Radio frequency signal modulation by impedance variation

Abstract

An RFID tag (1) is configured to transmit a predetermined code (3.sub.K) as a RF backscattered radiation (2) in response to an impinging RF signal (41). The RFID tag (1) is configured to react to an impinging signal at a predetermined reference frequency (23) with a reference backscattered signal (2.sub.R). The RFID tag (1) is also configured and to react to an impinging signal (41) at any of a group of transmission frequencies (21, 22) with coding backscattered signals (2.sub.F-G) whose amplitudes (20.sub.A, 20.sub.B) relative to the amplitude (20.sub.R) of the reference backscattered signal define the code (3.sub.K). An RFID reader (4), a kit (5) and a method for transmitting a message from a device (1) to a reader (4) as a RF backscattered radiation (2) in response to an impinging RF signal (41).

Claims

1. A method for transmitting a code comprising a series of juxtaposed symbols from a device to a reader as a RF backscattered radiation comprising: providing an RFID tag device configured to transmit RF backscattered radiation in response to an impinging RF signal, emitting with the reader a reference interrogation RF signal at a reference frequency to the RFID tag, receiving a reference backscattered signal at the reference frequency from the RFID tag in the reader, emitting with the reader at least a transmission signal at one trans mission frequency to the RFID tag, the transmission frequency being different from the reference frequency, receiving at least a coding backscattered signal at the transmission frequency from the RFID tag in the reader, comparing an amplitude of the reference backscattered signal with an amplitude of the coding backscattered signal, defining a symbol based on whether the amplitude of the reference backscattered signal is greater, equal, or smaller than the amplitude of the coding backscattered signal, wherein the symbol represents more than one digital bit.

2. The method of claim 1, comprising emitting a plurality of transmission signals at different transmission frequencies, receiving a corresponding plurality of coding backscattered signals, comparing amplitudes of the coding backscattered signals with the amplitude of the reference backscattered signal, defining for each coding backscattered symbol based on whether the amplitude of the reference backscattered signal is greater, equal, or smaller than the amplitude of the coding backscattered signal.

3. The method of claim 2, comprising determining the position of the symbols in the message based on the corresponding transmission frequencies.

4. The method of claim 2, wherein the RFID tag device has an antenna comprising, or connected to, an electrically conductive portions of the RFID device whose impedances are such that the amplitude of each the coding backscattered signals relative tithe amplitude of the reference backscattered signal yields the symbols of the code.

5. The method of claim 4, wherein said electrically conductive portions are part of one of: a dipole antenna, a resonator transmission line electrically connected between two antennas, and/or of meander line loaded antenna.

6. The method of claim 4, comprising printing the said electrically conductive portions on a support of the RFID tag device.

7. The method of claim 1, wherein the RFID tag device comprises at least one coding resonating unit each comprising a resonator transmission line connected between two antennas, the at least one coding resonating unit providing the coding backscattered signal at the transmission frequency.

8. The method of claim 1, wherein the RFID tag device comprises at least one meander line-loaded antenna, the at least one meander line-loaded antenna providing the coding backscattered signal at the transmission frequency.

9. A combination of a RFID device and reader configured to carryout the method of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood with the aid of the description of an embodiment given by way of example and illustrated by the figures, in which:

(2) FIG. 1 shows an exemplary view of a communication system comprising an RFID tag and a RFID reader, according to the invention.

(3) FIG. 2a-c show a view of embodiments of RFID tags relying on dipole antennas, according to the invention;

(4) FIG. 3 shows an exemplary view of backscattered signals generated by the RFID tags of FIGS. 1a-c;

(5) FIG. 4a-c show a view of others embodiments of RFID tags relying on dipole antennas, according to the invention;

(6) FIG. 5a-b show a view of embodiments of RFID tags relying on resonating units, according to the invention;

(7) FIG. 6 shows a view of an embodiment of a RFID tag relying on meander line loaded antennas, according to the invention.

DETAILED DESCRIPTION OF POSSIBLE EMBODIMENTS OF THE INVENTION

(8) The invention relates to a cost-effective system and an efficient method for transmitting a message from a device to a reader as a backscattered radiation in response to an impinging signal generated by the reader.

(9) In particular, the invention relates to a Radio-frequency identification (RFID) tag, notably a passive or chipless RFID tag, capable to transmit a message to a RFID reader as a RF backscattered radiation in response to a Radio Frequency (RF) impinging signal. In particular, the invention relates to a chipless RFID tag.

