JP2006191525A - Antenna, radio-controlled watch using the same, keyless entry system, and rfid system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna capable of demonstrating high characteristics even in a casing in which directions of electromagnetic waves incident from the outside of the casing are limited. <P>SOLUTION: In a magnetic sensor type antenna disposed inside the metallic casing to receive a magnetic field component of the electromagnetic wave, the antenna comprises a main magnetic path member in which a coil is wound around the core made of a magnetic body, a first sub-magnetic path member having a relative permeability equal to or smaller than the magnetic core, and a second sub-magnetic path member which connects both ends of the main magnetic path member and the first sub-magnetic path member without an air gap and has a relative permeability smaller than that of the first sub-magnetic path member and equal to or smaller than 100. The antenna can be used as the antenna of a radio-controlled watch having the metallic casing, movement, a non-metallic cover, a back cover made of metal and an antenna or as the magnetic antenna of a keyless entry system of an automobile and a house, an RFID system for exchanging information by a radio signal, or the like. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a timepiece that receives a magnetic field component in an electromagnetic wave including time information and adjusts the time, a radio timepiece, or a smart keyless entry system that detects the approach of an owner by electromagnetic waves and opens and closes a car or a house key ( Hereinafter, it is referred to as a keyless entry system), or a magnetic sensor type electromagnetic wave receiving antenna suitable for use in an RFID tag system or the like (hereinafter referred to as an RFID system) that transmits and receives information by a modulation signal placed on an electromagnetic wave. is there.

Here, the background art will be described using an antenna for a radio timepiece as an example.
A radio clock is a clock that receives time information transmitted by a carrier wave of a predetermined frequency and corrects its own time based on the time information, and is currently put into practical use in various forms such as a table clock, a wall clock, and a wrist watch.
A radio wave used in a radio clock or the like uses a long wave band of 40 kHz to 200 kHz or less, and one wavelength of the radio wave has a length of several kilometers. In order to efficiently receive this radio wave as an electric field, an antenna length exceeding several hundred meters is required, and it is practically difficult to use it for wristwatches, keyless entry systems, RFID systems, etc. that require miniaturization. It is necessary to receive a magnetic field component using a magnetic core.
Specifically, the carrier wave uses two types of radio waves of 40 kHz and 60 kHz in Japan. Even overseas, time information is mainly provided using frequencies below 100 kHz, so in order to receive radio waves of these frequencies, a magnetic material is used as a magnetic core to efficiently converge the magnetic field component of the electromagnetic wave. A magnetic sensor type antenna in which a coil is wound is mainly used.

Conventionally, as an antenna for a radio-controlled timepiece, for example, Patent Document 1 discloses a small antenna mainly used for a wristwatch in which a coil is wound around a magnetic core made of an amorphous metal laminate.
Patent Document 2 discloses a small antenna formed by winding a coil around a magnetic core made of ferrite.
Patent Document 3 discloses an antenna in which a conductive sealing member is provided between a metal case and the antenna.
Further, Patent Document 4 includes a main magnetic path in which a coil is wound around a magnetic core and a sub magnetic path in which a coil is not wound around the magnetic core, and is a closed loop magnetic path along the magnetic core. An antenna is disclosed in which an air gap is provided in a portion so that magnetic flux generated inside during resonance does not easily leak to the outside.

JP 2003-110341 A JP-A-8-271659 JP 2002-168978 A Japanese Patent No. 3512782

A wristwatch is mainly composed of a housing (case), a movement (driving unit module) and its peripheral components (a dial, a motor, a battery, etc.), a non-metallic (glass) lid, and a metal back lid. In the case of incorporating an antenna in this, conventionally, it is often provided outside the casing. However, recently, it has been required to provide an antenna inside the housing due to the trend of miniaturization and weight reduction. As shown in FIG. 9, the antenna moves the movement 22, the back cover 24, mainly the battery and the clock hands. It arrange | positions in the clearance gap between peripheral components 26, such as a motor. The antenna shown in the front view of FIG. 9 is indicated by a solid line to show the structure, but is actually housed in a space closed by the casing 25, the movement 22, the peripheral component 26, and the back cover 24.
The antennas of Patent Documents 1 and 2 described above are formed by a coil in which the magnetic field component of electromagnetic waves is converged using an amorphous foil or ferrite having a high relative permeability as a magnetic core, and the converged magnetic flux is wound around the outside of the magnetic core. It is an antenna that detects a component whose magnetic flux changes with time as a voltage. Therefore, in this respect, it is desirable that the casing is made of a resin material that does not inhibit the magnetic field component of electromagnetic waves. However, if a part of it is made of resin, there are restrictions in terms of design and design. In general, a watch has a design point as a selling point. For example, a metal casing is preferred in terms of luxury and aesthetics. In view of this, cases such as mid-to-high-end watches and automobiles are often made with a metal case. In this case, depending on the conventional antenna structure and arrangement, a metal case or the like functions as a shield against electromagnetic waves, and there is a problem that reception sensitivity is greatly reduced. Therefore, in Patent Document 3, the Q value is maintained by arranging the antenna outside the metal case and through a shield member. However, enlargement and design restrictions were inevitable.

