CA2522449A1 - Method and apparatus for focusing an rfid reader to avoid signal collisions of closely spaced rfid tags - Google Patents
Method and apparatus for focusing an rfid reader to avoid signal collisions of closely spaced rfid tags Download PDFInfo
- Publication number
- CA2522449A1 CA2522449A1 CA002522449A CA2522449A CA2522449A1 CA 2522449 A1 CA2522449 A1 CA 2522449A1 CA 002522449 A CA002522449 A CA 002522449A CA 2522449 A CA2522449 A CA 2522449A CA 2522449 A1 CA2522449 A1 CA 2522449A1
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- CA
- Canada
- Prior art keywords
- reader
- antennas
- main antenna
- tags
- field
- Prior art date
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V15/00—Tags attached to, or associated with, an object, in order to enable detection of the object
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
- G06K7/10019—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers.
- G06K7/10079—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. the collision being resolved in the spatial domain, e.g. temporary shields for blindfolding the interrogator in specific directions
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
- G06K7/10316—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers
- G06K7/10336—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers the antenna being of the near field type, inductive coil
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/12—Supports; Mounting means
- H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
- H01Q1/2208—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems
- H01Q1/2216—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems used in interrogator/reader equipment
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q21/00—Antenna arrays or systems
- H01Q21/06—Arrays of individually energised antenna units similarly polarised and spaced apart
- H01Q21/08—Arrays of individually energised antenna units similarly polarised and spaced apart the units being spaced along or adjacent to a rectilinear path
Abstract
A reader for radio frequency identification tags, and a method for narrowing the electromagnetic field of tags passing before the reader, the reader having: at least one main antenna emitting an electro-magnetic field; counter coil antennas located adjacent to said at least one main antenna, each the at least one main antenna being disposed between two of the counter coil antennas, the counter coil antennas emitting an electromagnetic field opposite in polarity to the electro-magnetic field of the main antenna, wherein the configuration of the at least one main antenna and the counter coil antennas narrows an enabling electromagnetic field experienced by radio frequency identification tags in front of the reader. Multiple readers are possible with synchronization of the clocks of the readers to avoid interference.
Description
METHOD AND APPARATUS FOR FOCUSING AN RFID READER TO AVOID
SIGNAL COLLISIONS OF CLOSELY SPACED RFID TAGS
FIELD OF THE INVENTION
[0001] The present invention relates to radio frequency identification (RFID) readers, and in particular to readers for RFID tags in close proximity to one another.
BACKGROUND
SIGNAL COLLISIONS OF CLOSELY SPACED RFID TAGS
FIELD OF THE INVENTION
[0001] The present invention relates to radio frequency identification (RFID) readers, and in particular to readers for RFID tags in close proximity to one another.
BACKGROUND
[0002] Radio frequency identification tags are used in a variety of industries for a number of reasons. For example, radio frequency identification tags can be used for inventory control and management, asset tracking, quality assurance or other applications known to those skilled in the art.
[0003] Passive radio frequency identification tags are powered by an electro-magnetic field generated by an RFID tag reader (interrogator). Once the tags enter an electro-magnetic field with sufficient energy to power the device, the tags begin to emit information. In one example, the emitted information can include a unique identifier associated with the tag.
[0004] In many applications in which the tags pass before a reader, the tags are set to continuously send the unique identifier, ensuring that the reader receives the unique identifier.
[0005] One problem encountered with the above is the situation in which a series of tags are placed closely together. In this case, multiple tags can enter the electro-magnetic field simultaneously, and thus simultaneously start to transmit their unique identifier.
Due to the collision between the multiple signals simultaneously transmitted, the reader is unable to determine any of the unique identifiers for the tags passing before it. This can be likened to three people continuously screaming their names simultaneously, thus preventing the listener from being able to determine any of the three names being shouted.
Due to the collision between the multiple signals simultaneously transmitted, the reader is unable to determine any of the unique identifiers for the tags passing before it. This can be likened to three people continuously screaming their names simultaneously, thus preventing the listener from being able to determine any of the three names being shouted.
[0006] Various solutions exist for the prevention of tag signal collisions.
Anti-collision tags exist which work on the basis of two-way communication between the reader and the tag. This, however, requires that the tags have both transmitting and receiving capabilities, thus making the tags more expensive.
