Ferrite sheet

A ferrite sheet includes a ferrite sintered body capable of being in direct and sufficiently close contact with a signal cable and has good noise removal properties. The ferrite sheet includes a flexible sheet having a foldable portion, a plurality of ferrite sintered bodies located in a region other than the foldable portion on the flexible sheet, an elastic body arranged around the ferrite sintered bodies on the flexible sheet, and an adhesive layer arranged on the elastic body such that the elastic body is bonded to itself when the flexible sheet is bent along the foldable portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a ferrite sheet and, in particular, a ferrite sheet for use on a signal cable to prevent leakage and ingress of radio waves and/or to reduce or remove noise superimposed on a signal.

2. Description of the Related Art

Various wave absorbers for use on signal cables to prevent noise leakage from or ingress into electronic apparatuses or electronic components have been provided.

One known example of wave absorbers of this type is a wave absorber that includes a ferrite sintered body whose both surfaces are covered with tape, as described in Japanese Unexamined Patent Application Publication No. 2002-204094. As illustrated inFIG. 21, in the wave absorber, both surfaces of ferrite sintered bodies63are covered with pieces of tape65and67. The wave absorber is attached to a signal cable61by bonding the tape67to the signal cable61.

However, when the wave absorber described in Japanese Unexamined Patent Application Publication No. 2002-204094 is attached on the signal cable61, the tape67is present between the signal cable61and the ferrite sintered bodies63. Therefore, it is difficult for this wave absorber to sufficiently remove noise.

FIG. 22is a graph illustrating frequency characteristics of impedance of a signal cable sandwiched between two ferrite sintered bodies, each having dimensions of 20.0 mm×15.0 mm×1.0 mm, for a distance (gap) between the ferrite sintered bodies of 0.2 mm, 0.3 mm, 0.4 mm, and 0.5 mm. As illustrated inFIG. 22, the mean value of impedance decreases with an increase in the gap. The mean value is reduced as much as approximately 10% from that for a gap of 0.3 mm to that for a gap of 0.4 mm, which is 0.1 mm larger than 0.3 mm. A reduction in the mean value of impedance results in a reduction in noise removal properties. This shows that the presence of the tape67between the signal cable61and the ferrite sintered bodies63increases the gap and thus results in the reduction in the noise prevention properties.

Depending on the material of the signal cable61, bonding of the tape67and the signal cable61may be insufficient. This may cause the tape67to peel off by vibration of the signal cable61, so there is a possibility to separate the ferrite sintered bodies63from the signal cable61.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodiments of the present invention provide a ferrite sheet that includes a ferrite sintered body capable of being in direct and sufficiently close contact with a signal cable and that has good noise removal properties.

A ferrite sheet according to a preferred embodiment of the present invention includes: a flexible sheet including a foldable portion; a plurality of ferrite sintered bodies located in a region other than the foldable portion on the flexible sheet; an elastic body disposed around the ferrite sintered bodies on the flexible sheet; and an adhesive layer arranged on the elastic body such that the elastic body is bonded to itself when the flexible sheet is bent along the foldable portion.

The ferrite sheet according to a preferred embodiment of the present invention is used when being bent along the foldable portion and sandwiching the signal cable. The ferrite sheet prevents leakage and ingress of radio waves and/or reduces or removes noise superimposed on a signal using the ferrite sintered bodies. In such a ferrite sheet, because the ferrite sintered bodies are in direct contact with the signal cable, good noise removal effects can be obtained. Because the elastic body is bonded to itself using the adhesive layer, the adhesion is excellent. Additionally, because the ferrite sheet is fixed such that the signal cable is sandwiched using the elastic body, each of the ferrite sintered bodies can be constantly in close contact with the signal cable by virtue of elasticity of the elastic body even when vibrations occur in the signal cable. Further increased noise removal effects can be obtained by virtue of the close contact of the ferrite sintered body and the signal cable.

In the ferrite sheet according to a preferred embodiment of the present invention, the ferrite sintered bodies may preferably be arranged substantially symmetrical with respect to the foldable portion. Therefore, when the ferrite sheet is bent along the foldable portion, the ferrite sintered bodies exactly coincide with each other in plan view, thus resulting in good noise removal effects.

The flexible sheet may preferably be substantially rectangular in plan view, and the foldable portion may be positioned in an approximately central region of the flexible sheet in a longitudinal direction thereof. The foldable portion positioned in the approximately central region prevents the adhesive layer from being exposed, and this can prevent the ferrite sheet from adhering to adjacent electronic components.

