DE102017122196A1 - Identification element and a method for identifying associated objects - Google Patents

Abstract

An identification element (100) based on a code which can be read by means of a high-frequency signal (S1) in order to identify an associated object, comprises: a first metal plate (110), a second metal plate (120), first electrically conductive pin elements (122) and at least one second electrically conductive pin member (124). The first metal plate (110) and the second metal plate (120) are arranged in parallel with each other to form a cavity (H) therebetween. The first electrically conductive pin members (122) extend between the parallel plates (110, 120) and extend between the first metal plate (110) and the second metal plate (120), each first pin member (122) having a minimum length (L0). which depends on the high frequency signal (S1). The at least one second electrically conductive pin element (124) extends between the first metal plate (110) and the second metal plate (120). Each second pin element (124) is surrounded by first pin elements (122) and has a length (L1, L2, ...) which is smaller than the minimum length (L0) of the first pin elements (122) and is chosen such that one or more cavity resonances with resonant frequencies (f) can be excited by the high-frequency signal (S1) and the excitable resonant frequency (s) (f) define a code that can be read out using the high-frequency signal (S1).

Description

The present invention relates to an identification element based on a code that can be read out by means of a high-frequency signal, to a method for identifying associated objects, and more particularly to a chipless RFID tag based on frequency tuning of coaxial cavities on a nail bed.

background

Known RFID tags (Radio Frequency Identification Tag) use a chip, which is excited by an electromagnetic alternating field to transmit information in response, the energy required for this is obtained from the electromagnetic alternating field. The transmitted information can be used as an identification of objects that carry the RFID tag as a label.

Chipless RFID tags are also known. They use, for example, printed circuits and are based on frequencies below 10 GHz and are disclosed, for example, in: Preradovic, S. and Karnakar, NC: "Chipless RFID: Barcode of the Future"; IEEE Microwave Magazine, 11 (7) 87-97 , For higher frequencies, however, the manufacturing tolerances are reduced and losses of the high frequency signal increase, which in turn leads to an increase in the cost of the end product and a lower performance.

Therefore, there is a need for other non-chip RFID tags that are simple in design, easy to manufacture, and especially for wavelengths in the millimeter range and below.

Summary

At least part of the above problems are solved by an identification element (chipless RFID tag) according to claim 1 and a method for identifying objects according to claim 7. The dependent claims define further advantageous embodiments of the identification element.

The present invention relates to an identification element for identifying an associated object based on a code which can be read out by means of a high-frequency signal. The identification element comprises: a first metal plate, a second metal plate, first electrically conductive pin elements and at least one second electrically conductive pin element. The first metal plate and the second metal plate are arranged in parallel (and advantageously electrically isolated from each other) to form a cavity therebetween. The first electrically conductive pin members extend between the parallel plates (and are optionally connected to either the first metal plate or the second metal plate), each first pin member having a minimum length that depends on the radio frequency signal. The at least one second electrically conductive pin member extends between the first metal plate and the second metal plate (and is optionally connected to one of the metal plates). Each second pin element is surrounded by first pin elements and has a length which is smaller than the minimum length of the first pin elements and is selected so that one or more cavity resonances with resonant frequencies can be excited by the high-frequency signal and the excitable resonance frequency (s) define a code that is readable using the high frequency signal.

This excitation may occur with slots or openings or couplings or with other structures such as e.g. a waveguide are excited. Without slots or any other mechanisms (such as a waveguide or horn antenna), the resonances would be hardly excitable. Therefore, optionally, one of the metal plates includes a plurality of openings to facilitate penetration of the high frequency signal into the cavity in an environment of the second pin elements. Optionally, the second pin members have different lengths such that the predetermined resonant frequencies are activatable across the apertures and the code is defined by forming apertures. For example, there is at least one second pin element and associated resonant frequency that is not activatable due to a lack of an opening in the environment, such that the code is defined by the location / number of openings.

Optionally, the pin elements form a regular pattern and all pin elements are mounted on one of the metal plates and the openings are formed on the other metal plate.

