JP2006086603A - Rfid tag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive RFID tag with high convenience by keeping an excellent characteristic without the need for carrying out individual adjustment for diversified operating environments. <P>SOLUTION: The RFID tag 1 includes an antenna coil and a circuit for carrying out transmission/reception operations at a prescribed operating frequency of 13.56 MHz or the like and the antenna coil is formed by winding an FPC 12 including a conductor pattern 13 around the surrounding of a core 11 made of a ferrite material. The ferrite material of the core 11 has a characteristic of including the prescribed operating frequency in a frequency region wherein a real number component of a complex permeability is sufficiently smaller than a flat frequency region of the frequency characteristic of the complex permeability and the imaginary component of the permeability is sufficiently greater than the flat frequency region at a higher frequency region than the flat frequency region of the frequency characteristic of the complex permeability. Thus, the Q value of the ferrite material is comparatively smaller and the characteristic deterioration due to variations in the operating environment can be avoided in the case that the RFID tag 1 is fitted to a metal or a nonmetal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technical field of an RFID (Radio Frequency Identification) tag that operates at a predetermined use frequency (for example, 13.56 MHz), and in particular, an electromagnetic induction type in which an antenna coil is configured using a core made of a ferrite material. The present invention relates to an RFID tag.

For the purpose of article management and the like, non-contact and small RFID tags are used. The RFID tag includes an antenna coil and various circuits (IC, capacitor, etc.), and performs wireless communication at a predetermined frequency between the reader / writer and the RFID tag, and data held in the IC of the RFID tag. Read or write new data. For an electromagnetic induction type RFID tag known as a general-purpose RFID tag, 13.56 MHz is defined as one of the operating frequencies. When configuring an RFID tag using 13.56 MHz, an antenna coil is formed by winding a conductor around a core made of a magnetic material, and the resonance frequency is set by appropriately setting the shape, material, and number of windings of the conductor. Can be optimized. Thereby, the resonance frequency of the antenna coil can be matched with 13.56 MHz which is a use frequency. In addition, a method is known in which a capacitor is formed in an RFID tag circuit and the capacitance value is changed by partially cutting the capacitor electrode, thereby adjusting the resonance frequency of the antenna coil (for example, Patent Document 1). reference).
JP 2003-187207 A

  As described above, the RFID tag adjusted in accordance with a predetermined use frequency is assumed to have various use environments during actual use. For example, as an RFID tag attachment object, both metal and non-metal such as plastic can be considered. In this case, the resonance frequency of the antenna coil is deviated from the use frequency depending on the presence or absence of the adjacent metal. Usually, since the Q value of the antenna coil is set high, the impedance at the operating frequency changes rapidly due to the change of the resonance frequency. Therefore, there is a problem that the communication distance is reduced depending on the use environment. The resonance frequency can be adjusted in advance on the assumption that the RFID tag is attached only to metal or non-metal, but in this case, it is difficult to realize an RFID tag that can be used in various usage environments. Low.

  Therefore, the present invention has been made to solve such a problem, and even in a situation where the usage environment such as attachment of an RFID tag to a metal or non-metal fluctuates, the communication distance due to the fluctuation of the resonance frequency can be reduced. The purpose of the present invention is to provide an RFID tag that prevents deterioration in performance such as a decrease and does not require individual adjustment for various use environments, and is inexpensive and highly convenient.

  In order to solve the above problem, the RFID tag according to claim 1 is an RFID tag including an antenna coil and a circuit that perform transmission and reception operations at a predetermined use frequency, and the antenna coil surrounds a core made of a magnetic material. The magnetic material is formed in a region where the imaginary component of the magnetic permeability is sufficiently larger than the value in the flat region on the high frequency side of the flat region of the frequency characteristics of the complex magnetic permeability. It has a characteristic that the used frequency is included.

