Belt-shaped ferrite sheet, and antenna device and cable using the same

Abstract

A ferrite sheet strip 1 comprises: a strip-shaped substrate 10; and a plurality of ferrite sheet pieces 20 disposed on a surface of the substrate 10. The plurality of ferrite sheet pieces 20 are arranged, with a gap 30 therebetween, in the longitudinal direction of the substrate 10. The gap 30 extends such that the gap is at least partially not parallel to the lateral direction of the substrate 10.

Description

[Technical Field]

[0001] The present invention relates to a strip-shaped ferrite sheet and an antenna device and a cable using the same, and more particularly to a strip-shaped ferrite sheet including a plurality of ferrite sheet pieces and an antenna device and a cable using the same. [Background technology]

[0002] Conventionally, IC tags have been known that include an IC chip and an antenna device electrically connected to the IC chip, and that receive power from a reader / writer and transmit and receive signals to and from the reader / writer in a non-contact manner using electromagnetic waves. In recent years, IC tags have been incorporated into cards and used as IC cards for transportation tickets, credit cards, etc. The antenna device provided in an IC tag is generally fabricated by winding a conductor around a substrate to form a coil, or by printing a coil pattern on the surface of the substrate.

[0003] When an antenna device is installed near a metal material, such as a metal card, magnetic flux is converted into eddy currents in the metal, causing problems such as a reduced communication distance or an inability to communicate. To prevent this, a method of laminating a soft magnetic sheet between the conductive loop coil and the metal material is widely used. By laminating the soft magnetic sheet, a route through which magnetic flux can pass is created, improving communication distance.

[0004] As described above, ferrite, for example, is used as a material for the soft magnetic sheet to prevent the influence of metal materials on the communication distance of the antenna device (see, for example, Patent Documents 1 and 2). Ferrite sheets used as soft magnetic sheets are usually distributed cut into rectangular sheets of about 100 mm x 100 mm, but from the viewpoint of ease of handling by users, there is also a demand for ferrite sheets formed in a strip shape (see, for example, Patent Document 3).

[0005] Ferrite sheets are used not only in the antenna devices described above but also as noise shields and noise filters, for example, as noise filters wrapped around the outside of cables (see, for example, Patent Document 4, etc.). In these cases, too, a ferrite sheet formed in a strip shape is required from the viewpoint of ease of wrapping around cables. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-124197 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-113370 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-123771 [Patent Document 4] Japanese Patent Application Publication No. 2019-114611 Summary of the Invention [Problem to be solved by the invention]

[0007] For ease of storage and portability, strip-shaped ferrite sheets are expected to be rolled up before use. However, because ferrite sheets are made of sintered ferrite, they are prone to breakage and have size limitations, making it difficult to form them into strips and then roll them up. Therefore, as an alternative, strip-shaped ferrite sheets can be formed by arranging multiple rectangular ferrite sheet pieces, each approximately 100 mm x 100 mm, along the longitudinal direction of a strip-shaped substrate. In this case, overlapping multiple ferrite sheet pieces changes their properties, so gaps must be provided between the multiple ferrite sheet pieces to account for the attachment tolerances.

[0008] When the above-described strip-shaped ferrite sheet is applied to an antenna device having a spiral loop coil provided around the outer periphery of the surface of a predetermined substrate, the strip-shaped ferrite sheet is cut to fit the size of the antenna device and then laminated on the antenna device, and gaps in the strip-shaped ferrite sheet may be included in the cut ferrite sheet and overlap with the loop coil portion of the antenna device, which may have an undesirable effect on the resonant frequency of the antenna device and may adversely affect the communication distance.

[0009] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a strip-shaped ferrite sheet that can be wound into a roll and continuously wrapped around a cable, etc., and that can suppress changes in the resonant frequency of the antenna device that occur when applied to the antenna device and the resulting deterioration in communication distance. [Means for solving the problem]

[0010] In order to achieve the above-mentioned object, the inventors conducted extensive research and discovered that when the gaps in the ferrite sheet extend overlapping the loop coil arranged along the outer periphery of the antenna device (extending parallel to the coil wire of the loop coil), the resonant frequency of the antenna device fluctuates significantly, whereas when the gaps intersect with the coil, they do not have a significant effect on the resonant frequency of the antenna device, and thus completed the present invention.