  In addition, as an antenna, a voltage is induced in the coil as a result of magnetic flux due to electromagnetic waves entering from the outside passing through the magnetic core. As shown in the equivalent circuit diagram of FIG. 7, this voltage resonates at a desired frequency by a capacitor C connected in parallel with the coil 8, and a Q-fold voltage is applied to the coil 8 by resonating. The resonance current flows through the coil 8. Due to this resonance current, a magnetic field is generated around the coil 8, and the magnetic flux mainly enters and exits from both ends of the magnetic core. Here, when a metal approaches the antenna, the magnetic flux generated by the resonance current penetrates the metal and generates an eddy current. That is, if there is a metal with low electrical resistance near the antenna, the magnetic field energy at the time of resonance is lost as eddy current loss and appears as loss of the antenna coil. As a result, the Q value is lowered and the antenna sensitivity is effectively reduced. This leads to a decrease in. In this regard, according to the antenna disclosed in Patent Document 4, the flow of magnetic flux toward the outside at the time of resonance is selectively guided to the sub magnetic path side provided with the air gap, so that the magnetic flux is hardly leaked to the outside. Therefore, it is said that the decrease in the Q value due to the eddy current loss can be suppressed. However, what is important in the antenna of this structure is that it is necessary to keep the air gap accurate and uniform in order to obtain stable characteristics. Actually, it is necessary to keep a gap width of several hundreds of μm or less uniform over the entire cross section, and in order to find the optimum condition, adjustment in the micron order is required. There is a problem.

  Similar problems exist in keyless entry systems or RFID systems that house magnetic sensor antennas in metal enclosures or in close proximity to metal parts. A keyless entry system is, for example, a remote control of a vehicle key such as a passenger car, which consists of a transmission / reception unit equipped with an antenna that opens and closes by a specific electromagnetic wave. The remote operation can be done without contact. In addition, an RFID (Radio Frequency Identification) system transfers information stored in a tag by an antenna that operates by a specific electromagnetic wave. For example, an RFID tag to which destination information such as a bus is input is used as a bus. If the RFID tag to which the timetable information is attached and embedded is embedded in the display board of the platform, the user can recognize various traffic information without contact. In these systems, it is required to increase the sensitivity of the antenna as well as to reduce the size of the housing and the antenna.

  From the above, the present invention has a magnetic sensor type antenna arranged in a metal casing, and can solve the problem of eddy current loss without increasing the installation area and obtain a highly sensitive output. An object of the present invention is to provide a small antenna that can be easily adjusted in sensitivity. In particular, the present invention provides a radio timepiece, particularly a radio timepiece, a keyless entry system, an antenna suitable for an RFID system, and the system using the same, which can exhibit high antenna characteristics in a limited small space.

  The present invention relates to a magnetic sensor type antenna that receives a magnetic field component of an electromagnetic wave from the outside, and a main magnetic path member in which a coil is wound around a magnetic core made of a magnetic material, and both ends of the main magnetic path member without an air gap. The antenna is composed of a sub magnetic path member having a relative magnetic permeability of 2 or more and smaller than the main magnetic path member that is connected to form a closed magnetic path. As a result, the magnetic flux entering the inside from the outside passes through both ends of the main magnetic path member and promotes resonance. On the other hand, the magnetic flux generated from the inside toward the outside tends to flow toward the closed magnetic circuit because there is no air gap. Return to the closed magnetic circuit. The ease of flow at this time is adjusted by the relative permeability, cross-sectional area of the secondary magnetic path member, and the area facing the main magnetic path, but this is less troublesome than adjusting the air gap and is extremely excellent in workability. ing.

