Abstract:
Systems and methods for optimizing performance of personal area network (PAN) systems that use electric fields as communication media between PAN transmitters carried by people and PAN receivers mounted on computers to which selective access is sought to be established. Multiple PAN receiver antennae are mounted on a keyboard, such that if a person with a PAN transmitter rests her arms on or near the keyboard, sufficient signal from the transmitter is sensed by one or more of the receiver antennae even though some of the signal is shunted away from the receivers through the arms. Also, a driven shield insulates a PAN receiver from nearby metal objects, e.g., a desk on which the PAN receiver is supported. Moreover, a multiple-electrode PAN transmitter reduces the deleterious effects on the signal from the PAN transmitter that can otherwise be caused by, e.g., loose metal coins that are present in a pocket in which the transmitter is carried. Further, differential receive electrodes prevents undesirable coupling of a PAN transmitted signal to a computer&#39;s receiver through a person who has positioned herself between the receiver and the person carrying the PAN transmitter to, for example, gain unauthorized access to the computer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to computer communications, and more particularly to methods and systems for providing effective short-range communication using electric fields. 
     2. Description of the Related Art 
     The concept of using a personal area network (PAN) as a medium for short range communication using a person&#39;s interaction with an electric field is discussed in U.S. Pat. No. 5,796,827, entitled System and Method for Near-Field Human-Body Coupling for Encrypted Communication with Identification Cards, owned by the same assignee as is the present invention and incorporated herein by reference. As disclosed in the above-mentioned patent, using the principles of PAN a small, lightweight transmitter is incorporated in a personal security card that is about the size of a credit card and that can be worn or otherwise carried by a person. The PAN transmitter automatically communicates information (for example, the person&#39;s identity, personal identification number (PIN), social security number, security clearance, and so on) to a PAN receiver via an electric field with which the person interacts. According to PAN principles, the receiver is associated with a computer that is positioned nearby the location of the person, such that the PAN transmitter communicates with the computer. 
     Owing to the principles underlying PAN communications, the PAN receivers are low power, low latency, low cost receivers that can be easily disposed on, e.g., a computer, computer mouse, keyboard, or security reader in a room. The receivers sense signals that are sent by the transmitter and that are coupled through the person&#39;s body. As mentioned above, these signals carry information, such as authenticating information indicating that the bearer of the transmitter is authorized to use a particular computer or enter a particular area, or that the bearer of the transmitter was present in a particular room at a particular time. 
     With the above in mind, it will be appreciated that many potential applications for PAN communication exist. Among the myriad applications of PAN communication systems is ensuring that only a person carrying a valid PAN transmitter can log on to a particular computer or computer system. Further applications include authenticating a person who desires to enter a restricted access area, or otherwise monitor the movement of people in a building, so that their whereabouts are known. Still further, PAN communication can be used to grant selective access to automatic teller machines (ATMs). All of the above applications, owing to the nature of PAN communication, require a person to do nothing other than bear a valid PAN transmitter. Thus, PAN communication systems are efficient and convenient solutions for a wide range of personal authentication nuisances. 
     As recognized by the present invention, while PAN systems are proven, highly effective communication systems, it happens that in certain applications PAN system performance can be further optimized. For example, when a person carrying a valid PAN transmitter wishes to access a computer having a PAN receiver mounted in the keyboard of the computer, the transmitted signal can be undesirably significantly attenuated when the user places his hands or arms on the keyboard. Still further, the present invention recognizes that undesirable coupling and shunting can occur between PAN receivers and a metal surface on which the receivers are supported. Moreover, the present invention recognizes that the signal strength from a PAN transmitter can be undesirably affected when the transmitter is carried in, for example, a person&#39;s pocket along with other metal objects such as metal coins. And, the present invention recognizes that unauthorized third persons might position themselves between a person carrying a valid PAN transmitter and a receiver to undesirably gain access to a computer or room that is associated with the PAN receiver. For example, the present invention recognizes that a signal from a PAN transmitter might be coupled to a PAN receiver of an ATM machine or a computer-controlled subway turnstile through a person who has interposed herself between a valid PAN transmitter and the receiver, thereby affording the person unauthorized access to the ATM machine or turnstile. 