[0011] Specifically, the strip-shaped ferrite sheet of the present invention comprises a strip-shaped base material and a plurality of ferrite sheet pieces provided on the surface of the base material, the plurality of ferrite sheet pieces being arranged along the longitudinal direction of the base material with gaps between them, and the gaps extending so as not to be at least partially parallel to the short direction of the base material.

[0012] When the strip-shaped ferrite sheet according to the present invention is applied to an antenna substrate having a loop coil disposed along the periphery of its surface, the strip-shaped ferrite sheet is cut along its short side to fit the size of the antenna substrate. In this way, the gaps between the ferrite sheet pieces in the strip-shaped ferrite sheet according to the present invention extend at least partially non-parallel to the short side of the strip-shaped substrate. Therefore, even if the gaps intersect with the loop coil disposed along the periphery of the antenna substrate, they do not overlap and extend parallel to the loop coil. Therefore, even if the strip-shaped ferrite sheet according to the present invention is cut and applied to an antenna device, fluctuations in the resonant frequency of the antenna device can be suppressed, thereby suppressing a deterioration in communication distance.

[0013] In the strip-shaped ferrite sheet according to the present invention, the gaps may have any shape, such as a straight line, a curved line, a broken line, a wavy line, or a zigzag line, but a straight line is particularly preferable.

[0014] Making the gap linear is particularly preferable because it is not necessary to make each of the multiple ferrite sheet pieces into a complex shape; for example, a linear gap can be formed by simply arranging multiple parallelogram- or trapezoid-shaped ferrite sheet pieces on a strip-shaped substrate.

[0015] In the strip-shaped ferrite sheet according to the present invention, the width of the gap is preferably 0.1 mm to 10 mm.

[0016] A gap width of less than 0.1 mm is undesirable because the ferrite sheet pieces may overlap, and a gap width of more than 10 mm is undesirable because the gap has a large effect on the resonant frequency of the antenna device when applied to the antenna device.

[0017] The antenna device of the present invention comprises an antenna substrate having a loop coil made of a conductive material on its surface, and a ferrite sheet laminated on the antenna substrate, wherein the ferrite sheet is cut from any of the above-mentioned strip-shaped ferrite sheets, and the gaps contained in the ferrite sheet extend so as not to be at least partially parallel to the extension direction of the loop coil.

[0018] In the antenna device according to the present invention, the ferrite sheet laminated on the antenna substrate is a ferrite sheet cut from the strip-shaped ferrite sheet according to the present invention, and therefore, as described above, even if the gaps in the strip-shaped ferrite sheet intersect with the loop coil of the antenna substrate, the entire gap does not overlap and extend parallel to the extension direction of the loop coil. Therefore, with the antenna device according to the present invention, fluctuations in the resonant frequency of the antenna device can be suppressed while using the strip-shaped ferrite sheet, and deterioration of the communication distance can be suppressed.

[0019] A cable according to the present invention is a cable having a noise filter wound around its outer periphery, the noise filter including any one of the above-mentioned strip-shaped ferrite sheets. In addition, in such a cable, it is preferable that any one of the above-mentioned strip-shaped ferrite sheets is wound continuously in a spiral shape around the outer periphery of the cable.

