Patent Application
20120086619
The present invention relates to a resonance-type, receiving antenna and receiving apparatus suitable for radiowave watches, keyless entry systems, RFID tag systems, etc.
Radiowave watches have a function to correct time by receiving magnetic field components of electromagnetic waves containing time information. Keyless entry systems enable owners of units transmitting and receiving particular electromagnetic waves to open and close keys of cars, houses, etc. without contact. RFID (radio frequency identification) systems send and receive information to and from tags with particular electromagnetic waves. For example, when RFID tags having destination information, etc. of buses, etc. are attached to buses, and when RFID tags having timetable information are embedded in timetable boards of bus stops, etc., users can recognize various types of transportation information without contact.
The keyless entry systems, etc. use radiowaves having frequencies of 40-200 kHz (several kilometers of wavelength). For example, two types of radiowaves of 40 kHz and 60 kHz are used in Japan, and mainly frequencies of 100 kHz or less are used overseas. For systems receiving electric field components of such long-wavelength radiowaves, antennas over several hundreds of meters are needed, not suitable for small radiowave wristwatches, small keyless entry systems and small RFID systems. Accordingly, it is preferable to use systems for receiving magnetic field components of long-wavelength radiowaves with magnetic sensor-type antennas comprising coils wound around magnetic cores.
As shown in the equivalent circuit of
In addition, receiving antennas for wristwatches, keyless entry systems, RFID systems, etc., whose magnetic core directions are changing every moment, are required to be omnidirectional, namely to have high receiving sensitivity in any directions of XYZ axes. As a technology for being omnidirectional, for example, JP 2002-217635 A discloses an antenna apparatus comprising coils perpendicularly wound around pluralities of rod-shaped, magnetic cores and connected in series. JP 2004-229144 A discloses a surface-mounted antenna comprising coils wound around pluralities of cross-shaped, magnetic cores projecting from a center base member. However, because of pluralities of rod-shaped, magnetic cores, these antennas are not suitable for small radiowave wristwatches, etc. with little space for antennas.
JP 2001-320223 A discloses a radiowave watch comprising an omnidirectional antenna comprising pluralities of coils wound around an integral, planar, ring-shaped, magnetic core in different directions. However, winding coils around the integral, ring-shaped, magnetic core needs time-consuming work.
JP 2000-105285 A discloses a portable radiowave watch comprising a housing, a watch module disposed at a center of the housing, an external operation means for the module, a groove surrounding the module in the housing, and an antenna received in the groove. The antenna is constituted by a C-type magnetic core and a coil wound around the magnetic core. However, the antenna of this structure has strong directivity.
JP 2005-102023 A discloses a receiving antenna structure disposed in a metal casing, which comprises a main magnetic path member comprising coils wound around a magnetic core, a sub-magnetic path member comprising a coil-free magnetic core, and a gap in a closed magnetic path along the magnetic core, thereby preventing magnetic flux from leaking outside during resonance. However, this antenna also has strong directivity.
Accordingly, an object of the present invention is to provide a small, omnidirectional, resonance-type, receiving antenna suitable for being arranged in narrow space in radiowave wristwatches, keyless entry systems, RFID systems, etc.
Another object of the present invention is to provide a receiving apparatus comprising such a resonance-type, receiving antenna.
The first resonance-type, receiving antenna of the present invention comprises a circular-ring-shaped, magnetic core constituting a closed magnetic path having one gap, a coil wound around the circular-ring-shaped, magnetic core, and a capacitor connected in parallel to both ends of the coil; an angle between a straight line extending from a geographical center of the circular-ring-shaped, magnetic core to a center of the gap and a straight line extending from the geographical center to a center of the coil being in a range of 10° to 90°.
The second resonance-type, receiving antenna of the present invention comprises a circular-ring-shaped, magnetic core constituting a closed magnetic path having one gap, two coils wound around the circular-ring-shaped, magnetic core, and a capacitor connected in parallel to both ends of each coil; an angle between a straight line extending from a geographical center of the circular-ring-shaped, magnetic core to a center of the gap and a straight line extending from the geographical center to a center of each coil being in a range of 10° to 90°.
In the first and second resonance-type, receiving antennas, the circular-ring-shaped, magnetic core preferably has a ratio of the longest diameter to the shortest diameter in a range of 1-2.
