JP4885093B2 - Booster antenna coil - Google Patents

Description

  The present invention relates to a booster antenna coil used for extending a communication distance in an RFID (Radio Frequency Identification) system, for example.

  In recent years, an IC chip that can store information electronically, and a system using a card or a tag that includes an interface for exchanging information between the IC chip and the outside, has attracted attention because of its various possibilities. Collecting. Such a system is generally called an RFID system, and is used for solid-state authentication and data transmission / reception in various situations by combining a small recording medium (card or tag) with an RFID reader / writer that reads / writes data from / to this system. Can be used.

  As for a small-sized recording medium, there are various names such as an RFID card, an IC card, a wireless card, an RFID tag, and an IC tag. Hereinafter, although referred to as an RFID tag, it is not intended to be limited to a specific type, but is a broad concept including all of the various cards and tags as described above. Such an RFID tag can store a large amount of information in the memory of the IC chip and prevent counterfeiting compared to the magnetic recording type used in conventional cards. Widely used as credit cards, electronic money, electronic tickets, telephone cards, ID cards, cargo management tags, and the like.

  As a method for transmitting and receiving information to and from the RFID reader / writer, a contact type in which an electrode contact provided on the surface of the RFID tag and a contact terminal provided on the RFID reader / writer are brought into contact with each other, an RFID tag and an RFID There is a non-contact type that is performed wirelessly through an antenna coil provided in a reader / writer. In particular, the non-contact type RFID tag has high durability because there is no wear due to contact, no mechanism for moving the RFID tag to the RFID reader / writer side, and a high degree of freedom in the direction of transmission and reception. It is expected to spread as a product that has both safety and convenience.

  By the way, the communication distance between the non-contact type RFID reader / writer and the RFID tag as described above is several centimeters. However, as described above, the RFID system, which can be used in various applications, can be used in various applications, and it is desirable that the communication distance can be further extended depending on the application field. In order to cope with this, it has been proposed to arrange a booster antenna between the RFID tag and the RFID reader / writer. This basically uses an RFID reader / writer antenna coil including a resonance circuit (hereinafter referred to as a P coil) and an RFID booster antenna coil including a resonance capacitor (hereinafter referred to as a Q coil). Technology.

  For example, Patent Document 1 discloses a technique for extending a communication distance by arranging a Q coil in a normal direction of a P coil. Patent Document 2 discloses a technique for extending a communication distance by arranging a Q coil for an RFID tag in front of the RFID tag. Furthermore, Patent Document 3 discloses a card case with a booster in which a booster is provided in a card case for a non-contact IC card.

JP 2000-138621 A JP 2005-323019 A JP 2005-332015 A Electrical Engineering Handbook, Japan, The Institute of Electrical Engineers of Japan, reprint 3 Showa 46 (first edition Showa 42), pages 132-133

  By the way, as described above, even when a booster antenna is configured between the RFID tag and the RFID reader / writer, there is a case where it is not possible to expect a sufficient extension of the communication distance. For example, in a coupled resonance circuit composed of a P coil for an RFID reader / writer and a Q coil for a booster, when the coupling coefficient is large, the resonance frequency is divided into two, thereby exhibiting a so-called bimodal characteristic. (Refer nonpatent literature 1). In this state, although the booster antenna is used, the current becomes small at the carrier frequency and the generated magnetic field strength becomes small, so that the communication distance cannot be sufficiently extended.

  On the other hand, a single-peak characteristic can be obtained by reducing the coupling coefficient, but in that case, the coupling between the RFID coil for the RFID reader / writer and the Q coil for the booster is reduced, and the communication distance is reduced. To do. Further, if the distance between the P coil and the Q coil is increased in order to reduce the coupling coefficient, the required space increases.

  Further, the booster coil as described above is an LC resonance due to the inductance L of the coil and the capacitance C of the capacitor, and the resonance frequency varies depending on the manufacturing accuracy of the parts and the temperature characteristics of L and C. Therefore, when an error occurs in the resonance frequency of the coil, there is a possibility that a stable communication distance cannot be obtained.

