JP2006287660A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna device which can stably communicate with a reader/writer without adjusting a resonance frequency according to a usage. <P>SOLUTION: An antenna device includes a sheet type substrate 11, a conductive material 12 provided on one side of the substrate 11, and a spiral antenna 10 provided on the other side of the substrate 11 and composed so that a resonance frequency of an LC resonance circuit composed with the substrate 11 becomes smaller than a communication frequency Fc. Thus, by presetting the resonance frequency not considering the conductive material smaller than the communication frequency, electric power of the communication frequency Fc supplied to the spiral antenna portion 10 becomes within a range where the communication between a reader/writer and the antenna device is enabled. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an antenna device used in a wireless communication system using an RFID (Radio Frequency Identification) tag, a non-contact IC (Integrated Circuit) card, or the like.

  In recent years, wireless communication systems using RFID technology have attracted attention. This communication system is generally composed of a data carrier capable of storing various data and a reader / writer that reads and writes (reads / writes) information without contact with the data carrier. The data carrier is called an RFID tag (wireless IC tag), a non-contact IC card, or the like according to its shape or size (hereinafter, collectively referred to as a non-contact IC card). Communication frequencies used for this non-contact IC card include a band of 135 kHz or less, a 13.56 MHz band, a 900 MHz band (915 MHz band, 950 MHz band), a 2.45 GHz band, and the like. Since this non-contact IC card is easy to handle for the user, it has recently been used for various entry / exit management such as an automatic ticket gate for transportation. In addition, applications to electronic money and article management are also being studied.

  For the non-contact IC card and its reader / writer, for example, a spiral antenna (loop-shaped planar coil) is used for the 13.56 MHz band. In general, a non-battery type IC card is often used as a non-contact type IC card. Electric power is supplied to the non-contact type IC card by electromagnetic induction via a carrier wave (AC magnetic field) generated by a reader / writer antenna, and a modulated data signal is transmitted to the carrier wave. The data is read / written by superimposing. Therefore, the strength and distribution state of the magnetic field generated from the reader / writer side affects the communication distance and stable communication operation. When an area in which data can be transmitted and received between a non-contact IC card and its reader / writer is a communication area, the magnetic field strength needs to be a predetermined value or more in a desired communication area. In general, in the communication area, it is preferable that the magnetic field strength is large. Note that, as described in Patent Document 1, the resonance frequency of the non-contact IC card and its reader / writer is generally designed so as to coincide with the communication frequency.

  Since this non-contact IC card is applied to various uses as described above, it may be considered that the conductor is used in the state of being close to the back surface of the spiral antenna. When the conductor receives electromagnetic waves from the reader / writer in such a state, an eddy current is generated on the surface of the conductor in a direction opposite to the direction of the current flowing through the spiral antenna, and as a result, power is supplied to the non-contact IC card. The carrier wave to be transmitted and the modulated data signal superimposed thereon are attenuated by the demagnetizing field induced on the conductor surface. Furthermore, since the resonance frequency is shifted to a higher frequency side than the set frequency by the conductor close to the back surface, the magnetic field strength at the communication frequency is significantly reduced. As a result, communication between the non-contact IC card and the reader / writer is virtually impossible.

Therefore, in order to cope with such applications, it is conceivable that a magnetic material having a low magnetic permeability is disposed close to (in close contact with) the back surface of the loop antenna. As a result, even if the conductor approaches by absorbing the electromagnetic wave radiated from the antenna on the side other than the direction intended for communication by the magnetic body, the influence of the conductor (the demagnetizing field due to the eddy current) Occurrence) can be prevented. In this way, a stable radiated electromagnetic field can be secured.
JP 2003-188765 A

  However, as described above, even when magnetic materials having a low magnetic permeability are arranged close to each other, if the thickness is thin, it is difficult to prevent the influence of the adjacent conductors. Therefore, in order to prevent the influence reliably, a certain amount of thickness is required, and as a result, there is a problem that the non-contact IC card becomes thick.

  In addition, when the magnetic bodies are arranged close to each other as described above, the resonance frequency changes according to the magnetic permeability and thickness of the magnetic body, so that the resonance frequency needs to be adjusted according to the type and thickness of the magnetic body. There is a problem.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an antenna device that can stably communicate with a reader / writer without requiring adjustment of the resonance frequency according to the application. It is to provide.

  The antenna device of the present invention includes a substrate and a spiral antenna that is provided on one surface of the substrate and configured so that the resonance frequency of the LC resonance circuit configured with the signal transmission / reception circuit is lower than the communication frequency. It is.

