Antenna for reader/writer

Description: TECHNICAL FIELD [Detailed description of the invention]

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INDUSTRIAL APPLICABILITY The present invention relates to a loop antenna used for a questioner of a non-contact data carrier system that performs short-range communication by electromagnetic induction between a questioner and a responder. More specifically, the present invention is a loop antenna used for transmitting a transmission signal from the interrogator to the responder and receiving a reply signal from the responder in the interrogator, and the reply signal from the responder. It relates to a loop antenna that prevents the transmitted signal from the interrogator from being detected when it is detected, thereby facilitating the detection of the reply signal and improving the reliability of reading.

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PROBLEM TO BE SOLVED: In recent years, a non-contact data carrier system which performs short-range communication between an interrogator and a responder by electromagnetic induction has attracted attention and is rapidly becoming widespread. For example, in an automatic ticket gate, an entry / exit management system, or the like, a non-contact information card system that uses a reader / writer as a questioner and a card such as an IC card or ID card as a responder is used.

In this non-contact data carrier system, the interrogator transmits an electromagnetic wave having a frequency of about several hundred K to several MHz to the responder in order to transmit information to the responder or further supply electric power. At the same time, it receives and detects the reply signal from the responder. In this case, the interrogator is usually provided with one loop antenna as a dual-purpose antenna for a transmitting antenna for transmitting a signal or power to the responder and a receiving antenna for receiving a reply signal from the responder. There is.

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[Problems to be Solved by the Invention] However, in the conventional non-contact data carrier system, when the interrogator receives and detects the reply signal from the responder, the loop antenna terminal of the interrogator has not only the reply signal from the responder but also the reply signal from the responder. The transmission signal sent by the interrogator toward the responder also appears. In this case, the larger the communication distance (that is, the distance between the interrogator and the responder), the stronger the strength of the transmitted signal transmitted from the interrogator to the responder, so that the transmitted signal appearing at the loop antenna terminal of the interrogator and the reply The ratio with the signal increases as the communication distance increases, and the transmission signal appearing at the loop antenna terminal of the interrogator is usually about 1 to 100,000 times stronger than the reply signal that should be detected. For this reason, a weak reply signal appears in the loop antenna terminal of the interrogator, which is harmful and strong for reception. Moreover, the reception strength of the transmission signal that is unnecessarily received when the reply signal from the responder is received by the loop antenna terminal of the interrogator is due to variations in the fabrication of the loop antenna of the interrogator and variations in the resonance capacitance. Not constant. Furthermore, since the inductance, capacitance, Q, etc. of the loop antenna change due to temperature fluctuations, the level of unwanted waves at the loop antenna terminal when receiving the reply signal from the responder also changes from moment to moment. Therefore, there is a problem that it is very difficult for the loop antenna of the interrogator to receive the reply signal from the responder and detect it accurately, and it is not easy to secure the reliability of reading the data. Therefore, there is also a problem that the circuit for reading the reply signal becomes complicated and expensive.

Such a problem is not only when the interrogator is provided with one loop antenna as a dual-purpose antenna for the transmitting antenna and the receiving antenna, but also when the transmitting antenna and the receiving antenna are separately provided. Even if it is, it has occurred in the same manner in the past. That is, even if the transmitting antenna and the receiving antenna are provided separately in the interrogator, a coupling occurs between the transmitting antenna and the receiving antenna, and the transmitted signal from the transmitting antenna is directly used for receiving. Since it is induced by the antenna, an unnecessary transmission signal appears at a high level at the receiving antenna terminal.

The present invention is intended to solve the above-mentioned problems of the prior art, and is used in a non-contact data carrier system in which short-range communication is performed by electromagnetic induction between an interrogator and a responder. When the antenna of the device receives the reply signal from the responder, the transmitted signal transmitted from the interrogator to the responder is prevented from appearing at the antenna terminal of the interrogator, thereby facilitating the detection of the reply signal from the responder. The purpose is to improve the reliability of reading.

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[Means for Solving the Problems] In order to achieve the above object, the present invention relates to an antenna for a reader / writer of a non-contact data carrier consisting of a questioner and a responder, and the reader / writer of the questioner. The antenna is composed of a transmitting antenna that transmits a signal to the responder and a receiving antenna that receives a signal from the responder, and the receiving antenna receives the signal by magnetic field coupling between the receiving antenna and the transmitting antenna. Provided is an antenna for a reader / writer, which comprises a loop coil in which magnetic fields having opposite polarities are induced in the antenna and arranged at positions where the magnetic fields having opposite polarities cancel each other out.