  According to the present invention, since the antenna coil of the RFID tag is used as a core using the high frequency side of the normally used flat region of the frequency characteristics of the complex permeability, the impedance has a resonance frequency due to the decrease in the Q value. It changes relatively slowly in the center. Therefore, it is possible to avoid a decrease in communication distance due to differences in environmental conditions without individually adjusting the resonance frequency depending on whether the RFID tag is attached to metal or non-metal. In addition, it is possible to realize an RFID tag that can maintain stable and stable communication characteristics and can be reduced in cost by being shared without adjustment for each use environment.

  The RFID tag according to claim 2 is an RFID tag including an antenna coil and a circuit that perform transmission and reception operations at a predetermined use frequency, and the antenna coil is formed by winding a conductor around a core made of a magnetic material, The real component and the imaginary component of the complex permeability of the magnetic material at the predetermined use frequency are both approximately 200 or more.

  According to this invention, the antenna coil of the RFID tag uses a frequency region in which both the real component and the imaginary component of the complex magnetic permeability are approximately 200 or more, so that it is mainly linked to the imaginary component of the magnetic permeability. As a result, the loss increases, the Q value decreases, and the impedance changes relatively slowly around the resonance frequency. Therefore, by the same operation as that of the first aspect of the invention, it is possible to maintain stable communication characteristics with respect to changes in the usage environment, and RFID that can reduce costs by sharing without adjustment for each usage environment A tag can be realized.

  The RFID tag according to claim 3 is the RFID tag according to claim 2, wherein the imaginary number component of the complex permeability of the magnetic material is approximately 600 or less.

  According to this invention, in addition to the operation of the invention according to claim 2, since the imaginary component of the complex permeability of the core is approximately 600 or less, the loss is prevented from increasing excessively, and the RFID tag A sufficient communication distance can be secured.

  The RFID tag according to claim 4 is the RFID tag according to any one of claims 1 to 3, wherein the magnetic material is a ferrite material containing a plurality of components.

  According to the present invention, since the ferrite material is used as the magnetic material of the core, the magnetic permeability can be adjusted appropriately by finely adjusting the component ratio of various metal oxides contained in the ferrite material. Good characteristics can be easily realized.

The RFID tag according to claim 5, in the RFID tag according to claim 4, as a component of the ferrite material, a _Fe 2 _{O 3} of 45-58 mol%, and 8 to 15 mol% NiO,. 25 to 32 mol% of ZnO is contained.

According to the present invention, the ferrite materials used for the core are three types of Fe ₂ O ₃ , NiO, and ZnO, and the optimum range of each component ratio is determined. The corresponding magnetic permeability can be easily adjusted.

  The RFID tag according to claim 6 is the RFID tag according to any one of claims 1 to 5, wherein the predetermined use frequency is 13.56 MHz.

  According to the present invention, since a general frequency of 13.56 MHz is set as a use frequency as an electromagnetic induction type RFID tag, good characteristics of the antenna coil are ensured as described above in the general-purpose RFID coil standard. be able to.

  According to the present invention, the antenna coil of the RFID tag is adjusted so as to have a working frequency on a higher frequency side than the flat region of the magnetic permeability of the magnetic material of the core and to have a small real number component and a large imaginary number component. As a result, the Q value of the antenna coil can be kept low, and performance degradation such as the communication distance of the RFID tag can be prevented even when the resonance frequency shifts in accordance with environmental changes. Therefore, good performance can be secured without making individual adjustments for various usage environments, for example, when both metal and non-metal are used as attachment objects, and an inexpensive and highly convenient RFID tag can be realized. Become.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. In the present embodiment, a case will be described in which the present invention is applied to an electromagnetic induction type RFID tag in which a conductor wire is wound around a core made of a ferrite material to constitute an antenna coil.

