Abstract:
One embodiment of a liquid-modulated antenna using an antenna of a type commonly used in the field of wireless identification which is placed within sufficient proximity of a source of liquid to allow the liquid to flow onto the antenna, thereby altering (modulating) the characteristics of the signal being transmitted from the antenna to a signal receiving unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the previous benefit of provisional patent application Ser. No. 61/687,787, filed 2012 Apr. 30 by the present inventor. The content of that application is incorporated herein by reference. 
     BACKGROUND 
     Prior Art 
     An antenna, as any other electronic component, is conventionally designed to be isolated from all sources of moisture to prevent any interference with its performance. From a different perspective however, applying liquids to antennas as part of the normal operation of the antennas can lead to the construction of novel and simple devices which will increase and, in the wider scope and implications of such a process, lead to new hybrid wireless-fluid technologies. It is such an application of liquids to antennas which underlies the embodiments described in this application. 
     The term “modulation,” which is conventionally used to refer to the encoding of one radio signal into a second signal to produce a third signal, is here used in the more general and prior sense of the term to mean the varying or altering of any one, or several, of the characteristics of a radio signal in order to convey information. In a liquid-modulated antenna, the liquid is the means of altering these characteristics. For the sake of clarity, and to avoid confusion of the process described with the more restricted identification of modulation with the combining of radio waves, signals will be described as “altered” rather than “modulated” throughout this application. 
     The electronic communication field of radio frequency identification (RFID) systems presents a commercial area in which several embodiments of the applicant&#39;s liquid-modulated antenna will be useful. RFID systems consist of RFID tag antennas, RFID readers set to match the signals of the antennas, and middleware connecting the two. Of special interest with respect to the embodiments is the type of RFID tag antenna known as the passive tag antenna which has no on-board power supply but draws the energy needed to generate a return signal from the energy transmitted to it by the RFID reader (hereafter called “the signal receiver”) with which it is matched. This type of tag antenna is the one most widely used in the field of RFID because of its simple design and low cost. The embodiments described in this application employ a passive tag antenna (hereafter called “the antenna”) in their construction. 
     To the knowledge of the applicant, no prior antenna has incorporated the application of a liquid as a component of its in-use operating mechanism, nor are there known any similar or related techniques of altering the signal of an antenna by intentionally applying a liquid to the antenna. 
     SUMMARY 
     An antenna, the characteristics of the transmitted signal of which are modulated by a source of liquid such that when the liquid is released onto the antenna, the signal being transmitted from the antenna to a device receiving the signal from the antenna will be altered and thereby inform the receiving device that a change of status has occurred with respect to an entity previously associated with the prior, un-modulated signal. The liquid-modulated antenna offers a simple, useful, and inexpensive method of augmenting current uses of antennas as these are applied to electronic information gathering in the fields of engineering, inventory control, delivery services, medicine, health and safety, and security. 
     The extensive range of commercial products potentially arising from this new feature of antenna design will be suggested by a consideration of the drawings and description which follow the introduction to liquid-modulated antennas given below. The introduction will proceed by way of a presentation of illustrative embodiments (a) through (g) as these can be applied to the field of RFID systems. The embodiments are introduced in order from the most simple to the most complex embodiments. 
     (a) The most simple type of embodiment of an RFID-based liquid-modulated antenna is constructed by placing the antenna where it can be contacted by liquid issuing from an intentionally constructed opening (e.g. the end of a tube, pipe, orifice), an unintended opening (leak), or as the result of an environmentally induced condition (e.g. condensation created by warming or the deposition of vapor). The antenna located below a dripping tube can function as a measuring device which indicates the rate of flow and quantity of the liquid deposited through the increasing alteration of the radio signal transmitted from the antenna to the signal receiver which occurs as the portion of the signal-transmitting area of the antenna uncovered by the liquid diminishes. The embodiment of (a) can also function in a simpler mode as a device having only the purpose of indicating that liquid is flowing. The embodiment of (a) used in combination with a hydraulic system can function as an alarm to indicate that a seal on the system has broken and that liquid is escaping. When combined with a liquid container, the embodiment of (a) can function as a level-indicator, the signal from the antenna undergoing increasing alteration as the rising level of liquid submerges an increasing portion of the transmitting area of the antenna. The embodiment of (a) when combined with a bag of frozen liquid, the antenna now being located below the bag, can indicate when the liquid of the bag is thawing: condensation forming on the outside of the thawing bag will drip onto the antenna, altering the signal returning to the signal receiver. 