In particular, in such a reader / writer antenna, the transmitting antenna is composed of at least two loop coils that generate magnetic fields of opposite polarities to each other, and magnetic fields of opposite polarities emitted from these loop coils. The receiving antennas are arranged so that the magnetic fields induced in the receiving antennas cancel each other out, and in this case, the magnetic field strength of the magnetic field transmitted from the transmitting antenna is the communication area as compared with the communication area. The loop diameter, number of turns, winding direction, absolute value of current and phase difference of current of each loop coil of the transmitting antenna are selected so that they are greatly reduced outside, or at least one of these factors is adjusted more precisely. Provide what you have.

The reader / writer antenna of the present invention comprises a separately provided transmitting antenna and a receiving antenna, and the receiving antenna is a magnetic field coupling between the receiving antenna and the transmitting antenna. Since magnetic fields of opposite polarities are induced by the above and the loop coils are arranged at positions where the magnetic fields of opposite polarities cancel each other out, the interrogator provided with the antenna for the reader / writer of the present invention has. Even while the transmitting antenna transmits information or supplies power to the responder, the receiving antenna cancels the transmitting signal from the transmitting antenna, so that the transmitting signal is the receiving antenna terminal. It is prevented from appearing in. Therefore, the receiving antenna can easily read the reply signal from the responder, and the data reading reliability is also improved.

In particular, in the reader / writer antenna of the present invention, at least two loop coils that generate magnetic fields of opposite polarities are provided as transmission antennas, and the magnetic fields of opposite polarities emitted from these loop coils are used for reception. The transmitting antenna so that the magnetic fields induced in the antenna cancel each other out, and in this case, the magnetic field strength of the magnetic field transmitted from the transmitting antenna is greatly reduced outside the communication area as compared with the communication area. By selecting at least one element of the loop diameter, number of turns, winding direction, absolute value of current and phase difference of current of each loop coil of, and adjusting these, the magnetic field strength is sufficiently high in the communication area and good communication is performed. While ensuring quality, it is possible to reduce the magnetic field strength outside the communication area and greatly suppress interference and interference with neighboring devices or neighboring communication systems.

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BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In each figure, the same reference numerals represent the same or equivalent components.

FIG. 1 is a configuration diagram of one aspect of a reader / writer antenna. The reader / writer antenna 1a includes a separately provided transmitting antenna 2 and a receiving antenna 3. Of these, the transmitting antenna 2 is composed of a multiple circular inner loop coil 2a and a single circular outer loop coil 2b formed coaxially in the same plane, and the inner loop coil 2a and the outer loop coil 2b are composed of the inner loop coil 2a and the outer loop coil 2b. It is formed from a single antenna conductor so that the winding directions are opposite to each other. Therefore, the inner loop coil 2a and the outer loop coil 2b generate magnetic fields having opposite polarities when transmitting the transmission signal.

Such a transmitting antenna 2 can be obtained, for example, by winding one conducting wire and forming an inner loop coil and an outer loop coil as shown in the figure. Alternatively, it may be formed by etching the conductor layer of a substrate having a conductor layer such as copper foil on the insulating layer.

0014. On the other hand, as shown in the figure, the receiving antenna 3 is composed of a circular loop coil whose loop diameter is larger than the inner loop coil 2a of the transmitting antenna and smaller than the outer loop coil 2b, and is composed of the inner loop coil 2a and the outer loop coil 2a. It is arranged substantially coaxially with the loop coil 2b. Here, the loop diameter of the receiving antenna 3 and the positions with respect to the inner loop coil 2a and the outer loop coil 2b are the mutual inductance between the receiving antenna 3 and the inner loop coil 2a, and the receiving antenna 3 and the outer loop coil 2b. It is appropriately determined that the mutual inductances have the same magnitude and opposite polarities and cancel each other out. Specifically, for example, the terminal voltage that appears when the transmission signal is sent from the inner loop coil 2a to the receiving antenna terminal and the terminal voltage that appears when the transmission signal is sent from the outer loop coil 2b become equal, and for reception. The coil constant and its position of the receiving antenna 3 may be determined so that the apparent terminal voltage of the antenna terminal becomes 0. The reader / writer antenna 1a of FIG. 1 and the reader / writer antenna 1b (FIG. 2), 1c (FIG. 3), 1d (FIG. 4), 1e (FIG. 7), and 1f (FIG. 9), which will be described later. When the transmitting antenna 2 and the receiving antenna 3 have high symmetry in the left-right or up-down structure as shown in 1g (FIG. 10), 1h (FIG. 11), and 1i (FIG. 12), reception is performed. The loop diameter of the antenna 3 and the position of the antenna 3 with respect to each loop coil constituting the transmitting antenna can be predicted relatively easily.

