JP2009177293A - Reception antenna and receiver using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop an antenna with low directivity, and to provide a reception antenna having a receivable direction of about 360 degrees on the same plane as a single antenna. <P>SOLUTION: A reception antenna of resonance type closed magnetic circuit includes an annular core consisting of a magnetic material, a coil wound around the core at least partially, and a capacitor connected in parallel with the coil, wherein the ratio Dx/Dy of the core width Dx of the coil in the axial direction and the core width Dy in the vertical direction is in the range of 0.5-2. <P>COPYRIGHT: (C)2009,JPO&INPIT

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 ( This is 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 mounted on an electromagnetic wave (hereinafter referred to as a keyless entry system). 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.

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. Conventional antennas are often provided outside the housing. However, recently, due to the trend toward smaller and lighter weight, it has been required to be provided inside the housing. As shown in FIG. 9, the periphery of the movement 22 and the back cover 24, mainly the battery, the motor for moving the clock hand, etc. It arrange | positions in the clearance gap between the components 26. FIG. The antenna 1 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 casing is preferably 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, the design of a wristwatch is a selling point. For example, a metal casing is preferred in terms of luxury and aesthetics. In view of this, cases such as middle and high-end watches and automobiles are often made of metal cases. In this case, depending on the conventional antenna structure and arrangement, a metal case or the like acts as a shield against electromagnetic waves, and there is a problem that reception sensitivity is greatly reduced.

  Further, as an antenna, a voltage is induced in the coil as a result of the magnetic flux caused by electromagnetic waves entering from the outside passing through the magnetic core. As shown in the equivalent circuit diagram of FIG. 13, this voltage resonates at a desired frequency by a capacitor C connected in parallel with the coil 8. By resonating, the coil 8 has Q times (Q is (Resonance circuit characteristic value) voltage is generated, and 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 order to solve this problem, in Patent Document 1, as shown in FIG. 12, a main magnetic path member in which a coil is wound around a magnetic core, and a sub magnetic path member in which a coil is not wound around a magnetic core, There is disclosed an antenna in which an air gap is provided in a part of a closed loop magnetic path along a magnetic core so that a magnetic flux generated inside does not easily leak outside during resonance. According to this antenna, the flow of the magnetic flux toward the outside at the time of resonance is selectively guided to the side of the secondary magnetic path member provided with the air gap, so that the magnetic flux is hardly leaked to the outside, and thus the Q value due to the eddy current loss. Can be suppressed.

  Patent Document 2 uses an antenna having a ring-shaped integral magnetic core, in which the cross-sectional area at the receiving coil forming portion where the coil is formed is larger than the cross-sectional area of the non-receiving coil forming portion where the coil is not formed. A radio-controlled watch that has been disclosed is disclosed. It is described that by using the antenna of this configuration, both the induced electromotive force v and the antenna characteristic Q can be increased, and the detection voltage V generated between both poles of the resonance capacitor can be increased.

Japanese Patent No. 3512782 JP 2006-10542 A

  Many radio timepieces are worn on a person's arm, so the watch is in an environment that can be used in any direction. On the other hand, radio waves carrying time information are always transmitted from a certain direction. The antenna mounted in the watch must be able to receive radio waves carrying this time information regardless of the orientation of the antenna. However, since the conventional antenna has directivity, a high radio wave detection sensitivity can be obtained in the axial direction around which the coil is wound, but the detection sensitivity is lowered in other directions. In the conventional antenna, when the incident angle of the radio wave is deviated by 45 degrees or more with respect to the axial direction around which the coil is wound, the detection sensitivity starts to extremely decrease. For this reason, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-266892, by using two antennas in a substantially vertical direction, the azimuth that can be received is expanded to 360 degrees, and the antenna component has no directivity.

  A similar problem exists in a keyless entry system or an RFID system in which a magnetic sensor type antenna is accommodated in a metal casing or close to a metal part. 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 hall, the user can recognize various traffic information without contact. Even in these systems, in order to obtain an antenna with no directivity, a plurality of antennas are actually used.