  Here, the signal transmission / reception circuit is a circuit provided between the spiral antenna and the modulation / demodulation circuit for demodulating the modulation data signal superimposed on the carrier wave or for superimposing the modulation data signal on the carrier wave. It is provided over the substrate, the substrate other than the substrate, or the substrate and the substrate other than the substrate. The signal transmission / reception circuit includes an element for finely adjusting the resonance frequency of the LC resonance circuit, for example, a capacitor (not shown), a parasitic capacitance in a wiring connecting the spiral antenna and the modulation / demodulation circuit, and the like. It is a concept.

  Further, the resonance frequency is a resonance frequency in an LC resonance circuit composed of a spiral antenna and a signal transmission / reception circuit, and does not take into account the effect of placing a conductor in close contact with the other surface of the substrate. Yes (corresponds to Fs described later). The conductor is made of, for example, a soft magnetic paramagnetic material such as aluminum, a soft magnetic diamagnetic material such as copper, or a soft magnetic ferromagnetic material such as iron, nickel, or permalloy. Yes, it is a separate individual from the antenna device. The communication frequency is a frequency used for communication between the reader / writer and the antenna device (corresponding to Fc described later). The spiral antenna is, for example, a loop-shaped planar coil.

  In the antenna device of the present invention, when the conductor is in close contact with the other surface of the substrate, the resonance frequency shifts to the high frequency side due to the influence of the conductor. Since it is set to be small, the power of the communication frequency supplied to the spiral antenna falls within a range of a size that allows communication between the reader / writer and the antenna device.

The resonance frequency Fs is preferably set so as to satisfy the equation (1), and more preferably the resonance frequency Fs is set so as to satisfy the equation (2).
0.52 Fc ≦ Fs <Fc (1)
Fc−Fs ≧ | Fc−Fy | (2)

  Here, Fc is a communication frequency. Fs is a resonance frequency in the LC resonance circuit, and does not consider the influence of the conductor. Fy is a resonance frequency in the LC resonance circuit, and is a resonance frequency to which the conductor is shifted under the influence of the conductor when the conductor is disposed in close contact with the other surface of the substrate.

  When Fs is set so as to satisfy Expression (1), the spiral antenna and the virtual spiral antenna are connected to the same carrier wave (AC) from the spiral antenna on the reader / writer side in a state where the conductor is disposed on the other surface of the substrate. When the magnetic field is received, the power Pa of the communication frequency supplied to the spiral antenna is surely larger than the power Pb of the communication frequency supplied to the virtual spiral antenna. Further, when Fs is set so as to satisfy Expression (2), the resonance frequency Fy is closer to the communication frequency Fc than the resonance frequency Fs, so that the power Pa obtained by the spiral antenna satisfies Expression (1) and Expression (2). ) Will be larger than when not satisfying.

The resonance frequency is preferably set so as to satisfy the equation (3), and more preferably set so as to satisfy the equation (4).
Pa-Pb> 0 (3)
Pa-Pc> 0 (4)

  Here, Pc is the power of the communication frequency supplied to the spiral antenna in the state where no conductor exists on the other surface of the substrate.

  When the expression (3) is satisfied, the spiral antenna and the virtual spiral antenna receive the same carrier wave (AC magnetic field) from the spiral antenna on the reader / writer side with the conductor disposed on the other surface of the substrate. In some cases, the power Pa of the communication frequency supplied to the spiral antenna is larger than the power Pb of the communication frequency supplied to the virtual spiral antenna. When Expression (4) is satisfied, the electric power Pa obtained by the spiral antenna satisfies Expression (3) and is larger than that when Expression (4) is not satisfied.

  Further, a conductor layer may be provided on the other surface of the substrate in advance. Here, the conductor layer is made of a soft magnetic paramagnetic material such as aluminum or a soft magnetic diamagnetic material such as copper. Thereby, since the electromagnetic wave which penetrates a conductor layer can be weakened beforehand, even if a conductor approaches the back, those influences are eased.

  In addition, a magnetic layer may be provided in advance on the other surface of the substrate, or a magnetic layer and a conductor layer may be stacked in this order in advance on the other surface of the substrate. Here, the magnetic layer is composed of a soft magnetic ferromagnet such as iron, nickel, permalloy or the like. As a result, the electromagnetic waves on the side other than the direction intended for communication pass through the magnetic layer and return to the direction intended for communication, and the conductor or conductor layer disposed on the other surface of the substrate. There is almost no weakening. As a result, even if the conductor approaches the back surface, there is almost no influence of them.