The third resonance-type, receiving antenna of the present invention comprises a rectangular-ring-shaped, magnetic core constituting a closed magnetic path having one gap, two coils wound around the rectangular-ring-shaped, magnetic core, and a capacitor connected in parallel to both ends of each coil; the axial directions of the two coils being perpendicular to each other; and the distances between the coils and the gap being different.
The fourth resonance-type, receiving antenna of the present invention comprises a circular-ring-shaped, magnetic core constituting a closed magnetic path having two or three gaps, two coils wound around the circular-ring-shaped, magnetic core, and a capacitor connected in parallel to both ends of each coil; an angle between a straight line extending from a geographical center of the circular-ring-shaped, magnetic core to a center of one gap and a straight line extending from the geographical center to a center of each coil being in a range of 10° to 90°.
The fifth resonance-type, receiving antenna of the present invention comprises a rectangular-ring-shaped, magnetic core comprising a closed magnetic path having two or three gaps, two coils wound around the rectangular-ring-shaped, magnetic core, and a capacitor connected in parallel to both ends of each coil; the axial directions of the two coils being perpendicular to each other.
To detect a magnetic flux generated in a Z-axis direction from the magnetic core of the resonance-type, receiving antenna of the present invention, a coreless coil or a coil wound around a ferrite core may be disposed as an additional coil.
In any of the above resonance-type, receiving antennas, the magnetic core is preferably obtained by laminating ribbons of a soft-magnetic, amorphous or nano-crystalline alloy, or by bundling thin wires of a soft-magnetic, amorphous or nano-crystalline alloy.
The receiving apparatus of the present invention comprises the above resonance-type, receiving antenna, and circuit devices disposed inside the resonance-type, receiving antenna.
a) is a schematic view showing a resonance-type, receiving antenna according to a further embodiment of the present invention.
b) is a schematic view showing a resonance-type, receiving antenna according to a still further embodiment of the present invention.
c) is a schematic view showing a resonance-type, receiving antenna according to a still further embodiment of the present invention.
a) is a schematic view showing a resonance-type, receiving antenna according to a still further embodiment of the present invention.
b) is a schematic view showing a resonance-type, receiving antenna according to a still further embodiment of the present invention.
c) is a schematic view showing a resonance-type, receiving antenna according to a still further embodiment of the present invention.
a) is a schematic view showing a resonance-type, receiving antenna according to a still further embodiment of the present invention.
b) is a schematic view showing a resonance-type, receiving antenna according to a still further embodiment of the present invention.
c) is a schematic view showing a resonance-type, receiving antenna according to a still further embodiment of the present invention.
a) is a schematic view showing one example of radiowave wristwatches comprising the resonance-type, receiving antenna of the present invention.
b) is a schematic view showing another example of radiowave wristwatches comprising the resonance-type, receiving antenna of the present invention.
a) is a schematic view showing one example of RFID systems comprising the resonance-type, receiving antenna of the present invention.
b) is a schematic view showing another example of RFID systems comprising the resonance-type, receiving antenna of the present invention.
The first resonance-type, receiving antenna of the present invention comprises a circular-ring-shaped, magnetic core 1 constituting a closed magnetic path having one gap 4, a coil 2 wound around the circular-ring-shaped, magnetic core 1, and a capacitor connected in parallel to both ends of the coil 2; an angle θ between a straight line (outer diameter) R4 extending from a geographical center O of the circular-ring-shaped, magnetic core 1 to a center of the gap 4 and a straight line (outer diameter) R2 extending from the geographical center O to the center of the coil 2 being in a range of 10° to 90°.
The second resonance-type, receiving antenna of the present invention comprises a circular-ring-shaped, magnetic core 1 constituting a closed magnetic path having one gap 4, two coils 2a, 2b wound around the circular-ring-shaped, magnetic core 1, and a capacitor connected in parallel to both ends of each coil 2a, 2b; angles θa, θb between a straight line (outer diameter) R4 extending from a geographical center O of the circular-ring-shaped, magnetic core 1 to a center of the gap 4 and straight lines (outer diameters) R2a, R2b extending from the geographical center O to the centers of the coils 2a, 2b being respectively in a range of 10° to 90°.
In the first and second resonance-type, receiving antennas, a Dmax/Dmin ratio of the longest diameter Dmax to the shortest diameter Dmin of the circular-ring-shaped, magnetic core 1 is preferably in a range of 1-2.
