This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2007-032410 filed on Feb. 13, 2007;
the entire contents of which are incorporated herein by reference.
The present invention relates to an antenna device and a wireless mobile terminal, and in particular to those provided with magnetic material.
As mounting space is limited in a small sized wireless mobile terminal, interference caused by electromagnetic coupling or capacitive coupling among an antenna and each portion of a circuit of the wireless mobile terminal may cause problems. In particular, the antenna may suffer from a reduction of radiation efficiency. For those problems, possible solutions of related art using magnetic material have been proposed as described hereafter.
A first possible solution is disclosed in Japanese Patent Publication of Unexamined Application (Kokai), No. 2001-156484, as to a mobile communication apparatus including a printed circuit board, a shield case for shielding a portion of the printed circuit board, and an antenna which may be pulled out of the shield case to be extended.
According to the above first solution, a shield effect may be improved by using two methods. One of the two methods is to strengthen electrical connections between the shield case and a ground pattern of the printed circuit board in a direction perpendicular to a direction of a radio frequency current induced on the shield case. Another one of the two methods is to layer magnetic films having an axis of easy magnetization in the direction of the radio frequency current induced on the shield case.
A second possible solution is disclosed in Japanese Patent Publication of Unexamined Application (Kokai), No. 2003-198412, as to a mobile communication apparatus including anisotropic magnetic material in a near magnetic field,produced by the apparatus.
According to the above secorid solution, the anisotropy may be directed in a same direction as magnetic field lines forming the radio frequency magnetic field are, so that the magnetic field may be absorbed by the anisotropic magnetic material.
A third possible solution is disclosed in Japanese Patent Publication (Toroku), No. 3713476, as to a mobile communication apparatus including a built-in L-shaped antenna, a printed circuit board facing the antenna, and a plate of magnetic material that is laid on the printed circuit board.
The mobile communication apparatus of the above third solution may reduce magnetic field strength on a surface of a ground layer of the printed circuit board, may reduce induced currents and may make antenna directivity stable.
A wireless mobile terminal may include a built-in antenna of a complex shape like being folded or branched so as to meet one need for a smaller size and a thinner shape of the wireless mobile terminal and another need for multi-resonance and a broader frequency range, which tend to conflict to each other. Above wording of “built-in antenna” means an antenna provided inside a housing of the wireless mobile terminal, or an antenna unitarily formed as a portion of an inner or outer face of the housing.
The built-in antenna may suffer from a reduction of radiation efficiency due to the above complex shapes. Upon including an element folded 180 degrees, e.g., the built-in antenna may suffer from a reduction of radiation efficiency, as antenna currents distributed on both sides of a fold portion are spatially directed in reverse to each other.
Upon being of a meander type which is well known for space efficiency, the built-in antenna may suffer from a reduction of radiation efficiency, as antenna currents distributed on portions neighboring to each other are spatially directed in reverse to each other. Upon including an element that branches into two parallel portions, the built-in antenna may suffer from an impedance mismatch due to capacitive coupling between the two parallel portions.
The first solution of the related art described above is of a wireless mobile terminal having an extendable antenna. This wireless mobile terminal may be configured to have lower impedance of the shield case so that a radio frequency current may easily flow on the shield case, and that the radio frequency current may keep from being conducted into the portion shielded by the shield case.
The first solution of the related art may hardly be applied to a wireless mobile terminal including a built-in antenna, as the antenna and the printed circuit board are relatively positioned in a manner different from those of the wireless mobile terminal having the extendable antenna. The first solution of the related art may not be applied in a case where it is difficult to define the direction of the axis of easy magnetization uniquely, as the direction of the axis of easy magnetization should be defined while the magnetic films are being layered.
The second solution of the related art described above is to absorb the near magnetic field of the mobile communication apparatus (a wireless mobile terminal). In order to improve radiation efficiency of a built-in antenna of the wireless mobile terminal, it is not enough only to absorb the near magnetic field. In addition, it is necessary to emit an electromagnetic field so efficiently that the built-in antenna features a required radiation pattern and a required antenna gain. That is, the second solution of the related art alone is not enough to improve the radiation efficiency of the built-in antenna.