     Fortunately, the present invention recognizes that it is possible to overcome the above-noted problems efficiently and effectively. 
     SUMMARY OF THE INVENTION 
     A personal area network (PAN) communication system includes a portable PAN transmitter, a computer, and more than one PAN receiver antenna associated with the computer such that communication can be established between the PAN transmitter and the computer. In accordance with PAN principles, communication between the transmitter and computer is established using an electric field. 
     In a preferred embodiment, a data input device such as a keyboard communicates with the computer, and the receiver antennae are mounted on the data input device. The system includes at least three, and preferably four, receiver antennae. At least one of the receiver antennae extends substantially from the left side to the right side of the keyboard. 
     As disclosed in detail below, the receiver antennae are associated with a receiver and the receiver is associated with a signal. With this in mind, the preferred system further includes logic means for selecting one or a combination of multiple antennas to produce a maximum received signal. In this way, an optimum combination of the receiver antennae is established by decoupling those antennae that might be shielded from, or otherwise attenuated from, the transmitter by, e.g., the person&#39;s arms. 
     In another aspect, a PAN communication system is disclosed that communicates information via an electric field from a PAN transmitter to a PAN receiver. The PAN receiver includes at least one receive electrode disposed above a driven shield. Furthermore, an insulator layer is sandwiched between the receive electrode and the driven shield. A buffer, such as a unity gain amplifier, is electrically connected to the driven shield and to the receiver. The driven shield, substantially electrically isolates the receive electrode from any or other grounding source in the vicinity of the receive electrode, increasing the impedance and lowering the capacitance of the receive electrode. 
     In still another aspect, in a PAN communication system, a PAN transmitter is disclosed. The transmitter includes plural transmitter electrodes. In a particularly preferred embodiment, the transmitter includes first and second driven electrodes, with each driven electrode being energized by a respective buffer circuit and with each buffer circuit being electrically connected to a signal source. 
     In yet another aspect, a PAN communication system includes at least one PAN receiver including differential receive electrodes and at least one portable PAN transmitter. Per present principles, the receive electrodes are positioned to measure the electrical potential difference across a person, whereby a person carrying a PAN transmitter will produce a substantial measured potential across the receive electrodes, while a person who does not have a PAN card on their person will produce substantially no electric potential across the receive electrodes. This prevents communication from the PAN transmitter to the receiver via a person without a PAN card. 
     Preferably, when a receive electrode is placed near the ground or other electrical body which may shunt, conduct, or otherwise reduce the received signal, a guard electrode is juxtaposed with and insulated from the receive electrode. Additionally, a guard driving follower amplifier is electrically connected from the receive electrode to the guarded electrode, to electrically isolate the receive electrode from the ground or electrical body. 
     In another aspect, a communication system for communicating data between a portable transmitter and a computer system nearby the transmitter using an electric field affected by a person bearing the transmitter includes a receiver that in turn includes plural receiver antennae. The receiver antennae are associated with the computer system such that at least some electric field lines from the person are not shunted away from at least one of the receiver antennae when the person moves an arm toward the computer system. 
     In yet another aspect, a communication system includes a receive electrode disposed above a metal surface and a driven shield disposed between the receive electrode and the metal surface to shield the receive electrode from the metal surface. 
     In still another aspect, the communication system includes an electrostatic transmitter including multiple driven electrodes, electrically isolated from at least one reference electrode. 
     In another aspect, a communication system includes a computer, an electrostatic receiver associated with the computer, and at least one receive electrode electrically connected to the receiver. A portable electrostatic transmitter is bearable by a first person for communicating with the computer via the receiver. Per the present invention, means are provided for preventing communication between the transmitter and receiver when a second person not bearing an electrostatic transmitter is interposed between the transmitter and the receiver. In one embodiment, the means for preventing includes a detector for detecting a predetermined characteristic in the signal when a first person bearing the transmitter moves a limb toward the receive electrode. In a particularly preferred embodiment, the predetermined characteristic is at least one of: an amplitude minimum, and a change of phase. 