The third resonance-type, receiving antenna of the present invention comprises a rectangular-ring-shaped, magnetic core 1 constituting a closed magnetic path having one gap 4, two coils 2a, 2b wound around the rectangular-ring-shaped, magnetic core 1, and a capacitor connected in parallel to both ends of each coil 2a, 2b; the axial directions of the two coils 2a, 2b being perpendicular to each other; and distances between the coils 2a, 2b and the gap 4 being different.
The fourth resonance-type, receiving antenna of the present invention comprises a circular-ring-shaped, magnetic core 1 constituting a closed magnetic path having two or three gaps 4a, 4b, two coils 2a, 2b wound around the circular-ring-shaped, magnetic core 1, and a capacitor connected in parallel to both ends of each coil 2a, 2b; an angle θa, θb between a straight line (outer diameter) R4 extending from a geographical center O of the circular-ring-shaped, magnetic core to a center of the gap 4 and a straight line (outer diameter) R2a, R2b extending from the geographical center O to a center of each coil 2a, 2b being in a range of 10° to 90°.
The fifth resonance-type, receiving antenna of the present invention comprises a rectangular-ring-shaped, magnetic core 1 constituting a closed magnetic path having two or three gaps 4a, 4b (4c), two coils 2a, 2b wound around the rectangular-ring-shaped, magnetic core 1, and a capacitor connected in parallel to both ends of each coil 2a, 2b; the axial directions of the two coils 2a, 2b being perpendicular to each other.
The receiving apparatus of the present invention comprises any one of the above resonance-type, receiving antennas, and circuit devices arranged inside the resonance-type, receiving antenna.
(1) Magnetic Core
The receiving antenna of the present invention comprises a ring-shaped, magnetic core having a gap or gaps. The term “circular-ring-shaped” used with respect to the shape of the magnetic core is not restricted to a true circle, but includes a deformed circle (for example, an egg shape, an ellipsoid, and an elongated circle) as long as it does not have corners. The term “rectangular-ring-shaped” generally means an outer shape of a square or a rectangle, but its corners need not be 90°, but may be properly rounded.
The magnetic core may be a combination of a C-type magnetic core, an I-type magnetic core, a U-type magnetic core, etc. Although the optimum gap width may differ depending on the permeability and required characteristics of a magnetic material used for the magnetic core, a smaller gap width is better when high-permeability, amorphous alloy ribbons, etc. are used. Specifically, the gap width is preferably in a range of 0.1-3 mm. The gap may be disposed in any portion of the magnetic core, and a gap 4a may be formed, for instance, by disposing an end surface of one magnetic core piece 1a close to a side surface of another magnetic core piece 1c as shown in
In the case of the circular-ring-shaped, magnetic core, a ratio of Dmax/Dmin, wherein Dmax is the longest diameter, and Dmin is the shortest diameter, is preferably in a range of 1-2. The circular-ring-shaped, magnetic core with Dmax/Dmin near 1 detects high voltage. When the Dmax/Dmin is more than 2, the detected voltage is extremely low, failing to obtain sufficient detection sensitivity. The Dmax/Dmin is more preferably 1-1.6.
The magnetic core can be formed by soft-magnetic ferrite, amorphous alloys, nano-crystalline alloys, etc., and are preferably obtained by laminating ribbons of soft-magnetic, amorphous alloys or nano-crystalline alloys, or by bundling thin wires of soft-magnetic, amorphous alloys or nano-crystalline alloys. Particularly amorphous alloys have such a wide resilient deformation range that a gap of their magnetic core can be expanded to insert a coil, and that their magnetic core can be easily arranged along an inner wall of the casing. Further, because the amorphous alloys have excellent impact resistance, they are not broken by impact by dropping, etc., suitable for mobile gears such as radiowave wristwatches, keyless entry systems, etc.
The preferred composition of the amorphous alloy is represented by the general formula of (Fe1-aTa)balSixByMz, wherein T is Co and/or Ni, M is at least one element selected from the group consisting of V, Mn, Nb, Ta, Cr, Mo and W, and a, x, y and z are atomic %, meeting the conditions of 1≦a≦0, 1≦x≦18, 5≦y≦17, 0≦z≦5, and 17≦x+y+z≦25.