The third solution of the related art described above is to lay the plate of magnetic material between the built-in antenna and a ground layer of the printed circuit board so as to reduce influence of an unbalanced current induced on the ground layer. The built-in antenna, however, may not be of a simple L-shape but may be of a complex shape as described earlier. That is, although possibly contributing to a thin shape of the wireless mobile terminal, the third solution of the related art may not contribute to alleviating limited mounting space for the built-in antenna or to downsizing of a mounting area for the built-in antenna.
Accordingly, an advantage of the present invention is to provide an antenna device configured to be of a complex shape so as to be included in a small sized wireless mobile terminal, and configured to improve radiation efficiency upon being provided with magnetic material. Another advantage of the present invention is to provide a wireless mobile terminal including a built-in antenna device that may be of a complex shape, provided with magnetic material, and configured to improve radiation efficiency thereby.
To achieve the above advantage, one aspect of the present invention is to provide an antenna device including an antenna element including a first portion and a second portion formed almost parallel to each other, and a plane-shaped piece of magnetic material provided between the first portion and the second portion, the magnetic material arranged almost parallel to the first portion and the second portion.
Another aspect of the present invention is to provide a wireless mobile terminal including a printed circuit board, an antenna element including a first portion and a second portion formed almost parallel to each other, the first portion and the second portion arranged almost parallel to the printed circuit board each, and a plane-shaped piece of magnetic material provided between the first portion and the second portion, the magnetic material arranged almost parallel to the printed circuit board, the magnetic material arranged almost parallel to the first portion and the second portion.
A first embodiment of the present invention will be described with reference to
The antenna element 12 is folded at a fold portion 12a about 180 degrees and downwards in
A portion of the antenna element 12 between one end coupled to the feed portion 10 and the fold portion 12a denoted by a bidirectional arrow is called a first portion 12c. A portion of the antenna element 12 between the fold portion 12a and the open end 12b denoted by a bidirectional arrow is called a second portion 12d. The first portion 12c and the second portion 12d are formed almost parallel to each other.
Between the first portion 12c and the second portion 12d, provided is a plane-shaped piece of magnetic material 13 which is included in the antenna device 11 and arranged almost parallel to the first portion 12c and the second portion 12d. In
If the antenna device 11 is activated, antenna currents distributed on the first portion 12c and on the second portion 12d are spatially directed in reverse so that a contribution to electromagnetic field radiation of the first portion 12c may cancel out a contribution to the electromagnetic field radiation of the second portion 12d.
The magnetic material 13 provided between the first portion 12c and the second portion 12d may produce an isolation effect that an electromagnetic field generated by the antenna current distributed on the first portion 12c and affecting the second portion 12d may be reduced. The magnetic material 13 may produce an isolation effect that an electromagnetic field generated by the antenna current distributed on the second portion 12d and affecting the first portion 12c may also be reduced.
As the above effect of canceling out the electromagnetic field radiation between the first portion 12c and the second portion 12d may be reduced thereby, the antenna device 11 may improve radiation efficiency.
The antenna current distributed on the first portion 12c has a relatively large amplitude and a relatively small amplitude near the feed portion 10 and near the fold portion 12a, respectively. The configuration shown in
A portion of the antenna element 14 between one end coupled to the feed portion 10 and the fold portion 14a denoted by a bidirectional arrow is called a first portion 14c. A portion of the antenna element 14 between the fold portion 14a and the open end 14b denoted by a bidirectional arrow is called a second portion 14d. The first portion 14c and the second portion 14d are formed almost parallel to each other.
Between the first portion 14c and the second portion 14d, provided is a same as the magnetic material 13 as shown in
As being different from the antenna device 11 shown in
If a path length of the first portion 14c is longer than a path length of the second portion 14d, the magnetic material 13 may be arranged in such a way as to isolate the second portion 14d from the first portion 14c as shown in
Between the first portion 12c and the second portion 12d, provided is a plane-shaped piece of anisotropic magnetic material 15 which is included in the antenna device 11B and arranged almost parallel to the first portion 12c and the second portion 12d.
For convenience of explanation, an orthogonal coordinate system is defined as shown in
The orthogonal coordinate system has a Y-axis which is perpendicular to the X-axis and almost parallel to the face of the anisotropic magnetic material 15. The orthogonal coordinate system has a Z-axis which is perpendicular to the X-axis and the Y-axis, and is almost perpendicular to the face of the anisotropic magnetic material 15.