  According to the antenna device of the present invention, even when the conductor is close to the back surface, the power of the communication frequency supplied to the spiral antenna is within a size range that allows communication between the reader / writer and the antenna device. As a result, it is not necessary to adjust the resonance frequency according to the application. Thereby, it is possible to stably communicate with the reader / writer.

  In addition, when the formula (1) or the formula (3) is satisfied, the communication with the reader / writer can be performed more stably when the spiral antenna is provided than when the virtual spiral antenna is provided. Can do. Furthermore, when the expression (2) or the expression (4) is satisfied, communication with the reader / writer can be performed more stably.

  In addition, when the conductor layer is provided on the other surface of the substrate in advance, even if the conductor approaches the back surface, the influence is mitigated, so the power of the communication frequency supplied to the spiral antenna is reduced. Is reduced. Thereby, it is possible to stably communicate with the reader / writer.

  In addition, when the magnetic layer is provided on the other surface of the substrate in advance, or when the magnetic layer and the conductor layer are laminated in this order, even if the conductor approaches the back surface, There is almost no decrease in the power of the communication frequency supplied to the spiral antenna. As a result, communication with the reader / writer can be performed more stably.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 shows a schematic configuration of the antenna device according to the present embodiment. In this antenna device, a spiral antenna portion 10 is formed on one surface of a substrate 11.

  The substrate 11 is, for example, an insulating film, and the spiral antenna unit 10 and a signal transmission / reception circuit (not shown) are provided on one surface of the substrate 11.

  The spiral antenna unit 10 is constituted by a spiral antenna (loop-shaped planar coil) having terminals p and terminals n at its ends, and is connected to a signal transmission / reception circuit via the terminals p and n. The spiral antenna unit 10 constitutes an LC resonance circuit together with this signal transmission / reception circuit, and transmits and receives signals to and from a reader / writer (not shown).

  Here, the signal transmission / reception circuit is a circuit provided between the spiral antenna and the modulation / demodulation circuit for demodulating the modulation data signal superimposed on the carrier wave or for superimposing the modulation data signal on the carrier wave. It is provided over the substrate, the substrate other than the substrate, or the substrate and the substrate other than the substrate. The signal transmission / reception circuit includes an element for finely adjusting the resonance frequency of the LC resonance circuit, such as a capacitor (not shown), and a parasitic capacitance (not shown) in the wiring connecting the spiral antenna and the modem circuit. Z)).

  By the way, the antenna device is normally used in pairs with a reader / writer, and the reader / writer is arranged with a predetermined distance from the spiral antenna unit 10. In the antenna device, power is supplied to the antenna device by electromagnetic induction via a carrier wave (AC magnetic field) generated by the reader / writer antenna, and data is read / written by superimposing a modulated data signal on the carrier wave. It has become.

  The communication frequency Fc used when transmitting and receiving data between the antenna device and its reader / writer is specifically a band of 135 kHz or less, or 13.56 MHz, and the magnetic field strength at the communication frequency Fc is communication. It should be as large as possible. For this reason, it is preferable that the resonance frequency on the antenna device side (hereinafter referred to as resonance frequency Fs) be the communication frequency Fc or the vicinity thereof. The resonance frequency on the reader / writer side (hereinafter referred to as resonance frequency Fr) is naturally set in advance at or near the communication frequency Fc.

  However, the resonance frequency Fs is likely to fluctuate due to the influence of the external environment. Therefore, in the antenna device according to the present embodiment, it is assumed that a conductor is disposed in close contact with the back surface of the spiral antenna unit 10. Specifically, when a conductor is placed in close contact with the back surface of the spiral antenna unit 10, the resonance frequency Fs is shifted to the high frequency side due to the influence of the conductor, so that the resonance frequency Fs is lower than the communication frequency Fc in advance. Shift to the frequency side. As a result, even when the conductor approaches the back surface of the spiral antenna unit 10, the power of the communication frequency Fc supplied to the spiral antenna unit 10 is within a range that allows communication between the reader / writer and the antenna device. It becomes possible.

  The conductor assumed above is, for example, a soft magnetic paramagnetic material such as aluminum, a soft magnetic diamagnetic material such as copper, or a soft magnetic ferromagnetic material such as iron, nickel, and permalloy. It is configured and is a separate individual from the antenna device.

  The resonance frequency Fr on the reader / writer side does not change even if the resonance frequency Fs is changed to the low frequency side, and remains at a preset frequency, that is, the communication frequency Fc or the vicinity thereof. As a result, even when the conductor is not on the back surface, the power of the communication frequency Fc supplied to the spiral antenna unit 10 is within a range in which communication is possible between the reader / writer and the antenna device. Therefore, it is not necessary to adjust the resonance frequency Fs according to the application, and communication with the reader / writer can be performed stably.

