Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/181,753, entitled “Wireless Systems Having Multiple Electronic Devices and Employing Simplified Fabrication And Matching And Associated Methods,” which was filed on Jul. 29, 2008 and which claims the benefit of U.S. Provisional Application No. 60/953,509, entitled “RFID Chip and Antenna Concepts,” which was filed on Aug. 2, 2007, the disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates wireless systems that employ multiple wireless electronic devices or components, and in particular to techniques for simplifying fabrication and matching in cases where multiple electronic devices are to be connected to one or more antennas in a wireless system. 
     BACKGROUND OF THE INVENTION 
     It is well known that wireless devices, such as radio frequency identification (RFID) tags or similar transponder devices, can be powered remotely by radio frequency (RF) energy. In particular, such devices may be powered by receiving RF energy that is either directed toward them (a directed source) or is ambient and converting the received RF energy into a direct current (DC) voltage. The DC voltage may then be used to power on-board electronics, such as a microprocessor, sensing circuitry, and/or an RF transmitter, or to charge a power storage device such as a rechargeable battery or a supercapacitor. Such devices are employed in a number of fields, such as RFID systems, security monitoring and remote sensing, among others. Furthermore, for many reasons, multiple wireless devices as described above often need to be connected to a single antenna. For example, this may be desirable to enable flexibility with a common form factor. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a wireless system is provided that includes a base station at a first location which transmits far field RF energy, and a local subsystem at a second location separate from the first location. The local subsystem includes a parent antenna and a plurality of near field devices. The parent antenna receives the far field RF energy and generates a near field in response thereto. In addition, each of the near field devices includes an IC chip operatively coupled to a near field conductor, such as a looped conductor, wherein the IC chip of each of the near field devices is wirelessly coupled to the near field through the near field conductor thereof. Also, the IC chip and the near field conductor of each of the near field devices is not directly physically connected to the parent antenna. In operation, the received far field RF energy induces a current in the parent antenna, and the parent antenna generates the near field in response to the current. The IC chip of each of the near field devices receives AC energy from the near field through the near field conductor of the near field device and, in one particular embodiment, converts the AC energy into a DC voltage. The near field devices may be selectively positioned relative to the parent antenna such that a total amount of DC energy generated by the near field devices is at a maximum. The IC chip of each of the near field devices is wirelessly coupled to the near field through inductive and/or capacitive coupling between the parent antenna and the near field conductor thereof. The IC chip of each of the near field devices may receive power and communications from the base station through the wireless coupling to the near field. 
     In one particular embodiment, the local subsystem includes a substrate and the near field devices are provided on and distributed along the substrate. The parent antenna may be provided on a first surface of the substrate, and the near field devices may provided on and distributed along the first surface. Alternatively, the parent antenna may be provided on a first surface of the substrate and the near field devices may provided on and distributed along both the first surface of the substrate and a second surface of the substrate opposite the first surface. As a further alternative, the local subsystem may include a substrate, and the near field devices mat be stacked on top of one another and provided on a first surface of the substrate. The parent antenna in this embodiment may be provided on the first surface of the substrate. In yet another embodiment, the local subsystem includes a substrate, a first one or more of the near field devices are stacked on top of one another and provided on a first surface of the substrate, a second one or more of the near field devices are stacked on top of one another and provided on a second surface of the substrate, and the parent antenna is provided on the first surface of the substrate opposite the first surface. In still another embodiment, the local subsystem includes a substrate, a first one or more of the near field devices are stacked on top of one another and provided on a first surface of the substrate, and a second one or more of the near field devices are provided on and distributed along a second surface of the substrate opposite the first surface. 
     In yet another particular embodiment, the IC chip of each near field device is neither directly above nor directly below the IC chip of another one of the near field devices. In an alternative embodiment, the near field devices include a first near field device and a second near field device stacked on top of the first near field device, wherein the second near field device is able to fit entirely within a boundary defined by the near field conductor and the IC chip of the first near field device. Alternatively, the near field devices may each be shifted linearly with respect to one another such that the IC chip of each near field device is positioned adjacent to the IC chip of one another one of the near field devices. 
     A wireless transmission method is also provided that includes steps of transmitting far field RF energy from a first location, receiving the far field RF energy at a second location separate from the first location and generating a near field in response thereto, wirelessly coupling to the near field, and receiving AC energy from the near field in response to the wirelessly coupling. 