(10) A RFID tag is any device attachable to an object and configured to provide a code, preferably being assigned to or collected by the device, using electromagnetic field in the Radio frequency in response of an interrogating radio wave. The code is preferably a unique identifier for identification and tracking purposes.

(11) A passive RFID tag refers to a RFID tag configured to generate the backscattered radiation uniquely from (energy provided by) the interrogating radio wave, i.e. devoid of energy source for storing and/or transmitting the given code.

(12) A Chipless RFID tag refers to a RFID tag devoid of integrated circuit, e.g. devoid of transistors, for storing and/or transmitting a given code.

(13) Radio Frequency refers to an oscillation rate (frequency) of an electromagnetic field in the frequency range from 20 kHz to 300 GHz.

(14) FIG. 1 shows an exemplary view of a method and a system for transmitting a code 3.sub.K from a device 1 to a reader 4. In particular, the device 1 is configured to provide a radio-frequency (RF) backscattered radiation 2 (i.e. a backscattered radiation having frequencies in the range of radio frequency) in response of an impinging RF signal 41 (i.e. an interrogating signal having frequencies in the range of radio frequency) generated by the reader 4.

(15) As illustrated in FIG. 1, the device 1 is configured to: provide a (reference) backscattered signal 2.sub.R in reaction to an impinging signal at a predetermined reference frequency 23; and provide at least a (coding) backscattered signal 2.sub.F, 2.sub.G in reaction to an impinging signal at least a transmission frequency 21, 22, wherein the code 3.sub.K is defined by comparing the amplitude 20.sub.A 20.sub.B of each coding backscattered signals 2.sub.F with the amplitude 20.sub.R of the reference backscattered signal (i.e. the backscattered signal at the predetermined reference frequency 23).

(16) As illustrated FIG. 1, the device 1 can be configured to, in reaction to an impinging signal at whichever transmission frequency of a group of predefined distinct (i.e. different) transmission frequencies 21, 22, to provide a distinct backscattered signal 2.sub.F, 2.sub.G at the interrogated transmission frequency. The code 3.sub.K can thus be defined by the relative amplitude of each of the coding backscattered signals relative to the amplitude of the reference backscattered signal.

(17) The code can comprise (e.g. being represented by) a series of juxtaposed symbols 31, 32, preferably the symbols being selected within a predefined list of symbols, notably comprising alphabetical symbols, alphanumerical symbols, numerical symbols, binary digits, typographical symbols, and/or graphical symbols.

(18) The relative amplitude of each coding backscattered signal can thus (relatively to the amplitude 20.sub.R of the reference backscattered signal) define a symbol 31, 32 (e.g. a single symbol up to a groups of symbols) of the code 3.sub.K. The provided symbol can be: one or more alphabetical symbols, one or more alphanumerical symbols, one or more numerical symbols, one or more binary digits, one or more typographical symbols, and/or one or more graphical symbols.

(19) The position of the provided symbols in the code (juxtaposition of symbols) can be defined in relationship with (e.g. function of) their transmission frequencies (e.g. from the lower to the highest frequencies). The relationship can be determined according to a given (amplitude) unit providing a measure of the amplitude of a backscattered signal and/or with respect to a given (ratio) unit (e.g. dB) providing a ratio between two amplitudes of electromagnetic waves.

(20) The code 3.sub.K and/or a symbol thereof can be defined by providing a coding backscattered signal (at a given coding frequency) whose amplitude is greater, (substantially) equal, or smaller than the amplitude of the reference backscattered signal, the relationship (greater/equal/smaller) defining the code 3.sub.K and/or a symbol.

(21) The code 3.sub.K and/or a symbol thereof can be defined by providing a coding backscattered signal (at a given coding frequency) whose amplitude is a multiple of the amplitude of the reference backscattered signal, the multiple defining the code 3.sub.K and/or a symbol.

(22) Depending on the code 3.sub.K, the amplitude 20.sub.R of the reference backscattered signal 20.sub.R is thus either the smallest or identical to smallest amplitude of the coding backscattered signals.

(23) The code 3.sub.K and/or a symbol thereof can be defined by providing a coding backscattered signal (at a given coding frequency) whose amplitude is a divisor of the amplitude of the reference backscattered signal, the divisor defining the code 3.sub.K and/or a symbol. Depending on the code 3.sub.K, the amplitude 20.sub.R of the reference backscattered signal 20.sub.R is thus either the largest or identical to largest amplitude of the coding backscattered signals.