  Next, in the antenna device having the above-described configuration, even when the conductor is disposed in close contact with the back surface of the spiral antenna unit 10 and the resonance frequency Fs is shifted to the high frequency side due to the influence of the conductor, A method for setting the power of the communication frequency Fc supplied to the spiral antenna unit 10 to be within the range of the size capable of communication between the reader / writer and the antenna device will be described. Hereinafter, a case where the communication frequency Fc is 13.56 MHz will be described.

  2 to 4 show Z21 (open circuit forward transfer impedance, open circuit forward transfer impedance,) in a transfer function of a two-terminal pair network composed of an LC resonance circuit of a reader / writer and an LC resonance circuit of an antenna device arranged to face each other through a predetermined space. The unit is ohm) in a logarithmic form (20 log (| Z21 |), the unit is dB). 2 to 4, the LC resonance circuit of the antenna device in the two-terminal pair network is the LC resonance circuit of the antenna device X including the spiral antenna unit 10 and the substrate 11, and the antenna device described above. The frequency characteristics of the logarithm display of Z21 and the case of the LC resonance circuit of the antenna device Y in which the conductor is disposed in close contact with the other surface of the substrate 11 are shown.

  FIG. 5A illustrates the case where the resonance frequency Fs of the antenna device X is 7.1 MHz, 7.7 MHz, 8.7 MHz, 10 MHz, 12.1 MHz, 13.2 MHz, or 17.5 MHz, and the resonance of the antenna device Y. Z21 at the communication frequency Fc (13.56 MHz) in the case where the frequency Fs is 11 MHz, 12 MHz, 13 MHz, 15.4 MHz, 18.6 MHz, 20.6 MHz, or 25.2 MHz is expressed in logarithm. The dotted arrow in FIG. 5A indicates the correspondence between the resonance frequency Fs of the antenna device X and the resonance frequency Fs of the antenna device Y, that is, the resonance frequency Fs before the conductor is placed in close contact with the antenna device X. The change of the resonance frequency Fy after arrangement | positioning is shown. FIG. 5B is a logarithmic representation of the shift amount ΔZ21 of Z21 that has shifted with the shift of the resonance frequency from Fs to Fy (corresponding to the dotted arrow in FIG. 5A).

  6A shows a case where the resonance frequency Fs of the antenna device X is 12.8 MHz, 13.6 MHz or 17.0 MHz and 17.5 MHz, and a case where the resonance frequency Fy of the antenna device Y is 13.6 MHz, 14.5 MHz or 18 This is a logarithm of Z21 at the communication frequency Fc (13.56 MHz) with the case of 1 MHz. The dotted arrow in FIG. 6A indicates the correspondence between the resonance frequency Fs of the antenna device X and the resonance frequency Fs of the antenna device Y, that is, the resonance frequency Fs before the conductor is placed in close contact with the antenna device X. The change of the resonance frequency Fy after arrangement | positioning is shown. FIG. 6B is a logarithmic representation of the shift amount ΔZ21 of Z21 that has shifted with the shift of the resonance frequency from Fs to Fy (corresponding to the dotted arrow in FIG. 6A).

  2 corresponds to the case where the resonance frequency Fs is 10 MHz in FIG. 5A, and FIG. 3 corresponds to the case where the resonance frequency Fs is 7.1 MHz in FIG. FIG. 4 corresponds to the case where the resonance frequency Fs is 17.5 MHz in FIG. 2 to 4 and FIGS. 5A and 5B, an 80 mm square spiral antenna unit 10A is used. In FIGS. 6A and 6B, a 10 mm square spiral antenna unit 10A is used. It is used.

  In FIGS. 2 to 6A and 6B, the antenna device X having the resonance frequency Fs smaller than the communication frequency Fc corresponds to this embodiment, and the antenna device X having the resonance frequency Fs equal to or higher than the communication frequency Fc is compared. It corresponds to an example.