  In view of the above, the present invention aims to develop an antenna with low directivity, and an object thereof is to provide a receiving antenna having a receivable direction of approximately 360 degrees on the same plane as a single unit. Provided are a reception antenna suitable for radio wave watches, particularly radio wave watches, keyless entry systems, and RFID systems, and a receiving apparatus using the same, which can exhibit high antenna characteristics in a limited small space.

The above problem is a resonant closed magnetic circuit receiving antenna having an annular core made of a magnetic material, a coil wound around at least a part of the core, and a capacitor connected in parallel to the coil. The ratio Dx / Dy between the core width Dx in the axial direction of the coil and the core width Dy in the vertical direction is 0.5-2. Although details will be described in the embodiments, the directivity is lower than that of the conventional antenna, and even if the incident radio wave is shifted to about 75 degrees with respect to the axial direction of the coil, it can be received with sufficient detection sensitivity.
Although there are antennas of similar shape at first glance, conventional antennas are not closed magnetic circuit resonance type antennas that measure the induced power induced by the magnetic field entering from the axial direction of the core by winding a coil around the annular core. Even if the core is a closed magnetic circuit resonance type, it is only long in one direction where the directivity is not taken into consideration.
By using an annular core having an aspect ratio close to 1, even if the magnetic flux 30 enters at an angle shifted from the axial direction of the coil, it can be received with high sensitivity. As shown in FIG. 7, since the magnetic flux 30 flows along the shape of the core, the magnetic flux flows in the axial direction of the coil regardless of the direction of the incident magnetic flux.
If the ratio Dx / Dy is less than 0.5 or more than 2, the directivity increases, and the intended receiving antenna of the present application cannot be obtained. By using a core having a ratio Dx / Dy of 0.7 to 1.5, and further a core having a ratio Dx / Dy of 0.8 to 1.3, a receiving antenna with further reduced directivity can be obtained. .

  In addition, the receiving antenna of the present invention includes a ring-shaped core made of a magnetic material, a coil wound around at least a part of the core, and a resonant closed magnetic circuit having a capacitor connected in parallel to the coil. An antenna is preferable, wherein the core is substantially annular. In order to reduce directivity, an annular shape is preferable to a polygonal shape. Further, assuming that a brittle material such as a ferrite material is used, a certain level of core strength is required. In the case of an annular shape, stress concentration is less than in a polygonal shape when compression molding is performed, and a core that is resistant to impact can be obtained. Here, the annular shape means that the outer diameter shape is generally a circle, and includes an ellipse and the like. Those having the same outer diameter shape and inner diameter shape are preferred.

  In addition, the receiving antenna of the present invention includes a ring-shaped core made of a magnetic material, a coil wound around at least a part of the core, and a resonant closed magnetic circuit having a capacitor connected in parallel to the coil. An antenna is characterized in that the core is made of a ferrite material, and the core has a polygonal shape with rounded corners. As described above, the ferrite material is highly brittle, and unless the corners are rounded, the core is easily cracked due to stress concentration when some force is applied from the outside.

  The core preferably has a magnetic gap at a portion where no coil is wound. Since the core part with this magnetic gap has higher impedance than the other parts, most of the incident radio waves pass through the inside of the core around which the coil is wound. As a result, the detection sensitivity is improved. Moreover, what was manufactured with the same material can be used for a core. If it is the same material, manufacture is easy and it is easy to make a miniaturized antenna.

  Further, the core preferably has a shape in which the cross-sectional area of the portion where the coil is not wound is smaller than the cross-sectional area of the portion where the coil is wound. Unlike a general open magnetic circuit type antenna, the S / N ratio of the closed magnetic circuit resonance type antenna increases or decreases depending on the cross sectional area of the core portion around which the coil is not wound. This is because it is necessary to adjust the thickness. The present inventor has already filed an application in Japanese Patent Application Laid-Open No. 2007-13862 for optimizing this closed magnetic circuit resonance type S / N ratio.

