RFID INFINITY ANTENNA

Abstract

An RFID antenna comprises two or more electroconductive sheets of uniform planar size, being parallel and aligned, with a space therein between. Each electroconductive sheet comprises: a feed connection point, which receives an electrical current from a feed to supply current to the electroconductive sheet; and a return connection point, opposite and parallel to the feed connection point of the electroconductive sheet, which acquires current from the electroconductive sheet and transfers current to a return. The electrical circuit pathway created from the feed to the return is equal distance for each electroconductive sheet. The two electroconductive sheets are connected together to complete a circuit that causes direction of electrical flow in the one electroconductive sheet to be opposite to direction of electric flow in the other electroconductive sheet.

Claims

1. An RFID antenna, comprising: two or more electroconductive sheets of uniform planar size with a space therein between, wherein said electroconductive sheets are parallel and aligned with respect to one another, each electroconductive sheet comprising: a feed connection point, which receives an electrical current from a feed to supply current to the electroconductive sheet, the feed connection point connecting to one edge of the electroconductive sheet; a return connection point, which acquires the electrical current from the electroconductive sheet and transfers the electrical current to a return, the return connection point connecting to another edge of the electroconductive sheet, opposite and parallel to the one edge of the electroconductive sheet to which the feed connection point is connected, wherein the electrical pathway of a circuit created from the feed to the return via a respective feed connection point and a respective return connection point is equal distance for each conductive sheet, and wherein the two electroconductive sheets are connected together to complete a circuit that causes direction of electrical flow in the one electroconductive sheet to be opposite to direction of electric flow in the other electroconductive sheet.

2. The RFID antenna of claim 1, wherein a magnetic field is generated between the electroconductive sheets and said magnetic field is uniform in the space therein between.

3. The RFID antenna of claim 1, wherein each of the two electroconductive sheets has a plurality of feed connection points and an equal number of respective return connection points.

4. The RFID antenna of claim 3, wherein the plurality of feed connection points and respective return connection points are spaced along the edge of the electroconductive sheet, respectively, with equal distance between each feed connection point and a respective return connection point, in parallel.

5. The RFID antenna of claim 1, wherein the electroconductive sheets are made with an aluminum-based metal.

6. An electrical current supplier that provides current to a feed of the RFID antenna of claim 1.

7. An RFID antenna, comprising: two or more electroconductive sheets of uniform planar size with a space therein between, wherein said electroconductive sheets are parallel and aligned with respect to one another, each electroconductive sheet comprising: a first edge set and a second edge set of parallel edges, wherein the second edge set is orthogonal to the first edge set, each of the first edge set and second edge set including: a feed connection point, which receives an electrical current from a feed to supply current to the electroconductive sheet, the feed connection point connecting to one edge of the electroconductive sheet; a return connection point, which acquires the electrical current from the electroconductive sheet and transfers the electrical current to a return, the return connection point connecting to another edge of the electroconductive sheet, opposite and parallel to the one edge of the electroconductive sheet to which the feed connection point is connected, wherein the electrical pathway of a circuit created from the feed to the return via a respective feed connection point and a respective return connection point is equal distance for each electroconductive sheet, wherein the two electroconductive sheets are connected together to complete a circuit that causes direction of electrical flow in the one electroconductive sheet to be opposite to direction of electric flow in the other electroconductive sheet, and wherein the feed of electrical current is alternately switched between the feed connection point of the first edge set and the feed connection point of the second edge set in a periodic manner, and the electrical current is switched in a uniform manner between the electroconductive sheets.

8. The RFID antenna of claim 7, wherein a magnetic field is generated between the electroconductive sheets and said magnetic field is uniform in the space therein between.

9. The RFID antenna of claim 8, wherein the magnetic field changes direction in an orthogonal manner when the electrical current is switched between the feed connection points of the first edge set and the second edge set, respectively.

10. The RFID antenna of claim 9, wherein the first edge set and the second edge set each have a plurality of feed connection points and an equal number of respective return connection points, respectively.

11. The RFID antenna of claim 10, wherein the feed connection points and respective return connection points are evenly spaced, in each of the first edge set and the second edge set, with equal distance between each feed connection point and a respective return connection point, in parallel.

12. The RFID antenna of claim 7, wherein the electroconductive sheets are made with an aluminum-based metal.

13. A switch, which switches in a periodic manner the feed of electrical current to the feed connection points of the first edge set and second edge set of the electroconductive sheets of claim 7.