     In a further embodiment, a transponder apparatus is provided that includes a main antenna element having a plurality of conductor elements, with each of the conductor elements being direct connection coupled to one another, and a plurality of devices, wherein each of the devices includes an IC chip operatively coupled to a conductor, such as a looped conductor, wherein each of the devices is positioned adjacent to a terminal end of a respective one of the conductor elements, wherein the conductor of each of the devices is capacitively coupled to the one of the conductor elements adjacent to which the device is positioned, wherein the conductor and the IC chip of each of the devices is not physically connected to the one of the conductor elements adjacent to which the device is positioned, and wherein each of the conductor elements has a slot provided therein which provides an inductive reactance. 
     In still a further embodiment, a transponder apparatus is provided that includes a plurality of separate antenna elements, and a plurality of devices, wherein each of the devices includes an IC chip operatively coupled to a conductor, such as a looped conductor, wherein each of the devices is positioned adjacent to a terminal end of a respective one of the antenna elements, wherein the conductor of each of the devices is capacitively coupled to the one of the antenna elements adjacent to which the device is positioned, wherein the conductor and the IC chip of each of the devices is not physically connected to the one of the antenna elements adjacent to which the device is positioned, and wherein each of the conductor elements has a slot provided therein which provides an inductive reactance. 
     In still a further embodiment, a wireless system is provided that includes a base station at a first location, the base station transmitting far field RF energy, and a local subsystem at a second location separate from the first location, the local subsystem including a parent antenna and a plurality of near field devices, the parent antenna receiving the far field RF energy and generating a near field in response thereto, wherein each of the near field devices includes an IC chip operatively coupled to a near field conductor, wherein the IC chip of each of the near field devices is wirelessly coupled to the near field through the near field conductor thereof, wherein the IC chip and the near field conductor of each of the near field devices is not directly physically connected to the parent antenna, wherein the local subsystem includes a substrate and wherein the near field devices are permanently or removeably attached to the substrate in a manner wherein the IC chip of each of the near field devices is able to receive energy from the base station through the wireless coupling to the near field that is sufficient to power the IC chip and wherein the IC chip of each of the near field devices is able to communicate with the base station through the wireless coupling to the near field. 
     In yet a further embodiment, a wireless transmission method is provided that includes transmitting far field RF energy from a first location, providing a parent antenna on a substrate at a second location separate from the first location, permanently or removeably attaching a plurality of near field devices each having an IC chip operatively coupled to a near field conductor to the substrate in a manner wherein the IC chip of each of the near field devices is able to receive energy from the base station through the wireless coupling to the near field that is sufficient to power the IC chip and wherein the IC chip of each of the near field devices is able to communicate with the base station through the wireless coupling to the near field, receiving the far field RF energy in the parent antenna at the second location and generating a near field in response thereto, wirelessly coupling the IC chip of each of the near field devices to the near field through the near field conductor thereof, wherein the IC chip and the near field conductor of each of the near field devices is not directly physically connected to the parent antenna, and receiving AC energy from the near field in the near field devices in response to the wirelessly coupling. 
     In still another embodiment, a wireless system is provided that includes a base station at a first location, the base station transmitting far field RF energy, and a local subsystem at a second location separate from the first location, the local subsystem including an antenna element and a plurality of near field devices, the antenna element receiving the far field RF energy, wherein each of the near field devices includes an IC chip operatively coupled to a near field conductor, wherein the IC chip of each of the near field devices is wirelessly coupled to the antenna element through the near field conductor thereof to create a network including the antenna element and the near field devices which enables the IC chip of each of the near field devices to communicate with one another, wherein the IC chip and the near field conductor of each of the near field devices is not directly physically connected to the antenna element, wherein the local subsystem includes a substrate and wherein the near field devices are permanently or removeably attached to the substrate in a manner wherein the IC chip of each of the near field devices is able to receive energy from the base station through the wireless coupling to the near field that is sufficient to power the IC chip and wherein the IC chip of each of the near field devices is able to communicate with the base station through the wireless coupling to the near field. 