  FIG. 1 is a perspective view showing the structure of the RFID tag 1 according to the present embodiment. An RFID tag 1 shown in FIG. 1 has a structure in which an FPC 12 is wound around a core 11 formed of a ferrite material in a plate shape. The FPC 12 is formed with a conductor pattern 13 that constitutes a conductor portion of the antenna coil. With the configuration shown in FIG. 1, the RFID tag 1 operates as an antenna coil having a desired resonance frequency. In general, the RFID tag 1 having a structure as shown in FIG. 1 is formed in a card shape having a thickness in an integrated state inside a resin case.

In FIG. 1, a core 11 is made of a ferrite material as a magnetic material that generates a magnetic flux based on an induction electromagnetic field from a reader / writer installed in the vicinity. This ferrite material is formed by sintering various materials such as a plurality of metal oxides. For example, the ferrite material contains metal oxides such as Fe ₂ O ₃ , NiO, and ZnO in a predetermined component ratio. Yes. In this embodiment, the component ratio of the ferrite material is optimized according to the relationship between the magnetic permeability and the characteristics of the antenna coil, which will be described in detail later. Also, the size and shape of the core 11 can be appropriately determined according to characteristics such as the resonance frequency.

  The FPC 12 is made of a base material in which a flexible resin (for example, PET) is formed to a predetermined thickness, and a linear conductor pattern 13 is formed on one surface. Further, an IC 14 and a capacitor 15 arranged at predetermined positions on the FPC 12 are connected to the conductor pattern 13. The IC 14 is responsible for reading and transmitting predetermined data in response to a command from the reader / writer, and storing and holding data received from the reader / writer. The capacitor 15 forms part of the resonance circuit in the antenna coil, and plays a role of adjusting the resonance frequency of the antenna coil by adjusting the capacitance value. For example, when the RFID tag 1 is manufactured, the resonance frequency of the antenna coil can be adjusted by partially cutting the electrode of the capacitor 15 to change the capacitance value.

  The conductor pattern 13 can be connected in a coil shape by connecting adjacent conductors at each end of the FPC 12 (predetermined location of the RFID tag 1 shown in FIG. 1) with the FPC 12 wound around the core 11. it can. Thereby, as shown in FIG. 1, the antenna coil by which the conducting wire was wound around the core 11 by the predetermined | prescribed winding number is comprised. Here, one end and the other end of the connected conductor pattern 13 need to be electrically connected by, for example, a wire rod (not shown) or a crossover pattern provided on the other surface of the FPC 12. The number of turns of the conductor pattern 13 when the FPC 12 is wound around the core 11 can be appropriately determined according to characteristics such as a resonance frequency. Further, the winding method of the FPC 12 around the core 11 may be such that the conductor pattern 13 is disposed on the core 11 either on the inside or on the outside of the FPC 12.

  Next, the relationship between the characteristics of the RFID tag 1 as an antenna coil and the characteristics of the core 11 made of a ferrite material will be described. The frequency characteristics of the antenna coil are strongly influenced by the usage environment. For example, the resonance frequency varies depending on whether the object to be attached is metal or nonmetal. When the Q value of the antenna coil is large, the peak of the frequency characteristic becomes steep, and the characteristic deterioration when the resonance frequency is shifted increases. Therefore, in order to keep the characteristics of the antenna coil stable to some extent against environmental fluctuations, it is necessary to suppress the Q value from becoming too large. On the other hand, when the Q value becomes too low, the communication distance of the RFID 1 Decrease is a problem. In the present embodiment, attention is paid to a ferrite material that can lower the Q value, and appropriate measures are taken against environmental fluctuations while ensuring the communication distance in the RFID tag 1 based on the setting of the magnetic permeability.

  The Q value of the antenna coil can be expressed by the following equation.

Q = fc / (fh−fl)
Where fc: resonance frequency
fh: frequency on the high frequency side that decreases by 3 dB from the level (voltage) of the resonance frequency
fl: Frequency on the low frequency side that decreases by 3 dB from the level (voltage) of the resonance frequency In this equation, when the Q value increases, it can be seen that the level decrease when deviating from the resonance frequency increases.

