Patent Description:
RFID tags are tested in their production process in order to detect and mark deficient ones. A deficiency may be detected by measuring the performance of RFID tags. For example measured frequency response indicates sensitivity and RF-bandwidth of an RFID tag. Inline testing poses challenges to accuracy and speed of the production process. In addition, RFID tags are implemented in multiple variations of size, shape and type. While one test equipment may not be suitable for all kinds of RFID tags, it is not reasonable to have optimized test equipment for all of them.

<CIT> discloses an RFID device tester including coupling elements for capacitively coupling a reader to an RFID device to be tested. <CIT> discloses testing RFID tags such that at least two electrodes are configured to capacitively couple to the tag placed in a reading zone.

Aim is to enable inline testing of different kind of RFID tags effectively.

Some embodiments are defined in the dependent claims.

According to a first aspect of the present invention, there is provided a test apparatus as defined in claim <NUM>.

The test apparatus for testing radio frequency identification, RFID, tags, comprises inter alia.

According to a second aspect of the present invention there is provided a method as defined in claim13. Said method is foreseen to test radio-frequency identification, RFID, tags using a test apparatus including a coupling element for providing coupling to an RFID tag to be tested. The method comprises inter alia.

providing an electromagnetic field suitable for coupling with an RFID tag by the field converter.

According to a third aspect of the present invention and defined in claim <NUM>, there is provided use of the test apparatus of the first aspect for testing near field RFID tags.

In the following, embodiments are discussed in more detail with reference to the attached drawings, of which:.

Figures are presented as illustrative examples and embodiments may not be limited solely to the illustrated parts, but modifications may be made under the scope as defined in the claims. Figures that may not fully present the claimed invention, aim to provide better understanding on the context and relating technical field.

There is provided a field converter, which is attachable to and detachable from a test apparatus. The field converter enables modifying electromagnetic field of the test apparatus, and the testing of different type and kind of radio-frequency identification, RFID, transponders or tags using the same test apparatus. An electromagnetic field of the test apparatus is converted to be suitable for the RFID tags, for type of the RFID tags, or for coupling with RFID tags, under the test. An electromagnetic field suitable for coupling with an RFID tag may refer to an electromagnetic field compatible with the RFID tag or coupling with such, or matching with the RFID tag, or enabling pairing with the RFID tag. For suitability and/or conversion one or more of the following parameters may be adapted: field polarization, field concentration, loading based tag detuning, electromagnetic field type, differential field separation, etc..

<FIG> illustrates, by way of an example, a side view of a test system for RFID tags. The test system comprises a housing <NUM>, which is configured to define a volume or space 10a within inner walls of the housing. The housing <NUM> may be electrically conductive. The housing <NUM> has an opening on one side, in <FIG> on its upper side. The opening enables arranging a reading zone or a test zone <NUM> for an RFID tag <NUM>. Plurality of RFID tags may be arranged to be fed to the test zone <NUM> in a continuous manner, e.g. on a roll <NUM>. The housing <NUM> is configured to enclose, within its inner walls, conductive electrodes 11A, 11B. The electrodes 11A, 11B are connected to a coupler <NUM>, for example via wires 12A, 12B. The coupler <NUM> is connected to a communication terminal <NUM>. The communication terminal <NUM> is configured to feed an excitation signal via the coupler <NUM> to the electrodes 11A, 11B and to read the response signal received from the electrodes 11A, 11B via the coupler <NUM>.

An excitation signal, fed by the communication terminal <NUM>, is split into two signals having a phase difference and then fed to the electrodes 11A, 11B, which has effect on the capacitive field inside the housing <NUM> and at the test zone <NUM>. The housing <NUM> is dimensioned such that electric field does not significantly couple to the housing or via the housing between the electrodes 11A, 11B, but rather the electric field is configured to couple to an RFID tag <NUM> at the test zone <NUM>. When the RFID tag <NUM> is capacitively coupled to the electrodes 11A, 11B, the RFID tag <NUM> is activated and configured to provide a response signal. The response signal may be detected by the electrodes 11A, 11B and passed to the coupler <NUM>. The coupler <NUM> is configured to combine the differential response signals and the combined response signal may be read from the communication terminal <NUM>.