  Further, the present invention provides a magnetic sensor type antenna that receives a magnetic field component of an electromagnetic wave from the outside, and a main magnetic path member in which a coil is wound around a magnetic core made of a magnetic material, and a ratio that is equal to or smaller than the magnetic core. A first sub magnetic path member having a magnetic permeability, and both ends of the main magnetic path member and the first sub magnetic path member are connected without an air gap to form a closed magnetic path. The antenna includes a second sub magnetic path member having a relative permeability smaller than that of the magnetic path member. As a result, the magnetic flux entering the outside from the inside passes through both ends of the main magnetic path member, and the magnetic flux going from the inside to the outside easily flows to the closed magnetic path side because there is no air gap. Since the relative magnetic permeability of the secondary magnetic path member 1 is set to be relatively high, the magnetic flux can easily pass through the second secondary magnetic path member having a lower relative permeability, and most of them return to the closed magnetic path. To do. Therefore, there is little eddy current loss, and the amount of magnetic flux that has entered the magnetic core is effectively increased through the coil, resulting in a highly sensitive antenna.

  Here, the sub magnetic path member is preferably a flexible composite material obtained by mixing soft magnetic ferrite powder, soft magnetic metal powder, or soft magnetic metal flakes, and resin or rubber. That is, the magnetic flux incident from the outside is received by the main magnetic path member, but the magnetic flux radiated from the inside is hardly leaked to the outside, and the balance of the closed magnetic path of the present invention can be adjusted by the second sub magnetic path member. I can do it. The sub magnetic path member or the second sub magnetic path member is smaller than the relative magnetic permeability of the main magnetic path member, but if it is 100 or more, it is difficult to receive the magnetic flux concentrated in the main magnetic path. 100-5 are preferable, More preferably, it is 60-10. Therefore, a composite material having flexibility is preferable because an appropriate relative magnetic permeability can be adjusted by adjusting the mixing ratio of the soft magnetic powder and the resin material, and the thickness can be easily adjusted. In addition, since it has flexibility, the air gap can be easily filled and the degree of processing is high, so it is easy to handle. However, flexibility is not essential.

  In the antenna of the present invention, the magnetic core of the main magnetic path member is composed of a laminate in which soft magnetic ferrite or soft magnetic metal thin plates are laminated, and the first sub magnetic path member is also laminated in which soft magnetic metal thin plates are laminated. Alternatively, it can be composed of soft magnetic ferrite. At this time, it is preferable that the lamination direction of the laminated main magnetic path of the metal thin plate and the first sub magnetic path be the same direction. Thereby, the eddy current from each thin plate is reduced with respect to the eddy current generated when the layers are stacked, the loss can be suppressed, and the antenna characteristics can be further improved. The soft magnetic material constituting the magnetic core is preferably a high relative permeability material of about 5000 to 100,000 such as silicon steel, permalloy, amorphous metal, nanocrystalline metal, and ferrite, and the first sub magnetic path member is the main magnetic path member. About 300-5000 smaller than that is preferable.

  In the antenna of the present invention, when the periphery of the antenna core is surrounded by a metal member, it is preferable to bend the end of the magnetic core in the direction of a non-metal part, for example, a glass lid in a radio wave wristwatch. The bending angle is vertical or oblique, and an arbitrary angle can be set depending on the situation inside the casing. By bending the end portion of the magnetic core for converging the magnetic field component so as to be directed in the magnetic flux inflow direction, the tip portion converges a large amount of magnetic flux incident on the inside of the housing, thereby forming a highly sensitive antenna. In addition, this shape reduces the amount of magnetic flux penetrating through the metal case due to the property that magnetic flux due to resonance current from the capacitor connected in parallel with the voltage induced in the coil wound around the magnetic core mainly enters and exits from both ends of the magnetic core. As a result, the eddy current generated in the metal case can be reduced and the electrical Q value can be kept high, leading to high sensitivity as an antenna.

The present invention also relates to a radio-controlled timepiece in which a magnetic sensor type antenna is incorporated in a wristwatch having a metal casing, a movement (including peripheral parts), a non-metallic lid, and a metallic back lid. The main magnetic path member is disposed on the inner side of the metal casing using any one of the antennas described above, and the sub magnetic path member including the first and second sub magnetic paths is disposed on the peripheral edge side of the metal casing. Radio wave watch. Generally, there are many space restrictions on the inner side of the housing, and the sub magnetic path side cannot always be arranged. In the first place, if the sub magnetic path side for sensitivity adjustment faces the inside of the watch, there is a problem in adjustment workability. In this regard, if the secondary magnetic path member is formed of a flexible composite material and is provided along the peripheral edge side, the space can be effectively utilized, and the thickness and area of the secondary magnetic path can be easily adjusted and the assembly is facilitated. Are better. In this way, the adverse effect caused by the eddy current can be offset and a further effect can be expected. However, this does not prevent the main magnetic path member from being disposed on the peripheral edge side of the metal casing and the sub magnetic path member from being disposed on the inner side of the metal casing. In this case, the magnetic field entering from the outside easily converges to the core of the main magnetic path close to the metal casing, while the sub magnetic path is far from the metal casing, so that the magnetic field leaking from the inside to the outside is not easily directed toward the casing. It can be expected that eddy currents hardly occur. Therefore, it can be said that it is desirable to select these configurations according to individual circumstances and desired effects.
As described above, the antenna of the present invention is suitable for use in a small radio wristwatch that receives a radio wave including time information and adjusts the time. Further, it is suitable for use in a keyless entry system that remotely controls the opening and closing of a key of a passenger car or a residence. Furthermore, the present invention is suitable for use in an RFID system that transmits and receives information using a tag storing information.

