The present invention relates to a magnetic sensor-type, radio wave-receiving antenna suitable for radio-controlled timepieces receiving radio waves including time information for time adjustment, smart keyless entry systems for detecting the access of owners by radio waves to open keys of automobiles or a houses, etc. (hereinafter referred to as “keyless entry systems”), or RFID tag systems for giving and receiving information by modulation signals carried by radio waves (hereinafter referred to as “RFID systems”), etc.
A radio-controlled timepiece receiving time information conveyed by a carrier wave having a predetermined frequency to adjust its own time based on that time information has been finding various applications such as clocks, wristwatches, etc.
The radio waves used for the radio-controlled timepieces, etc. are 40-200 kHz, having as long wavelengths as several kilometers. Because antennas as long as more than several hundred meters are needed to efficiently receive these radio waves, it is practically difficult to use them in wristwatches, keyless entry systems, RFID systems, etc. Accordingly, magnetic cores having the same function as that of the antennas are generally used for receiving radio waves.
Two radio waves of 40 kHz and 60 kHz are used as carrier waves for time information in Japan. Radio waves having frequencies of 100 kHz or less are mainly used overseas to provide time information. To receive radio waves of these frequencies, magnetic sensor-type antennas having coils wound around magnetic cores are mainly used.
A wristwatch is mainly constituted by a housing, a movement (driver module) and its peripheral parts (dial, motor, battery, etc.), a non-metal (glass) cover, and a rear metal cover. When an antenna is contained in a wristwatch, it is conventionally disposed outside the housing in many cases.
However, the recent trend of reducing size and weight has required an antenna to be disposed in a housing.
When a radio wave coming from outside passes through a magnetic core, voltage is induced in a coil. As shown in the equivalent circuit of FIG. 22, this voltage resonates at a desired frequency by a coil 8 and a capacitor C connected to the coil 8 in parallel. A Q-times voltage is generated in the coil 8 by resonance, to cause current to flow. This resonance current causes the coil 8 to generate a magnetic field, whose magnetic flux mainly flows in and out of both ends of the magnetic core. If there is a metal around the antenna, the magnetic flux generated by this resonance current penetrates the metal, generating eddy current. Thus, if there is a metal near the antenna, the energy of a magnetic field is lost as eddy current at the time of resonance, resulting in antenna coil loss and thus decrease in a Q value and antenna sensitivity.
JP 2003-110341 A discloses a small antenna comprising a magnetic core constituted by an amorphous metal laminate, and a coil wound around it. JP 8-271659 A discloses a small antenna comprising a magnetic core made of ferrite and a coil wound around it. These small antennas are disposed mainly outside the housings of the wristwatches. From the aspect of not hindering the receiving of radio waves as described above, a wristwatch comprising the antenna described in JP 2003-110341 A or JP 8-271659 A preferably has a resin housing.
However, the resin housing poses restrictions in design and ornamentation. Generally, design is a selling point for wristwatches, and metal housings are preferred for high-quality impression and beautifulness. Accordingly, most high-quality timepieces have metal housings. However, if the small antenna described in JP 2003-110341 A or JP 8-271659 A is mounted in a wristwatch with a metal housing the metal housing acts as a radio wave shield, resulting in drastic reduction of receiving sensitivity.
JP 2002-168978 A discloses an antenna comprising a conductive seal member between a metal housing and an antenna. The antenna of this reference is disposed outside the metal housing via a shield member to keep a Q value. However, because the seal member is indispensable, it suffers restrictions in size reduction and design.
Japanese Patent 3,512,782 discloses an antenna comprising a magnetic main path member comprising a coil wound around a magnetic core, and a magnetic sub-path member comprising a magnetic core without a coil, an air gap being provided in part of a closed magnetic loop along the magnetic core, such that a magnetic flux generated inside at the time of resonance less leaks outside. Japanese Patent 3,512,782 describes that this antenna selectively guides a magnetic flux flowing outward at the time of resonance to the magnetic sub-path member, thereby making the magnetic flux less likely to leak outside to suppress the reduction of a Q value due to an eddy current loss.