The anisotropic magnetic material 15 may be made of nano-granular material or nano-columnar material. The anisotropic magnetic material 15 has a uniquely defined axis of hard magnetization. Assume that the anisotropic magnetic material 15 is arranged in such a way as to direct a axis of hard magnetization almost parallel to the Y-axis as denoted by a block arrow in
In the orthogonal coordinate system shown in
A left hand side of Eq. 1 represents magnetic flux density produced by a magnetic field applied to the anisotropic magnetic material 15 as a vector in the orthogonal coordinate system. A right hand side of Eq. 1 represents a product of the relative magnetic permeability of the anisotropic magnetic material 15 represented as a matrix in the orthogonal coordinate system and the magnetic field represented as a vector.
Eq. 1 represents a characteristic of anisotropic magnetic material in which intrinsic magnetic permeability works on a magnetic field component of a direction of an axis of hard magnetization, and does not work (i.e., works as magnetic permeability of free space) on a magnetic field component of another direction.
There is a fact that an upper limit value of relative magnetic permeability of general (isotropic) magnetic material decreases more in a higher frequency range, which is known as Snoek's limit. At a frequency of 1 GHz, e.g., an upper limit value of relative magnetic permeability of magnetic material such as ferrite is no greater than 10.
It is known though that anisotropic magnetic material has relative magnetic permeability of a higher value, e.g., expected to be 50 at 1 GHz, in a direction of an axis of hard magnetization. Accordingly, as shown in
The anisotropic magnetic material 15 may prevent magnetic fields generated by the antenna currents distributed on the first portion 12c and on the second portion 12d more effectively from mutually affecting thereby. The antenna device 11B, consequently, may improve radiation efficiency more than the antenna device 11 does.
In
As being different from the antenna device 11B shown in
If the path length of the first portion 14c is longer than the path length of the second portion 14d, the anisotropic magnetic material 15 may be arranged in such a way as to isolate the second portion 14d from the first portion 14c as shown in
In
In
According to the first embodiment of the present invention described above, a wireless mobile terminal includes a built-in antenna device having an antenna element folded at a fold portion as mounting space is limited, etc., and includes a plane-shaped piece of magnetic material provided between portions of the antenna element on both sides of the fold portion, so as to prevent radiation efficiency from dropping due to antenna currents distributed on both sides of the fold portion and spatially directed in reverse to each other.
A second embodiment of the present invention will be described with reference to
The antenna element 22 is branched at a branch portion 22a, e.g., aiming at multi-resonance. One branch of the antenna element 22 ends at an open end 22b, and another branch of the antenna element 22 ends at an open end 22c.
A portion of the antenna element 22 between the branch portion 22a and the open end 22b denoted by a bidirectional arrow is called a first portion 22d. A portion of the antenna element 22 between the branch portion 22a and the open end 22c denoted by a bidirectional arrow is called a second portion 22e. The first portion 22d and the second portion 22e are formed almost parallel to each other.
Between the first portion 22d and the second portion 22e, provided is a same as the magnetic material 13 of the first embodiment. The magnetic material 13 is included in the antenna device 21 and arranged almost parallel to the first portion 22d and the second portion 22e. In
The antenna device 21 has a resonant frequency depending on a path length between the feed portion 20 and the open end 22b. The antenna device 21 has another resonant frequency depending on a path length between the feed portion 20 and the open end 22c.
As separation between the first portion 22d and the second portion 22e decreases and capacitive coupling between those portions 22d and 22e increases, lower one of the two resonant frequencies increases. In that case, as the antenna device 21 would equivalently have a greater size, the above capacitive coupling may cause impedance of the antenna device 21 to decrease and may cause a mismatch at each of the resonant frequencies thereby.
The magnetic material 13 provided between the first portion 22d and the second portion 22e may reduce electromagnetic coupling between those portions 22d and 22e, as described with respect to the first embodiment. The above coupling reduction may apparently look like an increase of the separation between the first portion 22d and the second portion 22e in a radio frequency range covering the above resonant frequencies. The capacitive coupling between those portions 22d and 22e may decrease, and the impedance of the antenna device 21 may be kept from decreasing thereby.
Assume that a path length between the feed portion 20 and the open end 22b including the first portion 22d is longer than a path length between the feed portion 20 and the open end 22c including the second portion 22e. The first portion 22d and the second portion 22e, then, may contribute to resonance at relatively lower and higher ones of the resonant frequencies, respectively.