  The present invention has been proposed in order to solve the above-described problems of the prior art, and the object thereof is to sufficiently extend the communication distance, secure a stable communication distance, and require a small space. It is to provide a booster antenna coil.

In order to achieve the above object, the present invention includes a first antenna coil, a capacitor, and a power source, and includes a first resonance circuit that resonates at a predetermined resonance frequency, a second antenna coil, and a capacitor. A booster antenna coil including a coupled resonant circuit having a second resonant circuit that resonates at a resonant frequency has any of the following characteristics.

(1) The first antenna coil and the second antenna coil are disposed at a position where a bimodal characteristic occurs.
(2) In the first resonance circuit, a carrier frequency for communication with the outside is set between two peaks of a bimodal characteristic.
(3) When there is no second resonance circuit including the second antenna coil with respect to the magnetic field intensity of the magnetic field generated from the second antenna coil due to the induced current caused by the current flowing through the first antenna coil. The value of the current flowing through the first antenna coil is set by the power supply so that the value of the ratio of the magnetic field strengths of the magnetic fields generated from the first antenna coil exceeds 1.
(4) A coupling coefficient between the first resonance circuit including the first antenna coil and the second resonance circuit including the second antenna coil is approximately 0.015 to 0.1. The inductance of the first antenna coil, the inductance of the second antenna coil, and the mutual inductance of the first antenna coil and the second antenna coil are set .
(5) A magnetic member is disposed between the first antenna coil and the second antenna coil.

  In the invention as described above, in the coupled resonance circuit constituted by the first antenna coil and the second antenna coil, the carrier frequency is matched between the two peaks of the bimodal characteristic, and the coupling coefficient is set to 0.015 to 0. By adjusting to 0.1, the current flowing through the second antenna coil increases, the generated magnetic field strength increases, and the communication distance can be sufficiently extended. Furthermore, stable communication can be obtained even if an error occurs in the resonance frequency of the second antenna coil. The same applies to the case where the ratio between the magnetic field strength of the second antenna coil and the magnetic field strength of the first antenna coil without the second antenna coil is set to exceed 1.

  Note that when the carrier frequency is out of the two peaks of the bimodal characteristic, the magnetic field strength ratio is 1 even when the resonance frequencies of the first antenna coil and the second antenna coil are different. If it exceeds, the effect of extending the communication distance can be expected.

  Moreover, since the coupling coefficient between both coils can be controlled by disposing a magnetic member between the first antenna coil and the second antenna coil, the gap between the first antenna coil and the second antenna coil can be controlled. Space can be reduced.

  As described above, according to the present invention, it is possible to provide a booster antenna coil that can sufficiently extend the communication distance, secure a stable communication distance, and requires a small space.

  The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described. Each embodiment is, for example, a booster antenna applied to an RFID reader / writer, but the specific structure of the RFID reader / writer and the RFID tag that communicates with the RFID reader / writer is not limited to a specific one. Is omitted.

  Further, in the following description, the basic configuration of each embodiment will be described, and the operational effects of each embodiment will be described based on the measurement results based on the examples produced corresponding to each embodiment.

[First Embodiment]
[Constitution]
First, the basic configuration of the present embodiment will be described with reference to FIGS. 1 and 2. That is, in this embodiment, a P coil 11 and a resonance circuit 12 provided on the RFID reader / writer 1 side, a Q coil 21 and a capacitor 22 constituting the booster antenna 2, and an RFID tag 3 that performs communication with the RFID reader / writer 1. Etc. are constituted.

  The P coil 11 and the Q coil 21 are antenna coils for transmitting and receiving radio waves formed so that a conductor is wound, and are electrically connected to an RFID circuit (not shown). For example, the P coil 11 and the Q coil 21 may be formed on an insulating substrate by etching, printing, or the like using copper or aluminum, or may be configured by a wire or a lead, but is not limited thereto.

  The P coil 11 and the Q coil 21 are arranged so that their normal directions are substantially the same (coaxial and parallel). However, the positional relationship between the P coil 11 and the Q coil 21 is not limited to this. Various support structures for the P coil 11 and the Q coil 21 are conceivable depending on the application. The shape and material of the case, frame, etc., whether or not part or all of the case is exposed to the outside, portable type, portable type, installation type, etc. are free.