  In general, the magnetic permeability of a magnetic material such as a ferrite material is expressed as a complex magnetic permeability composed of a real component μ ′ and an imaginary component μ ″. FIG. 2 is a diagram illustrating an example of frequency characteristics of the real component μ ′ and the imaginary component μ ″ of the permeability of a general ferrite material. As shown in FIG. 2, when the frequency is low, the real component μ ′ of the magnetic permeability is large and the imaginary component μ ″ is small, and the change in both frequency characteristics is flat (hereinafter referred to as a flat region). ). Here, it is known that the imaginary component μ ″ of the magnetic permeability generally corresponds to the loss of the magnetic material, and in the frequency characteristic of FIG. 2, the loss of the magnetic material is kept sufficiently small in the flat region. I understand that.

  On the other hand, in the region on the higher frequency side than the flat region, the real component μ ′ and the imaginary component μ ″ first increase and have respective peaks, and gradually decrease as the frequency becomes higher. Thus, in the high frequency region, the real component μ ′ is smaller than that in the flat region described above, and the imaginary component μ ″ corresponding to the loss is large. In general, as a method of using a ferrite material, a use frequency is set in a flat region and not set in a region exceeding the flat region. For this reason, it is generally desirable to set the 13.56 MHz, which is the frequency used in the present embodiment, to be included in the flat region as shown in FIG.

  However, the present embodiment is characterized in that the characteristics of the ferrite material are determined by paying attention to the frequency characteristics on the higher frequency side than the flat region, which is different from the general setting described above. FIG. 3 is a diagram illustrating an example of frequency characteristics of the real component μ ′ and the imaginary component μ ″ of the permeability of the ferrite material used in the present embodiment. As is clear when FIG. 3 is compared with FIG. 2, the frequency characteristic of FIG. 3 has a shape in which the frequency characteristic of FIG. 2 is shifted to the left. Further, the values of the real component μ ′ and the imaginary component μ ″ of the magnetic permeability in FIG. 3 are considerably larger than those in FIG. That is, it can be seen that 13.56 MHz, which is the frequency used in the present embodiment, is a frequency higher than the flat region and is included in the region A on the higher frequency side than the peak of the frequency characteristics. Originally, this region A is a region where the loss of the ferrite material increases and the frequency characteristics deteriorate, but in the case of this embodiment, a desirable characteristic can be obtained in reducing the Q value. In this embodiment, as described below, the setting of the real component μ ′ and the imaginary component μ ″ of the permeability of the ferrite material is optimized, thereby stabilizing the characteristics against fluctuations in the usage environment of the RFID 1 It is.

In the present embodiment, a method of changing the component ratio of the metal oxide contained in the ferrite material is used for the purpose of adjusting the magnetic permeability of the ferrite material of the core 11. Here, three types of Fe ₂ O ₃ , NiO, and ZnO are assumed as metal oxides contained in the ferrite material, and the relationship between the component ratio and the properties of the ferrite material was verified. Table 1 shows that when four types of ferrite materials having different component ratios of these three kinds of metal oxides are used as the core 11, the characteristics of the ferrite material itself as a magnetic material and the ferrite material is used for the core 11 of the RFID 1. Shows the characteristics.

表１においては、本発明を適用した実施例１及び実施例２と、これら各実施例と比較するための比較例１及び比較例２とについて、それぞれフェライト材料及びそれを用いたＲＦＩＤタグ１の各種特性を示している。なお、表１の特性の検証に際してのフェライト材料よりなるＲＦＩタグ１のサイズを図４に示す。また、ＲＦＩＤタグ１の共振周波数は、非金属に取り付けたときの共振周波数と金属に取り付けたときの共振周波数の中央に設定している。

In Table 1, the ferrite material and the RFID tag 1 using the same for Example 1 and Example 2 to which the present invention is applied, and Comparative Example 1 and Comparative Example 2 for comparison with each of these Examples, respectively. Various characteristics are shown. FIG. 4 shows the size of the RFI tag 1 made of a ferrite material when verifying the characteristics shown in Table 1. The resonance frequency of the RFID tag 1 is set at the center between the resonance frequency when attached to a non-metal and the resonance frequency when attached to a metal.