     The invention can also include a general purpose computer programmed according to the inventive steps herein to dynamically determine an optimum combination of PAN receive electrodes that are associated with a PAN receiver system. The invention can also be embodied as an article of manufacture—a machine component—that is used by a digital processing apparatus and which tangibly embodies a program of instructions that are executable by the digital processing apparatus to undertake the present invention. This invention is realized in a critical machine component that causes a digital processing apparatus to perform the inventive method steps herein. 
     The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic top plan view of a computer keyboard incorporating multiple PAN receiver antennae, with a user&#39;s arms shown in phantom to illustrate the shunting of the signal from the transmitter through the user&#39;s arms, and with the keys omitted for clarity; 
     FIG. 2 is a schematic diagram of the electrical circuitry of the system shown in FIG. 1; 
     FIG. 3 is a schematic view of a computer program storage product; 
     FIG. 4 is a flow chart showing the logic steps used by the present invention to establish an optimum antenna combination for the system shown in FIG. 1; 
     FIG. 5 is a schematic diagram of a system for shielding a PAN receive electrode in, e.g., a computer keyboard, from a metal surface that keyboard might be supported on; 
     FIG. 6 is a schematic view of a multi-electrode PAN transmitter disposed in a pocket of a person adjacent loose change or other metal objects; 
     FIG. 7 is a schematic diagram of the electrical circuitry of the system shown in FIG. 6; 
     FIG. 8 is a schematic view of a PAN receiver system including a differential PAN receiver with a guard electrode functioning to prevent an unauthorized person from accessing a computer having a PAN receiver by positioning himself between the PAN receiver and a person with a valid PAN transmitter; 
     FIG. 9 is a schematic view of a PAN receiver system functioning to permit a person with a valid PAN transmitter to access a computer having a PAN receiver; 
     FIGS. 10A-10C are schematic views of three positions of a person with a valid PAN transmitter moving their hand towards a PAN receiver; and 
     FIG. 11 is a graph showing the behavior of a PAN signal sensed by a PAN receiver as a person having a valid PAN transmitter lifts his arm toward the receiver, showing in dashed line the signal amplitude as a function of distance of the hand from the receiver, and showing in solid line the signal phase as a function of distance of the hand from the receiver. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to FIG. 1, a communication system is shown, generally designated  10 , which includes a portable, lightweight, personal area network (PAN) transmitter  12  that can be borne by a person  14  for communication of data via an electric field, represented by lines  16 A and  16 B, to one or more PAN receiver antennae  18 A,  18 B,  18 C,  18 D that are associated with a computer  20 . Antennae are also referred to herein as “electrodes”. In the particular embodiment shown, four receiver antennae  18  are mounted on an input device, and more particularly on a keyboard  22 , that is electrically connected to the computer  20 . It is to be understood that the receiver antennae  18  can be otherwise associated with the computer  20 . For example, the receiver antennae  18  can be mounted on the computer  20  itself, or on a peripheral component thereof such as other input devices including mice, trackballs, keypads, joysticks, and voice activated input devices. 
     It is to be further understood that the computers of the present invention can be general purpose computers appropriate for their intended functions and programmed to undertake appropriate method steps set forth herein. For example, the computer  20  can be a desktop computer such as a personal computer or laptop computer made by International Business Machines Corporation (IBM) of Armonk, N.Y. Alternatively, the computers of the present invention may be any computer, including computers sold under trademarks such as AS400, with accompanying IBM Network Stations or, Unix computers, or OS/2 servers, or Windows NT servers, or IBM RS/6000 250 workstations, or other equivalent devices. 
     The above-referenced U.S. patent sets forth details about PAN communication systems; accordingly, for clarity and brevity of disclosure these details will not be repeated herein. By way of brief explanation, however, the PAN transmitter  12  can communicate data via the electrostatic field  16  to the PAN receiver antennae  18 , and thence to the computer  20 . This data might include, for example, the person&#39;s identity, personal identification number (PIN), computer user identification number, password, social security number, security clearance, access authentication data, and so on. The PAN transmitter may encrypt data to provide enhanced security, as described in U.S. Pat. No. 5,796,827. Thus, using PAN principles the person  14  need only wear or otherwise carry the PAN transmitter  12  and, when the person  14  is within a few meters of the computer  20 , the PAN transmitter  12  automatically communicates the person&#39;s authentication data to the computer  20  to allow the person  14  to log on to the computer  20  without undue delay and without sacrificing security. 