Keyless entry systems and RFID systems also suffer the problem that a metal hinders an antenna from transmitting and receiving radio waves. The keyless entry system and the RFID system also contain a magnetic sensor-type antenna disposed in a metal housing or near metal parts. The keyless entry system capable of doing the remote control of an automobile key, etc. comprises a receiving unit having an antenna for doing a switching operation by a particular electromagnetic wave, and a unit for transmitting an electromagnetic wave. When a key holder, a transmitting unit, goes close to or away from the receiving unit, a door can be opened or closed without touching the key. The RFID (radio frequency identification) system gives and receives information stored in a tag through an antenna operated at a particular electromagnetic wave. For instance, when an RFID tag, to which destination information, etc. are input, is mounted to a bus, etc., and when an RFID tag, to which timetable information is input, is embedded in a display board, etc. at a bus stop, various transportation information can be seen. In these systems, too, the size reduction and sensitivity increase of an antenna are required.
Accordingly, an object of the present invention is to provide a high-sensitivity magnetic sensor-type antenna disposed in a metal housing, which is free from an eddy current loss without needing large installation area and volume, and a radio-controlled timepiece, a keyless entry system and an RFID system, each of which comprises such magnetic sensor-type antenna.
As a result of intense research in view of the above object, the inventors have found that a high-sensitivity magnetic sensor-type antenna with a suppressed eddy current loss can be obtained without needing a shield by (a) bending end portions of a magnetic core in the antenna in a direction away from a metal housing, (b) providing a magnetic core with a magnetic sub-path member having a smaller specific permeability than that of the magnetic core, or (c) disposing a magnetic core in a magnetic material case. The present invention has been completed based on such findings.
Thus, the first magnetic sensor-type antenna of the present invention comprises a magnetic core and a coil wound around the magnetic core for receiving a radio wave, the antenna being disposed in a housing, and end portions of the magnetic core being bent in a direction away from the housing or a metal part of the housing.
The magnetic core preferably further has bent tip end portions. The magnetic core preferably has pluralities of branched end portions, at least one of which is bent in a direction away from the housing or a metal part of the housing. Also, at least one of the remaining end portions may be bent in a different direction.
End portions of the magnetic core are preferably shaped along an inner wall of the housing. The end portions of the magnetic core are preferably inclined by about 20-50° to a portion having the coil. The tip end portions of the magnetic core are preferably bent such that they are in parallel with the portion having the coil.
The second magnetic sensor-type antenna of the present invention for receiving a radio wave comprises a magnetic main path member comprising a magnetic core and a coil wound around the magnetic core, and a magnetic sub-path member attached to the magnetic core, the magnetic sub-path member having a smaller specific permeability than that of the magnetic core.
In a preferred embodiment, there is a gap of 0.025-3 mm between one end of the magnetic sub-path member and the magnetic core. In another preferred embodiment, the ends of both magnetic sub-path members are positioned in a center portion of the magnetic core with a gap of 0.025-3 mm therebetween.
The magnetic sub-path member preferably has a specific permeability of 2 or more, lower than that of the magnetic main path member. A cross section area ratio of the magnetic sub-path member to the magnetic core is preferably /100-1/2.
A further example of the magnetic sensor-type antenna of the present invention comprises a magnetic main path member comprising a magnetic core and a coil wound around the magnetic core, and a magnetic sub-path member attached to the magnetic core; the magnetic sub-path member being constituted by a first magnetic sub-path member, and a second magnetic sub-path member sandwiched by the first magnetic sub-path member and the magnetic core without an air gap; and the second magnetic sub-path member having a smaller specific permeability than that of the first magnetic sub-path member.
In any magnetic sensor-type antenna, the magnetic core is preferably a bundle of plural metal wires, or a laminate of plural thin ribbons. When the magnetic core is a laminate of plural thin ribbons, the magnetic sub-path member is preferably disposed on a stratum-appearing surface of the magnetic main path member. More preferably, the magnetic sub-path member is a laminate of plural thin ribbons, and disposed such that its lamination direction is the same as that of the magnetic main path member.
The third magnetic sensor-type antenna of the present invention for receiving a radio wave comprises a magnetic core, a coil wound around the magnetic core, and a case receiving the magnetic core and the coil, the case having a specific permeability of 2 or more, smaller than that of the magnetic core.
The magnetic core has a body portion disposed in the case and end portions exposed from the case. The case is preferably constituted by (a) a soft magnetic case portion for receiving a body portion of the magnetic core, and end portions extending from the soft magnetic case portion for receiving the end portions of the magnetic core, the end portions of the case having a smaller specific permeability than that of the soft magnetic case portion, or (b) a soft magnetic case portion for receiving a body portion of the magnetic core, and non-magnetic case portions extending from the soft magnetic case portion for receiving end portions of the magnetic core. In any case, the soft magnetic case portion preferably has a specific permeability of 2 or more.