     (b) In a more complex type of embodiment, the antenna is mounted on a substrate together with a piece of frozen liquid. This combination of the antenna and frozen liquid can function as a temperature alarm for an item to which it is attached, the frozen liquid thawing and then flowing onto the antenna when the temperature of the label rises above the freezing point of the liquid. Different freezing points for the apparatus can be set by employing liquids which have different freezing points. 
     (c) In a variant of the temperature sensor embodiment of (b), the piece of frozen liquid can be replaced with a liquid-filled cell, the membrane of which is designed to rupture at a specific air pressure, thereby allowing the embodiment of (c) to function as a pressure alarm as the liquid from the ruptured cell flows onto the antenna and alters the signal being sent to the signal receiver. The embodiment of (c) will be useful in monitoring the state of pressure-sensitive cargo being transported by airplane. 
     (d) In a variant of the pressure alarm embodiment of (c), the liquid-filled cell, antenna, and substrate are retained and to this combination of parts is added a cover of deformable material which covers the area of the substrate containing the cell and antenna. In the case of this embodiment of (d), the cell is ruptured manually (e.g. by being pressed between thumb and forefinger) or mechanically (e.g. by being passed between rollers), forcing the liquid contents of the cell onto the antenna. An apparatus so constructed can be affixed to an item for purposes of inventory tracking and control to indicate a change in the status of the item on the part of the person handling the item. If the handler observes, for example, a defect in the item, the handler can send an alarm to the signal receiver matched with the antenna of the apparatus by rupturing the cell, thereby spreading the liquid of the cell onto the antenna and altering the signal being sent to the signal receiver, creating the alarm when the signal being returned to the receiver fails to match that previously set on the receiver. As a result of the alarm, the item is withdrawn from the inventory stream. If the item affixed with the embodiment of (d) is a part or sub-assembly being delivered for installation on a larger assembly (e.g. computer, motor, jet engine), the person installing the part at the end of the delivery stream can rupture (hereafter called “activate”) the apparatus as a means of informing the signal receiver matched with the antenna that the part has now been delivered and installed. Insofar as the embodiment of (d) can function as a kill-switch for the purpose of inventory tracking and control, the same combination of parts (liquid-filled cell, antenna, substrate, and deformable cover) can also function in a free-standing mode as, in effect, a wireless (RF) ticket. The holder of such a wireless ticket uses it for access until a ticket-taker voids the ticket by activating the cell, forcing the liquid onto the antenna and altering the signal being sent to the signal receiver, thereby cancelling the ticket for further use. 
     (e) In a variant of the substrate-mounted embodiment of (d), the same combination of cell, antenna, and cover can be mounted on other substrates such as identity cards where such a combination can be mounted alongside other information media conventionally carried on such cards (e.g. photograph, optical barcode, magnetic strip) in order to add another level of security. A security guard activates the cell by pressing the card between thumb and forefinger or by sliding the card through mechanical rollers, thereby cancelling the card. In a different role from that of cancelling the card, the activation of the cell can be used to provide a higher level of on-demand identity authentication for the card user: the same liquid which flows onto the antenna to alter the signal of the antenna is at the same time creating a “blot signature,” a unique alteration of the antenna signal which necessarily results from the variable pattern and area of flow of the liquid over the antenna which occurs each time such a cell is activated. Such a random alteration of the signal creates what is, in effect, an on-demand password signature for the card holder for the time and place that the cell of the card is activated. This feature of the embodiment of (e) will be useful in restricted areas requiring high security levels. Beyond its application to identity cards, the embodiment of (e) can be applied to other documents such as passports. 
     (f) When the embodiment of (d) is mounted on a wristband, it can be worn as an alarm by medical patients and others who need to summon assistance. The wearer of the wristband can activate the cell, sending an altered signal to the signal receiver to indicate that assistance is needed. 
     (g) A related variant of the wristband embodiment of (f) is another type of liquid-modulated antenna patient alarm which is constructed by inserting the antenna into the end of a liquid-filled soft tube of sufficient length to rest comfortably in the mouth of the user between the teeth of the upper and lower jaws. The liquid, in this case a thick, viscous liquid or gel, fills the tube only as far as the edge of the inserted antenna. When the tube is inserted into the mouth with the antenna-end protruding, the apparatus is activated as an alarm by biting down on the tube, squeezing the liquid from the filled portion of the tube into the empty portion of the tube where the antenna has been inserted. When the previously uncovered area of the antenna lying within the tube becomes covered with the squeezed liquid, the signal being sent to the signal receiver is altered and indicates by the alteration that the user of the apparatus needs assistance. The embodiment of (g) will be useful to a person who cannot conveniently activate the patient alarm of embodiment (f) because of injuries to the hands. 
    
