DE102006057369A1 - Radio frequency identification tag for e.g. identifying metal container, has radio frequency identification scanning antenna with conductor loop that is aligned diagonally or perpendicularly to attachment surface - Google Patents

Abstract

The tag (12) has an attachment surface (13) attached to a surface (18) of an object (14) that is to be identified. A radio frequency identification (RFID) scanning antenna (10) has a conductor loop that is aligned diagonally or perpendicularly to the attachment surface, where the loop for the attachment surface has an angle of about 90 degrees. The loop is arranged on a core (32) made of a fluid reinforcing material or ferrite. A metal layer is arranged between the attachment surface and the coil, where a side having the attachment surface is completely covered by the layer.

Description

The The present invention relates to an RFID tag having a mounting surface for attachment of the RFID tag on a surface of an RFID tag object to be identified and with an antenna that at least has a conductor loop.

Further The invention relates to the use of such an RFID tag for identifying a metallic object and an object that marked with such a label.

RFID tags (also called RFID tags) are used for example for labeling of objects. They are accompanied by an electromagnetic field stimulated suitable properties, so they also generate one electromagnetic field, with which information is transmitted back to the antenna become. The needed Energy is taken from passive RFID labels the electromagnetic field that inspired them.

The For example, RFID tag may contain a fixed value. As well it is known that the RFID tag was transmitted on at pickup Data such as an identification code, responds. One Such RFID label has been in every German passport since autumn 2005 to find.

RFID tags The prior art are usually based on Folieninletts. The Film inlays comprise a plastic film applied to Antenna and an RFID chip.

All RFID labels built according to this principle have a planar Antenna coil. For reading out the RFID labels, these become parallel aligned with the generally annular or frame shaped RFID reader antenna, so that their magnetic field penetrate the antenna coil of the RFID tag can.

The Attachment of such a label on a metallic or brings magnetic surface it comes with that, the flooding of the antenna of the RFID label is deteriorating, as the magnetic field lines of the RFID reader antenna from the metallic or magnetic surfaces to get distracted.

As well becomes the efficiency of the RFID tag induced in the metallic or magnetic surfaces parasitic eddy currents deteriorated.

Farther is due to different substrates, on which an RFID label can be attached, the antenna resonant circuit of the RFID tag detunes, resulting in a significant reduction in reading range of the RFID tag.

It It is therefore an object of the invention to provide an RFID tag, the above longer distances reliable is readable, indifferent on which surface it is mounted.

to solution This object is achieved by an RFID tag having the features of the appended claim 1 proposed.

advantageous Uses of such RFID tag are given in the dependent claims.

advantageous Embodiments of the invention are the subject of the dependent claims.

Accordingly, according to the invention an RFID tag provided with a mounting surface, with which the label on any (inner or outer) surface or surface of a Object can be fastened, which identified by the RFID tag or marked shall be. The RFID tag further has one with at least one Conductor loop provided antenna. According to the invention, the at least one conductor loop the antenna at an angle or substantially perpendicular to the mounting surface.

magnetic field lines become so strong from a magnetic surface of an object distracted that they are almost parallel to the surface. One too parallel conductor loop is only one of low perpendicular to this component of the magnetic field flooded. However, if the conductor loop becomes oblique or nearly vertical the surface arranged, it will turn from the now perpendicular to the Conductor loop extending magnetic field lines flooded.

Thereby The reading range of the RFID tag can be significantly increased.

One such RFID tag according to the invention is suitable for marking a metallic object.

In An advantageous embodiment is in the at least one conductor loop a core of a flux-enhancing Material arranged. This material can be paramagnetic, ferromagnetic or ferrimagnetic. Especially ferrimagnetic material prefers. The flux-enhancing Effect of the material improves the reception characteristics of the antenna, so that the reading range continues to increase.

In a further preferred embodiment the core consists of a ferrite ceramic. These, mostly sintered, Materials improve by their properties, such as low core losses, the reception characteristics of the Antenna continues.

Prefers is provided that the at least one conductor loop in one Area led around the core in which, in essence, the maximum magnetic flux density is that of the RFID reader antenna is generated magnetic field. This let yourself determine experimentally. At this point is the effect of the conductor loop optimal.

Farther For example, it is preferable to make the core flat to the dimensions of the to not overly influence the object to be marked. One with a very flat core provided RFID tag can be almost like the well-known foil labels also very good inside hide flat objects.

