Abstract:
A reconfigurable antenna is provided having a liquid metal in contact with an electrolyte with the liquid metal being in a first configuration. A plurality of electrodes includes a first electrode in contact with the liquid metal and a second electrode in contact with the electrolyte. A voltage source connected across the first and second electrodes applies a voltage of a predetermined magnitude and a predetermined polarity in order to move the liquid metal from the first configuration to a second configuration and to measure resultant current flow and modify the applied voltage based on the resultant current flow. Cessation of the applied voltage locks the liquid metal in this second configuration.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation-in-part application that is based on and claims priority to U.S. Patent Non-Provisional application Ser. No. 15/043,826, filed on 15 Feb. 2016, with the United States Patent and Trademark Office, the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure is related generally to electromagnetic wave communications, and, more particularly, to a system and method for dynamically reconfiguring one or more electromagnetic wave antennae to accommodate different format or performance requirements. 
       BACKGROUND 
       [0003]    An antenna is a structure used to transmit or receive electromagnetic radiation, typically for communication or detection purposes. Thus, for example, cellular band antennae are ubiquitous on the upper and side surfaces of buildings in populated areas, and the red aviation warning lights of radio station antennae towers dot the countryside. Since the radiation transmission and reception characteristics of an antenna are largely a function of the antenna&#39;s size and shape (configuration), the antennae we see every day take on a wide variety of shapes and sizes. 
         [0004]    While the present disclosure is directed to a system that can eliminate certain shortcomings, it should be appreciated that such a benefit is neither a limitation on the scope of the disclosed principles nor of the attached claims, except to the extent expressly noted in the claims. Additionally, the discussion of technology in this Background section is reflective of the inventors&#39; own observations, considerations, and thoughts, and is in no way intended to accurately catalog or comprehensively summarize the art currently in the public domain. As such, the inventors expressly disclaim this section as admitted or assumed prior art. Moreover, any identification or implication above or otherwise herein of a desirable course of action reflects the inventors&#39; own observations and ideas, and should not be assumed to indicate an art-recognized desirability. 
       SUMMARY 
       [0005]    In keeping with an embodiment of the disclosed principles, a selectively reconfigurable antenna system is provided having a first material layer and a second material layer defining a cavity there between. A first reservoir at least partially contains a liquid metal and a second reservoir least partially contains a liquid electrolyte. The liquid metal and the electrolyte are in contact at a metal oxide layer in the cavity. A plurality of electrodes include a first electrode in contact with the liquid metal and a second electrode in contact with the electrolyte such that the metal oxide layer breaks down when a negative potential is applied to the second electrode relative to the first electrode. 
         [0006]    In another embodiment, a method is provided for configuring an antenna. A liquid metal and an electrolyte are placed between two surfaces such that the liquid metal and the electrolyte are in contact with each other at an interface layer. A voltage applied between the electrolyte and a portion of the liquid metal operates to move the portion of the liquid metal toward the electrolyte. Stopping (or ceasing) the application of voltage when the liquid metal reaches a predetermined configuration locks the liquid metal in that configuration. 
         [0007]    In yet another embodiment of the described principles, a reconfigurable antenna is provided having a liquid metal in contact with an electrolyte, with the liquid metal being in a first configuration. A plurality of electrodes include a first electrode in contact with the liquid metal and a second electrode in contact with the electrolyte. A voltage source is connected across the first and second electrodes and is configured to apply a voltage of a predetermined magnitude and a predetermined polarity in order to move the liquid metal from the first configuration to a second configuration. 