     In yet another embodiment, a local subsystem for use in a wireless system having a base station structured to transmit far field RF energy to the local subsystem is provided that includes a substrate, a parent antenna provided on the substrate, the parent antenna being structured to receive the far field RF energy and generate a near field in response thereto, and a plurality of near field devices permanently or removeably attached to the substrate, wherein each of the near field devices includes an IC chip operatively coupled to a near field conductor, wherein the IC chip of each of the near field devices is structured to be wirelessly coupled to the near field through the near field conductor thereof, wherein the IC chip and the near field conductor of each of the near field devices is not directly physically connected to the parent antenna, and wherein the near field devices are permanently or removeably attached to the substrate in a manner wherein the IC chip of each of the near field devices is able to receive energy from the base station through the wireless coupling to the near field that is sufficient to power the IC chip and wherein the IC chip of each of the near field devices is able to communicate with the base station through the wireless coupling to the near field. 
     Therefore, it should now be apparent that the invention substantially achieves all the above aspects and advantages. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the aspects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain the principles of the invention. As shown throughout the drawings, like reference numerals designate like or corresponding parts. 
         FIG. 1  is a schematic diagram of a system for providing power to and/or communicating with wireless devices using a near field technique according to one embodiment of the present invention; 
         FIG. 2  is a schematic diagram of one non-limiting embodiment of a near field wireless device that may be employed in the system shown in  FIG. 1 ; 
         FIG. 3  is a block diagram of the near field wireless device of  FIG. 2  according to one particular embodiment; 
         FIG. 4  is a block diagram of one particular, non-limiting embodiment of the energy harvesting circuitry that may be employed in the near field wireless device of  FIG. 2 ; 
         FIG. 5  is a top plan view and  FIG. 6  is a bottom plan view of a local subsystem employed in the system shown in  FIG. 1  according to one particular embodiment; 
         FIG. 7  is a top plan view of a local subsystem employed in the system shown in  FIG. 1  according to another particular embodiment; 
         FIG. 8  is a top plan view and  FIG. 9  is a partial front elevational view of a local subsystem employed in the system shown in  FIG. 1  according to yet another particular embodiment; 
         FIG. 10  is a partial front elevational view of a local subsystem employed in the system shown in  FIG. 1  according to still another particular embodiment; 
         FIG. 11  is a schematic diagram illustrating the construction of a local subsystem according to one particular embodiment; 
         FIG. 12  is a partial top plan view and  FIG. 13  is a schematic diagram which together illustrate another embodiment of a local subsystem which reduces and minimizes thickness of a stack of near field devices; 
         FIG. 14  is a schematic diagram which shows yet another embodiment of a local subsystem which reduces and minimizes the thickness of a stack of near field devices; 
         FIG. 15  is a schematic diagram of a transponder apparatus according to a further embodiment of the present invention; 
         FIG. 16  is a schematic diagram of a transponder apparatus according to an alternate embodiment; and 
         FIGS. 17-20  are schematic diagrams of a transponder apparatus according to further alternate embodiments. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a schematic diagram of a system  2  for providing power to and/or communicating with wireless devices using a near field technique, such as near-field inductive coupling, near-field capacitive coupling, or a combination thereof, while in the far field of a directed or ambient energy source according to one embodiment of the present invention. The definition of the near-field is generally accepted as a region that is in proximity to an antenna or another radiating structure where the electric and magnetic fields do not have a plane-wave characteristic but vary greatly from one point to another. Furthermore, the near-field can be subdivided into two regions which are named the reactive near field and the radiating near field. The reactive near-field is closest to the radiating antenna and contains almost all of the stored energy, whereas the radiating near-field is where the radiation field is dominant over the reactive field but does not possess plane-wave characteristics and is complicated in structure. This is in contrast to the far-field, which is generally defined as the region where the electromagnetic field has a plane-wave characteristic, i.e., it has a uniform distribution of the electric and magnetic field strength in planes transverse to the direction of propagation. As used herein, the terms near-field and far-field shall have the meaning provided above. In addition, as used herein, inductive coupling shall mean the transfer of a signal or energy from one circuit component to another through a shared magnetic field, and capacitive coupling shall mean the transfer of a signal or energy from one circuit component to another due to discrete or parasitic capacitance between the circuit components. 