In the magnetic sensor-type antenna comprising a case, the magnetic main path member is preferably fit in the case. The case is preferably injection-molded, or obtained by curing a curable slurry charged into a mold, in which the magnetic main path member comprising the magnetic core and the coil wound around the magnetic core is placed.
When the magnetic sensor-type antenna is disposed in a metal housing, the end portions of the magnetic core are preferably bent in a direction away from the metal housing. When the magnetic sensor-type antenna is disposed in a metal or non-metal housing together with other metal parts than the antenna, the end portions of the magnetic core are preferably bent in a direction away from the metal parts. The tip end portions of the magnetic core are preferably substantially in parallel with a bottom surface of the metal or non-metal housing.
The radio-controlled timepiece of the present invention comprises any one of the magnetic sensor-type antennas of the present invention in a metal housing.
The keyless entry system of the present invention comprises a transmitter and a receiver, at least one of the transmitter and the receiver containing any one of the magnetic sensor-type antennas of the present invention.
The RFID system of the present invention comprises the antenna of the present invention in an RFID tag.
Because the end portions of the magnetic core in the antenna of the present invention are bent in a direction away from a housing, it is less influenced by the housing even when the housing is made of a metal. Accordingly, even when the antenna is disposed in a radio-controlled timepiece having a metal housing, high sensitivity and Q value can be obtained. In a preferred embodiment, branched tip end portions are spread substantially in parallel with a bottom surface of the housing, the magnetic flux coming from any directions can be captured, resulting in higher sensitivity.
The mounting of a member for forming a magnetic sub-path in addition to the main magnetic circuit provides the following effects: Because a magnetic flux flowing from a magnetic sub-path member also enters a main magnetic path, the amount of a magnetic flux passing through the main magnetic path increases, resulting in higher output voltage. When the case receiving the magnetic main path member constitutes the magnetic sub-path member, a brittle magnetic core can be protected from impact, resulting in high output voltage. The use of a case having such a shape as not to magnetically shut the end portions of the magnetic main path member provides the antenna with little loss.
The construction of a contact portion of the magnetic sub-path member and the magnetic main path member with a low-permeability material, through which a magnetic flux passes therebetween, reduces a plane-passing magnetic flux by fringing, thereby suppressing the generation of eddy current. The adjustment of inductance (magnetic circuit constants) by changing the cross section area of the low-permeability material and its contact area with the magnetic main path member, which can be done precisely, is much easier and better operable than when the adjustment is done by changing an air gap by the positional adjustment of the magnetic main path member and the magnetic sub-path member.
In a preferred embodiment, the magnetic main path member constituted by laminated thin metal ribbons is used, so that a magnetic flux flowing between the magnetic main path member and the magnetic sub-path member substantially passes the end surfaces of the thin metal ribbons of the magnetic main path member. In this case, there is preferably little eddy current generated in the ribbon surface of the magnetic main path member.
Using the antenna of the present invention having the above characteristics, as high sensitivity and Q value as those of radio-controlled timepieces, in which antennas are disposed at positions evading metal housings or metal parts, can be obtained without needing increased installation areas in the radio-controlled timepieces. Accordingly, a radio-controlled timepiece comprising the antenna of the present invention is little restricted in design. In addition, because of little radiation of a magnetic flux by a resonance current, high effective sensitivity is obtained. Such antenna is suitable not only for radio-controlled timepieces, but also for keyless entry systems, RFID systems, etc.
An antenna 10a shown in
An antenna 10b shown in
An insulating layer is preferably disposed between the thin sheets 14b. The insulating layer lowers eddy current generated in each thin sheet 14b, thereby suppressing loss. When the magnetic core is formed by a thin amorphous ribbon, etc., it is necessary to conduct a heat treatment at 350-450° C., preferably at 380-430° C., to improve magnetic properties. When the heat treatment temperature is lower than 350° C., sufficient magnetic properties cannot be obtained. The heat treatment at higher than 450° C. makes the thin ribbon too brittle, making it likely that the thin ribbon is broken when its end portions are bent, or when the housing drops. The heat treatment is carried out preferably in an inert atmosphere such as a nitrogen gas, etc.
