NL2026233B1

NL2026233B1 - Tag interrogation system

Info

Publication number: NL2026233B1
Application number: NL2026233A
Authority: NL
Inventors: Jasper Compaijen Paul; Jacques Van Der Burgt Chiron; Gerhard Jaakob Frans Ottokar Johanan Van Lakwijk Reinbrand
Original assignee: Nedap Nv
Priority date: 2020-08-07
Filing date: 2020-08-07
Publication date: 2022-04-13

Abstract

A tag interrogation system (1) for interrogating respective UHF RFID tags in an interrogation zone (IZ) is disclosed herein. The system comprises transceiver means (1 1, 12) configured to induce at least an interrogation field in a first field range including the interrogation zone, and a further field in a range overlapping the first field range in an exclusion zone (EZ) outside the interrogation zone.

Description

Tag interrogation system

BACKGROUND The present invention pertains to a tag interrogation system.

The present invention further pertains to a tag interrogation method.

The present invention still further pertains to a record carrier comprising a computer program with instructions to cause a programmable apparatus to perform a tag interrogation method.

UHF RFID is a powerful technology for stock keeping, as many items can be uniquely identified in a short period of time without having a direct line-of- sight. When an RFID transceiver interrogates an RFID tag, the location of the tag can be estimated based on the received signal strength of the tag and the shape of the antenna used by the transceiver. It is desired that interrogation of tags can be restricted to a well-defined region, for example to distinguish tags of objects that are being transported through a gate from one zone to another zone from tags of objects that are in the neighborhood of the gate. Also when scanning a box with articles it is desired that the tag interrogation process is restricted to the tags in that box while excluding tags of articles in nearby boxes.

Antenna design for UHF RFID is very challenging, since generally low cost and small form-factor are key requirements. Therefore, it is not uncommon for antennas to have relatively strong side-lobes and back-lobes. Furthermore, a well-defined and narrow antenna beam is practically impossible at low cost price and small form-factor.

SUMMARY It is an object of the present invention to provide an improved method and system that enables a rapid determining of a location of an UHF RFID tag. It is an object of the present invention to provide a record carrier comprising a computer program with instructions to enable a programmable device to perform the improved inventory tracking method.

This object is achieved with an improved interrogation system as claimed in claim 1. The claimed invention deliberately uses at least one transceiver and at least one transmitter to deliberately create a tag confusion in zones that should be excluded. Tag confusion refers to a collection of interference phenomena that occur when a tag perceives two or more signals simultaneously with a relatively small difference in power, such that the tag cannot properly demodulate the commands transmitted by a transceiver. The wording transceiver is used herein to denote a component which is capable of transmitting and of receiving. The wording transmitter specifically refers to a component that is capable of transmitting. A transmitter may be part of a transceiver that additionally comprises a receiver as a component for receiving.

For creating tag confusion it suffices that only a transmitter is present to locally prevent tags from responding to commands of the at least one transceiver. In some embodiments the at least one transmitter is part of a further transceiver, so that the further transceiver is also capable to interrogate tags in an area where it has a relatively high transmission power as compared to the at least one transceiver. The interrogation system may comprise any number of additional transmitters to locally prevent tags from responding to commands. Likewise it may comprise any number of additional transceivers to locally interrogate tags and/or to locally prevent tags from responding to commands of other transceivers.

In some embodiments antennas for each transceiver and/or transmitter are provided as mutually disjunct components, which can be positioned independently from each other. This may be preferred in applications where the interrogation zone and the exclusion zone need to be adapted regularly.

In an embodiment, the transmission means comprise a common multi- beam antenna. In an example thereof, the multi-beam antenna is configured to render a respective beam for each of said first and second UHF-RFID reader which beams partly overlap in the exclusion zone. A non-overlapped part of the at least one of the beams is provided in the interrogation zone. In another example thereof, the second UHF-RFID reader is replaced with a transmitter. In this case, the further field is still capable to create confusion in the range where the beams overlap. Although the transmitter replacing the second UHF-RFID reader is not capable of interrogating tags in the non-overlapped part of its beam, it could still be used to transmit commands to the tags therein. The UHF RFID tags may have an activation power threshold value and a confusion power threshold value. The activation power threshold value is a minimal power value required to activate the tags. This threshold value depends on the type of tags used. Modern developments render more sensitive tags possible. Battery powered tags may have a relatively low activation threshold in comparison to passive tags. An interrogation of the UHF RFID tags by the at least one transceiver is impeded if an absolute difference between the power received from the interrogation field and the power received from the further field (or further fields) is less than the confusion power threshold value. With the interrogation system in operation, the interrogation field and the further field respectively have a first spatial transmission power distribution and a second spatial transmission power distribution. The first spatial transmission power distribution has a value greater or equal than the activation threshold power value within the interrogation zone. Furthermore, for positions in the interrogation zone a local value of the first spatial transmission power distribution minus the local value of the second spatial transmission power distribution is greater than the confusion threshold power value. For positions in the exclusion zone the local value of the first spatial transmission power distribution is less than the activation threshold power value and/or the local value of the first spatial power distribution minus the local value of the second spatial transmission power distribution is less than or equal to the confusion threshold power value.