<FIG> illustrates, by way of an example, a roll of RFID tags. The RFID tags <NUM> may be arranged on a continuous roll <NUM>, a line or a conveyor belt, for example. The RFID tags <NUM> may be supplied to a test zone (<NUM> of <FIG>) one by one on a roll <NUM> or alike continuous support, which is configured to be conveyed through the test zone (<NUM> of <FIG>). Plurality of RFID tags may be continuously fed to a test zone and tested inline. Two or more continuous feeds of RFID tags may be arranged to be tested in parallel. RFID tags <NUM> having elongated shape may be fed to the reading zone along their longitudinal or transverse direction.

A test apparatus, or a reader, is configured to communicate with an RFID tag via electromagnetic coupling. Electromagnetic field originating from an RFID antenna may be divided into a near field and a far field. A near field may be around a coupling element, e.g. antenna, up to one wavelength (λ), or order of a few centimeters in the ultra high frequency, UHF, range, while a far field may be up to <NUM> meters or order of meters in the case of UHF RFID. The near field and the far field differ in their energies and types of coupling: the near field can make use of inductive coupling or capacitive coupling alone, while in the far field the electric and magnetic field components are always both present and in a known ratio. RFID testing in production line is done predominantly in the near field, therefore the RFID tags to be tested and the used test apparatus should have mutually matching coupling elements, e.g. antenna types, in order to ensure coupling and reliable test results. For example, a far field antenna typically creates an electric field, which will evolve into a combination of electric and magnetic fields in the far field. A far field RFID tag is sensitive to this electric field component, which is used to energize them. Once energized, the RFID tag can reflect back in a modulated manner a portion of the RF energy. In UHF RFID this is referred to as tag backscatter. Small close range tags are sometimes designed to operate using inductive coupling. This type of tag will need a near field reader antenna, or coupling elements, to generate the magnetic field to energize the RFID tag. A magnetic field is created in the near field region in order to allow the test apparatus coupling elements to energize an RFID tag under test. The energized RFID tag may reply by modulating a reflected signal in the magnetic field, which the test apparatus detects and decodes. Practically all tag testing is done at a very short distance from the tested tag, that is, in near filed. This leads to the fact that different test apparatus is required for testing different kind of RFID tags.

<FIG> illustrate, by way of an example, RFID tags. The illustrated RFID tags are some of the near field tag types used in the UHF frequencies. UHF refers to frequencies of <NUM> - <NUM> according to ITU (International Telecommunication Union), and frequencies of <NUM> - <NUM> according to IEEE (Institute of Electrical and Electronics Engineer). The illustrated RFID tags differ among each other in shape such that <FIG> shows a sharp edged loop tag, <FIG> shows a tag having rounded edges and <FIG> shows a round shaped tag. All the RFID tags of <FIG> comprise a chip <NUM> and a loop antenna <NUM>. The RFID tags may be passive. <FIG> illustrates a simple loop tag. <FIG> comprises additional conductors <NUM> external to the loop <NUM>. The conductors may be in form of a wire or a foil, for example. <FIG> comprises an additional conductor <NUM> inside the loop <NUM>. The antenna loop <NUM> with additional conductors <NUM> may have effect of extending range of the antenna. However, with small sized, near field RFID tags, read range may include meters, but the RFID tags still lack far field properties. Generally, a loop antenna represents an inductive antenna, which reacts to magnetic field, which induces a current in the loop of the RFID tag.