As for the method of forming the receiving antenna 3, the receiving antenna 3 may be formed by winding one conducting wire or by etching the substrate, as in the above-described transmitting antenna. In particular, when the transmitting antenna 2 is formed by etching one conductor layer of a double-sided substrate having conductor layers on both sides, the receiving antenna 3 is formed by etching the other surface of the double-sided substrate. However, it is preferable from the viewpoint of simplifying the manufacturing process.

By equipping the interrogator with the reader / writer antenna 1a including the transmitting antenna 2 and the receiving antenna 3 as described above, the receiving antenna 3 of the interrogator receives the reply signal from the responder. While the interrogator's transmitting antenna 2 (inner loop coil 2a and outer loop coil 2b) sends a transmitting signal to the responder for information transmission or power supply, the inside of the receiving antenna 3 Then, since the transmission signals having opposite polarities from the transmission antenna 2 cancel each other out, it is greatly suppressed that an unnecessary voltage is generated by the transmission signal at the terminal of the reception antenna 3. Therefore, the receiving antenna 3 can easily detect the reply signal with high read reliability.

Further, when magnetic fields having opposite polarities are generated from the inner loop coil 2a and the outer loop coil 2b constituting the transmission antenna in this way, the magnetic fields generated from the inner loop coil 2a and the outer loop coil 2b are combined. It is preferable to adjust each loop coil so that the total magnetic field strength is significantly reduced outside the communication area as compared with the communication area. In particular, the magnetic field strength of the magnetic field transmitted from the transmission antenna 2 is transmitted. It is preferable to adjust so that the attenuation is inversely proportional to the nth power (n> 3) of the distance from the transmission antenna 2 within a range sufficiently shorter than the wavelength (Japanese Patent Application No. 7-120810). See the scope of patent claims). As a result, the magnetic field strength is sufficiently increased in the communication area to ensure good communication quality, while the magnetic field strength is reduced outside the communication area to greatly suppress interference and interference with neighboring devices or neighboring communication systems. Is possible.

As an adjustment method in this case, at least one element of the loop diameter, the number of turns, the winding direction, the absolute value of the current, and the phase difference of the current of each of the loop coils 2a and 2b may be appropriately adjusted. Further, although not shown, a variable inductance, a variable capacitor or a variable resistor may be connected to the inner loop coil 2a and the outer loop coil 2b to adjust them in order to facilitate fine adjustment, and the loop coil may be adjusted. Is formed on the substrate, an adjustment pattern made of a metal foil or the like may be arranged around the loop coil on the substrate, and the arrangement and area of the pattern may be adjusted.

In the reader / writer antenna of the present invention, a transmitting antenna and a receiving antenna are separately provided, and a magnetic field of opposite polarity is induced in the receiving antenna by magnetic field coupling between the receiving antenna and the transmitting antenna. In addition, various modes can be taken as long as the receiving antennas are arranged so that the magnetic fields of opposite polarities cancel each other out. There are no particular restrictions on the shape, number of turns, number of turns, arrangement, etc. of each loop coil constituting the transmitting antenna and the receiving antenna.

For example, in the reader / writer antenna 1a of FIG. 1, the transmitting antenna 2 is composed of two loop coils 2a and 2b that generate magnetic fields having opposite polarities when transmitting a transmission signal. Like the reader / writer antenna 1b shown, the transmitting antenna 2 may be composed of a single loop coil. In this case, the receiving antenna 3 may be arranged so that its loop surface is perpendicular to the loop surface of the transmitting antenna 2. At this time, the magnetic flux generated when the transmitting antenna 2 transmits the transmission signal (broken line in the figure), and among the magnetic fluxes entering the receiving antenna 3, the magnetic flux 2x on one side of the loop surface of the transmitting antenna 2 And the magnetic flux 2y on the other surface side are made equal. As a result, in the receiving antenna 3, the magnetic fluxes 2x and 2y generated by the transmitting antenna 2 cancel each other out. Therefore, the transmission signal prevents unnecessary voltage from being generated at the terminal of the receiving antenna 3.