(24) The code 3.sub.K and/or a symbol thereof can be defined by providing a coding backscattered signal (at a given coding frequency) whose amplitude is a ratio of the amplitude of the reference backscattered signal, the ratio defining the code 3.sub.K and/or a symbol. The amplitude 20.sub.R of the reference backscattered signal 20.sub.R can be advantageously defined as being either the smaller or larger amplitude the device 1 can provide.

(25) Advantageously, the applicant found that a modification of the amplitude 20.sub.A, 20.sub.B, 20.sub.R of each of said coding backscattered signals (2.sub.A-E) relative to the amplitude 20.sub.R) of the reference backscattered signal can be pursued (obtained) by modifying the electrical impedance of an electrical conductive portion of the device 1, this electrical conductive portion being involved in the generation of the coding backscattered signal. In particular, these portions can be portions of antennas or are portions electrically connected to one or more antennas.

(26) Moreover, the applicant found that a manufacturing of these electrical conductive portions by a printing process can provide a cost-efficient device. In fact, a code (e.g. a unique identifier) can be assigned to the device by printing these electrical conductive portions so as they have the desired electrical impedance, notably by dimensioning these portions and/or selecting an adequate (electrical conductive) printed material.

(27) These portions can be printed on a (common) support, notably by serigraphy, by semiconductor lithography, by electrical conductive-inkjet printing, by 3D printing of electrical conductive material, or by a combination thereof.

(28) The support can be a printed circuit board, or any other non conductive material such as PET (Polyethylene Terephthalate), PS (Polystyrene), PC (Polycarbonate), ABS (Acrylonitrile Butadiene Styrene), PLA (Polylactic acid), paper, cardboard or many others. The support can be a part of an existing package of an object or a part of the object itself.

(29) The reader 4 is thus arranged to emit an interrogation RF signal 41, to receive backscattered signals 2 from the device 1, and to reconstruct a code 3.sub.K encoded in the backscattered signals. In particular, the reader 4 is further arranged to: measure the reference amplitude 20.sub.R of the reference backscattered signal 2.sub.R at the reference frequency 23, measure the coding amplitude 20.sub.A-E of the coding backscattered signal 2.sub.F-G at each transmission frequency of the group of transmission frequencies 21, 22, and determine the code 3.sub.K of the device 1 based on the coding amplitude 20.sub.A-E relative to the reference amplitude 20.sub.R.

(30) The impinging signal (interrogation RF signal) 41 can be broad-frequency impinging signal that (simultaneously) interrogating all the transmission frequencies of the group of transmission frequencies.

(31) Advantageously, the device 1 can be a RFID tag 1, in particular a passive RFID, notably a chipless RFID tag. The code can be advantageously a unique identifier assigned to the RFID tag for identification and/or tracking purposes, notably of an object on which the RFID tag is attached. The reader can be thus a RFID reader 4.

(32) As illustrated in FIG. 1, the RFID tag 1 is thus configured to transmit a code 3.sub.K as a RF backscattered radiation 2 in response to an impinging RF signal 41. In particular, the RFID tag 1 is configured to: react to an impinging signal at the (predetermined) reference frequency 23 with a reference backscattered signal 2.sub.R, and to react to an impinging signal 41 at any of the group of transmission frequencies 21, 22 with coding backscattered signals 2.sub.G, 2.sub.F whose amplitudes 20.sub.A, 20.sub.B relative to the amplitude 20.sub.R of the reference backscattered signal define the code 3.sub.K.

(33) The reference frequency 23 and the transmission frequencies of the group being within the Radio Frequency (RF) range.

(34) The group of transmission frequencies comprises at least a transmission frequency, preferably a plurality of transmission frequencies 21, 22, notably the number of transmission frequencies being a power of 2.

(35) FIGS. 2a-c and 4a-c show a view of embodiments of RFID tags relying on dipole antennas, while FIG. 3 shows the related backscattered signals. In particular, these embodiments relying on dipole antennas printed on a (common) support 10 of the RFID 1.

(36) In these embodiments, the reference backscattered signal 2.sub.R at the reference frequency 23 (cf. FIG. 3) is provided by a reference dipole antenna 24.sub.R.