     As seen in  FIG. 1 , the system  2  includes a base station  4  which acts as a far field (directed or ambient) source by generating and transmitting RF energy  6 . The system  2  further includes a local subsystem  8  which itself includes a far source parent antenna  10  and a plurality of near field wireless devices  12 , sometimes referred to as satellites, described in greater detail elsewhere herein. The far source parent antenna  10  may be any suitable antenna form, such as, without limitation, a dipole, a patch or a serpentine. In operation, when the far source parent antenna  10  receives the RF energy  6 , the received RF energy  6  induces a current in the far source parent antenna  10 . The current flowing through the far source parent antenna  10  causes a near field  14  (shown by the flux lines in  FIG. 1 ) to be generated in the vicinity of the far source parent antenna  10 . In other words, the base station  4  (the far field source) creates a near field  14  in the vicinity of the far source parent antenna  10 . As described in greater detail herein, the near field wireless devices  12  receive power and/or communicate with the base station  4  by wirelessly coupling to the near field  14  using, for example, near-field inductive coupling, near-field capacitive coupling, or a combination thereof. 
       FIG. 2  is a schematic diagram of one non-limiting embodiment of the near field wireless device  12  that may be employed in the system  2  shown in  FIG. 1 . The near field wireless device  12  in this particular embodiment includes a substrate  16  made of a non-conductive material such as, without limitation, plastic, on which is provided an IC chip  18 , which may be, without limitation, an RFID chip. In addition, a tuned loop conductor  20  is operatively coupled to the IC chip  18 . In particular, the tuned loop conductor  20  is preferably directly connected to two or more connecting pads (not shown) provided as part of the IC chip  18  so as to be in electrical connection with the internal components of the IC chip  18  as described elsewhere herein. The tuned loop conductor  20  is preferably tuned to the frequency of the near field  14  that is generated by the far source parent antenna  10  in the local subsystem  8 . 
     In the embodiment shown in  FIG. 2 , the tuned looped conductor  20  has a rectangular shape. It should be understood that this is meant to be exemplary, and that other shapes, such as a triangle, a circle or a tetrahedron are also possible. In fact, if a triangular or tetrahedral shape is employed, a plurality of near field devices  12  could be physically connected to one another to form a three-dimensional shape, such as a sphere, where each vertex thereof will include a tuned loop conductor  20 . Also, it should be understood that in the embodiments described herein, the use of a looped conductor is not meant to be limiting, and that other conductor configurations suitable for making the required coupling may also be employed. 
       FIG. 3  is a block diagram of the near field wireless device  12  showing the components of the IC chip  18  according to one particular embodiment. The near field wireless device  12  includes energy harvesting circuitry  22  that is operatively coupled to on-board electronic circuitry  24 , which in turn is operatively coupled to load circuitry  26  which could include a transmitter. In operation, the energy harvesting circuitry  22  is structured to receive the AC energy of the near field  14  and, as described in greater detail below, harvest energy therefrom by converting the received AC energy into DC energy, e.g., a DC voltage. The DC voltage is then used to power the on-board electronic circuitry  24  and the load circuitry  26 . The on-board electronic circuitry  24  may include, for example, a processing unit, such as, without limitation, a microprocessor, a microcontroller or a PIC processor, additional logic circuitry, and a sensing circuit for sensing or measuring a particular parameter (such as temperature, in which case a thermistor may be included in the sensing circuit). The load circuitry  26  in the present embodiment may be structured to transmit an RF information signal to a receiving device, such as the base station  4 . The RF information signal may, for example, include data that identifies the near field wireless device  12  and/or data that is sensed by a component provided as part of the on-board electronic circuitry  24 . For instance, the load circuitry  26  functioning as a transmitter may transmit an RF signal that represents a temperature as measured by a thermistor provided as part of the on-board electronic circuitry  24 . In addition, the on-board electronic circuitry  24  may further include an energy storage device, such as a rechargeable battery or a capacitor (such as a supercapacitor) for storing energy from the DC voltage, which energy is then used to power the components of the on-board electronic circuitry  24 . 
