DE102012105437A1 - RFID transponder with an inverted F-antenna - Google Patents

Abstract

The invention is a device that is needed to reduce the footprint of an RFID transponder having an inverted F antenna. The frequency response should be maintained. The unavoidable loss of coverage should be kept as low as possible. Thus, the so-called "electrical length" should be maintained and the mechanical length of the RFID transponder should be reduced with the lowest possible level loss. This is achieved in that the distance between the base surface and the antenna surface varies meandering over the length of the base body of the RFID transponder.

Description

The invention relates to an RFID transponder according to the preamble of the independent claim 1.

Such RFID (Radio Frequency Identification) transponders are used for the electronic identification of objects. In the RFID transponder, for example, an identification number as well as further information for the corresponding object can be stored. By means of an associated reader (RFID reader), the information can be read from the RFID transponder and, if necessary, also written into it.

State of the art

In the prior art is from the document US20060145927A1 a corresponding RFID transponder with a "PIFA" (Planar Inverted F-Antenna), in particular for mounting on a metallic surface known. For many applications, however, the space requirement of such an antenna is too large.

From the pamphlets WO93 / 12559 and WO96 / 27219 a PIFA antenna is known in whose antenna surface a meander-shaped structure is incorporated, wherein the antenna surface is parallel to the base surface. This maintains the electrical length of the antenna for receiving appropriate wavelengths while reducing the physical length of the antenna. However, such an antenna has the disadvantage that due to the smaller antenna area only a lower power is absorbed, which significantly reduces the range of an RFID transponder having such an antenna.

task

The invention is therefore based on the object to reduce the footprint of an RFID transponder of the type mentioned above the prior art, while maintaining the frequency response and the largest possible range of the RFID transponder upright.

In other words, an RFID transponder with an inverted F antenna is to be specified, which has the smallest possible footprint and at the same time is suitable to receive signals having the largest possible wavelength, with the highest possible level.

This object is achieved with an RFID transponder of the type mentioned by the features of the characterizing part of the independent claim 1.

Advantageous embodiments of the invention are specified in the dependent subclaims.

The invention is a device that is needed to reduce the footprint of an RFID transponder having an inverted F antenna. The frequency response should be maintained. The unavoidable loss of coverage should be kept as low as possible. Thus, the so-called "electrical length" should be maintained and the mechanical length of the RFID transponder should be reduced with the lowest possible level loss. This is achieved in that the distance between the base surface and the antenna surface varies meandering over the length of the base body of the RFID transponder.

An advantage of the present invention is that the dimensions of the RFID transponder while maintaining its electrical length and thus its frequency response, reduce. Thus, an inventive RFID transponder, for example, when mounting on a metal body requires a smaller area.

Another advantage is that the base body can be manufactured in an injection molding process with little effort, and that the antenna surface and / or the base surface and / or their electrically conductive connection by means of the "molded interconnect device" (MID) technology by appropriate Coating this base body can also be produced with relatively little effort and with correspondingly low cost.

On the one hand, it is advantageous to form the electrically conductive connection of the antenna surface and the base surface in the form of a connection surface, because such a connection surface can be realized simply and therefore inexpensively by means of the MID technology.

On the other hand, it is advantageous to realize the electrically conductive connection of the antenna surface and the base surface in the form of a plurality of vias arranged in a row, because by their number and arrangement the impedance of the antenna can be selectively tuned to the respective requirements.

Moreover, it is advantageous that the base body further has a special plated-through hole, because it enables the electrical connection of the RFID chip arranged on the antenna surface both on the base surface and on the other hand on the antenna surface. In this case, the RFID chip has at least two contacts, namely a first contact and a second contact, wherein the first contact is connected via the feed point to the antenna surface and wherein the second contact is connected by means of the special via via a connection point to the base.

In this case, it is furthermore advantageous in terms of manufacturing technology to arrange the RFID chip on the antenna surface, because this facilitates easy handling during the connection, in particular when soldering the first contact of the RFID chip to the feed point of the antenna surface and the second contact of the RFID chip facilitates the special via. It is also advantageous to arrange the RFID chip in a region of the antenna surface, which has the smallest possible distance from the base, because the RFID chip is thereby mechanically well protected and the special via can be made relatively short.

In an advantageous embodiment, the RFID transponder has a housing which encloses an arrangement comprising the base body with the antenna surface and the base surface and the RFID chip in all geometric directions, because this arrangement is protected from harmful environmental influences. In particular, this applies if the housing is hermetically sealed, because then no moisture, for example in the form of humidity, can penetrate into the housing.