         [0008]    Other features and aspects of embodiments of the disclosed principles will be appreciated from the detailed disclosure taken in conjunction with the included figures. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    While the appended claims set forth the features of the present techniques with particularity, these techniques, together with their objects and advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings of which: 
           [0010]      FIG. 1  is a plan view schematic showing a liquid metal configuration in a one-dimensional channel via the application of voltage having a selected magnitude and polarity; 
           [0011]      FIG. 2  is a plan view schematic of a two dimensional reconfigurable antenna in accordance with an embodiment of the disclosed principles; 
           [0012]      FIG. 3  is a plan view schematic showing a multi-element two dimensional reconfigurable antenna in accordance with an embodiment of the disclosed principles; 
           [0013]      FIG. 4  is a perspective view of a three-dimensional antenna array formed in accordance with an embodiment of the disclosed principles; 
           [0014]      FIG. 5  is a perspective view of a configurable radio frequency (RF) shield system in accordance with an embodiment of the disclosed principles; 
           [0015]      FIG. 6  is a plan view of several additional antenna types created in various embodiments of the disclosed principles as well as a perspective side view of an alternative antenna type; and 
           [0016]      FIG. 7  is a flow chart illustrating an exemplary process of configuring a liquid metal reconfigurable antenna in accordance with one or more embodiments of the disclosed principles. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Before presenting a fuller discussion of the disclosed principles, an overview is given to aid the reader in understanding the later material. As noted above, antennae are used for many purposes and for many different portions of the electromagnetic spectrum, from microwaves to consumer band radio, both AM and FM, up to long wavelength radio. These uses cover wavelengths across about 8 orders of magnitude. However, even within a narrow band of use, such as FM radio, different antenna designs may be needed to fully accommodate the relevant portion of the spectrum. For example, cellular communications and WiFi communications use approximately adjacent portions of the spectrum but typically benefit from differently tuned antennae. 
         [0018]    Other contexts also often provide a benefit through tuned or customized antenna shapes. For example, monopoles, dipoles, Vivaldis, Patch antennae and Bow-tie antennae all rely on specific antenna shapes for their functions. The different antenna shapes alluded to above can certainly be produced today, but once made they are typically limited to their as-produced form. This means that in order for the underlying radio system to be used for another type or degree of use, an entirely new antenna or antenna array is needed. 
         [0019]    However, in an embodiment of the disclosed principles, an electronically reconfigurable antenna system allows the configuration or reconfiguration of an antenna in the field whenever needed and however often needed. Thus, for example, a linear antenna may be lengthened or shortened, cross members may be created, configured, or eliminated, and planar antenna structures can be changed in shape and extent, all while the antenna system remains deployed. 
         [0020]    Gallium forms a eutectic alloy with Indium to create a metal (EGaIn) with an essentially room temperature melting point. However, Gallium and its alloys have not typically been used in room temperature liquid metal electronic applications because Gallium forms an oxide skin almost instantaneously when exposed to oxygen. Thus, despite its high toxicity, Mercury has instead been long employed to meet most room temperature liquid metal requirements. 
         [0021]    However, the Gallium oxide layer has the benefit that it imparts structural stability to the alloy when it is formed into a given shape. Moreover, the oxide layer can be broken down via the application of an electric field, allowing the EGaIn to be reconfigured. In an embodiment of the disclosed principles, an electrode array is employed to address and steer the liquid EGaIn into different two-dimensional and limited three-dimensional configurations. 
         [0022]    With this overview in mind, and turning now to a more detailed discussion in conjunction with the attached figures,  FIG. 1  shows a simplified view of one “pixel”  100  of the described liquid metal antenna system. As can be seen, the liquid metal (e.g., a eutectic alloy of Gallium and Indium, EGaIn)  101  is initially located in a source reservoir  103  and in a channel  104  formed by an upper surface  105  and a lower surface  106  over a first electrode  107 . The remainder of the channel  104  is filled with an electrolyte  109 , (e.g., sodium hydroxide, NaOH). A second electrode  111  is located in the channel  104  beyond the first electrode  107 . The liquid metal reservoir  103  or a similar reservoir for the electrolyte may contain controlled ports to control the introduction or withdrawal of the associated liquid. 