(37) The dimensions (in particular the length 290 of their conductive strip 29.sub.A-29.sub.F) and the electrical impedance (of the conductive strip 29.sub.A-29.sub.F) of each dipole antenna 24.sub.A-24.sub.E, 24.sub.R determine the frequency at which the dipole antenna reacts (i.e. the reference frequency) as well as with what intensity (i.e. amplitude attenuation).

(38) As illustrated in FIG. 2a, the reference dipole antenna 24.sub.K, notably the length of his conductive strip 29.sub.C, can thus be dimensioned so as to react to a (predefined) reference frequency, while his electrical conductivity can be selected so as to provide a given reference amplitude attenuation. The width and the electrical conductivity of the conductive strip 29.sub.C determine the electrical conductivity of the reference dipole antenna 24.sub.R.

(39) The RFID of FIG. 2a is configured to provide a plurality of backscattered signals 2.sub.A, 2.sub.D at given (transmission) frequencies 22, 23 (cf FIG. 3), each backscattered signal being generated by a (coding) dipole antenna 24.sub.A, 24.sub.B so as to define a given code 3.sub.A.

(40) In this exemplary embodiment, the code 3.sub.A is represented by a juxtaposition of (a same) symbol S.sub.1, the symbol S.sub.1 being (in this example) defined by a backscattered signal having (substantially) the same amplitude as the amplitude of the reference backscattered signal 2.sub.R. By the term substantially the same amplitude, it is meant an identical amplitude or a similar amplitude (e.g. a difference less than variations in the backscattered signal due to components manufacturing errors, notably antenna manufacturing errors, thermal errors, reader uncertainty or ambient noise).

(41) The RFID tag of FIG. 2a can thus transmit the code 3.sub.A (in response of an impinging signal) by means of a first and a second backscattered signal 2.sub.A, 2.sub.D having (substantially) the same amplitude as the reference amplitude 20.sub.R of the reference backscattered signal 2.sub.R provided by the reference dipole antenna 24.sub.R. (cf. FIG. 3).

(42) In the exemplary embodiments of FIGS. 2b and 3b, the code 3B, 3.sub.C assigned to the RFID tag 1 comprises at least a symbol S.sub.2, S.sub.3, S.sub.4 being defined by an amplitude 20.sub.A, 20.sub.B being different (i.e. larger or smaller) than the reference amplitude 20.sub.R (cf. FIG. 3).

(43) A modification of amplitude of the backscattered signal can be provided by modifying the electrical impedance of the related coding dipole antenna 24.sub.C, notably by modifying the dimensions of the conductive strip 29.sub.D, 29.sub.E, 29.sub.F of (related) the dipole antenna.

(44) As illustrated in FIGS. 2b and 2c, in particular, an increase of the amplitude can be obtained by enlarging the width 293, 294 of the conductive strip 29.sub.D, 29.sub.E of the dipole antenna that leads to a decrease of the electrical impedance of the dipole antenna.

(45) Similarly, as illustrated in FIG. 2c, in particular, a decrease of the amplitude can be obtained by reducing the width of the conductive strip 29.sub.E (even up to a complete elimination the strip) of the dipole antenna that leads to an increase of the electrical impedance of the dipole antenna.

(46) Alternatively or complementarily, as illustrated in the exemplary embodiments of FIGS. 4a-4c, an increase or a decrease of the amplitude can be obtained using another material for manufacturing (e.g. printing the conductive strip 29.sub.G-29.sub.J of) the dipole antenna, the material having another electrical resistivity (also called specific electrical resistance).

(47) The printable material can be a conductive metal, a conductive ceramic and/or a conductive polymer, such as heated to liquid state metals (e.g. copper or aluminium), any metal or carbon doped inks (e.g. silver and silver chloride inks or epoxies) or melted polymers (e.g. carbon doped polylactic acidPLA).

(48) These particular embodiments furthermore provide not only an efficient encoding and transmission of data, but also a cost-effective manufacturing of the RFID tag as a given code can be assigned to the RFID by printing particular shaped and/or dimensioned dipoles antenna with one or more printable materials having different electrical resistivity.

(49) Alternatively, or complementarily, backscattered signals can be provided by a group of resonating units 25.sub.A-25.sub.D and 25.sub.R, as illustrated in FIGS. 5a and 5b.