An antenna 10c shown in
An antenna 10d shown in
An antenna 30a shown in
An antenna 30b shown in
An antenna 50a shown in
An antenna 50c shown in
Pluralities of branched tip end portions 52c, 52d can catch the incoming magnetic flux in a wide area. Though more branching catches more magnetic flux, design should be made to avoid the decrease of receiving sensitivity by the housing or a metal part in the housing. When the antenna is disposed in a metal housing or a housing having a metal part, at least one of the branched portions is directed away from the metal housing or a metal part in the housing. With the tip end portions 52c, 52d placed at an edge of the housing to spread along an inner wall of the housing, design can be made to fully use the inner space of the housing.
An antenna having a magnetic sub-path member will be explained referring to the drawings. An antenna 20a shown in
The gap G is preferably 0.025-3 mm, more preferably 0.1-2 mm. When the gap G is less than 0.025 mm, the magnetic sub-path members 25a, 25a have too small resistance to receive the incoming magnetic flux. When it exceeds 3 mm, the magnetic sub-path members 25a, 25a have undesirably large resistance to keep current flowing. When there is one gap G like in this embodiment, it is particularly preferably 0.2-2 mm, practically about 1 mm.
In the antenna 20a having the magnetic sub-path members 25a, 25a, part of the incoming magnetic flux flows into a main magnetic circuit (magnetic core 24a) via the magnetic sub-path members 25a, 25a, resulting in an effectively large amount of a magnetic flux passing through the coil 8. Each magnetic sub-path member 25a, 25a preferably has a smaller cross section area than that of the magnetic core 24a. A cross section area ratio of the magnetic sub-path member 25a to the magnetic core 24a is preferably 1/10000-2, more preferably 1/1000-1/2, particularly 1/100-1/5. With the cross section area ratio within this range, the magnetic sub-path members and the magnetic core 24a, a main circuit, exhibit their functions clearly, resulting in a larger amount of a magnetic flux passing through the coil 8.
When the antenna 20a is placed in the metal housing, the end portions of the magnetic core 24a and/or the end portions of the magnetic sub-path members 25a, 25a should be directed away from the metal housing. When part of the housing is made of a metal, the end portions of the magnetic core 24a and/or the end portions of the magnetic sub-path members 25a, 25a are directed away from the metal part. For instance, when the antenna is installed in a radio-controlled wristwatch, it is preferably directed toward a glass cover. With the end portions of the magnetic core 24a and/or the end portions of the magnetic sub-path members 25a, 25a directed toward the incoming magnetic flux, a lot of magnetic flux can be gathered, thereby providing the antenna with high sensitivity. Because a magnetic flux generated by a resonance current generated by the coil 8 and a capacitor connected in parallel to the coil 8 flows mainly into and out of both end portions of the magnetic core 24a, the orientation of the end portions of the magnetic core 24a away from the metal housing reduces the amount of a magnetic flux passing through the metal housing. As a result, less eddy current is generated in the metal housing, resulting in a higher electric Q value and a higher sensitivity of the antenna.
The Q value is defined as ωL/R, wherein ω represents the angular frequency of a radio wave, R represents the resistance of a resonance circuit constituted by the antenna 20a and a capacitor, and L is the self-inductance of the coil 8. R is a sum of the DC resistance and AC resistance of the coil 8. When the antenna 20a is disposed in the metal housing, the antenna 20a has an increased AC resistance, because a resonance voltage as large as Q times the applied voltage is generated at both ends of the coil 8 due to the resonance occurring in the magnetic core 24a by the coil 8 and the capacitor, thereby generating a magnetic flux near both ends of the antenna 20a. When a magnetic flux generated by resonance passes through the metal housing, an eddy current loss occurs. The magnetic flux enters one end of the magnetic core 24a and exits from the other end thereof via the coil 8. In the antenna 20a having the magnetic sub-path members 25a, 25a, however, part of the magnetic flux returns to the magnetic sub-path members 25a, 25a and passes the coil 8 again. As a result, a substantially large voltage is generated. A magnetic flux generated by a resonance current returns to the magnetic core 24a via the magnetic sub-path members 25a, 25a, so that the total amount of a magnetic flux radiated from both ends of the antenna 20a can be reduced. When the antenna 20a is placed in the metal housing, too, a smaller amount of a magnetic flux passes through the metal, thereby suppressing increase in AC resistance. Thus, increase in the resistance R is minimized, resulting in an increased Q value and thus a reduced loss by eddy current, etc.