Anti-collision tags exist which work on the basis of two-way communication between the reader and the tag. This, however, requires that the tags have both transmitting and receiving capabilities, thus making the tags more expensive.
[0007] An alternative solution is to space the tags further apart as they pass by the reader. However, in many practical situations this may not be possible or could lead to delays or excessive space usage.
SUMMARY
SUMMARY
[0008] The present method and apparatus overcome the deficiencies of the prior art by providing a reader that is capable of focusing the electro-magnetic field more narrowly than traditional readers, thus ensuring that only one tag is within a field strong enough to energize the tag. Traditional read-only tags can be used in this scenario, thus enabling a less expensive solution. Further, the size of the field can be widened or narrowed pursuant to a series of variables, and thus the present method and apparatus can be adapted for a multiplicity of applications.
[0009] Traditional readers only contain one antenna. This antenna provides a relatively wide electro-magnetic (EM) field. The applicant has found that by placing an antenna that generates a first polarity electro-magnetic field between antennas that generate an opposite electro-magnetic field, the first polarity electro-magnetic field can be narrowed, thus allowing more precise reading of radio frequency identification tags.
[0010] By varying parameters such as the distance between the antennas, the relative strengths of the positive and negative eiectro-magnetic fields, and the distance that the radio frequency identification tags pass before the antennas, the width of the electro-magnetic field generated and the particular requirements for the application can be configured.
[0011] Further, if a series of positive antennas, placed between the negative antennas, have their clocks synchronized, the present method and apparatus can be used to allow multiple readers in sequence.
[0012] The present application therefore provides a reader for radio frequency identification tags comprising: at least one main antenna emitting an electro-magnetic field; counter coil antennas located adjacent to said at least one main antenna, each said at least one main antenna being disposed between two of said counter coil antennas, said counter coil antennas emitting an electromagnetic field opposite in polarity to said electro-magnetic field of said main antenna, wherein said configuration of said at least one main antenna and said counter coil antennas narrows an enabling electromagnetic field experienced by radio frequency identification tags in front of said reader.
[0013? The present application further provides a method of narrowing an enabling electromagnetic field experienced by a radio frequency identification tag passing before a reader comprising the steps of: generating a first polarity field at a main antenna in said reader; and generating a second polarity field at each of a pair of counter coil antennas, said counter coil antennas being placed adjacent to and on either side of said main antenna, and said second polarity field being opposite in sign to said first polarity field, whereby said electromagnetic field experienced by a radio frequency identification tag passing before a reader is narrowed in width.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present application will be better understood with reference to the drawings in which:
Figure y is a schematic view of a series of tags passing before an antenna in accordance with the prior art;
Figure 2 is a schematic diagram of a preferred embodiment of various RFID tags passing before a series of antennas in accordance with the preferred embodiment of the present invention;
Figure 3 is a diagram showing the electro-magnetic strength that a tag encounters as it passes before a reader in accordance with the prior art;
Figure 4 is a diagram showing the relative strengths of the electro-magnetic fields from the various antennas as observed by an RFID tag;
Figure 5 is a diagram showing the cumulative electro-magnetic field experienced by the tag in figure 4;
Figure 6 is a diagram showing the field power encountered by exemplary tags based on a positive field antenna;
Figure 7 is a diagram showing the field power encountered by exemplary tags based on two negative field antennas; and Figure 8 is a diagram showing the field power encountered by exemplary tags based on a combination of positive and negative field antennas.
DETAILED DESCRIPTION OF THE DRAWINGS
[0015] As indicated above, Figure 1 illustrates a prior art reader where tags pass before the reader. A traditional reader would have between two and seven tags in a zone in one example, depending on the distance between the tags and the reader.
[0016] In order to overcome this disadvantage, it is desirable to focus the electro-magnetic field generated by the reader on a tag placed directly in front of the tag without overlapping a tag that is adjacent to the one being read.
[0017] Reference is now made to Figure 2, Figure 2 illustrates six tags, labelled as 1 to 6. In various scenarios these tags would be passing before the reader, for example, on a linear or circular conveyor. The tags do not, however, need to be conveyed in any particular way for the present apparatus and method, and in some cases it is envisioned that the reader could be moving rather than the tags.
[0018] As illustrated in Figure 2, antennas A, B and C are positioned adjacent to each other. This is not necessarily a linear configuration, but merely indicates that the antennas are positioned in close proximity to each other. In the example of Figure 2, A
generates a positive electro-magnetic field and B and C generate negative electro-magnetic fields. The effect of the positive electro-magnetic field between the two negative electro-magnetic fields is to narrow the eiectro-magnetic field as encountered by a tag.