By the way, when Z21 described above is V2, the voltage on the output port side (antenna device side) of the two-terminal-pair network and the current input from the input port side (reader / writer side) is I1, V2, Z21 and I1 are , V2 = Z21xI1. As a result, if the current input from the input port side is I2, and the load connected to the output port side (specifically, the IC connected to the subsequent stage of the LC resonance circuit) is ZL, the current is supplied to the output port side. The electric power P2 is P2 = V2xI2 = Z21xI1xI2 = Z21xI1xV2 / ZL = (Z21) ² x (I1) ² / ZL. Here, ZL has a very large impedance (constant), and I1 flowing through the ZL is very small and can be regarded as almost constant. Therefore, P2 increases in proportion to the square of Z21. Therefore, it can be considered that the frequency characteristic of P2 and the frequency characteristic of Z21 have the same tendency. Therefore, the following description will be made using Z21 instead of P2.

First, the antenna device X of the present embodiment will be described. As shown in FIG. 2, in the antenna device X, the resonance frequency Fs is 10 MHz as described above, and the resonance frequency Fr on the reader / writer side is around 13.56 MHz. When the antenna device Y is configured by closely arranging a conductor on the antenna device X, the resonance frequency on the antenna device side changes from 10 MHz (Fs) to 15.4 MHz (Fy) (d in FIG. 5A). On the other hand, the resonance frequency Fr on the reader / writer side is substantially constant. Here, if Z2 of the two-terminal pair network including the LC resonance circuit of the antenna device X is dB2, and Z21 of the two-terminal pair network including the LC resonance circuit of the antenna device Y is dB0, the communication frequency Fc is 13. Z21 at 56 MHz has changed from 39.75 (dB) (= dB2) to 33.9 (dB) (= dB0), and it can be confirmed that Z21 is reduced due to the influence of the conductor ( (See FIG. 5B).
Displacement amount ΔZ21 = dB0−dB2 = −5.85 (dB) <0 (dB)

Similarly, as shown in FIG. 3, in the antenna device X, the resonance frequency Fs is 7.1 MHz as described above, and the resonance frequency Fr on the reader / writer side is around 13.56 MHz. When the antenna device Y is configured by closely arranging a conductor on the antenna device X, the resonance frequency on the antenna device side changes from 7.1 MHz (Fs) to 11 MHz (Fy) (a in FIG. 5A). The resonance frequency Fr on the reader / writer side is substantially constant. As a result, Z21 at 13.56 MHz, which is the communication frequency Fc, has changed from 30.59 (dB) (= dB2) to 26.06 (dB) (= dB0). Can be confirmed (see FIG. 5B).
Displacement amount ΔZ21 = dB0−dB2 = −4.53 (dB) <0 (dB)

  In addition, in the case where the resonance frequency Fs of the antenna device X is 7.7 MHz, 12.1 MHz, and 13.2 MHz, the resonance frequency Fy of the antenna device Y is 12 MHz, 18.6 MHz, and 20.6 MHz. As shown in FIGS. 5A and 5B, it has the same tendency as in FIGS. 2 and 3 described above (see FIG. 5B). Thus, in these frequency bands, Z21 tends to decrease. In the case of FIGS. 6A and 6B as well, the trend is decreasing in the case of dB1 when the resonance frequency Fs of the antenna device X is 12.8 MHz and the resonance frequency Fy of the antenna device Y is 13.6 MHz. It is in.

However, when the resonance frequency Fs of the antenna device X is 8.7 MHz and the resonance frequency Fy of the antenna device Y is 13 MHz, the tendency is different from the above frequency band. Specifically, Z21 at 13.56 MHz, which is the communication frequency Fc, has changed from 30.59 (dB) (= dB2) to 26.06 (dB) (= dB0). , Z21 can be confirmed to increase (see FIG. 5B).
Displacement amount ΔZ21 = dB0−dB2 = 13.79 (dB)> 0 (dB)

  Thus, Z21 tends to increase in the range above the dotted line in FIG. 5 (B), and it is confirmed from FIG. 5 (A) that the resonance frequency Fs is approximately in the range of 8 MHz to 9 MHz. it can.

Next, the antenna device X according to the comparative example will be described. As shown in FIG. 4, in the antenna device X according to the comparative example, the resonance frequency Fs of the spiral antenna unit (virtual spiral antenna) is 17.5 MHz that is equal to or higher than the communication frequency Fc (13.56), and the resonance frequency on the reader / writer side. Fr is in the vicinity of 13.56 MHz. When a conductor is arranged in the antenna device X to configure the antenna device Y according to the comparative example, the resonance frequency on the antenna device side changes from 17.5 MHz (Fs) to 25.2 MHz (Fy) (FIG. 5 ( (Refer to g in A)), the resonance frequency Fr on the reader / writer side is substantially constant. Here, Z21 of the two-terminal pair network including the LC resonant circuit of the antenna device X according to the comparative example is dB3, and Z21 of the two-terminal pair network including the LC resonant circuit of the antenna device Y according to the comparative example is dB1. Z21 at 13.56 MHz which is the communication frequency Fc has changed from 56.88 (dB) (= dB3) to 23.51 (dB) (= dB1), and Z21 drastically decreases due to the influence of the conductor. This can be confirmed (see FIG. 5B).
Displacement amount ΔZ21 = dB1-dB3 = −33.37 (dB) <0 (dB)

