JP7510106B2 - Magnetic sheet and wireless communication tag - Google Patents

Description

The present invention relates to a magnetic sheet and a wireless communication tag for use in a wireless communication antenna that uses RFID (Radio Frequency Identification) technology.

Conventionally, in order to improve the communication characteristics of wireless communication antennas using RFID technology, a method has been widely adopted in which a conductive loop coil is formed in a spiral shape on a plane and a soft magnetic sheet is laminated in parallel to this coil.

Patent document 1 discloses an invention in which an antenna module is composed of an antenna coil and a magnetic sheet laminate. However, when the antenna coil is mounted on an electronic device and placed near metal, the resonant frequency may change. For this reason, patent document 1 discloses an antenna module that is pre-attached to a metal shield plate to prevent a large change in the resonant frequency even when the antenna coil is mounted near metal.

However, the antenna design required to achieve the desired resonant frequency differs between cases where there is no metal near the antenna coil and cases where the antenna coil is mounted near a metal or has a conductor attached to it in advance, so it is necessary to use different antenna modules.

Patent documents 2 and 3 disclose technology that allows ordinary wireless communication antennas to be used near metals without design changes by stacking various layers on the wireless communication antenna.

However, in the method of Patent Document 2, the wireless communication antenna is sandwiched between a metal layer (upper surface of the coil) and a magnetic layer (lower surface of the coil), so both sides of the wireless communication antenna need to be processed.

Furthermore, by placing a metal layer on top of the wireless communication antenna, there is an issue that some of the magnetic flux on the wireless communication tag is shielded, reducing the communication area.

In the auxiliary sheet for IC tags shown in Patent Document 3, the resonance frequency is adjusted by adjusting the thickness of the dielectric layer, but when using a magnetic sheet with high magnetic permeability and sufficient magnetic shielding ability, the thickness of the dielectric layer required for adjustment increases, so the total thickness of the sheet material increases and a considerable amount of mounting space is required.

JP2005-340759 Patent Publication 2005-070855 Patent Publication 2007-233508

The present invention provides a magnetic sheet that can be attached to one side of a wireless communication antenna designed for installation or attachment to a non-metallic object to create a wireless communication tag that exhibits good communication sensitivity on both metallic and non-metallic surfaces.

The present invention is a magnetic sheet used by laminating it to an antenna for wireless communication, characterized in that a metal pattern layer in which a plurality of metal foils are arranged and electrically insulated by a plurality of linear openings, a magnetic layer, and a conductive layer are laminated in that order (Invention 1).

The present invention also relates to a magnetic sheet according to invention 1, in which the opening ratio, which is the ratio of the area of the openings to the area of the metal pattern layer, is 0.1 to 50% (invention 2).

The magnetic sheet according to invention 1 or 2 is also characterized in that the metal pattern layer is formed of polygonal or circular metal foil, or a combination thereof (invention 3).

The present invention also relates to a magnetic sheet according to any one of inventions 1 to 3, in which a metal pattern layer, a magnetic layer, and a conductive layer are laminated via an adhesive layer (invention 4).

The present invention also relates to a magnetic sheet according to any one of inventions 1 to 4, in which the reduction in effective permeability due to the metal pattern layer and the conductor layer contained in the magnetic sheet is offset by the increase in effective permeability due to the magnetic layer (invention 5).

The present invention also relates to a magnetic sheet according to any one of inventions 1 to 5, in which both the effective permeability measured on a metal surface and the effective permeability measured on a non-metal surface are 0.8 to 1.2 (invention 6).

The present invention also relates to a wireless communication tag in which a wireless communication antenna layer, a metal pattern layer in which a plurality of metal foils are arranged and electrically insulated by a plurality of linear openings, a magnetic layer, and a conductive layer are laminated in this order (Invention 7).