An antenna 20b shown in
An antenna 20c shown in
An antenna 20d shown in
An antenna 20e shown in
An antenna 20f shown in
An antenna 20g shown in
An antenna 20h shown in
Because each antenna 20g, 20h comprises a sheet-shaped magnetic core 24g, 24h, onto which a sheet-shaped magnetic sub-path member 25g, 25h is attached, it is easily produced and installed in a small area. When the magnetic sub-path members 25g, 25h are made of composites of resins and magnetic materials, etc., the composites per se have the same magnetic properties as having a gap G. Accordingly, even if there is no mechanical gap, it may be regarded that there is magnetically a gap G. This makes it possible to have a gap G without using an intermediate member.
An antenna 20i shown in
An antenna 20j shown in
In the antenna 20 comprising a magnetic sub-path member 25, not only the incoming magnetic flux passes through the magnetic core 21, around which the coil 8 is wound, but also part of the magnetic flux passes through the magnetic sub-path member 25 to return to the magnetic core 21, circulating in a main magnetic circuit. Accordingly, the incoming magnetic flux is divided to a main magnetic circuit and another closed magnetic circuit and efficiently circulated, resulting in a high output voltage.
An antenna 40a shown in
An antenna 40b shown in
An antenna 40c shown in
An antenna 40d shown in
An antenna 40e shown in
An antenna 40f shown in
An antenna 60a shown in
An antenna 60b shown in
An antenna 60c shown in
An antenna 60d shown in
a) shows an antenna comprising a magnetic core 74 constituted by a thin ribbon laminate, a coil 8 wound around the magnetic core 74, and a magnetic sub-path member 7 penetrating the coil 8 and longitudinally circulating by substantially one turn. The magnetic sub-path member 7 is constituted by a thin ribbon laminated to the magnetic core 74, and penetrates the coil 8 together with the magnetic core 74. Ends of the magnetic sub-path member 7 are opposing with a gap G on a side surface of the coil 8 at around a center. The gap G is as wide as 0.025-3 mm. To keep a constant width, the gap G is filled with a resin 76. Though most of the magnetic flux enters the magnetic core 74 from one end and flows toward the other end, part of the magnetic flux enters the magnetic sub-path member 7 and returns to the magnetic core 74. Accordingly, the magnetic flux passes through the coil 8 in a large amount, resulting in high sensitivity.
The antenna shown in
A magnetic sensor-type antenna 1a shown in
The coil 8a is wound around a center portion of the magnetic core 4a in about 800-1400 turns. The magnetic sub-path member 3a is attached to the magnetic core 4a without an air gap. The specific permeability of the magnetic sub-path member 3a is less than that of the magnetic main path member 5a, preferably 5-100. When the specific permeability of the magnetic sub-path member 3a is 100 or less, most of the magnetic flux generated by a resonance current passes through the magnetic main path member 5a, so that the coil suffers less reduction of the Q value, resulting in high sensitivity. When the specific permeability is higher than 100, the magnetic flux passes more through the magnetic sub-path member 3a, resulting in lower voltage induced by the coil, and thus likelihood of reduced sensitivity. When the specific permeability is less than 5, the magnetic flux scarcely circulates the magnetic sub-path member 3a, so that the magnetic sub-path member 3a fails to fully exhibit its own function. The flowability of the magnetic flux depends on the permeability and cross section area of the magnetic sub-path member 3a and, and its area opposing the magnetic main path member 5a. The adjustment of the permeability and cross section area of the magnetic sub-path member 3a and its area opposing the magnetic main path member 5a is much easier than the adjustment of an air gap provided in the magnetic sub-path member 3a, thereby making the working extremely easier.
A magnetic sensor-type antenna 1b shown in
With the magnetic main path member 5b and the first magnetic sub-path member 7b having parallel lamination directions, an eddy current is suppressed. This reason will be explained referring to
The first magnetic sub-path member 7b, in
The magnetic main path member 5b and the first magnetic sub-path member 7b may be formed not only by thin ribbons, but also by rods, sheets or wires. Materials for the magnetic main path member 5b and the first and second magnetic sub-path members 7b, 3b may be, in addition to metals, ferrites, amorphous alloys and nanocrystalline materials, soft composites comprising magnetic powder such as ferrite powder and amorphous alloy powder dispersed in flexible polymers (resins or rubbers) for having an electromagnetic wave-absorbing function.
Though not particularly restricted, the first and second magnetic sub-path members 7b, 3b may preferably have such a structure as comprising an electromagnetic wave-reflecting layer having conductive fibers dispersed in a flexible polymer, first electromagnetic wave-absorbing layers having flat magnetic metal powder dispersed in a flexible polymer, and second electromagnetic wave-absorbing layers having granular magnetic metal powder dispersed in a flexible polymer, the first and second electromagnetic wave-absorbing layers being thermally press-bonded in this order to both surfaces of the electromagnetic wave-reflecting layer. Alternatively, they may comprise either one of the first and second electromagnetic wave-absorbing layers.
