MXPA06007131A - Ultra high frequency radio frequency identification tag - Google Patents

Abstract

An antenna design for radio frequency identification ("RFID") tags. More particularly, the present invention relates to design for RFID tags particularly operating in the ultra high frequency ("UHF") operating band. The antenna comprises:i) a first antenna element (10) , where the first antenna element comprises a first conductor (24) and a second conductor (26) and the first antenna element (20) is selected to provide a desired operating frequency range of the antenna;and ii) a second antenna element (22) , where the first portion is attached to the first conductor and the second portion is attached to the second conductor, and where the second antenna element (22) is selected to provide a desired impedance value of the antenna.

Description

RADIO FREQUENCY IDENTIFICATION LABEL FOR ULTRA HIGH FREQUENCY TECHNICAL FIELD OF THE INVENTION The present invention relates to an antenna design for radio frequency identification tags ("RFID", for its acronym in English). More particularly, the present invention relates to a design for RFID tags that operate particularly in the ultra high frequency operating band ("UHF"). BACKGROUND OF THE INVENTION Radio frequency identification ("RFID") has been proposed for use in various applications in which an RFID tag is associated with an object, which is subsequently interrogated or read to obtain related information by the object. For example, U.S. Pat. Nos. 6,232,870 and 6,486,780, and PCT publication WO 00/10122 discloses various functions and applications for RFID systems, and exemplifies the use of RFID tags in libraries. U.S. Pat. No. 5,963,134 also describes certain uses for RFID systems in libraries and for other applications. The design of a typical RFID tag reflects its origin in the semiconductor and printed circuit board industries. Although functional, the design has several features that increase the costs of the article Ref: 173893 finished and its efficiency, especially at ultra high frequencies ("UHF"). In a resonant RFID tag, the electrical inductance of an antenna is connected in parallel with a capacitor, so that the resonant frequency of the circuit thus formed is tuned to a specified value. In more advanced forms, the RFID tag circuit may include an integrated circuit electrically and mechanically attached to the antenna on a substrate, where the voltage induced in or to the antenna by a read signal provides power to operate the integrated circuit. Various methods have been developed for the design of RFID tags, such as those disclosed in the following references: US Pat. No. 6,501,435, U.S. Pat. No. 6,100,804, and PCT publication WO 00/26993. SUMMARY OF THE INVENTION One aspect of the present invention provides a radio frequency identification ("RFID") tag for ultra high frequency ("UHF"). The UHF RFID tag comprises: a) a dielectric substrate; b) an antenna attached to the dielectric substrate, wherein the antenna comprises: i) a first antenna element, wherein the first antenna element comprises a first conductor and a second conductor, wherein each conductor has a first extrusion and a second end opposite to the first end, where the first antenna element is selected - to provide a desired range - of operating frequencies of the antenna; and ii) a second antenna element, wherein the second antenna element comprises a first portion and a second portion, wherein the first portion is attached to the second end of the first conductor and the second portion is attached to the second end of the second conductor, and wherein the second antenna element is selected to provide a desired impedance value of the antenna; and e) an integrated circuit connected to the first end of the first conductor and to the first end of the second conductor. In a preferred embodiment of the UHF RFID tag described above, the integrated circuit has a first impedance value, the second antenna element has a second impedance value, the magnitude of the real component of the second impedance value is essentially similar to the magnitude of the real component of the first impedance value, and the magnitude of the imaginary component of the second impedance value is essentially similar to the magnitude of the imaginary component of the first impedance value, and the phase of the imaginary component of the first impedance value and the phase of the Imaginary component of the second impedance value are opposite. In another aspect of this embodiment, the first impedance value has a first real component value and a first imaginary component value, the second impedance value has a second value of real component and a second value of imaginary component, the first value of real component is essentially similar to the second value of real component, and the first value of imaginary component is essentially similar to the second value of imaginary component, where the magnitude of the imaginary component of the second impedance value is essentially similar to the magnitude of the imaginary component of the imaginary component of the first impedance value, and the phase of the imaginary component of the first impedance value and the phase of the imaginary component of the second impedance value are opposite. In another aspect of this embodiment, the first impedance value has a first component value, real and a first imaginary component value, the second impedance value has a second -value of real component and a second value of imaginary component, where the first value of the real component is equal to the second value of the real component and the first value of the imaginary component is equal to the second value of the imaginary component, the magnitude of the imaginary component of the second value of the impedance is equal to the magnitude of the imaginary component of the component imaginary of the first impedance value, and the phase of the imaginary component of the first impedance value and the phase of the -imaginary component of the second impedance value are opposite. In another preferred embodiment of the UHF RFID tag described above, the first portion of the antenna has a first real component value and a first imaginary component value, and the second antenna portion has a second real component value a second. value of imaginary component; where the second portion of the antenna is selected to provide a second value of real component and a second value of imaginary component that help to balance the first value of real component and the first value of imaginary component, to provide a second value of impedance of the antenna essentially similar to the first impedance value of the integrated circuit. In another aspect of this embodiment, the first portion of the antenna has a first value of real component and a first value of imaginary component, and the second portion of the antenna has a second value of