Optionally, at least two first pin elements (or 3 or 4 or more) are laterally arranged between each two second pin elements. The number may also be different in the horizontal and / or vertical direction.

wobei λ eine Wellenlänge des Hochfrequenzsignales ist.Optional applies to a distance R between the first metal plate and the second metal plate and the minimum length L the following: $$\text{L}>\text{R}-\lambda /\mathrm{4,}$$

where λ is a wavelength of the high frequency signal.

In particular, the first pin elements constitute a nail bed which defines a waveguide structure without electrical contact between openings (fabrication holes). The minimum length L is defined by the equation (1) so that wave propagation in the lateral direction is suppressed, while local cavity resonances on the shorter second pin elements are possible (excitable). Their frequency (s) depends on the length of the respective second pin element, so that a coding is possible over different lengths, which can be read out via an excitation by the high-frequency signal and corresponding openings / couplings.

As compared to conventional RFID tags, an advantage of embodiments is that the use of shorter wavelengths allows for more precise localization.

• - Anregen von zumindest einer Hohlraumresonanzfrequenz durch ein Hochfrequenzsignal;
• - Detektieren der zumindest einen Hohlraumresonanzfrequenz aus einem rückkehrenden Hochfrequenzsignal; und
• - Identifizieren des Objektes anhand eines Codes, der durch die anregbaren Hohlraumresonanzfrequenzen definiert ist.

The present invention also relates to a method for identifying at least one object by an associated identification element. The method comprises the steps:

• - exciting at least one cavity frequency by a high frequency signal;
• - detecting the at least one cavity resonance frequency from a returning high frequency signal; and
• - Identifying the object based on a code, which is defined by the excitable cavity resonance frequencies.

list of figures

• 1 zeigt eine schematische Darstellung eines Identifikationselementes gemäß einem Ausführungsbeispiel der vorliegenden Erfindung, das durch einen Lesegerät auslesbar ist.
• 2 zeigt eine Querschnittsansicht durch einen Teil des Identifikationselementes.
• 3A, 3B veranschaulichen eine Abhängigkeit der Resonanzfrequenz von der relativen Höhe der zweiten Stiftelemente und der Einstellung der Güte.
• 4A, 4B zeigen Querschnittsansichten durch zweite Stiftelemente unterschiedlicher Länge und die damit verbundene Änderung der elektrischen/magnetischen Feldstärke.
• 5A, 5B zeigen Darstellungen der Metallplatten vor dem Zusammenfügen.
• 6 zeigt eine Draufsicht auf die Stiftelemente und die lokalisierten Resonanzen unterschiedlicher Polarität.
• 7 zeigt eine mögliche Kodierung von zwei verschiedenen Identifikationselementen und die dazugehörigen Codes.

The embodiments of the present invention will be better understood from the following detailed description and the accompanying drawings of the different embodiments, which should not, however, be construed as limiting the disclosure to the specific embodiments, but for explanation and understanding only.

• 1 shows a schematic representation of an identification element according to an embodiment of the present invention, which is readable by a reader.
• 2 shows a cross-sectional view through a part of the identification element.
• 3A . 3B illustrate a dependence of the resonant frequency on the relative height of the second pin elements and the grade setting.
• 4A . 4B show cross-sectional views through second pin elements of different lengths and the associated change in the electric / magnetic field strength.
• 5A . 5B show representations of the metal plates before assembly.
• 6 shows a plan view of the pin elements and the localized resonances of different polarity.
• 7 shows a possible coding of two different identification elements and the associated codes.

Detailed description

1 shows a schematic representation of an identification element 100 , which is given by a resonator with a high quality factor (Q-factor) and an antenna 180 a high frequency signal S1 from a reader 210 receives. The reader 210 For example, when reading, it is at a distance R and is adapted to be from a returning high frequency signal S2 the identification element 100 by a detection of the for the identification element 100 to identify specific cavity resonances.

The distance R , over which a reliable identification can be made, depends on the frequencies of the cavity resonances, which also includes the high-frequency signal to be used S1 determined, from. According to embodiments, the cavity resonances are at frequencies of more than 10 GHz, for example in a range of 20 ... 50 GHz or even in the terahertz range or millimeter waves from 100 GHz (wavelengths of 3 mm or less).