It is also advantageous if the housing consists of an electrically insulating material, because this ensures that the RFID transponder is installed electrically insulated, i. optionally has no electrical contact with a metal body on which it is mounted. Thus, an exclusively electromagnetic coupling between the RFID transponder and the metal body is guaranteed.

As an alternative to the use of a housing, the said arrangement can also be surrounded by a lacquer or a lacquer-like seal, in particular hermetically and / or electrically insulating. For this purpose, the paint or varnish-like seal may consist of an electrically insulating material.

The use of a paint over a housing has the advantage of low manufacturing costs and small dimensions. The advantages of a housing contrast, in its mechanical robustness.

For the production of large quantities, it is particularly advantageous if the MID-capable material is suitable for the so-called "two-shot molding" method, because then in particular the plated-through holes can be realized in this way simply and therefore inexpensively. Namely, in a first injection molding process with a first part of an injection mold having a first associated first pin, the base body can be produced with a passage opening and in a second injection molding process with a second part of the injection mold with an activatable material, a corresponding layer can be applied at the edge of the passage opening , For this purpose, the second part of the injection mold on a second pin, which has a smaller diameter than the first pin and which passes through the through hole during the second injection process. The activatable material is intended to be activated first and then coated electrically conductive during purging with a corresponding electrically conductive material.

In this case, the first and the second part of the injection mold can be arranged oppositely directed each other. The injection molding tool can then rotate the injection mold between the two injection molding processes in each case by 180 °, which gestat a rational production gestat.

For smaller quantities and forms of the base body which are designed to be as flexible as possible, it is advantageous if the MID-capable material is suitable for the so-called "laser direct structuring" (LDS) method is. In this case, areas of this material are activated by a laser to be later targeted to be provided with an electrically conductive layer. Through the LDS method, the design of the base body and the conductive layers deposited thereon can be changed with little effort, eg, for test purposes or for short-term design adjustments by merely changing the path of the laser for the activation process, eg reprogramming the movement of a robotic arm , So that the passage opening can be activated by the laser, it must be funnel-shaped, ie hourglass-shaped executed at both ends, which requires an additional effort in the production. This production form is therefore particularly well suited for RFID transponders whose height, ie their distance between antenna surface and base, is relatively low, because this reduces the size of the passage opening in the antenna surface. This manufacturing method is therefore well suited to the implementation of that design, which provides for the use of said electrically conductive connection surface, because this only a single via, namely the special feedthrough is necessary.

Thus, it is particularly advantageous for this reason, if the passage opening and thus also the special feedthrough are made as short as possible. The special plated-through hole should thus advantageously begin at a location of the meander-shaped antenna surface, which has the smallest possible distance to the base surface.

In order to keep the connection distance from the RFID chip to the feed point low, it may also be advantageous to arrange the feed point in a region of the antenna surface which has as small a distance as possible from the base surface.

It is particularly advantageous if the RFID transponder is arranged on a metal body, because this improves the antenna properties. In particular, this applies if the metal body is significantly larger than the RFID transponder, so that it, for example at least in one direction parallel to the base surface at least twice the dimension, e.g. at least twice the length, owns.

Advantageously, the housing has at least on one side a flat inner surface and a flat outer surface. Then, the base surface of the base body may be disposed on the flat inner surface of the housing. The metal body may have at least one planar area on at least one side, and the RFID transponder may be arranged with the flat outer side of its housing on the planar area of the metal body.

With the wall thickness of the housing or the necessary strength of the electrically insulating lacquer layer thus the distance of the base of the base body to the surface of the metal body can be determined and should be as low as possible according to the respective technical specifications. For example, this distance may be less than 2 mm, preferably less than 1.5 mm and in particular less than 1 mm in order to enable a suitable electromagnetic coupling between the RFID transponder and the metal body.

It is particularly advantageous if the metal body is a metal sheet, because this allows the antenna effect to be realized with a low material expenditure and correspondingly low weight. The dimensions of the metal sheet should be significantly larger than the dimensions of the RFID transponder. For example, the metal sheet should be at least twice as large as the base area of the RFID transponder in at least one direction.

embodiment

An embodiment of the invention is illustrated in the drawing and will be explained in more detail below. Show it:

1a a prior art RFID transponder in an oblique plan view;

1b the electrical components of this RFID transponder in a schematic cross-sectional view;

2a a prior art meander-shaped structured antenna surface in a plan view;

2 B this antenna surface with a base surface and a connection surface in an oblique plan view;

2c the antenna surface having the base surface and the connection surface, and a dielectric base body in an oblique plan view;

3a a first RFID transponder according to the invention in an oblique plan view;

3b the first RFID transponder in a cross-sectional view;

3c the presentation 3b with some specific height terms;

4a a second RFID transponder according to the invention in an oblique plan view;

4b the second RFID transponder in a cross-sectional view;

4c the second RFID transponder in modified form;

5a the first RFID transponder having a housing on a metal body;

5b the second RFID transponder having a housing on a metal body;

6a the RFID transponder having a housing on a metal sheet in an oblique plan view;

6b the RFID transponder with a housing on a metal sheet in cross section.