  Among the items in Table 1, the Q value and the communication distance were measured by configuring the RFID tag 1 for evaluation having the size shown in FIG. In FIG. 4, the size of the core 11 is set to a length of 60 (mm), a width of 20 (mm), and a thickness of 3 (mm), and the number of windings of the conductor pattern 12 around the core 11 is set to 8 turns. . Further, the communication distance of the evaluation RFID tag 1 was measured by installing a reader / writer antenna along the axial direction of the coil 11 and varying the distance between the RFID tag 1 and the antenna.

  In Examples 1 and 2, in order to set a relatively low Q value, the magnetic permeability of the ferrite material is adjusted to a component ratio such that the operating frequency is matched in the vicinity of the region A shown in FIG. On the other hand, in Comparative Example 1, the component ratio of the ferrite material is adjusted so that the Q value is set sufficiently high, and in Comparative Example 2, the ferrite material is set so that the Q value is set lower than in Examples 1 and 2. The component ratio of is adjusted. As can be seen from Table 1, when the NiO component ratio is large among the components of the ferrite material, the Q value increases, and when the ZnO component ratio is large, the Q value tends to decrease. Therefore, in the case of the present embodiment, it is necessary to adjust the component ratio so that NiO is larger and ZnO is smaller than that of a ferrite material having general characteristics (for example, Comparative Example 2).

  For Examples 1 and 2, the communication distance was measured for each of Comparative Examples 1 and 2 in consideration of environmental fluctuations as shown in Table 1. In Example 1, when the attachment object is both non-metallic and metallic, a communication distance of 500 (nm) is secured, and the difference is small. In addition, Example 2 has the same tendency as Example 1. On the other hand, in the case of the comparative example 1, the communication distance does not reach 500 (mm) in the case where the attachment object is both non-metallic and metallic. As for Comparative Example 2, the non-metal and the metal have a smaller communication distance than Comparative Example 1.

  In Examples 1 and 2, since the Q value is lowered by adjusting the component ratio of the ferrite material, even if the use frequency and the resonance frequency are different, the influences thereof can be suppressed. Under the conditions of Table 1, the frequency used of the RFID tag 1 is set at the center of both resonance frequencies for the two states of non-metal and metal, so the resonance frequency actually deviates from both states, Since the Q value is low, it is possible to suppress a decrease in communication distance due to the influence of frequency deviation.

  On the other hand, in the case of the comparative example 1, a large communication distance can be secured when the use frequency and the resonance frequency substantially coincide with each other. However, since the Q value is high when corresponding to the two states as described above, the frequency shift is large. Will greatly affect the communication distance. In the case of Comparative Example 2, the permeability of the ferrite material is set so that the operating frequency matches the frequency region that is higher than the region A of FIG. And in the comparative example 2, since Q value becomes small and loss increases compared with Example 1, 2, the deterioration of the sensitivity of an antenna coil is large, and there exists a tendency for a communication distance to fall. As described above, it has been confirmed that there is an optimum range for setting the permeability of the ferrite material in order to ensure the characteristics of the antenna coil.

  In order to ensure good characteristics of the antenna coil in the RFID tag 1 of the present embodiment, attention was paid to the range of permeability of the ferrite material forming the core 11 and necessary conditions were examined. As the magnetic permeability of the ferrite material, it is desirable to set both the real component μ ′ and the imaginary component μ ″ to approximately 200 or more. If the permeability of the imaginary component μ ″ is lower than this, the Q value becomes too large, and if the permeability of the real component μ ′ is lower than this, the Q value becomes too small. . As shown in Table 1, Examples 1 and 2 both satisfy this condition, and Comparative Examples 1 and 2 do not satisfy this condition. Further, it is desirable to set the imaginary component μ ″ of the ferrite material to about 600 or less. By setting in this way, it is possible to prevent the loss of the core 11 from becoming too large and the communication distance of the RFID 1 from deteriorating.