  An example of a coupled resonant circuit composed of the RFID reader / writer 1 and the booster antenna 2 is shown in the circuit diagram of FIG. Since the resonance frequency follows the specifications of the P coil 11, the Q coil 21, the resistors R1 to R3, and the capacitors C1 to C3, a component that can obtain a desired resonance frequency is selected. For example, if the specifications of the P coil 11, the Q coil 21, and the resistors R1 to R3 are fixed, the resonance frequency of each coil can be changed to a desired value by selecting the capacitance of the capacitors C1 to C3. By using a variable capacitor or the like, it may be configured to easily change to a desired frequency. In the experiment, it is convenient to use a variable capacitor.

  In the present embodiment, the coupling coefficient of the resonance circuit is set large so as to exhibit the bimodal characteristics. At this time, the carrier frequency is set between the two peaks of the bimodal characteristic, and the coupling coefficient is set so that the magnetic coupling is 0.015 to 0.1.

In addition, it will be as follows when the type | formula which calculates | requires the characteristic of the P coil 11 and the Q coil 21 is shown. First, the mutual inductance of the P coil 11 and the Q coil 21 can be expressed by Equation 1 under the following conditions.
M: Mutual inductance Np: Number of turns of P coil Nq: Number of turns of Q coil a: Radius of P coil b: Radius of Q coil z: Distance on central axis k: Coupling coefficient

したがって、Ｐコイル１１とＱコイル２１の位置関係から、結合係数ｋを計算によって導くことができる。 Therefore, the coupling coefficient k is proportional to the mutual inductance M. Further, the coupling coefficient k can be expressed by Equation 2 under the following conditions.
Lp: Inductance of P coil Lq: Inductance of Q coil

Therefore, the coupling coefficient k can be derived from the positional relationship between the P coil 11 and the Q coil 21 by calculation.

Further, the resonance frequency fo of the Q coil 21 can be expressed by Equation 3 when the inductance Lq of the Q coil 21 and the capacitance Cq of the capacitor are used.

[Function and effect]
The operational effects of the present embodiment as described above will be described based on a plurality of actually produced examples and comparative examples.

[Stable communication distance: Examples 1 to 9]
First, the data of the result of having performed simulation about the magnetic field intensity by a predetermined input voltage about comparative example 1 and Examples 1-9 to which this embodiment is applied are shown. Here, the simulation was performed paying attention to the magnetic field strength for the following reason.

なお、式４における条件は、次の通りである。
Ｚ：コイル中心からの距離（ｍ）
ａ：コイルの半径
Ｈ（ｚ）：コイル中心からの距離Ｚでの磁界の強さ（Ａ／ｍ）
Ｎ：巻き数
Ｉ：コイル電流（Ａ） First, as shown in Equation 4 below, the magnetic field on the antenna central axis is proportional to the current in the antenna coil portion.

In addition, the conditions in Formula 4 are as follows.
Z: Distance from coil center (m)
a: Radius of coil H (z): Strength of magnetic field at distance Z from coil center (A / m)
N: Number of turns I: Coil current (A)

  Then, as shown in Equation 5 below, the induced voltage Vm of the RFID tag 3 is proportional to the strength H of the magnetic field. In other words, if the magnetic field is increased, the induced voltage increases accordingly, and further improvement of the communication distance can be expected. Therefore, the length of the communication distance can be determined by showing the difference in magnetic field strength between when the Q coil 21 is present and when it is not present.

なお、式５における条件は、次の通りである。
Ｖｍ：誘起電圧
Ｆ：周波数
Ｎ：巻き数
Ｓ：受信コイル断面積
Ｈ：磁界強度
μ_０：4π×１０^−７ Ｔ／（Ａ／ｍ）
α：比例定数

In addition, the conditions in Formula 5 are as follows.
Vm: Induced voltage F: Frequency N: Number of turns S: Receiving coil cross-sectional area H: Magnetic field strength μ ₀ : 4π × 10 ⁻⁷ T / (A / m)
α: Proportional constant

Here, Comparative Example 1 corresponding to the A below, for Examples 1 to 9 corresponding to B to J, the conditions shown in Table 1, in the circuit diagram of FIG. 2, current _I p of the P coil 11, Q coil 21 The current I _q was simulated (carrier frequency 13.56 MHz). The simulation input voltage was 1V.