[0020] The cable according to the present invention uses the above-mentioned strip-shaped ferrite sheet as a noise filter, and therefore can be produced by continuously winding the strip-shaped ferrite sheet as is, which is preferable because it can be produced easily. [Effects of the Invention]

[0021] The strip-shaped ferrite sheet according to the present invention can be wound into a roll and continuously wrapped around a cable or the like, and can be suitably applied to an antenna device while suppressing fluctuations in the resonant frequency of the antenna device and suppressing deterioration of the communication distance. Therefore, the antenna device according to the present invention can suppress fluctuations in the resonant frequency of the antenna device and suppress deterioration of the communication distance while using the strip-shaped ferrite sheet. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a plan view showing a strip-shaped ferrite sheet according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a plan view showing an antenna device according to one embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a plan view showing an antenna substrate used in an antenna device according to one embodiment of the present invention. [Figure 6] FIG. 6 is a plan view showing a state in which a strip-shaped ferrite sheet according to one embodiment of the present invention is applied to the antenna substrate of FIG. [Figure 7] 7(a) to 7(e) are diagrams showing the positions of gaps in the antenna device of the first embodiment. [Figure 8] FIG. 8 is a graph showing the results of Experimental Example 1 of Example 1. [Figure 9] FIG. 9 is a graph showing the results of Experimental Example 2 of Example 1. [Figure 10] 10(a) to 10(e) are diagrams showing the positions of gaps in the antenna device of the second embodiment. [Figure 11] FIG. 11 is a graph showing the results of Experimental Example 1 of Example 2. [Figure 12] FIG. 12 is a graph showing the results of Experimental Example 2 of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description of preferred embodiments is merely exemplary in nature and is not intended to limit the present invention, its application, or its uses.

[0024] First, a strip-shaped ferrite sheet according to one embodiment of the present invention will be described with reference to FIGS. 1 and 2. As shown in FIGS. 1 and 2, the strip-shaped ferrite sheet 1 according to one embodiment of the present invention is composed of a strip-shaped substrate 10 and a plurality of ferrite sheet pieces 20 provided on the surface of the substrate 10. The ferrite sheet pieces 20 are configured by providing an adhesive 22 on the underside of a ferrite sintered body 21 and similarly providing an adhesive 23 on the upper surface of the ferrite sintered body 21. The adhesives 22 and 23 are, for example, double-sided tape. The ferrite sheet pieces 20 are adhered to the substrate 10 by the adhesive 22. Specifically, the plurality of ferrite sheet pieces 20 are arranged along the longitudinal direction of the substrate 10 with a predetermined gap 30 between them.

[0025] The substrate 10 is a strip-shaped thin film, i.e., a shape having a longitudinal direction and a lateral direction. The size is not particularly limited as long as it can be wound into a roll, but for example, the lateral direction is 50 cm and the longitudinal direction is 100 m. The material of the substrate 10 is not particularly limited, but a resin material such as polyethylene terephthalate (PET) can be used. In FIG. 1, the substrate 10 is provided only on the lower surface, but it may also be provided on the upper surface so as to be adhered to the adhesive 23.

[0026] The ferrite sintered body 21 is a sintered body made of magnetic ferrite. The type of ferrite used is not particularly limited as long as it has magnetic properties, and for example, Ni-Zn ferrite or Mn-Zn ferrite can be used. The ferrite sintered body is divided into small pieces. The method for producing the ferrite sintered body 21 is also not particularly limited, and for example, a method of coating a plastic film with ferrite dispersion paint can be used. Specifically, the following methods can be used.

[0027] First, a paint is prepared by mixing 70 to 120 parts by weight of polyvinyl alcohol resin, 15 to 25 parts by weight of butyl butyl phthalate as a plasticizer, and 400 to 600 parts by weight of solvent per 1,000 parts by weight of ferrite powder. Examples of solvents that can be used include glycol ethers, methyl ethyl ketone (MEK), toluene, methanol, ethanol, and n-butanol. Considering the dispersibility of the ferrite powder, ease of mixing, and drying speed, the preferred composition range for the paint is 80 to 110 parts by weight of polybutyral resin, 18 to 22 parts by weight of butyl butyl phthalate, and 450 to 550 parts by weight of solvent per 1,000 parts by weight of ferrite.

[0028] The paint can be produced using, for example, a ball mill, but is not limited to, this. A uniform paint can be obtained by first filling and mixing the solvent and ferrite, and then adding and mixing the resin and plasticizer. It is important to thoroughly degas the resulting paint under reduced pressure in a vacuum container to prevent cracks from forming in the coating film when it is applied and dried.