According to the antenna of the present invention, the magnetic flux incident from the outside is received by the main magnetic path member, and the radiated magnetic flux at the time of resonance is guided from the main magnetic path to the sub magnetic path member to efficiently return the magnetic circuit. be able to. As a result, a high output voltage can be obtained and the Q value can be kept high. Further, at this time, by using a flexible composite material having a low relative permeability by using a secondary magnetic path member having no air gap, it is possible to adjust the feedback of magnetic flux and obtain a high Q value and sensitivity.
As described above, the sensitivity and the Q value equivalent to the case where the metal watch is disposed away from the metal part are obtained while the installation area in the radio timepiece is the same. In addition, the effective sensitivity can be increased by suppressing the outflow of magnetic flux due to the resonance current. And workability and assemblability are good. Due to the above synergistic effect, a highly sensitive antenna with a small installation area but a high degree of freedom in arrangement and relatively small design constraints.
Such an antenna can be suitably used in a small high-performance radio timepiece, radio wave wristwatch, keyless entry system, RFID system, or the like.

Hereinafter, embodiments of the antenna of the present invention will be described with reference to the drawings.
FIG. 1 is a front view (a) and a side view (b) of an antenna showing a first embodiment, and is a schematic diagram for explanation with a case such as a bobbin omitted (the same applies to the following embodiments). As shown in the figure, the magnetic core 1a of the antenna is made of an amorphous alloy, a nanocrystalline magnetic alloy such as Fe—Cu—Nb—Si—B, or a soft magnetic metal foil strip (plate thickness of 20 μm or less) such as an Fe—Si based magnetic alloy. It is punched in a barbell shape, and 30 to 40 thin plates 6a are laminated and integrated through an insulator. A main magnetic path member 4a is formed by winding a coil 2a of about 800 to 1400 turns around the center of the magnetic core. From both ends of the coil 2a, end portions of the magnetic core 1a protrude. A secondary magnetic path member 3a having a relative permeability of 100 or less is connected to the lower end surfaces 5a, 5a at both ends of the projecting magnetic core 1a without providing an air gap to form a closed magnetic circuit. This secondary magnetic path member makes a return route of magnetic flux at resonance, but the optimal value varies depending on the material, shape and dimensions of the housing metal where the antenna is placed, so the relative permeability of the member, The optimum value is determined by appropriately increasing or decreasing the cross-sectional area, the contact area with the main magnetic path, and the like. This is described below.

  FIG. 2 is a schematic diagram of a front view (a) and a side view (b) of an antenna showing a second embodiment. This antenna is composed of a magnetic core 1b made of a laminate of soft magnetic thin metal plates like the magnetic core 1a and a coil 2b wound in the same manner, and further comprises a main magnetic path member 4b, which is equivalent to or equivalent to the magnetic core 1b. The relative permeability is such that an air gap does not occur between the first sub magnetic path member 7b having the following relative magnetic permeability, the lower end surfaces 5b of the main magnetic path member, and the first sub magnetic path member 7b. A second sub magnetic path member 3b of 100 or less is connected to form a closed magnetic path. The first sub magnetic path member 7b is made of soft magnetic ferrite or amorphous alloy, nanocrystalline magnetic alloy such as Fe-Cu-Nb-Si-B, or soft magnetic metal foil strip such as Fe-Si based magnetic alloy (plate thickness). 20 μm or less) may be laminated, or a laminate or a bulk material similar to the magnetic core 1 b may be used. However, the relative permeability is equal to or less than that of the magnetic core 1b. For example, when the relative permeability of the magnetic core 1b is 100000 to 80000, that of the first sub magnetic path member 7b is about 100000 to 300. In addition, a second secondary magnetic path member 3b having a smaller relative permeability is interposed between the two. The relative permeability is set to 100 or less, and the return route of the magnetic flux at the time of resonance is adjusted by adjusting the cross-sectional area orthogonal to each other and the contact area with the main magnetic path. Also, in this example, the main magnetic path member 4b and the first sub magnetic path member 7b are made to have the same stacking direction, that is, the eddy currents caused by the flow of magnetic flux at resonance are set so that the thin plates do not cross each other. It is difficult to occur.