  And the magnetic field intensity of the P coil 11 and the Q coil 21 in the carrier frequency of 13.56 MHz was calculated on the calculation conditions shown in Formula 4 and Table 2.

Furthermore, the relative value of the magnetic field intensity is normalized by the magnetic field intensity Hq (Z = 50 mm) generated from the Q coil by the magnetic field intensity Hp (Z = 50 mm) in the absence of the Q coil (generated from the P coil). It calculated | required like Formula 6.

  The relationship between the magnetic field strength (relative value) obtained as described above and the coupling coefficient is shown in the graphs of FIGS. FIG. 3 is a graph showing a case where the resonance frequency of the Q coil is changed to the high frequency side (B → C → E → G → I). FIG. 4 is a graph showing a case where the resonance frequency of the Q coil is changed to the low frequency side (B → D → F → H → J).

  3 and 4, when the coupling coefficient K is about 0.015 to 0.1, the magnetic field strength (relative value) surely exceeds 1, that is, the magnetic field is stronger than when the Q coil 21 is not provided. Therefore, it can be expected that the communication distance is extended as compared with the case where the Q coil 21 is not provided.

When the coupling coefficient K is in the range of about 0.015 to 0.1, stable communication can be obtained even if the resonance frequency of the Q coil is shifted by ± 0.5 MHz. The relationship between the specific error range X of the resonance frequency of the Q coil and the coupling coefficient K suitable for this is as follows.
・ X = 13.56 ± 0.05 MHz → K = 0.015 is optimal ・ X = 13.56 ± 0.1 MHz → K = 0.015 to 0.03 is optimal ・ X = 13.56 ± 0.25 MHz → K = 0.03 to 0.04 is optimal ・ X = 13.56 ± 0.5 MHz → K = 0.04 to 0.06 is optimal

  3 and 4, there is a range in which the relative value exceeds 1 even when the coupling coefficient K is smaller than 0.015 or larger than 0.1. Therefore, such a range is also included in the present invention, and the coupling coefficient K is not strictly limited to 0.015 to 0.1.

[Existence of bimodal characteristics]
In order to demonstrate that the bimodal characteristic is generated with the above setting, when the resonance frequency of the Q coil 22 is 13.56 MHz (above B), the frequency characteristic of the current Iq flowing through the Q coil 22 The results of simulation are shown in Table 3 and the graph of FIG. As is apparent from Table 3 and FIG. 5, when the coupling coefficient is 0.01 (B4), it exhibits a unimodal characteristic, but when it is greater than 0.01 (B1 to B3), it exhibits a bimodal characteristic. It can be seen that the carrier frequency of 13.56 MHz is halfway between the two peaks of the bimodal characteristic.

[Second Embodiment]
[Constitution]
This embodiment has substantially the same configuration as that of the first embodiment. However, as shown in FIG. 6, the magnetic member 4 is arranged between the P coil 11 and the Q coil 21. For example, the magnetic member 4 may be a sheet of soft magnetic ferrite rubber or soft magnetic metal, but is not limited thereto. Further, the magnetic member 4 may be separated from the P coil 11 or the Q coil 21 or may be in close contact with the P coil 11 or the Q coil 21. FIG. 7 shows an example in which the Q coil 21 is disposed on the magnetic member 4.