[0029] The method for applying the ferrite dispersion paint is not particularly limited, but a roll coater or doctor blade can be used. A doctor blade is preferably used for the reasons of film thickness accuracy and paint stability. The paint is applied to a plastic film to the desired thickness using a doctor blade, and then dried at 80 to 130°C for 30 to 60 minutes to obtain a ferrite molded sheet.

[0030] The plastic film used to apply the ferrite dispersion coating is not particularly limited, but sandblasted films of various materials such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyimide can be used. Polyethylene terephthalate (PET) film is preferred due to the workability of the film surface and its thermal stability during coating and drying. By using a sandblasted plastic film, the unevenness of the plastic film can be transferred to the ferrite molded sheet, resulting in a molded sheet with the desired surface roughness.

[0031] The resulting ferrite molded sheet is then fired to obtain a ferrite sintered body 21. For example, 5 to 20 ferrite molded sheets are stacked on an alumina plate with a porosity of 30%. Regarding firing conditions, it is important to establish processes for removing resin components and growing ferrite particles using an electric furnace or the like. Resin removal is performed at 150°C to 550°C for 5 to 80 hours, and ferrite particle growth is performed at 850°C to 1200°C for 1 to 5 hours. To prevent thermal deformation or cracking of the sheet, it is preferable to remove the resin components by increasing the temperature from room temperature at a rate of 10 to 20°C / hour and then maintaining a constant temperature. It is also preferable to subsequently increase the temperature at a rate of 30 to 60°C / hour, maintain a constant temperature, sinter thoroughly, grow ferrite particles, and then gradually cool. The holding temperature and time for each process can be optimally selected depending on the number of ferrite molded sheets to be processed. The ferrite sintered body 21 is obtained by the above process, after which double-sided tape as adhesives 22 and 23 is applied to the upper and lower surfaces, and the ferrite sintered body 21 is divided using a roller or the like to form ferrite sheet pieces 20. In order to divide the ferrite sintered body 21 into small pieces, predetermined grooves may be formed in the ferrite molded sheet stage. The grooves may be continuous or discontinuous, and multiple small recesses may be formed instead. The sintered body is divided into triangles, rectangles, polygons, or combinations of these shapes of any size by the pre-formed grooves. Alternatively, the sintered body may be divided into irregular shapes without forming grooves.

[0032] As described above, the gaps 30 are provided between the multiple ferrite sheet pieces 20, but at least some of the gaps 30 extend so as not to be parallel to the short-side direction of the substrate 10. Specifically, in this embodiment, the gaps 30 are linear gaps extending in a direction inclined relative to the short-side direction of the substrate 10. However, the gaps 30 are not limited thereto, and may be curved, broken line, wavy line, zigzag, or other shapes. If the width of the gaps 30 is too short, the ferrite sheet pieces 20 may overlap, which is undesirable. If the width of the gaps 30 is too long, the gaps 30 undesirably have a significant impact on the antenna communication distance when the strip-shaped ferrite sheet 1 is applied to an antenna device. For this reason, the width of the gaps 30 is preferably 0.1 mm to 10 mm. Here, the width of the gaps 30 refers to the shortest distance between one ferrite sheet piece 20 and an adjacent ferrite sheet piece 20.

[0033] Next, an antenna device according to one embodiment of the present invention using the above-mentioned strip-shaped ferrite sheet 1 will be described with reference to Figures 3 and 4. As shown in Figures 3 and 4, an antenna device 40 according to this embodiment includes an antenna substrate 42 having a planar spiral loop coil 41 made of a conductive material provided on its surface, and a ferrite sheet 2 laminated on the antenna substrate 42. The ferrite sheet 2, which will be described in detail later, is formed by cutting the above-mentioned strip-shaped ferrite sheet 1 according to this embodiment.

