DE102017122196B4 - Identification element and a method for identifying associated objects - Google Patents

Abstract

Identification element (100) for identifying an associated object based on a code that can be read out by means of a high-frequency signal (S1), with the following features: a first metal plate (110) and a second metal plate (120), which are arranged parallel to one another to form a to form a cavity (H) therebetween;first electrically conductive pin elements (122) extending between the parallel arranged plates (110,120), each first pin element (122) having a minimum length (L0) which depends on the radio frequency signal (S1); and at least a second electrically conductive pin member (124) extending between the first metal plate (110) and the second metal plate (120), each second pin member (124) being surrounded by first pin members (122) and having a length (L1, L2 , ...) which is smaller than the minimum length (L0) of the first pin elements (122) and is selected so that one or more cavity resonances with resonance frequencies (fres) can be excited by the high-frequency signal (S1), which define the code , which can be read using the high-frequency signal (S1).

Description

The present invention relates to an identification element based on a code that can be read using a radio frequency signal, to a method for identifying associated objects, and in particular to a chipless RFID tag based on frequency tuning of coaxial cavities on a bed of nails.

background

Known RFID tags (Radio Frequency Identification Tag) use a chip that is excited by an alternating electromagnetic field to transmit information in response, with the energy required for this being obtained from the alternating electromagnetic 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. For example, they use 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. However, for higher frequencies, manufacturing tolerances decrease and high-frequency signal losses increase, which in turn leads to an increase in the cost of the end product and lower performance. Also revealed US2017/0187124 A1 a slot array antenna with pin elements of different lengths that protrude into a cavity. US 2013/0015248 A1 reveals a conventional, chipless RFID tag.

Therefore, there is a need for other RFID tags that do not have a chip, are simple in design, easy to manufacture, and operate particularly at 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 that can be read using a high-frequency signal. The identification element includes: 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 parallel to each other (and advantageously electrically isolated from each other) to form a cavity therebetween. The first electrically conductive pin elements extend between the parallel plates (and are optionally connected to either the first metal plate or the second metal plate), with each first pin element having a minimum length that depends on the radio frequency signal. The at least one second electrically conductive pin element 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 that is smaller than the minimum length of the first pin elements and is selected such that one or more cavity resonances with resonance frequencies can be excited by the high-frequency signal and the excitable resonance frequency(s) define a code that can be read using the high-frequency signal.

This excitation can be excited with slots or openings or couplings or with other structures such as a waveguide. Without slots or any other mechanisms (such as a waveguide or horn antenna) the resonances would hardly be excitable. Therefore, one of the metal plates optionally includes a plurality of openings to facilitate penetration of the high-frequency signal into the cavity in a vicinity of the second pin elements.

Optionally, the second pin elements have different lengths, so that the predetermined resonance frequencies can be activated via the openings and the code is defined by forming openings. For example, there is at least a second pin element and an associated resonance frequency that cannot be activated due to a non-existent opening in the environment, so that the code is defined by the location/number of openings.

Optionally, the pin elements form a regular pattern and all the pin elements are fixed 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 arranged laterally between each two second pin elements. The number can also be different in the horizontal and/or vertical direction.

wobei λ eine Wellenlänge des Hochfrequenzsignales ist.Optionally, the following applies to a distance R between the first metal plate and the second metal plate and the minimum length L: $$\text{L}>\text{R}-\raisebox{1ex}{$\mathrm{<figure-callout\; id="4"\; label="\lambda "\; filenames="DE102017122196B4\_0006.png"\; state="\{\{state\}\}">\lambda </figure-callout>}$}\!\left/ \!\raisebox{-1ex}{$4$}\right.,$$

where λ is a wavelength of the radio frequency signal.

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

Compared to conventional RFID tags, an advantage of exemplary embodiments is that the use of shorter wavelengths allows 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 through an associated identification element. The procedure includes the steps:

• - Exciting at least one cavity resonance frequency by a high-frequency signal;
• - Detecting the at least one cavity resonance frequency from a returning high-frequency signal; and
• - Identifying the object using a code defined by the excitable cavity resonance frequencies.

Short description of the characters

• 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 accompanying drawings of the various embodiments, which, however, should not be construed as limiting the disclosure to the specific embodiments, but are intended for explanation and understanding only.

