WO2009034534A2

WO2009034534A2 - Multiple-port rfid and method of manufacturing and using thereof

Info

Publication number: WO2009034534A2
Application number: PCT/IB2008/053664
Authority: WO
Inventors: Gaetano Marrocco
Original assignee: Universita' Degli Studi Di Roma 'tor Vergata'
Priority date: 2007-09-11
Filing date: 2008-09-11
Publication date: 2009-03-19
Also published as: WO2009034534A3; ITRM20070466A1

Abstract

A multiple-port RFID including a reader which radiates a query signal and one or more passive multiple-port tags, each of which includes at least two chips connected to the same antenna or each to a different antenna, so that the port impedance of each chip is different, in such a manner that the features of the reply signal of each chip allow to detect one or more physical-chemical or geometric magnitudes of the target on which the multiple-port tag is applied, said magnitudes affecting both the reception of the query signal and the emission of the reply signal.

Description

MULTIPLE-PORT RFID AND METHOD OF MANUFACTURING AND USING

THEREOF

Field of the invention

The present invention relates to the field of so-called RFID (Radio Frequency Identification) devices, i.e. devices adapted for identifying objects in general and/or monitoring some physical-chemical magnitudes related thereto.

State of the art

A RFID system typically consists of an apparatus, commonly referred to as a reader, which queries a transponder, commonly referred to as a tag, which replies to the request by sending its identification, commonly referred to as an ID. The reader queries the tag by emitting an electromagnetic signal that hits the tag which, if passive, takes the energy for replying therefrom thus sending its identification.

A tag is formed by electronic devices including storage means and an antenna for communicating with the reader and for picking up the radiated energy in order to support communications.

The electronic devices, normally integrated in a single chip, are connected by means of a pair of terminals, referred to as a port.

For some tag types, the reply message may vary in relation to the query message sent by the reader.

Said reply is retrieved from an internal memory of the tag.

The widest applications are found in some RFID systems formed by passive tags in the area of logistics, safety and bioengineering and, in general, where there is the need to identify at least one object, animal or human being, and more in general a target.

Active tags, which are more cumbersome as they have their own power source, are further provided with at least one sensor adapted to detect and measure a specific magnitude and a microcontroller which handles the acquisition of the data and the communication thereof to the reader. The reception and trasmission frequencies are typically in the UHF band.

Such systems may allow the real-time monitoring of determined magnitudes.

Furthermore, data related to a moving target may be acquired when a network of readers exists in the surrounding environment. i The possibility of monitoring a magnitude opens the way to innumerable applications which involve all fields of science, medicine, industry and agriculture.

Therefore, monitoring a magnitude imposes electronic configurations based on a microcontroller which typically requires a source of energy inside the tag. In all cases, the greater volume with respect to passive tags, having solely the identification function, and above all the higher electric complexity and the resultant higher cost hinder their wide-scale spread.

Summary of the invention

It is the object of the present invention to provide a multiple-port RFID based on passive RFID technology, and thus cost-effective, adapted to provide the measure of a magnitude related to an observed target.

The present invention thus aims at reaching the objects discussed above by making a multiple-port RFID in accordance with claim 1.

Another object of the invention is to provide a method for manufacturing multiple- port tags and a method of decoding the signals reflected by the tag in order to be able to obtain an estimate of at least one physical-chemical or geometric property of the target, such as for example the dielectric permittivity or the electric conductivity or its geometry.

A further object of the present invention is to provide a querying procedure of a multiple-port tag by a reader.

Therefore, the present invention suggests to reach such objects by disclosing a method for manufacturing and a method for arranging a multiple-port tag, in addition to a method for estimating a physical-chemical or geometric magnitude of a target, in accordance with claims 7, 8 and 10, respectively. The multiple-port RFID, object of the present invention, advantageously allows to: a) classify the equivalent dielectric constant of the target in a discrete set of values, returning the closest value to the real value; b) estimate the dielectric constant or other physical-chemical or geometric features of the target, or of the over-time variations thereof, within a continuous set of values.

The dependent claims describe preferred embodiments of the invention.