It is further preferred that the magnetic permeability number μ ' _{r of} the core should be greater than 4, and preferably between about 25 and 60. Simulation results show usable ranges for permeability numbers μ ' _r above about 25 and above, even with metallic substrates and relatively low operating frequencies - the higher the better. Materials with larger permeability μ ' _r are currently available only with much effort.

Between the mounting surface and the at least one conductor loop is more preferably one Metal layer arranged, preferably such that the fastening surface having Side of the RFID tag completely is covered. The metal layer can influence a shield the antenna power influencing object material something.

The Operating frequency (resonant frequency) of the RFID tag is preferred in the range of 3 MHz to 30 MHz. Particularly preferred is an operating frequency in an ISM band, more preferably at 13.56 MHz. Under operating frequency is to be understood in this context as the frequency with which the RFID tag is excited by the RFID reader antenna, and on the the information exchange takes place.

According to one Another aspect of the invention, an object is provided for the Identification is provided with an RFID tag according to the invention.

Preferably the RFID tag is located in the vicinity of one of the edges of an object surface. This is particularly advantageous because in this area the strength of the even more so from the field generated by the RFID reader antenna is great if the object is metal or the like, the antenna power influencing, materials is constructed or such materials (For example, in a composite material) contains.

Besides that is it is preferable to arrange the RFID tag on the object such that the coil surface of Antenna to the edge is at least obliquely arranged. As special Advantageously, a substantially vertical arrangement has been found.

Around a further increased To achieve reading range, it is preferably provided that the RFID tag is arranged in the middle of an edge of the object.

With The invention or its advantageous embodiments, it is possible a Passive RFID label in the RF frequency range to create, over longer distances (more than 1 meter read range) is reliably readable, no matter on which Surface of the transponder is mounted (metal, plastic, wood, Etc.).

embodiments The invention will be explained in more detail with reference to the accompanying drawings. In this shows:

1 a schematic perspective view of a device for RFID detection with an RFID reader antenna, an at least partially metallic object and an RFID tag;

2a an illustrative perspective view of a conventional RFID label on a non-conductive surface with magnetic field lines of an RFID field;

2 B an explanatory perspective view as in 2a wherein the conventional RFID tag is mounted on a conductive surface;

3 a schematic perspective view of a metallic conductive surface in an RFID field;

4 a diagram of the detuning, which is subject to a conventional RFID label when it is mounted on a conductive surface;

5a a perspective view of an embodiment of an RFID tag according to the invention;

5b a longitudinal cross section through the RFID label from 5a ;

6 a perspective view of another embodiment of an RFID tag according to the invention on a metal sheet;

7 a schematic representation of the induced by the field of the RFID reader antenna eddy currents in a side surface of the metallic object;

8th a representation like in 7 when a ferrite core is disposed on the side surface;

9 a perspective view of a conductive surface with preferred placement points of the RFID tag;

10 a conventional RFID tag with a ferrimagnetic layer;

11 a schematic cross-sectional view of a metallic or magnetic surface with an RFID tag with a vertical antenna, wherein additionally the magnetic fields of the RFID antenna and the eddy currents are located;

12a a schematic cross-sectional view of the amount of magnetic field of an RFID reader antenna;

12b a schematic cross-sectional view of the phase of a magnetic field RFID reader antenna;

13a a schematic cross-sectional view as in 12a in which the influence of a metal container is included;

13b a schematic cross-sectional view as in 12b in which the influence of a metal container is included;

14a a schematic cross-sectional view as in 13a wherein the RFID reader antenna is staggered to the container;

14b a schematic cross-sectional view as in 13b wherein the RFID reader antenna is staggered to the container;

15 a graph of normalized magnetic flux through a ferrimagnetic core placed on the edge of the metal container;

16 a plot of normalized magnetic flux within a ferrimagnetic core placed on the edge of a metal container;

17 a perspective view of a preferred embodiment of the RFID tag according to the invention;

RFID tags Among other things, they are used to uniquely mark objects. Other applications include the monitoring of object parameters, which can be read wirelessly, and on the transport of variable data about the identified object. Other applications are conceivable.

A structure of an arrangement for reading out RFID tags is schematically shown in FIG 1 shown. The RFID reader antenna 10 generates an electromagnetic field from the RFID tag 12 is recorded. The RFID label 12 , on the object to be identified 14 Here is an example of a metal container 14 is shown, then provides an answer to the RFID reader antenna by means of an electromagnetic field 10 , The RFID label 12 is with a mounting surface 13 on a surface 18 of the metal container 14 attached. The RFID label 12 has one to the mounting surface 13 at least obliquely, preferably perpendicular antenna coil (in 1 not shown) with at least one conductor loop 31 (also in 1 not shown) around a ferrite core 32 is wound.

in the Following will be first explains why such a structure is chosen has been.