[0034] Specifically, the antenna device 40 includes, from bottom to top, an adhesive 22, a ferrite sintered body 21, an adhesive 23, an antenna substrate 42, and a loop coil 41. The antenna device 40 also includes components required to function as an antenna, such as a capacitor, but these components are not described or illustrated here. The antenna device 40 is attached to a metal card with the adhesive 22 and processed as required to be used as an IC card. The ferrite sintered body 21 in the antenna device 40 also includes a gap 30. As described above, the gap 30 is formed in a linear shape extending in a direction inclined relative to the short-side direction of the substrate 10, and therefore extends in a direction inclined relative to the short-side direction of the antenna device 40. Therefore, the gap 30 extends so as to intersect with the loop coil 41. The antenna device may also be attached to a metal housing.

[0035] The antenna substrate 42 is made of an insulating resin material such as PET, and the loop coil 41 is made of a conductive material such as metal. There are no particular limitations on the method for forming the loop coil 41, but it can be formed, for example, by painting or printing a conductive paste.

[0036] Next, an example of a method for applying the strip-shaped ferrite sheet 1 according to this embodiment to an antenna device will be described with reference to Figures 5 and 6. Note that in Figures 5 and 6, the loop coil 41 is shown as a rectangle for the sake of simplicity.

[0037] Before the strip-shaped ferrite sheet 1 is applied, the antenna substrate 42 is also formed in a strip shape as shown in Fig. 5. Loop coils 41 made of a conductive material are arranged on the strip-shaped antenna substrate 42 at predetermined intervals along the longitudinal direction of the antenna substrate 42. When applying the strip-shaped ferrite sheet 1 to the strip-shaped antenna substrate 42, the strip-shaped ferrite sheet 1 is first superimposed and adhered to the surface of the antenna substrate 42 opposite the surface on which the loop coils 41 are provided, as shown in Fig. 6. Thereafter, the strip-shaped antenna substrate 42 is cut together with the strip-shaped ferrite sheet 1 between the multiple loop coils 41, thereby forming the antenna device 40 having a planar rectangular shape as shown in Fig. 3.

[0038] As described above, the antenna device 40 is cut between the loop coils 41. However, the spacing between the gaps 41 does not necessarily match the spacing between the gaps 30 in the strip-shaped ferrite sheet 1, so the positions of the gaps 30 vary for each cut antenna device 40. In other words, in the antenna device 40 shown in FIG. 3, the gaps 30 extend from the right short side toward the lower long side of the antenna device 40. However, there may also be gaps 30 extending from the upper long side toward the lower long side or from the upper long side toward the left short side. Thus, the placement of the gaps 30 varies for each cut antenna device 40. However, in all cases, the gaps 30 are formed in a linear shape extending in a direction inclined with respect to the short-side direction of the substrate 10, and therefore extend in a direction inclined with respect to the short-side direction of the antenna device 40. Therefore, the gaps 30 extend so as to intersect with the loop coils 41.

[0039] Such gap 30 may affect the resonant frequency of the antenna device 40. However, as will be described in detail in the following examples, when gap 30 extends overlapping the coil wire of loop coil 41 (extending parallel to the coil wire of loop coil 41), the resonant frequency of the antenna device is significantly deteriorated. On the other hand, when gap 30 does not extend overlapping the coil wire of loop coil 41 but simply intersects it, it does not have a significant effect on the resonant frequency of antenna device 40. In the antenna device 40 according to this embodiment, as described above, gap 30 is formed in a linear shape extending in an inclined direction with respect to the short-side direction of antenna device 40. Therefore, although antenna device 40 according to this embodiment has gap 30, the resonant frequency is not significantly affected by gap 30.

[0040] Furthermore, in addition to the linear gap 30 extending in a direction inclined with respect to the short side direction of the antenna device 40 as in this embodiment, gaps in the curved, bent, wavy, zigzag, etc. shapes exemplified above do not extend overlapping with the coil wire of the loop coil 41 but simply intersect with it, so even in antenna devices having gaps of these shapes, the resonant frequency is not significantly affected by the gap.