FIG. 3 is a schematic diagram of an antenna front view (a) and a side view (b) showing a third embodiment. In this antenna, a main magnetic path member 4c including a magnetic core 1c and a coil 2c has the same configuration as that of the above-described embodiment. Here, the first sub magnetic path member 7c is constituted by a laminated body in which a plurality of thin plates 8c having a relative permeability equal to or lower than that of the magnetic core 1c are laminated. This is the same as in the second embodiment. Then, a second sub magnetic path member 3c is connected between the first sub magnetic path member 7c and the lower end surface 5c of the main magnetic path member 4c so as not to generate an air gap. A first sub magnetic path member 7c is connected to the other surface of the member 3c to constitute a closed magnetic path. Further, in this example, the main magnetic path member 4c and the first sub magnetic path member 7c cross each other and the eddy current is generated more easily than in the second embodiment. By shifting the axis of the first auxiliary magnetic path member 7c, the magnetic flux flows in parallel as much as possible so as to suppress the eddy current. And the return route of the magnetic flux at the time of resonance can be adjusted similarly to the said Example.
The magnetic core of the main magnetic path member and the first sub magnetic path member may be in the form of a rod, plate, or wire of ferrite, amorphous, nanocrystalline material, etc. in addition to the metal thin plate.

  The sub magnetic path member or the second sub magnetic path member used in the embodiment is obtained by dispersing metal magnetic powder (ferrite powder, amorphous alloy powder, etc.) in a flexible polymer material (resin material or rubber material). Thus, a flexible composite material having an electromagnetic wave absorbing function can be used. For example, an electromagnetic wave reflection layer in which a conductive fibrous material is dispersed in a flexible polymer material, and a first electromagnetic wave absorption in which a metal magnetic material flat shape powder is dispersed in a flexible polymer material on both front and back surfaces There are layers in which a layer and a second electromagnetic wave absorbing layer in which a metal magnetic particle-shaped powder is dispersed in a flexible polymer material are sequentially laminated and thermocompression bonded. The conductive material dispersed in the electromagnetic wave reflection layer is, for example, carbon fiber or metal fiber, which is dispersed in a flexible polymer material and formed into a sheet shape. In addition, the metal magnetic powder used in the electromagnetic wave absorption layer is manufactured by grinding with an attritor the granular shape powder produced from nanocrystalline magnetic alloy such as Fe-Cu-Nb-Si-B system by water atomization method. There is a flat powder having an average particle diameter of 0.1 to 50 μm and an average thickness of 3 μm, which is dispersed in a flexible polymer material and formed into a sheet shape to form an electromagnetic wave absorbing layer. On the other hand, flat metal powder such as carbonyl iron alloy, amorphous alloy, Fe-Si alloy, molybdenum permalloy, supermalloy, etc. is used as a metal magnetic flat powder and dispersed in a flexible polymer material to form a sheet. To form an electromagnetic wave absorbing layer. In addition, the flexible polymer material is an organic material that is flexible and has a specific gravity of 1.5 or less, preferably a weather-resistant resin such as chloroprene rubber, butyl rubber, urethane rubber, silicone resin, vinyl chloride resin. And phenol resin. In addition, for example, a single layer structure in which the first electromagnetic wave absorbing layer and the second electromagnetic wave absorbing layer described above are used independently is also desirable, and a conventionally used flexible composite material having a low relative permeability can be used. . After all, in the present invention, the structure of the composite material is not limited as long as the relative permeability is satisfied.

  By using such a flexible composite material, the part using the composite material has magnetic characteristics having a gap by itself, and it can be regarded magnetically as if it has an air gap. As a result, the magnetic flux can be returned to the closed magnetic path without providing an air gap that is troublesome to adjust. Moreover, since it is not necessary to provide an air gap, it is advantageous in that it is easy to manufacture without requiring subtle accuracy and can maintain stable performance. In addition, the magnetic core and the coil are conventionally housed in a resin case. However, the magnetic core and the coil are made into a resin case that also accommodates the secondary magnetic path member. It is also possible to integrally mold the sub magnetic path member by pouring the raw material of the material into a part of the injection-molded coil bobbin. Further, after the first sub magnetic path member as described above is accommodated in the resin case, the flexible composite material is formed in the gap formed between the main magnetic path member and the first sub magnetic path member. The second sub magnetic path member can be integrally formed by pouring the raw material. If such a means is used, it is further inexpensive and excellent in productivity.