Silicon Si makes the amorphous alloy less brittle, so that amorphous alloy ribbons can be easily produced. To obtain this effect, Si is preferably 1 atomic % or more. To improve the soft magnetic properties (particularly to decrease the residual magnetic flux density), Si is preferably 18 atomic % or less. 5 atomic % or more of boron B is effective to form amorphous alloys. To obtain the preferred soft magnetic properties, B is preferably 17 atomic % or less.
Cobalt (Co) and nickel (Ni) are effective to improve the saturation magnetic flux density, and particularly Co has excellent corrosion resistance. To obtain effective antenna characteristics with small space, Co- or Ni-based alloy compositions are preferable. Fe-based alloys need resin coatings, etc. for rust prevention.
(2) Coil
Though not restrictive, the number of coils wound around the magnetic core is preferably 1-2. When a circular-ring-shaped, magnetic core is provided with one or two coils, an angle θ between a straight line R4 extending from a geographical center O of the circular-ring-shaped, magnetic core to a center of the gap 4 and a straight line R2 extending from the geographical center O to a center of each coil 2 should be in a range of 10° to 90°. When the angle θ is less than 10°, the detection sensitivity remarkably decreases to an undesirable level. When the angle θ exceeds 90°, the directivity becomes undesirably strong. It has been found that although two perpendicular coils seems to provide the magneto-sensitive axis directions with 90° difference, the influence of the gap 4 makes an angle between the axial directions of two coils different from an angle between the magneto-sensitive axes.
As shown in
The receiving antenna of the present invention preferably comprises an additional coil (Z-axis coil) in parallel to the ring-shaped, magnetic core 1, to detect a magnetic flux in the Z-axis direction (axial direction) of the ring-shaped, magnetic core 1. With the Z-axis coil, a magnetic flux in the Z-axis direction can be detected, in addition to magnetic fluxes in the X- and Y-axis directions which are detected by the coil 2 wound around the ring-shaped, magnetic core 1, resulting in high detection sensitivity in all directions. Because a larger area inside the Z-axis coil provides higher detection sensitivity in the Z-axis direction, the Z-axis coil is arranged preferably between an inner surface of the casing and an outer periphery of the circuit device. Though the Z-axis coil may be coreless, it may have a magnetic core. It is preferable to use a circuit capable of detecting voltages QV by the X-axis coil, the Y-axis coil and Z-axis coil and selecting the highest voltage.
[4] Receiving Apparatus
To be free from the influence of incoming radiowaves, the receiving apparatus of the present invention preferably comprises circuit devices (capacitors, batteries, resistors, etc.) arranged inside the magnetic core. This structure provides the receiving apparatus with higher detection sensitivity of radiowaves. In this case, the ring-shaped, magnetic core is preferably constituted by soft-magnetic ribbons or soft-magnetic, thin wires for miniaturization and higher impact resistance. In the case of a radiowave watch, for example, improved receiving sensitivity is obtained by arranging the circular-ring-shaped, magnetic core along an inner surface of the casing.
Because a capacitor is connected in parallel to a coil wound around the magnetic core in the receiving antenna of the present invention, magnetic flux generated by resonance current does not substantially penetrate the metal casing, resulting in less eddy current generated in the metal casing, and higher antenna sensitivity.
The present invention will be explained specifically referring to Examples below without intention of restriction.
The circular-ring-shaped, magnetic core 1 was formed by laminating 10 ribbons of a Co-based, amorphous alloy (ACO5) having a width of 1 mm and a thickness of 22 μm, which was coated with a 2-μm-thick epoxy resin, winding the resultant laminate to have a gap 4 of 1 mm and a diameter of 40 mm, and integrally heat-curing the epoxy resin. The above Co-based, amorphous alloy is ACO5 available from Hitachi Metals, Ltd. A peripheral surface of the circular-ring-shaped, magnetic core 1 was supported by a bobbin (not shown). The coil 2 was formed by winding a 0.1-mm-thick magnet wire (enameled wire) to 1000 turns around a core of 1 mm in width and 250 μm in thickness, and removing the core. The coil 2 was connected in parallel to the capacitor 3 to constitute a resonance circuit.