[0041] As described above, the strip-shaped ferrite sheet of this embodiment can be wound into a roll, can suppress fluctuations in the resonant frequency of the antenna device, and can be suitably applied to the antenna device while suppressing deterioration of the communication distance; further, the antenna device of this embodiment can suppress fluctuations in the resonant frequency of the antenna device while utilizing the strip-shaped ferrite sheet, and can suppress deterioration of the communication distance.

[0042] Next, a method for applying the strip-shaped ferrite sheet 1 according to this embodiment to a cable will be described. In this embodiment, a noise filter is wrapped around the outer periphery of the cable, and the strip-shaped ferrite sheet 1 is used as the noise filter. As described above, it has long been known that ferrite sheets can be used as noise filters to suppress electromagnetic noise generated from cables. In this embodiment, the strip-shaped ferrite sheet 1 is wrapped around the outer periphery of the cable to suppress electromagnetic noise generated from the cable. The method for wrapping the strip-shaped ferrite sheet 1 around the outer periphery of the cable is not particularly limited, but from the viewpoint of workability, it is preferable to continuously wrap the strip-shaped ferrite sheet 1 spirally along the axial direction of the cable. [Example]

[0043] The following examples are provided to explain in detail the ferrite sheet strip and the antenna device using the same according to the present invention. In these examples, an experiment was conducted to examine the effect of gaps provided in the ferrite sheet on the resonant frequency of the antenna device.

[0044] [Example 1] First, as Example 1, an experiment was conducted on the relationship between the position and width of a gap provided in a ferrite sheet and the resonant frequency of the antenna device when the gap extends parallel to the short-side direction of the antenna device.

[0045] (Experimental Example 1) First, we performed a simulation using the electromagnetic field simulation software EMpro (Keysight Technologies) to investigate the relationship between the gap position and width and the resonant frequency of the antenna device. A 0.045mm thick ferrite sheet was placed on a 0.2mm thick metal plate with a 0.01mm space between them, and a 0.02mm thick loop coil was placed on top of that with a 0.1mm space between them to create a model antenna device. The metal plate was rectangular with long sides of 80mm and short sides of 50mm. The ferrite sheet was the same size as the metal plate, and the loop coil had a 75mm outer perimeter on the long side and a 45mm outer perimeter on the short side.

[0046] As shown in Figures 7(a) to 7(e), the antenna device was placed at five different positions (positions indicated by arrows and dashed lines) with gap widths of 0.1 mm, 0.2 mm, 0.3 mm, 0.5 mm, 1.0 mm, 5 mm, and 10 mm. The resonant frequency of the antenna device was simulated for each position and gap width. Specifically, gaps were placed at the center of the antenna device (a), to the right of the center of the antenna device (b), further inside the innermost periphery of the loop coil (c), on the coil wire of the loop coil (d), and further outside the outermost periphery of the loop coil (e). All gaps were linear, extending in the short direction of the antenna device. Figure 8 shows the simulation results for each position. Figure 8 shows the change in resonant frequency (MHz) relative to the resonant frequency at the position shown in Figure 7(a).

[0047] As shown in Figure 8, for all gap widths, the resonant frequency of the antenna device increased as the gap shifted from the center to one end (right side), with the highest resonant frequency being in case (d) where the gap overlapped with the coil wire of the loop coil. Furthermore, in case (e) where the gap was positioned further outboard than the loop coil, the resonant frequency was lower than in case (d). There was also a tendency for the resonant frequency to increase as the gap width increased.

[0048] (Experimental Example 2) Next, to verify the results of Experimental Example 1, actual measurements were performed using an actual antenna device to investigate the relationship between the position and width of the gap and the resonant frequency of the antenna device. The antenna device was the same size as the model in Experimental Example 1 above. The gaps were provided at the positions shown in Figures 7(a), (b), (d), and (e). The gap width was 0.5 mm or 1.0 mm. The resonant frequency was measured using an impedance analyzer E4990A (manufactured by Keysight Technologies). The measurement results are shown in Figure 9. The resonant frequency without a gap was also measured, and Figure 9 shows the change in resonant frequency (MHz) when a gap was provided at each position relative to the resonant frequency without a gap.