  In the receiving antenna of the present invention, the second coil is wound substantially parallel to the axial plane of the core, and the induced voltage induced by the magnetic flux passing through the inside of the second coil is measured. What is provided with a measurement means is preferable. As shown in FIG. 4, by measuring the voltage value of the induced voltage of the second coil, it becomes possible to detect the radio wave in the axial direction of the annular core, and not only in the same plane but also in almost the three axial directions. It is possible to receive radio waves from all directions. The second coil may be wound directly around the outer peripheral side of the core, or may be wound around another member such as a bobbin. It is preferable to use an electronic circuit that measures the voltage QV obtained from the first coil and the second coil and selects the value with the higher voltage.

  The core is preferably made of a ferrite material, and the ferrite material has a relative magnetic permeability of 1500 or less. Although details will be described in Examples, when the relative permeability exceeds 1500, the induced voltage is lowered and the characteristics as an antenna are lowered.

  In a receiving apparatus using these receiving antennas, it is preferable that an electronic component (an electronic circuit, a capacitor, a battery, a resistor, or the like) is arranged on the inner diameter portion of the core. Since incident radio waves are not interfered with these electronic components, the detection sensitivity of radio waves is higher than that of a conventional receiving apparatus in which a receiving antenna is arranged in the electronic components.

  Further, when using a receiving antenna in which a second coil is wound substantially parallel to the axial plane of the core and having a measuring means for measuring an induced voltage at both ends of the second coil, the second coil is used. The coil is preferably wound around the outer periphery of the core. By winding the second coil on the outer peripheral side of the core, the core serves as a shielding material against the magnetic field generated from the electronic component disposed inside, and the second coil is based on the electronic component. The influence of induction can be reduced. Moreover, since it functions as an antenna core material also in the axial direction of the core, the sensitivity in the Z-axis direction is increased.

  In the case of a receiver having a structure in which electronic components are arranged inside the core, a soft magnetic ribbon or a soft magnetic wire is used for the core in consideration of weight reduction, space saving, impact resistance, etc. Is preferred. For example, in the case of a radio timepiece or the like, the antenna of the present invention having high reception sensitivity can be obtained by winding a soft magnetic ribbon or a soft magnetic wire along the inner peripheral side of the housing. Moreover, what plated the circumference | surroundings of the cyclic | annular plastic material can be used as a core, and what applied the soft magnetic material in the ring shape to the printed circuit board can be used as a core.

According to the antenna of the present invention, the magnetic flux incident from the outside is received by the annular core and resonated in the core, so that the magnetic flux efficiently returns in the magnetic circuit. As a result, a high output voltage can be obtained and the Q value can be kept high.
In addition, it is possible to manufacture a non-directional antenna in the same plane that cannot be obtained with a conventional rod-shaped antenna with a single core, compared to a conventional omni-directional antenna component that combines two rod-shaped antennas. The number of components can be reduced, and the manufacturing cost can be reduced.
Further, unlike a conventional antenna in which a main magnetic path and a sub magnetic path are separately manufactured and combined, an integrally molded core can be used, so that the manufacturing process is simplified and the manufacturing cost can be reduced.
Also, by providing a magnetic gap at the location of the core around which the coil is not wound, the magnetic flux incident from the outside can easily pass through the inside of the core wound with the coil, and a high output voltage can be obtained.
Further, by reducing the cross-sectional area of the core where the coil is not wound, the S / N ratio is improved as compared with an annular core having a uniform cross-sectional area, and as a result, a high output voltage is obtained.

  In addition, by disposing an electronic component on the inner diameter side of the annular core, it is possible to manufacture a device having higher radio wave detection sensitivity than a conventional receiving device. In addition, if a material with high mechanical strength such as soft magnetic alloy ribbon is used for the annular core and an annular core with a large diameter is used, the annular core is arranged along the inner peripheral side of the metal casing into which the antenna is inserted. A core can also be placed. By arranging the circuit components inside the annular core, the magnetic flux incident from the outside can be received by the antenna without being affected by these circuit components, resulting in high output voltage and noise. It can be set as a receiver with few. Furthermore, because the core can be placed along the shape of the housing, not just the configuration of the electronic components, there are no restrictions on the design of the housing, and products that satisfy user needs, especially for luxury watches such as radio watches. Easy to provide.