In that case, the magnetic material 13 may be arranged in such a way as to isolate the second portion 22e from the first portion 22d as shown in
Between the first portion 22d and the second portion 22e, provided is a same as the anisotropic magnetic material 15 of the first embodiment. The anisotropic magnetic material 15 is included in the antenna device 21A and arranged almost parallel to the first portion 22d and the second portion 22e.
For convenience of explanation, an orthogonal coordinate system is defined as shown in
The orthogonal coordinate system has a Y-axis which is perpendicular to the X-axis and almost parallel to the face of the anisotropic magnetic material 15. The orthogonal coordinate system has a Z-axis which is perpendicular to the X-axis and the Y-axis, and is almost perpendicular to the face of the anisotropic magnetic material 15. Assume that the anisotropic magnetic material 15 is arranged in such a way as to direct the axis of hard magnetization almost parallel to the Y-axis as denoted by a block arrow in
Electromagnetic coupling between the first portion 22d and the second portion 22e, which are perpendicular to the direction of the axis of hard magnetization of the anisotropic magnetic material 15 or to the Y-axis, may be further reduced in this case than in the case shown in
The above further coupling reduction may apparently look like a further increase of the separation between the first portion 22d and the second portion 22e. The lower resonant frequency may be kept from increasing, and the impedance of the antenna device 21 may be kept from decreasing, thereby.
According to the second embodiment of the present invention described above, a wireless mobile terminal includes a built-in antenna device having an antenna element branched at a branch portion, e.g., aiming at multi-resonance, and includes a plane-shaped piece of magnetic material provided between two portions of the antenna element after being branched. The antenna device may prevent impedance from decreasing thereby.
A third embodiment of the present invention will be described with reference to
The antenna element 32 is an antenna folded at a fold portion 32a about 180 degrees and downwards in
A portion of the antenna element 32 between one end coupled to the feed portion 30 and the fold portion 32a denoted by a bidirectional arrow is called a first portion 32c. A portion of the antenna element 32 between the fold portion 32a and the grounded end 32b denoted by a bidirectional arrow is called a second portion 32d. The first portion 32c and the second portion 32d are formed almost parallel to each other.
Between the first portion 32c and the second portion 32d, provided is a plane-shaped piece of magnetic material 33 which is included in the antenna device 31 and arranged almost parallel to the first portion 32c and the second portion 32d. In
In
The magnetic material 33 provided between the first portion 32c and the second portion 32d may reduce capacitive coupling between those portions 32c and 32d in a radio frequency range, as described with respect to the second embodiment. A lower resonant frequency of the antenna device 31 may be kept from increasing, and the impedance of the antenna device 31 may be kept from decreasing, thereby.
The magnetic material 33 may be replaced with anisotropic magnetic material arranged in such a way that an axis of hard magnetization is almost perpendicular to the first portion 32c or the second portion 32d.
In that case, coupling between the first portion 32c and the second portion 32d may be further reduced for a same reason as explained with respect to the first embodiment or the second embodiment. The lower resonant frequency of the antenna device 31 may be kept from increasing, and the impedance of the antenna device 31 may be kept from decreasing, to a greater extent thereby.
According to the third embodiment of the present invention described above, a folded antenna element having a grounded end may prevent impedance from decreasing by including magnetic material provided between portions, being parallel to each other, on both sides of a fold portion.
A fourth embodiment of the present invention will be described with reference to
The wireless mobile terminal 2 has a housing formed by a first housing portion 25 and a second housing portion 26 mechanically connected to each other in a vertical direction as shown in
As explained with reference to
The first portion 22d is formed by, e.g., a metal sheet stuck to or a conductive pattern plated on an inner face (directed inside the housing) of the first housing portion 25. The second portion 22e is formed by, e.g., a conductive pattern plated on an outer face (directed outside the housing) of the first housing portion 25. The second portion 22e is coupled to the first portion 22d and the feed portion 20 via a connection penetrating between the outer face and the inner face of the first housing portion 25.