The effect of the present invention is that by laminating the magnetic sheet of the present invention on a wireless communication antenna for nonmetallic devices, a wireless communication tag can be made that can communicate with sufficient sensitivity even on a metal surface without changing the coil pattern or circuit of the wireless communication antenna for nonmetallic devices. In addition, by making a wireless communication tag by laminating the magnetic sheet of the present invention on a wireless communication antenna for nonmetallic devices, the same wireless communication tag can communicate with sufficient sensitivity on both metal and nonmetallic surfaces.

When a conventional magnetic sheet or metal shielding sheet is attached to a non-metallic wireless communication antenna, the inductance of the wireless communication tag changes, causing the resonant frequency to deviate from the carrier frequency, generally resulting in a decrease in communication sensitivity.

In the present invention, the magnetic flux can be adjusted by adjusting the magnetic permeability of the magnetic layers constituting the magnetic sheet, the arrangement of the metal foil in the metal pattern layer, and the layer structure of the conductive layer, thereby offsetting increases and decreases in effective magnetic permeability, and the resonant frequency of the wireless communication tag to which the sheet is attached can be made to be the carrier frequency.

FIG. 1 is a schematic cross-sectional view showing an example of a magnetic sheet of the present invention. FIG. 1 is a schematic cross-sectional view showing an example of a magnetic sheet of the present invention. 3 is an example of an arrangement of metal foils in a metal pattern layer according to the present invention. 1 is an example of a state in which the magnetic sheet of the present invention is used. FIG. 2 is a schematic diagram illustrating the state of magnetic flux when the magnetic sheet of the present invention is in use.

The magnetic sheet of the present invention is used by being laminated to a wireless communication antenna 20 as shown in FIG. 4, and can be effective in wireless communication using electromagnetic induction. In wireless communication using electromagnetic induction, a wireless communication tag 3 and a reader/writer 30 are arranged facing each other, and communication is carried out using the magnetic flux generated between them. The wireless communication antenna on which the magnetic sheet of the present invention is laminated may have either a planar or three-dimensional structure.

As shown in FIG. 1, the magnetic sheet 1 of the present invention is formed by laminating a metal pattern layer 10 in which a plurality of metal foils 13 are arranged and electrically insulated by openings 14, a magnetic layer 11, and a conductive layer 12 in that order.

The metal pattern layer 10 has a number of electrically insulated metal foils 13 arranged thereon. The metal foils 13 are separated and insulated by openings 14, and exist on the same plane without overlapping in the stacking direction of the sheet. The metal pattern layer 10 has the effect of reducing inductance by allowing some of the magnetic flux that would normally pass through the position of the metal pattern layer 10 to pass through the openings 14 that are not blocked by the metal foil 13, and by reflecting and shielding the remaining magnetic flux by the metal foil 13, and also has the effect of reducing inductance by the magnetic flux of opposite phase generated by eddy currents flowing through the metal foil 13.

In the metal pattern layer 10, the ratio of the area of the openings 14 to the area of the metal pattern layer 10 is defined as the aperture ratio, and the aperture ratio is preferably 0.1 to 50%, more preferably 1 to 40%, and even more preferably 3 to 20%. By setting the aperture ratio of the metal pattern layer within the above range, a wireless communication tag using the magnetic sheet of the present invention can exhibit good communication characteristics on both metal and non-metal surfaces.

The openings 14 in the metal pattern layer 10 need only provide insulation between the multiple metal foils 13, and are preferably linear gaps, and the shape of the gaps may be straight or curved. The positions, frequency, and shapes of the openings 14 are not limited as long as they are provided to achieve the aforementioned opening ratio, but it is preferable for a large number of openings 14 to be distributed within the metal pattern layer 10, as this will result in a uniform distribution of magnetic flux. The openings 14 may be voids, or may contain an insulating material such as resin.