  The operation of the antenna of the present invention will be described below. First, Q is defined as ωL / R, where ω is the angular frequency of the radio wave, R is the resistance of the resonance circuit composed of the antenna and the capacitor, and L is the self-inductance of the coil section. R described here is the sum of the DC resistance and AC resistance of the coil. In particular, the AC resistance of an antenna placed in a metal case increases. The reason for this is that resonance occurs between a coil around which a magnetic core that collects magnetic flux is wound and a capacitor added outside, resulting in a Q-fold resonance voltage. A high voltage is generated at both ends of the coil due to this resonance current. This is because magnetic flux is generated near both ends. It is eddy current loss that occurs when the magnetic flux due to the resonance phenomenon penetrates the metal. It is important to reduce this eddy current loss. Here, by providing a closed magnetic path with a low relative permeability member or a low relative permeability member and a secondary magnetic path member, the magnetic flux flowing into the magnetic core passes through the coil. In addition to flowing out from the other end of the magnetic core, a part of the magnetic core is returned to the closed magnetic path by the sub magnetic path member or the first and second sub magnetic path members, and again merges with the magnetic flux flowing in from the outside, and the inside of the coil is Passes through and generates more voltage. In addition, the magnetic flux generated by the resonance current recirculates through the sub magnetic path member or the closed magnetic path by the first and second sub magnetic path members, thereby reducing the total amount of magnetic flux that is output from both ends of the antenna. The magnetic flux penetrating through the adjacent metal casing is reduced, eddy current loss is reduced, and an increase in AC resistance is equivalently suppressed. Therefore, the increase in the resistance component R described above can be minimized, and an antenna having a high Q value can be obtained.

FIG. 4 shows a front view and a side view of a radio wave wristwatch incorporating these antennas. In the front view, the antenna is shown by a solid line for easy understanding of the arrangement. The radio-controlled wristwatch 20 includes a housing case 21 made of metal (for example, stainless steel), a movement 22 and peripheral components 26, a glass lid 23, and a metal (for example, stainless steel) back cover 24, and moves the antenna. 22 (including the peripheral component 26) and the back cover 24, and laid in the lateral direction. Here, the antenna is arranged by bending the end portion 101 of the magnetic core in the direction of the glass lid 23 so as to rise from the bottom surface. As a result, the magnetic core end portion 101 serving as the entrance and exit of the magnetic flux has a structure facing the incident direction of the electromagnetic wave. A watch is a movement that consolidates driving functions and occupies most of the volume, and a display surface (clockface) for humans is also essential. For this reason, the antenna must be arranged near the back cover. In this case, although the antenna is surrounded by metal parts, according to this embodiment, the magnetic core end portion 101 from which the magnetic flux due to the resonance current of the antenna flows out most is removed from the metal around the bottom portion of the magnetically shielded casing. It is erected by bending toward the non-metal part (glass lid, etc.) so as to be separated. Thereby, the amount of magnetic flux flowing from the outside is large, more magnetic flux near the glass surface far from the housing bottom metal can be captured, and the influence of the metal approaching of the housing bottom can be minimized. In addition, the tip end portion 102 at the end of the magnetic core is formed in a different direction so that the electromagnetic wave can easily enter.
In the radio-controlled wristwatch, the end of the magnetic core that stands up may appear on the surface as part of the design of the clock face. For example, the end of the magnetic core penetrates the dial and appears on the display surface, which is used as a design. At this time, the end of the magnetic core protrudes to the display portion, so that the sensitivity becomes higher. On the contrary, the end portion does not need to be erected vertically. It is only necessary to have a direction and an angle at which the magnetic flux can be easily received depending on the surrounding conditions.
In addition, as shown in FIG. 5, the antenna is arranged such that the main magnetic path member 4 side faces the inside (center) side in the housing and the sub magnetic path member 7 side runs along the peripheral edge side of the housing 21. Thus, the antenna characteristics can be further improved. This is because an AC magnetic flux incident from the outside is generated as an AC voltage at both ends of the coil, and a capacitor connected in parallel with the AC voltage electrically resonates with the coil. This electrical resonance flows again into the coil as a resonance current, and a resonance magnetic flux is generated at both ends of the coil. This is because the secondary magnetic path member minimizes the resonance magnetic flux from leaking to the housing side, which is the closest metal. Further, such an arrangement is an arrangement having a relatively high degree of freedom and excellent sensitivity adjustment and assemblability.