real component and a second value of imaginary component, wherein the second portion of the antenna is selected to provide a second value of real component and a second value of imaginary component that help to balance the first value of the real component - and the first value of the imaginary component, to provide a second value of impedance of the antenna - same as the first impedance value of the integrated circuit. In another embodiment -preferred from the UHF RFID tag described above, the first portion of the second antenna element and the second portion of the second antenna element are in the form of closed curves. In another preferred embodiment of the UHF RFID tag described above, the first portion of the second antenna element and the second portion of the second antenna element are polygonal in shape. In yet another preferred embodiment of the above-described RFID U? F tag, the first portion of the second antenna element is different from the second portion of the second antenna element. In another preferred embodiment of the UHF RFID tag described above, the first portion of the second antenna element is similar in shape to the second portion of the second antenna element. In yet another preferred embodiment of the UHF RFID tag described above, the first portion of the second antenna element is different in size from the second portion of the second antenna element. In another preferred embodiment of the UHF RFID tag described above, the first conductor and the second conductor include meanders. In another preterm embodiment of the UHF RFID tag described above, the first conductor and the second conductor are made of a wire, shaped conductive sheets, or printed conductive cups. In another preferred embodiment of the UHF RFID tag described above, the The first antenna element is made of a different conductive material than the second antenna element. In yet another preferred embodiment of the UHF RFID tag described above, the dielectric substrate includes a dielectric constant e < 10 * e0 between 850 MHz and 960 MHz, where 8o is the permittivity of the free space (e0 = 8.85 x 10"12 C2 / N-m2) In another preferred embodiment of the UHF RFID tag described above, the dielectric substrate includes a first side and a second side opposite the first side, • where the antenna is attached to the first side, and the integrated chip is attached to the second side.In another preferred embodiment of the UHF RFID tag described above, the distance between the first portion of the second antenna element and the first conductor is different from the distance between the second portion of the second antenna element and the second conductor In another preferred embodiment of the UHF RFID tag described above, the length of the first conductor is different than the length of the second conductor Another aspect of the present invention provides a method of manufacturing an ultra high frequency radio frequency identification ("RFID") tag ("UHF"). This method comprises the steps of: a) providing a dielectric substrate; b) selecting an antenna comprised of a first antenna element and a second antenna element, wherein the first antenna element is selected to provide a range of desired operating frequencies for the antenna, wherein the second antenna element is selected to provide a desired impedance value, wherein the first antenna element comprises a first conductor and a second conductor, wherein each conductor has a first end and a second end opposite the first end, and wherein the second antenna element comprises a first portion and a second portion portion; and c) attaching the antenna to the dielectric substrate so that the first portion of the second antenna element is attached to the second end of the first conductor, and the second portion of the second antenna element is attached to the second end of the second conductor; and d) attaching an integrated circuit to the first end of the first conductor and to the first end of the second conductor. In a preferred embodiment of the method described above, the integrated circuit has a first impedance value, and the second antenna element has a second impedance value, where the magnitude of the real component of the second impedance value is essentially similar to the magnitude of the real component of the first impedance value, the magnitude of the imaginary component of the second impedance value is essentially similar to the magnitude of the imaginary component of the first impedance value, and the phase of the imaginary component of the first impedance value and the phase of the imaginary component of the second value of the impedance are opposite. In another aspect of this embodiment, the first impedance value has a first value of real component and a first value of imaginary component, where the second value of impedance has a second value of real component and a second value of imaginary component, where first The actual component value is essentially similar to the second real component value and the first imaginary component value is essentially similar to the second imaginary component value, the magnitude of the imaginary component of the second impedance value is essentially similar to the magnitude of the imaginary component component. imaginary component of the first impedance value, where the phase of the imaginary component of the first impedance value and the phase of the imaginary component of the second impedance value are opposite. In another aspect of this embodiment, the first impedance value has a first value of real component and a first value of imaginary component, where the second value of impedance has a second value of real component and a second value of imaginary component, where the The first value of the real component is equal to the second value of the real component and the first value of the imaginary component is equal to the second value of the imaginary component, the magnitude of the imaginary component of the second value of the impedance is equal to the magnitude of the component. of the imaginary component of the first impedance value, where the phase of the imaginary component of the first impedance value and the phase of the imaginary component of the second impedance value are opposite. In another preferred embodiment of the method described above, the first portion of the antenna has a first real component value and a first imaginary component value, and the second antenna portion has a second real component value and a second component value imaginary, where the second portion of the antenna is selected to provide a second value. of real component and a second value of imaginary component that help to balance the first value of real component and the first value of imaginary component, to provide a second value of impedance of the antenna essentially similar to the first value of impedance of the integrated circuit. In another aspect of this