The 1a shows an RFID transponder known from the prior art 1 standing on a metal body 2 is arranged in an oblique top view. The RFID transponder 1 comprises a dielectric base body 13 on which a first conductive coating, namely an antenna surface 11 is applied. Furthermore, the base body has 13 on a side opposite a second electrically conductive coating, namely a base 12 , Between the base 12 and the metal body 2 is a dielectric layer 18 arranged.

The RFID transponder 1 points in its base body 13 an electrically conductive connection in the form of a series of plated-through holes 15 on, through which the antenna surface 11 electrically conductive with the base 12 connected is. Furthermore, the RFID transponder has 1 in his base body 13 a special via 16 indicating the electrical connection of the RFID chip 17 to the base 12 and depending on the arrangement of the RFID chip 17 possibly also to the antenna surface 11 allows.

The 1b Represents the electrical components of the RFID transponder 1 As a circuit arrangement in cross-section. It is irrelevant at which point the RFID chip 17 located. For the impedance of the antenna, on the other hand, it is very important at which point the RFID chip 17 over the feeding point 161 at the antenna surface 11 and via a connection point 162 to the base 12 connected.

Through the further dielectric layer 18 exists between the base area 12 and the metal body 2 a distance d. About this distance d is the base area 12 with the metal body 2 Electromagnetically coupled.

The 2a shows a corresponding to the prior art meander-shaped structured antenna surface 11' in a top view. It is easy to see that the electrical length of this antenna surface 11' is significantly larger than its mechanical length.

The 2 B represents this antenna surface 11' with an electrically conductive connection in the form of a connection surface 19' and a floor space 2' in an oblique plan view. The antenna surface 11' Despite its meandering structure, it runs parallel to the base area 2' and is still on the interface 19' with this base 2' electrically connected. The antenna surface 11' , the connection area 19' and the base area 12' are made together as a U-shaped bent unit in one piece.

The 2c shows how this U-shaped unit on a dielectric base body 13' is arranged. In addition, the base body has a through hole with a special via 16' over which the antenna surface 11' at a further point electrically conductive to the base 12' is connected so that a "Planar Inverted F antenna" (PIFA) is present.

The 3a shows a first RFID transponder according to the invention 1 , This has a dielectric base body 13'' on. On one side of the base body 13'' is an electrically conductive antenna surface 11'' arranged. On an opposite side of the base body 13'' indicates the RFID transponder 1 an electrically conductive base 12'' on. Furthermore, the antenna surface 11'' via an electrically conductive connection surface 19 '' electrically conductive with the base 12'' connected. The antenna surface 11'' , the base area 12'' and the interface 19 '' are each in the form of one on the base body 13'' executed in MID technology applied electrically conductive coating.

Furthermore, the length L, the width B and the height H of the base body 13'' entered into the drawing, it being apparent that the arbitrary at any point of the base body 13'' eigezeichnet height H along the length L varies meandering. The base area 12'' runs along the length L and width B, so that with the amount of height H, the distance between the base 12'' and the antenna surface 11'' meandering and passing through two maxima and a minimum.

The 3b shows the first RFID transponder 1 in a cross section. It is very easy to see that the RFID chip 17'' in an area of the antenna surface 11'' is arranged, which is a very small distance from the base 12'' having. The RFID chip 17'' is on the one hand about a feed point 161'' electrically conductive with the antenna surface 11'' connected. On the other hand, the RFID chip 17'' by means of a special through-hole 16'' , which from the antenna surface 11'' through the base body 13'' to the base area 12''' leads, via a connection point 162'' electrically conductive with the base 12'' connected.

The 3c shows the first RFID transponder 1 in a cross-section with some relevant quantities, namely the maximum height H _MAX , the minimum height H _MIN , the mean height H _MIT and the maximum deviation ΔH _MAX related thereto. H _MAX denotes the maximum distance between the antenna surface 11'' and the base area 12'' , H _MIN denotes the minimum distance between the antenna surface 11'' and the base area 12'' , H _MIT denotes the mean between H _MAX and H _MIN . ΔH _MAX denotes the maximum deviation of the height H from H _MIT .