[Function and effect]
[Extension of communication distance: Examples 13 to 16]
The data of the result of having measured the communication distance about Comparative Examples 3 and 4 and Examples 13 to 16 of this embodiment are shown in Table 4 and the graph of FIG. Comparative examples 3 and 4 and Examples 13 to 16 which are measurement targets are the following L, M1 to M4 and N (carrier frequency 13.56 MHz).
L: When there is only a P coil and no Q coil (Comparative Example 3)
M1 to M4: There are P coils and Q coils, and the coupling coefficient K is changed (Examples 13 to 15)
N: There are a P coil and a Q coil, and a magnetic member is disposed between the P coil and the Q coil (Example 16)

And conditions of P coil 11, Q coil 21, and magnetic member 4 are as follows.
・ P coil: Radius 3.5mm, number of turns 7T, resonance frequency 13.56MHz
-Q coil: radius 18mm, number of turns 3T, resonance frequency 13.56MHz
Magnetic member: Soft magnetic ferrite rubber sheet, thickness 500 μm, size radius 20 mm, closely attached to Q coil

  As is apparent from Table 4 and FIG. 8, the communication distance of Comparative Example 3 in which only the P coil 11 is used without using the Q coil 21 of the conventional method is 40 mm, and even when the Q coil 21 is used, the coupling coefficient is In Comparative Example 4 where K is 0.15, the communication distance is 42 mm, which is about the same as Comparative Example 3. However, it can be seen that when the coupling coefficient K is 0.1 or less, the communication distance is dramatically increased to 68 to 78 mm.

  In particular, by disposing the magnetic sheet between the P coil 11 and the Q coil 21, even if the coupling coefficient K is lowered and the distance between the P coil 11 and the Q coil 21 is shortened, the communication distance is increased to 72 mm. Yes. Therefore, it is advantageous for downsizing.

[Stable communication distance: Examples 17 to 26]
The data of the result of having measured the communication distance about Examples 17-26 of this embodiment are shown in the graph of Table 5 and FIG. Examples 17 to 26, which are measurement objects, are obtained by arranging a magnetic member (magnetic sheet) between the P coil 11 and the Q coil 21, and correspond to the following S1 to S7 and T1 to T3 (carrier frequency) 13.56 MHz).
S1 to S7: A soft magnetic ferrite rubber sheet is used as the magnetic sheet, and the error of the resonance frequency of the Q coil 21 is +0.46 to -0.44 MHz. T1 to T3: Soft as the magnetic sheet A magnetic metal sheet is used, and the resonance frequency error of the Q coil 21 is ± 0.15 MHz.

And conditions of P coil 11, Q coil 21, and magnetic member 4 are as follows.
・ P coil condition: Radius 3.5mm, number of turns 7T, resonance frequency 13.56MHz
・ Q coil condition: External form 38 × 26mm, number of turns 3T
・ P coil and Q coil distance: 5mm
-Magnetic sheet: 40 x 28 mm in size, closely attached to the Q coil

  As is apparent from Table 5 and FIG. 9, by interposing a magnetic sheet between the P coil 11 and the Q coil 21, stable communication can be obtained even if the resonance frequency of the Q coil 21 changes. Specifically, a sufficient communication distance can be obtained even if the resonance frequency of the Q coil 21 is shifted by 0.5 MHz.

[Adjustment of Coupling Coefficients: Examples 24, 27, and 28]
The data obtained as a result of measuring the communication distance for Examples 24, 27, and 28 of this embodiment are shown in Table 6 and the graph of FIG. In Examples 24, 27, and 28, which are measurement targets, a magnetic member (magnetic sheet) is disposed between the P coil 11 and the Q coil 21 and corresponds to the following T1, T4, and T5 (carrier frequency) 13.56 MHz).
T1: As described above, a soft magnetic metal is used as the magnetic sheet, and the thickness of the magnetic sheet is 100 μm. T4: A soft magnetic metal is used as the magnetic sheet, and the thickness of the magnetic sheet is T5: A magnetic sheet using soft magnetic metal, and a magnetic sheet thickness of 500 μm

And conditions of P coil 11, Q coil 21, and magnetic member 4 are as follows.
・ P coil condition: Radius 3.5mm, number of turns 7T, resonance frequency 13.56MHz
・ Q coil condition: External form 38 × 26mm, number of turns 3T, resonance frequency 13.56MHz
・ P coil and Q coil distance: 5mm
-Magnetic sheet: 40 x 28 mm in size, closely attached to the Q coil

  As apparent from Table 6 and FIG. 10, the coupling coefficient can be adjusted by changing the thickness of the magnetic sheet interposed between the P coil 11 and the Q coil 21.