modality, the first portion of the antenna has a first value of real component and a first value of imaginary component, and the second portion of the antenna has a second value of real component and a second value of imaginary component, the second portion of. antenna is selected to provide a second component value, real and a second value of imaginary component that help balance the first real component value and the. first value of imaginary component to provide a second value of impedance of the antenna, equal to the first impedance value of the integrated circuit. In another preferred embodiment of the method described above, the first portion of the second antenna element and the second portion of the second antenna element are in the form of closed curves. In another preferred embodiment of the method described above, the first portion of the second antenna element and the second portion of the second antenna element have a polygonal shape. In yet another preferred embodiment of the method described above, the first portion of the second antenna element is different in shape from the second portion of the second antenna element. In another preferred embodiment of the method described above, the first portion of the second antenna element is similar in shape to the second portion of the second antenna element. In another preferred embodiment of the method described above, the first portion of the second antenna element is of a different size than the second portion of the second antenna element. BRIEF DESCRIPTION OF THE FIGURES The present invention will be further explained with reference to the attached Figures, where similar structures are designated with similar numbers in the different views, and where: Figure 1 is a top view of a modality of the tag. RFID of the present invention. Figure 2 is a graph illustrating the calculated impedance of a folded dipole antenna of the prior art. Figure 3 is a graph illustrating the calculated impedance of the antenna with the RFID tag of the present invention. DETAILED DESCRIPTION OF THE INVENTION The present invention is useful for radio frequency identification ("RFID") tags operating in the ultra high frequency ("UHF") band, which generally ranges from 850 MHz to 960 MHz; preferably 868 MHz for Europe, 915 MHz for the USA. and 956 MHz for Japan. RFID tags can be active or passive. Passive RFID tags, particularly those operating in the UHF band, use radio frequency signals from an incident electromagnetic field sent by an RFID reader to supply power to the tag. The radio frequency reader can provide an interface between a data management system and the RFID tag, or between the user and the RFID tag. When the RFID tag receives the radio frequency signal from the incident electromagnetic field, the antenna absorbs the energy of the radio frequency received from the radio frequency signal and directs the power to the integrated circuit in the RFID tag. The integrated circuit converts a portion of the radio frequency energy absorbed into electrical potential energy and stores this energy in a section of the internal circuits of the integrated circuit. The electric potential energy appears as a voltage in the internal connections of power supply in the integrated circuit. The other circuits in the integrated circuit, including the microprocessor, optional memory and the coding and decoding circuits for communications work through this stored energy. The incident electromagnetic energy of the RFID reader may contain data or instructions encoded in the radio frequency signal. The instructions may include commands for the RFID tag, to communicate its serial number or the content of data records in the integrated circuit. Using the energy stored in the integrated circuit, the integrated circuit can in turn communicate to the RFID reader the details of the data stored in the resident memory of the integrated circuit. The distance at which a label can be "read", ie, participate in a reciprocal communication with the RFID reader, depends on the output power of the RFID reader, the surrounding environment and the efficiency with which the RFID tag interacts with the incident electromagnetic field. The range in which the RFID tag can "write" new data into its memory is generally less than the "read" range, due to the higher overall voltages that are required for a "write" operation. For UHF RFID tags in particular, the RFID tag communicates with the RFID reader by modulating the load on the RFID antenna, causing a portion of the incident electromagnetic energy to be retrodiscated to the RFID reader. The reader receives the electromagnetic radiation and decodes the modulated signal. Since the RFID reader's energy emission is limited by government regulations, it is very likely that an improved reading range will be possible only with more efficient antenna designs with labels. Accordingly, a greater efficiency in the absorption of the antenna from the incident radio frequency energy and the transfer of the energy absorbed to the integrated circuit is desired. An antenna with UHF RFID tag must be efficient to absorb the incident electromagnetic radiation and re-scatter the electromagnetic radiation to the RFID reader. In addition, the connection between the antenna with RFID tag and the integrated circuit must be efficient to supply enough power to the integrated circuit, even at the upper limit of the operating distance, that is, at great distances separating the RFID reader and the RFID tag. , for example three meters. The efficiency of the interaction of the electromagnetic field with the RFID tag depends on the design of the antenna with RFID tag and the efficiency of the coupling of the electromagnetic energy of the antenna to the integrated circuit. This efficiency is related to the impedance of the antenna, and the impedance of the integrated circuit. Moderately efficient UHF antennas can be made with dipoles or two conductors, preferably of the order of half a wavelength. At 900 MHz, the wavelength of free space is approximately 300 mm. The efficient coupling of the electromagnetic energy between the antenna and the integrated circuit essentially depends on coinciding, or exactly matching, the impedance of the antenna with the impedance at the input connections of the integrated circuit. The impedance Z can be represented by a complex number, where the real component (represented as Re Z) represents the resistive loads in which a current that varies with time in phase with the voltage <; f = 0, where f is defined as the phase angle between the voltage and current waveforms) produces a dissipative (resistive) loss function. The imaginary component (represented as Im Z) represents a voltage that varies with respect to the time it advances (f = p / 2, inductive) or retards (f = -p / 2, capacitive) the current that "varies with respect to the time in the load restricted by the characteristic phase