  compared to the frequency response  1010  for meshed CNT thread patch  1030  of an embodiment of the invention.  FIG. 10  shows an exemplary shift in frequency  1100  and reduction in gain reduction when compared to that of a standard copper patch antenna  1005  which is used as a baseline standard.  FIG. 10  further shows there is about a 2 GHz or 7% shift  1025  in frequency and noticeable bandwidth reduction of about 400 MHz (16%)  1020  from the center frequency of the baseline. The shift is noticeable but acceptable for operation of the mesh antenna, especially when taken in light of the dual-functionality to operate also as a gas detector. 
         [0041]      FIG. 11  depicts a graph of a radiation pattern of an embodiment of the present invention. The exemplary broadside radiation pattern  1100  maintained with one embodiment of a CNT meshed patch antenna. The meshed patch yields a small gain reduction  1105  when compared with traditional solid metal patch design  1110 , such a reduction is acceptable for wireless communication fidelity. 
         [0042]      FIG. 12  depicts a graph  1201  of frequency shifts (indicative of an impedance change) in the detected signal based on the amount of gas present achieved by an embodiment of the present invention. Reference  1220  identifies a key showing the amounts of NH 3  introduced into the atmosphere surrounding a patch sensor of, for example,  FIG. 8 . The graph  1201  plots S 11  (shown as  1210 ) versus frequency  1205 . Permittivity (ε r ) of the semiconducting SWNT threads increases linearly when in the presence of the NH 3 . The estimated change for an applied signal  1200  is plotted from ε r =5 to ε r =5.15 in the presence of 1000 ppm of NH 3  and subsequent increases of 0.15 with each additional 3000 ppm. A measureable resonant frequency  1205  shift of −60 MHz  1215  is thus shown in  FIG. 12  as a prediction to occur as the concentration of NH 3  is increased around the meshed patch antenna. Through comparing the shift to a signal from predetermined baseline gas concentration  1220 , to one can determine the presence of a particular gas. There is, also a slight reduction in the signal bandwidth. The frequency shift  1215  is thus detectable but small enough to guarantee continuous bandwidth for wireless communications functionality. 
         [0043]    In other exemplary embodiments, RF signals may also be processed such that the resonant or center frequency shift  1215  will be compared to predetermined profiles of gases to determine the presence of a specific gas surrounding the sensor. Profiles may be calculated based on findings of predetermined results and thus compared to instant readings from the embodiment. This is because the center frequency shifts in direct response to the change in the permittivity of the CNT layer that occurs due to the presence of a reactive gas  1220 . Ultimately the exemplary embodiment would have the frequency shift  1215  in the resonant frequency detected on semiconductive thread lines while maintaining communication of wireless signals on the first conductive thread lines of the mesh structure. Further embodiments may have the detected RF signal originate from conductive thread lines of the mesh or from a source completely external and separate from the mesh. 
         [0044]    By bundling the nanotubes together into longer fibers such as threads or ropes, it has been determined that since nanotubes can be made into a thread, it can be woven together on a larger scale similar to and/or in conjunction with textile threads. When implemented with textiles, air between layers may become the substrate or layers of textile threads may become the substrate for the nanotube threading. 
         [0045]    Thus, specific embodiments not detailed herein will include the mesh pattern that may be incorporated into articles of clothing, wristbands, lightweight aircrafts, and have off-chip designs for processing may also be realized in the future. Fabrication steps will also include factors such as various crystalline structure as well as specific programmable functionality for gas detection and communication systems integration. Other embodiments are also able to detect EMI, moisture, temperature, humidity, and those environmental factors affecting dielectric properties and permittivity. Further future embodiments may include structures of different weave patterns, layers, or separate transmitting and receiving communication lines. 
         [0046]    While the foregoing is directed to embodiments of the present disclosure, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.