In addition, the shape of the receiving antenna of the present invention is such that the magnetic flux caused by the 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 amount penetrating the housing is reduced, and as a result, the eddy current generated in the metal housing can be reduced and the electrical Q value can be kept high, leading to high sensitivity as an antenna. In addition, the effective sensitivity can be increased by suppressing the outflow of magnetic flux due to the resonance current.
Also, since it is an integral core, it is easy to assemble.
Due to the above synergistic effect, it is possible to obtain a high-sensitivity receiving apparatus having a high degree of freedom in arrangement and relatively small design constraints.

  Such an antenna can be suitably used in an antenna apparatus such as a small high-performance radio timepiece, radio wave wristwatch, keyless entry system, and RFID system. Especially, the analog display of radio clocks and radio watches has a structure in which the mechanism to rotate the long hand, short hand, second hand, etc. is gathered at the center of the case, so avoid the center of the case and place the core around the case. The effect that can be arranged is great.

EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited by these Examples.
Examples will be described below. Here, the output voltage and the like of the antenna of the present invention and the conventional antenna were measured and compared along the test apparatus imitating the radio wave wristwatch shown in FIG. 14 and the equivalent circuit shown in FIG.
In FIG. 13, L is a coil composed of the antenna magnetic core 1 and the winding 8. R is the sum of the DC resistance and AC resistance of the coil. An electromotive voltage V is generated in the coil due to the time variation of the magnetic flux. Here, a capacitor C is connected in parallel with the antenna, the capacitor C and the coil L described above are electrically resonated, and a voltage QV that is Q times the electromotive voltage V is generated at both ends of the capacitor to operate as an antenna. To do. In the comparative test, an evaluation antenna was placed in a 1 mm-thick metal (stainless steel SUS403) casing 70 imitating the radio wave wristwatch shown in FIG. 14, and the voltage QV by the equivalent circuit was measured.

(Examples 1-3)
As Example 1, the antenna 10a shown in FIG. An annular core 1a made of Mn—Zn ferrite material (Hitachi Metals Ferrite ML25D) was used as the magnetic core. The annular core 1a has a donut shape with an outer diameter of 6 mm, an inner diameter of 3 mm, and a height of 3 mm, and has a constricted shape with a small cross-sectional area at one location. After the Mn—Zn ferrite material is compression-molded into this shape and sintered, the constricted portion is impacted and cracked to have a magnetic gap. On the side opposite to the constricted portion of the annular core, an enamel-coated copper wire having a wire diameter of 0.1 mm was wound in a range of 3 mm in width by 120 turns to form the core 2. The receiving antenna of the present invention was manufactured by connecting the capacitor 3 in parallel with the core.
Further, as Example 2, the core is the same material, outer shape, and dimensions as the core of Example 1, but is not cracked at the constricted part and remains integrally molded and sintered. Was used. Other than that, a receiving antenna was manufactured under the same conditions as in Example 1. On the opposite side of the annular core from the constricted portion, an enamel-coated copper wire having a wire diameter of 0.1 mm was wound in a range of 3 mm in width by 120 turns.
Further, as Example 3, an annular core having a constricted portion and having a circular outer diameter contour and an inner diameter contour was used. The dimensions of the outer diameter, inner diameter, and height are the same as those in Examples 1 and 2. On the opposite side of the annular core from the constricted portion, an enamel-coated copper wire having a wire diameter of 0.1 mm was wound in a range of 3 mm in width by 120 turns.
The above antenna is installed in a metal case 70 shown in FIG. 14, and an output voltage is applied by applying a magnetic field having a frequency of 125 kHz to 145 kHz and a magnetic field strength of 4.4 nT as an effective value of an alternating magnetic field corresponding to the magnetic field component of the electromagnetic wave. Was measured. The results are shown in Table 1.
The antenna of Example 1 having a cracked magnetic gap at the constricted portion can obtain the highest output voltage, and then the output voltage of the antenna of Example 2 having the constricted portion of Example 2 is high, In the three types of antennas of Example 3 having a uniform cross section, the output voltage of the antenna is the lowest. FIG. 3 shows the relationship between the output voltage and frequency of the receiving antennas of the first and third embodiments.
However, an antenna made of the same material with a length of 6 mm, a width of 1.5 mm, and a height of 3 mm and an enamel-coated copper wire with a wire diameter of 0.1 mm wound in a range of 3 mm in 120 turns (comparative example) An output voltage far higher than that of 1) was obtained. Similarly, after winding a coil around this rod-shaped core, an antenna (comparative example) was formed by applying to the both ends of the core via the outside of the coil wound with resin and iron powder slurry. In 2), it was found that the same output voltage can be obtained.