[0019] Thus, in Figure 1, the electro-magnetic field as labelled by lines 110 and 112 is relatively wide, and in the example of Figure 1 captures tags 2 to 6.
Conversely, in Figure 2, the electro-magnetic field as depicted with lines 210 and 212 is relatively narrow, and only tag 4 is within this electro-magnetic field. Thus only tag 4 will be sending its unique identifier and antenna A will be able to receive this identifier without any collisions occurring.
[0020] As will be appreciated by those skilled in the art, in order to generate positive and negative electro-magnetic fields, antenna A can have windings in the opposite direction to the windings of antennas B and C. One skilled in the art will appreciate that the field is a wave, and when the terms positive and negative are used above they are meant to illustrate that opposite polarity fields are being generated. The positive field will become negative at different points in the current cycle, but it is imperative that antenna A has an opposite polarity field to antennas B and C.
[0021] Further, the present application is not meant to be limited to a reader with only three antennas. The applicant envisions the use of various configurations of antennas, including 3, 5, 7 or more antennas, as explained in more detail below.
[0022] Reference is now made to Figure 3. Figure 3 shows the electro-magnetic field experienced by a tag as it passes a reader. Figure 3 depicts the configuration of Figure 1. As can be seen, a threshold 310 is the minimum electro-magnetic field required in order for a tag to be powered and to send its unique identifier.
Once this threshold is crossed, the tag begins to emit its identifier and does not cease until the threshold is again crossed and the electro-magnetic field is below the threshold value.
As can be seen in Figure 3, the tag is active for a relatively wide area.
[0023] Referring to Figure 4, Figure 4 shows the electro-magnetic fields experienced by a tag passing before the antenna configuration of Figure 2. As can be seen in Figure 4, the electro-magnetic field 402 generated by antenna A is the same as the electro-magnetic field 302 as depicted in Figure 3. Further, the field 404 is the combined field from antennas B and C.
[0024] As is be seen in Figure 5, when the electro-magnetic fields from the positive and the negative fields are added together, the resulting field experienced by the tag is depicted as 502.
[0025] Threshold 510 is the same as threshold 310 from Figure 3 and, as can be seen in a comparison between Figure 5 and Figure 3, the configuration of Figure 2 provides a much narrower electro-magnetic field. Thus, the tag that is passing before the reader A will be activated later and will deactivate earlier, and thereby providing for fewer collisions between signals emitted from adjacent tags.
[0026] The configuration of Figure 2, when combined with other parameters such as the distance between the antennas and the tags being read and the distance between the tags themselves can therefore be engineered to ensure that no collisions occur at a particular point in the tags passing before the antenna, thereby ensuring that for a period the unique identifier stored in the tag is conveyed to the antenna without any collision.
[0027] Reference is now made to Figures 6 to 8. Figure 6 illustrates a specific example of an antenna configuration and tag configuration for use with the above apparatus and method. The example of Figure 6 is merely meant to illustrate the principles of the present invention and is not meant to limit the scope of the invention to the specific diameters, number of windings, field generated, or the power received at each tag.
[0028] Referring to Figure 6, this figure illustrates an exemplary configuration showing a series of 7 tags that are energized with a traditional antenna. fn the example of Figure 6, the antenna and each of the tags are the same size, and are approximately l2mm in length with a diameter of 3mm. The tags are preferably spaced 7mm apart.
[0029] The main antenna in the present example includes 480 turns. Further, in order to be energized, a tag requires a field power of 2000mA/m to be energized.
[0030] In the example of Figure 6, it can be seen that three tags receive a field power that is higher than 2000mA/m. These three tags will be energized if antenna A
is the only antenna, and thus the reader cannot read the signal of any of the tags due to signal collisions.
[0031] Referring to Figure 7, Figure 7 illustrates the field generated by the counter coils. In the example of Figure 7, the antennas with counter coils each have 100 turns and pursuant to the example of Figure 7 generate the negative field power illustrated.
Specifically, the field power of the tag directly in front of the antenna has a negative value of 2400mA/m and a central tag has a negative value of 1100mA/m.