2 shows a cross-sectional view through a part of the resonator 100 , The resonator 100 includes a first metal plate 110 and a second metal plate arranged parallel thereto 120 and a cavity formed therebetween H , The metal plates 110 . 120 do not have to be isolated (but could) In the cross section shown are along the second metal plate 120 a plurality of first pin elements 122 arranged, which are electrically conductive and have a minimum length Lo. The minimum length Lo is chosen so that between the respective pin element 122 and the first record 110 a maximum distance d is formed which is smaller than a quarter of the wavelength λ from the high-frequency signal S1 , The periodicity of the pin elements 122 is, for example, less than or approximately equal to half a wavelength λ (eg, 0.4 * λ) and the width of the pin elements 122 is, for example, about ¼ (or smaller, for example, 0.16 * λ) of the wavelength λ of the high-frequency signal used S1 ,

The first metal plate 110 is an example of a perfect electrically conductive plate (PEC), so that its surface is orthogonal to the electric field strength (the parallel components disappear). The level, up to the pin elements 122 is an imaginary magnetic conductive plane (a so-called AMC surface, artificial electric conductor), since the electric field strength E between the pin elements 122 tangent to this plane (no normal component). The choice of the maximum distance d or the minimum length Lo ensures that an alternating electromagnetic field is not present in the cavity H can spread. The first metal plate 110 For example, it may comprise copper (or silver), while the second metal plate may include the pin elements 122 may have aluminum as an example. Other metals are also possible.

The effect described is in the US 2015/0194718 A1 used to provide a waveguide for terahertz frequencies, where the wave signal can propagate there in a cavity area along a longitudinally extending metal track, but not into that through the pin elements 122 formed nail bed can get. The structures described there could be used in further embodiments to introduce resonances laterally from the cavity in this cavity with a horn as a waveguide.

Embodiments of the present invention utilize such a bed of nails to form a resonator with a high Q factor Q, the length of the pin elements being changed locally. As long as the pin elements 122 have the minimum length Lo, is a wave propagation or excitation of resonances at the respective positions of the pin elements 122 not possible. However, if individual pin elements are made shorter, a resonance can be locally excited at the local positions.

3A shows an example of a dependence of the resonance frequency _res from the relative height L1 / L0 of the shortened pin elements 124 , where the value "1" is the height with the minimum length L0 (L1 = L0) and the value "0" corresponds to a vanishing length (L1 = 0) of the corresponding pin element 124 represents. Moreover, in the 3A the quality factor Q is shown, which also depends on the length of the pin elements. It goes without saying that the quality also depends on what materials are used (eg aluminum for the second metal plate including the pin elements and copper for the first metal plate).

A first graph 310 shows one of the two possible polarizations, while the second graph 320 the other polarization shows. The polarizations correspond to the orientation of the magnetic field H that around the shortened pin elements 124 is induced. Below the graphs 310 . 320 is shown schematically as the length of the pin elements 124 grows from left to right and at the same time the quality factor Q with the growing length L1 decreases. In addition, the shows 3 that the resonant frequency _res with decreasing pen length L1 increases, so with very short pen lengths L1 a very high resonance frequency _res is reached and at the same time a high quality factor Q is achieved.

According to embodiments, it is particularly advantageous if the quality factor Q is very high. A high quality factor Q results in that the width of the resonance is small and also the signal strength is very high. This in turn means that many adjacent frequencies can be encoded without obstructing each other and still being uniquely identifiable. Therefore, according to embodiments, the individual resonators are very weakly coupled to the cavity and should in particular have the highest possible quality factor Q.