Brief description of the drawings

Further features and advantages of the invention will be more apparent in the light of the detailed description of some preferred, but not exclusive, embodiments of a multiple-port RFID and method of manufacturing and using thereof, illustrated by way of non-limitative example, with the aid of the accompanying drawings, in which: Fig. 1 shows the interaction between a reader and a multiple-port tag, which replies to a query with N different replies, as many are the chips defining the tag;

Fig. 2 shows a multiple-port tag including an antenna and three chips connected to said antenna by means of an equal number of ports of different impendence;

Fig. 3 shows a multiple-port tag including three chips connected to an equal number of antennas of different shape and impendence;

Fig. 4 shows two possible multiple-port tag embodiments including an antenna and two chips connected to said antenna by means of a distributed matching network having two different impendence ports;

Fig. 5 refers to a flow chart related to a querying procedure of a multiple-port tag by a reader;

Fig. 6 shows a chart which may be used to estimate the dielectric permittivity of a target;

Fig. 7, 8 and 9 refer to an example in which the multiple-port tag includes two chips connected to two antennas of equal shape and different dimensions, applied by means of an adhesive substrate to a generic object;

Fig. 10 shows a tag embodiment with two chips consisting of two meander antennas for classifying the content of bottles;

Fig. 11 , 12, 13 and 14 refer to an experimental setup aimed at monitoring the filling level of a box. Detailed description of preferred embodiments of the invention

A preferred variant of multiple-port tag includes an antenna connected to at least two chips by means of as many different impedance ports (Fig. 2).

In another preferred embodiment, the multiple-port tag includes two or more antennas, each of which is connected to one or more chips (Fig. 3). When a reader queries a multiple-port tag, each chip defining the tag, on the basis of the sequence communicated by the reader, responds by modulating the query waveform.

Therefore, as many digital modulation signals as the chips which a multiple-port tag includes are reflected (Fig. 1).

The chemical-physical features and the geometry of the material means forming the target, on which the tag is placed, induce a specific electric and magnetic energy distribution when the query signal emitted by the reader hits the target. Such an effect influences the phase and amplitude of the current induced on the conductors included in the tag, and thus the antenna gain and the impedance of each tag port.

Subsequently, the signal reflected by each chip of the tag is further influenced by the antenna gain and port impedance, thus providing information about the features of the target.

When the features of the target are such that the impedance of a port does not provide the necessary matching to the corresponding chip, the latter does not receive the energy required for sending the reply message containing its identification to the reader. A multiple-port tag with different input impedances of each port replies with as many signals of different amplitude.

A specific case is that in which a single chip, named singular, receives energy in order to be able to reply to the reader, while all the other chips belonging to the same tag are not matched to the corresponding port. In order for a query to be profitable also when a singular chip replies, a second query is required to the reader to obtain the value of the measurand magnitude stored from the chip for which the corresponding port is matched. The difference between the amplitudes of the various signals emitted by the tag, and thus between the powers carried thereby, depends on the geometric and chemical-physical conformation of the target.

The reader queries a multiple-port tag and picks up the reply signals thus identifying the object and estimating the value and/or the variations of the geometric and/or chemical-physical features of the material forming the target. The geometry of the conductors forming a multiple-port tag, both in the configuration with one antenna and several chips and in the configuration with several antennas each provided with a chip, may either be of the wire or of the planar type, based on slots, dipoles, loops or patches. In order to construct a multiple-port tag including several antennas, according to a preferred embodiment, proceed as follows:

- gluing a conductor defining a single antenna onto a substrate;

- interrupting the galvanic continuity of the conductor in some points;

- connecting a chip at each of said points. Any connecting modes of said chips to the conductor may be used.

A method of manufacturing multiple-port tags, for example adapted to monitor the dielectric permittivity of the target, includes the following steps:

1. Selecting a sequence of dielectric permittivity reference values {ε-i, ε₂,... , εu} the number of which is equal to the number of ports of the antenna and in the variation range of the most likely permittivity of the target to be monitored.