    
     
       DRAWINGS 
       Figures 
       In the drawings, closely related figures have the same number but different alphabetic suffixes. 
         FIG. 1A to 1B  show a signal receiver and tag antenna exchanging radio signals, then the return of a weaker signal to the receiver as liquid drips onto the antenna from the end of a tube. 
         FIG. 2  shows a similar antenna placed below a bag of thawing liquid from which condensate is dripping in accordance with another embodiment. 
         FIG. 3  shows a similar antenna placed below a hydraulically operated piston from which liquid is leaking in accordance with another embodiment. 
         FIG. 4  shows a similar antenna partially submerged in a container of liquid in accordance with another embodiment. 
         FIG. 5A to 5B  show pre-activation and post-activation views of a similar antenna mounted on a substrate together with a piece of frozen liquid in accordance with another embodiment. 
         FIG. 6A to 6B  show pre-activation and post-activation aspects of a similar antenna mounted on a substrate together with a pressure-sensitive liquid-containing cell in accordance with another embodiment. 
         FIG. 7A to 7C  show pre-activation, post-activation, and cross sectional views of a similar antenna which has been mounted on a substrate together with a liquid-containing cell and deformable cover in accordance with another embodiment. 
         FIG. 8A to 8B  show pre-activation and post-activation views of a similar antenna mounted on a substrate together with a liquid-containing cell and deformable cover in accordance with another embodiment. 
         FIG. 9  shows a similar antenna mounted together with a liquid-containing cell and deformable cover on a wristband in accordance with another embodiment. 
         FIG. 10A to 10B  shows pre-activation and post activation views of a similar antenna inserted into a partially liquid-filled tube in accordance with another embodiment. 
     
    
    
     REFERENCE NUMERALS 
     
       
         
               
               
               
               
             
           
               
                   
               
             
             
               
                 11 
                 antenna 
                 12 
                 signal receiver 
               
               
                 13 
                 tube 
                 14 
                 bag containing thawing liquid 
               
               
                 15 
                 hydraulic piston 
                 16 
                 liquid container 
               
               
                 17 
                 liquid 
                 18 
                 piece of frozen liquid 
               
               
                 19 
                 first rectangular substrate 
                 20 
                 air pressure sensitive liquid-filled 
               
               
                   
                   
                   
                 cell 
               
               
                 21 
                 liquid-filled cell 
                 22 
                 deformable cover 
               
               
                 23 
                 second rectangular substrate 
                 24 
                 wristband 
               
               
                 25 
                 mounting for cell/antenna/ 
                 26 
                 liquid-filled tube 
               
               
                   