In some embodiments, the transceiver means use mutually different carrier frequencies for inducing the interrogation field and the further field. This is particularly advantageous if components for inducing the interrogation field and for inducing the further field operate independent from each other. Interferences caused by a small frequency difference causes failures in the tag's power circuit. Frequency differences comparable to typical transmission channel distances of about 500-600 kHz cause beats that have similar timing as the tag to reader modulation and thus disturb the operation of the demodulator. Larger differences typically cause the modulation on the reader signal to be disturbed and no longer come through properly. This makes the series of bits an incomprehensible knit.

Using mutually different carrier frequencies is advantageous, in that off- the-shelf RFID-Tag readers can be used to serve as the at least one transceiver and the at least one transmitter. In some situations it may be undesired to operate with two different frequencies. In that case an embodiment is preferred wherein a carrier signal generator of the component for inducing the interrogation field and a carrier signal generator of the component for inducing the further field are mutually synchronized, or wherein the components for inducing the interrogation field and for inducing the further field use a common carrier signal generator. This latter measure is cost-effective.

In some embodiments of the tag interrogation system, the transmission means is configured to modulate the further field in a manner deviating from a communication protocol specified for the tags to be interrogated. The further field may for example be modulated with a random pattern or a blockwave. The presence of a further field with sufficient strength will therewith reduce the number of tags that can be interrogated in the exclusion zone. This measure can be used in embodiments wherein the interrogation field and the further field have a same carrier frequency, but it can also be combined with the measure of using mutually different carrier frequencies.

In again other embodiments of the tag interrogation system the transmission means is configured to issue commands to be executed by the receiving tag so as to interfere with the communication protocol to be executed with the at least one transceiver. In this embodiment, a tag in the exclusion zone may receive and execute commands originating from the at least one transceiver as well as from the at least one transmitter, but the commands from the transmitter prevent that the transceiver can complete a communication session. The commands issued by the transmitter may for example set session flags or change session states to achieve this.

In some embodiments of the tag interrogation system the at least one transmitter is configured to provide the further field as a further interrogation field. In these embodiments the at least one transmitter is part of a further transceiver that is capable to receive responses from the tags. In these embodiments, each of the at least one transceiver and the further transceiver is capable to interrogate tags in a proper interrogation zone, but in a range covered 5 by both the at least one transceiver and the further transceiver an exclusion zone is formed wherein the tags are not capable to decode the commands from any of the transceivers or these commands are mutually non-consistent or conflicting. In some embodiments of the tag interrogation system the transceiver means are accommodated in a common housing. In examples thereof electronic components of the transceiver means that are configured to induce at least an interrogation field and of the transceiver means configured to induce a further field are provided on a common printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the present invention are described in more detail with reference to the drawings. Therein: FIG. 1 schematically shows an embodiment of a tag interrogation system according to the present invention; FIG. 2 schematically shows a further embodiment of a tag interrogation system according to the present invention; FIG. 3A, 3B show exemplary measurement data. DETAILED DESCRIPTION OF EMBODIMENTS.

In the following detailed description numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be understood by one skilled in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, and components have not been described in detail so as not to obscure aspects of the present invention.

FIG. 1 schematically shows a tag interrogation system 1 for interrogating respective UHF RFID tags in an interrogation zone IZ. The system comprises transceiver means 11, 12 configured to induce at least an interrogation field IF in a first field range including the interrogation zone IZ, and a further field FF in a range overlapping the first field range in an exclusion zone EZ outside the interrogation zone IZ. The transceiver means 11, 12 can interrogate UHF RFID tags present in the interrogation zone IZ, whereas the presence of the further field FF in the exclusion zone, where it overlaps the first field range locally disturbs interrogation of tags. Therewith the transceiver means 11, 12 can more efficiently interrogate specifically those tags present in the interrogation zone.

In the embodiment shown in FIG. 1, the transceiver means 11, 12 comprise a first transceiver 11 to induce the interrogation field IF with which it interrogates the tags 30 in the interrogation zone IZ, and at least a transmitter 12 to induce the further field FF, with which tags 30a, 30b, 30c are prevented from responding in the exclusion zone EZ. The transceiver 11 comprises transmitting and receiving facilities so that it can perform a tag interrogation by transmitting tag commands and receiving tag responses, for example as specified by EPC UHF Gen2 Air Interface standard. It is sufficient that the transmitter 12 is present to locally inhibit interrogation. The transmitter 12 may be part of a further transceiver, which additionally comprises receiving facilities, but that is not necessary.