[Application to Metal Antenna] Examples 13 to 20
When the metal plate approaches the P coil 11, an eddy current is generated by the magnetic flux from the antenna coil, and a magnetic field (demagnetizing field) in the opposite direction is generated. The same effect can be obtained even when the L value of the antenna coil decreases due to the influence of the demagnetizing field and the resonance frequency is shifted to the high frequency side. This is the same principle as that stable communication can be obtained even if the resonance frequency of the Q coil 21 is shifted.

  Communication between the comparative examples 3 and 4 and the examples 13 to 20 in which a metal plate is arranged at a distance of 2 mm from the P coil 11 (with an external metal) and those without a metal plate (without an external metal) The results of the distance measurement are shown in Table 7 (carrier frequency 13.56 MHz). The metal plate was an aluminum plate having a thickness of 2 mm and a size of 120 × 120 mm. Comparative Examples 3 and 4 correspond to L and M1, and Examples 13 to 20 correspond to M2 to M4 and S1 to S4.

  As is apparent from Table 7, according to the present embodiment, a sufficient communication distance can be obtained even when there is a metal under the P coil 11, so that it can be used as a metal-compatible antenna. In addition, even when there is a metal under the P coil 11 and the resonance frequency of the Q coil 21 is further shifted, stable communication is possible.

[Third Embodiment]
[Constitution]
This embodiment has substantially the same configuration as that of the first embodiment, but the setting range of the carrier frequency is different. That is, in the above embodiment, the carrier frequency is set between two peaks of the bimodal characteristic. However, even if it falls outside the two peaks, if the magnetic field strength ratio exceeds 1, the effect of extending the communication distance can be expected.

  Therefore, in the present embodiment, the communication distance is extended by setting the carrier frequency in a range where the ratio of the magnetic field intensity shown in Expression 6 exceeds 1. For example, as shown in FIGS. 11 to 13, the carrier frequency is set in a range where the magnetic field intensity ratio exceeds 1.

  Here, FIG. 11 shows the case where the peak of the bimodal characteristic is symmetric, FIG. 12 shows the case where the peak of the bimodal characteristic is asymmetric, and FIG. 13 shows that the peak of the bimodal characteristic is symmetric. This is the case where the magnetic field strength ratio exceeds 1 even between two peaks. In any case, if the carrier frequency is set within the illustrated setting range, the communication distance can be extended.

[Function and effect]
The data of the results of measuring the magnetic field strength for Comparative Examples 1 and 5 and Examples 29 and 30 of this embodiment are shown in Table 8 and the graph of FIG. Comparative examples 1 and 5 and Examples 29 and 30 which are measurement targets are the following L, R, T and U.
L: When there is only a P coil and no Q coil (Comparative Example 1)
R: There are a P coil and a Q coil, the resonance frequency of the P coil and the Q coil is 13.56 MHz, and the coupling coefficient K is 0.12 (Comparative Example 5)
U: There are a P coil and a Q coil, and the resonance frequency of the P coil and the Q coil is 13.56 MHz and the coupling coefficient is 0.05 so that the magnetic field strength ratio exceeds 1 (Example 29)
W: There are a P coil and a Q coil, and the resonance frequency of the P coil and the Q coil is 14.32 MHz and the coupling coefficient is 0.12 so that the magnetic field strength ratio exceeds 1 (Example 30)

The conditions of the P coil 11 and the Q coil 21 are as follows.
・ P coil: Radius 3.5mm, number of turns 7T
・ Q coil: radius 15mm, number of turns 3T
-Carrier frequency: 13.56 MHz
・ Field strength observation point: 40mm from the center of the Q coil

  The calculation of the magnetic field intensity was performed according to the following procedure. In the circuit diagram of FIG. 2, the output current Iq of the Q coil 21 is simulated (input voltage is 1.0 V). When there was no Q coil 21, the output current Iq of the P coil 11 was simulated. According to Equation 4, the strength of the magnetic field between the state without the Q coil 21 and the state with the Q coil 21 was calculated. The magnetic field strength ratio was calculated according to Equation 6.