         [0023]    Turning to  FIG. 2 , in order to reconfigure the liquid metal  205  away from its first configuration  206 , a voltage V- 113  (also referred to as a bias or potential difference) is applied by a voltage source  115  between the first electrode  107  and the second electrode  111 . The conductive path between the first and second electrodes  107 ,  111  includes a portion of the electrolyte  109 ,  209  and a portion of the liquid metal  101 ,  205 . The application of voltage  113  induces an electrical field across the oxide interface layer  108  at the point in the conduction path where the liquid metal  101  meets the electrolyte  109 . The electrical field breaks down the oxide layer and raises the surface tension, causing the liquid metal to flow toward the lower voltage, forming a second configuration  208 . While the breakdown of the oxide layer is a progressively variable phenomenon with variations in voltage  113 , it has been found that an applied voltage V- 113  of −0.5V causes observable deformation of the metal in the EGaIn/NaOH system described above, and that an applied voltage  113  of −1.5 V causes not only observable deformation but also significant movement of the metal. The applied potential  113  drops primarily across the oxide interface since the metal is highly conductive, although the NaOH is much less so. 
         [0024]    If the applied voltage  113  is negative, with the potential at the first electrode  107  being higher than the potential at the second electrode  111 , then the liquid metal will flow toward the second electrode  111 . Otherwise, the liquid metal will flow back toward the first electrode  107 . 
         [0025]    It will be appreciated that the extent to which the liquid metal flows is largely determined by the magnitude of the applied voltage. Within a scale of movement of 1 to 2 millimeters, a voltage of −1.5V is sufficient to cause movement of the metal without leading to excess current consumption. A voltage of −0.5 would still generally cause movement of the metal, but may be too low in some cases to reliably override other influences on the metal, e.g., gravity in static arrays and inertia in moving arrays. 
         [0026]    Higher or lower voltage levels than −1.5V may also be used depending upon electrode spacing (e.g., more than or conversely less than 1-2 mm), since it is the local electric field and not the overall voltage differential that impacts the EGaIn oxide layer. As noted above, NaOH is less conductive than EGaIn, so while the applied voltage drops primarily across the oxide interface, there will be some voltage drop in the NaOH over distance. Thus, while −1.5V between electrodes is sufficient for small movements such as 1-2 mm, higher voltages such as 5V may be beneficial for centimeter scale movements between two electrodes. 
         [0027]    Continuing with  FIG. 2 , the array  201  includes a plurality of electrodes  203  in a flat regular array. Each electrode  203  is individually addressable to induce movement in the liquid metal  205 , which is again drawn from a liquid metal reservoir  207 . Similarly, an electrolyte  209  such as NaOH is present in the array  201  and is drawn from and returns to an electrolyte reservoir  215 , which may be outside of or within the cavity  104 . 
         [0028]    In general, the liquid metal antenna is designed to affect a radiation pattern, radiation direction, electrical length, center frequency, one or more side lobes, a gain, a scan angle or polarization. The antenna formed in this manner may be driven during operation by one or more edge connectors  211 , e.g., at the periphery of the array  201 . The edge connectors  211  may be elongate with a slightly pointed tip as shown in order to pierce the oxide layer of the liquid metal and remain in good contact. In the event that a plurality of such edge connectors  211  are linked to the antenna, the driving device may determine which connector  211  exhibits the best matched impedance and lowest loss and may drive the antenna via that connector  211 . In an embodiment, the edge connectors  211  are attached to one layer of the channel, e.g., layer  105 , while the remaining contacts  203  are attached to the other layer, e.g., layer  106 . 
         [0029]    In addition, where multiple antenna structures rise from a common edge, a continuous strip of liquid metal along that edge may be used as an interconnection between the antenna structures. Moreover, one or more antenna structures may be driven from connectors on different edges, e.g., top and bottom, bottom and side, and so on. Also, although the antenna shape being constructed may be tuned for best response at a particular frequency or frequency range, it is also contemplated that the same system may be used to create a detuned structure, e.g., for shielding and so on. 