14. A method of producing an alternating magnetic field in an RFID antenna, the RFID antenna comprising: two or more electroconductive sheets of uniform planar size with a space therein between, wherein said electroconductive sheets are parallel and aligned with respect to one another, each electroconductive sheet comprising: a first edge set and a second edge set of parallel edges, wherein the second edge set is orthogonal to the first edge set, each of the first edge set and second edge set including: a feed connection point, which receives an electrical current from a feed to supply current to the electroconductive sheet, the feed connection point connecting to one edge of the electroconductive sheet; a return connection point, which acquires the electrical current from the electroconductive sheet and transfers the electrical current to a return, the return connection point connecting to another edge of the electroconductive sheet, opposite and parallel to the one edge of the electroconductive sheet to which the feed connection point is connected, wherein the electrical pathway of a circuit created from the feed to the return via a respective feed connection point and a respective return connection point is equal distance for each conductive sheet, the method comprising: connecting the two electroconductive sheets together to complete a circuit that causes direction of electrical flow in the one electroconductive sheet to be opposite to direction of electric flow in the other electroconductive sheet, and switching the feed of electrical current between the feed connection point of the first edge set and the feed connection point of the second edge set in a periodic manner, the switching being uniform between the electroconductive sheets.

15.-18. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0019] Embodiments will now be described, by way of example only, with reference to the accompanying drawings, which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several figures, in which:

[0020] FIG. 1 is an illustrative view of a magnetic field generated along the planar loop of a conventional antenna;

[0021] FIG. 2 is a measurement of the magnetic field drop off of the antenna of FIG. 1;

[0022] FIG. 3 is a RFID system including a base station and RFID tags;

[0023] FIG. 4 is a section view of the antenna according to one embodiment of the present invention;

[0024] FIG. 5A is an illustrative view of the magnetic field generated from the antenna of FIG. 4 when current flows clockwise;

[0025] FIG. 5B is an illustrative view of the magnetic field generated from the antenna of FIG. 4 when current flows counterclockwise;

[0026] FIG. 5C is an illustrative view of the magnetic field density of an electroconductive sheet of the antenna of FIG. 4;

[0027] FIG. 6 is a section view of the antenna according to another embodiment of the present invention;

[0028] FIG. 7 is a view of the electrical current supply according to FIG. 6;

[0029] FIG. 8 is a top illustrative view of the embodiment of FIG. 6;

[0030] FIG. 9 is a section view of the electroconductive sheet according to the embodiment of FIG. 6;

[0031] FIG. 10 is a measurement of the magnetic field drop off of the antenna of FIG. 6;

[0032] FIG. 11 is a section view of the antenna according to another embodiment of the present invention;

[0033] FIG. 12A is a top illustrative view of the embodiment of FIG. 11 with an H.sub.x field current driver;

[0034] FIG. 12B is a top illustrative view of the embodiment of FIG. 11 with an H.sub.y field current driver;

[0035] FIG. 13 is a variation of the embodiment of FIG. 11;

[0036] FIG. 14 is a view of the RFID system with an antenna according to another embodiment of the present invention;

DESCRIPTION OF EMBODIMENTS

[0037] The invention will now be described by reference to the preferred embodiments. This does not intend to limit the scope of the present invention but to exemplify the invention. The size of the component in each figure may be changed in order to aid understanding. The orientation of a component in each figure may be illustrative and may further change in order to aid understanding. Some of the components in each figure may be omitted if they are not important for explanation.

[0038] FIG. 3 shows a block diagram of an RFID system 10 utilizing the RFID antenna according to various embodiments of the invention. An RFID base station 20 includes, in part, a reader 50, which acts as a control for the base station 20 to operate and correspond with one or more RFID tags 60. The reader 50 controls the functionality of the base station 20 and may correspond with an external computer, monitor, or display 36, which allows a user to interface with the base station 20. The reader 50 includes a controller 30 and a radio wave frequency interface 40 (herein known as “RF interface 40”).

[0039] The controller 30 comprises a control unit 34 and memory 32. The control unit 34 communicates with the RF interface 40 for operation of data transmission and data receipt to and from the RFID tags 60. The memory 32 can store application information for the base station 20 or identification information of an RFID tag 60, e.g., tag identification numbers.

[0040] The RF interface 40 includes a receiver 42 and a transmitter 44. The receiver 42 and transmitter 44 allow the base station 20 to receive and transmit information, respectively.