2. Arranging antennas, dimensioned according to any known optimization algorithm, acting for example on their shape and size and on the position of the ports so that the n-th port has an input impendence matched to the input impendence of the chip when this is arranged on a reference target with permittivity ε_n of the type similar to the candidate targets. In case of multiple-port tag including several antennas, these may be scaled versions of a same basic shape. The scaling coefficient is related to the reference permittivity value associated to the specific port. In case of multiple-port tag including a single antenna, the single radiating element or antenna is connected to two or more chips by means of an impendence matching network made with concentrated or distributed constant elements so that the impedances seen from the two or more ports are subject to the same above-mentioned constraints. Possible, non-limiting embodiments of the matching network are shown in Fig. 4 and consist in two reciprocally engaged stubs, either connected to the antenna or radiating dipole (Fig. 4a) or placed in a specular position with respect to the radiating dipole (Fig. 4b). The vertical dimensions si and S₂ and the horizontal dimensions I₁ and I₂ of the stubs need to be optimized by any method in order to obtain the required impendence condition. Instead of the stubs, coupling loops in specular positions with respect to the radiating element may be used. 3. Storing in the memory of each chip the identification code of the other chips defining the same tag for allowing to discriminate information when several multiple-port tags reply to the reader request. Furthermore, the permittivity value SN, matched to the impedance value of the corresponding port, is stored. Therefore,

- the ID identification code, or simply ID, of the chip connected to the port,

- the list of identification codes of the chips connected to the other ports defining the multiple-port tag, - a value of the measurand magnitude of the target for which the port impedance is matched to the chip, are univocally associated to each port. A reader, in accordance with the present invention, includes:

- radio reception and transmission means; - storage means in which the reference values of the examined magnitude are stored;

- processing means, adapted to decode a signal radiated by a tag, to measure the power thereof and to estimate a geometric and/or physical-chemical property of the target, as well as the over-time variation thereof in relation to the reference values stored in said storage means.

Specifically, the measurement curves or tables which allow, for the specific application and for the specific grade of antennas, to associate reply signals of a multiple-port tag to the magnitudes to be measured, are stored in said storage means of the reader. A preferred embodiment is examined below, wherein the measurand magnitude is the dielectric permittivity of the target. However, such an example is not intended to be limitative.

In relation to the measurand magnitude, e.g. the dielectric permittivity, a relationship of the ε = f(M) type, referred to as the decoding curve, is identified which allows to obtain a curve, similar to the one shown in Fig. 6, in which, in turn, M is a function of the powers related to the signals reflected by the chips defining the multiple-port tag and influenced by the variations of the measurand magnitude. Alternatively, or additionally, M may represent the ratio between minimum powers which must be provided to the reader in order to independently activate the two chips.

Specifically, said curve is obtained a priori by using an electromagnetic calculation program which allows to represent the geometry of the multiple-port tag and thus to estimate the reply signals generated by its chips, i.e. to estimate the minimum powers required to the reader to remotely activate the two tags upon the variation of the permittivity of a reference target having features close to the candidate targets. A same analysis method may be used to monitor further features of the target, such as for example the shape or other magnitude, such as temperature or mechanical strain.

A method for estimating a measurand magnitude, e.g. permittivity, of the target will now be described with reference to the block chart in figure 5, distinguishing the case in which the reader receives a single reply from the case in which it receives two replies:

- querying a tag arranged on the target (step 1);

- receiving the reply from said tag and extracting at least one ID identification code (step 2); - if there is only one reply (step 3), e.g. when there is a singular chip, a new query is carried out (3.1) by the reader to obtain (3.2) the permittivity value stored in said storage means or memory of the chip;

- on the other hand, if two replies with two different IDs are received (step 4), i.e. if the permittivity of the target is such that more than one chip is sufficiently matched to the port impedance, then calculating the powers, Pi and P₂, associated to said replies, (4.1), calculating (4.2) a value M₁₂ equal to the ratio P₁/P₂ and accessing (4.3) the abscissa axis of the aforesaid decoding curve or measurement table from which the permittivity of the target on the ordinate axis in relation to said value of M₁₂ is estimated (4.4). Furthermore, the values of the distance between reader and tag, with which such permittivity value is identified, is obtained from the same curve. The procedure may further be carried out by calculating Mi₂ as a ratio between the minimum input powers Pi and P₂ required to the reader to remotely activate the two chips placed on the tag. Therefore, the method is advantageously adapted to measure further magnitudes by producing corresponding measurement charts or tabies.