Example 4
The directivity of the antenna manufactured in Example 1 was investigated. The results are shown in FIG.
The x-axis is the output voltage in the axial direction around which the coil is wound, and the y-axis is the output voltage in the vertical direction. Assuming that the output voltage in the x-axis direction is 1, an output voltage of 0.35 times or more with respect to the x-axis direction was obtained even at a position shifted by 75 degrees from the x-axis.
On the other hand, when the directivity was measured in the same manner with the antenna of (Comparative Example 2), as shown by the broken line in FIG. Only an output voltage less than 35 times is obtained.
From this experiment, it was found that the antenna using the annular core of the present invention has low directivity and can receive radio waves from almost all directions as long as it is in the same plane.

(Example 5)
The effect of antenna characteristics due to the difference of materials was investigated. The antenna characteristics of the antenna of Example 2 were compared with those of the antenna (Example 5) manufactured in the same manner as Example 3 except that a Ni—Zn ferrite material (Hitachi Metals ferrite NL40S) was used as a material. The relationship between the antenna output voltage and frequency is also shown in FIG. A higher output voltage was obtained when the Ni—Zn ferrite material (relative permeability 400) of Example 5 was used than when the antenna of Example 2 using Mn—Zn ferrite material (relative permeability 2500) was used. .

(Example 6)
The directivity was examined by changing the ratio Dx / Dy between the core width Dx in the coil axis direction of the annular core and the core width Dy in the vertical direction.
When the ratio Dmin / Dmax is 0.5 or more and 2 or less, with respect to the magnetic flux entering obliquely by 60 degrees or more with respect to the axial direction of the wound coil, the output voltage in the axial direction of the wound coil is 0. An output voltage of 35 times or more was obtained. Further, when the ratio Dmin / Dmax is 0.7 or more and 1.5 or less, the output is 0.35 times or more with respect to the output voltage in the axial direction of the wound coil with respect to the magnetic flux entering obliquely by 65 degrees or more. A voltage was obtained. Further, when the ratio Dmin / Dmax is 0.8 or more and 1.3 or less, the output is 0.35 times or more with respect to the output voltage in the axial direction of the wound coil with respect to the magnetic flux entering obliquely by 70 degrees or more. A voltage was obtained.

(Example 7)
An antenna having another shape according to the present invention will be described.
FIG. 5 is a schematic diagram of a rectangular receiving antenna. FIG. 5A shows a receiving antenna using a ferrite core having a ratio Dx / Dy of 0.6. FIG. 5B shows a receiving antenna using a ferrite core having a ratio Dx / Dy of 1.3. The corners are rounded, and the shape is easy to come out of the mold when the ferrite core is compression molded. In addition, a crack is provided in a part opposite to the position where the coil is wound, and a magnetic gap is provided so that the return of the magnetic flux flows into the coil side.
FIG. 6 is an example of a receiving antenna provided with a reception reinforcing member 4 for converging radio waves in a part of the core. FIG. 6A shows a reception reinforcing member 4 a made of a laminate of Fe-based amorphous ribbons arranged on a convex core in parallel with the axial direction of the coil 2. FIG. 6A shows a combination of a C-shaped core and an auxiliary core material 5 made of the same material, and a reception reinforcing member 4b made of a laminate of an Fe-based amorphous ribbon is attached to the side surface of the auxiliary core material 5 as a coil 2. It was installed in parallel with the axial direction. FIG. 6B shows a core made of a laminate of Fe-based amorphous ribbons, and uses a core in which 20 sheets of Fe-based amorphous ribbons punched into the shape shown in the figure are stacked.