angle The complex impedance of the antenna and the complex impedance of the integrated circuit can be represented by a sum of a real component and an imaginary component.It can be manipulated the complex representations of impedance, voltage and current Using the usual mathematical rules for complex variables, an efficient coupling of the electromagnetic energy in the input connections between the antenna and the integrated circuit is obtained by designing the real component of the impedance of the antenna (Re to be close to, and preferably equal to, the real component of the impedance of the integrated circuit input (Re Z? C) Match the actual components of the impedances of the The antenna and the integrated circuit help to minimize the reflection of electromagnetic energy at the boundary between the connection points of the antenna with the circle. integrated, making the RFID tag more efficient. This phenomenon is taught in The Art by Electronics, by Paul Horowitz and Winfield Hill. { Cambridge University Press, Cambridge, England) 1980, pp. 565-568, which is incorporated herein by reference. In various bands of operating frequencies, including in particular the UHF operating bands, the imaginary impedance of. the antenna and the imaginary impedance of the integrated circuit (Im ZANT and Im ZtCl respectively) will affect the efficiency of power transfer to the integrated circuit. The term "power factor" is used to characterize the efficiency with which the electromagnetic energy of the radio frequency absorbed sent by the RFID reader absorbed by the antenna will be converted into energy stored in the integrated circuit. (The definition and explanation of the power factor is discussed in more detail in The Art of Electronics, by Paul Horowitz and Winfield Hill (Cambridge University Press, Cambridge, England) 1980, p.29, which is incorporated herein by reference. ) The power factor reaches its maximum when the current and voltage are in phase, which can be achieved by balancing the imaginary component (capacitive) of the input impedance of the integrated circuit with the imaginary (inductive) impedance component of the antenna . The operation of a simple dipole antenna is well understood among those skilled in the art, and can be described by Maxwell's equations. Simple dipole antennas are discussed in greater detail in Elements of Physics, by George Shortley and Dudley Williams, Prentice-Hall, Inc., Englewood Cliffs, NJ, USA, 1971, which is incorporated herein by reference. The general physical length of a dipole antenna can be decreased by using meanders 30, which are curved portions or an imbricate circuit path over the dipole antenna, to increase the effective electrical length. { signal path) of the dipole antenna, maintaining a preferred physical length. The meanders may be uniform or non-uniform. Another variation of the dipole antenna, which is also known in the art, is the folded dipole, where the two distal free ends which extend oppositely to the integrated circuit are folded on themselves, and are electrically connected. The impedance of an example of a folded dipole antenna, where the length of the straight section of the folded dipole antenna is 140 mm, is calculated as follows: ZDIPO OR FOLDED d = 140 mm) = (24.58 O, - j 13 .93 O) at f = 915 MHz, where the length of one end of the folded dipole antenna is from one end to the other. This calculation was made using NEC (Numerical Electromagnetics Code) Win-Pro, commercially available from Nittany Scientific, located in Riverton, UT, USA. If the length of this exemplary folded dipole is effectively reduced by 1%, the calculations. show that the impedance changes to: FOLDED ZDIPOLO (I = 0 .99 * I0) = (4 .83 O, -j 8 .635 O) at f = 915 MHz - This large displacement in the antenna impedance calculated from a relatively small displacement in the physical length characteristic of the folded dipole illustrates the sensitivity of the folded dipole antenna to small variations in its overall length. The RFID tag of the present invention provides antenna designs that efficiently couple radio frequency energy received by the antenna with the RFID of the integrated circuit, particularly the RFID tags operating in the UHF operating band. The design of the antenna is compact, making it suitable for RFID tags or similar applications where it is desirable to minimize the overall size of the RFID tag. The design of the antenna can be easily modified to help match and balance the complex impedance of the antenna and the complex input impedance of the integrated circuit to the selected operating frequency. Figure 1 illustrates one embodiment of the RFID tag 10 of the present invention. The RFID tag 10 is especially useful in the UHF ranges and, therefore, may be an UHF RFID tag 10. The RFID tag 10 includes a dielectric substrate 12 with a first side 14 and a second side 16 opposite the first side 16. antenna 18 is attached to first side 14 of dielectric substrate 12. Preferably, antenna 18 is attached to dielectric substrate 12 by any device known in the art, for example by lamination with an adhesive film. curable and sensitive to pressure, -or by direct deposit on the substrate. The RFID tag 10 also includes an integrated circuit 36 attached to the first side 14 of the dielectric substrate 12. Preferably, the integrated circuit 36 is attached to the dielectric substrate 12 by any device known in the art, for example anisotropic conductive film adhesives, solder or thermo-compression union. The antenna 18 includes a first antenna element 20 and a second antenna element 22. The first antenna 20 is preferably a dipole antenna including a first conductor 24 and a second conductor 26. In a preferred embodiment, the conductors 24,26 include Meanders 30. - Meanings 30 help decrease the overall physical length of the dipole antenna and help increase the electrical length (signal path). Each conductor 24,26 includes a first end 27 and a second end 28 opposite the first end 27. The second antenna element includes a first portion 32 and a second portion 34. In a preferred embodiment, the first portion 32 and the second portion 34 are shaped like closed curves or polygons. In one example, as illustrated in Figure 1, the first portion 32 may have the shape of a circle, and the second portion 34 may have the shape of an ellipse. However, portions 32,34 of the second antenna element can have any shape. The portions 32,34 of the second antenna element can have similar or similar shapes. The portions 32,34 of the second antenna element can be of similar or different sizes. However, the person skilled in the art can select the shape and size of the portions 32,34 of the second element and antenna to help balance the impedance of the antenna 18 with the impedance of the integrated circuit 36, as will be discussed below. The first end 27 of the conductors 24,26 is electrically connected to the integrated