     As recognized by the present invention, however, it is possible that as the person  14  extends the arms toward the keyboard  22 , the person&#39;s body interacts with the electric field in such a way that some field lines  16 B can undesirably be shunted away from the receiver antennae  18 . Accordingly, the present invention provides plural receiver antennae  18  as shown, and more particularly the invention includes, from left to right looking down on the keyboard  22 , left, center, and right generally co-linear antennae  18 A,  18 B,  18 C, and a fourth elongated antenna  18 D that extends substantially across the front of keyboard  22 , from a left side  24  of the keyboard  22  to a right side  26  along a bottom edge  28  thereof. With this structure, at least some field lines  16 A are not shunted away from all receiver antennae  18 , but instead reach one or more of the receiver antennae  18  as shown. 
     FIG. 2 shows further components of the communication system  10 . As shown in FIG. 2, the antennae  18  are electrically connected to a multiplexer  30 , and the multiplexer  30  in turn is electrically connected to a PAN receiver, generally designated  32 . The PAN receiver  32  includes appropriate PAN receiver components including an amplifier  34  to which the multiplexer  30  is connected, with the amplified output of the amplifier  34  being sent to a detector  36 . Digitized signals from the detector  36  are then sent to the computer  20 . The computer  20  executes the logic shown in FIG. 4, and based on the results thereof selectively couples and decouples the antennae  18 A-D from the receiver  32  by sending appropriate select and deselect signals to the multiplexer  30  via respective select lines A-D. 
     More specifically, as intended by the present invention, to optimize communication signal strength between the transmitter  12  and the receiver that is associated with the receiver antennae  18 , receiver antennae  18  that are shielded from field lines  16 B by, e.g., the person&#39;s arms, are electrically decoupled from the receiver. In accordance with the present invention, to this end a PAN module  38  is incorporated into the computer  20  to undertake inventive method steps set forth below in reference to FIG.  4 . It is to be understood that the control components such as the PAN module  38  are executed by logic components such as are embodied in logic circuits on, e.g., an application specific chip (ASIC) or in software contained in an appropriate electronic data storage, e.g., read only memory (ROM), random access memory (RAM), or hard disk drive and/or optical disk drive, or DASD array, magnetic tape, electronic read-only memory, or other appropriate data storage device that is conventionally coupled to the computer  20  for executing the module  38 . For example, the control components can be embodied in a computer diskette  40  shown in FIG.  3 . The diskette  40  shown in FIG. 3 has a computer usable medium  42  on which are stored computer readable code means (i.e., program code elements). 
     The flow charts herein illustrate the structure of the present logic. Those skilled in the art will appreciate that the flow charts illustrate the structures of logic elements, such as computer program code elements or electronic logic circuits, that function according to this invention. Manifestly, the invention is practiced in its essential embodiment by a machine component that renders the logic elements in a form that instructs a digital processing apparatus (that is, a computer) to perform a sequence of function steps corresponding to those shown. In other words, the PAN module  38  may be a computer program that is executed by a processor within the associated server computer  20  as a series of computer-executable instructions. In an illustrative embodiment of the invention, the computer-executable instructions may be lines of compiled C ++  compatible code, or assembly code running in a microcontroller. 
     FIG. 4 shows the logic for establishing an optimum combination of receiver antennae  18 . Commencing at block  44 , all receiver antennae  18  are initially selected, i.e., are initially coupled to the receiver  32 . At block  46 , a first one of the antennae  18 , e.g., the left antenna  1   8 A, is decoupled from the receiver  32  by sending the appropriate signal to the multiplexer  30  via the select line A. It is to be understood that if desired, the logic loop beginning at block  46  can be commenced only after the signal strength received by the receiver  32  decreases below a predetermined threshold. 
     Moving to decision diamond  48 , it is determined whether the strength of a signal, e.g., the signal sensed by the receiver  32  or the signal output by the receiver  32 , has increased as a result of the decoupling at block  46 . Stated more broadly, at decision diamond  48  it is determined whether a signal increases or decreases as a result of the decoupling of the antenna  18  at block  46 . If the signal does not exhibit the predetermined change (increase), the antenna decoupled at block  46  is recoupled to the receiver  32  at block  50  by sending an appropriate select signal to the multiplexer  30  along the select line A. The process then moves to block  52  to test the next antenna, e.g., the center antenna  18 B, by looping back to block  46  and proceeding in accordance with the principles discussed above. 