Further, in the reader / writer antenna 1a of FIG. 1, the transmitting antenna 2 is composed of an inner loop coil 2a and an outer loop coil 2b formed coaxially in the same plane. Like the reader / writer antenna 1c shown, two separate circular loop coils 2a and 2b are juxtaposed as the transmitting antenna 2 so that the loops do not overlap each other, and are placed on both of the loop coils 2a and 2b. Elliptical receiving antennas 3 may be arranged so as to overlap each other. In this case, in order to generate magnetic fields of opposite polarities from the two loop coils 2a and 2b when transmitting the transmission signal, for example, the antenna terminal is set so that the current flows in the opposite directions through the loop coils 2a and 2b. Just connect.

The reader / writer antenna 1d in FIG. 4 (plan view (a) and side view (b)) is a loop coil 2a that generates magnetic fields of opposite polarities to each other as a transmission antenna 2. A single antenna conductor is provided so that 2b are adjacent to each other and their winding directions are opposite to each other, and the receiving antenna 3 made of a loop coil is provided with the two loop coils 2a of the transmitting antenna. This is an example in which the loop surface of the receiving antenna 3 is provided at substantially the center of 2b so as to be parallel to the loop surfaces of the loop coils 2a and 2b of the transmitting antenna.

The transmitting antenna 2 as shown in FIG. 4 can be formed, for example, by routing one conducting wire in a figure of eight. Alternatively, as shown in FIG. 5, an S-shaped conductor pattern as shown by the solid line in the figure is formed on one side of the double-sided substrate 4 having conductor layers on both sides of the insulating layer by etching, and on the other side. An S-shaped conductor pattern as shown by a broken line in the figure may be formed by etching, and both patterns may be formed by connecting them with through holes h1 and h2.

When the transmitting antenna 2 is formed of two loop coils that generate magnetic fields having opposite polarities to each other, these loop coils are formed as one as shown in FIG. 4 or the above-mentioned FIG. It can be appropriately determined whether the form can be formed by winding the conducting wire or from separate independent loop coils as shown in FIG. 3, but magnetic fields having opposite polarities are generated. The former is preferable from the viewpoint that it is not necessary to individually set the direction and phase of the current flowing through each loop coil and the design of the transmitting antenna is easy.

FIG. 6 is an explanatory diagram of a magnetic field line generated by the transmitting antenna 2 of FIG. As shown in the figure, the magnetic field generated from the loop coil 2a of the transmitting antenna 2 and the magnetic field generated from the loop coil 2b have opposite polarities. Therefore, also in this transmission antenna 2, the total magnetic field strength of the magnetic fields generated from these loop coils 2a and 2b is larger outside the communication area than in the communication area, as in the case of the transmission antenna of FIG. 1 described above. It is preferable to appropriately adjust at least one element of the loop diameter, the number of turns, the absolute value of the current, and the phase difference of the current of each loop coil 2a and 2b so as to decrease.

Further, as shown in FIG. 6, the magnetic flux density becomes high in the vicinity of the contact points of the two loop coils 2a and 2b of the transmitting antenna 2. Therefore, as shown in FIG. 4, when the loop coil of the receiving antenna 3 is arranged parallel to the loop surface of the loop coils 2a and 2b in the region where the magnetic flux density is high, the loop coil of the receiving antenna 3 is used. Will strongly induce voltages of opposite polarities from the loop coil 2a and the loop coil 2b of the transmitting antenna. Here, as in the case of FIG. 1, the mutual inductance of the loop coil of the receiving antenna 3 and the loop coil 2a of the transmitting antenna and the mutual inductance of the loop coil of the receiving antenna 3 and the loop coil 2b of the transmitting antenna If the coil constants of the loop coil of the receiving antenna 3 are set so that the inductance has the same magnitude and the polarity is opposite, they cancel each other out in the receiving antenna 3. Therefore, also in this embodiment, it is possible to greatly suppress the generation of unnecessary voltage due to the transmission signal at the terminal of the receiving antenna 3.

In the vicinity of the contact points of the two adjacent loop coils 2a and 2b of the transmitting antenna of FIG. 4, the magnetic flux density becomes high as described above. Therefore, by using such a transmitting antenna, the magnetic flux density becomes high. The angular range of the responder's antenna with respect to the interrogator's transmitting antenna, which is required to allow the responder to receive the transmitted signal from the interrogator with a predetermined receiving sensitivity, can be greatly expanded.