3B illustrates how the quality can be adjusted with the distance or the coupling between the cavity with the second pin member and the slot. Q _u Contains the losses due to the limited conductivity of the materials (eg copper and aluminum). Q _ext contains the coupling between the cavity and the second pin member and the slot and is therefore highly dependent on the position of the slot. Q ₁ is the measured quality in practice and includes both the material losses and the position of the slot. Mathematically, the following applies: $$\frac{1}{Q_l}=\frac{1}{Q_{ext}}+\frac{1}{Q_u},$$

4A and 4B show cross-sectional views through pin elements 124 with shorter lengths L1 . L2 (second pin element). In the 4A is a very short second pin element 124 (Length L2 ) while in the 4B a longer second pin element 124 (Length L1 ) (L2 <L1). Also, in the 4A . 4B the electromagnetic fields E and H shown, wherein the electric field lines E between the electrically conductive pin elements 122 . 124 and the first metal plate 110 extend and the magnetic field lines H extend perpendicular to the plane of the drawing. The orientation of the H-field results from the direction of the E-field according to the known law of induction and the orientation of the E-field is determined by the incident high-frequency signal S1 (Eg its wavelength) and the distance of the pin elements 122 . 124 certainly. In practice, the resonator 100 be milled or etched from a metal block so that the pin elements 122 . 124 eg with the second metal plates 120 are connected.

From the 4B It can be seen that the inductance of the longer pin element 124 is bigger, so there is a stronger magnetic field H is excitable while for the shorter pin element 124 in the 4A only a very weak magnetic field is excitable. This causes the resonance frequency _res for the shorter pin element 124 from the 4A is correspondingly higher than for the longer pin element 124 from the 4B ,

Thus, a second pin element allows 124 through its defined height L1 encode a bit of information (the presence of a particular resonant frequency _res ). If accordingly several second pin elements 124 in the nail bed with different heights L1 . L2 , ..., can have different resonance frequencies _res be encoded.

5A shows by way of example a nail bed of first pin elements 122 on the second metal plate 120 in which four second pin elements 124 are formed. The second pin elements 124 have different lengths L1 . L2 . , .. on, so they have different resonance frequencies _res correspond. If all four pin elements 124 each with a different length L1 . L2 . , .. are present, can have four frequencies f1 _res . f2 _res . f3 _res . f4 _res as resonance frequencies _res be detected. However, it is also possible that some of these pin elements 124 an equal length L0 have like the first pin elements 122 , In this case, the corresponding resonant frequency is absent (not excitable), giving it a binary code of one value 0 equivalent.

5B shows a plan view of the first metal plate 110 electrically insulated on the second metal plate 120 from the 5A attachable. To prevent the penetration of the high-frequency signal into the cavity H which comes out of the nail bed 5A is given to facilitate, are in the first metal plate 110 openings 115 near the second pin elements 124 intended. In the 5B are exemplary only two slots 115 indicated.

6 shows schematically as the openings 115 as slots in the vicinity of the respective second pin elements 124 to be ordered. The circles around the second pin elements 124 make the magnetic field H with the two possible polarizations. Depending on how the electric field lines run there, the magnetic field can H be excited in a clockwise or counterclockwise direction.

The openings 115 in the first metal plate 110 (in the 6 transparent) thus act as receiving antennas 180 (please refer 1 ) between the resonators and the free space. The position of the openings 115 is chosen so that the overall quality factor of the structure is as high as possible.

So that the cavity resonances on the second pin elements 124 do not inhibit each other, are between two adjacent second pin elements 124 in the embodiment of the 6 three first pin elements 122 arranged. In other embodiments, the number of first pin elements 122 between the second pin elements 124 are arranged, but it is advantageous if at least two first pin elements 122 between two adjacent second pin elements 124 are arranged.

The 7 shows a possible coding of two different identification elements: with a first code 710 and a second code 720 , There are a total of four resonance frequencies f1 _res . f2 _res . f3 _res . f4 _res coded. A first resonance frequency f1 _res of about 38.2 GHz, a second resonant frequency f2 _res at a frequency of about 38.7 GHz, a third resonant frequency f3 _res of about 39 GHz and a fourth resonant frequency f4 _res of about 39.45 GHz. In the identification element to the first code 710 are all resonant frequencies f1 _res . f2 _res . f3 _res . f4 _res excitable while in the identification element to the second code 720 only the second to fourth resonant frequency f2 _res . f3 _res . f4 _res are excitable. Thus, the first code represents 710 an encoding of 1111, while the second code represents an encoding of 0111.

It is understood that the four shown second pin elements 124 just an example. In further embodiments, in principle any number of second pin elements 124 to be available. The number is limited only by the existing area, as between two second pin elements 124 at least some first pin elements 122 are to be trained.