The electromagnetic wave-reflecting layer is preferably, for instance, a sheet formed by dispersing carbon fibers or metal fibers in a flexible polymer. The magnetic metal powder is preferably flat powder obtained by disintegrating granular powder produced by a water atomization method from nanocrystalline magnetic alloys such as Fe—Cu—Nb—Si—B, etc. The flat powder preferably has an average particle size of 0.1-50 μm and an average thickness of about 1-5 μm. To provide a preferred electromagnetic wave-absorbing layer, this flat powder is preferably dispersed in a flexible polymer and formed into a sheet. Flat magnetic metal powders of carbonyl iron alloys, amorphous alloys, Fe—Si alloys, molybdenum Parmalloy, Supermalloy, etc. may also be used for the electromagnetic wave-absorbing layer. The flexible polymer is preferably soft and has a specific gravity of 1.5 or less and weathering resistance. Specifically, chloroprene rubbers, butyl rubbers, urethane rubbers, silicone resins, vinyl chloride resins, phenol resins, etc. are usable.
The use of such a soft composite provides a magnetic gap despite no physical gap. Accordingly, the first and second magnetic sub-path members 7b, 3b made of the soft composite can return a magnetic flux to a closed magnetic path without an air gap, whose adjustment is difficult.
When the magnetic main path member 5b is contained in a resin case, the first and second magnetic sub-path members 7b, 3b are preferably contained in the same case. A molten soft composite may be injection-molded into a hollow portion of the resin case, to integrally mold the first and second magnetic sub-path members 7b, 3b. Also, a soft composite can be injected into a gap between the magnetic main path member 5b and the first magnetic sub-path member 7b contained in the resin case, to mold the second magnetic sub-path member 3b integrally with other members. Such methods produce the antenna inexpensively.
A magnetic sensor-type antenna 1c shown in
A magnetic sensor-type antenna 1d shown in
An antenna shown in
The case 7a is preferably made of a composite of soft magnetic ferrite or soft magnetic powder or flake, and a plastic polymer such as a resin or a rubber, etc. The specific permeability of the case 7a is smaller than that of the magnetic core 4, preferably 5-100, more preferably 10-60. When the specific permeability is more than 100, it is difficult to concentrate a magnetic flux in the magnetic main path member. When the case 7a is made by a composite, a proper specific permeability can be achieved by controlling a ratio of soft magnetic powder to a resin, etc., and the thickness of the case 7a can be easily changed. The composite is also easily worked because of softness. If the magnetic sub-path member is difficult to assemble, the case 7a (magnetic sub-path member) may be formed by applying a viscous paint containing soft magnetic powder such as soft magnetic ferrite powder, etc. to the magnetic main path member.
Though it is unexpectedly difficult to attach the magnetic sub-path member to a small, brittle antenna in a practical assembling, the use of a case made of a soft magnetic material can easily exhibit a function as a magnetic sub-path member only by its contact with the end portions of the magnetic core 4. Accordingly, a high-sensitivity antenna can be obtained without needing the positioning of the magnetic main path member and the magnetic sub-path member. Thus, the use of the case per se as a magnetic sub-path member makes it easy to assemble the magnetic main path member and the magnetic sub-path member with reduced numbers of parts, and makes it possible to install the antenna in a housing without needing another case.
An antenna shown in
An antenna shown in
An antenna shown in
An antenna shown in
An antenna shown in
An antenna shown in
The antenna 1 has a basic shape shown in
The case 7 absorbs impact from outside to protect the magnetic core 4, and functions as a magnetic sub-path to make it unnecessary to have a magnetic sub-path member separately, thereby needing only a limited space. Such antenna 1 is easily disposed in the housing 95 without hindering other parts such as the movement 92, etc. Incidentally, if the case 7 has a curved shape adapted for the inner wall of the housing 95, it is easily disposed in the housing 95.
The antenna 1 is arranged such that the end portions of the magnetic core 4 extend from the bottom surface toward the glass cover 93. Accordingly, the end portions or tip end portions of the magnetic core are in alignment with the direction of the incoming radio wave. As long as they are directed to easily receive radio waves, the direction of the end portions and their angles to the bottom surface are not restrictive.