(Example 7)
FIG. 8 is a diagram showing another shape of the core of the receiving antenna of the present invention. FIG. 8 (a) shows a structure in which thin strips of soft magnetic material are wound and the ends are overlapped. FIG. 8B is a diagram in which the punched plate-like soft magnetic material is bent and the ends are overlapped. FIG. 8C shows a ribbon-shaped soft magnetic material wrapped with a ribbon whose end is half or less than the abdomen. The narrow portions at both ends are end portions. It is carried on the shoulder of the border of the abdomen. The narrow portions at both ends can be stretched as they are to form reception reinforcing members. FIG. 8 (d) is obtained by winding a ribbon-like soft magnetic material. The inner diameter side end portion extends from the side surface of the core to the outer diameter side, and the outer diameter side end portion extends in the opposite direction, and both end portions are used as reception reinforcing members.

(Example 8)
FIG. 9 is a schematic diagram of the radio-controlled timepiece, and the arrangement of the receiving antenna 10 and the like is intentionally shown by a solid line for easy understanding. The radio-controlled wristwatch includes a metal (for example, stainless steel) case 21, a movement 22, peripheral components, a glass lid 23, and a metal (for example, stainless steel) back cover 24. It arrange | positions between 22 and the back cover 24. FIG.
Many conventional receiving antennas have a complicated structure, such as using a member such as a bobbin to fix it to an electronic board, etc., or fixing it by a complicated process such as welding. It was hanging. Since the receiving antenna of the present invention has a relatively simple shape, it can be easily installed in the housing.
According to the embodiment using the receiving antenna of the present invention, since it is a closed magnetic circuit resonance type receiving antenna, there is no generation of eddy current due to leakage magnetic flux from the core even if it is placed near the casing, and detection of radio waves. Sensitivity is not lowered.

FIG. 10 is an example using a core wound with an amorphous ribbon along the inner peripheral surface of the housing case 21. As in FIG. 9, the antenna in the front view is shown by a solid line so that the arrangement and the like can be easily understood. The radio-controlled wristwatch includes a metal (for example, stainless steel) case 21, a movement 22, peripheral components, a glass lid 23, and a metal (for example, stainless steel) back cover 24, and the antenna 10 is moved to the movement 22. And the back cover 24.
The core is a 1 mm wide Co-based amorphous ribbon (thickness: 18 μm) wound in a circular shape. The core is wound into a coil, and a capacitor is provided in parallel with the coil. Further, the second coil 6 and measuring means (not shown) for measuring the induced voltage due to the magnetic flux passing through the coil are provided on the outer peripheral side of the core.
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 the conventional receiving antenna, the periphery is surrounded by metal parts. However, according to the embodiment using the receiving antenna of the present invention, since it is a closed magnetic circuit resonance type receiving antenna, it is arranged near the casing. There is no generation of eddy currents due to magnetic flux leaking from the core, and the detection sensitivity of radio waves is not lowered. Moreover, it can receive with respect to almost all directions of the magnetic flux which flows in from the exterior of a housing | casing. Furthermore, since the second coil 6 for receiving the magnetic flux passing in the axial direction of the core is wound around the outer peripheral side of the core, the magnetic field generated from the internal electronic components (not shown) Therefore, the second coil is not affected. Therefore, reception of radio waves in the axial direction of the core, which is relatively difficult to detect, is not hindered, and all radio waves in the three axial directions can be received in the metal casing.