circuit 36, preferably by individual terminals (not shown). In a preferred embodiment, the second end 28 of the first conductor 24 is connected or electrically connected to the first portion 32 of the second antenna element 22, and the second end 28 of the second conductor 26 is connected or electrically connected to the second portion 34 of the second antenna element 22. the length "c" measured between the second end 28 of the first conductor 24 and the curved portion of the first conductor 24 (as illustrated in Figure 1) may be the same or different than the length "d" measured between the second end 28 of the second conductor 26 and the curved portion 3 of the second conductor 24. The lengths c and d, respectively, may be selected by the art connoisseur to help balance the impedance of the antenna 18 with the impedance of the integrated circuit 36, as will be discussed below. In order to fine tune the band of operational frequencies of the RFID antenna 18, the length of the first conductor 24 and the second conductor 26, which make up the first antenna element 20 can be modified. By selecting the length of the first conductor 24 and the second conductor 26, the first antenna element 20 can be selected to determine the range of operating frequencies of the antenna 18 of the RFID tag 10. The lengths of the conductors 24,26 can be the same or different. The preferred lengths of conductors 24, 26 are in the range of between 85 mm and 170 mm, and the most preferred lengths of conductors 24, 26 are approximately 140 mm. The design of the first antenna element 20 also helps to match the real part of the impedance of the antenna 18 with the real part of the input impedance of the integrated circuit 36. The design of the first antenna element 20 provides a device by means of which the real part of the impedance of the antenna 18 can be increased, or decreased if desired, to essentially match or equalize the range of the input impedance of the integrated circuit 36. The design of the second antenna element 22 helps to modify the current distribution at the second ends 28 of the first and second conductors 2-4, 26 of the first antenna element 20. When modifying the current distribution at the second ends 28 of the conductors 24,26, the second antenna element modifies the imaginary component of the impedance of the antenna 18 to balance the imaginary component of the input impedance of the integrated circuit 36. When the actual impedance of the antenna 18 and the integrated circuit 36 are essentially coincident, and the imaginary components of the impedance of the antenna 18 and the integrated circuit 36 are balanced, the radio frequency energy absorbed by the antenna is efficiently transferred from the antenna 18 to the circuit integrated 36. At the second end 28 of each conductor 24,26, a second antenna element 22 is electrically connected to the second end 28 of the conductors 24,26. To help balance the capacitive reactance of the integrated circuit 36, the first portion 32 and the second portion 34 of the second antenna elements 22 are selected to introduce a reactance primarily inductive to the impedance of the antenna 18 and an associated phase shift in the radio frequency signal. The second antenna elements 22 may also have a smaller portion of associated capacitive reactance, although the net inductive impedance of the second antenna elements 22 helps to balance the capacitive impedance of the integrated circuit. The portions 32,34 of the second antenna elements 22 can be in the form of closed curves, with a circumference that can be up to 1/8 of the wavelength of the radio frequency signal, and up to 1/2 of the length wave of the radio frequency signal. The magnitude of the effect of the impedance of the second antenna element 22 is. determined by the distribution of electric currents over the length of the first portion 20 of the antenna 18, and at the second end 28 of each conductor 24,26. The presence of the second antenna element 22 helps to modify the boundary conditions for electric currents, compared with the current distribution in dipole antennas known in the prior art. The modified boundary conditions introduce an additional phase shift in the current distribution in the antenna, compared to the phase shifts of the dipole antennas known in the prior art. The phase shifts in the distribution of electric currents introduced by the second antenna element 22 have the effect of modifying the reflection of radio frequency energy at the second ends 28 of the first antenna element 20, compared with the dipole antenna known in the prior art. By selecting the second antenna elements 22 based on the teachings of the present specification, the imaginary component of the impedance of the antenna 18 can be selected to be inductive, thereby balancing the imaginary (capacitive) component of the integrated circuit 36 .

The design of the antenna 18 helps to - match the real part of the antenna impedance, Re ZANT * with the real component of the integrated circuit input impedance, Re Zt.c, to help efficiently couple the radio signal frequency of the antenna 18 with the. integrated circuit 36. The imaginary part of the impedance of the antenna 18, IMANT ZANT / balances the imaginary part of the impedance of the input of the integrated circuit 36, Im Ztc, although preferably they are of opposite phases. Under these conditions of matched and balanced impedance components, the radio frequency energy absorbed by the antenna 18 is efficiently coupled with that of the integrated circuit. One embodiment of the preferable operating conditions of the RFID tag 10 is summarized as follows: Re ZJC ~ 'or ZN and ¡Im Zid ~ | lm ZAN I with f (Z? C) * = -f (ZAN) where f is the phase angle of the complex impedance. Even if it is not possible to exactly match the complex impedance of the antenna 18 with the complex impedance of the integrated circuit input to the RFID operating frequency, an essential or near match of match impedance at the operating frequencies will produce a more efficient coupling of the antenna 18 with integrated circuit 36, compared to a poor match. Figure 2 is a graph illustrating the calculated impedance of a folded dipole antenna of the prior art with a dipole length (distance a of 140 mm and a length between ends (distance b) of 10 mm. real Re ZAN ° e the impedance of the antenna as a function of the frequency The line 52 graphs the imaginary component, Im AT / of the impedance of the antenna as a function of the frequency.Note the values for Re ZAT O Im ZANT data for a radio frequency range of 915 MHz, to 915 MHz, ZAN PREVIOUS TECHNICAL DIPOLO = (24.6 O, -j 13.6 O) Figure 2 shows the calculated values of the real and imaginary components of the complex impedance of an antenna Folded dipole from the previous technique The calculus were made using a program of antenna models (NEC: Numerical Electromagnetics Code, commercially available