       FIG. 4  is a block diagram of one particular, non-limiting embodiment of the energy harvesting circuitry  22  that may be employed in the near field wireless device  12 . As seen in  FIG. 4 , this embodiment of the energy harvesting circuitry  22  includes a matching network  28  which is electrically connected to the tuned loop conductor  20 . The matching network  28  is electrically connected to a voltage boosting and rectifying circuit preferably in the form of a one or more stage charge pump  30 . Charge pumps are well known in the art. Basically, one stage of a charge pump significantly increases the effective amplitude of an AC input voltage with the resulting increased DC voltage appearing on an output capacitor. The voltage could also be stored using a rechargeable battery. Successive stages of a charge pump, if present, will essentially increase the voltage from the previous stage resulting in an increased output voltage. In operation, the tuned loop conductor  20  receives the AC energy of the near field  14  and provides that energy to the charge pump  30  through the matching network  28 . The charge pump  30  rectifies the received AC signal to produce a DC signal that is amplified as compared to what it would have been had a simple rectifier been used. In one particular embodiment, the matching network  28  is chosen (i.e., its impedance is chosen) so as to maximize the voltage of the DC signal output by charge pump  30 . In other words, the matching network  28  matches the impedance of the tuned loop conductor  20  to the charge pump  30  solely on the basis of maximizing the DC output of the charge pump  30 . In the preferred embodiment, the matching network  28  is an LC circuit of either an L topology (which includes one inductor and one capacitor) or a π topology (which includes one inductor and two capacitors) wherein the inductance of the LC circuit and the capacitance of the LC circuit are chosen so as to maximize the DC output of the charge pump  30 . Furthermore, the matching network  28  may be chosen so as to maximize the output of the charge pump  30  using a trial and error (“annealing”) empirical approach in which various sets of inductor and capacitor values are used as matching elements in the matching network  28 , and the resulting output of the charge pump  30  is measured for each combination, and the combination that produces the maximum output is chosen. 
       FIG. 5  is a top plan view and  FIG. 6  is a bottom plan view of a local subsystem  8  according to one particular embodiment. The local subsystem  8  in this embodiment includes a far source parent antenna  10  in the form of a dipole antenna provided on the top surface  34  of a non-conductive substrate  32 , which may be, for example, a fiberglass material as used in printed circuit boards or any other appropriate substrate. As seen in  FIGS. 5 and 6 , a first plurality of near field devices  12  are provided on the top surface  34  of the substrate  32 , and a second plurality of near field devices  12  are provided on the bottom surface  36  of the substrate  32 . The near field devices  12  may be permanently attached to the substrate  32  using a suitable adhesive material, or alternatively, may be removeably attached to the substrate  32  using a suitable mechanism such as a clear peel-able plastic tape. In either case, due to the presence of the substrate  16 , there is no contact or direct physical connection between the far source parent antenna  10  and the tuned loop conductor  20  of any of the near field devices  12 . However, as described in greater detail elsewhere herein, each near field device  12  is wirelessly coupled to the near field  14  (and preferably the reactive near field portion thereof) generated by the far source parent antenna  10  as a result of inductive and/or capacitive coupling between the tuned loop conductor  20  and the near field  14 . Eliminating the need for a direct physical connection between the far source parent antenna  10  and the near field devices  12  simplifies fabrication and impedance matching as such multiple physical connections would require considerable attention in manufacturing. 
     It should be understood that while near field devices  12  are shown on both the top surface  34  and the bottom surface  36  of the substrate  32 , this is meant to be exemplary only, and that near field devices  12  may be provided on only a single surface of the substrate  32  in some embodiments. In fact, it is not necessary that the near field devices be attached to the substrate on any surface thereof, as the present invention will function as described herein as long as a near field device  12  is in the vicinity of the far source parent antenna  10  in an area where the near field  14  is strong enough for energy to be harvested therefrom as described herein. 
       FIG. 7  is a top plan view of a local subsystem  8  according to another particular embodiment. In this embodiment, the local subsystem  8  includes a conventional (prior art) RFID tag  38  available from a number of commercial sources such as, without limitation Texas Instruments, Inc. The RFID tag  38  includes a substrate  40 . An RFID antenna  42  is provided on the top surface  46  of the substrate  40  and serves as the far source parent antenna  10 . An RFID chip  44 , similar in structure and functionality to the IC chip  18 , is operatively coupled to the RFID antenna  42  in a conventional manner. In addition, as seen in  FIG. 7 , a plurality of near field devices  12  are provided on the top surface  46  of the substrate  40  (although not shown, a second plurality of near field devices  12  may be provided on the bottom surface of the substrate  40 ). The near field devices  12  may be permanently attached to the substrate  40  using a suitable adhesive material, or alternatively, may be removeably attached to the substrate  40  using a suitable mechanism as described elsewhere herein. In either case, there is no contact or direct physical connection between the far source parent antenna  10  (the RFID antenna  42 ) and the tuned loop conductor  20  of any of the near field devices  12 . However, as described elsewhere herein, each near field device  12  is wirelessly coupled to the near field  14  generated by the far source parent antenna  10  as a result of inductive and/or capacitive coupling between the tuned loop conductor  20  and the near field  14 . 