The reader / writer antenna 1e in FIG. 7 (plan view (a) and side view (b) in FIG. 7) serves as a transmission antenna 2 and is a transmission antenna of the reader / writer antenna 1d in FIG. This is an example in which the receiving antenna 3 is provided so that the loop surface thereof is perpendicular to the loop surface of the loop coils 2a and 2b of the transmitting antenna. Further, FIG. 8 is an explanatory diagram of the magnetic field lines in this case. When the receiving antenna 3 is provided in this way, the magnetic flux (broken line in the figure) generated when the transmitting antenna 2 transmits the transmitting signal is the magnetic flux (broken line in the figure) generated when the transmitting antenna 2 is transmitted, and is received, similarly to the reader / writer antenna 1b of FIG. When the magnetic flux 2x on one surface side of the loop surface of the transmitting antenna 2 and the magnetic flux 2y on the other surface side are equal to each other among the magnetic fluxes entering the transmitting antenna 3, the magnetic flux generated by the transmitting antenna 2 is generated. 2x and 2y cancel each other out in the receiving antenna 3. Therefore, even in this embodiment, the generation of an unnecessary voltage due to the transmission signal at the terminal of the receiving antenna 3 is greatly suppressed.

The reader / writer antenna 1f of FIG. 9 has a transmission antenna 2 and a loop coil having winding directions opposite to each other, similar to the reader / writer antenna 1d of FIG. The loop coils are routed so as to be adjacent to each other so that the loop coils that generate magnetic fields of opposite polarities are adjacent to each other, but the three loop coils 2a, 2b, and 2c are adjacent to each other in a row as loop coils. It is a thing. In this case, the polarities of the two loop coils 2a and 2c at both ends are in the same direction, and the loop coils 2a and 2c and the loop coil 2b at the center are opposite in polarity. Therefore, the mutual inductance between the loop coil of the receiving antenna 3 and the loop coils 2a and 2c at both ends of the transmitting antenna and the mutual inductance of the loop coil of the receiving antenna 3 and the loop coil 2b at the center of the transmitting antenna Set the coil constant of the loop coil of the receiving antenna 3 so that and have the same size and opposite polarity. As a result, it is possible to prevent the receiving antenna 3 from generating an unnecessary voltage due to the transmission signal.

The reader / writer antenna 1g of FIG. 10 is formed by forming loop coils 2a and 2c at both ends of the transmission antenna 2 of the reader / writer antenna 1f of FIG. 9 in a non-circular shape. As described above, the shape of the loop coil of the transmitting antenna and the receiving antenna used in the present invention is not limited to a circular shape, and can take various shapes.

In the reader / writer antenna 1h of FIG. 11, the transmitting antenna 2 is a loop in which three loop coils 2a, 2b, and 2c are adjacent to each other and are adjacent to each other, similarly to the reader / writer antenna 1f of FIG. Although the coil winding methods are reversed from each other, the reader / writer antenna 1h in FIG. 11 has loops of the loop coils 2a and 2c at both ends as compared with the transmission antenna 2 of FIG. The diameter is reduced and the number of turns of the loop coil 2b in the central portion is reduced.

Further, the receiving antenna 3 of the reader / writer antenna 1h shown in FIG. 11 is provided with auxiliary coils 3p and 3q. When the loop coil of the receiving antenna 3 is a winding coil, the auxiliary coils 3p and 3q are deformed, and when the loop coil is a pattern of the conductor layer on the substrate by etching, it is auxiliary. By cutting the patterns of the coils 3p and 3q, it is possible to accurately adjust the balance of the mutual induction inductance between the receiving antenna 3 and the transmitting antenna 2. Therefore, it is preferable that the receiving antenna 3 is provided with auxiliary coils 3p and 3q for adjusting the mutual induction inductance.

In the reader / writer antenna 1i of FIG. 12, similarly to the reader / writer antenna 1a of FIG. 1, the transmitting antenna 2 is coaxially formed in the same plane as the inner loop coil 2a and the outer side. It is composed of a loop coil 2b, and the loop coil of the receiving antenna 3 is arranged substantially coaxially with the inner loop coil 2a and the outer loop coil 2b. The receiving antenna 3 is provided with auxiliary coils 3p, 3q, 3r, and 3s for accurately adjusting the balance of the mutual induction inductance between the receiving antenna 3 and the transmitting antenna 2.