     If, however, decoupling a receiver antenna  18  does result in an improved signal strength, the antenna is left decoupled, and the process moves from decision diamond  48  to block  52 . Thus, it will be appreciated that the receiver antennae  18  are serially decoupled and tested, with the testing being perpetually repeated, if desired, as long as the person  14  operates the keyboard  22  to decouple and recouple antennae  18  as appropriate to optimize signal strength as the person  14  moves to interrupt the field lines  16 . 
     FIG. 5 shows a receiver system for a PAN communication system, generally designated  54 , that includes at least one PAN receive electrode  56  and a driven shield  60  separated from each other by an insulator  62 . The electrical potential of the driven shield  60  is maintained substantially equal to the receive electrode  56  by a unity gain amp  64 , minimizing the capacitive coupling of the receive electrode  56  to the environment, represented by a metal support  58  having a support surface  61 . For example, the electrode  56  can be one or more of the antennae  18  shown in FIG. 1, and the metal support  58  can be a metal desk on which the keyboard  22  is disposed, that might otherwise decrease the signal detected by the system  54  by shunting electric field away from the receive electrode  56  and into the metal support  58 . To minimize the power output required of the unity gain amp  64 , the driven shield  60  is insulated from the support  58  by insulation  65 . The output of the receiver electrode  56  is sent to receiver circuitry  66 . 
     Moreover, the present invention recognizes that the driven shield  60  increases the antenna impedance and lowers the antenna capacitance of the system  54 . 
     FIGS. 6 and 7 show a PAN system, generally designated  68 , that includes a PAN transmitter  70 . In turn, the PAN transmitter  70  includes plural plate-like transmitter electrodes  72 A,  72 B,  72 C. More specifically, the PAN transmitter  70  includes at least first and second driven electrodes  72 A,  72 B, with the driven electrodes  72 A,  72 B being juxtaposed with a reference electrode  72 C. As can be appreciated in reference to FIG. 7, the driven electrodes  72 A,  72 B are coplanar with each other and both are separated from the reference electrode  72 C by an insulator  73  that is sandwiched between the reference electrode  72 C and the driven electrodes  72 A,  72 B. In the geometry shown, the driven electrodes  72 A,  72 B are contiguous to each other along a common edge  74 , it being understood that the electrodes  72 A,  72 B nonetheless are electrically insulated from each other by a narrow gap, with the driven electrodes  72 A,  72 B together being closely spaced from and parallel to the reference electrode  72 C. 
     To render the electrodes  72 A,  72 B independently driven, respective first and second buffer circuits  76 ,  78  are electrically connected to the electrodes  72 A,  72 B. In one preferred embodiment, the buffer circuits  76 ,  78  include unity gain amplifiers. Also, signal generator  80  such as an oscillator is electrically connected to each buffer circuit  76 ,  78 . 
     It may now be appreciated that the PAN transmitter  70  can be carried in, e.g., a person&#39;s pocket  82  (FIG. 6) that contains metal objects such as loose coins  84  that could undesirably shunt transmitted energy. Because two or more independently driven electrodes  72 A,  72 B are incorporated in the present invention, however, an electrode, such as the electrode  72 B, from which energy is shunted by the coins  84  substantially does not affect the performance of the other electrode  72 A. 
     Now referring to FIGS. 8 and 9, the present PAN communication system, generally designated  94 , is shown for preventing an unauthorized person  86  from gaining access to a PAN system computer (e.g., an ATM machine) by standing between a PAN receiver  88  and an authorized person  90  bearing a PAN transmitter  92 . As shown, the communication system  94  includes at least one pair of PAN receive electrodes  96  and  100 , configured as a differential receiver. 
     Additionally, when a receive electrode is placed near an electrical ground, as with receive electrode  100 , the system  94  includes a guarded electrode  102  that is positioned underneath receive electrode  100  to isolate the receive electrode  100  from the environment/ground  105 . For example, the receive electrode  100  and guarded electrode  102  can be embedded in a rubber mat on which a person can stand and thereby indirectly coupled to the receive electrode  100 . Accordingly, the guarded electrode  102  preferably is insulated from ground  105  by insulation “I”. 