Some associated realistic value ranges are given below: 2.5 mm <H _MAX <4 mm; and 1 mm <H _MIN <2.5 mm; and 0.25 mm <ΔH _MAX <0.75 mm.

A realistically dimensioned RFID transponder could thus have the following values: H _MAX = 3 mm; and H _MIN = 2 mm; and ΔH _MAX = 0.5 mm.

Measurements empirically obtained in laboratory tests have shown that such values can be used to maintain good coverage with the lowest possible base area.

The 4a shows a second RFID transponder according to the invention 1 , This has a dielectric base body 13''' on. On one side of the base body 13''' is an electrically conductive antenna surface 11''' arranged in the form of an electrically conductive coating. On an opposite side, the second RFID transponder 1 an electrically conductive base 12''' in the form of another electrically conductive coating. Furthermore, the antenna surface 11''' via an electrically conductive connection, in the form of a series of vias 15''' is executed, electrically conductive with the base 12''' , connected.

Furthermore, the length L, the width B and the height H of the base body 13'' entered into the drawing, it being apparent that the arbitrary at any point of the base body 13'' eigezeichnet height H along the length L varies meandering. The base area 12'' runs along the length L and width B, so that with the height H also the distance between the base 12'' and the antenna surface 11'' meandering, passing through three maxima and two minima.

The 4b shows the same arrangement in a cross section. It is very easy to see that the RFID chip 17''' in such a minimum, ie in a region of the antenna surface 11''' , which is a minimum distance to the base 12'' has arranged. The RFID chip 17'' is on the one hand to a feed point 161''' electrically conductive with the antenna surface 11''' connected. On the other hand, the RFID chip 17''' by means of a special through-hole 16''' passing through the base body 13''' leads, via a connection point 162''' electrically conductive with the base 12''' connected.

The 4c shows this RFID transponder in a modified form, namely with a much larger number of maxima and minima, namely in this case eight maxima and seven minima. However, it goes without saying that a different number of maxima and minima is possible. For example, the number of maxima and the number of minima can each be between 1 and 35.

The 5a represents the first RFID transponder according to the invention 1 out 3a and 3b in addition, a corresponding housing 14 and on a metal body 2 is arranged. Due to the wall thickness of the housing 14 in this area is the distance d between the base 12'' and the metal body 2 specified. The distance d should be as small as possible, so that the best possible electromagnetic coupling between the base 12'' and the metal body 2 arises. For example, the distance d may be less than 2 mm, preferably less than 1.5 mm and in particular less than 1 mm.

The 5b represents the second RFID transponder according to the invention 1 out 4a and 4b in addition, a corresponding housing 14' and on the metal body 2 is arranged. Due to the wall thickness d, the associated housing 14' in this area, the distance d is between the base area 12''' and the metal body 2 specified. The distance d is as small as possible, so that the best possible electromagnetic coupling between the base 12''' and the metal body 2 arises. For example, the distance d may be less than 2 mm, preferably less than 1.5 mm and in particular less than 1 mm.

The 6a and 6b show the RFID transponder according to the invention 1 with the associated housing 14 on a metal sheet 2' whose length, at least in the longitudinal direction, ie in the direction of the length L, is significantly greater, ie at least twice as large as the length L of the RFID transponder 1 ,

LIST OF REFERENCE NUMBERS

 1

RFID transponder

11

 antenna area

12

 Floor space

13

 base body

14

 casing

15

 Row of vias

16

 special through-hole

161

 feedpoint

162

 connection point

17

 RFID chip

18

 dielectric layer

19

 interface

 2

metal body

d

 Distance between the base and the metal body

L

 Length of base area / RFID transponder

B

 Width of the base area / RFID transponder

H

 Height of the RFID transponder

H _MAX

 maximum height of the RFID transponder

H _MIN

 minimum height of the RFID transponder

H _MIT

 average height of the RFID transponder

ΔH _MAX

Difference between H _MAX and H _MIN between H _MIT or and H _MIT

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 20060145927 A1 [0003]
• WO 93/12559 [0004]
• WO 96/27219 [0004]

Claims (16)