[0041] In reading an RFID tag 60, the base station 20 will interrogate a tag by generating an RF signal (or “radio frequency signal”) over a carrier frequency. The RF signal is coupled to an antenna 100, from which the RF signal is emitted and picked up by an antenna 62 of the RFID tag 60. Successful recognition of an RFID tag will ostensibly occur if the RFID tag 60 is located in a “read zone” that is defined by the base station 20. The read zone is within a transmitting range of the base station 20.

[0042] With the transmitter 44, the base station 20 may transmit an RF signal to interrogate the receiving RFID tag 60. For reading such tags, the antenna 100 of the base station generates and transmits a carrier signal of continuous electromagnetic waves. The RFID tags 60 will respond by modulating the carrier signal with information contained within the RFID tag. The modulated carrier signal is then sent back to the base station 20 and recognized by the receiver 42 via the antenna 100.

[0043] The antenna itself transmits carrier waves through a magnetic field, powered in part by the RF interface 40 through a modulator (not shown) of the receiver 42 and transmitter 44. The antenna of the invention acts as a multidimensional antenna. Instead of using a planar wire loop of conventional loop antennas, an antenna is formed from an electric circuit, in part, over a wider area to produce a substantial magnetic field. A more substantial magnetic field may consequently produce a larger read zone.

First Embodiment

[0044] FIG. 4 is a perspective side view of the antenna 100 according to a first embodiment. The antenna 100 comprises a plurality of electroconductive sheets 120. For purposes of explanation, the embodiment will refer to two electroconductive sheets 120a and 120b. Said electroconductive sheets 120, alternatively known as “sheets,” “surfaces,” “plates,” or “units,” may be made out of a material that has a low resistance R value. In a preferred embodiment of the invention, the antenna 100 is made from aluminum-based metal sheets, which are a cost-saving and effective option. The antenna 100 may also be fashioned from the housing of a conventional loop antenna system if the housing is made from a low-resistance electroconductive material.

[0045] The electroconductive sheets 120a and 120b are planar and formed to be uniform in size. The electroconductive sheets 120 are further parallel and aligned with respect to one another. A space is formed therein between, with the electroconductive sheets 120 themselves supported with an internal or external support structure (not pictured) made of non-conductive materials. The alignment of the electroconductive sheets 120 is not affected by the support structure.

[0046] Each electroconductive sheet 120 includes at least two connection points 130: a feed connection point 130a, and a return connection point 130b.

[0047] The feed connection point 130a (alternatively known as “feed point 130a”) connects to one edge of an electroconductive sheet 120 and originally receives an electrical current, e.g., from an electrical feed 110 so as to supply current thereto. An “edge” of the electroconductive sheet 120 may be the physical edge of the plane of the electroconductive sheet 120, or may be, e.g., an overhanging portion connected to the edge of the sheet.

[0048] The return connection point 130b (alternatively known as a “return point 130b,” “return,” or “sink point”) is located on another edge of the electroconductive sheet 120, opposite and parallel to the one edge of the electroconductive sheet 120 to which the feed connection point 130a is connected. The return point 130b acquires the electrical current from the electroconductive sheet 120 that was given by the feed point 130a.

[0049] The electroconductive sheets 120 are connected together with a connection 160, which is any connecting means such as a substrate, wire, or cable. Using the two electroconductive sheets 120a and 120b, an electrical pathway of a circuit may be created from the feed point 130a and return point 130b of one electroconductive sheet 120a, to the feed connection point 130a and return point 130b of another electroconductive sheet 120b. That is, the two electroconductive sheets 120 are connected together to complete a circuit, which causes the direction of electrical flow of current in the one electroconductive sheet 120a to be opposite to direction of electric flow of current in the other electroconductive sheet 120b.

[0050] As previously stated, the electrical circuit of the antenna 100 of the invention is given supply current I.sub.0 from the modulator (not shown) of either the receiver 42 or the transmitter 44 of the RF interface 40. The feed 110 of electrical current to the antenna 100 is AC at, e.g., 13.56 MHz frequency, which is an RFID industry standard. The AC feed 110 provides electrical current to one electroconductive sheet 120a, 120b and returns the current from the other electroconductive sheet 120b, 120a.

[0051] It can be appreciated by those skilled in the art that by utilizing an AC power signal, the current alternates direction so that connection points 130 of an electroconductive sheet 120 may act as both a feed and a return. As such, the circuit may alternate the direction of the current flow such that a feed connection point 130a may also act as a return connection point 130b in an electroconductive sheet 120 in a subsequent alteration or current cycle.