     In accordance with the present invention, the receive electrodes  100  and  96  detect the potential difference across the person  86  standing near the receive electrodes  100  and  96 . A unity gain follower  104  maintains the electrical potential of the guarded electrode  102  substantially equal to that of the receive electrode  100 , isolating the receive electrode  100  from the ground  105 . Also a differential amplifier  98  receives signals from the receive electrode  96  and the unity gain follower  104  as shown, amplifies the detected difference therebetween, and applies the differential signal to the receiver  88 . 
     With this structure, when the unauthorized person  86  stands between the receive electrodes  96  and  100 , the receive electrode  100  has substantially the same electric potential as the receive electrode  96 , such that communication from the PAN transmitter  92  to the receiver  88  via the unauthorized person  86  is substantially prevented. On the other hand, when an authorized person  90  bearing a PAN transmitter  92  (FIG. 9) stands between receive electrodes  96  and  100 , receive electrode  100  has a substantially different electric potential than the receive electrode  96 . When this occurs, communication from the PAN transmitter  92  to the receiver  88  is permitted. A third person  107  who bears a PAN transmitter  109  but who is not standing between or otherwise interacting with receive electrodes  96  and  100 , however, does not communicate with the receiver  88 . This is because the electric field lines  108  from the transmitter  109  are shunted to ground, and consequently the third person  107  does not create a potential difference between the receive electrode  96  and the guarded electrode  100 . 
     FIGS. 10A-10C show an alternate method for preventing an unauthorized person from gaining access to a PAN computer by interposing himself between a PAN transmitter and a PAN receiver antennae  18  that is associated with the computer. Three successive positions are shown of an authorized person  90  bearing a PAN transmitter  92  reaching toward a PAN receiver antennae  18  mounted on, e.g., an ATM machine. FIG. 11 shows a plot of signal amplitude and phase detected at receiver antennae  18  as a function of distance between the person&#39;s hand  1   18  and receive antennae  18 , as shown in FIG.  10 . The letters A, B, and C on the graph in FIG. 11, correspond to FIGS. 10A,  10 B, and  10 C. 
     Specifically, as recognized by the present invention, by placing the PAN transmitter  92  on the front part of the person  90 , for example in a shirt pocket or around the neck, as with an identification badge, a direct signal path  110  is provided between the PAN transmitter  92  and receiver antennae  18  when the person  90  is in the position shown in FIG.  10 A. The body of the person  90  provides the return path for the electric signal, illustrated by electric field lines  111 , to the earth  120 . The resulting relatively strong amplitude and positive phase is shown at location A in FIG.  11 . As the person  90  moves their arm  112  towards the receiver antennae  18  to induce field lines  114 , as shown in FIG. 10B, the amplitude of the receiver signal dips toward a minimum, as indicated in dashed lines and the phase of the signal changes, as indicated in solid lines in FIG. 11, at location B. 
     As shown in FIG. 10C, when the hand  118  touches the PAN receiver antennae  18 , a low impedance connection is made between the PAN transmitter  92  and the PAN receiver antennae  18 . The PAN transmitter  92  communicates indirectly to the receiver antennae  18 . The earth  120  provides the return signal path via the electric field  116 . This indirection gives rise to the phase change, indicated on location C on the graph in FIG.  11 . The signal strength is shown to be relatively smaller than location A since the electric field  116  must make its way around the arm  112 . 
     An analog detector, such as an electrical circuit like the receiver  88  shown in FIGS. 8 and 9, or a digital detector, such as the computer  20  shown in FIG. 1, can detect the predetermined characteristic of phase and amplitude and thereby validate that the person reaching toward the receive electrode bears a PAN transmitter. If no such characteristic is determined, however, the detector can output a signal indicating that an unauthorized person has interposed herself between the transmitter and receiver. 
     While the particular SYSTEM AND METHOD FOR OPTIMIZING PERSONAL AREA NETWORK (PAN) ELECTROSTATIC COMMUNICATION as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and is thus representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular means “at least one” unless otherwise recited.