Currently available RFID labels 52 are mostly based on foil inlays. Such an RFID label 52 is schematic in 2a shown. The foil inlays consist of a plastic foil 54 applied antenna 56 (consisting of an inductor and a capacitor) and an RFID chip (not shown).

to Production of these RFID labels are almost the foil inlays any housing installed, such as in badges for Access control systems, transport containers, foils, paper or stickers.

All RFID labels built according to this principle 52 have a planar antenna coil 58 whose conductor loops are parallel to a mounting surface of the RFID label 58 run. For reading the RFID labels 52 this becomes parallel to the RFID reader antenna 10 aligned so that the antenna coil 58 of the RFID tag of their magnetic field 20 can be flooded.

However, such an RFID label 52 , as in 2 B shown on metallic or magnetic surfaces 18 mounted, effects occur which affect the performance of the RFID tag 52 (ie the reading range) considerably restrict, or the RFID label 52 render inoperative.

This is how the antenna works 56 of the RFID label only minimally from the magnetic field 20 flooded because the magnetic field lines of the RFID reader antenna 10 through the metallic or magnetic surfaces 18 to get distracted.

As in 3 shown, induces the magnetic field 20 the RFID reader antenna 10 additionally in the metallic or magnetic surfaces 18 eddy currents 22 , which in turn is a magnetic field 24 generate and with the magnetic field 20 the RFID reader antenna 10 interfere.

Depending on the background (metal, plastic, etc.) there is also a detuning of the resonant frequency of the antenna 56 of the RFID tag 52 , By way of example, this detuning is dependent on the distance of the RFID tag to a metallic surface in 4 shown.

These Effects are complicated technical measures compensable in principle. For reasons of economy (significant technical effort) and handling (size and weight) However, this is generally dispensed with.

A solution for partial compensation of the first two listed effects (deflection of the magnetic field lines and eddy current effects) could be based on that between the antenna 56 and the magnetic or conductive surface 18 on which the RFID tag is mounted, a ferrimagnetic layer is inserted (see 10 ). Due to the lack of cost-effectiveness, the technical effort involved is not worthwhile in most cases because of the read range, which is only slightly increased to a few centimeters.

alternative could do this RFID labels even at a greater distance (ideally a few centimeters - vacuum or air) to metallic or magnetic surfaces be mounted to the disturbing To reduce influence of the three aforementioned effects. This Approach is usually not practical, because the RFID tag thereby in its structural size considerably increases, the disturbing ones However, effects can not be compensated or not sufficiently, so that the reading range remains substantially the same.

11 shows a metal surface 18 that the magnetic field 20 the RFID reader antenna is exposed. By that of the eddy currents 22 generated magnetic field 24 becomes the magnetic field 20 the RFID reader antenna 10 distracted. The inventively arranged antenna coil 30 of the RFID tag 12 The embodiment described here makes use of this circumstance. Both the effect of the deflection and the eddy current effects can be partially compensated by this arrangement.

Will such an RFID tag 12 on a metallic or magnetic surface 18 mounted, it is compared to the RFID tag 52 of the prior art with an increased reading range reliably readable.

Will be in the antenna coil 30 of the RFID label, a core made of a flux-enhancing material, such as a ferrite ceramic, introduced, so that a further increased reading range can be achieved.

The 5a and 5b such as 6 show concrete embodiments of the RFID labels according to the invention. The antenna coil 30 is with several conductor windings 31 around the ferrite core 32 wound. Next is a capacitance in the form of a capacitor 28 for tuning the operating frequency as well as in the RFDI chip 26 with the object information and the control available. The ferrite core 32 with the components 30 . 26 . 28 is on a metal layer 34 attached to the bottom 35 of the ferrite core 32 completely covered. The bottom 42 forms the attachment surface 13 of the RFID tag.

As in 6 It is shown due to the vertical antenna arrangement and the ferrimagnetic core - ferrite core 32 - in the antenna coil 30 at the RFID label 12 possible, the two disturbing effects of the deflection of magnetic field lines and eddy current effects, caused by the mounting of RFID tags 12 on metallic or magnetic surfaces 18 to compensate better again. The RFID label 12 now has a further increased reading range of a few tens of centimeters.