[0032] As illustrated above, the ratio of the number of turns on the coils of the main antenna to the counter coil antennas is 480:100. Other ratios are possible and the ratios may vary based on the configuration and proximity of the tags to each other.
[0033] Figure 8 combines Figures 6 and 7 to provide the main coil and the two counter coils. As will be seen, the net effect of the main coif and the two counter coils is to produce only one tag with a field power higher than 2000mA/m. Specifically, the central tag in the example of Figure 8 has a field power of 7800mA/m, whereas the next tag over has only 1100mA/m field power. Thus the reader can read the central tag without collisions.
[0034] As illustrated in Figures 6, 7 and 8, the tag immediately to the left or right of the tag being read receives a field power of 3500mA/m generated by the central coil and a negative value of 2400mA/m generated by the counter coils, resulting in a net of 1100mA/m per meter. This is less than the 2000mA/m needed by the tags to be read and thus the tag does not generate a signal.
[0035] The above examples require that the tags be placed in one line.
However, it is also possible to read tags using the same three coiled antennas with more than one line of tags. Further, the tags can be aligned in a linear position or in a circular position with one or more lines.
[0036] As indicated above, the present apparatus and method is not limited to three antennas, and five, seven or more antennas could be used. If multiple readers are thus used, there is however the potential for signal interference from adjacent readers.
Thus, as will be realized by those skilled in the art, in order to place more than one reader in the same unit, the clocks of the antenna need to be synchronized. It is therefore possible to create multiple readers with positive and negative coils as long as the clocks of the antenna are synchronized.
[0037] Generally, the results of the field of the central antenna and that of its counter antennas being in opposite phases demonstrates that the resulting field is focused on the center and the values of the field on each side are null. Due to this process, only the tags situated directly in front of the positive electro-magnetic antenna will be powered and communicate. The tags on either side will not have enough energy to power up and communicate.
[0038] As will be appreciated by those skilled in the art, the value of the electro-magnetic field decreases proportional to the distance squared. Thus the tags no longer situated in the center of the antennas are subjected to the negative field of tags B and C
since they are closer to these "counter antennas" than the tags situated in the center that are primarily subjected to the central antenna.
[0039] Further, a tag situated on the sides of the tag being read do experience a positive field derived from the central antenna. However, this central antenna is farther away from the counter antennas and a stronger field results from the nullified field.
[0040] Various alternatives to the above are also possible. For example, the positive EM antenna A does not need to be in line with antennas B or C but could be placed further forward or further back from these antennas in relation to the tags being read.
Other options and configurations would be apparent to those skilled in the art having read the above.
[0041] The above described embodiments of the present application are meant to be illustrative of preferred embodiments and are not intended to limit the scope of the present application. Various modifications, which would be readily apparent to one skilled in the art, are intended to be within the scope of the present application. The only limitations to the scope of the present application are set forth in the claims appended hereto.
[0013? The present application further provides a method of narrowing an enabling electromagnetic field experienced by a radio frequency identification tag passing before a reader comprising the steps of: generating a first polarity field at a main antenna in said reader; and generating a second polarity field at each of a pair of counter coil antennas, said counter coil antennas being placed adjacent to and on either side of said main antenna, and said second polarity field being opposite in sign to said first polarity field, whereby said electromagnetic field experienced by a radio frequency identification tag passing before a reader is narrowed in width.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present application will be better understood with reference to the drawings in which:
Figure y is a schematic view of a series of tags passing before an antenna in accordance with the prior art;
Figure 2 is a schematic diagram of a preferred embodiment of various RFID tags passing before a series of antennas in accordance with the preferred embodiment of the present invention;
Figure 3 is a diagram showing the electro-magnetic strength that a tag encounters as it passes before a reader in accordance with the prior art;
Figure 4 is a diagram showing the relative strengths of the electro-magnetic fields from the various antennas as observed by an RFID tag;
Figure 5 is a diagram showing the cumulative electro-magnetic field experienced by the tag in figure 4;
Figure 6 is a diagram showing the field power encountered by exemplary tags based on a positive field antenna;
Figure 7 is a diagram showing the field power encountered by exemplary tags based on two negative field antennas; and Figure 8 is a diagram showing the field power encountered by exemplary tags based on a combination of positive and negative field antennas.
DETAILED DESCRIPTION OF THE DRAWINGS
[0015] As indicated above, Figure 1 illustrates a prior art reader where tags pass before the reader. A traditional reader would have between two and seven tags in a zone in one example, depending on the distance between the tags and the reader.