[0049] As shown in Figure 9, similar to the results of Experimental Example 1, for all gap widths, the resonant frequency of the antenna device increased as the gap shifted from the center toward one end, with the highest resonant frequency being in case (d) where the gap overlapped with the coil wire of the loop coil. Furthermore, in case (e) where the gap was positioned further outboard than the loop coil, the resonant frequency was lower than in case (d). There was also a tendency for the resonant frequency to increase as the gap width increased.

[0050] From the results of Example 1, it is clear that when the gaps in the ferrite sheet extend parallel to the extension direction of the coil wire on the coil wire, this has a significant impact on the resonant frequency of the antenna device, which is thought to reduce the communication distance of the antenna device.

[0051] [Example 2] Next, as Example 2, an experiment was conducted to examine the relationship between the position and width of the gap and the resonant frequency of the antenna device when the gap provided in the ferrite sheet extends at an angle relative to the short side direction of the antenna device, i.e., extends diagonally.

[0052] (Experimental Example 1) First, we performed a simulation using the electromagnetic field simulation software EMpro (Keysight Technologies) to investigate the relationship between the gap position and width and the resonant frequency of the antenna device. A 0.045mm thick ferrite sheet was placed on a 0.2mm thick metal plate with a 0.01mm space between them, and a 0.02mm thick loop coil was placed on top of that with a 0.1mm space between them to create a model antenna device. The metal plate was rectangular with long sides of 80mm and short sides of 50mm. The ferrite sheet was the same size as the metal plate, and the loop coil had a 75mm outer perimeter on the long side and a 45mm outer perimeter on the short side.

[0053] As shown in Figures 10(a) to 10(e), the antenna device was placed at five different positions (positions indicated by arrows and dashed lines) with gap widths of 0.14 mm, 0.21 mm, 0.35 mm, and 0.7 mm. The resonant frequency of the antenna device was simulated for each position and gap width. Specifically, the gaps were arranged in the following directions: (a) a line extending from the upper right portion of the antenna device to the lower left portion; (b) a line extending from the upper right corner of the antenna device to the center of the lower portion; (c) a line extending from the upper right portion of the antenna device to the lower right portion; (d) a line extending from the center of the right side of the antenna device to the lower right portion; and (e) a line extending from the lower right portion of the antenna device to the lower right portion. The simulation results for each position are shown in Figure 11. The resonant frequency without a gap was also measured, and Figure 11 shows the change in resonant frequency (MHz) when a gap was provided at each position relative to the resonant frequency without a gap.

[0054] As shown in Fig. 11, the variation in the resonant frequency was small in all cases, and no significant difference was observed depending on the gap width. Although not shown in Fig. 11, when the gap width was set to 10 mm and 20 mm under the same conditions as the gap positions in Fig. 10(a) to (e), the variation in the resonant frequency was small at a gap width of 10 mm, as in the cases of 0.14 mm to 0.7 mm, but it was confirmed that the variation in the resonant frequency became large at a gap width of 20 mm.

[0055] (Experimental Example 2) Next, to verify the results of Experimental Example 1, actual measurements were performed using an actual antenna device to examine the relationship between the gap position and width and the resonant frequency of the antenna device. The antenna device was the same size as the model used in Experimental Example 1. The gaps were provided at the positions shown in Figures 10(a), (b), and (e). The gap width was 0.5 mm or 1.0 mm. The resonant frequency was measured using an impedance analyzer E4990A (manufactured by Keysight Technologies). The measurement results are shown in Figure 12. The resonant frequency without a gap was also measured, and Figure 12 shows the change in resonant frequency (MHz) when a gap was provided at each position relative to the resonant frequency without a gap. For comparison, Figure 12 also shows the results for Experimental Example 2 of Example 1 when a gap was provided at the position shown in Figure 7(d).