An effect of frequency detuning the antenna of the RFID tag 12 caused by the different substrates on which the RFID tag 12 Can be mounted through the ferrite core 32 and the vertical arrangement of the antenna coil 30 but not yet compensated. That's what the metal layer is for 34 provided that shields the influences of different object materials on the frequency.

• • Die Antennenspule 30 sollte im Bereich der maximalen magnetischen Flussdichte im ferrimagnetischen Kern 32 platziert sein.
• • Die Unterseite 35 des RFID-Etiketts 12 sollte komplett mit der metallischen Schicht 34 abgedeckt sein.
• • Die Öffnung der vertikal stehenden Antennenspule 30 des RFID-Etiketts 12 sollte möglichst parallel zur Kante 40 der metallischen bzw. magnetischen Fläche 18 ausgerichtet sein und mittig, dicht und vollflächig aufliegend direkt an der Kante 40 der metallischen bzw. magnetischen Fläche 18 montiert sein.

The following factors are relevant to the design and assembly of the HF RFID tag 12 crucial for achieving the maximum reading range on metallic or magnetic surfaces 18 or objects:

• • The antenna coil 30 should be in the range of maximum magnetic flux density in ferrimagne table core 32 be placed.
• • The bottom 35 of the RFID tag 12 should be complete with the metallic layer 34 be covered.
• • The opening of the vertical antenna coil 30 of the RFID tag 12 should be as parallel to the edge as possible 40 the metallic or magnetic surface 18 be aligned and centered, tight and full-surface resting directly on the edge 40 the metallic or magnetic surface 18 be mounted.

• • Ferrimagnetischer Kern 32 mit einer Permeabilität μ' bestimmter Größe und idealerweise mit keinem Verlust μ'' (jeweils im HF-Frequenzbereich).
• • Breite des ferrimagnetischen Kerns 32.
• • Länge des ferrimagnetischen Kerns 32.
• • Höhe des ferrimagnetischen Kern 32.
• • Fläche einer Leiterschleife 31 bzw. einer Windung der Antennenspule 30.
• • Anzahl der Leiterschleifen bzw. Windungen der Antennenspule
• • Durchmesser bzw. Querschnittsfläche des Drahtes bzw. Leiters der Antennenspule 30.
• • Breite der Antennenspule 30 auf dem ferrimagnetischen Kern 32.
• • Position der Antennenspule 30 auf dem ferrimagnetischen Kern 32.
• • Induktivität der Antennenspule 30.
• • Kapazität – Kondensator 28 – zur Einstellung der Induktivität der Antennenspule 30 auf die Arbeitsfrequenz des RFID-Etiketts 12.
• • Verluste (Widerstand) der Antennenspule 30 zur Einstellung der Güte bzw. Bandbreite der Antennen.
• • Induzierte Spannung in der Antennenspule 30.
• • Leistungsaufnahme des RFID-Chips 26.

Depending on the geometric and functional constraints of the application, the following mechanical and electrical design parameters of the RFID tag can be optimized:

• • Ferrimagnetic core 32 with a permeability μ 'of a certain size and ideally with no loss μ "(each in the RF frequency range).
• • Width of the ferrimagnetic core 32 ,
• Length of the ferrimagnetic core 32 ,
• Height of the ferrimagnetic core 32 ,
• • Area of a conductor loop 31 or one turn of the antenna coil 30 ,
• • Number of conductor loops or windings of the antenna coil
• • Diameter or cross-sectional area of the wire or conductor of the antenna coil 30 ,
• • Width of the antenna coil 30 on the ferrimagnetic core 32 ,
• • Position of the antenna coil 30 on the ferrimagnetic core 32 ,
• • inductance of the antenna coil 30 ,
• • Capacitance - Capacitor 28 - To adjust the inductance of the antenna coil 30 on the working frequency of the RFID label 12 ,
• • Losses (resistance) of the antenna coil 30 for setting the quality or bandwidth of the antennas.
• • Induced voltage in the antenna coil 30 ,
• • Power consumption of the RFID chip 26 ,

By customizing one or more of these parameters, the RFID tag 12 be optimally adapted to its respective purpose.

The following is based on the 7 to 9 and 12a to 14b optimal attachment of the RFID labels to the metallic surface 18 , for example, the metal container 14 explained in more detail.

In 12a is the result of a simulation of the magnitude of the magnetic field strength of the magnetic field lines of the uninfluenced magnetic field 20 the RFID reader antenna 10 shown. 12b shows the direction of the magnetic field lines.

The influence of the metal container or metal container 14 on this magnetic field 20 the RFID reader antenna 10 is in the 13a and 13b such as 14a and 14b shown. Here is the view from the top of the reading antenna 10 and the metal container 14 shown.