[0016] In order to overcome this disadvantage, it is desirable to focus the electro-magnetic field generated by the reader on a tag placed directly in front of the tag without overlapping a tag that is adjacent to the one being read.
[0017] Reference is now made to Figure 2, Figure 2 illustrates six tags, labelled as 1 to 6. In various scenarios these tags would be passing before the reader, for example, on a linear or circular conveyor. The tags do not, however, need to be conveyed in any particular way for the present apparatus and method, and in some cases it is envisioned that the reader could be moving rather than the tags.
[0018] As illustrated in Figure 2, antennas A, B and C are positioned adjacent to each other. This is not necessarily a linear configuration, but merely indicates that the antennas are positioned in close proximity to each other. In the example of Figure 2, A
generates a positive electro-magnetic field and B and C generate negative electro-magnetic fields. The effect of the positive electro-magnetic field between the two negative electro-magnetic fields is to narrow the eiectro-magnetic field as encountered by a tag.
[0019] Thus, in Figure 1, the electro-magnetic field as labelled by lines 110 and 112 is relatively wide, and in the example of Figure 1 captures tags 2 to 6.
Conversely, in Figure 2, the electro-magnetic field as depicted with lines 210 and 212 is relatively narrow, and only tag 4 is within this electro-magnetic field. Thus only tag 4 will be sending its unique identifier and antenna A will be able to receive this identifier without any collisions occurring.
[0020] As will be appreciated by those skilled in the art, in order to generate positive and negative electro-magnetic fields, antenna A can have windings in the opposite direction to the windings of antennas B and C. One skilled in the art will appreciate that the field is a wave, and when the terms positive and negative are used above they are meant to illustrate that opposite polarity fields are being generated. The positive field will become negative at different points in the current cycle, but it is imperative that antenna A has an opposite polarity field to antennas B and C.
[0021] Further, the present application is not meant to be limited to a reader with only three antennas. The applicant envisions the use of various configurations of antennas, including 3, 5, 7 or more antennas, as explained in more detail below.
[0022] Reference is now made to Figure 3. Figure 3 shows the electro-magnetic field experienced by a tag as it passes a reader. Figure 3 depicts the configuration of Figure 1. As can be seen, a threshold 310 is the minimum electro-magnetic field required in order for a tag to be powered and to send its unique identifier.
Once this threshold is crossed, the tag begins to emit its identifier and does not cease until the threshold is again crossed and the electro-magnetic field is below the threshold value.
As can be seen in Figure 3, the tag is active for a relatively wide area.
[0023] Referring to Figure 4, Figure 4 shows the electro-magnetic fields experienced by a tag passing before the antenna configuration of Figure 2. As can be seen in Figure 4, the electro-magnetic field 402 generated by antenna A is the same as the electro-magnetic field 302 as depicted in Figure 3. Further, the field 404 is the combined field from antennas B and C.
[0024] As is be seen in Figure 5, when the electro-magnetic fields from the positive and the negative fields are added together, the resulting field experienced by the tag is depicted as 502.
[0025] Threshold 510 is the same as threshold 310 from Figure 3 and, as can be seen in a comparison between Figure 5 and Figure 3, the configuration of Figure 2 provides a much narrower electro-magnetic field. Thus, the tag that is passing before the reader A will be activated later and will deactivate earlier, and thereby providing for fewer collisions between signals emitted from adjacent tags.
[0026] The configuration of Figure 2, when combined with other parameters such as the distance between the antennas and the tags being read and the distance between the tags themselves can therefore be engineered to ensure that no collisions occur at a particular point in the tags passing before the antenna, thereby ensuring that for a period the unique identifier stored in the tag is conveyed to the antenna without any collision.
[0027] Reference is now made to Figures 6 to 8. Figure 6 illustrates a specific example of an antenna configuration and tag configuration for use with the above apparatus and method. The example of Figure 6 is merely meant to illustrate the principles of the present invention and is not meant to limit the scope of the invention to the specific diameters, number of windings, field generated, or the power received at each tag.
[0028] Referring to Figure 6, this figure illustrates an exemplary configuration showing a series of 7 tags that are energized with a traditional antenna. fn the example of Figure 6, the antenna and each of the tags are the same size, and are approximately l2mm in length with a diameter of 3mm. The tags are preferably spaced 7mm apart.