The flexible sheet may preferably be substantially rectangular in plan view, and the elastic body may preferably be disposed on at least the foldable portion and both end regions of the flexible sheet. Therefore, when the ferrite sheet is bent along the foldable portion, the elastic body disposed on the foldable portion can be bonded to itself and the elastic body arranged on both end regions of the flexible sheet can be bonded to itself using the adhesive layer, and the ferrite sheet can be fixed so as to sandwich the signal cable. As a result, the ferrite sintered bodies and the signal cable can be in sufficiently close contact with each other.

The foldable portion may preferably include a bending facilitating section. The bending facilitating section may be a cut section formed in the elastic body or an indentation section formed in the flexible sheet. The bending facilitating section may be a section where the elastic body is not formed on the flexible sheet, a dividing section where the flexible sheet is divided, or a section where the loose sheet is bonded to itself. The provision of the bending facilitating section enables the flexible sheet to be easily bent along the foldable portion, thus facilitating attachment of the ferrite sheet to the signal cable.

In the ferrite sheet according to a preferred embodiment of the present invention, a fixing sheet on which no elastic body is provided may preferably be added to the flexible sheet. Bending the ferrite sheet along the foldable portion and fixing the ferrite sheet with the fixing sheet placed thereon enables the ferrite sheet to be firmly fixed to the signal cable.

Each of the ferrite sintered bodies may include divided ferrite sintered body sections. The divided ferrite sintered body sections mean that each section is small and thin. Therefore, the ferrite sintered body has a reduced tendency to break and chip. The ferrite sintered body sections are allowed to be bent therebetween, so the ferrite sheet can be widely attached to even a curved signal cable.

The plurality of ferrite sintered bodies may have different sizes from each other. Therefore, even if misalignment occurs during attachment, an overlapping area between the ferrite sintered bodies in plan view has a reduced tendency to change. As a result, stable noise absorbing properties can be obtained.

In accordance with various preferred embodiments of the present invention, the ferrite sheet includes a flexible sheet including a foldable portion, a plurality of ferrite sintered bodies disposed in a region other than the foldable portion on the flexible sheet, an elastic body arranged around the ferrite sintered bodies on the flexible sheet, and an adhesive layer arranged on the elastic body such that the elastic body is bonded to itself when the flexible sheet is bent along the foldable portion. Therefore, the ferrite sintered bodies are in direct and sufficiently close contact with the signal cable. As a result, good noise removal effects can be obtained.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments will be described below with reference to the accompanying drawings.

First Preferred Embodiment

FIG. 1is a plan view of a ferrite sheet according to a preferred first embodiment, andFIG. 2is a cross-sectional view thereof. As illustrated inFIG. 1, a ferrite sheet11A according to the first preferred embodiment preferably includes a flexible sheet13having a foldable portion12(whose area is indicated by dashed lines) and two ferrite sintered bodies15disposed on the sheet13. The foldable portion12is positioned in an approximately central region of the sheet13in the longitudinal direction thereof. The foldable portion12indicates any region at which the ferrite sheet11A is foldable on the sheet13. The ferrite sintered bodies15are disposed in a region other than the foldable portion12and arranged substantially symmetrical with respect to the foldable portion12. As illustrated inFIG. 2, an elastic body17is arranged around the ferrite sintered bodies15on the sheet13. An adhesive layer19is arranged on the elastic body17such that the elastic body17is bonded to itself when the sheet13is bent along the foldable portion12.

The sheet13is preferably composed of resin or rubber and is preferably substantially rectangular in plan view. A surface of the sheet13on which the ferrite sintered bodies15and the elastic body17are to be formed has adhesion. This adhesion of the sheet13fixes the ferrite sintered bodies15and the elastic body17onto the sheet13. When the sheet13is composed of a material having elasticity, the ferrite sheet11A is attachable to a signal cable having various thicknesses.

Each of the ferrite sintered bodies15preferably is predominantly composed of Ni—Zn and preferably is substantially rectangular in plan view. The elastic body17preferably is composed of urethane.

In an example of the first preferred embodiment, the sheet13has dimensions of about 14 mm long by about 9 mm wide (which is the size of one side measured from the foldable portion12), and the ferrite sintered body15has dimensions of about 10 mm long by about 5 mm wide by about 0.5 mm high, for example. It is, of course, understood that the materials and dimensions of the sheet13, the ferrite sintered body15, and the elastic body17are merely examples.