  As shown in Table 8 and FIG. 14, in Comparative Example 1 in which only the P coil 11 is disposed, the magnetic field strength ratio remains 1. Moreover, even if the comparative example 5 is provided with the Q coil 21, the carrier frequency is set at a position where the magnetic field intensity ratio is 0.9.

  On the other hand, in Examples 29 and 30, the Q coil 21 is provided, and the carrier frequency is set in a range where the magnetic field strength ratio exceeds 1 by controlling the resonance frequency and coupling coefficient of the P coil 11 and the Q coil 21. . In Example 29, the carrier frequency is set at a position where the magnetic field strength ratio is 2.3. This Example 29 is the same as the first embodiment because the carrier frequency is between two peaks of a bimodal characteristic. In Example 30, the carrier frequency is set at a position where the magnetic field strength ratio is 5.3. In Example 30, the carrier frequency is at a position that deviates from the two peaks of the bimodal characteristics.

Furthermore, the data of the result of actually measuring the communication distance for the above Comparative Examples 1 and 5 and Examples 29 and 30 are shown in Table 9 and the graph of FIG.

  As is apparent from Table 9 and FIG. 15, the communication distance of Comparative Example 1 in which only the P coil 11 is used without using the conventional Q coil 21 is 40 mm, and even when the Q coil 21 is used, the magnetic field strength is increased. In Comparative Example 5 with a ratio of 0.9, the communication distance is 40 mm, which is the same as Comparative Example 1. However, when the magnetic field strength ratio is set to exceed 1, it can be seen that the communication distance is dramatically increased. That is, in Example 29, a communication distance of 63 mm is obtained, and in Example 30, a communication distance of 78 mm is obtained. In particular, in Example 30 in which the carrier frequency is outside the two peaks of the bimodal characteristic, an effect of further extending the communication distance can be obtained as compared with Example 29.

[Other Embodiments]
The present invention is not limited to the embodiment as described above, and the material, size, shape, number, arrangement, and the like of each member can be appropriately changed. For example, the size and shape of the P and Q coils are not limited to those illustrated in FIG. Therefore, it may be circular, elliptical, square, or other shapes.

  Moreover, the specific numerical value in each embodiment is an illustration, and this invention is not limited to said numerical value. For example, the carrier frequency only needs to be set between two peaks of a bimodal characteristic, and the specific value of the frequency and the position between the two peaks are arbitrary. is there. For stable communication, it is desirable to set the carrier frequency between two peaks. However, as described above, even if the carrier frequency is out of the two peaks, if the magnetic field strength ratio exceeds 1, the effect of extending the communication distance can be expected.

  The distance, position, and direction between the P coil and the Q coil may be set as long as the effect of the present invention can be obtained. Therefore, the axes do not necessarily have to be parallel to each other, and the axes do not have to coincide with each other (for example, one may be arranged to be inclined with respect to the other, or may be arranged in an orthogonal direction. ). Further, the Q coil of the booster antenna can be applied to the RFID tag side.

1 is a perspective view showing an RFID system to which a first embodiment of the present invention is applied. FIG. 2 is a circuit diagram of FIG. 1. In the Example which applied embodiment of FIG. 1, it is explanatory drawing which shows the relationship between a coupling coefficient and magnetic field intensity | strength when the resonant frequency of Q coil changes to the high frequency side. In the Example which applied embodiment of FIG. 1, it is explanatory drawing which shows the relationship between a coupling coefficient and magnetic field intensity | strength when the resonant frequency of Q coil changes to the low frequency side. It is explanatory drawing which shows the frequency characteristic of the output current of Q coil in the Example which applied embodiment of FIG. It is a perspective view which shows the RFID system to which the 2nd Embodiment of this invention is applied. It is a top view which shows the booster antenna of the magnetic member composite type which has arrange | positioned Q coil of embodiment of FIG. It is explanatory drawing which shows the relationship between the coupling coefficient and the communication distance of the Example which applied embodiment of FIG. 6, and its comparative example. It is explanatory drawing which shows the relationship between the resonant frequency of Q coil and the communication distance in the Example to which embodiment of FIG. 6 is applied. It is explanatory drawing which shows the relationship between the thickness of a magnetic sheet and the communication distance in the Example which applied embodiment of FIG. It is explanatory drawing which shows the setting range of the carrier frequency in the 3rd Embodiment of this invention. It is explanatory drawing which shows the setting range of the carrier frequency in the 3rd Embodiment of this invention. It is explanatory drawing which shows the setting range of the carrier frequency in the 3rd Embodiment of this invention. It is explanatory drawing which shows the relationship between the magnetic field intensity ratio of the Q coil in 3rd Embodiment of this invention, and a carrier frequency. It is explanatory drawing which shows the relationship between the magnetic field intensity ratio and communication distance of embodiment of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... RFID reader / writer 2 ... Booster antenna 3 ... RFID tag 4 ... Magnetic member 11 ... P coil 21 ... Q coil