[0052] Along the connection 160, opposing the feed 110 in the circuit is a tuning element 140. When the electrical current reaches the return point 130b of an electroconductive sheet 120a, the electrical current is supplied to another electroconductive sheet 120b by its feed connecting point via the tuning element 140. The tuning element 140 acts as a return such that, not only is a respective feed point 130a and a respective return point 130b equal distance for each electroconductive sheet 120a and 120b, the electrical pathway for each sheet 120 will be the same. That is, the current provided in each respective feed point 130a will be the same measurement. The tuning element 140 is placed so as to be equal distance from the AC power feed 110 via either electroconductive sheet 120.

[0053] FIGS. 5A and B are illustrative examples of the magnetic field H, or H field, generated by the antenna of the present embodiment. FIG. 5A illustrations when current flows “clockwise” through the sheet antenna 100, and FIG. 5B illustrations when current flows “counter-clockwise” through the sheet antenna 100. It should be noted that the directions along the Cartesian coordinate system are meant to be illustrative and in no way mean to limit the embodiments of the invention. The illustrative purpose is to show the relationship of the electrical current flow and subsequent magnetic field generated.

[0054] From FIG. 5A, the electroconductive sheets 120 are shown as placed along the X-Y plane. As the feed 110 provides current to the feed point 130a of electroconductive sheet 120a, current I.sub.x moves along the X-axis towards the return point 130b. Current flows in a path from minimum resistance for a circuit, so the return point 130b will be typically parallel to, i.e., in a straight line from, the feed point 130a. Subsequently, current is provided from the return point 130b of electroconductive sheet 120a via the tuner 140 to the feed point 130a of electroconductive sheet 120b; the current −I.sub.z is transmitted through sheets along the Z-axis in the −Z direction. Current −I.sub.x is directed through the electroconductive sheet 120b and is returned from the return point 130b of electroconductive sheet 120b in the −X direction to complete a circuit. The magnetic field H.sub.y generated from the antenna 100 is in the +Y direction along the Y-axis, according to Ampere's Law.

[0055] FIG. 5B illustrates the case when the current is supplied first to electroconductive sheet 120b. In this example, the electric current I.sub.z is transmitted between the two electroconductive sheets 120 in the +Z direction. A magnetic field −H.sub.y is subsequently generated from the antenna 100 in the −Y direction along the Y-axis. However, for the purposes of RFID tag detection, an H field generated in the positive coordinate direction is the same as that generated in the negative coordinate direction. That is, in the FIGS. 5A and 5B, the −Y direction H field −H.sub.y is the same as the +Y direction H field H.sub.y. The connection points 130 of a respective sheet 120 may both feed current and return current, depending on the direction of the alternating current feed 110.

[0056] In the antenna 100 of FIGS. 5A and 5B, a near uniform H field can be created in the direction along the Y-axis. Due to the combination of a low resistance electroconductive sheet and even current distribution between such sheets, the H field inside the antenna's sheet volume, i.e., between the two electroconductive sheets, is near constant and may gradually decrease when moving away from the antenna 100. Experimental results have shown that some residual fields may exist on top and bottom of the antenna's sheet volume due to, e.g., fringing fields generated from a antenna's sheet edge. However, the magnetic field outside the antenna's sheet volume along the Z-axis is ideally measured at zero.

[0057] It is noted that, as the size of the antenna 100 increases, there may be an effect of current distribution across an electroconductive sheet 120 not being even. In the case of a single feed point 130a, the density of the current is higher at the feed point 130a and decreases rapidly along either side of the feed.

[0058] FIG. 5C is a top view of an electroconductive sheet 120 illustrating the distribution of current along the X-Y plane. If current is illustrated to flow as directed in the X-axis, with a feeding point 130a at the center, along the Y-axis, of the electroconductive sheet 120, current density is at a minimum along the edge of either side of the feeding point 130a. As seen from FIG. 50, the current along the edge of the feed point 130a becomes less dense the farther away from the feed point 130a, and also said current is comparatively less dense than the current measured at the edge of the return point 130b. As a generated magnetic field is understood to be proportional to the current density, the magnetic field will decrease the farther away it gets from the feeding point 130a when measured along the X-axis and Y-axis.

[0059] The effects of the aforementioned may be negligible in antennas with smaller-sized electroconductive sheets 120, but the effect is noticeable and critical for a larger physical antenna with a greater sheet volume, e.g., at a size of 600 mm by 400 mm.