From the magnetic field strength can be seen that in each case at the edges 40 of the metal container 14 an increase in the magnetic field strength occurs. The deflection of the magnetic field lines on the metallic surface 18 of the metal container 14 is in the representation of the direction of the magnetic field in 13b and 14b to see. It can also be seen that these magnetic field lines directly on the metallic surface 18 always parallel to this.

The result of the simulation of the arrangement 1 in the surface 18 of the metal container 14 induced eddy currents 22 is in 7 shown. The direction of the arrows indicates the current direction of the eddy currents, while the saturation shows the strength of the eddy currents.

It can be seen that due to the asymmetrical arrangement of RFID reader antenna 10 and metal containers 14 the induced eddy currents 22 also an asymmetrical distribution in the surface of the metal container 14 Experienced. Analogous to the distribution of eddy currents 22 the distribution of the magnetic field strength behaves along the surface 18 of the metal container 14 that is in the middle of the edges 40 of the metal container 14 There are very strong increases in the magnetic field strength (see dark mark). These are in accordance with an asymmetrical arrangement of RFID reader antenna 10 and metal containers 14 also different pronounced.

By positioning the ferrimagnetic core material of the RFID tag 12 directly at the elevation of the magnetic field at the middle of the edge 40 of the metal container 14 (please refer 8th ), the strong magnetic field concentration can be cleverly exploited.

From the simulation results arise, as in 9 see, preferred mounting positions 38 in the middle of the edges 40 a metallic or magnetic surface 18 , By attaching the RFID label 12 at these mounting positions 38 the greatest possible reading range can be achieved.

It should be noted that the antenna coil 30 as in 6 parallel and with the opening towards the edge 40 the metallic or magnetic surface 18 is aligned.

15 shows a simulation of the magnetic flux within the ferrimagnetic core material of the ferrite core 32 , The flux values are normalized to the flux at zero centimeter position for an antenna coil without a core.

A increase the permeability μ 'of the ferrimagnetic Nuclear material shows a significant increase in the magnetic flux.

The Simulation results together with the limited availability of ferrimagnetic material with high μ-values at Market allow the use of ferrimagnetic material with values from μ 'between 25 and 60 as the most appropriate appear.

In the 16 The simulation shown also shows that the variation of the length L of the ferrimagnetic core material has a significant influence on the size of the magnetic flux within the ferrimagnetic core 32 Has. It shows that the correct geometry, placement and the right material (value of μ ') of the ferrimagnetic core 32 as well as the skillful placement of the antenna coil 30 on the ferrimagnetic core 32 the optimal utilization of the maximum magnetic flux within the core 32 allow.

In a particularly preferred embodiment, the placement of the antenna coil takes place 30 on the ferrimagnetic antenna coil core ferrite core 32 - according to the in 16 shown values. That is, the position of the antenna coil 30 the position of the maximum of the magnetic flux within the ferrite core 32 equivalent.

17 shows a prototype of an RFID tag 12 with vertical antenna coil 30 ferrimagnetic antenna coil core ferrite core 32 And metallic underlay - metal layer 34 -.

Due to the different boundary conditions of different operating environments of an RFID tag 12 are the above mentioned mechanical and electrical design parameters of the RFID tag 12 adapted in a particularly preferred embodiment of this operating environment.

With these particularly preferred embodiments of a passive RF RFID tag 12 and the described assembly, it is possible on metallic or magnetic surfaces 18 Reading distances of more than 1 meter.

The three disturbing effects described above (magnetic field deflection, eddy current effect and frequency detuning), which affect the performance of RFID tags available to date 52 massively restricted, can hereby be significantly reduced or cleverly exploited.

The For this necessary technical measures are by the enormous Profit at reading distance economically justifiable. To the considerably enlarged reading range come in addition the benefits of the freely usable ISM frequency of 13.56 MHz and the maintenance-free passive RFID tags.

With currently available RFID labels 52 it is not possible to achieve comparable reading ranges. So far, it is necessary to switch to passive RFID tags on non-ISM frequencies (for example in the UHF range at about 868 MHz to 950 MHz) or to use complex maintenance-requiring active RFID tags (with active battery-powered transmitter module) to metallic or magnetic surfaces or objects to reach these reading ranges.

The frequencies in the UHF range at approx. 868 MHz to 950 MHz are not world-wide freely usable ISM (Industrial Scientific and Medical) frequencies. The ISM frequencies are only subject to a minimum of restrictions. After the RFID labels 12 The use of a freely usable frequency band in the high frequency range HF (for example, at a frequency of 13.56 MHz) is a clear advantage.