When there is more than one multiple-port tag in the environment, the reader isolates the replies from each multiple-port tag (step 2). The sub-steps or intermediate steps included in step 2 are listed below: - receiving the IDs of the chips defining the different tags existing in the query region (step 2.1);

- for each received ID, querying the corresponding chip and reading in its memory the ID of all the chips which form the same multiple-port tag (step 2.2); - grouping all the IDs belonging to a same multiple-port tag (step 2.3);

- identifying the chips which, despite belonging to a multiple-port tag, are the only ones to receive energy to reply to the reader (step 2.4), then processed in step 3;

- thus, sorting the groups made in step 2.3, and identifying pairs of IDs (step 2.5), each pair being then singularly processed in step 4. A higher number of power ratios M,_j = P/P_j offers- more possibilities of comparison, even statistic comparison, between a target and a reference target, according to appropriate decoding curves, adapted to allow the classification in relation to shape, permittivity and/or electric conductivity. EXAMPLES By way of example only, three possible embodiments of the invention are described, one of which also checked by means of prototypes and experimentation.

1. The first example aims at monitoring the permittivity of the target, on which a two-port tag is applied, obtained with two meander dipoles having the same shape but different size (Fig.7), each dipole being connected to a chip with input impedance Z_Chi_P = 50 - J200 Ω which is specifically matched to the impedance of the antenna when this is arranged on a target having permittivity &2 - 4. The target is assumed to be a homogenous dielectric half-space of infinite extension. The larger antenna has an input impedance of Z_Ai = 50 + J200 Ω and is specifically matched to the impedance of the antenna when this is arranged on a target having permittivity εi = 3. Such a double-port tag is thus adjusted to a reference permittivity {ε_t, s₂} = {3,4} and consists of (Fig. 8) said two antennas connected to as many chips, supported by an insulating dielectric substrate, e.g. acetate, paper or silicone. It therefore appears as a label adapted to be positioned, for example, on the side surfaces or on the lid of a container (Fig. 9) the dielectric permittivity of which is intended to be monitored. The curve in Fig. 6 is numerically calculated and loaded on said storage means belonging to the reader, which uses this curve at step 4.3 of the preceding flow chart in Fig. 5.

The amplitude of the permittivity range of the target may be distinguished by the reader according to the distance between reader and tag. Such a range is indicated on the curve by the pair of equivalent markers. The entire permittivity range 2.7 < ε < 4 may be distinguished up to a maximum distance of 4 meters. A smaller range, i.e. 2.9 < ε < 3.45, may instead distinguished up to 5 meters. For example, if the reader, having queried the target according to the aforesaid procedure, receives two reply signals in such a manner that the ratio between the powers M ₁₂ is 2, the estimated permittivity value ε_targ_et obtained from the curve is equal to 3.3, which may be identified for a distance of up to 6m. Similarly, if the ratio between the received powers is 8, then the estimated permittivity value is 2.9, detectable up to a 5m distance between tag and reader. 2. The second example relates to a double-port tag applied on a surface of a liquid container (Fig. 10) for monitoring the integrity of the container and, specifically, for determining whether it contains water or a flammable and toxic liquid having the same appearance, e.g. chlorobenzene. The tag again consists of two meander antennas (as in the preceding example) shaped so that the antenna named MLAw is well matched to the chip of impedance Z_Chi_p = 15 - j450 Ω when such a tag is arranged on a water containing bottle, while the antenna named MLAc_B is well matched to the same chip impedance when the content of the bottle is chlorobenzene. In such a case, the reference values of the measurand are the complex impedances of water (εw=80-j7) and of chlorobenzene (SCB=5.61-J0.2). Upon the query by the reader, the tag with the antenna MLAw transmits a code IDw₁ while the tag with the antenna MLACB transmits a code IDCB- The antennas are designed considering a simplified model of a bottle consisting of flat and parallel layers (Fig.10), having dimensions t_G=3mm and t_L=8cm. The matching of the antenna MLA_W is better than that of the antenna MLACB, SO that the first antenna will always send its identification, regardless of the type of content of the container or bottle.