The shape of the metal foil 13 may be fixed or irregular. In the case of a fixed shape, it can be selected from, for example, polygons, circles, annuli, sectors, and other geometric shapes. The metal foils 13 are arranged in the above shapes or combinations thereof with the openings 14 to form a tile shape with lattice-like openings, a staggered tile shape, stripes, honeycomb shapes, geometric patterns, and the like, to form the metal pattern layer 10. In the case of an irregular shape, the shape of each metal foil 13 is not specified, but it is preferable that metal foils 13 having approximately the same shape and area are arranged to form the metal pattern layer 10.

The arrangement of the metal foil 13 may or may not have regularity, and the pattern and width of the openings 14 can be set arbitrarily. Figure 3 shows an example of an arrangement of the metal foil 13. From the viewpoint of versatility of the magnetic sheet, it is preferable that the pattern and openings are arranged in a uniform and regular manner, since the same functionality can be obtained regardless of which part of the sheet is cut out and used when processing it into a wireless communication tag.

The material of the metal foil 13 used in the metal pattern layer 10 may be any material that is conductive or shielding, for example, a conductor such as a metal or alloy, and the thickness is not limited. Preferably, a metal foil is used, for example, aluminum foil, copper foil, silver foil, etc.

In addition, in the present invention, metal foil refers to a thin metal layer, and includes metal layers formed by plating or sputtering, as they have the same functions.

The metal pattern layer 10 may be formed by arranging individual metal foils directly on the magnetic layer 11 or on a substrate, or by partially removing the metal foil by etching or the like.

In the magnetic sheet of the present invention, the magnetic layer 11 has a magnetic shielding effect between the wireless communication antenna 20 and the metal pattern layer 10 and the conductive layer 12. This ensures a magnetic path in the magnetic layer even when metal is present near the wireless communication tag 3. As the magnetic layer 11, a soft magnetic sheet can be used, such as a sheet in which a sintered body such as spinel magnetic ferrite is sandwiched between films, a sheet in which a sintered body such as spinel magnetic ferrite is sandwiched between films and divided to make it flexible, a sheet formed by mixing ferrite soft magnetic powder or metal soft magnetic powder with resin or rubber and forming it into a sheet, or a sheet coated with paint containing the soft magnetic powder. The soft magnetic material of the sheet can be NiZnCu ferrite, MnZn ferrite, amorphous alloy, permalloy, electromagnetic steel, silicon steel, sendust alloy, Fe-Al alloy, or quenched solidification material of soft magnetic ferrite, cast material, rolled material, forged material, or sintered material, amorphous foil, laminated material of amorphous foil, metal powder, carbonyl iron, reduced iron, atomized powder (pure iron, iron containing Si, Cr, Al, etc., permalloy, Co-Fe, etc.), amorphous powder (iron containing B, P, Si, Cr, etc., cobalt, nickel produced by atomizing with water), etc., and the thickness of the sheet can be set arbitrarily. In particular, when applied to wireless communication tags using the MHz band as a carrier frequency, NiZnCu ferrite sheets with high magnetic shielding ability and low loss are suitable, and sintered plates or flexible sheets divided from sintered plates are also preferable.

In the magnetic sheet of the present invention, the provision of the conductive layer 12 shields a portion of the magnetic flux that has passed through the magnetic layer 11, contributing to preventing the resonance frequency of the wireless communication tag 3 from fluctuating whether it is on a metal surface or a non-metal surface. The material of the conductive layer 12 is not particularly limited as long as it is a conductive material with magnetic shielding properties, and for example, a conductor such as a metal or alloy can be used, and the thickness is also not limited. Preferably, a metal foil can be used, for example, aluminum foil.

The magnetic sheet 1 of the present invention may be laminated without an adhesive layer, and the method of laminating each layer is not limited. As shown in FIG. 2, the magnetic sheet 2 of the present invention may be laminated by laminating a metal pattern layer 10, a magnetic layer 11, and a conductive layer 12 with an adhesive layer 15 interposed therebetween. The adhesive layer is a layer formed by an adhesive or pressure-sensitive adhesive, and an adhesive material such as double-sided tape can also be used, and the material is not particularly limited.