• 1 shows a schematic representation of an identification element according to an exemplary embodiment of the present invention, which can be read by a reading device.
• 2 shows a cross-sectional view through part of the identification element.
• 3A , 3B illustrate a dependence of the resonance frequency on the relative height of the second pin elements and the quality setting.
• 4A , 4B show cross-sectional views through second pin elements of different lengths and the associated change in electric/magnetic field strength.
• 5A , 5B show representations of the metal plates before assembly.
• 6 shows a top 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 provided by a resonator with a high quality factor (Q factor) and receives a high-frequency signal S1 from a reading device 210 via an antenna 180. When reading, the reading device 210 is, for example, at a distance R and is designed to identify the identification element 100 from a returning high-frequency signal S2 by detecting the cavity resonances specific to the identification element 100.

The distance R, over which reliable identification can take place, depends on the frequencies of the cavity resonances, which also determine the high-frequency signal S1 to be used. According to exemplary 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 comprises a first metal plate 110 and a second metal plate 120 arranged parallel thereto and a cavity H formed therebetween. The metal plates 110, 120 do not have to be (but could be) insulated. In the cross section shown, a plurality of first pin elements 122 are arranged along the second metal plate 120, which are electrically conductive and have a minimum length L0. The minimum length L0 is chosen so that a maximum distance d is formed between the respective pin element 122 and the first plate 110, which is smaller than a quarter of the wavelength λ of that High frequency signal S1. The periodicity of the pin elements 122 is, for example, less than or approximately equal to half a wavelength λ (e.g. 0.4*λ) and the width of the pin elements 122 is, for example, approximately ¼ (or smaller; e.g. 0.16*λ) of the wavelength λ used high frequency signal S1.

The first metal plate 110 is, for example, a perfectly electrically conductive plate (PEC; perfect electrical conductor), so that its surface is orthogonal to the electric field strength (the parallel components disappear). The plane to which the pin elements 122 extend is an imaginary magnetically conductive plane (a so-called AMC surface; artificial magnetic conductor), since the electric field strength E between the pin elements 122 is tangential to this plane (no normal component). The choice of the maximum distance d or the minimum length L0 ensures that an alternating electromagnetic field cannot propagate in the cavity H. The first metal plate 110 can, for example, have copper (or silver), while the second metal plate with the pin elements 122 can, for example, have aluminum. Other metals are also possible.

The effect described is in the US 2015/0194718 A1 used to create a waveguide for terahertz frequencies, whereby the wave signal can propagate in a cavity area along an elongated metal track, but cannot get into the nail bed formed by the pin elements 122. The structures described there could be used in further exemplary embodiments to introduce resonances to the side of the cavity into this cavity using a horn as a waveguide.

Embodiments of the present invention utilize such a bed of nails to form a resonator with a large quality factor Q, where the length of the pin elements is locally changed. As long as the pin elements 122 have the minimum length L0, wave propagation or excitation of resonances at the respective positions of the pin elements 122 is not possible. However, if individual pin elements are made shorter, a resonance can be excited locally at the positions there.

3A shows an example of a dependence of the resonance frequency fres on the relative height L1/L0 of the shortened pin elements 124, where the value “1” corresponds to 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. Furthermore, 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 the materials used (e.g. 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 shows the other polarization. The polarizations correspond to the orientation of the magnetic field H that is induced around the shortened pin elements 124. Below the graphs 310, 320 it is shown schematically how the length of the pin elements 124 increases from left to right and at the same time the quality factor Q decreases with the increasing length L1. In addition, it shows 3 that the resonance frequency _fres increases as the pin length L1 decreases, so that with very short pin lengths L1 a very high resonance frequency _fres is achieved and at the same time a high quality factor Q is achieved.

According to exemplary embodiments, it is particularly advantageous if the quality factor Q is very high. A high quality factor Q means that the width of the resonance is small and the signal strength is also very high. This in turn means that a large number of neighboring frequencies can be encoded without them interfering with each other and still being clearly identifiable. Therefore, according to exemplary 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 also be adjusted with the distance or the coupling between the cavity with the second pin element and the slot. Q _u contains the losses due to the limited conductivity of the materials (e.g. copper and aluminum). Q _ext contains the coupling between the cavity and the second pin element and the slot and is therefore highly dependent on the position of the slot. Q ₁ is the quality measured in practice and contains both the material losses and the position of the slot. Mathematically speaking, 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) shown, while in the 4B a longer second pin element 124 (length L1) is shown (L2<L1). In addition, there are 4A , 4B the electromagnetic fields E and H are shown, with the electrical field lines E between the electrically conductive pin elements 122, 124 and the first th 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 induction law and the orientation of the E field is determined by the incident high-frequency signal S1 (eg its wavelength) and the distance between the pin elements 122, 124. In practice, the resonator 100 can be milled or etched from a metal block so that the pin elements 122, 124 are connected to the second metal plate 120, for example.