  6A and 6B, the resonance frequency Fs of the antenna device X according to the comparative example is 13.6 MHz and 17.0 MHz, and the resonance frequency Fy of the antenna device Y according to the comparative example is Also in the case of 14.5 MHz and 18.1 MHz, Z21 tends to decrease.

  Now, an antenna device Y (Y1) configured by arranging a conductor in the antenna device X of the present embodiment, and an antenna device Y configured by arranging a conductor in the antenna device X according to the comparative example. (Y2) is compared, it is confirmed that Z21 of the two-terminal pair network including the LC resonant circuit of the antenna device Y1 is larger than Z21 of the two-terminal pair network including the LC resonant circuit of the antenna device Y2. (See the two-dot chain line h in FIG. 5A and the two-dot chain line i in FIG. 6A). Note that a two-dot chain line h in FIG. 5A is Z21 of the antenna device Y1 when the resonance frequency Fs changes from 13.2 MHz to 20.6 MHz, and the resonance frequency Fs changes from 13.56 MHz or more. 6 is slightly larger than Z21 of the antenna device Y1, and the two-dot chain line i in FIG. 6A is Z21 of the antenna device Y1 when the resonance frequency Fs changes from 13.6 MHz to 14.5 MHz, and the resonance frequency Fs is slightly smaller than Z21 of the antenna device Y1 when shifted from less than 13.56 MHz.

Here, by using the conversion formula of Z21 and P2, the two-terminal pair circuit including the LC resonance circuit of the antenna device Y2 and Z21 of the two-terminal pair network including the LC resonance circuit of the antenna device Y1 as power Pa. When Z21 of the net is converted into electric power Pb, the converted Pa and Pb satisfy the following expression (3). Note that the electric power Pa is within a size range that allows communication between the reader / writer and the antenna device.
Pa-Pb> 0 (3)

  This is because when the antenna device Y1 and the antenna device Y2 receive the same carrier wave (AC magnetic field) from the reader / writer spiral antenna, the power Pa obtained by the antenna device Y1 is greater than the power Pb obtained by the antenna device Y2. Is also shown to be large.

  Therefore, in the antenna device X according to the present embodiment, even when the conductor approaches the back surface, the power of the communication frequency Fc supplied to the spiral antenna unit 10A is large enough to allow communication between the reader / writer and the antenna device. Therefore, it is not necessary to adjust the resonance frequency according to the application. Thereby, it is possible to communicate with the reader / writer stably.

Further, in the antenna device X of the present embodiment, as described above, Z21 tends to increase when the resonance frequency Fs is in the range of approximately 8 MHz to 9 MHz, so that the range is higher than the dotted line in FIG. Such a resonance frequency Fs is preferable. Here, when the conversion formula of Z21 and P2 is used to convert dB0 to power Pa and dB2 to power Pc, the power shift amount ΔP2 in the frequency band is as follows.
Pa-Pc> 0 (4)

  Thus, when the resonance frequency Fs is set so as to satisfy the expression (4), communication with the reader / writer can be performed more stably.

Note that the upper limit of the resonance frequency Fs of the antenna device X of the present embodiment is a frequency that satisfies the following formula (1), but Fs <0.98Fc is satisfied in consideration of manufacturing errors and the influence of the external environment. The frequency is preferable. In addition, the lower limit of the resonance frequency Fs of the antenna device X of the present embodiment is a frequency that is a region above the two-dot chain line in FIG. 5A (in FIG. 5A, slightly lower than 0.52Fc). However, considering the manufacturing error and the influence of the external environment, the frequency satisfying the following formula (1) is preferable, as in the case of the upper limit.
0.52 Fc ≦ Fs <Fc (1)

  As described above, when the resonance frequency Fs is set so as to satisfy the expression (1), even if the conductor approaches the back surface, the power of the communication frequency Fc supplied to the spiral antenna unit 10A is the same as that of the reader / writer. The size is within a range that allows communication with the antenna device. As a result, since it is not necessary to adjust the resonance frequency according to the application, it is possible to communicate with the reader / writer stably.