[0056] As shown in Fig. 12, in both cases, the variation in the resonant frequency was smaller than when there was no gap, and no significant difference was observed depending on the gap width, similar to the results of Experimental Example 1. In particular, the variation in the resonant frequency was clearly smaller than when there was a gap at the position shown in Fig. 7(d).

[0057] From the results of Example 2, it can be said that when the gap provided in the ferrite sheet extends at an angle to the short side direction of the antenna device, the variation from the resonant frequency when there is no gap is small and does not have a significant impact on the communication distance of the antenna device.

[0058] From the results of Examples 1 and 2, it is considered that when the gap 30 extends overlapping the coil wire of the loop coil 41 (extending parallel to the coil wire of the loop coil 41), it will have a large effect on the resonant frequency of the antenna device, significantly worsening the communication distance. On the other hand, when the gap 30 does not extend overlapping the coil wire of the loop coil 41 but simply intersects with it, it will have a small effect on the resonant frequency of the antenna device 40, and therefore will not have a large effect on the communication distance.

[0059] As shown in the above results, even if the gap is linear and extends in the short-side direction of the antenna device, there is no significant fluctuation in the resonant frequency of the antenna device if the gap is located in the center of the antenna device and does not extend over the coil wire. However, as described above, when a strip-shaped ferrite sheet and a strip-shaped antenna substrate are used, the position of the gap in the antenna device varies from antenna device to antenna device, resulting in some antenna devices being manufactured with the gap extending over the coil wire. To ensure that the gap does not extend over the coil wire, a separate alignment process is required, which is inconvenient. On the other hand, when the gap extends at an angle to the short-side direction of the antenna device as in Example 2, the gap does not extend over the coil wire regardless of the position of the gap on the antenna device. This eliminates the need for an alignment process, thereby reliably suppressing fluctuations in the resonant frequency of the antenna device due to the gap and suppressing a reduction in communication distance.

[0060] As described above, the strip-shaped ferrite sheet of the present invention can be wound into a roll, can suppress fluctuations in the resonant frequency of the antenna device, and can be suitably applied to the antenna device while suppressing deterioration of the communication distance; the antenna device of the present invention is extremely useful because it can suppress fluctuations in the resonant frequency of the antenna device while utilizing the strip-shaped ferrite sheet, and can suppress deterioration of the communication distance. [Explanation of symbols]

[0061] 1 Ferrite strip sheet 2 Ferrite sheet (after cutting) 10 Base material 20 Ferrite sheet pieces 21 Ferrite sintered body 22, 23 Adhesive 30 gap 40 Antenna device 41 Loop coil 42 Antenna substrate

Claims

1. A strip-shaped substrate; a plurality of ferrite sheet pieces provided on the surface of the substrate, Each of the plurality of ferrite sheet pieces includes a ferrite sintered body divided into small pieces, The plurality of ferrite sheet pieces are arranged along the longitudinal direction of the base material with gaps between them, The strip-shaped ferrite sheet is characterized in that the gaps extend at least partially so as not to be parallel to the short-side direction of the substrate.

2. 2. The strip-shaped ferrite sheet according to claim 1, wherein the gaps are linear.

3. 3. The strip-shaped ferrite sheet according to claim 1, wherein the width of the gap is 0.1 mm to 10 mm.

4. an antenna substrate having a loop coil made of a conductive material provided on its surface; a ferrite sheet laminated on the antenna substrate, The ferrite sheet is cut from the strip-shaped ferrite sheet according to any one of claims 1 to 3, An antenna device, characterized in that the gaps included in the ferrite sheet extend at least partially so as not to be parallel to the extension direction of the loop coil.

5. A cable with a noise filter wrapped around its outer periphery, A cable, wherein the noise filter includes the strip-shaped ferrite sheet according to any one of claims 1 to 3.

6. A cable as described in Claim 5, characterized in that the strip-shaped ferrite sheet is continuously wrapped around the outer circumference of the cable in a spiral pattern.

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