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

Thus, a second pin element 124 allows a bit of information to be encoded (the presence of a specific resonance frequency _fres ) through its defined height L1. Accordingly, if a plurality of second pin elements 124 are arranged in the nail bed with different heights L1, L2, ..., different resonance frequencies _fres can be encoded.

5A shows an example of 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, ..., so that they correspond to different resonance frequencies _fres . If all four pin elements 124 are present, each with a different length L1, L2, ..., four frequencies f1 _res , f2 _res , f3 _res , f4 _res can be detected as resonance frequencies _fres . However, it is also possible for some of these pin elements 124 to have the same length Lo as the first pin elements 122. In this case, the corresponding resonance frequency is not present (cannot be excited), so that it corresponds to a binary code with a value of 0.

5B shows a top view of the first metal plate 110, which is electrically insulated on the second metal plate 120 from the 5A can be attached. In order to prevent the high-frequency signal from entering the cavity H through the nail bed 5A To facilitate this, openings 115 are provided in the first metal plate 110 near the second pin elements 124. In the 5B Only two slots 115 are indicated as an example.

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

The openings 115 in the first metal plate 110 (in the 6 shown transparently) thus act as receiving antennas 180 (see 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, between two adjacent second pin elements 124 in the exemplary embodiment from the 6 three first pin elements 122 arranged. In further exemplary embodiments, the number of first pin elements 122 arranged between the second pin elements 124 can be changed, although it is advantageous if at least two first pin elements 122 are arranged between two adjacent second pin elements 124.

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

It is understood that the four second pin elements 124 shown represent only an example. In further exemplary embodiments, any number of second pin elements 124 can in principle be present. The number is only limited by the available area, since at least some first pin elements 122 have to be formed between two second pin elements 124.

In addition, if the quality factor Q is chosen high enough, the corresponding resonance frequencies are _fres , as shown in the 7 are shown, are very well localized, so that many frequencies that are close together can be coded. Setting the highest possible quality factor can be used to suppress unwanted reflections (so-called clutter).

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

Another possibility for coding is that the second metal plate 120 has all possible second pin elements 124 (i.e. with all possible different heights). However, whether a cavity is accessible or not is defined by the appropriate formation of slots or openings 115 in the first metal plate 110. This exemplary embodiment offers the advantage that the second metal plate 120 with the nail bed can be designed the same for all identification elements and the coding is carried out by using different first metal plates 110 with different openings 115.

The features of the invention disclosed in the description, the claims and the figures can be essential for the implementation of the invention both individually and in any combination.

Reference symbol list

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

Spacing of metal plates

L0

Minimum length of the first pin elements

L1, L2, ..

Lengths of the second pin elements

fres

Resonance frequency(s)

S1

High frequency signal

S2

returning high frequency signal

Claims (7)

Identification element (100) for identifying an associated object based on a code that can be read out using a high-frequency signal (S1), with the following features: a first metal plate (110) and a second metal plate (120), which are arranged parallel to one another in order to form a to form cavity (H) therebetween; first electrically conductive pin elements (122) extending between the parallel plates (110,120), each first pin element (122) having a minimum length (L0) which depends on the radio frequency signal (S1); and at least one second electrically conductive pin element (124) extending between the first metal plate (110) and the second metal plate (120), each second pin element (124) being surrounded by first pin elements (122) and having a length (L1, L2, ...), which is smaller than the minimum length (L0) of the first pin elements (122) and is selected so that one or more cavity resonances with resonance frequencies ( _fres ) can be excited by the high-frequency signal (S1), which are Define a code that can be read using the high-frequency signal (S1). Identification element (100). 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 a vicinity of the second pin elements (124). Identification element (100). Claim 2 , wherein the second pin elements (124) have different lengths (L1, L2, ...), so that the predetermined resonance frequencies can be activated via the openings (115) and the code is defined by forming the openings (115). Identification element (100) according to one of the preceding claims, wherein the pin elements (122, 124) form a regular pattern and all of the pin elements (122,124) are attached 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) at least two first pin elements (122) are arranged laterally. Identification element (100) according to one of the preceding claims, wherein the following applies to a distance (R) between the first metal plate (110) and the second metal plate (120) and the minimum length (L0): $$\text{Lo}>\text{R}-\raisebox{1ex}{$\lambda $}\!\left/ \!\raisebox{-1ex}{$4$}\right.,$$

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 until 6 with: Exciting at least one cavity resonance frequency ( _fres ) by a high-frequency signal (S1); Detecting the at least one cavity resonance frequency ( _fres ) from a returning high-frequency signal (S2); and identifying the object using a code defined by the excitable cavity resonance frequencies ( _fres ).

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