as NEC WINPro from Nittany Scientific, Inc.) Note that the complex impedance a 915 MHz is approximately (-24.575 O - j 13.93O). Near the radio frequency of interest (915MHz), the folded dipole antenna of the prior art has a small component of real impedance (resistive) and a small component of imaginary impedance with negative (ie, capacitive) phase. The small magnitude of the real component (24 O resistive) of the impedance of the folded dipole does not coincide with the real component of greater magnitude (65 O resistive) of the input impedance of the integrated circuit. The small magnitude (13.93 O capacitive) of the imaginary component of the impedance of the folded dipole does not coincide with the largest magnitude (720 O capacitive) of the imaginary component of the input impedance of the integrated circuit. The phase (-j, capacitive) of the imaginary component of the impedance of the folded dipole is equal to the phase (-j, capacitive) of the imaginary component of the input impedance of the integrated circuit. Accordingly, the imaginary component of the folded dipole antenna does not balance the imaginary component of the circuit input impedance to essentially cancel each other. Under these conditions of unmatched real components and unbalanced imaginary components of the impedances of the antenna and the integrated circuit, the electromagnetic signal absorbed by the antenna will be coupled with that of the integrated circuit with little efficiency, that is, little energy transfer. Figure 3 is a graph illustrating the calculated impedance of the antenna 18 of the RFID tag of the present invention, where the distance a is equal to 140 mm and the distance b equals 10 mm. Note that the scale of this graph is different from the scale of the graph in Figure 2, to more clearly show the higher impedance values characteristic of the antenna design of the present invention. Line 54 graphs the real component Re ZN of the impedance of antenna 18 as a function of frequency. The line 56 graphs the imaginary component, Im of the impedance of the antenna 18 as a function of the frequency. Note that the values. for Re ZANT and Im ZANT dice for a frequency of 915 MHz; Z AN DIPOLO PRESENT INVENTION = (67.0 O + j 751.5 O). The calculations were made using the aforementioned antenna model program (NEC: Numerical Electromagnetics Code). Near the radio frequency of interest (915MHz), antenna 18 shows a real impedance component. { resistive) and an imaginary impedance component with a positive (ie, inductive) phase. The magnitude of the real component (67 O resistive) of the impedance of the antenna of the present invention thereof. example approximately matches the actual component (65 O resistive) of the input impedance of the integrated circuit 36. The magnitude (751 O inductive) of the imaginary component of the impedance in the antenna of the present invention in this example roughly matches the magnitude (720 O capacitive) of the imaginary component of the input impedance of the integrated circuit 36. The phase (+ j, inductive) of the imaginary component of the impedance of the antenna of the present invention in this example is opposite to the phase (-j , capacitive) of the imaginary component of the input impedance of the integrated circuit 36. The imaginary component of the antenna impedance of the present invention in this example and the input impedance of the integrated circuit 36 are roughly balanced, so that essentially cancel each other. In this preferred embodiment, real coincidental components and balanced imaginary components of the impedances of the antenna 18 and the integrated circuit 36, the electromagnetic signal absorbed by the antenna 18 is coupled with that of the integrated circuit 36 with high efficiency, compared to the dipole antenna folded from the prior art discussed in relation to Figure 2. The dielectric substrate 12 can be any dielectric material known in the art. Examples of dielectric materials suitable for the substrate 12 include polyethylene terephthalate (commonly known as polyester or PET), polyethylene naphthate (commonly known as PEN), PET and P? N copolymers, polyimide and polypropylene. Preferably, the thickness of the dielectric substrate 12 is in the range of 0.010 to 0.200 mm, and more preferably in the range of 0.025 to 0.100 mm. However, the dielectric substrate may have any thickness, and may even have a non-uniform thickness. An example of an appropriate integrated circuit 36 is commercially available from Philips Semiconductors, based in Eindhoven, The Netherlands, with the part number SL3ICS30. The antenna 18 may be of any type of conductive material, such as wire, conductive metal pattern (such as those formed of metal foils such as etched aluminum, etched copper, plated copper and the like), a printed conductor pattern (such as those made from conductive inks). or other materials containing metal, optionally including processing steps to improve their conductivity), compressed copper powder (for example as disclosed in U.S. Patent Application 2003/0091789, incorporated herein by reference) , printed or compressed graphite or carbon black, or other conductive materials known to those skilled in the art. The antenna 18 shown in Figure 1 is a dipole antenna with a first conductor 24 and a second conductor 26. However, other antennas known in the art can be used in combination with the second antenna element 22, for example, a folded dipole, a spiral antenna, a "Z" antenna, a curved antenna or its accessories, such as slotted antennas. The operation of the present invention will be described in relation to the following detailed examples. These examples are offered to illustrate the various specific and preferred modalities and techniques. However, it should be understood that various variations and modifications may be made that fall within the scope of the present invention. EXAMPLES A preferred embodiment of the RFID tag 10 of the present invention was made, as illustrated in Figure 1. The dimensions of the antenna 18 are illustrated in Figure 1, and the antenna of this example included a distance "a" of 140 mm and a distance "b" of 10 mm. A comparative example of a folded prior dipole antenna of the prior art was also made. Antenna 18 was plated with 0.118 mm thick copper on a 0.025 mm thick polyimide substrate 12, commercially available from Dupont Electronics, headquartered in Wilmington, DE, USA, under the trade name film Kapton E Photoresistive material, commercially available from MacDermid, Inc., based in Wilmington, DE, USA, under the tradename MacDermid SF 320-, was laminated onto the surface of the plated copper film. : The photoresistive material was applied to the substrate, in the form of the desired final antenna 18. The exposed copper was scraped, leaving copper in the pattern of the desired final antenna. The remaining photoresistive material of the copper was removed, using