<FIG> illustrate only examples of RFID tags, which may have multiple different shapes and constructions. Different kind of RFID tags pose different requirements for inline testing and test apparatus. For example, typically shape and size of a test zone <NUM> of a test apparatus corresponds to a shape and size of the RFID tags <NUM> to be tested. The test zone <NUM> is enabled via the opening of the housing <NUM>. The test zone <NUM> is arranged in the vicinity of the opening of the housing <NUM>. Opening may be larger in areal dimensions than the area of an RFID tag <NUM> to be tested. Location, size and shape of the opening have direct effect to the same of the test zone <NUM>. A conductive plate <NUM> may be deployed in electrical connection with the housing <NUM>, on the opening. The conductive plate <NUM> including an opening, e.g. a central opening, may be selected according to desired shape and dimensions of the test zone <NUM>. The conductive plate <NUM> may be attachable to and detachable from the housing <NUM>. The plate <NUM> may be shaped, e.g. curved, in order to contribute sliding of the roll <NUM> of the RFID tags <NUM> on its surface.

<FIG> illustrate examples of passive RFID tags, which are configured to function in near field. Compared to far field tags, coupling elements or antennas, the illustrated RFID tags are small in size and have shorter range. As discussed in the previous, an antenna, or coupling elements, of a test apparatus shall match antennas, or coupling elements, of the RFID tags to be tested. The matching here may refer to type, size, shape, and generally contribute to coupling between the antennas, or coupling elements.

<FIG> illustrates, by way of an example, a top view of a test apparatus. Electrodes 11A, 11B are enclosed in a housing <NUM>. The housing <NUM> is configured to outline a unitary volume or space 10a. A conductive plate <NUM> is illustrated between dotted lines in <FIG>. The conductive plate <NUM> is placed on top of opening of the housing <NUM> in order to outline a test zone <NUM> for the RFID tags to be tested. The test apparatus is initially configured for far field RFID tags using its conductive plates to capacitively couple to dipole type tags of similar scale. In case near field tags are to be tested, a field converter <NUM> may be introduced. The field converter <NUM> is an attachable/detachable part for the test apparatus. Attachment/detachment of the field converter <NUM> enables testing both near and far field RFID tags without changing the test apparatus. The field converter <NUM> is configured to couple with the electric field, caused by the electrodes 11A, 11B, and to provide a near field for an RFID tag to be tested. Use of a field converter <NUM> enables to modify a capacitive near field of the test apparatus to an inductive near field. This way the same apparatus may be used for different kind of RFID tags. In addition, field converters <NUM> of different designs may be employed to match with further variation of RFID tags to be tested. This provides means for configuring the position, distance, shape and/or size of the electrodes of a test apparatus in order to match with various tag types and shapes.

<FIG> illustrates, by way of an example, a side view of a test apparatus. The test apparatus of <FIG> corresponds to that of <FIG>, and the same parts are referred with the same reference numbers. Electrodes 11A, 11B may be deployed as patterns on a printed circuit board, PCB, which is placed inside the housing <NUM>. The electrodes 11A, 11B, and a field converter <NUM> are within an unitary volume 10a, defined by the inner walls of the housing <NUM>. An RFID tag <NUM> at a test zone <NUM> is a near field RFID tag. It may lack connection to the electrodes 11A, 11B. A distance between outer ends of the electrodes 11A, 11B is configured to be approximately the same as the length of the antenna of the RFID tag <NUM> to be tested. The distance between the outer ends of the electrodes 11A, 11B may be within ±<NUM> % of the length of the antenna of the RFID tag <NUM> to be tested. A near field RFID tag <NUM> might not match with the placement of the electrodes 11A, 11B, since those are planned for bigger far field RFID tags, while the near field RFID tag <NUM> has small dimensions. In addition, inductive coupling is used with near field RFID tags, and the same should be tested in order to provide reliable results. Testing of near field RFID tags is enabled by introducing the field converter <NUM> to the test apparatus. The field converter <NUM> may be placed between the electrodes 11A, 11B and the test zone <NUM>. A horizontal plane of the electrodes 11A, 11B may correspond to a horizontal plane of the PCB. The test zone <NUM>, or a horizontal plane of it, is at a certain distance from the horizontal plane of the electrodes 11A, 11B. A horizontal plane of the field converter <NUM> is placed between the two. The horizontal planes of the electrodes 11A, 11B, the reading zone <NUM> and the field converter <NUM> may be parallel. The electrodes 11A, 11B, are physically separated from the field converter <NUM>. The field converter <NUM> may have legs or touch points, via which it is supported to the PCB or to the housing <NUM>. The field converter <NUM> is arranged on top of the electrodes 11A, 11B such that it at least partly covers both electrodes 11A, 11B, when seen from the test zone <NUM>. This may enhance coupling between the field converter <NUM> and the electrodes 11A, 11B. The field converter <NUM> is placed closer to the reading zone <NUM> than the electrodes 11A, 11B. This may enhance the near field coupling with the RFID tag <NUM> to be tested.