(50) The RFID tag 1 can thus comprises a group of resonating units comprising: a reference resonating unit 25.sub.R with a resonator transmission line 29.sub.J electrically connected between two antennas, the reference resonating unit 25.sub.R providing the reference backscattered signal 2.sub.R; and one or more coding resonating units 25.sub.A-D, each comprising a resonator transmission line 251.sub.A, 251.sub.C electrically connected between two antennas 253.sub.A, 253.sub.C; each coding resonating unit providing one coding backscattered signal at one transmission frequency of the group of transmission frequencies 22, 23.

(51) In particular, at least a portion (preferably the entire) resonator transmission line of each resonating unit is advantageously printed on a (same) support 10 of the RFID tag.

(52) Each antenna of each resonating unit is advantageously a monopole antenna.

(53) A code 3.sub.G-H can be assigned to the RFID tag 1 by means of one or more resonator transmission lines whose electrical inductivities provide, in response of an impinging signal, coding backscattered signals with predefined amplitudes with respect to the reference amplitude (of the reference backscattered signal). As previously described, desired electrical inductivity can be obtained (notably during the printing process) by dimensioning each resonator transmission line, notably the length and/or the width thereof (e.g. lines 29.sub.L and 29.sub.M) and/or by selecting an adequate material having a particular electrical resistivity (e.g. lines 29.sub.M and 29.sub.N).

(54) Alternatively or complementarily, backscattered signals can be provided by a group of meander line loaded antennas 26.sub.A-B, 26.sub.R, as illustrated in FIG. 6.

(55) The RFID tag 1 can thus comprise a group of meander line loaded antennas 26.sub.A-B, 26.sub.R comprising: a reference meander line loaded antenna 26.sub.R providing the reference backscattered signal 2.sub.R, and one or more coding meander line loaded antennas 26.sub.A-B, each coding meander line loaded antenna providing one coding backscattered signal at one transmission frequency of the group of transmission frequencies 22, 23.

(56) In particular, at least a portion 29.sub.O, 29.sub.P, 29.sub.Q of meander line loaded antennas, the portion being located between the antennas, is advantageously printed on a (same) support 10 of the RFID tag. Preferably, the entire meander line loaded antenna is printed on the support.

(57) A code 3.sub.G-H can be thus assigned to the RFID tag 1 by means of one or more meander line loaded antennas whose electrical inductivities provide, in response of an impinging signal, coding backscattered signals with predefined amplitudes with respect to the reference amplitude (of the reference backscattered signal).

(58) The desired electrical inductivity can be obtained (notably during the printing process) by: selecting a shape of the meander line loaded antenna, notably the number of meanders; and/or by dimensioning the (selected) shape, notably the length and/or the width of the meaner (e.g. meander lines 29.sub.O) and/or by using a material with a particular electrical resistivity (e.g. meander line 29.sub.P).

(59) Alternatively or complementarily, backscattered signals can be provided by other antennas having other geometrical shape, such as spiral-shaped antennas, notably having geometrical shape being entirely or at least partially printable on a support.

(60) A code 3 can be thus assigned to the RFID tag by means of one or more of such antennas whose electrical inductivities provide, in response of an impinging signal, coding backscattered signals with predefined amplitudes with respect to the reference amplitude (of the reference backscattered signal).

(61) The desired electrical inductivity can thus be obtained (notably during the printing process) by: selecting a particular shape of the antenna, notably between a catalogue of different shapes; and/or by dimensioning the (selected) shape, notably the length and/or the width of the printable portion of the antenna, and/or by using a material with a particular electrical resistivity, notably selected within a catalogue of printable materials.

NUMERICAL REFERENCES USED IN THE DRAWINGS

(62) 1.sub.A-I RFID tag 10 Support 2 RF backscattered radiation 2.sub.A-G Backscattered signal 2.sub.R Reference Backscattered signal 20.sub.A-B Amplitude 20.sub.R Reference amplitude 21 1.sup.st Radio Frequency 22 2.sup.nd Radio Frequency 23 Reference Radio Frequency 24.sub.A-K Dipole antenna 24.sub.R Reference dipole antenna 25.sub.A-D Resonating unit 251.sub.A, 251.sub.C Resonator transmission line 252.sub.A, 252.sub.C Antenna 253.sub.A, 253.sub.C Antenna 25.sub.R Reference resonating unit 26.sub.A-B Meander line loaded antenna 26.sub.R Reference Meander line loaded antenna 29.sub.A-Q Printed electrical conductive portion 290 Length 291-294 Width 3.sub.A-K Code 31, 32 Symbol 4 RFID reader 41 RF signal 5 Kit S.sub.1-11 Symbol