An embodiment comprising such a further transceiver is shown in FIG. 2. In the embodiment shown therein, the transmission means comprise a multi- beam antenna 125 and at least a first and a second UHF-RFID reader 110, 120 that serve as a first and a second transceiver. The multi-beam antenna 125 is provided with a plurality of antenna elements 121, 122 and coupled to the readers 110, 120 via coupling unit 130. In a transmission mode, a first splitter/combiner SC1 splits an output signal of the first reader 110 into a first and a second component C11, C12. Likewise a second splitter/combiner SC2 splits an output signal of the second reader 120 into a third and a fourth component C21, C22. A third splitter/combiner SC3, combines the first component C11 and the fourth component C22 subjected to a phase shift and provides the combined signal to the first antenna element 121. Likewise, a fourth splitter/combiner SC4, combines the third component C21 and the second component C12 subjected to a phase shift and provides the combined signal to the second antenna element 122. Therewith a respective beam B1, B2 is rendered for each of the readers 110, 120. The beams overlap in a central area.

This central area functions as an exclusion zone, wherein tags locally are prevented from responding to either of the readers 110, 120. Also a first interrogation zone IZ1 is present in an area covered by the first beam B1, where it is not overlapped by the second beam B2. Likewise, a second interrogation zone IZ2 is present in an area covered by the second beam B2, where it is not overlapped by the first beam B1. In an alternative embodiment one of the readers, e.g. the second reader 120 is replaced by a mere transmitter.

In that case an additional exclusion zone comes in the place of the second interrogation zone 1Z2. By way of example all components of the system 1 are accommodated in a common housing 15. FIG. 3A, 3B show measurement results obtained with exemplary commercially available tags.

Therein the horizontal axis and the vertical axis of FIG. 3A respectively show the power of the at least one transceiver and the at least one transmitter in dBm.

For this experiment, the curve C1 therein shows the power of the at least one transmitter that is minimally required as a function of the power of the at least one transceiver to suppress the number of tag observations of the at least one transceiver to at most 1 observation per second.

The curve C133 therein shows the power of the at least one transmitter that for this experiment was maximally allowed as a function of the power of the at least one transceiver to enable the at least one transceiver to perform more than 133 tag observations per second.

FIG. 3B is obtained from the same experimental data.

The horizontal axis thereof corresponds to the horizontal axis of FIG. 3A.

In FIG. 3B, the vertical axis however specifies the difference in power between the at least one transceiver and the at least one transmitter at the location of the observed tags.

The curve CT’ therein shows the maximum difference in power between the at least one transceiver and the at least one transmitter for which the number of tag observations of the at least one transceiver is restricted to at most 1 observation per second.

The curve C133’ therein shows the minimum required difference in power between the at least one transceiver and the at least one transmitter that enables the transceiver to perform at least 133 tag observations per second.

For this example it is concluded that the activation threshold power value is in the order of 17 dBm, and that the observation rate at a location is substantially reduced if the local value of the spatial power distribution of the at least one transmitter is not more than about 3 to 5 dB weaker than the local value of the spatial power distribution of the transceiver. If the local value of the spatial power distribution of the at least one transmitter is more than about 10 dB weaker than the local value of the spatial power distribution of the transceiver then the observation rate is substantially unaffected.

In some embodiments battery powered tags may be used, in that case the activation threshold power value may be substantially lower. Also it 1s expected that future externally energized tags will typically be capable to operate at lower power levels.

In summary, the present disclosure provides a tag interrogation method and system for interrogating respective UHF RFID tags in an interrogation zone IZ. In operation at least an interrogation field in a first field range including the interrogation zone IZ, and at least a further field is induced in a range overlapping the transceiver field range in an exclusion zone EZ outside the interrogation zone. As specified herein, various embodiments are possible. For example: The at least one transceiver 11 and the at least one transmitter 12 of the transceiver means 11, 12 may be provided as mutually separate components, as shown in FIG. 1. Alternatively, one or more components may be shared. For example, FIG. 2 shows that the transceiver means 11, 12 have a common multi- beam antenna 125. Also components of both transceiver means are mounted on a common printed circuit board 16. The printed circuit board 16 and the multi- beam antenna 125 are accommodated in a housing 15.

For creating an exclusion zone EZ, it is sufficient if the transceiver means 11, 12 comprise a single transceiver and a single transmitter (which is not capable of receiving). However the system may be extended in that the transmitter is itself part of a receiver or in that further transmitters and receivers are present.