A field converter, or an electromagnetic field converter, may be used with different kind of test apparatuses. A test apparatus may comprise different structure, comprising various kind and/or number of parts and/or coupling elements, for example replacing electrodes 11A, 11B. A coupling element is configured to arrange coupling with tested RFID tags. A coupling element may comprise an antenna, one or more electrodes, a coupler or alike means for coupling, optionally in near field. Coupling elements illustrated in the Figs. and in the description may be replaced by other kind of coupling elements.

<FIG> illustrate, by way of an example, a field converter. Field converter <NUM>, or an electromagnetic field converter, may be of a different shape or size, not limited by the examples illustrated in the <FIG>. A field converter <NUM> comprises an antenna part <NUM>, or a coupling element, and a conductor part <NUM>. The antenna part <NUM> may comprise a dipole antenna. The conductor <NUM> may be arranged to form a magnetic coil. Antenna parts <NUM> may extend towards edge parts of the field converter <NUM>. The conductor <NUM> may be placed in the middle of the field converter <NUM>. The field converter <NUM> is arranged to convert an electric field of an antenna for inductive coupling to a loop tag. The field converter <NUM> may be arranged to convert an electric field of an antenna to a confined and/or focused electric field. The confined and/or focused electric field is suitable for a tag otherwise too small for the antenna. The field converter <NUM> is able to direct the coupling electric field such that it matches with the dimensions and arrangement of the tags to be tested. The field converter <NUM> is arranged to match a test apparatus or setup to the tags to be tested. A field converter illustrated in the <FIG> enables extending the coupling area. In the <FIG> a field converter comprises a partial loop <NUM>, which may be an incomplete loop of three quarters. The loop is placed in the centre of the field converter, which may be arranged to convert a capacitive field to an inductive field. The loop may have elongated form. A field converter may comprise a dipole element configured to couple to an electric field antenna and a conductor, or a loop, for providing an inductive near field. The conductor may be looped back to itself in an elongated fashion. This enables extending the coupling time of a moving tag. The conductor may comprise a form of an open loop, like an elongated letter U or C. The loop may form a pair of conductor rails for a tag <NUM> along its direction of movement, which is illustrated with an arrow <NUM> in the <FIG>. A tag <NUM>, like a near field tag, is illustrated to move in order to pass a test point. The loop of the tag <NUM> is arranged to couple with the loop <NUM> of the field converter. As the tag <NUM> passes over the test point, its coupling to the field converter remains strong and uniform along the loop <NUM> of the field converter. This enables steady coupling to a moving tag, during an extended time and/or range of movement, correspondingly. The time of testing is extended without reducing speed of a production line. Reliable tests may be performed without compromising the production speed. In addition, the test setup or apparatus is adjustable for different kind of tags by use of the field converter.

<FIG> illustrates, by way of an example, a method for testing RFID tags. The method may comprise providing a capacitive coupling by an antenna or a coupling element. The antenna is part of a test apparatus for testing RFID tags. The method comprises coupling to the antenna <NUM> and providing an electromagnetic field suitable for coupling with an RFID tag <NUM>. This is implemented by an electromagnetic field converter, which may be detachably attachable to the test apparatus.