As illustrated inFIG. 3, the ferrite sheet11A is used when sandwiching a signal cable21by being folded along the foldable portion12such that the ferrite sintered bodies15and the elastic body17are positioned inside. As illustrated inFIG. 4, which illustrates a cross-sectional view in use, the elastic body17is bonded to itself using the adhesive layer19, thereby fixing the ferrite sheet11A to the signal cable21.

Because the ferrite sintered bodies15are in direct contact with the signal cable21, good noise removal effects can be obtained. Because the elastic body17is bonded to itself via the adhesive layer19, the adhesion is excellent. In addition, because the ferrite sheet11A is fixed to the signal cable21such that the signal cable21is sandwiched using the elastic body17. Therefore, even when vibrations occur in the signal cable21, the ferrite sintered bodies15can be constantly and continuously in close contact with the signal cable21by virtue of the elasticity of the elastic body17.

Because the ferrite sintered bodies15and the elastic body17are disposed on the flexible sheet13, the signal cable21can be sandwiched between the ferrite sintered bodies15so as to be in direct and sufficiently close contact therewith irrespective of the size of the signal cable21.

Because the elastic body17is disposed around the ferrite sintered bodies15, even if the ferrite sintered bodies15are broken, the elastic body17can prevent fragments of the broken ferrite sintered bodies15from flying.

Additionally, in the first preferred embodiment, because the foldable portion12is disposed in an approximately central region of the sheet13, the adhesive layer19is not exposed and thus the ferrite sheet11A does not adhere to adjacent electronic components. Because the ferrite sintered bodies15are arranged substantially symmetrical with respect to the foldable portion12, the ferrite sintered bodies15in use coincide with each other in plan view, thus resulting in good noise removal properties.

As illustrated inFIG. 2, in the ferrite sheet11A of the first preferred embodiment, the thickness of the elastic body17is smaller than that of each of the ferrite sintered bodies15. This enables the ferrite sintered bodies15to be pressed against the signal cable21when the signal cable21is sandwiched, as illustrated inFIG. 4. Therefore, the adhesion of the ferrite sintered bodies15to the signal cable21can be further increased.

The thickness of the elastic body17formed on the foldable portion12and on both end regions of the sheet13may be larger than that of each of the ferrite sintered bodies15. That is, as illustrated inFIGS. 5A-5C, an elastic body portion17alocated on the foldable portion12and on both end regions of the sheet13may have a larger thickness than the ferrite sintered body15, whereas an elastic body portion17bat the other area may have a smaller thickness than the ferrite sintered body15. This enables the elastic body portion17ato sufficiently support the ferrite sintered bodies15positioned outside the signal cable21and being not in contact therewith when the signal cable21is sandwiched, as illustrated inFIG. 6. This can prevent breakage of the ferrite sintered bodies15.

When the elastic body17is disposed on the foldable portion12and on both end regions of the sheet13, the elastic body17is bonded to itself, thus enabling the ferrite sintered bodies15to be in direct and sufficiently close contact with the signal cable21. As a result, as illustrated inFIG. 7, the elastic body17may not be formed in a region other than the foldable portion12and both end regions of the sheet13.

Second Preferred Embodiment

As illustrated inFIG. 8, a ferrite sheet11B according to a second preferred embodiment is basically the same as the ferrite sheet11A according to the first preferred embodiment in that the ferrite sintered bodies15and the elastic body17are disposed on the sheet13, but is different in that the elastic body17disposed on the foldable portion12between the ferrite sintered bodies15has a cut section31. The provision of the cut section31to the elastic body17facilitates bending of the sheet13along the foldable portion12, thus facilitating attachment of the ferrite sheet11B to the signal cable.

In the ferrite sheet11B of the second preferred embodiment, the cut section31is formed in a straight line. However, the cut section31may be formed in a broken line or a chain line. The cut section31may reach the sheet13or may have a depth that does not reach the sheet13.

A bending facilitating section for facilitating bending of the sheet13is not limited to the cut section31formed in the elastic body17. As illustrated inFIG. 9, the bending facilitating section may be an indentation section33formed in the sheet13. The indentation section33may be substantially triangular, as illustrated inFIG. 9, or substantially semi-circular, as illustrated inFIG. 10.

As illustrated inFIGS. 11A and 11B, the bending facilitating section may be a section35where the elastic body17is not formed on the sheet13. The section35, where the elastic body17is not formed on the sheet13, facilitates bending of the sheet13, thus facilitating attachment of the ferrite sheet11B to the signal cable.