[0060] FIG. 6 shows an alternative configuration of the first embodiment of the invention. The antenna 200 comprises two sheets 220, including a plurality of feed points 230a and a plurality of return points 230b. The feed points 230a and return points 230b are directly proportional in number with respect to each electroconductive sheet 220. FIG. 6. Illustrates two feed points 230a and two return points 230b, but this number is not limited to two and may include multiple connection points for each electroconductive sheet 220.

[0061] As current is provided from the RF interface 40 as a feed 210, transformers 270 are used to split the input and to provide equal current to each feed point 230a of a sheet 220. Splitting into multiple flows of current creates multiple electronic pathways. Each current pathway is then returned by being steered into a corresponding return point 230b. The current of each pathway is subsequently transferred to another electroconductive sheet 220 via connectors 260, with respective tuning elements 240. It is noted that the tuning elements 240 are measured from the feed 210 to be equal distance for each electroconductive sheet 220. This is to ensure that there are equal pathways of current flow between each return point 230b.

[0062] FIG. 7 is an electronic schematic of a broadband transformer power splitter used as a transformer 270 for a feed 210. By illustration, four feed points 230a are provided. By splitting with transformers, the current may be evenly distributed to the multiple feed points 230a of an electroconductive sheet 220 (not shown).

[0063] FIG. 8 is a top view showing the flow of current of one electroconductive sheet 220. As by illustration, as part of the electric circuit, current I.sub.x flows along the sheet in the +X direction along the X-axis. With a completed electric circuit, a magnetic field H.sub.y is generated along the Y-axis, in this case, in the +Y direction. The connection between the feed points 230a and the return points 230b uniformly steer current along the electroconductive sheet 220 itself. The multiple connection points 230 may or may not be evenly spaced with respect to one another, but may be configured in a formation so as to achieve the desired result of an even magnetic field. A uniform magnetic field can thus be achieved in a large dimension antenna.

[0064] A current flowing down a very long electroconductive sheet will create a near-uniform magnetic field above the sheet surface for most of its length. FIG. 9 shows the magnetic field B.sub.y across an electroconductive sheet 220 along the X-Y plane. At any point P inside the sheet volume, the magnetic field B is experimentally measured as nearly constant, and can be valued according to B=μ.sub.0J.sub.0b/2, with the magnetic constant μ.sub.0, measure of current J.sub.0, and a sheet with material thickness b.

[0065] FIG. 10 shows the measurement of the magnetic field H.sub.y for the variation of the antenna 200 of the first embodiment. As previously stated, when measured directly above and below the electroconductive sheets 220 (along the Z-axis), the magnetic field strength is ideally measured as zero, with some residual field interference. From an X-Y planar perspective, outside the edges of the electroconductive sheets 220, the magnetic field drops off as 1/R.sup.3 in near field, and 1/R in far field. For example, at the frequency of 13.56 MHz, the magnetic near field ends approximately at 3.5 m from the antenna of the invention. However, a uniform magnetic field may be generated inside the sheet volume of the antenna 200, as shown in FIG. 10. This has an advantage over conventional RFID loop antennas because the magnetic field is substantially stronger over a wider coordinate area in the invention.

Second Embodiment

[0066] The first embodiment describes the case where an antenna is able to generate a uniform magnetic field in one direction along the Cartesian coordinate system. The second embodiment describes an antenna that is able to generate a magnetic field in multiple directions.

[0067] FIG. 11 is a perspective side view of an antenna 300 according to the second embodiment. The antenna 300 comprises of a plurality of electroconductive sheets 320. As from the figure, two electroconductive sheets 320a and 320b are illustrated.

[0068] The electroconductive sheets 320a and 320b are further planar and formed to be uniform in size, with a space formed therein between, as in the first embodiment. It is recognized that the electroconductive sheets 320 are formed to be rectangular such that they have two parallel sets of edges, a first edge set 322, and a second edge set 324, orthogonal to the first edge set 322. Each of the first and second edge sets may be interchangeable with respect to position on the electroconductive sheet 320, so long as the edge sets are orthogonal to each other. The electroconductive sheets 320 are aligned with each other, as in the first embodiment.

[0069] Each set of parallel edges 322, 324 includes one or more feed connection points 330a, 350a and a corresponding number of return connection points 330b, 350b, respectively. As illustrated from FIG. 11, the first edge set 322 has feed connection points 330a and return connection points 330b; the second edge set 324 has feed connection points 350a and return connection points 350b.

[0070] A feed 310 provides current to the feed connection points 330a of a first edge set 322 or the feed connection points 350a of a second edge set 324. Like the first embodiment, an electrical pathway is created between feed points 330a, 350a and return points 330b, 350b, respectively, for each electroconductive sheet 320. Connectors 360 and tuning elements 340 help boost the current between the two electroconductive sheets 320.