RFID transponder ( 1 ), comprising an inverted F-antenna, comprising: - an electrically conductive antenna surface ( 11 ); A flat electrically conductive base ( 12 ); An electrically conductive connection ( 15 . 19 ) of the antenna surface ( 11 ) and the base area ( 12 ); A base body ( 13 ) formed at least predominantly of a dielectric material; the antenna surface ( 11 ) and the base area ( 12 ) on two opposite sides of the base body ( 13 ), wherein the RFID transponder ( 1 ) further comprises: - an RFID chip ( 17 ), on the one hand via a feed point ( 161 ) electrically to the antenna surface ( 11 ) and the other is electrically connected to the base ( 12 ), characterized in that - the dielectric material is a molded interconnect device (MID) capable material, and - that the antenna surface ( 11 ) and the base area ( 12 ) by an MID method on the base body ( 13 ) are generated; - that the base body ( 13 ) has a length (L), a width (B) and a height (H), wherein the height (H) of the base body ( 13 ) varies meandering along its length (L), and - that the base area ( 12 ) along the length (L) and width (B) of the base body ( 13 ), so that the distance between the base ( 12 ) and the antenna surface ( 11 ) is formed by the height (H) and over the length (L) of the base body ( 13 ) varies meandering. RFID transponder ( 1 ) according to claim 1, characterized in that the electrically conductive connection of the antenna surface ( 11 ) and the base area ( 12 ) in the form of an electrically conductive connection surface ( 19 ) or in the form of one or more vias ( 15 ), which are preferably in a row, is executed. RFID transponder ( 1 ) according to one of the preceding claims, characterized in that the RFID chip ( 17 ) on the antenna surface ( 11 ), and that the base body ( 13 ) a special via ( 16 ), which the electrical connection of the RFID chip ( 17 ) to the base area ( 12 ). RFID transponder ( 1 ) according to one of the preceding claims, characterized in that the RFID transponder ( 1 ) a housing ( 14 ) comprising an assembly comprising the base body ( 13 ), the RFID chip ( 17 ), the antenna surface ( 11 ) with the feed point ( 161 ) and the base area ( 12 ), in all directions encloses. RFID transponder ( 1 ) according to claim 4, characterized in that the housing ( 14 ) consists of an electrically insulating material. RFID transponder ( 1 ) according to one of claims 4 to 5, characterized in that the housing ( 14 ) is hermetically sealed. RFID transponder ( 1 ) according to one of claims 1 to 3, characterized in that the RFID transponder ( 1 ) has a varnish-like seal, which comprises the said arrangement comprising the base body ( 13 ), the RFID chip ( 17 ), the antenna surface ( 11 ) with the feed point ( 161 ) and the base area ( 12 ), in all directions encloses. RFID transponder ( 1 ) according to one of the preceding claims, characterized in that the MID-capable material is suitable for "two shot molding" method. RFID transponder ( 1 ) according to one of the preceding claims, characterized in that the MID-capable material is suitable for "laser direct structuring" (LDS) method. RFID transponder ( 1 ) according to one of the preceding claims, characterized in that the feed point ( 161 ) at a point of the meandering antenna surface ( 11 ), which has a minimum distance (H) to the base surface ( 12 ) having. RFID transponder ( 1 ) according to one of claims 3 to 10, characterized in that the special plated-through hole ( 16 ) at a point of the meandering antenna surface ( 11 ), which has a minimum distance (H _MIN ) to the base area ( 12 ) having. RFID transponder ( 1 ) according to one of the preceding claims, characterized in that the RFID chip ( 17 ) at a point of the meandering antenna surface ( 11 ), which has a minimum distance (H _MIN ) to the base surface ( 12 ) having. Device consisting of a metal body ( 2 ), in particular a metal sheet ( 2' ), and the RFID transponder ( 1 ) according to one of the preceding claims, characterized in that the RFID transponder ( 1 ) on the metal body ( 2 ) is arranged. Device according to claim 13, characterized in that the housing ( 14 ) has at least on one side a flat inner surface and a flat outer surface, and that the base surface ( 12 ) of the base body on the flat inner surface of the housing ( 14 ) is arranged and that the metal body ( 2 ) has at least one planar area on at least one side and that the RFID transponder ( 1 ) with the flat outside of its housing ( 14 ) at the planar region of the metal body ( 2 ) is arranged. Device according to one of claims 13 to 14, characterized in that the base area ( 12 ) of the metal body ( 2 ) is less than 2 mm, preferably less than 1.5 mm and in particular less than 1 mm spaced. Device according to one of claims 13 to 15, characterized in that the metal body ( 2 ) at least in one direction parallel to the base surface ( 12 ) at least twice the size of the base area ( 12 ) having.

Images