Example 9
FIG. 11 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. In the front view, the antenna is shown by a solid line for easy understanding of the arrangement. The key body mainly includes a metal case 74, a key opening / closing button 73, a circuit board 71 for receiving / transmitting, and the receiving antenna 10. The receiving antenna is provided with a second core 6 wound in the circumferential direction on the outer peripheral side of the core. As shown in the figure, the core is made of an amorphous ribbon having a width of 1 mm and a number of turns of 10 wound so as to match the inner shape of the housing case. The outer periphery of the key body is formed in a substantially arc shape so that the space in the key body can be used effectively. A printed wiring board 71 is disposed on the inner peripheral side of the core of the receiving antenna. A printed wiring board incorporates a wide variety of wiring and circuit components.

  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 a receiving antenna showing one embodiment of the present invention. It is a figure which shows the low directivity of the receiving antenna of this invention. It is a figure which shows the relationship between a frequency and a detection voltage. It is a schematic structure figure of the receiving antenna which shows another example of the present invention. It is a schematic structure figure of the receiving antenna which shows another example of the present invention. It is a schematic structure figure of the receiving antenna which shows another example of the present invention. It is the figure which showed typically a mode that the receiving antenna of this invention received the magnetic flux from the outside. It is a figure which shows the example of another core shape of the receiving antenna of this invention. 1 is a schematic structural diagram of a radio-controlled wristwatch using a receiving antenna of the present invention. FIG. 6 is a schematic structural diagram of a radio-controlled wristwatch using another receiving antenna of the present invention. 1 is a schematic structural diagram of an RFID system using a receiving antenna of the present invention. It is a schematic structure figure of the conventional antenna. It is a figure which shows the equivalent circuit of the antenna of this invention. 1 is a schematic diagram of an apparatus in which an embodiment of the present invention was tested.

Explanation of symbols

1: magnetic core, 2: coil, 3: capacitor, 4: reception reinforcing member, 5: auxiliary core material, 6: second coil, 10: antenna, 21: metal casing, 22: movement, 23: glass lid,
24: Back cover, 25: Resin casing, 26: Peripheral parts, 30: Magnetic flux, 70: Metal casing

Claims (11)

A receiving antenna of a resonance type closed magnetic circuit having an annular core made of a magnetic material, a coil wound around at least a part of the core, and a capacitor connected in parallel to the coil, the axial direction of the coil A receiving antenna, wherein the ratio Dx / Dy of the core width Dx of the core and the core width Dy in the vertical direction thereof is 0.5-2. A resonant closed magnetic circuit receiving antenna having an annular core made of a magnetic material, a coil wound around at least a part of the core, and a capacitor connected in parallel to the coil, wherein the core is substantially Receiving antenna characterized by being circular in shape. A receiving antenna having a resonant closed magnetic circuit having an annular core made of a magnetic material, a coil wound around at least a part of the core, and a capacitor connected in parallel to the coil, wherein the core is a ferrite A receiving antenna comprising a material and the core having a polygonal shape with rounded corners. The receiving antenna according to claim 1, wherein the core has a magnetic gap at a portion where no coil is wound. 5. The receiving antenna according to claim 1, wherein the core has a shape in which a cross-sectional area of a portion where the coil is not wound is smaller than a cross-sectional area of a portion where the coil is wound. . The receiving antenna includes measurement means for measuring an induced voltage that is induced by a magnetic flux that is wound around a second coil substantially parallel to the axial plane of the core and that passes through the inside of the second coil. The receiving antenna according to any one of claims 1 to 5, wherein the receiving antenna is provided. 5. The receiving antenna according to claim 1, wherein the core is made of a ferrite material, and the relative permeability of the ferrite material is 1500 or less. An annular core made of a magnetic material, a coil wound around at least a part of the core, a receiving antenna of a resonance type closed magnetic circuit having a capacitor connected in parallel to the coil, and an inner diameter portion of the core A receiving apparatus comprising an electronic component arranged. 9. The receiving apparatus according to claim 8, further comprising a measuring means for measuring an induced voltage at both ends of the second coil, the second coil being wound substantially parallel to the axial plane of the core. The receiving device according to claim 9, wherein the second coil is wound around an outer peripheral side of the core. The receiving device according to claim 8, wherein the core is formed by winding a soft magnetic ribbon or a soft magnetic wire.

Images