As a method of adjusting the mutual induction inductance between the receiving antenna 3 and the transmitting antenna 2, in addition to providing the auxiliary coil as shown in FIGS. 11 and 12, each loop coil of the transmitting antenna or A variable capacitor or variable resistor may be connected to the loop coil of the receiving antenna to adjust it, or a metal foil or the like may be placed around the loop coil to adjust the arrangement and area of the metal foil. May be done by.

As described above, the reader / writer antenna of the present invention is basically composed of a transmitting antenna and a receiving antenna, and preferably, the transmitting antenna has magnetic fields having opposite polarities when transmitting a transmission signal. It is composed of at least two loop coils that generate the above. Then, in the receiving antenna, the magnetic fields transmitted from the transmitting antenna cancel each other out, thereby preventing the transmitting signal from being detected by the receiving antenna.

Further, in the present invention, in addition to such a basic configuration, various means can be provided in the receiving antenna so that the transmission signal from the transmitting antenna is severely blocked. That is, even if the magnetic fields from the transmitting antenna are canceled by the receiving antenna, there is a stray coupling capacitance due to electrostatic coupling between the receiving antenna and the transmitting antenna, so that the leakage current flows to the receiving antenna. .. FIG. 13 is a general explanatory view of such a leakage current. When a current flows through the coil of the transmitting antenna 2 as shown by an arrow, the current flows through the stray coupling capacitance C as shown by an arrow. Indicates that is flowing.

In the present invention, in order to greatly suppress the influence of the stray coupling capacitance C and solve the problem of leakage current, for example, a bifilar choke is provided on the receiving antenna so that the stray coupling capacitance C is greatly suppressed. It can be provided or the receiving antenna can be electrostatically shielded.

Among these, as a mode in which the bifilar choke is provided, for example, as shown in FIG. 14, the bifilar choke 5 is provided after the loop coil of the receiving antenna 3, and the bifilar choke 5 and the receiving circuit main body are provided. A matching transformer 6 can be provided between them. In this case, it is preferable that the two coils constituting the bifilar choke have a large impedance with respect to the current in the same direction. Therefore, for example, the number of turns of the coil may be increased or a core such as ferrite may be inserted into the coil. preferable. As a result, the leakage current can be greatly suppressed, and the voltage drop due to the leakage current at the receiving antenna terminal can be substantially eliminated. On the other hand, the current due to the reply signal from the responder does not attenuate because the voltage drop does not occur due to the flow in the bifilar choke in the opposite direction. Therefore, the original target signal can be detected satisfactorily.

On the other hand, as a mode of electrostatically shielding the receiving antenna, for example, as shown in FIG. 15, a shielded wire (or coaxial cable) 7 is used for the receiving antenna 3, and the shielded jacket 7a is connected to the ground. Can be done. In this case, the inner conductor 7b of the shielded wire 7 is used as an antenna. Further, a part of the shield outer cover 7a is cut off with a part of the shielded wire 7 7x so that a loop is not formed on the shield outer cover 7a.

Further, as shown in FIG. 16, the receiving antenna 3 may be covered with the conductive pipe material 8 and shielded by grounding the pipe material. As shown in the cross-sectional view of FIG. 16B, the pipe material 8 is composed of a C-shaped pipe covering the antenna conductor 3a covered with the insulating material 9, and one end thereof is grounded.

FIG. 17 (top view (a), side view (b), bottom view (c)) shows the antenna for reader / writer as shown in FIG. 1 for transmission. A disk-shaped transmitting antenna plate 10x and a receiving antenna plate 10y are arranged on the opposite loop surfaces of the antenna 2 and the receiving antenna 3, respectively, and the surface of the transmitting antenna plate 10x opposite to the loop coils 2a and 2b is grounded. A plate 11x (a portion filled with dots in FIG. 17 (a)) is provided, and a ground plate 11y (a portion filled with dots in FIG. 17 (c)) is also provided on the surface of the receiving antenna plate 10y opposite to the loop coil. In addition, an insulating plate 12 is arranged between the ground plate 11x and the ground plate 11y, and the ground plate 11x and the ground plate 11y are grounded.