the methods suggested by the manufacturer of the material. After removing the photoresist material, the copper antenna 19 formed in its final form on the polyimide 12 substrate was left. The resulting 0.018 mm copper traces were of the same thickness as the initial thickness of the copper sheet. The traces of copper were 1,000 mm wide, except for the two short traces connected to the connection terminals of the integrated circuit; these two traces were 0.100 mm wide. He is online. the integrated circuit to the ends 27. The antenna 20 had an 'a' dimension of 140 mm and a 'b' dimension of 10 mm. The first portion of the second antenna element was formed as a circle with a radius of 5 mm, and joined the end 28 of the first conductor 24, with a dimension 'c' of 4mm. The second portion of the second antenna element was formed as a circle with a radius of 5 mm attached to the end 28 of the second conductor 26, with a dimension 'd' of 58 mm. An appropriate integrated circuit 36 is commercially available from Philips Semiconductors, based in? Indhoven, The Netherlands, 'with the part number SL3ICS30 to the polyimide substrate 12 by an anisotropic conductive film adhesive. This integrated circuit 36 had known characteristics of input impedance of ZIC = (65 O - j 720 O) at 915 MHz. The antenna of the comparative example was formed using the same procedures and dimensions as the antenna of the present invention described above, except in that the comparative antenna had no second antenna elements, and its ends 28 were joined. Since the ways of measuring the real and imaginary impedance of the antenna provide questionable results, due to the loads of the measurement forms on the antenna, which affect the measured values, a preferred way to evaluate the balance between the complex impedance of the antenna and the IC is to measure the reading distance. A greater reading distance indicates more balanced impedances. The reading distance of the UHF RFID tag 10 of the present invention was measured with a 915 MHz RFID reader, commercially available from SAMSys Technologies, Richmond Hill, Ontario, Canada, under the trade name SAMSYS, part number MP9320, operated with an output power of 1 watt. The RFID reader was connected to a polarized circular antenna, commercially available from Cushcraft Corporation, Manchester, NH, USA, under the tradename CUSHCRAFT, part number S9028PC. The reading distance of the comparative example of the simple dipole antenna,. with the same integrated circuit Philips model SL3ICS30 was less than 0.3 m. The reading distance of the exemplary UHF RFID tag 10 of the present invention was 1.5 m.

Table 1. Real and Imaginary Impedance Components of the Integrated Circuit, Comparative Example and Example of the Present Invention The tests and their results described above are solely for the purpose of illustration, rather than prediction, and it would be expected that the variations in the testing procedures will produce different results. The present invention was described with reference to various embodiments thereof. The detailed description and previous examples were given only for clarity. No unnecessary limitations should be extracted from them. All of the above patents and patent applications are hereby incorporated by reference. It will be apparent to those skilled in the art that changes can be made in the described embodiments without departing from the scope of the present invention. Accordingly, the scope of the present invention should not be limited to the exact details and structures described herein, but by the structures described by the language of the claims, and the equivalents of such structures. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (27)

1. CLAIMS Having described the foregoing invention, the content of the following claims is claimed as property: 1. An ultra high frequency ("UHF") radio frequency identification ("RFID") identification tag, characterized in that it comprises: a) a dielectric substrate; b) an antenna attached to the dielectric substrate, wherein the antenna comprises: i) a first antenna element, wherein the first antenna element comprises a first conductor and a second conductor, wherein each conductor has a first end and a second end opposite the first end, wherein the first antenna element is selected to provide a desired range of operating frequencies of the antenna; and ii) a second antenna element, wherein the second antenna element comprises a first portion and a second portion, wherein the first portion is attached to the second end of the first conductor and the second portion is attached to the second end of the second conductor. , and wherein the second antenna element is selected to provide a desired impedance value of the antenna; and e) an integrated circuit connected to the first end of the first conductor and the first end of the second conductor.
2. 2. The UHF RFID tag - according to claim 1, characterized in that the integrated circuit has a first impedance value, and where the antenna has a second impedance value, and where the magnitude of the real component of the second impedance value is essentially similar to the magnitude of the real component of the first impedance value, and the magnitude of the imaginary component of the second impedance value is essentially similar to the magnitude of the imaginary component of the first impedance value, and where the phase of the imaginary component of the first impedance value and the phase of the imaginary component of the second impedance value are opposite.
3. 3. The UHF RFID tag according to claim 2, characterized in that the first impedance value has a first real component value and a first imaginary component value, wherein the second impedance value has a second real component value and a second value of imaginary component, where the first value of real component is equal to the second value of real component and where the magnitude of the imaginary component of the second value of impedance is equal to the magnitude of the imaginary component of the imaginary component of the first value of impedance , and where the phase of the imaginary component of the first impedance value and the phase of the imaginary component of the second impedance value are opposite.
4. 4. The UHF RFID tag according to claim 2, characterized in that the first portion of the antenna has a first real component value and a first imaginary component value, and the second antenna portion has a second real component value and a second value of imaginary component, and where the second portion of the antenna is selected to provide a second-value of real component and a second value of imaginary component that help to balance the first value of real component and the first value of imaginary component for provide the second impedance value of the antenna, essentially similar to the first impedance value of the integrated circuit.