When the reader queries the two-port tag in an appropriate reading distance range, depending on the power emitted by the tag and on the sensitivity of the chip (e.g. in the range between 0.5m and 2m, in the case in which the power emitted by the reader is 3.2W EIRP and the sensitivity of the chip is 10μW), said tag will reply only with the code IDw if the bottle contains water, thus simply identifying the code thereof. On the other hand, if the bottle contains chlorobenzene, the second antenna MLA_CB will also be activated transmitting back its identification ICB and indicating that the bottle with code IDw has been adulterated.

3. A third example consists in monitoring the filling level of a container. In this specific case, the content is powdered sugar and the container is a 20 cm side cubic box made of plastic material (Perspex) (Fig.11). The multiple-port tag again consists of a pair of facing meander antennas (Fig.12). One of the two antennas is optimized for the chip when the container is empty, while the second antenna is optimized when the level h of the sugar is 10 cm, and thus the reference values of the measurand in the antenna designing are h = {0 cm, 10 cm}. The considered chip has impedance Z_Chi_P = 50 - J200 Ω . In order to simplify measuring the input impedance of the two antennas, the plastic container was placed on a 1 m x 1 m size copper sheet which acts as image plane and therefore only half of the antennas needed to be constructed. By varying the filling level of the container from h=0 cm to h=10 cm, the power transmission coefficient τ was measured, for the two ports, which represents the proportional share of the power picked up by the single antenna which is absorbed by its chip and, in case of perfect impendence matching, must be unitary. The patterns of T₁ and τ₂, which have been computer simulated and measured in laboratory (Fig.13), show the different matching of the two antennas MLAi and MLA₂. Fig. 14 instead shows the decoding curve Mi₂(h)=Pi/P₂ which allows to relate the variation of powers reflected back to the reader with the variation of the sugar level h. The pattern of this curve is monotonic and a satisfactory dynamic (1<Mi₂<5) is appreciated when the sugar level varies in the 2cm<h<8cm range. For a further variation (h>8cm), i.e. when the sugar level exceeds double the height of the antennas, a saturation phenomenon of the power reply is observed. In such a case, the antennas do not notice the further modification of the target.

The specific embodiments described herein do not limit the content of this application which covers all the variants of the invention defined in the claims.

Claims

1. A multiple-port RFID including: a reader, adapted to irradiate a query signal, and at least one multiple-port tag, which includes: - at least one antenna connected to two or more chips, or at least two antennas each connected to one or more chips so that each port has a impedance different from the others at the corresponding chip;

- an adhesive substrate for keeping the antenna in contact with the surface of a target to be examined, so that the query signal received and later reflected by the multiple-port tag is a function of a chemical-physical or geometric magnitude of the target to be measured.

2. An RFID, according to claim 1 , wherein the impedance provided at a port is matched to the impedance of the chip connected to the same port, when the tag which includes said port and said chip is arranged on a target having a determined value of the chemical-physical or geometric magnitude to be measured.

3. An RFID, according to claim 1 , wherein each chip of said multiple-port tag is provided with own storage means in which the chemical-physical or geometric magnitude of the target, whereby the impedance of the corresponding port is matched, and the IDs of all the other chips of the same tag may be stored.

4. An RFID, according to claim 1 , wherein the geometry of the conductors constituting said at least one or two antennas is of the wire or planar type, and based on slots, dipoles, loops or patches.

5. An RFID, according to claim 1 , wherein said adhesive substrate is made of acetate and/or paper and/or silicone.

6. An RFID, according to claim 1 , wherein said reader includes:

- radio reception and transmission means;

- own storage means, in which reference values of the examined magnitude are stored;

- processing means, adapted to decode a signal radiated by a tag, to measure the power thereof and to estimate a geometric and/or physical-chemical property of the target, as well as the over-time variations thereof, in relation to the reference values stored in said storage means.