FIG. 18 (FIG. 18A) shows a transmitting antenna (inner loop) composed of an insulated conductor in order to more tightly shield the receiving antenna of the reader / writer antenna as shown in FIG. This is an example in which the coil turns 3, the outer loop coil turns 1), the receiving antenna (loop coil turns 1), and the copper shield tube 13 are housed and shielded. Further, FIG. 3B is an enlarged explanatory view of the A1 portion of the inner loop coil 2a of the transmission antenna shielded by the shield tube 13 as shown in FIG. 3A, and FIG. 3C is an enlarged explanatory view of the inner loop coil. It is an enlarged sectional view of the B part of 2a. As described above, in the shield tube 13, the conductive pipe 13a is fitted to the insulator 13b from both sides as shown by the arrows in the A1 portion so that the conductive loop of the conductive pipe 13a does not close. The A2 part of the outer loop coil of the transmitting antenna and the A3 part of the receiving antenna corresponding to the A1 part of the inner loop coil are similarly configured.

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[Example] Example 1, Comparative Example 1 The antenna 1a for a reader / writer of the present invention having the embodiment shown in FIG. 1 was produced. In this case, the coil constants of the inner loop coil 2a and the outer loop coil 2b constituting the transmitting antenna 2 are set as shown in Table 1 (Example 1).

For comparison, a reader / writer antenna was manufactured in the same manner as in Example 1 except that the transmitting antenna was composed of a single loop coil. In this case, the coil constants of the loop coil of the transmitting antenna were set as shown in Table 1, and the current was determined so that the magnetic field strength at the target distance of 15 cm was 100 dBμV / m.

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[Table 1] Radius (mm) Number of turns (times) Current (A) Example 1 Inner loop coil 2a: 50 3 1.5 Outer loop coil 2b: 61. 2 1.5 Comparative Example 1 Single loop coil: 50.0 3 0.102 The magnetic field strength distribution by these transmitting antennas, that is, the relationship between the distance from the transmitting antenna and the magnetic field strength was measured using a search coil. The result is shown in FIG.

From FIG. 19, in the transmitting antenna of the comparative example, the magnetic field strength gradually decreases in inverse proportion to the cube of the distance from the antenna, but in the transmitting antenna of the first embodiment, the magnetic field strength is low. It is inversely proportional to the fifth power of the distance from the antenna, and decreases sharply as the distance from the antenna increases. Therefore, it is possible to increase the magnetic field strength in the communication area and sufficiently reduce the magnetic field strength outside the communication area to greatly suppress interference and interference with neighboring devices or neighboring communication systems.

Further, when the loop coil of the receiving antenna is wound once and the loop diameter is variously changed, the mutual inductance M (3-2a) between the loop coil of the receiving antenna and the inner loop coil of the transmitting antenna is changed. ), Mutual inductance M (3-2b) between the loop coil of the receiving antenna and the outer loop coil of the transmitting antenna, the loop coil of the receiving antenna and the inner and outer loop coils of the transmitting antenna have opposite polarities. As described above, these were connected in series, and the mutual inductance M (3-2a, 3-2b) with the coil of this transmission antenna when this was regarded as one transmission coil was obtained. The result is shown in FIG.

From FIG. 20, the inner loop coil 2a of the transmitting antenna has a radius of 50 mm and is wound three times, and the outer loop coil 2b has a radius of 61.2 mm and is wound twice, and these are coaxially arranged in the same plane. In this case, when the loop coil of the receiving antenna is wound once with a radius of 58.4 mm, M = 0, and it can be seen that the coupling between the receiving antenna and the transmitting antenna is lost (indicated by the arrow in the figure). Place). Therefore, it can be seen that the coil constant of the receiving antenna may be the coil constant at the point where the coupling between the receiving antenna and the transmitting antenna is lost.

【００４９】

According to the present invention, in a non-contact data carrier system in which short-range communication is performed between an interrogator and a responder by electromagnetic induction, a reply signal from the responder is received by an antenna of the interrogator. At this time, the transmission signal transmitted from the interrogator to the responder is prevented from appearing at the antenna terminal of the interrogator, thereby facilitating the detection of the reply signal from the responder and improving the reliability of reading.

Further, in the present invention, at least two loop coils that generate magnetic fields having opposite polarities are provided as the transmission antenna, and the loop diameter, the number of turns, the winding direction, the absolute value of the current, and the phase difference of the current of these loop coils are provided. By selecting at least one element of the above and setting it appropriately, the magnetic field strength is high in the original communication area, but the magnetic field strength decreases sharply as the distance from the antenna increases, and the communication area Outside, the magnetic field strength can be surely set to a predetermined value or less.