The metal pattern layer 10, magnetic layer 11, and conductive layer 12 that constitute the magnetic sheet of the present invention may have an insulating layer between each layer as necessary. For example, a resin may be used as the insulating layer, and the adhesive layer may also be used as the insulating layer.

The magnetic sheet 2 and wireless communication antenna 20 of the present invention must be insulated, and the magnetic sheet 2 and installation surface 40 can be insulated as necessary. A protective material layer 16 may be further provided on the outside of the metal pattern layer 10 surface and the conductive layer 12 surface of the magnetic sheet 2. The protective material layer 16 may also be an adhesive layer. By using the protective material layer 16 as an adhesive layer, it can be used to attach the magnetic sheet 2 and the wireless communication antenna 20, and the magnetic sheet 2 and the installation surface 40.

The effective permeability of the magnetic sheet of the present invention is determined mainly by the decrease in effective permeability due to the metal pattern layer 10 and the conductor layer 12, and the increase in effective permeability due to the magnetic layer 11. In order to enable a wireless communication antenna designed for nonmetallic use to communicate equally on both nonmetallic and metallic surfaces, it is preferable that the decrease in effective permeability due to the metal pattern layer 10 and the increase in effective permeability due to the magnetic layer 11 are offset. It is preferable that the magnetic permeability, structure, and thickness of the magnetic material, and the metal conductivity, thickness, area, and shape of the metal pattern layer are set so that the density of the magnetic flux, which varies depending on the magnetic material and layer structure of the magnetic layer, can be offset by the metal pattern layer. The effective permeability of the magnetic sheet may also vary depending on the material and thickness of the conductor layer 12 and the adhesive layer 15, and it is preferable that the combination of each layer is designed taking this into consideration. In other words, the effective permeability of the magnetic sheet of the present invention is preferably 0.8 to 1.2, and more preferably 0.9 to 1.1, both when measured on a metal surface and when measured on a non-metal surface.

The magnetic sheet of the present invention preferably has a difference between the effective permeability measured on a metal surface and the effective permeability measured on a nonmetallic surface of within 5%, and more preferably within 3%. The fact that the effective permeability on a metal surface is equivalent to that on a nonmetallic surface means that the resonant frequency does not vary depending on whether the material of the installation surface is metallic or nonmetallic. Therefore, the smaller the difference between the effective permeability measured on a metal surface and the effective permeability measured on a nonmetallic surface, the better the communication distance can be expected under both conditions.

An example of the magnetic sheet of the present invention in use is shown in FIG. 4, and an explanation of the state of the magnetic flux when in use is shown in FIG. 5. The magnetic sheet of the present invention is a magnetic sheet used by laminating it to a wireless communication antenna, and can be effective in wireless communication using electromagnetic induction. In wireless communication using electromagnetic induction, a wireless communication tag 20 and a reader/writer 30 are placed opposite each other, and communication is carried out using the magnetic flux generated between them.

When the magnetic sheet 2 of the present invention is laminated with the wireless communication tag 20, the wireless communication antenna 20 is placed on the metal pattern layer side 10 of the magnetic sheet 2. The magnetic sheet of the present invention is preferably placed perpendicular to the winding axis direction of the coil of the wireless communication antenna 20, and is placed so as to pass the magnetic flux generated by the reader/writer 30 and the wireless communication antenna 20.

By stacking the metal foils 13 forming the metal pattern layer 10 so that they are included in two or more positions within the coil surface of the wireless communication antenna 20, the magnetic flux generated during communication is shielded in the areas where the metal foils 13 are present, reducing the magnetic flux that passes through the metal pattern layer 10, and adjusting the magnetic flux that has increased due to the magnetic layer 11.

In a structure in which a metal pattern layer is provided on the front surface of the wireless communication antenna 20 for the reader/writer 30, the coupling between the coils of the reader/writer 30 and the wireless communication antenna 20 is reduced, resulting in a reduction in the communication area and a decrease in communication sensitivity. On the other hand, in the magnetic sheet of the present invention, the metal pattern layer 10 is disposed on the back surface of the wireless communication antenna 20, so that the coupling between the wireless communication tag and the reader/writer 30 is better than in the previously described configuration, and therefore the reduction in communication area and the decrease in sensitivity can be suppressed.