The magnetic material 13 may be provided on the inner face or the outer face of the first housing portion 25, or as an inner layer within a thickness of the first housing portion 25. How to provide the magnetic material 13 will be described with reference to
In
As shown in
As shown in
As shown in
As shown in a middle of
As shown on a right hand side of
Upon being provided, as shown in
The cross sections of the wireless mobile terminal 2 shown in
As shown in each of the cross sections, the magnetic material 13 may be arranged in such a way as to isolate the second portion 22e from the first portion 22d. The wireless mobile terminal 2 may direct a radiation pattern upwards at the lower resonant frequency without being completely blocked by the magnetic material 13.
For the wireless mobile terminal 2 of the fourth embodiment described above, the magnetic material 13 may be replaced with the anisotropic magnetic material 15 as explained with respect to the second embodiment. The anisotropic magnetic material 15 may be arranged in such a way as to direct the axis of hard magnetization almost perpendicular to the first portion 22d or the second portion 22e of the antenna element 22.
The wireless mobile terminal 1 of the first embodiment may be configured as a combination of the antenna device 11, a housing and a printed circuit board, in a manner similar to the fourth embodiment. In that case, the fold portion 12a or the fold portion 14a shown in
According to the fourth embodiment of the present invention described above, a wireless mobile terminal may be provided on a surface of a housing portion with an antenna element and a piece of magnetic material, and may improve space efficiency thereby.
A fifth embodiment of the present invention will be described with reference to
The antenna component 52 is formed plate-like and includes an antenna element and anisotropic magnetic material. The antenna component 52 is, like the antenna component 29 of the fourth embodiment, formed by a plate-like piece of dielectric material, a plane-shaped piece of anisotropic magnetic material and a conductive layer for an antenna element, which are arranged in layers.
The antenna component 52 may be formed by a portion of a housing of the wireless mobile terminal 5 (not shown as a whole) provided with the antenna element and the anisotropic magnetic material, as described with respect to a first half of the fourth embodiment. A relative position between the anisotropic magnetic material and the antenna element will be shown later in
The antenna component 52 is provided with a conductive pattern going up and down between an upper face and a lower face of the antenna component 52, as shown in
The antenna element 53 starts from the feed end 53a, goes up and down between the upper face and the lower face of the antenna component 52 through plural via holes including a via hole 53b, while being partially meander-shaped, and then reaches an open end 53c. In
The orthogonal coordinate system defined in
At least a portion of the antenna component 52 including the meander-shaped portion of the antenna element 53 is provided with a layer formed by a plane-shaped piece of anisotropic magnetic material 54 (not shown in
The antenna component 52 is provided with the anisotropic magnetic material 54, e.g., in such a manner as shown in one of
Assume, e.g., that the antenna element 53 works as a one-fourth wavelength monopole antenna. Antenna currents may be distributed on one segment and on a next segment of the antenna element 53 which are neighboring to each other, both parallel to the Y—and provided on the upper face and on the lower face, respectively, of the antenna component 52. The above antenna currents are spatially directed in reverse to each other, and may cause a reduction of radiation efficiency of the antenna element 53 thereby.
The antenna component 52 of the fifth embodiment may be provided with the anisotropic magnetic material 54 between the above segments of the antenna element 53 in such a way as to direct the axis of hard magnetization almost perpendicular to those segments. The antenna component 52 may reduce mutual interaction via magnetic fields produced by and between the above antenna currents directed in reverse, so as to improve the radiation efficiency of the antenna element 53 thereby.
According to the fifth embodiment of the present invention described above, a meander-shaped antenna element formed on both upper and lower faces of an antenna component or of a housing portion may be provided with anisotropic magnetic material, and may improve radiation efficiency thereby.
A sixth embodiment of the present invention will be described with reference to
The antenna component 62 is formed plate-like and includes an antenna element and anisotropic magnetic material. The antenna component 62 is, like the antenna component 29 of the fourth embodiment, formed by a plate-like piece of dielectric material, a plane-shaped piece of anisotropic magnetic material and a conductive layer for an antenna element, which are arranged in layers.
The antenna component 62 may be formed by a portion of a housing of the wireless mobile terminal 6 (not shown as a whole) provided with the antenna element and the anisotropic magnetic material, as described with respect to the first half of the fourth embodiment.