       FIG. 8  is a top plan view and  FIG. 9  is a partial front elevational view of a local subsystem  8  according to yet another particular embodiment. The local subsystem  8  in this embodiment includes a far source parent antenna  10  in the form of a dipole antenna provided on the top surface  34  of a non-conductive substrate  32 . As seen in  FIGS. 8 and 9 , a plurality of near field devices  12 , identified as  12 A,  12 B and  12 C, are provided on the top surface  34  of the substrate  32  in a manner in which they are stacked on top of one another. Preferably, the bottom most near field device  12 A is permanently or removeably attached to the substrate  32  as described elsewhere herein, the near field device  12 B is stacked on top of and permanently or removeably attached to the near field device  12 A, and the near field device  12 C is stacked on top of and permanently or removeably attached to the near field device  12 C. Due to the presence of the substrate  16  of the near field device  12 A, there is no contact or direct physical connection between the far source parent antenna  10  and the tuned loop conductor  20  of any of the near field devices  12 . However, as described elsewhere herein, each near field device  12 A,  12 B,  12 C is wirelessly coupled to the near field  14  generated by the far source parent antenna  10  as a result of inductive and/or capacitive coupling between the tuned loop conductor  20  thereof and the near field  14 . It should be understood that while near field devices  12  are shown on only the top surface  34 , near field devices  12  may also be provided in a stacked manner on the bottom surface of the substrate  32  in some embodiments. In addition, according to one specific embodiment, a plurality of near field devices  12  in addition to the stacked near field devices  12 A,  12 B,  12 C may also be provided on either or both surfaces of the substrate  32  in a configuration in which they are positioned adjacent to one another (rather than stacked) as shown in, for example,  FIGS. 5 and 6 . An example of such an embodiment is shown in  FIG. 10 . 
     In the embodiments of  FIGS. 5-10 , the near field devices  12  may be selectively positioned with respect to the far source parent antenna  10  (e.g., on the associated substrate  32 ) such that the total amount of DC energy that is harvested by the energy harvesting circuitry  22  of each of the near field devices  12  is maximized (different amounts may be harvested by each depending on position). This may be accomplished through a trial and error approach by moving the near field devices  12  around and measuring the harvested DC energy until a configuration is found wherein the total energy harvested is at a maximum. 
     As will be appreciated, in most embodiments of the near field device  12 , the thickest component will be the IC chip  18 . As a result, when multiple near field devices  12  are stacked as shown in  FIGS. 9 and 10  wherein the IC chips  18  are positioned directly on top of one another, the stack will have a maximum thickness. According to one particular embodiment of the local subsystem  8 , this thickness may be reduced and minimized by alternating the position of the IC chips of each near field device  12  when the near field devices  12  are stacked. This reduction of thickness is facilitated by making the substrate  16  and the tuned loop conductor  20  of each near field device  12  of a flexible material such that they can bend when stacked on top of one another to take up empty space that otherwise would be present therebetween. Construction of a local subsystem  8  according to this embodiment is illustrated in  FIG. 11  wherein the arrows represent one near field device  12  being stacked on top of another near field device  12 . 
       FIGS. 12 and 13  illustrate another embodiment of a local subsystem  8  which reduces and minimizes the thickness of the stack of near field devices  12 . In this embodiment, the near field devices  12  are constructed such that the substrate  16  of each near field device  12  in the stack is able to fit within the interior of the near field device  12  immediately below it as bound on one end by the inner edge of the IC chip  18  thereof. More preferably, the near field devices  12  are constructed such that the substrate  16  of each near field device  12  in the stack is able to fit within the tuned loop conductor  20  of the near field device  12  immediately below it. In this configuration, the near field devices are able to be stacked like Russian dolls.  FIG. 14  shows yet another embodiment of a local subsystem  8  which reduces and minimizes thickness of the stack of near field devices  12 . In this embodiment, the near field devices  12 A,  12 B,  12 C,  12 D are stacked such that the near field devices  12 A,  12 B,  12 C,  12 D are each shifted linearly with respect to one another in the stack. As a result, the IC chips  18  thereof will be positioned adjacent to one another rather than directly on top of one another. Again, this reduction of thickness is facilitated by making the substrate  16  and the tuned loop conductor  20  of each near field device  12  of a flexible material such that they can bend when stacked on top of one another to take up empty space that otherwise would be present therebetween. 