In addition, the conductive layer 12 can block the influence of the material of the installation surface 40. As a result, fluctuations in inductance of the wireless communication tag 3 are suppressed, and communication is possible on both non-metallic and metallic installation surfaces 40 even when a wireless communication antenna designed for non-metallic use is used.

The magnetic sheet 2 is preferably installed so that the ratio of the area of the openings 14 in the metal pattern layer 10 to the area of the coil surface of the wireless communication antenna 20 is 0.1 to 50%, more preferably 1 to 40%, and even more preferably 3 to 20%. In addition, it is preferable for a large number of openings in the metal pattern layer to be distributed within the coil surface, as this results in a uniform distribution of magnetic flux.

In addition, the present invention may be such that a wireless communication tag is produced by laminating each layer in a predetermined order on the wireless communication antenna 20 without previously preparing a magnetic sheet in which the metal pattern layer 10, magnetic layer 11, and conductive layer 12 are laminated. That is, the wireless communication tag 3 is produced by laminating the wireless communication antenna layer 20, the metal pattern layer 10 in which a plurality of fixed or irregular metal foils 13 are arranged and electrically insulated by openings 14, the magnetic layer 11, and the conductive layer 12 in that order.

The present invention will be further explained below based on examples and comparative examples, but the present invention is not limited to these examples.

The magnetic sheets of Examples 1 to 5 are made by attaching a metal pattern layer, a magnetic layer, and a conductive layer in order via an adhesive layer. The metal pattern layer is made by providing 6 mm square aluminum foil (thickness 100 μm) on a PET substrate (thickness 80 μm), and arranging the aluminum foil in a grid pattern with gaps of 0.50, 0.15, 0.33, 1.5, and 2.1 mm wide. The magnetic layer is made of NiZnCu flexible ferrite sheet (magnetic thickness 100 μm, upper and lower holding films each 10 μm) with a magnetic permeability of μ': 150, μ'': 5 at 13.56 MHz, and the conductive layer is made of Al foil (100 μm) with an adhesive layer on the installation surface side. The magnetic sheet is made by laminating the magnetic layer and conductive layer in order via an adhesive layer on the substrate surface of the metal pattern layer. The adhesive layer used in both cases was double-sided tape NeoFix10PB (thickness 10 μm) manufactured by Nichiei Kako Co., Ltd. The wireless communication antenna (tag) used in this study had an insulating adhesive layer on the antenna side, so no insulating layer (protective layer) was provided on the metal pattern layer of the magnetic sheet.

The magnetic sheet is cut into a circle with a diameter of 46 mm using a FAYb laser marker LP-S series (manufactured by Panasonic Corporation), and a wireless communication antenna (tag) with a diameter of 38 mm (BullsEye NTAG203WPP60) is attached to the metal pattern layer side of the magnetic sheet of the present invention.

The inductance value of the wireless communication tag is calculated using a T8200UD IC card tester resonance frequency inspection machine (manufactured by Testram Co., Ltd.) as a reader/writer to which a 13 mm diameter circular antenna for evaluation is connected.

The evaluation on a non-metallic surface is when the wireless communication antenna and magnetic sheet are laminated and the wireless communication antenna is placed facing and in close contact with the reader/writer, while the evaluation on a metallic surface is when an Al plate (thickness 1 mm) is further laminated on the magnetic sheet side of the laminate of the wireless communication antenna and magnetic sheet and the wireless communication antenna is placed facing and in close contact with the reader/writer.

The effective magnetic permeability of a magnetic sheet is calculated by dividing the inductance value obtained on the non-metallic or metallic surface of a wireless communication tag with a magnetic sheet laminated thereon by the inductance value of the wireless communication tag alone.