In addition, when the quality factor Q is set high enough, the corresponding resonance frequencies are _res as they are in the 7 are very well localized, so that very many densely spaced frequencies can be encoded. The setting of the highest possible quality factor can be used to suppress unwanted reflections (so-called clutter).

Essential aspects of embodiments of the present invention may be summarized as follows. Coaxial cavities in a nail bed are used to identify identification elements 100 form, with the height L1 the second pin elements 124 each defining the resonant frequency of the cavity and used to encode different RFID codes in the frequency domain. The code can thereby determined by the presence or absence of a cavity and / or a coupling mechanism, such as the apertures (slots) 115 or other rectangular waveguide.

Another way to make a coding is given by the fact that the second metal plate 120 all possible second pin elements 124 (ie with all possible different heights). However, whether a cavity is accessible or not, is by the corresponding formation of slots or openings 115 in the first metal plate 110 Are defined. This embodiment offers the advantage that the second metal plate 120 can be made the same with the nail bed for all identification elements and the coding by the use of different first metal plates 110 with different openings 115 is carried out.

The features of the invention disclosed in the description, the claims and the figures may be essential for the realization of the invention either individually or in any combination.

LIST OF REFERENCE NUMBERS

100

identification element

110.120

metal plates

122

first electrically conductive pin elements

124

at least one second electrically conductive pin element

H

cavity

R

Distance of the metal plates

L0

Minimum length of the first pin elements

L1, L2, ..

Lengths of the second pin elements

_res

Resonant frequency (s)

S1

RF signal

S2

returning high frequency signal

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2015/0194718 A1 [0019]

Cited non-patent literature

• Preradovic, S. and Karnakar, N.C .: "Chipless RFID: Barcode of the Future"; IEEE Microwave Magazine, 11 (7) 87-97 [0003]

Claims (7)

An identification element (100) for identifying an associated object based on a code readable by means of a high-frequency signal (S1), comprising: a first metal plate (110) and a second metal plate (120) arranged parallel to one another about a first metal plate (110) Cavity (H) to form therebetween; first electrically conductive pin members (122) extending between the parallel plates (110, 120), each first pin member (122) having a minimum length (L0) that depends on the high frequency signal (S1); and at least one second electrically conductive pin member (124) extending between the first metal plate (110) and the second metal plate (120), each second pin member (124) surrounded by first pin members (122) and a length (L1, L1). L2, ...), which is smaller than the minimum length (L0) of the first pin elements (122) and is selected such that one or more cavity resonances with resonant frequencies (f _res ) can be excited by the high frequency signal (S1) Define code which can be read using the high-frequency signal (S1). Identification element (100) according to Claim 1 wherein one of the metal plates (110) has a plurality of openings (115) to facilitate penetration of the high frequency signal (S1) into the cavity (H) in an environment of the second pin elements (124). Identification element (100) according to Claim 2 wherein the second pin members (124) have different lengths (L1, L2, ...) such that the predetermined resonant frequencies are activatable via the apertures (115) and the code is defined by forming the apertures (115). An identification member (100) according to any one of the preceding claims, wherein the pin members (122, 124) form a regular pattern and all of the pin members (122, 124) are mounted or milled or etched on one of the metal plates (120) and the openings (115) on the other Metal plate (110) are formed. Identification element (100) according to one of the preceding claims, wherein between each two second pin elements (124) laterally at least two first pin elements (122) are arranged. Identification element (100) according to one of the preceding claims, wherein for a distance (R) between the first metal plate (110) and the second metal plate (120) and the minimum length (L0) the following applies: $$\text{Lo}>\text{R}-\lambda /\mathrm{4,}$$

where λ is a wavelength of the high frequency signal (S1). Method for identifying at least one object by an associated identification element (100) according to one of Claims 1 to 6 with: exciting at least one resonant cavity frequency (f _res ) by a high frequency signal (S1); Detecting the at least one cavity resonance frequency (f _res ) from a returning high frequency signal (S2); and identifying the object based on a code defined by the excitable cavity resonance frequencies (f _res ).

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