In the previous description and figures the test apparatus is presented with two electrodes. However, one electrode may be present instead, and there may be further different designs and constructions. A test apparatus comprising a far field antenna may be converted for a near field antenna by introducing an attachable/detachable field converter. The field converter is configured to capacitively couple with the far field antenna of the test apparatus and to provide an inductive near field. The far field antenna of the test apparatus and the near field antenna of the field converter are separated, or lack physical contact. The field converter may be detachably attached to the test apparatus between the far field antenna and a test zone. Different kind of field converter shapes and designs may be used, depending, for example, on a model and a size of a test apparatus, location of a far field antenna of a test apparatus, a size of a reading zone, a distance between a far field antenna and a reading zone. The field converter may be a plane-like part including projections, which may aid in coupling with the original antenna of the test apparatus. Further, a field converter shall be matched with the RFID tag to be tested.

Efficiency of testing may be improved by ensuring coupling with the RFID tag to be tested, as discussed in previous. In addition, coupling should be maintained long enough to enable functional testing on a continuously moving production line. RFID tags may continuously propagate for example <NUM>/s, which means that a test time for a single RFID tag may be approximately <NUM>. On production point of view, faster throughput time is desired, thus the test time is seen to decrease. A field converter may enable extending a test zone along the direction of movement, by extending the inductive conductors of the test apparatus, along the running direction of RFID tags. This enables providing extended time for testing, and thus efficiency and reliability to coupling. Good and reliable coupling enable the use of less energy for testing or energizing RFID tags. This enables testing using less power, causing less disturbances and losses, and avoiding the activation of neighbouring tags. Too much power may energize neighbouring tags and thus disturb testing. A lower test power also reduces crosstalk between multiple test systems.

An attachable/detachable field converter, or modifier, enables to modify a field of a test apparatus in accordance to RFID tags to be tested. A single test apparatus may be modified for different type of RFID tags, and may be used for both far field and near field RFID tags. This avoids need of a specific test apparatus for each RFID tag type. A test apparatus suitable for far field RFID tags may be modified for near field or loop tags. The attachable/detachable field converter enables providing the test antenna, or coupling element, physically closer to a reading zone and/or an RFID tag under test. In one embodiment, the field converter is configured to collect a capacitive field of the test apparatus and to transform it into an inductive field, which corresponds to the inductive field of an RFID tag under test. Better coupling is achieved between the test apparatus and the RFID tag under test. The RFID tag, as excited by the inductive field, is configured to cause a response signal in the magnetic field, which is passed on by the field converter as a change in the capacitive coupling. Via the field converter the signal is carried through the capacitive coupling and the electrodes, to the communication terminal, which supplied the excitation signal to the test apparatus. Thus, the field converter requires no changes to controlling the test apparatus connected to the communication terminal or alike control device. The field converter is configured to reciprocally exchange information between an antenna, or a coupling element, of the test apparatus and the RFID tag under test.

The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the previous description, numerous specific details are provided, such as examples of structures, lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention.

Claim 1:
A test apparatus for testing radio frequency identification, RFID, tags on a production line, comprising:
- a test zone (<NUM>) for an RFID tag to be tested,
- a housing (<NUM>) which comprises an opening configured to form at least partly the test zone (<NUM>),
- a coupling element (11A, 11B) configured to provide a coupling with an RFID tag in the test zone (<NUM>),
characterized in that the test apparatus further comprises
- a field converter (<NUM>), which is detachably attachable to the test apparatus, such that the coupling element (11A, 11B) and the field converter (<NUM>) are placed in the housing (<NUM>),
- the field converter (<NUM>) configured to couple with the coupling element (11A, 11B), wherein the field converter (<NUM>) is configured to provide an electromagnetic field suitable for an RFID tag at the test zone (<NUM>),
- wherein the detachably attachable field converter is configured to modify the electromagnetic field of the test apparatus in accordance to the RFID tags to be tested.