[0029] The main antenna in the present example includes 480 turns. Further, in order to be energized, a tag requires a field power of 2000mA/m to be energized.
[0030] In the example of Figure 6, it can be seen that three tags receive a field power that is higher than 2000mA/m. These three tags will be energized if antenna A
is the only antenna, and thus the reader cannot read the signal of any of the tags due to signal collisions.
[0031] Referring to Figure 7, Figure 7 illustrates the field generated by the counter coils. In the example of Figure 7, the antennas with counter coils each have 100 turns and pursuant to the example of Figure 7 generate the negative field power illustrated.
Specifically, the field power of the tag directly in front of the antenna has a negative value of 2400mA/m and a central tag has a negative value of 1100mA/m.
[0032] As illustrated above, the ratio of the number of turns on the coils of the main antenna to the counter coil antennas is 480:100. Other ratios are possible and the ratios may vary based on the configuration and proximity of the tags to each other.
[0033] Figure 8 combines Figures 6 and 7 to provide the main coil and the two counter coils. As will be seen, the net effect of the main coif and the two counter coils is to produce only one tag with a field power higher than 2000mA/m. Specifically, the central tag in the example of Figure 8 has a field power of 7800mA/m, whereas the next tag over has only 1100mA/m field power. Thus the reader can read the central tag without collisions.
[0034] As illustrated in Figures 6, 7 and 8, the tag immediately to the left or right of the tag being read receives a field power of 3500mA/m generated by the central coil and a negative value of 2400mA/m generated by the counter coils, resulting in a net of 1100mA/m per meter. This is less than the 2000mA/m needed by the tags to be read and thus the tag does not generate a signal.
[0035] The above examples require that the tags be placed in one line.
However, it is also possible to read tags using the same three coiled antennas with more than one line of tags. Further, the tags can be aligned in a linear position or in a circular position with one or more lines.
[0036] As indicated above, the present apparatus and method is not limited to three antennas, and five, seven or more antennas could be used. If multiple readers are thus used, there is however the potential for signal interference from adjacent readers.
Thus, as will be realized by those skilled in the art, in order to place more than one reader in the same unit, the clocks of the antenna need to be synchronized. It is therefore possible to create multiple readers with positive and negative coils as long as the clocks of the antenna are synchronized.
[0037] Generally, the results of the field of the central antenna and that of its counter antennas being in opposite phases demonstrates that the resulting field is focused on the center and the values of the field on each side are null. Due to this process, only the tags situated directly in front of the positive electro-magnetic antenna will be powered and communicate. The tags on either side will not have enough energy to power up and communicate.
[0038] As will be appreciated by those skilled in the art, the value of the electro-magnetic field decreases proportional to the distance squared. Thus the tags no longer situated in the center of the antennas are subjected to the negative field of tags B and C
since they are closer to these "counter antennas" than the tags situated in the center that are primarily subjected to the central antenna.
[0039] Further, a tag situated on the sides of the tag being read do experience a positive field derived from the central antenna. However, this central antenna is farther away from the counter antennas and a stronger field results from the nullified field.
[0040] Various alternatives to the above are also possible. For example, the positive EM antenna A does not need to be in line with antennas B or C but could be placed further forward or further back from these antennas in relation to the tags being read.
Other options and configurations would be apparent to those skilled in the art having read the above.
[0041] The above described embodiments of the present application are meant to be illustrative of preferred embodiments and are not intended to limit the scope of the present application. Various modifications, which would be readily apparent to one skilled in the art, are intended to be within the scope of the present application. The only limitations to the scope of the present application are set forth in the claims appended hereto.
Claims (17)
1. A reader for radio frequency identification tags comprising:
at least one main antenna emitting an electro-magnetic field;
counter coil antennas located adjacent to said at least one main antenna, each said at least one main antenna being disposed between two of said counter coil antennas, said counter coil antennas emitting an electromagnetic field opposite in polarity to said electro-magnetic field of said main antenna, wherein said configuration of said at least one main antenna and said counter coil antennas narrows an enabling electromagnetic field experienced by radio frequency identification tags in front of said reader.
at least one main antenna emitting an electro-magnetic field;
counter coil antennas located adjacent to said at least one main antenna, each said at least one main antenna being disposed between two of said counter coil antennas, said counter coil antennas emitting an electromagnetic field opposite in polarity to said electro-magnetic field of said main antenna, wherein said configuration of said at least one main antenna and said counter coil antennas narrows an enabling electromagnetic field experienced by radio frequency identification tags in front of said reader.