Because indispensable movement and dial occupy most of the timepiece in volume, the antenna 1 has to be disposed near the rear cover 94, thereby being surrounded by metal parts. However, because the end portions of the magnetic core are directed not toward the housing 95 but toward non-metal parts (glass cover 93, etc.), the antenna 1 easily receives radio waves from outside. Namely, with the end portions of the magnetic core, which are most important to receive electromagnetic waves, directed toward non-metal parts such as a glass cover 93, etc., the radio wave-shielding effect of the metal housing 95 can be minimized. When part of the housing 95 is made of a non-metal material, the end portions of the magnetic core may be directed toward the non-metal part of the housing.
When the housing 95 is made of a metal, the magnetic sub-path member 7 is preferably away from the housing 95 to reduce the generation of eddy current. However, there are generally so many restrictions in space in the housing 95 that the magnetic sub-path member 7 cannot necessarily be arranged away from the housing 95. In addition, if the magnetic sub-path member 7 for adjusting sensitivity were directed inward the housing 95, its adjustment would be difficult. When the magnetic sub-path member 7 made of a soft composite is arranged along the inner periphery of the housing 95, the adjustment of thickness and area of the magnetic sub-path member 7 is easy, with space in the housing 95 effectively used. Thus, despite the disadvantage of eddy current, overwhelming advantages can be obtained. Of course, when there is no restriction in space, etc., the magnetic sub-path member 7 may be arranged separate from the housing 95. When the magnetic sub-path member 7 is separate from the metal housing 95, the incoming radio wave is easily focused in the magnetic core of the magnetic main path member, but less focused in the magnetic sub-path member 7. Thus, the effect of avoiding the generation of eddy current can be expected.
The uprising end portions of the magnetic core may appear on a dial surface of the timepiece as part of design. For instance, the end portions of the magnetic core may penetrate the dial. With such design, the end portions of the magnetic core exposed on the dial increase the sensitivity of the antenna.
The end portions of the magnetic core in the antenna 1 are bent toward an upper surface of the key, such that they are deviated from the direction of a metal member constituting the circuit board 81. As depicted, the outer side surface of the magnetic core has a substantially circular shape complementary to the inner surface of the housing 84. A magnetic sub-path member 7 is received in a notch of the magnetic core between their end portions. With the antenna 1 having such a shape, a space inside the key body can be used effectively.
As shown in
The present invention will be explained in further detail referring to Examples below, without intension of restricting the present invention thereto.
Using a 1-mm-diameter round ferrite rod available from Hitachi Metals, Ltd. having 7.5-mm-high bent portions at both ends and a 16-mm-long center portion between the bent portions as a magnetic core, it was insulated, and a 0.07-mm-diameter enameled copper wire was wound by 1200 turns around the insulated surface of the ferrite core in a 12-mm-long range, to produce the antenna shown in
A 15-μm-thick amorphous metal foil was punched in a U shape of 1 mm in width and 16 mm in distance between 7.5-mm-high bent portions, and 30 of these thin foils were laminated to form a 0.45-mm-thick laminate, whose surface was insulated. A 0.07-mm-diameter enameled copper wire was wound by 1200 turns around a center portion of the laminate in a 12-mm-long range, to produce an antenna having the shape shown in
An antenna was produced in the same manner as in Example 1, except for using a 1-mm-diameter round ferrite rod available from Hitachi Metals, Ltd. having a total length of 16 mm and no bent portions between both ends as a magnetic core.
With each antenna of Examples 1 and 2 and Comparative Example 1 installed in a test apparatus having a metal case 70 like a radio-controlled wristwatch, a magnetic field of 14 pT was applied from outside to measure an output voltage. The shape of the test apparatus used for voltage measurement is shown in
An antenna having a magnetic sub-path member was produced to measure output voltage and a Q value. The antenna of Example 2 was provided with a magnetic sub-path member 25d to produce the antenna shown in
A 15-μm-thick amorphous metal foil was punched to a width of 1 mm and a length of 31 mm, and 30 of the thin foils were laminated to a thickness of 0.45 mm. After insulating a surface of the resultant laminate core, a 0.07-mm-diameter enameled copper wire was wound by 1200 turns around it in a 12-mm-long range. Both end portions of the laminate were bent by 7.5 mm, and one amorphous metal foil was placed on the resultant magnetic core to provide an antenna. A small gap was provided between the bent end portions of the magnetic core and both end portions of the metal foil.