                 cover unit 
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION 
     FIG.  1 A to  1 B 
     First Embodiment 
     An antenna  11 , in this case a disc-shaped, passive tag antenna (an antenna having no onboard source of power) is shown first exchanging an unaltered radio signal with its matched signal receiver  12 . The antenna is then shown placed flat, below the end of a tube  13  from which liquid is dripping onto the antenna, the accumulating liquid causing the antenna to return an altered signal to the signal receiver, signified in the figure by the broken line rendering of the signal returning to the signal receiver. 
     Operation— FIG. 1   
     The liquid-modulated antenna of the embodiment is operated by observing the alteration in the signal that the antenna transmits when a liquid deposited on the antenna, whether intentionally or unintentionally, alters the signal returning from the antenna to the signal receiver matched with the antenna. Response to the altered signal by the operator of the signal receiver will vary according to the specific application of the embodiment. In one case, the altered signal will activate an alarm; in another, it will indicate simply that liquid is flowing from the opening of the tube; in another, the regular and quantifiable alteration of the signal will indicate specific characteristics of the liquid flowing from the tube (e.g. quantity, viscosity) as it spreads over the surface of the antenna at a particular rate or in a particular manner. The antenna will need to be cleaned or replaced periodically if multiple uses are intended. 
     FIG.  2 - 4   
     Additional Embodiments 
     Additional “drip” embodiments are shown in  FIGS. 2 ,  3 , and  4 . In each embodiment the antenna is located where liquid can flow onto the surface of the antenna: from the surface of a bag  14 , as condensate ( FIG. 2 ); from a piston  15 , as hydraulic fluid ( FIG. 3 ), from the rising level of liquid  17  within a container  16  ( FIG. 4 ).  FIGS. 2 and 3  show embodiments functioning as alarms:  FIG. 2  for condensate dripping from the surface of a bag filled with a frozen item which is thawing;  FIG. 3  for hydraulic fluid leaking from a piston having a broken seal.  FIG. 4  shows an embodiment which functions as a meter, the altered signal returning from the antenna indicating that liquid rising within the container has reached a particular level. 
     The principle of the liquid-modulation of antennas which underlies the embodiment can be observed in an experiment conducted by the applicant using a pair of walkie-talkies: when the end of the exposed and straightened 10 centimeter-long copper wire antenna of the transmitting walkie-talkie was inserted by 1 centimeter increments into a line of gel, voltage readings taken at the amplifier of the receiving walkie-talkie decreased consistently by approximately 0.006 millivolts per centimeter of antenna inserted. 
     FIGS.  5 - 10   
     Alternative Embodiments 
     Several additional variants of the basic embodiment just described can be constructed using the same antenna  11  in different mountings as shown in  FIGS. 5 to 10 .  FIGS. 5 and 6  show the antenna mounted on a first rectangular substrate  19  for environmental sensor applications. In  FIG. 5  the antenna  11  is mounted on the first rectangular substrate together with a round piece of frozen liquid  18 . If the temperature rises above the freezing point of the frozen liquid, the piece will melt and flow over the antenna ( FIG. 5B ), sending an alarm to the signal receiver  12 . In  FIG. 6 , the antenna  11  is mounted on first rectangular substrate  19  together with a liquid-filled cell  20  the membrane of which will rupture at a known level of air pressure, causing the liquid to flow over the antenna ( FIG. 6B ), sending an alarm to the signal receiver  12 . 
     In  FIG. 7 , the antenna  11  is mounted on the first rectangular substrate  19  together with a liquid-filled cell  21 , both the antenna and cell being covered with a deformable plastic cover  22 . This embodiment can be attached to items moving through an inventory system to note changes in the status of an item to which it is attached (e.g. the need to withdraw the item from the inventory stream should the handler of the item observe a defect in the item). The same embodiment and substrate can also be used in a free-standing mode un-affixed to an item to function as a wireless electronic admission ticket: the user retains such a ticket for access until a ticket-taker cancels the ticket by squeezing and rupturing the cell so that the liquid flows over the antenna and alters the signal being sent to the signal receiver. 
     In  FIG. 8 , the same combination of antenna, liquid-filled cell, and deformable cover of  FIG. 7  is mounted on a second rectangular substrate  23  similar in size and shape to an identity card or credit card to show the manner in which a liquid-modulated antenna can augment information media of the type conventionally found on such cards (e.g. photograph, optical barcode, magnetic strip). The apparatus consisting of parts  11 ,  21 , and  22  when mounted on the card can be activated to cancel the card, or, in a different role, to provide a unique identifying signal for the card user: the inherently random nature of the spreading of the liquid onto the antenna after the rupturing of the cell will result in the covering of a variable area of the antenna with the liquid and thereby cause the antenna to return a unique signal to the signal receiver  12 . This unique identifying signal can be termed a “blot signature.” These identity and security-based embodiments can also be applied to other substrates such as documents and passports. 
       FIGS. 9 to 10  show two embodiments that can function as patient alarms. In  FIG. 9 , the same combination of antenna, liquid-filled cell, and deformable cover of  FIG. 7  is shown mounted on a wristband  24 . The patient wearing the wristband-mounted embodiment summons assistance by manually activating the cell, the liquid of which flows onto the antenna  11  and alters the signal being sent to the signal receiver  12 , thereby triggering an alarm. The embodiment shown in  FIG. 10 , antenna  11  inserted into the unfilled portion of a partially filled liquid tube  26 , can function as an orally activated alarm for patients who cannot use their hands. After an attendant has placed the tube-end of the apparatus into the mouth of a patient, the patient can summon assistance by biting down on the tube: liquid from the filled portion of the tube is squeezed into the unfilled portion of the tube into which the antenna has been previously inserted and finally covers a portion of the antenna sufficient to alter the signal being sent from the antenna to the signal receiver. This embodiment will be useful to attendants who must leave a manually disabled patient temporarily unattended. 
     CONCLUSION, RAMIFICATIONS, AND SCOPE 
     Accordingly, the reader will see that the liquid-modulated antenna of the various embodiments can be used to create new and useful products by augmenting the current designs of antennas with a different design of antenna which does not isolate the antenna from liquids but deliberately uses liquids as active components in the construction and operation of the antenna. 
     Although the description of the embodiments in this application contains many specific details, these details should not be construed as limiting the scope of the embodiments but rather as providing illustrations of a group of several embodiments. For example, other antennas incorporating liquid-modulation in their construction may use antennas which differ in design from the example of the disc-shaped passive tag antenna used to illustrate the embodiments in this application. Thus the scope of the embodiments should be determined by the appended claims and their legal equivalents rather than by the examples given.