As illustrated inFIG. 12, the bending facilitating section may be a dividing section37where the sheet13is divided. The dividing section37, where the sheet13is divided into two parts at the foldable portion12, facilitates bending of the sheet13, thus facilitating attachment of the ferrite sheet11B to the signal cable.

As illustrated inFIG. 13A, to facilitate bending of the sheet13, the sheet13may be bonded to itself at a loose portion. This facilitates bending of the sheet13, while at the same time facilitating holding of the ferrite sheet11B by grasping a bonded section39of the sheet13. As a result, handling of the ferrite sheet11B is facilitated. Using a single sheet13is not necessarily required to bond the sheet13to itself. As illustrated inFIG. 13B, two sheets may be bonded together at the foldable portion12.

Third Preferred Embodiment

As illustrated inFIGS. 14A and 14B, a ferrite sheet11C according to a third preferred embodiment includes a fixing sheet43added to one side of the sheet13in the longitudinal direction thereof. The elastic body17is not disposed on the fixing sheet43. The fixing sheet43is formed integrally with the sheet13, on which the elastic body17is disposed. Other configurations are substantially the same as in the ferrite sheet11A of the first preferred embodiment.

According to the ferrite sheet11C, as illustrated inFIG. 15, when the ferrite sheet11C is bent along the foldable portion12, the fixing sheet43can be placed on the elastic body17and a surface of the sheet13on which the elastic body17is not formed. A surface of the fixing sheet43that is to adhere to the elastic body17and the sheet13has adhesion. This adhesion fixes the fixing sheet43. This can resist separation of the elastic body17bonded to itself on both end regions of the ferrite sheet11C. As a result, the ferrite sheet11C can be firmly fixed to the signal cable21.

To firmly fix the ferrite sheet11C to the signal cable21, it is preferable that the fixing sheet43have a length of about 1 mm or longer, for example. The position of the fixing sheet43added to the sheet13is not limited to in the longitudinal direction thereof. As illustrated inFIG. 16, the fixing sheet43may be added along a shorter side of the sheet13.

Fourth Preferred Embodiment

As illustrated inFIGS. 17A and 17B, in a ferrite sheet11D according to a fourth preferred embodiment, each of the ferrite sintered bodies15is divided into a plurality of sections. Other configurations are substantially the same as in the ferrite sheet11A of the first preferred embodiment.

The ferrite sheet11D is attached to the signal cable21, as illustrated inFIG. 18. Because each of the ferrite sintered bodies15is divided into a plurality of sections, which means that each section is small and thin, the ferrite sintered body has a reduced tendency to break and chip, the size and shape of the ferrite sheet11D can be altered easily, and the manufacturing cost can be reduced. Because the divided ferrite sintered body sections are aligned, they are bendable. Thus, the ferrite sheet11A can support a curve of the signal cable21.

Fifth Preferred Embodiment

As illustrated inFIGS. 19A and 19B, a ferrite sheet11E according to a fifth preferred embodiment includes ferrite sintered bodies15aand15bpreferably having different sizes. More specifically, the size of the ferrite sintered body15apreferably is larger than that of the ferrite sintered body15b. Other configurations are substantially the same as in the ferrite sheet11A of the first preferred embodiment.

In the ferrite sheet11E, because the ferrite sintered bodies15aand15bhave different sizes, even if the signal cable21becomes misaligned when the ferrite sheet11E is attached on the signal cable21, as illustrated inFIG. 20, an overlapping area between the ferrite sintered bodies15aand15bhas a reduced tendency to change. Therefore, stable noise absorbing properties can be obtained.

Other Preferred Embodiments

A ferrite sheet according to the present invention is not limited to the above-described preferred embodiments. It is, of course, understood that various modifications may be made within the scope thereof. For example, two ferrite sintered bodies formed on the sheet in the above-described preferred embodiments can be replaced with three or more ferrite sintered bodies. The elastic body can be composed of non-woven fabric, Japanese paper, or rubber. Alternatively, the elastic body itself may have adhesion.

As described above, various preferred embodiments of the present invention are useful for a ferrite sheet to prevent leakage or ingress of radio waves and/or to reduce or remove noise. In particular, it is excellent in that the ferrite sintered bodies are in direct and sufficiently close contact with the signal cable and the ferrite sheet has good noise removal properties.