7. A method of manufacturing a multiple-port tag, provided with at least two antennas each connected to at least one chip, including the following steps:

- gluing a conductor defining a single antenna;

- interrupting the galvanic continuity of the conductor in some points;

- connecting a chip at each of said points.

8. A method of arranging a multiple-port tag for estimating a chemical-physical or geometric magnitude of a target, by using a multiple-port RFID according to claim 1 , including the following steps:

- selecting a sequence of reference values of a chemical-physical or geometric magnitude of the target in a number equal to the number of the ports and in the variation range of the most likely value of the chemical-physical or geometric magnitude of the target to be monitored;

- arranging antennas, dimensioned according an optimization algorithm, acting at least on shape and size and on the position of the ports, so that the n-th port has an input impendence matched to the input impendence of the corresponding chip when this latter is arranged on a target having a known value of the chemical- physical or geometric magnitude to be monitored;

- storing the identification code of the other chips defining the same multiple-port tag in the storage means of each chip in order to enable the discrimination of information belonging to the same multiple-port tag; - storing the reference value of the magnitude which affects the matching of the corresponding port, in the storage means of each chip.

9. A method according to claim 8, wherein said arrangement of antennas may be implemented by scaling the size of an antenna, maintaining the same shape thereof, so that the scaling coefficient is related to the reference value of the measurand magnitude, either chemical-physical or shape-related, which is associated to the specific port, or may be implemented with a single antenna connected to two or more chips by means of an impedance matching network made of concentrated or distributed constant elements.

10. A method of estimating a chemical-physical or geometric magnitude of a target, by means of a multiple-port RFID according to claim 1 and implementing a method of arranging a multiple-port tag according to claim 8, including the following steps: a) obtaining one or more curves of the ε = f(M) type, referred to as the decoding curves of signals radiated by the chips, wherein M is a function of the powers related to the signals radiated by the chips defining a multiple-port tag, applying it to a reference target, or M is equal to the ratio of the minimum powers which must be inputted to the reader to activate each chip; b) performing a first querying of the tag placed on the target by means of the reader; c) receiving the reply from the tag and extracting at least an identification code; d) if there is only one ID reply, whereby there is a singular chip or a single-port tag, performing a second querying of the tag (3.1) to obtain (3.2) the value of the magnitude stored in said storage means of the chip, being a singular chip the only chip of a multiple port tag which receives the energy needed to reply to the reader; d') or if several distinct ID replies are received, detecting the powers (Pi, P2) two- by-two associated to said replies (4.1); calculating a value Mi₂ equal to the ratio P₁/P₂ (4.2) and accessing the abscissa axis of said decoding curve (4.3) from which an estimate of the chemical-physical or geometric magnitude of the target in relation to said value Mi₂ is obtained from the ordinate axis (4.4).

11. A method of estimating according to claim 11 , wherein if more than two ID replies are received in step c), a logical grouping of the chips belonging to the same tag is performed by discriminating the singular chips.

12. A method of estimating according to claim 12 wherein said grouping includes the following steps:

- (step 2.2) for each received ID, querying the corresponding chip and reading in the storage means thereof the ID of all the chips which form the same multiple- port tag; - (step 2.3) forming groups including all the IDs belonging to a same multiple-port tag;

- (step 2.4) identifying those chips which, despite belonging to a multiple-port tag, are the only ones which receive the energy to reply to the reader, then processed in step d); - (step 2.5) sorting the groups previously formed in step 2.3, which are then processed two-by-two in step e).

13. A method of estimating according to claim 11 , wherein the decoding curves are traced by means of an electromagnetic calculation program adapted to represent the geometry of a multiple-port tag and to estimate the reply signals generated by its chips as the measurand magnitude of the target varies starting from a reference value.

14. A method of estimating according to claim 11 or 14, wherein there are indicated on the same curve the values of the distance between reader and tag within which determined values of the measurand magnitude may be also identified.

15. A method of estimating according to claim 11 or 14, wherein said measurand magnitude is the dielectric permittivity or the dielectric constant or the geometric shape of the target.