In Example 1, the gap 4 was resiliently expanded to insert the circular-ring-shaped, magnetic core 1 into the coil 2, and fixed by an epoxy adhesive at an angle θ of 30°. In Comparative Example 1, the angle θ between the coil 2 and the gap 4 was 180° as shown in
With respect to the antennas of Example 1 (θ=30°) and Comparative Example 1 (θ=180°), the magnetic-flux-detecting sensitivity in all directions) (360° was measured in an XY plane, whose origin was the geographical center O of the circular-ring-shaped, magnetic core 1, and the results are shown in
In the antenna of Comparative Example 1, the detection sensitivity of the coil 2 was about 5 mV, maximum, in axial directions (directions perpendicular to a radius of the circular-ring-shaped, magnetic core 1 passing the center of the coil 2, 90° and 270°), and substantially 0 mV, minimum, in directions (0° and 180°) perpendicular to the axial directions. Namely, the antenna clearly had directivity. In the antenna of Example 1, however, the detection sensitivity of the coil 2 was about 1.2 mV, minimum, in directions (45° and 225°) deviated by 15° from directions perpendicular to the axial directions, and about 5.2 mV, maximum, at angles (135° and 315°) deviated by 15° from the axial directions (120° and 300°). Thus, the voltage was at the maximum in directions deviated by 15° from the axial directions of the coil 2 in Example 1. A ratio (minimum voltage/maximum voltage) of the minimum voltage to the maximum voltage was 0% (0/5) in Comparative Example 1, and 23% (1.2/5.2×100) in Example 1.
With respect to the same antenna as in Example 1 except for changing the angle θ of the coil 2, the magnetic-flux-detecting sensitivity was measured in all directions (360°) in an XY plane, whose origin was the geographical center θ of the circular-ring-shaped, magnetic core 1, to calculate the minimum voltage/the maximum voltage. The results are shown in Table 1. The (minimum voltage/maximum voltage) ratio exceeded 20% at an angle θ in a range of 10° to 90°, but as low as 12.3% or less outside this range.
(1)Vmin means the minimum voltage, and Vmax means the maximum voltage.
To increase detection sensitivity in directions perpendicular to the axial directions of the coil, a coil was added to the antenna of
the magnetic-flux-detecting sensitivity was measured in all directions) (360° in an XY plane, whose origin was the geographical center O of the circular-ring-shaped, magnetic core 1. The detection sensitivity of the coil 2a with θ=+30° was at least about 1.3 mV in directions (45° and 225°) deviated by 15° from directions perpendicular to the axial directions, and about 5.4 mV at maximum at angles (135° and 315°) deviated by 15° from the axial directions (120° and 300°). The (minimum voltage/maximum voltage) ratio of the coil 2a was 24% (1.3/5.4×100).
The detection sensitivity of the coil 2b with θ=−30° was at least about 1.2 mV in directions (135° and 315°) deviated by 15° from directions perpendicular to the axial directions, and about 5.4 mV at maximum at angles (45° and 225°) deviated by 15° from the axial directions (60° and 240°). The (minimum voltage/maximum voltage) ratio of the coil 2b was 22% (1.2/5.4×100).
The circular-ring-shaped, magnetic core 1 of Example 3 was deformed such that an outer diameter R4 of the circular-ring-shaped, magnetic core 1 passing through a center of the gap 4 was the longest diameter Dmax, and that an outer diameter perpendicular to R4 was the shortest diameter Dmin, to examine the change of antenna directivity with the Dmax/Dmin ratio. Although the detected maximum voltage was 90% or more of Example 2 at the Dmax/Dmin of 2 or less, it was reduced to 80% or less of Example 2 when the Dmax/Dmin exceeded 2. Oppositely, even when the circular-ring-shaped, magnetic core 1 was deformed with R4 as Dmin, and an outer diameter perpendicular to R4 as Dmax, the same tendency was appreciated. The same tendency was appreciated also in the circular-ring-shaped, magnetic core 1 of Example 1. Accordingly, the Dmax/Dmin ratio is preferably in a range of 1-2.
a)-4(c) show an example of rectangular-ring-shaped, resonance-type, receiving antennas of the present invention. A rectangular-ring-shaped, magnetic core 1 was formed by punching a ribbon of 50 mm in width and 22 μm in thickness made of the same Co-based, amorphous alloy (ACO5) as in Example 1 to form 10 rectangular-ring-shaped ribbon pieces of 15 mm×30 mm×1.5 mm (width), laminating them with a 2-μm-thick epoxy resin coating on each ribbon piece, and heat-curing the epoxy resin. A gap 4 was 1 mm.