The antenna component 62 is provided with a conductive pattern on a lower face of the antenna component 62, as shown in
The antenna element 63 is provided on the lower face of the antenna component 62 while being at least partially meander-shaped, and reaching an open end 63b. In
The orthogonal coordinate system defined in
At least a portion of the antenna component 62 including the meander-shaped portion of the antenna element 63 is provided with a layer formed by a plane-shaped piece of anisotropic magnetic material 64. The anisotropic magnetic material 64 is arranged so as to isolate the antenna element 63 from another antenna element (not shown) provided on the upper face of the antenna component 62, or vice versa.
The antenna element 63 is provided to the antenna component 62, e.g., in a same way as the first portion 22d of the fourth embodiment is provided as shown in one of
Assume, e.g., that the antenna element 63 works as a one-fourth wavelength monopole antenna. Antenna currents may be distributed on one segment and on a next segment of the antenna element 63 which are neighboring to each other and both parallel to the Y-axis. As the above antenna currents are spatially directed in reverse to each other, those portions parallel to the Y-axis may make relatively smaller contribution to radiation.
As antenna currents distributed on segments of the antenna element 63 which are parallel to the X-axis are, however, spatially directed in a same direction, those segments parallel to the X-axis may make relatively greater contribution to radiation. The antenna currents distributed on the segments of the antenna element 63 which are parallel to the X-axis may produce a magnetic field which is almost parallel to the Y-axis.
As relative magnetic permeability of the anisotropic magnetic material 64 is small in a direction of the Y-axis, the above magnetic field may not so much be blocked by the anisotropic magnetic material 64. The wireless mobile terminal 6 may direct a radiation pattern upwards, i.e., in an opposite direction against the printed circuit board 60 in
The antenna element 63 and the antenna element 65 may be thought as one branched antenna element. This configuration is similar to the configuration of the fourth embodiment shown in
According to the sixth embodiment of the present invention described above, a meander-shaped antenna element formed on a face of an antenna component or of a housing portion facing a printed circuit board may be provided with anisotropic magnetic material, and may effectively form a radiation pattern in an opposite direction against the printed circuit board.
A seventh embodiment of the present invention will be described with reference to
The antenna component 72 is formed plate-like and includes an antenna element and anisotropic magnetic material. The antenna component 72 is, like the antenna component 29 of the fourth embodiment, formed by a plate-like piece of dielectric material, a plane-shaped piece of anisotropic magnetic material and a conductive layer for an antenna element, which are arranged in layers.
The antenna component 72 may be formed by a portion of a housing of the wireless mobile terminal 7 (not shown as a whole) provided with the antenna element and the anisotropic magnetic material, as described with respect to the first half of the fourth embodiment.
The antenna component 72 is provided with a conductive pattern on an upper face of the antenna component 72, forming an antenna element 73. One end of the antenna element 73 is coupled through a via hole 73a to a feed end 73b provided on a lower face of the antenna component 72. The feed end 73b is coupled to the feed portion 71 through a connection material like, e.g., a spring pin connector.
The antenna element 73 is provided on the upper face of the antenna component 72 while being at least partially meander-shaped, and reaching an open end 73c. In
The orthogonal coordinate system defined in
At least a portion of the antenna component 72 including the meander-shaped portion of the antenna element 73 is provided with a layer formed by a plane-shaped piece of anisotropic magnetic material 74.
The antenna element 73 is provided to the antenna component 72, e.g., in a same way as the second portion 22e of the fourth embodiment is provided as shown in one of
Assume, e.g., that the antenna element 73 works as a one-fourth wavelength monopole antenna. Antenna currents may be distributed on one segment and on a next segment of the antenna element 73 which are neighboring to each other and both parallel to the Y-axis. As the above antenna currents are spatially directed in reverse to each other, those segments parallel to the Y-axis may make relatively smaller contribution to radiation.
As antenna currents distributed on segments of the antenna element 73 which are parallel to the X-axis are, however, spatially directed in a same direction, those portions parallel to the X-axis may make relatively greater contribution to radiation. On a ground circuit of the printed circuit board 70, however, a current may be distributed in reverse and may cancel out the above antenna currents distributed on the segments of the antenna element 73 parallel to the X-axis, and the electromagnetic radiation may be reduced thereby.
As the anisotropic magnetic material 74 has the axis of hard magnetization and a high magnetic permeability in a direction of the Y-axis which is almost perpendicular to the direction of the antenna currents distributed spatially in a same direction, mutual interaction via a magnetic field between the segments of the antenna element 73 being almost parallel to the X-axis and the ground circuit of the printed circuit board 70 may be reduced. The antenna element 73 may improve radiation efficiency thereby.