Further, in the antenna device X of the present embodiment, when the conductor is in close contact with the back surface of the spiral antenna unit 10, the resonance frequency Fs is shifted to the high frequency side due to the influence of the conductor. The resonance frequency Fs is preferably a frequency that satisfies the following expression (2).
Fc−Fs ≧ | Fc−Fy | (2)

  As described above, when the expression (2) is satisfied, when the conductor is disposed in close contact with the other surface of the substrate, the resonance frequency Fy is closer to the communication frequency Fc than the resonance frequency Fs. The obtained electric power Pa satisfies the formula (1) and becomes larger than the case where the formula (2) is not satisfied. As a result, communication with the reader / writer can be performed more stably.

  In particular, as in the case c in FIG. 5A and the case j in FIG. 6A, the power of the communication frequency Fc is maximized by setting the resonance frequency Fy to or near the communication frequency Fc. be able to. As a result, communication with the reader / writer can be performed more stably.

(Adjustment method of resonance frequency Fs)
By the way, in the present embodiment, the resonance frequency Fs is set in a wide range within a range of less than 13.56. To accurately adjust the resonance frequency Fs over such a wide frequency band, FIG. 7 is provided with a spiral antenna unit 20 composed of a parent antenna unit 20-1 and a child antenna unit 20-2 as shown in FIG. 7 rather than a spiral antenna unit 10 having a simple shape as shown in FIG. Is preferred.

  Since the length of one side of the parent antenna unit 20-1 is relatively larger than that of the child antenna unit 20-2, the inductance per turn is also relatively larger than that of the child antenna unit 20-2. Therefore, the resonance frequency of the antenna device can be greatly changed by changing the number of turns of the parent antenna unit 20-1. On the other hand, since the length of one side of the child antenna unit 20-2 is relatively smaller than that of the parent antenna unit 20-1, the inductance per turn is also relatively smaller than that of the parent antenna unit 20-1. small. Therefore, the resonance frequency of the antenna device can be finely adjusted by changing the number of turns of the child antenna unit 20-2.

[Second Embodiment]
Next, a second embodiment will be described. Compared with the antenna device according to the first embodiment, the antenna device according to the present embodiment is provided with the conductor layer 12 on the surface opposite to the spiral antenna portion 10A as shown in FIG. Is different. Therefore, hereinafter, the same configuration, operation, and effect as those of the first embodiment will be omitted as appropriate, and will be described in detail in comparison with the first embodiment.

  Here, the conductor layer 12 is made of, for example, a soft magnetic paramagnetic material such as aluminum or a soft magnetic diamagnetic material such as copper. Thereby, since the electromagnetic wave which penetrates the conductor layer 12 can be weakened beforehand, even if a conductor approaches the back, those influences can be relieved.

  Further, the transition of the resonance frequency Fs and the power characteristics of the communication frequency Fc due to the provision of the conductor layer 12 are the same as those of the antenna device Y1 that has appeared in the description of the first embodiment. That is, the antenna device of the present embodiment has the same characteristics as the antenna device Y1.

  Therefore, in the antenna device according to the present embodiment, even if the conductor approaches the back surface, the influence thereof is alleviated, so that the reduction in power of the communication frequency supplied to the spiral antenna is alleviated. Thereby, it is possible to stably communicate with the reader / writer.

[Third Embodiment]
Next, a third embodiment will be described. Compared with the antenna device according to the second embodiment, the antenna device according to the present embodiment includes a magnetic layer 13 between the substrate 11 and the conductor layer 12, as shown in FIG. It differs in the point provided. Therefore, hereinafter, the same configuration, operation, and effects as those of the second embodiment will be omitted as appropriate, and will be described in detail in comparison with the second embodiment. The magnetic layer 13 is made of a soft magnetic ferromagnetic material such as iron, nickel, and permalloy.

  FIG. 10 shows frequency characteristics of power obtained from the reader / writer side by the antenna device X of the first embodiment, the antenna device Y1 of the second embodiment, and the antenna device W of the present embodiment. It is a thing.

  When the substrate 11 and the conductor layer 12 are arranged in close contact like the antenna device Y1 of the second embodiment, the electromagnetic wave radiated from the spiral antenna unit 10A is on the side other than the direction intended for communication. Is slightly canceled out by the conductor layer 12, so that the power at the communication frequency Fc is reduced as shown in FIG.