The SAMUSUNG Galaxy S4 mini is used as the reader/writer for evaluating the communication distance, and the maximum communication distance is evaluated.

The results of Examples 1 to 5 showed that the effective magnetic permeability of each sheet was 0.9 to 1.1 on both metal and non-metal surfaces. Evaluation of communication distance also confirmed that communication was equally possible on both metal and non-metal surfaces.

In Comparative Example 1, a wireless communication antenna (tag) without a magnetic sheet was evaluated. It was demonstrated that a wireless communication antenna designed for use on non-metallic surfaces provided sufficient communication characteristics on non-metallic surfaces, but was unable to communicate on metallic surfaces.

Comparative example 2 shows data for a wireless communication antenna laminated with a NiZnCu flexible ferrite sheet (magnetic material thickness 100 μm, upper and lower holding films each 10 μm) with a magnetic permeability of μ': 150, μ'': 5 at 13.56 MHz, similar to the magnetic layer used in the examples. It was confirmed that the effective magnetic permeability on both the metal and non-metal surfaces was 1.5 or more, resulting in a large difference between the resonant frequency and carrier frequency of the wireless communication tag, making communication impossible.

Comparative Example 3 shows data for a wireless communication antenna laminated with a metal-compatible sheet (AMS-007 (for BullsEye) μ': 60, manufactured by Fine Label Co., Ltd.) made by mixing soft magnetic powder with resin. The effective permeability was 1.14 on metal surfaces, but fluctuated greatly to 1.48 on non-metal surfaces, resulting in a decrease in the communication distance on non-metal surfaces.

The present invention provides a magnetic sheet that can be used to turn a wireless communication antenna for nonmetallic use into a wireless communication tag that can communicate with sufficient sensitivity even on a metal surface without changing the coil pattern or circuit. In addition, by laminating the magnetic sheet of the present invention to a wireless communication antenna for nonmetallic use, the same wireless communication tag can be used for communication on both metal and nonmetal surfaces. This eliminates the need to use different designs for wireless communication antennas on metal and nonmetal surfaces, which contributes to improved cost and productivity. In addition, the product of the present invention can be simply attached to one side of an existing wireless communication antenna, which simplifies the labor required compared to using conventional technology. It also has high magnetic shielding performance and is not dependent on the usage environment, making it highly versatile.

Reference Signs List 1, 2 Magnetic sheet 3 Wireless communication tag 10 Metal pattern layer 11 Magnetic layer 12 Conductive layer 13 Metal foil 14 Opening 15 Adhesive layer 16 Protective material layer (adhesive layer)
20 Wireless communication antenna 30 Reader/writer 40 Installation surface

Claims (7)

A magnetic sheet for use in a wireless communication antenna, characterized in that a metal pattern layer in which a plurality of metal foils are arranged and electrically insulated by a plurality of linear openings, a magnetic layer, and a conductive layer are laminated in that order. The magnetic sheet according to claim 1, wherein the opening ratio, which is the ratio of the area of the openings to the area of the metal pattern layer, is 0.1 to 50%. The magnetic sheet according to claim 1 or 2, wherein the metal pattern layer is formed by polygonal or circular metal foil, or a combination thereof. A magnetic sheet according to any one of claims 1 to 3, in which a metal pattern layer, a magnetic layer, and a conductive layer are laminated via an adhesive layer. A magnetic sheet according to any one of claims 1 to 4, in which the reduction in effective permeability due to the metal pattern layer and the conductor layer contained in the magnetic sheet is offset by the increase in effective permeability due to the magnetic layer. A magnetic sheet according to any one of claims 1 to 5, in which both the effective permeability measured on a metal surface and the effective permeability measured on a non-metal surface are 0.8 to 1.2. The wireless communication tag is formed by sequentially laminating a wireless communication antenna layer, a metal pattern layer in which a plurality of metal foils are arranged and electrically insulated by a plurality of linear openings, a magnetic layer, and a conductive layer.

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