         [0030]    As can be seen, the array of electrodes allows the liquid metal to be drawn into any number of patterns. Moreover, although the liquid metal reservoir allows an electrical connection to be made to the configured shape, e.g., to drive it with an RF signal, the electrodes themselves may also be used, once shaping is complete, to supply a driving signal to an isolated element of the pattern. Thus, as shown in  FIG. 3 , a pattern  300  that includes isolated elements  301 ,  303  may be driven via the respective electrodes  305 ,  307 ,  309 ,  311  underlying the elements  301 ,  303 . 
         [0031]    Many antenna shapes and arrays can be formed using the disclosed principles. A simple monopole configuration has been shown, and the example array  400  shown in  FIG. 4  includes many repeated elements  401  and is an example of a three-dimensional dipole array, and may also be a phased array. In addition to the monopole and dipole configurations, other antenna shapes that are usable alone or in two or three-dimensional arrays include Vivaldis  600 , patches  602 , and bowties  604 , as shown in  FIG. 6 , as well as any other desired antenna shape. Although the illustration of  FIG. 4  shows a three-dimensional array made up of individual two-dimensional arrays, an array itself may also be three-dimensional, either by curving or bending in a shape, e.g., an aircraft exterior surface or the like, or by incorporating additional lines of electrodes that rise out of an otherwise planar array. An example of a curved antenna is antenna  606  of  FIG. 6 . The illustrated curved antenna  606  is a patch antenna conformed to a curved surface  608 , but it will be appreciated that any shape of antenna or antenna array may be created on a curved surface using the disclosed principles. 
         [0032]    In implementation, the electrode array, e.g., the array shown in  FIG. 3 , includes a top plane and a bottom plane ( 105  and  106  in  FIG. 1 ) which provide a flat interior space within which the liquid metal and electrolyte are able to move. The top and bottom planes themselves are preferably nonconductive so as not to interfere with the action of the configured antenna. 
         [0033]    It will be appreciated that the ability to configure a metallic layer also provides benefits outside of regular antenna operation. For example, a configurable metallic layer may be used to temporarily shield sensitive components from strong electromagnetic radiation. In an embodiment of the disclosed principles, such a shield uses the electromotive ability to steer liquid metal to form such a shield. 
         [0034]    An example of this concept is shown in  FIG. 5 . As can be seen, the liquid metal  501 , which may be EGaIn, resides in a liquid metal reservoir  503  beneath a shield cavity  505 . The shield cavity  505  contains an array of electrodes (not shown) usable to selectively draw the liquid metal  501  up into the shield cavity  505 . The shield cavity  505  is initially filled with an electrolyte  507  such as NaOH, which when displaced flows to an electrolyte reservoir  509 . In this way, selective actuation of the electrodes in the shield cavity  505  can be used to shield an RF-sensitive system  511  from an RF source  513 . The electrodes may be left free-floating with respect to voltage after the shaping step in order to allow full shielding of the RF-sensitive system  511 . It will be appreciated that the electromagnetic shield may instead be configured as an iris or aperture rather than as a curtain depending upon the details of a given installation environment. 
         [0035]    With respect to many embodiments it will be appreciated that the resultant current flow of an applied voltage may be measured, e.g., by voltage source  115  or otherwise, to determine the progress of the metal flow and to adaptively adjust the applied voltage (or the location at which voltage is applied) in response. In this context, it is the presence or absence of non-trivial current flow rather than its precise magnitude that reflects the configuration of the liquid metal circuit. For example, when the liquid metal is being driven between a first contact and a second contact via a voltage applied across those contacts, and has not yet touched the second contact, the resultant current will be limited to the minor current allowed through the NaOH. 