Active RFID tags are many times more expensive, need to be serviced, and are not available for ISM frequencies compared to passive RFID tags. Therefore, the use of an RFID tag described here 12 especially advantageous.

10

RFID reader antenna

12

RFID tag

13

mounting surface

14

metal containers (Object)

16

nonconductive surface

18

senior surface

20

magnetic field (RFID reader antenna)

22

eddy currents

24

magnetic field (Eddy currents)

26

chip

28

capacitor

30

antenna coil

31

conductor loop

32

ferrite

34

metal layer

35

bottom

36

position the RFID reader antenna

38

preferred mounting positions

40

edge of the metal container

42

bottom metal layer

52

RFID tag (SDT)

54

Plastic film

56

antenna

58

antenna coil

L

Length of the ferrite core

Claims (19)

RFID label ( 12 ) with a mounting surface ( 13 ) for fixing the RFID tag ( 12 ) on a surface ( 18 ) one with the RFID tag ( 12 ) to be identified object ( 14 ) and with an antenna ( 30 ), which has at least one conductor loop ( 31 ), characterized in that the at least one conductor loop ( 31 ) of the antenna ( 30 ) obliquely or substantially perpendicular to the mounting surface ( 13 ) is aligned. RFID tag according to claim 1, characterized in that the at least one conductor loop ( 31 ) to the mounting surface ( 13 ) has an angle of more than 20 °, in particular about 80 ° to 100 °, more preferably about 90 °. RFID tag according to one of the preceding claims, characterized in that in the at least one conductor loop ( 31 ) a core ( 32 ) is arranged from a flux-enhancing material. RFID tag according to claim 3, characterized in that the core ( 32 ) consists of a paramagnetic, ferromagnetic or ferrimagnetic material. RFID tag according to claim 4, characterized in that the core ( 32 ) consists of a ferrite. RFID tag according to one of claims 4 or 5, characterized in that the at least one conductor loop ( 31 ) in an area around the core ( 32 ), in which the core has the maximum magnetic flux density. RFID tag according to one of claims 4 to 6, characterized in that the core ( 32 ) one perpendicular to the mounting surface ( 13 ) measured height, which is substantially smaller than the measured parallel to the mounting surface width and / or length (6). RFID tag according to one of claims 4 to 7, characterized in that for the core ( 32 ) a material having a relative magnetic permeability μ _r 'greater than 4, preferably between about 25 and 60 is used. RFID tag according to one of the preceding claims, characterized in that between the mounting surface ( 13 ) and the at least one conductor loop ( 31 ) a metal layer ( 34 ) is arranged. RFID tag according to claim 9, characterized in that the mounting surface ( 13 ) side ( 35 . 42 ) of the RFID tag ( 12 ) completely from the metal layer ( 34 ) is covered. An RFID tag according to any one of the preceding claims, characterized in that the antenna is connected through a plurality of conductor loops ( 31 ) formed antenna coil ( 30 ), whose coil center axis to the mounting surface ( 13 ) forms an angle in the range of -20 ° to 20 °, preferably parallel to the mounting surface ( 13 ) lies. RFID tag according to one of the preceding claims, characterized characterized in that the operating frequency of the RFID tag in the range from 3MHz to 30MHz, especially at 13.56MHz. RFID tag according to one of the preceding claims, characterized in that the RFID tag ( 12 ) at least one capacity ( 28 ) having. Use of an RFID tag ( 12 ) according to one of claims 1 to 13 for identifying a metallic object ( 14 ). Object ( 14 ) for identification with an RFID tag ( 12 ), characterized in that the RFID tag ( 12 ) is designed according to one of claims 1 to 13. Object according to claim 15, characterized in that the RFID tag ( 12 ) in the vicinity of one of the edges ( 40 ) of a surface ( 18 ) of the object ( 14 ) is arranged. Object according to claim 16, characterized in that the RFID tag ( 12 ) is arranged so that the coil surface of the antenna ( 30 ) to the edge ( 40 ) is arranged at least obliquely, in particular substantially vertically. Object according to one of claims 16 or 17, characterized in that the RFID tag ( 12 ) in the middle of the edge ( 40 ) of the surface ( 18 ) of the object ( 14 ) is arranged. Object according to one of claims 15 to 18, characterized in that the surface ( 18 ) of the object ( 14 ) is formed conductive, in particular made of a metal or such on has.