On the other hand, in the RFID tag 1 of the present embodiment, in order to ensure the characteristics of the antenna coil, attention was paid to the component ratio of the ferrite material forming the core 11, and necessary conditions were examined. Regarding the three kinds of metal oxides in Fe ₂ O ₃ , NiO and ZnO contained in the ferrite material, the Fe ₂ O ₃ component ratio is in the range of 45 to 58 mol%, and the NiO component ratio is 8 to 15 mol%. It is desirable to set the range and the ZnO component ratio in the range of 25 to 32 mol%, respectively. As shown in Table 1, Examples 1 and 2 both satisfy this condition, and Comparative Examples 1 and 2 do not satisfy this condition.

In the above conditions, only Fe ₂ O ₃ , NiO, and ZnO are assumed as the components of the ferrite material, but other components can be used without being limited to these three types. For example, in addition to the three materials, Cu for lowering the firing temperature of the ferrite material may be added.

  As described above, in the present embodiment, the RFID tag 1 corresponding to a predetermined use frequency can be configured without performing individual adjustments, regardless of whether it is attached to metal or non-metal. In this case, the resonance frequency of the RFID tag 1 may be set at the time of metal attachment, non-metal attachment, or between the two, and may be set appropriately according to the situation. Regardless of the setting, when the resonance frequency of the RFID tag 1 shifts under different environmental conditions, the Q value is low, so the level drop due to impedance fluctuation can be suppressed, and it can be shared in various usage environments without individual adjustments. The RFID tag 1 that can be realized can be realized, and the cost can be reduced and the convenience can be improved.

It is a perspective view which shows the structure of the plate-shaped RFID tag which concerns on this embodiment. It is a figure which shows an example of the frequency characteristic of the real component (mu) 'and imaginary component (mu)' 'of the magnetic permeability of a general ferrite material. It is a figure which shows an example of the frequency characteristic of the real number component (mu) 'and imaginary number component (mu)' 'of the magnetic permeability of the ferrite material used by this embodiment. It is a figure which shows the size of the RFI tag which consists of a ferrite material in the case of verification of the characteristic of Table 1.

Explanation of symbols

1 ... RFID tag 11 ... core 12 ... FPC
13 ... Conductor pattern 14 ... IC
15 ... Capacitor

Claims (6)

An RFID tag including an antenna coil and a circuit that performs a transmission / reception operation at a predetermined use frequency,
The antenna coil is formed by winding a conductor around a core made of a magnetic material, and the magnetic material has a higher imaginary component of the magnetic permeability than the flat region of the frequency characteristics of the complex magnetic permeability. An RFID tag having a characteristic that the predetermined use frequency is included in a region sufficiently larger than a value in An RFID tag including an antenna coil and a circuit that performs a transmission / reception operation at a predetermined use frequency,
The antenna coil is formed by winding a conductor around a core made of a magnetic material, and both the real component and the imaginary component of the complex permeability of the magnetic material are approximately 200 or more at the predetermined use frequency. RFID tag to do.   The RFID tag according to claim 2, wherein an imaginary component of the complex permeability of the magnetic material is approximately 600 or less.   The RFID tag according to claim 1, wherein the magnetic material is a ferrite material containing a plurality of components. As a component of the ferrite material, a _Fe 2 _{O 3} of 45-58 mol%, and 8 to 15 mol% NiO, according to claim 4, characterized in that 25 to 32 mol% of ZnO are contained RFID tag. 6. The RFID tag according to claim 1, wherein the predetermined use frequency is 13.56 MHz.

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