         [0036]    Once the liquid metal touches the second contact however, the circuit between the two contacts will be shorted, resulting in a current flow increase of an order of magnitude or more (while the voltage is held). In this way, the location of the leading edge of the metal can be determined and a third contact energized (and the second contact grounded or left floating) to extend the metal path in whatever direction is desired from that point onward. The current between the second and third contacts will then be used to determine when the leading edge of the liquid metal reaches the third contact and so on. 
         [0037]    Although the various embodiments described above have used the term “electrode” to describe elements providing a source of electrical potential or current, there is no intent to distinguish such an element from an anode, and the electrodes described herein may provide any desired magnitude and polarity of voltage. Moreover, there is no intent to limit the electrode shape to a rod or disc. In particular, it will be appreciated that an electrode for use within the described principles may also be formed in the shape of all or a portion of a desired antenna shape and that the electrode so formed may be of a screen or mesh construction if desired. 
         [0038]    While the gap between the top plane and bottom plane have not been specified, it will be appreciated that the metal meniscus and surface tension are beneficial forces in the actions described herein, which are partially capillary driven. As such, gaps of about 1.0 millimeter are contemplated, although other gap sizes are usable as well. 
         [0039]    Although NaOH has been used as the electrolyte in the examples herein, it will be appreciated that other electrolytes such as HCL (Hydrochloric acid) and H 2 SO 4  (Sulfuric acid) and others may be used instead as long as they allow sufficient conductivity without impeding the operation of the formed antenna. Moreover, although the examples herein use EGaIn as the liquid metal, it will be appreciated that other liquid metals may be used, e.g., pure Gallium, other alloys of Gallium, Mercury and Mercury alloys. Other liquid metals such as Francium, Rubidium and Cesium are generally less preferred due to other constraints such as cost, toxicity and so on. However, if these aspects are suitably accounted for then even these additional metals may also be used within the described principles. 
         [0040]    It will be appreciated that the described principles may be applied in many applications and in many ways. As such, there is no attempt made to describe every such manner of use. However, the flow chart  FIG. 7  does illustrate an example process  700  of configuring a liquid metal reconfigurable antenna in accordance with one or more embodiments of the disclosed principles. 
         [0041]    At stage  702  of the process  700 , a liquid metal  205  and an electrolyte  209  are placed between two surfaces  105 ,  106  such that the liquid metal  205  and the electrolyte  209  are in contact at an interface layer  108  which includes a surface oxide (e.g., an oxide of EGaIn in the example system). At stage  704 , a voltage  113  is applied between electrodes  107 ,  111  which are in contact with the liquid metal  205  and the electrolyte  209  respectively. 
         [0042]    At stage  706 , the applied voltage at least party breaks down the surface oxide and thus, via capillary action, causes movement of the liquid metal  205  against the electrolyte  209  toward the far electrode  111 . At this point, either of two mechanisms can halt the advance of the liquid metal  205 . First, if the application of voltage is stopped or reversed, the liquid metal  205  will no longer advance. Second, if the liquid metal is allowed to reach the far electrode  111 , the liquid metal  205  will stop its movement until a further electrode is energized. For the example process  700 , it is assumed that the liquid metal is to be stopped at some point midway between electrodes. 
         [0043]    Thus, at stage  708 , the application of voltage  113  is ceased, causing the surface oxide layer to re-form and stopping the movement of the liquid metal. This final state, e.g., as shown in the second configuration  213  of the liquid metal  205  in  FIG. 2 , matches a desired predetermined configuration. However, further manipulations of the liquid metal via the same steps but with different far electrodes will yield any desired configuration, such as any of the antenna configurations shown in  FIG. 6 . 
         [0044]    It will be appreciated that systems and techniques for reconfiguring electromagnetic antennae have been disclosed herein. However, in view of the many possible embodiments to which the principles of the present disclosure may be applied, it should be recognized that the embodiments described herein with respect to the drawing figures are meant to be illustrative only and should not be taken as limiting the scope of the claims. Therefore, the techniques as described herein contemplate all such embodiments as may come within the scope of the following claims and equivalents thereof.