Creating confusion in the exclusion zone can be achieved in various ways. For example by using different carrier frequencies for creating the interrogation field and the further field. Alternatively, or in addition this may be achieved by deliberately modulating the further field in a manner to disturb the interrogation by the interrogation field. One way thereof is to modulate the further field such that the tag is not capable to decode the signals received from the interrogation field. Another way is to deliberately provide further commands via the further field that are decoded by the tags, but that interfere with the interrogation protocol, e.g. by changing sessions or by setting flags.

It is recommended that in operation the timing of the at least one transceiver and the at least one transmitter is synchronized such that they ramp power up and down simultaneously.

In the claims the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single component or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CONCLUSIONS

A tag interrogation system (1) for interrogating respective UHF RFID tags in an interrogation zone (IZ), the system comprising transceiver means (11, 12) configured to generate at least one interrogation field in a first field range comprising the interrogation zone, and generate a further field in a range that overlaps the first field range in an exclusion zone (EZ) outside the interrogation zone.

The tag interrogation system (1) according to claim 1, the transceiver means (11, 12) comprising at least a first transceiver (11) to induce the interrogation field and at least one transmitter (12) to induce the further field.

The tag interrogation system (1) according to claim 1, wherein the transmission means comprises a multi-beam antenna (125) and at least a first and a second UHF RFID reader (110, 120), the multi-beam antenna configured to generate a respective beam (B1, B2) for each of the first and second UHF RFID readers, at least one of the beams providing an interrogation field, which beams partially overlap in the knockout zone (EZ), and wherein a non-overlapping portion of the at least one of said beams is provided in the interrogation zone (IZ).

The tag interrogation system (1) according to any one of the preceding claims, wherein the UHF RFID tags (30) have an activation threshold value and a power confusion threshold value, the activation threshold value being a minimum power value required to activate said tags, wherein interrogation of the UHF RFID tags (30) by the at least one transceiver (11) is hindered if an absolute difference between the power received from the interrogation field and the power received from the other field is less than said confusion threshold, wherein the interrogation field and the further field have a first transmit power spatial distribution (P11 (x,y, z)) and a second transmit power spatial distribution (P12 (x, y, z)) respectively, the first transmit power spatial distribution (P11 (x, y, (z)) having a value greater than or equal to the activation threshold power value within the interrogation zone (IZ), where for each position e (x, y, z) in the interrogation zone (IZ) a local value of the first transmit spatial power distribution (P11 (x, y, z)) minus the local value of the second transmit spatial power distribution (P12 (x, y, z) )) is greater than said confusion threshold and wherein for each position (x, y, z) in the shutdown zone (EZ) the local value of the first spatial transmit power distribution (P11 (x, y, z)) is less than the activation threshold of the power, and/or the local value of the first transmitting spatial power distribution (P11 (x, y, z)) minus the local value of the second transmitting spatial power distribution (P12 (x, y, z)) is less than or equal to the said confusion threshold.

The tag interrogation system (1) according to any one of the preceding claims, wherein the tags are battery powered.

The tag interrogation system (1) according to any one of the preceding claims, wherein the transceiver means (11, 12) use mutually different carrier frequencies for generating the interrogation field and the further field.

The tag interrogation system (1) according to any one of claims 1 to 5, wherein a carrier signal generator of a component for generating the interrogation field and a carrier signal generator of a component for generating the further field are synchronized with each other.

The tag interrogation system (1) according to any one of claims 1 to 5, wherein a component for generating the interrogation field and a component for generating the further field use a common carrier signal generator.

The tag interrogation system (1) according to any one of the preceding claims, wherein the at least one transmitter is configured to modulate the further field in a manner different from a communication protocol specified for the tags to be interrogated.

The tag interrogation system (1) according to any one of claims 1-8, wherein the at least one transmitter is configured to issue instructions to be executed by the receiving tag to interfere therewith with the communication protocol to be executed with the at least one transceiver.

The tag interrogation system (1) according to any one of the preceding claims, wherein the transmission means is arranged to provide the further field as a further interrogation field.

The tag interrogation system (1) according to any one of the preceding claims, wherein the transceiver means are housed in a common housing (15).

The tag interrogation system (1) according to claim 12, wherein electronic components of the transceiver means configured to generate at least one interrogation field and of the transceiver means configured to generate a further field are on a common printed circuit board ( 16) are fitted.

14. A building consisting of a first room (R1), a second room (R2), a wall (W) between the first room (R1) and the second room (R2) and a tag interrogation system (1) according to one of the preceding claims, wherein the interrogation zone (IZ) is provided with a gate (G) for allowing access between the rooms.

A tag interrogation method for interrogating respective UHF RFID tags in an interrogation zone (1Z), the method comprising: inducing at least one interrogation field in a first field range including the interrogation zone; and inducing at least one further field in a range that overlaps the field range of the transceiver in an exclusion zone outside the interrogation zone.

A data carrier comprising a computer program with computer program instructions which, when executed by a programmable device, perform the steps of claim 15.