According to the seventh embodiment of the present invention described above, a meander-shaped antenna element formed on an opposite side of an antenna component or of a housing portion against a printed circuit board may be provided with anisotropic magnetic material. The antenna element may keep radiation efficiency from being affected by a current distributed on the printed circuit board and being reduced thereby.
An eighth embodiment of the present invention will be described with reference to
Ordinary magnetic material of high permeability is formed by metal or alloy including Fe, Co or their oxide as constituents. At a higher frequency, transmission loss of the ordinary magnetic material caused by eddy currents tends to be greater, and it tends to be more difficult to use the ordinary magnetic material as base material thereby.
Accordingly, needed is non-conductive material of high permeability having transmission loss as small as possible, which may be used as base material in a higher frequency range.
As one of trials to provide such material of high permeability, nano-granular material of high permeability has been provided by using thin film technologies like a sputtering method. It has been confirmed that the nano-granular material has an excellent feature in the higher frequency range.
Such material of high permeability may be used as the anisotropic magnetic material of the previous embodiments. A piece of such material of high permeability includes a base material portion and a composite magnetic membrane formed on the base material portion.
The composite magnetic membrane includes plural pillar-shaped elements and at least one inorganic insulator formed among the pillar-shaped elements.
The pillar-shaped elements contain magnetic metal or magnetic alloy selected from at least one of Fe, Co, and Ni. The pillar-shaped elements are formed by being overlaid on the base material portion in a manner where a longer dimension is directed perpendicular to a surface of the base material portion.
The inorganic insulator is selected from at least one of an oxide, a nitride, a carbide and a fluoride of metal. The composite magnetic membrane has magnetic anisotropy in a direction parallel with, or included in, the surface of the base material portion.
The above material of high permeability includes, e.g., a base material portion 91 as shown in
The composite magnetic membrane 92 includes a plurality of pillar-shaped component 93's on a surface of the base material portion 91. The pillar-shaped component 93 has a longer dimension oriented perpendicular to the surface of the base material portion 91. The pillar-shaped component 93 contains magnetic metal or magnetic alloy selected from at least one of Fe, Co, and Ni. In
Among a plurality of the pillar-shaped component 93's, formed is at least one inorganic insulator 94 selected from at least one of an oxide, a nitride, a carbide or a fluoride of metal. The composite magnetic membrane 92 has magnetic anisotropy in a surface in parallel with the surface of the base material portion 91.
The composite magnetic membrane 92 has an anisotropic magnetic field Hk1 in the surface in parallel with the surface of the base material portion 91, and an anisotropic magnetic field Hk2 in parallel with the surface of the base material portion 91 and perpendicular to the anisotropic magnetic field Hk1. The composite magnetic membrane 92 has magnetic anisotropy where a ratio of these anisotropic magnetic fields (Hk2/Hk1) is no less than one. These anisotropic magnetic fields Hk1, Hk2 are shown in
The above notation Hk represents a value of a magnetic field at an intersection point of following two tangents of a magnetization curve in a first quadrant (magnetization>0, applied magnetic field>0) where the magnetic field is applied in the surface of the composite magnetic membrane 92. One of the two tangents is at a value of the magnetic field where a variation of the magnetization with the applied magnetic field is greatest (i.e., where the magnetization is almost zero). Another one of the two tangents is at a value of the magnetic field where the variation of the magnetization with the applied magnetic field is smallest (i.e., where the magnetization is completely saturated).
According to the eighth embodiment of the present invention described above, a piece of magnetic material including pillar-shaped elements and a composite magnetic membrane may be provided. The pillar-shaped elements are made of magnetic metal or magnetic alloy, and have a high volume percentage. The composite magnetic membrane has a large ratio of a real part (μ′) to an imaginary part (μ″) of permeability (μ′/μ″). According to the eighth embodiment, an antenna device including an antenna printed board containing the magnetic material may also be provided.
The particular hardware or software implementation of the present invention may be varied while still remaining within the scope of the present invention. It is therefore to be understood that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described herein.
Number | Date | Country | Kind |
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2007-32410 | Feb 2007 | JP | national |