  On the other hand, in the antenna device W of the present embodiment, since the magnetic layer 13 is provided between the substrate 11 and the conductor layer 12, electromagnetic waves on the side other than the direction intended for communication are generated by the magnetic body. It passes through the layer 13 and returns to the direction intended for communication, and is hardly canceled by the conductor layer 12. Therefore, as shown in FIG. 10, compared with the power reduction amount D1 at the communication frequency Fc (13.56 MHz) in the antenna device Y1 of the second embodiment, the antenna device W of the present embodiment The amount of power decrease D2 at the communication frequency Fc is very small. As a result, even if the resonance frequency Fw of the antenna device W is not at or near the communication frequency Fc, it is possible to ensure sufficient power at the communication frequency Fc.

  Moreover, since there is almost no magnetic flux which penetrates the conductor layer 12 and comes out to a back surface, even if a conductor approaches a back surface, it is hardly influenced by them.

  As described above, in the antenna device W of the present embodiment, even if the conductor approaches the back surface, there is almost no reduction in the power of the communication frequency supplied to the spiral antenna. As a result, communication with the reader / writer can be performed more stably.

  Although the present invention has been described with reference to one embodiment and one modification, the present invention is not limited to these, and various modifications can be made.

  For example, in the above-described embodiment and modification, the application example of the present invention in which the communication frequency Fc is 13.56 MHz has been described. However, the present invention can be applied to other frequencies, for example, a band of 135 kHz or less. Is possible.

  Further, in the above-described embodiment and modification, the spiral antenna unit 10A and the IC are provided on the common substrate 11, but may be separately provided on different substrates. In this case, the conductor layer 12 and the magnetic layer 13 may be provided only on the back surface of the substrate 11 provided with the spiral antenna unit 10 </ b> A, or may be provided on the back surfaces of both the substrates 11.

1 is a schematic configuration diagram of an antenna device according to a first embodiment of the present invention. It is a figure for demonstrating the frequency characteristic of the antenna apparatus of FIG. It is a figure for demonstrating the other frequency characteristic of the antenna apparatus of FIG. It is a figure for demonstrating the other frequency characteristic of the antenna apparatus of FIG. It is a figure for demonstrating the resonant frequency characteristic of the antenna apparatus of FIG. It is a figure for demonstrating the other resonant frequency characteristic of the antenna apparatus of FIG. It is a figure for demonstrating the adjustment method of a resonant frequency. It is a schematic block diagram of the antenna apparatus which concerns on the 2nd Embodiment of this invention. It is a schematic block diagram of the antenna apparatus which concerns on the 3rd Embodiment of this invention. It is a figure for demonstrating the frequency characteristic of the antenna apparatus of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,20 ... Spiral antenna part, 11 ... Board | substrate, 12 ... Conductor layer, 13 ... Magnetic material layer, 20-1 ... Parent antenna part, 20-2 ... Child antenna part, Fc ... Communication frequency, Fr, Fs, Fy , Fw, resonance frequency, p, n, terminals, Pa, Pb, Pc, power, dB0, dB1, dB2, Z21, impedance, W, X, Y, Y1, Y2, antenna device.

Claims (7)

A substrate,
An antenna device comprising: a spiral antenna provided on one surface of the substrate and configured such that a resonance frequency of an LC resonance circuit configured with a signal transmission / reception circuit is lower than a communication frequency. The antenna device according to claim 1, wherein the resonance frequency is set so that Fs and Fc satisfy the following relationship, where Fc is the communication frequency and Fs is the resonance frequency.
0.52 Fc ≦ Fs <Fc (1) When a conductor is brought into close contact with the other surface of the substrate, Fs is set so that Fs, Fc, and Fy satisfy the following relationship, where Fy is a resonance frequency that has been changed due to the influence of the conductor. The antenna device according to claim 2, wherein the antenna device is provided.
Fc−Fs ≧ | Fc−Fy | (2) A virtual power configured so that the power of the communication frequency supplied to the spiral antenna with a conductor disposed on the other surface of the substrate is Pa, and the resonance frequency of the LC resonance circuit is equal to or higher than the communication frequency. Assuming a spiral antenna, assuming that the power of the communication frequency supplied to the virtual spiral antenna with a conductor in close contact with the other surface of the substrate is Pb, Pa and Pb satisfy the following relationship: The antenna device according to claim 1, wherein the resonance frequency is set.
Pa-Pb> 0 (3) If the power of the communication frequency supplied to the spiral antenna in the state where no conductor is present on the other surface of the substrate is Pc, the resonance frequency is set so that Pa and Pc satisfy the following relationship: The antenna device according to claim 4, wherein:
Pa-Pc> 0 (4) The antenna device according to claim 1, further comprising a conductor layer on the other surface of the substrate. The antenna device according to claim 1, further comprising a magnetic layer between the substrate and the conductor.

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