Hereinafter, the test results of the examples will be described. Here, the output voltage and the like of the antenna of the present invention were measured along the test apparatus imitating the radio wave wristwatch shown in FIG. 6 and the equivalent circuit shown in FIG.
In FIG. 7, L is a coil composed of the main magnetic path member 4 and the winding 8 of the antenna. R is the sum of the DC resistance and AC resistance of the coil. A voltage V due to the time variation of the magnetic flux is detected in this coil. Here, a capacitor C is connected in parallel with the antenna, the capacitor C and the coil L described above electrically resonate, and a Q-fold voltage is generated at both ends of the capacitor to operate as an antenna. In the test, an evaluation antenna with different conditions was placed in a 1 mm-thick metal (stainless steel SUS403) housing 70 imitating the radio wave watch shown in FIG. 6, and the voltage V by the equivalent circuit was measured.

Example 1
In Example 1, the first sub magnetic path member and the second sub magnetic path member have the antenna structure shown in FIG. 2, and the magnetic core has Mn—Zn ferrite (Hitachi Metals ferrite MT80D) and the cross section is 1 .5 mm square and 16 mm length were used, and winding 8 was formed by winding 1200 turns of enamel-coated copper wire having a wire diameter of 0.07 mm, which insulated the surface of the ferrite core, in a range of 12 mm in length. Next, the first sub magnetic path member uses a ferrite plate having a plate thickness of 0.5 mm, a width of 1.5 mm, and a relative permeability of 500, and the second sub magnetic path member is a flexible having a relative permeability of about 50. The composite material was closely attached, and the Q value and sensitivity (output voltage) were measured when the cross-sectional area of contact with the magnetic core was constant and the thickness t of the flexible composite material was changed. The shape of the winding coil is not particularly limited, but a circular shape is desirable for manufacturing.
This antenna was installed in a metal case 70 shown in FIG. 6, and an output voltage was measured by applying a magnetic field having a frequency of 40 kHz and a magnetic field strength of 14 pT as an effective value of an alternating magnetic field corresponding to the magnetic field component of the electromagnetic wave from the outside. The results are shown in Table 1.

(Example 2)
In Example 2, the sub magnetic path member has the antenna structure shown in FIG. 1 and uses Mn—Zn ferrite (Hitachi Metals Ferrite MT80D) as a magnetic core, a cross section of 1.5 mm square, and a length of 16 mm. The winding 8 was formed by winding 1200 turns of enamel-coated copper wire having a wire diameter of 0.07 mm, which insulated the surface of the ferrite core, in a range of 12 mm in length. The sub magnetic path member is formed by using a flexible composite material having a plate thickness of 0.5 mm, a width of 1.5 mm, and a relative magnetic permeability of 50, in close contact with the main magnetic path member (magnetic core). At this time, the Q value and sensitivity (output voltage) when the thickness t of the flexible composite material was changed were measured.
This antenna was installed in a metal case 70 shown in FIG. 6, and an output voltage was measured by applying a magnetic field having a frequency of 40 kHz and a magnetic field strength of 14 pT as an effective value of an alternating magnetic field corresponding to the magnetic field component of the electromagnetic wave from the outside. The results are shown in Table 2.

  As described above, it was confirmed that the Q value and the sensitivity were improved by providing the sub magnetic path member from Examples 1 and 2. The Q value and sensitivity change by changing the thickness of the flexible composite material. Thereby, the optimal value which draws out the effect of a submagnetic path member can be adjusted. For example, in this example, the Q value and the sensitivity are both high in the case of Example 1 in the case of t = 0.5 to 1.0 mm, and in the case of Example 2, t = 1.0 to 2.0 mm. It is. Even when the main magnetic path member and the first sub magnetic path member are formed of a laminate or when the material is changed, a high Q value and sensitivity can be easily achieved by changing the thickness of the second sub magnetic path member. Can be put out. The same adjustment is possible by changing the contact area instead of adjusting the thickness, that is, adjusting the cross-sectional area. These are remarkable effects compared with the case where adjustment is performed by providing an air gap because gap adjustment is required on the order of microns.