       FIG. 15  is a schematic diagram of a transponder apparatus  50  according to a further embodiment that employs capacitive coupling with inductive tuning as described below. The transponder apparatus  50  includes a main antenna element  52  provided on a substrate  56 . The main antenna element  52  includes four conductor elements  54 A,  54 B,  54 C, and  54 D, which, in the embodiment shown, each have a square spiral shape such that they are nested within one another. As seen in  FIG. 15 , the conductor elements  54 A,  54 B,  54 C, and  54 D are each direct connection (DC) coupled to one another at a direct connection (DC) coupling point  58 . In addition, a looped conductor device  60  (identified as  60 A,  60 B,  60 C,  60 D), each identical in structure to the near field device  12  shown in  FIG. 2 , is provided on the substrate  56  in the vicinity of the terminal end  64 A,  64 B,  64 C,  64 D of a terminal segment  66 A,  66 B,  66 C,  66 D of a respective conductor element  54 A,  54 B,  54 C,  54 D. The IC chip  18  of each looped conductor device  60 A,  60 B,  60 C,  60 D is not, in the embodiment shown, directly connected to the associated conductor element  54 A,  54 B,  54 C,  54 D (there is an air gap between IC chip  18  of each looped conductor device  60 A,  60 B,  60 C,  60 D and the associated conductor element  54 A,  54 B,  54 C,  54 D). Instead, each IC chip  18  is coupled to the associated conductor element  54 A,  54 B,  54 C,  54 D through capacitive coupling between the looped conductor  20  of the associated looped conductor device  60 A,  60 B,  60 C,  60 D and the associated conductor element  54 A,  54 B,  54 C,  54 D. In other words, each looped conductor  20  is capacitively coupled to a respective conductor element  54 A,  54 B,  54 C,  54 D (by being in the capacitive field thereof, which may or may not overlap the near field), and as a result, each IC chip  18  is coupled to a respective conductor element  54 A,  54 B,  54 C,  54 D so that energy and signals can be transferred from the conductor element  54 A,  54 B,  54 C,  54 D to the associated IC chip  18 . In particular, the two points at which the looped conductor  20  is connected to the IC chip have a capacitive connection to the associated conductor element  54 A,  54 B,  54 C,  54 D at two points where the associated conductor element  54 A,  54 B,  54 C,  54 D has been slit to provide an inductive matching slot in the conductor (an inductive matching circuit) to balance out the capacitive connection. Such a configuration allows energy and signals (e.g., data and/or power signals) received by the main antenna element  52  from, for example, a base station such as the base station  4  (e.g., an RFID reader), to be transferred to the looped conductor devices  60 A,  60 B,  60 C,  60 D (i.e., to the IC chips  18  thereof). In addition, the direct connection between each of the conductor elements  54 A,  54 B,  54 C, and  54 D enables looped conductor devices  60 A,  60 B,  60 C,  60 D to be able to communicate with one another. 
     The capacitive coupling just described introduces a number of new capacitances into the transponder apparatus  50  and as a result will alter the resonance properties of the main antenna element  52 . Thus, in order to balance/counteract this effect, each conductor element  54 A,  54 B,  54 C,  54 D is provided with a respective slot  68 A,  68 B,  68 C,  68 D therein. Preferably, the slot  68 A,  68 B,  68 C,  68 D is provided in the terminal segment  66 A,  66 B,  66 C,  66 D of the associated conductor element  54 A,  54 B,  54 C,  54 D beginning in the vicinity of the terminal end  64 A,  64 B,  64 C,  64 D thereof. Each slot  68 A,  68 B,  68 C,  68 D will introduce an inductive reactance that balances/counteracts the resonance change to a desired extent and which maintains a desired impedance matching between the IC chip  18  and the associated conductor element  54 A,  54 B,  54 C,  54 D. The dimensions of each slot  68 A,  68 B,  68 C,  68 D will be determined by the desired added inductive reactance, which in turn will be determined by the amount of capacitance added by the capacitive coupling described above. As a result, the transponder apparatus  50  can be said to include capacitive coupling with inductive tuning. 