2. The reader of claim 1, wherein said at least one main antenna and said counter coil antennas are located in a single line.
3. The reader of claim 1 or 2, wherein said reader has multiple main antennas.
4. The reader of claim 3, wherein said multiple main antennas include a single clock.
5. The reader of claim 3, wherein said multiple main antennas each have a clock, said clock for each of said multiple main antennas being synchronized with the clock of the other of the multiple main antennas.
6. The reader of claim 1, wherein each of said at least one main antenna and each of said counter coil antennas includes a coil.
7. The reader of claim 6, wherein said coil of each of said at least one main antenna has more turns than said coil of each of said counter coil antennas.
8. A method of narrowing an enabling electromagnetic field experienced by a radio frequency identification tag passing before a reader comprising the steps of:
generating a first polarity field at a main antenna in said reader; and generating a second polarity field at each of a pair of counter coil antennas, said counter coil antennas being placed adjacent to and on either side of said main antenna, and said second polarity field being opposite in sign to said first polarity field, whereby said electromagnetic field experienced by a radio frequency identification tag passing before a reader is narrowed in width.
generating a first polarity field at a main antenna in said reader; and generating a second polarity field at each of a pair of counter coil antennas, said counter coil antennas being placed adjacent to and on either side of said main antenna, and said second polarity field being opposite in sign to said first polarity field, whereby said electromagnetic field experienced by a radio frequency identification tag passing before a reader is narrowed in width.
9. The method of claim 8, wherein said radio frequency identification tags pass said reader in a linear configuration.
10. The method of claim 8, wherein said radio frequency identification tags pass said reader in a circular configuration.
11. The method of claim 8, wherein said radio frequency identification tags pass said reader in two rows.
12. The method of any of claims 8 to 11, wherein said main antenna and said counter coil antennas are located in a single line.
13. The method of any of claims 8 to 12, wherein said reader has multiple main antennas.
14. The method of claim 13, wherein said multiple main antennas include a single clock.
15. The method of claim 13, wherein said multiple main antennas each have a clock, said method further comprising the step of synchronizing said clock for each of said multiple main antennas with the clock of the other of the multiple main antennas.
16. The method of any of claims 8 to 15, wherein said first polarity field from said main antenna and said second polarity field from said counter coil antennas are generated by coils.
17. The method of claim 16, wherein said coil of said main antenna has more turns than said coil of each of said counter coil antennas.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002522449A CA2522449A1 (en) | 2005-10-06 | 2005-10-06 | Method and apparatus for focusing an rfid reader to avoid signal collisions of closely spaced rfid tags |
| PCT/CA2006/001617 WO2007038858A1 (en) | 2005-10-06 | 2006-10-03 | Method and apparatus for focusing an rfid reader to avoid signal collisions of closely spaced rfid tags |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002522449A CA2522449A1 (en) | 2005-10-06 | 2005-10-06 | Method and apparatus for focusing an rfid reader to avoid signal collisions of closely spaced rfid tags |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2522449A1 true CA2522449A1 (en) | 2007-04-06 |
Family
ID=37905933
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002522449A Abandoned CA2522449A1 (en) | 2005-10-06 | 2005-10-06 | Method and apparatus for focusing an rfid reader to avoid signal collisions of closely spaced rfid tags |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2522449A1 (en) |
| WO (1) | WO2007038858A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5249555B2 (en) * | 2007-11-06 | 2013-07-31 | 株式会社ユニバーサルエンターテインメント | Game device |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5280286A (en) * | 1992-06-12 | 1994-01-18 | Smart Tag Systems, Inc. | Surveillance and identification system antennas |
| JP3760908B2 (en) * | 2002-10-30 | 2006-03-29 | 株式会社日立製作所 | Narrow directional electromagnetic antenna probe and electromagnetic field measuring device, current distribution exploration device or electrical wiring diagnostic device using the same |
-
2005
- 2005-10-06 CA CA002522449A patent/CA2522449A1/en not_active Abandoned
-
2006
- 2006-10-03 WO PCT/CA2006/001617 patent/WO2007038858A1/en active Application Filing
Also Published As
| Publication number | Publication date |
|---|---|
| WO2007038858A1 (en) | 2007-04-12 |
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