Claims (5)

The first antenna coil comprises a capacitor and a power supply, a first resonant circuit resonating with a predetermined resonant frequency, includes a second antenna coil and a capacitor, and a second resonant circuit resonating with a predetermined resonance frequency A coupled resonant circuit having
The first antenna coil and the second antenna coil are disposed at a position where a bimodal characteristic occurs,
In the first resonance circuit including the first antenna coil , a carrier frequency for communication with the outside is set between two peaks of a bimodal characteristic,
When there is no second resonance circuit including the second antenna coil with respect to the magnetic field strength of the magnetic field generated from the second antenna coil due to the induced current caused by the current flowing through the first antenna coil, the first A booster antenna coil, wherein a value of a current flowing through the first antenna coil is set by the power source so that a value of a ratio of magnetic field strengths of magnetic fields generated from the antenna coil exceeds 1. The first antenna coil comprises a capacitor and a power supply, a first resonant circuit resonating with a predetermined resonant frequency, includes a second antenna coil and a capacitor, and a second resonant circuit resonating with a predetermined resonance frequency A coupled resonant circuit having
The first antenna coil and the second antenna coil are disposed at a position where a bimodal characteristic occurs,
In the first resonance circuit including the first antenna coil , a carrier frequency for communication with the outside is set between two peaks of a bimodal characteristic,
The coupling coefficient between the first resonance circuit including the first antenna coil and the second resonance circuit including the second antenna coil is approximately 0.015 to 0.1 . A booster antenna coil , wherein an inductance of one antenna coil, an inductance of the second antenna coil, and a mutual inductance of the first antenna coil and the second antenna coil are set . The first antenna coil comprises a capacitor and a power supply, a first resonant circuit resonating with a predetermined resonant frequency, includes a second antenna coil and a capacitor, and a second resonant circuit resonating with a predetermined resonance frequency A coupled resonant circuit having
The first antenna coil and the second antenna coil are disposed at a position where a bimodal characteristic occurs,
When there is no second resonance circuit including the second antenna coil with respect to the magnetic field strength of the magnetic field generated from the second antenna coil due to the induced current caused by the current flowing through the first antenna coil, the first A booster antenna coil, wherein a value of a current flowing through the first antenna coil is set by the power source so that a value of a ratio of magnetic field strengths of magnetic fields generated from the antenna coil exceeds 1. The first antenna coil comprises a capacitor and a power supply, a first resonant circuit resonating with a predetermined resonant frequency, includes a second antenna coil and a capacitor, and a second resonant circuit resonating with a predetermined resonance frequency A coupled resonant circuit having
The first antenna coil and the second antenna coil are disposed at a position where a bimodal characteristic occurs,
The first resonance circuit including the first antenna coil and the second resonance circuit including the second antenna coil are set to different resonance frequencies.
When there is no second resonance circuit including the second antenna coil with respect to the magnetic field strength of the magnetic field generated from the second antenna coil due to the induced current caused by the current flowing through the first antenna coil, the first A booster antenna coil, wherein a value of a current flowing through the first antenna coil is set by the power source so that a value of a ratio of magnetic field strengths of magnetic fields generated from the antenna coil exceeds 1.   The booster antenna coil according to any one of claims 1 to 4, wherein a magnetic member is disposed between the first antenna coil and the second antenna coil.

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