(Other examples)
FIG. 8 shows a front view of a key body for a keyless entry system, which is a kind of RFID tag incorporating the antenna of the present invention. The key body 80 mainly comprises a resin casing 74, a key opening / closing button 73, a circuit board 71 for receiving and transmitting, and a receiving antenna 90. FIG. 8 shows the state in which the upper half of the housing case is removed for easy understanding of the arrangement of the components inside the key body 80. In the vicinity of the receiving antenna 90, a circuit board 71 on which an electronic component 72 using metal wiring or metal is mounted is disposed. Further, the metal emergency key 75 is housed inside the key body. Therefore, in the key body for the keyless entry system, many metal parts are arranged in the vicinity of the receiving antenna 90, so that the receiving environment of the receiving antenna 90 is metal even if the housing case 74 to be accommodated is made of resin. It can be said that it is close to the reception environment when accommodated in the case made of a product. In keyless entry systems and RFID systems that use transceivers and tags, the antenna of the present invention is effective because the antenna is required to be housed in a narrow space surrounded by metal in the housing in the same manner as a radio timepiece. The effect can also be obtained in the same manner as in the above embodiment. Further, as shown in the drawing, the outer periphery of both ends is formed in a substantially arc shape so as to match the inner surface shape of the housing case, and the end portion faces the inner side in order to effectively use the space in the key body. The sub magnetic path member is provided along the peripheral edge side in order to effectively use the space in the key body.

  The antenna of the present invention can be used for radio wave receiving antennas used in radio timepieces, keyless entry systems such as automobiles and houses, and RFID tag systems. In particular, it is suitable for radio wristwatches because of its great freedom of shape.

1 is a schematic structural diagram of an antenna showing a first embodiment of the present invention. FIG. 5 is a schematic structural diagram of an antenna showing a second embodiment of the present invention. FIG. 5 is a schematic structural diagram of an antenna showing a third embodiment of the present invention. It is the front view and side view which show the example which has arrange | positioned the antenna of this invention in a wristwatch. It is a front view which shows the example which has arrange | positioned another antenna in a wristwatch. 1 is a schematic diagram of an apparatus in which an embodiment of the present invention was tested. It is a figure which shows the equivalent circuit of the antenna of this invention. It is a figure which shows the example which applied the antenna of this invention to the key main body for keyless entry systems. It is the front view and side view which show the radio wristwatch which incorporates the conventional antenna.

Explanation of symbols

1a to 1d: Magnetic cores 2a to 2c: Winding 3a: Sub magnetic path members 3b to 3d: Second sub magnetic path members 4a to 4d: Main magnetic path members 6a to 6c: Laminated magnetic cores 7b to 7d: First sub Magnetic path member 8: Coil, winding 21: Metal casing 22: Movement 23: Glass lid 24: Back lid 25: Resin casing 26: Peripheral component 70: Metal casing 72: Electronic component 80: Key Body 90: receiving antenna

Claims (9)

In a magnetic sensor type antenna that receives a magnetic field component of an electromagnetic wave from the outside, a closed magnetic circuit is formed by connecting a main magnetic path member in which a coil is wound around a magnetic core made of a magnetic material and both ends of the main magnetic path member without an air gap. And an auxiliary magnetic path member having a relative magnetic permeability of 2 or more and smaller than the main magnetic path member. In a magnetic sensor type antenna that receives a magnetic field component of an electromagnetic wave from the outside, a main magnetic path member in which a coil is wound around a magnetic core made of a magnetic material, and a first magnetic permeability that is equal to or smaller than that of the magnetic core. The sub magnetic path member, and both ends of the main magnetic path member and the first sub magnetic path member are connected without an air gap to form a closed magnetic path. An antenna comprising a second sub magnetic path member having a low magnetic permeability. The said secondary magnetic path member is a soft composite material formed by mixing soft magnetic ferrite powder, soft magnetic metal powder, or soft magnetic metal flakes, and resin or rubber. antenna. The magnetic core of the main magnetic path member is composed of a laminate in which soft magnetic ferrite or soft magnetic metal thin plates are laminated, and the first sub magnetic path member is a laminate in which soft magnetic metal thin plates are laminated or soft magnetic ferrite. The antenna according to claim 2 or 3, wherein 2. At least a part of an end portion of a magnetic core constituting the main magnetic path member is bent in a non-metallic direction when at least the periphery of the main magnetic path member is surrounded by a metal member. The antenna in any one of -4. In a radio timepiece in which a magnetic sensor type antenna is incorporated in a wristwatch having a metal casing, a movement (including peripheral parts), a non-metallic lid, and a metallic back lid, the magnetic sensor type antenna is defined in claims 1 to 5. A radio-controlled timepiece using the antenna according to any one of the above. 7. The radio timepiece according to claim 6, wherein the antenna has a main magnetic path member disposed on an inner side of the metal casing and a sub magnetic path member disposed on a peripheral edge side of the metal casing. A keyless entry system, wherein the magnetic sensor type antenna according to any one of claims 1 to 5 is used in any one of a transmitter and a receiver having the antenna built therein. An RFID system comprising the magnetic sensor antenna according to claim 1 incorporated in an RFID tag.

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