Without being disposed in a metal housing, a magnetic field of 14 pT was applied to each antenna of Examples 2-4 and Comparative Example 1 to measure output voltage and a Q value. The measurement results are shown in Table 2.
With a magnetic sub-path member attached to part of the magnetic core, part of a magnetic flux flowing into the magnetic core was retained, resulting in high Q value and output voltage. In the antenna having the magnetic sub-path member, less magnetic flux leaked, so that advantageous results are expected even when disposed in a metal housing.
The antenna 20c of
The antenna 20d of
A linear antenna was obtained in the same manner as in Example 5, except that winding was provided to a magnetic core of 1.5 mm in width, 16 mm in total length, and 2.5 mm in height of an upright winding stopper, and that no magnetic sub-path member was mounted.
With each antenna of Examples 5 and 6 and Comparative Example 2 installed in the test apparatus shown in
The antenna 20g shown in
The antenna 20h shown in
The antenna 20h shown in
With each antenna not disposed in a metal housing, an alternating magnetic field of 14 pT at a frequency of 40 kHz as effective values was applied to measure output voltage. The measurement of a Q value was conducted at a drive voltage of 0.05 V using an impedance meter. The results are shown in Table 4.
Examples 7-10 exhibited higher output voltage and Q value than Comparative Example 1, confirming the effect of having a magnetic sub-path member with a magnetic gap G. However, the output voltage and the Q value were lower in Example 10 having a gap G of 4.0 mm than in Example 9 having a gap G of 3.0 mm. Also, when the gap G is less than 1.0 mm, the output voltage tends to decrease.
In Examples 11-16, the gap G for providing a well-balanced combination of output voltage and a Q value was 0.5 mm. Though a smaller gap G tends to lower output voltage, a higher output voltage was obtained even in Example 12 having a gap G of 0.025 mm than in Comparative Example.
Output voltage measurement was not conducted in Reference Example 2, which resembles the structure of JP 2002-168978 A with a conductive shield member, because its output voltage appeared to be incommensurably lower than those of Examples 7-16. When the gap G is 0 mm, it is considered that a magnetic flux is not well captured, resulting in drastic decrease in output voltage. Why a high Q value was obtained at a gap G of 8.0 mm appears to be due to the fact that the influence of the copper sheet disappeared.
As described above, the magnetic sub-path member with a magnetic gap could retain part of the magnetic flux flowing into the magnetic core, resulting in high Q value and output voltage. The preferred size of the gap G is between about 0.025 mm and about 3 mm, despite some difference by the antenna structure. Because the antenna with a magnetic sub-path member radiates only a small amount of magnetic flux by a resonance current, advantageous results were obtained even when the antennas of Examples 7-10 and 12-16 were disposed in a metal housing.
The antenna shown in
An antenna was assembled in the same manner as in Example 17, except for using a second magnetic sub-path member (soft composite) 3b having a thickness t shown in Table 5. With each antenna installed in the metal case 70 shown in
The antenna shown in
An antenna was assembled in the same manner as in Example 23 except for changing the thickness of the magnetic sub-path member (soft composite) 3a as shown in Table 6. With each antenna installed in the metal case 70 shown in
It was confirmed that the provision of the magnetic sub-path member contributed to improving the Q value and sensitivity. The Q value and sensitivity depended on the thickness of the soft composite. Accordingly, to obtain the maximum effect of the magnetic sub-path member, the first and/or second magnetic sub-path member should be in a preferred thickness range. The thickness t providing high Q value and sensitivity was, for instance, 0.5-1.0 mm in Examples 17-22, and 1.0-2.0 mm in Examples 23-27.
It is considered that even when the magnetic main path member and the first magnetic sub-path member are laminates or made of different materials from above, high Q value and sensitivity can be easily obtained by changing the thickness of the second magnetic sub-path member. The same adjustment can be done by a contact area, too. Thus, the adjustment of a Q value and sensitivity by the thickness of the magnetic sub-path member or by the contact area with the magnetic core is much easier than the micron-level adjustment of a gap, which is necessary for an air gap.
As shown in
The key body comprising the antenna of the present invention exhibited excellent output voltage and Q value.
Number | Date | Country | Kind |
---|---|---|---|
2003-397989 | Nov 2003 | JP | national |
2003-413642 | Dec 2003 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP2004/017740 | 11/29/2004 | WO | 00 | 9/15/2005 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2005/053096 | 6/9/2005 | WO | A |
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20060214866 A1 | Sep 2006 | US |