[0071] Using feed points 330a, 350a and return points 330b, 350b at orthogonal edges of the electroconductive sheet 320, the feed 310 may distribute current in multiple directions along the X-Y axes. The feed 310 drives current alternatively to produce an H field in the Y-axis direction (hereinafter, the “H.sub.y field current driver 310a”) and to produce an H field in the X-axis direction (hereinafter, the “H.sub.x field current driver 310b”). Electrical current may be alternately switched between the feeds 310 of the feed points 330a, 350a so that only one edge set of a sheet will be supplied with electrical current at a time. In this manner, current will be periodically given to the feed points 330a, 350a so that current is switched in a uniform manner between each electroconductive sheet 320. The speed of switching between feeds 310 may realize an antenna 300 that may quickly generate a magnetic field in multiple directions.

[0072] FIGS. 12A and 12B are top views of the antenna 300 that illustrate the switching of current in the configuration of the second embodiment. From FIG. 12A, current I.sub.x is supplied to the feed points 330a in the +X direction along the X-axis. Like the antenna 100 of the first embodiment, a magnetic field is generated that is perpendicular to the current flow; in this case, the magnetic field H.sub.y is in the +Y direction along the Y-axis.

[0073] FIG. 12B shows the antenna 300 when the feed 310 is switched to drive current I.sub.y to the feed points 350a in the +Y direction along the Y-axis. Continuing the electric circuit, a magnetic field −H.sub.x may be generated in the −X direction along the X-axis.

[0074] The above configuration realizes two electric circuits. The circuits will be active at a time and cycled through in sequence. By periodically switching current feeds to the antenna in the directions along the, e.g., X and Y axes, a magnetic field may be likewise generated for the directions of the Y or X axes, respectively. Thus, it becomes possible to generate a magnetic field in two directions without, e.g., a secondary antenna, thus saving time and resources while expanding the scope of the read zone for the RFID antenna.

[0075] Both the first and second embodiment may be stationary, or may be made as a portable antenna system, such as that shown in FIG. 13. Any portable means, such as wheels or mobile components 570, may be added to the antenna volume. The base station 20 may be part of an overall portable system where a large antenna 500 of the configuration of, e.g., the second embodiment, is placed to generate a greater magnetic field.

Third Embodiment

[0076] As presented, a uniform magnetic field may be generated from the antennas of the first and second embodiment. In order to increase the read zone to be even greater, a method has been employed to stack antennas onto one another so that the H field may be generated in one or more directions, and propagated along the Z-axis. The stacked antenna 600 may be stationary or made portable through mobile components 670.

[0077] To create a stacked antenna 600, multiple antennas of the first and/or second embodiment may be placed onto each other along the Z-axis. Multiple electroconductive sheets 120 for the stacked antenna 600 may be used. However, it is realized that certain redundancy may occur with the electroconductive sheets 120 that adjoin one another in the antenna stack. Therefore, a third embodiment of the invention realizes a stacked antenna any variation of embodiment 1 and/or embodiment 2 that avoids sheet redundancy.

[0078] FIG. 14 is an example of an antenna 600 of the third embodiment, using a layout of the first embodiment for illustrative purposes. The stacked antenna may employ at least three electroconductive sheets for the desired effect to generate multiple H fields. In the figure, four electroconductive sheets 120 are illustrated, however the antenna 600 is not limited to four. The electroconductive sheets 120 are configured so that either the “middle” stacked electroconductive sheets 120b and 120c may act as both a “driving” sheet where current is driven or a “return” sheet where current is returned, i.e., an antenna of the first embodiment (or second embodiment) may be created with electroconductive sheets 120a and 120b, 120b and 120c, and 120c and 120d.

[0079] The feed 610 of the antenna 600 uses a transformer and switches the current supply so as to drive current to the feed points 130a of individual sheets 120. Timing the supply of current in an appropriate manner will utilize each sheet 120 in such a manner as to create multiple magnetic fields. By using the switches, as illustrated in FIG. 14, there is no conflict of current flow between the electroconductive sheets 120.

[0080] It will be understood to a skilled person that the functions achieved by the constituting elements recited in the claims are implemented either alone or in combination by the constituting elements shown in the embodiment and the variation.

INDUSTRIAL APPLICABILITY

[0081] The present invention can be used in the field of RFID tag detection and transmission and for use with RFID systems and systems necessitating the use of an antenna generating a magnetic field.