       FIG. 16  is a schematic diagram of a transponder apparatus  50 ′ according to an alternate embodiment, which is similar to the transponder apparatus  50 . However, in the transponder apparatus  50 ′, the size of the DC coupling point  58  has been increased to an extent that the main antenna element  52  largely comprises a patch antenna. 
       FIG. 17  is a schematic diagram of a transponder apparatus  70  according to yet a further embodiment. The transponder apparatus  70  includes four separate antenna elements  72 A,  72 B,  72 C, and  72 D provided on a substrate  74  which are not connected to one another. In the embodiment shown, each of the antenna elements  72 A,  72 B,  72 C, and  72 D has a square spiral shape such that they are nested within one another. It should be understood that this is exemplary only, and that all of the antenna elements  72 A,  72 B,  72 C and  72 D may have a common different shape, or that the shapes may differ among the group of antenna elements  72 A,  72 B,  72 C and  72 D. As seen in  FIG. 17 , a looped conductor device  60  (identified as  60 A,  60 B,  60 C,  60 D), each identical in structure to the near field device  12  shown in  FIG. 2 , is provided on the substrate  74  in the vicinity of the terminal end  76 A,  76 B,  76 C,  76 D of a terminal segment  78 A,  78 B,  78 C,  78 D of a respective antenna element  72 A,  72 B,  72 C, and  72 D. The IC chip  18  of each looped conductor device  60 A,  60 B,  60 C,  60 D is not, in the embodiment shown, directly connected to the associated antenna element  72 A,  72 B,  72 C, and  72 D. Instead, each IC chip  18  is coupled to the associated antenna element  72 A,  72 B,  72 C, and  72 D through capacitive coupling between the looped conductor  20  of the associated looped conductor device  60 A,  60 B,  60 C,  60 D and the associated antenna element  72 A,  72 B,  72 C, and  72 D. In other words, each looped conductor  20  is capacitively coupled to a respective antenna element  72 A,  72 B,  72 C, and  72 D, and as a result, each IC chip  18  is coupled to a respective antenna element  72 A,  72 B,  72 C, and  72 D so that energy and signals (e.g., data and/or power signals) can be transferred from the antenna element  72 A,  72 B,  72 C, and  72 D to the associated IC chip  18 . Such a configuration allows energy and signals received by each respective antenna element  72 A,  72 B,  72 C, and  72 D from, for example, a base station such as the base station  4  (e.g., an RFID reader), to be transferred to the associated looped conductor device  60 A,  60 B,  60 C,  60 D (i.e., the IC chip  18  thereof). 
     As described elsewhere herein, the capacitive coupling just described will alter the resonance properties of each antenna element  72 A,  72 B,  72 C, and  72 D. Thus, in order to balance/counteract this effect, each antenna element  72 A,  72 B,  72 C, and  72 D is provided with a respective slot  80 A,  80 B,  80 C,  80 D therein. Preferably, the slot  80 A,  80 B,  80 C,  80 D is provided in the terminal segment  78 A,  78 B,  78 C,  78 D of the associated antenna element  72 A,  72 B,  72 C, and  72 D beginning at the terminal end  76 A,  76 B,  76 C,  76 D thereof. Each slot  80 A,  80 B,  80 C,  80 D will introduce an inductive reactance that balances/counteracts the resonance change to a desired extent. The dimensions of each slot  80 A,  80 B,  80 C,  80 D will be determined by the desired added inductive reactance, which in turn will be determined by the amount of capacitance added by the capacitive coupling described above. As a result, the transponder apparatus  70  can be said to include capacitive coupling with inductive tuning. 
       FIGS. 18 and 19  are schematic diagrams of a transponder apparatuses  70 ′ and  70 ″ according to alternative further embodiments wherein the spacing between the antenna elements  72 A,  72 B,  72 C, and  72 D has been altered.  FIG. 20  is a schematic diagram of a transponder apparatus  70 ′″ according to still a further alternative embodiments wherein the looped conductor devices  60 A,  60 B,  60 C,  60 D, the terminal segment  78 A,  78 B,  78 C,  78 D and the slots  80 A,  80 B,  80 C,  80 D are positioned in the central region of the transponder apparatus  70 ′″ (wherein they are surrounded by the remainder of the antenna elements  72 A,  72 B,  72 C, and  72 D) as opposed to the outer periphery thereof. 
     While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, deletions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as limited by the foregoing description but is only limited by the scope of the appended claims.

Technology Category: 5