Therefore, the magnetic field strength transmitted from the interrogator to the responder is sufficiently high in the communication area to ensure good communication quality, while the magnetic field strength is reduced outside the communication area to be a neighboring device or a neighborhood. It greatly suppresses interference and interference with the communication system, and at the same time, suppresses unnecessary detection of the transmission signal sent from the interrogator to the responder when the interrogator detects the reply signal from the responder. , It is possible to facilitate the detection of the reply signal from the responder and improve the reliability of reading.

[Simple explanation of drawings]

FIG. 1 is a configuration diagram of an aspect of an antenna for a reader / writer of the present invention.

FIG. 2 is a configuration diagram of another aspect of the reader / writer antenna of the present invention.

FIG. 3 is a configuration diagram of another aspect of the reader / writer antenna of the present invention.

FIG. 4 is a configuration diagram of another aspect of the antenna for a reader / writer of the present invention (FIG. 4 (a), FIG. 4 (b), side view).

FIG. 5 is an explanatory diagram of a transmitting antenna used for the reader / writer antenna of the present invention.

FIG. 6 is an explanatory diagram of magnetic field lines emitted by a transmitting antenna used for the reader / writer antenna of the present invention and their effects on the receiving antenna.

FIG. 7 is a configuration diagram of another aspect of the antenna for a reader / writer of the present invention (FIG. 7 (a) plan view, FIG. 7 (b) side view).

FIG. 8 is an explanatory diagram of magnetic field lines emitted by a transmitting antenna used for the reader / writer antenna of the present invention and their effects on the receiving antenna.

FIG. 9 is a configuration diagram of another aspect of the reader / writer antenna of the present invention.

FIG. 10 is a configuration diagram of another aspect of the reader / writer antenna of the present invention.

FIG. 11 is a configuration diagram of another aspect of the reader / writer antenna of the present invention.

FIG. 12 is a configuration diagram of another aspect of the reader / writer antenna of the present invention.

FIG. 13 is an explanatory diagram of a leakage current due to electrostatic coupling between a transmitting antenna and a receiving antenna.

FIG. 14 is an explanatory diagram of a bifilar choke that prevents leakage current.

FIG. 15 is an explanatory diagram of a case where a receiving antenna is shielded by using a shielded wire in order to prevent leakage current.

FIG. 16 is an explanatory diagram of a case where a receiving antenna is shielded by using a pipe material in order to prevent a leakage current.

FIG. 17 is an explanatory diagram of a case where a receiving antenna is shielded by using a ground plate in order to prevent leakage current.

FIG. 18 is an explanatory diagram of a case where a receiving antenna and a transmitting antenna are shielded by using a shield tube in order to prevent leakage current.

FIG. 19 is a diagram showing the relationship between the distance from the antenna and the magnetic field strength of the transmitting antennas of the reader / writer antennas of Examples and Comparative Examples.

FIG. 20 is a diagram showing the relationship between the loop diameter of the loop coil of the receiving antenna and the mutual inductance of the receiving antenna and the inner or outer loop coil of the receiving antenna and the transmitting antenna for the reader / writer antenna of the embodiment.

[Explanation of symbols] 1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i Reader / writer antenna 2 Transmission antenna 2a, 2b Transmission antenna loop coil 3 Reception antenna Auxiliary coil of 3p, 3q, 3r, 3s receiving antenna 4 board 5 Bifilar Chalk 6 Matching transformer 7 Shielded wire 7a Shield outer cover 7b internal conductor 8 Pipe material 10x transmitting antenna plate 10y receiving antenna plate 11x ground plate 11y ground plate 12 Insulation plate 13 Shield tube

Continuation of front page (72) Inventor Susumu Yanagibori 12-3 Satsuki-cho, Kanuma-shi, Tochigi Sonyke Within Michal Co., Ltd. (56) References Japanese Patent Application Laid-Open No. 63-236401 (JP, A) Japanese Patent Application Laid-Open No. 4-248704 (JP, A) Japanese Patent Application Laid-Open No. 56-83000 (JP, A) Japanese Patent Application Laid-Open No. 7-79182 (JP, A) JP-A-57-89305 (JP, A) Tokko Sho 44-21683 (JP, B1) Jitsuko Akira 50-27880 (JP, Y1) Special table SHO 63-502394 (JP, A) (58) Surveyed field (Int.Cl.⁷, DB name) H01Q 7/00 H04B 5/00 H01Q 21/00 --25/04 H01Q 3/00 --3/46 H01Q 1/00 --1/52