5. 5. The UHF RFID tag according to claim 4, characterized in that the first portion of the antenna has a first value of real component and a first value of imaginary component, and the second portion of the antenna has a second value of component real and a second value of imaginary component, and where the second portion of the antenna is selected to provide a second value of real component and a second value of imaginary component, which help to balance the first value of real component and the first value of imaginary component to provide the second impedance value of the antenna equal to the first impedance value of the integrated circuit.-
6. 6. The UHF RFID tag according to claim 1, characterized in that the first portion of the second antenna element and the second portion of the second antenna element are in the form of closed curves. The UHF RFID tag according to claim 1, characterized in that the first portion of the second antenna element and the second portion of the second antenna element have a polygonal shape. 8. The UHF RFID tag according to claim 1, characterized in that the first portion of the second antenna element is different from the second portion of the second antenna element. The RFID UHF tag according to claim 1, characterized in that the first portion of the second antenna element is similar in shape to the second portion of the second antenna element. The RFID UHF tag according to claim 1, characterized in that the first portion of the second antenna element is of a different size than the second portion of the second antenna element. 11. The UHF RFID tag according to claim 1, wherein the first conductor and the second conductor include meanders. The RFID UHF tag according to claim 1, characterized in that the first conductor and the second conductor are made of a wire, conductive sheets with shapes, or printed conductive traces. 13. The UHF RFID tag according to claim 1, characterized in that the first antenna element is made of a different conductive material than the second antenna element. 14. The UHF RFID tag according to claim 1, characterized in that the dielectric substrate includes a dielectric constant e <; 10 * e0 between 850 MHz and 960 MHz, where e0 is the permittivity of the free space (e0 = 8.85 x 10 ~ 12 C2 / N.m2). 15. The UHF RFID tag according to claim 1, characterized in that the dielectric substrate includes a. first side and a second side opposite to the first side, where the antenna is attached to the first side and the integrated chip is attached to the second side. The RFID UHF tag according to claim 1, characterized in that the distance between the first portion of the second antenna element and the first conductor is different from the distance between the second portion of the second antenna element and the second conductor. 1
7. 7. The UHF RFID tag according to claim 1, characterized in that the length of the first conductor is different from the length of the second conductor. 1
8. 8. A method of manufacturing an ultra-high frequency ("UHF") radio frequency identification ("RFID") tag, characterized in that it comprises the steps of: a) providing a dielectric substrate; b) selecting an antenna comprised of a first antenna element and a second antenna element, wherein the first antenna element is selected to provide a range of desired operating frequencies of the antenna, where the second antenna element is selected to provide a desired impedance value, wherein the first antenna element comprises a first conductor and a second conductor, wherein each conductor has a first end and a second end opposite the first end, and wherein the second antenna element comprises a first portion and a second portion portion; and c) attaching the antenna to the dielectric substrate so that the first portion of the second antenna element is connected to the second end of the first conductor and the second portion of the second antenna element is connected to the second end of the second conductor; and d) joining an integrated circuit with the first end of the first conductor and the first end of the second conductor. The method according to claim 18, characterized in that the integrated circuit has a first impedance value, and where the antenna has a second impedance value, and where the magnitude of the real component of the second-impedance value is essentially similar to the magnitude of the real component of the first impedance value, and the magnitude of the imaginary component of the second impedance value is essentially similar to the magnitude of the imaginary component of the first impedance value, and. where the phase of the imaginary component of the first value of impedance and the phase of the imaginary component of the second impedance value are opposite. The method according to claim 19, characterized in that the first impedance value has a first real component value and a first imaginary component value, where the second impedance value has a second real component value and a second imaginary component value, where the first value of the real component is equal to the second value of the real component, and where the magnitude of the imaginary component of the second impedance value is equal to the magnitude of the imaginary component of the first impedance value, and where the The phase of the imaginary component of the first impedance value and the phase of the imaginary component of the second impedance value are opposite. 21. The method according to claim 19, characterized in that the first portion of the antenna has a first value of real component and a first value of imaginary component, and the second portion of the antenna has a second value of component real and a second imaginary component value, and wherein the second portion of the antenna is selected to provide a second real component value and a second imaginary component value that help balance the first real component value and the first real value Imaginary component to provide the second impedance value of the antenna, essentially similar to the first impedance value of the integrated circuit. The method according to claim 21, characterized in that the first portion of the antenna has a first real component value and a first imaginary component value, and the second antenna portion has a second real component value and a second value - of imaginary component, and wherein the second portion of the antenna is selected to provide a second value of real component and a second value of imaginary component that helps to balance the first value of real component and the first value of imaginary component to provide the second value of the impedance of the antenna, which is equal to the first impedance value of the integrated circuit. 23. The method according to claim 18, characterized in that the first portion of the second antenna element and the second portion of the second antenna element are in the form of closed curves. The method according to claim 18, characterized in that the first portion of the second antenna element and the second portion of the second antenna element have a polygonal shape. 25. The method according to claim 18, characterized in that the first portion of the second antenna element is different from the second portion of the second antenna element. 26. The method according to claim 18, characterized in that the first portion of the second antenna element is similar in shape to the second portion of the second antenna element. 27. The method according to claim 18, characterized in that the first portion of the second antenna element is of a different size from the second portion of the second antenna element.