In any examples shown in
With respect to the rectangular-ring-shaped, resonance-type, receiving antennas shown in
A conventional receiving antenna shown in
a) shows another example of circular-ring-shaped, resonance-type, receiving antennas of the present invention. This circular-ring-shaped, resonance-type, receiving antenna comprises a circular-ring-shaped, magnetic core 1 constituted by arcuate magnetic core pieces 1a, 1b for forming a closed magnetic path with two gaps 4a, 4b, and two coils 2a, 2b each wound around each magnetic core piece 1a, 1b, angles θa, θb between a straight line R4 extending from a geographical center O of the circular-ring-shaped, magnetic core 1 to a center of one gap 4a and straight lines R2a, R2b extending from the geographical center O to centers of two coils 2a, 2b being +30° and −30°, respectively. Accordingly, an angle (θ+θb) of the centers of two coils 2a, 2b relative to the geographical center O is 60°. Also, two gaps 4a, 4b were 180° relative to the geographical center O. A capacitor was connected in parallel to each coil 2a, 2b to constitute a resonance circuit.
The circular-ring-shaped, magnetic core 1 was formed by laminating five ribbons of 1 mm in width and 14 μm in thickness made of a Co-based, amorphous alloy (ACO5) and each coated with an epoxy resin in a thickness of 2 μm, winding them to have a diameter of 40 mm, and then heat-curing them. Each gap 4a, 4b was 1 mm. A periphery of the circular-ring-shaped, magnetic core 1 was supported by a bobbin (not shown).
Each coil 2a, 2b was produced by winding a 0.1-mm-thick magnet wire (enameled wire) by 1000 turns around a core of 2 mm in width and 1.5 mm in thickness, and removing the core. Each magnetic core piece 1a, 1b was inserted into each coil 2a, 2b, and fixed with an epoxy adhesive at such a position that the angles θa, θb were +30° and −30°, respectively.
With respect to this antenna, the detection sensitivity of a magnetic flux was measured in all directions (360°) in an XY plane whose origin was a geographical center O of the circular-ring-shaped, magnetic core 1. The results are shown in
b) and 8(c) show modified examples of the antenna of
When the circular-ring-shaped, magnetic core 1 shown in
a) shows a further example of rectangular-ring-shaped, resonance-type, receiving antennas. The rectangular-ring-shaped, magnetic core 1 is constituted by an L-shaped, magnetic core piece 1a of 20 mm in each outer side and 1.5 mm in width, an I-shaped, magnetic core piece 1b of 22 mm in length and 1.5 mm in width, and an I-shaped, magnetic core piece 1c of 19 mm in length and 1.5 mm in width. Each magnetic core piece was produced by punching a 14-μm-thick ribbon made of the same Co-based, amorphous alloy (ACO5) as in Example 1 to obtain 10 ribbon pieces, laminating them with a 2-μm-thick epoxy resin coating on each ribbon piece, and heat-curing them. Gaps 4a, 4b were 0.5 mm, and a gap 4c was 1.5 mm.
Each coil 2a, 2b was produced by winding a 0.1-mm-thick magnet wire (enameled wire) by 100 turns around a core of 2 mm in width and 300 μm in thickness, and then removing the core. The coil 2a was mounted to the I-shaped magnetic core piece 1b, and the coil 2b was mounted to the I-shaped magnetic core piece 1c. The axial directions of both coils 2a, 2b were perpendicular to each other. The distance between the coil 2a and the gap 4b was the same as the distance between the coil 2b and the gap 4a. A capacitor was connected in parallel to each coil 2a, 2b to constitute a resonance circuit.
The detection sensitivity of a magnetic flux was measured in all directions (360°) in an XY plane whose origin was the geographical center O of the rectangular-ring-shaped, magnetic core 1, in the same manner as in Example 1. The results are shown in
The resonance-type, receiving antenna shown in
a) and 12(b) schematically show examples of radiowave wristwatches containing the receiving antenna 10 of the present invention.
The conventional receiving antenna has a complicated structure comprising members such as a bobbin fixed to a circuit board, etc., and their arrangement needs time-consuming work such as complicated fixing steps, for instance, welding, etc. On the other hand, the receiving antenna of the present invention having a simple structure can be easily arranged in the casing.
The circular-ring-shaped, magnetic core 1 was produced by laminating pluralities of ribbons of a Co-based, amorphous alloy (ACO5) each having a width of 1 mm, a thickness of 18 μm and a predetermined length and a 2-μm-thick epoxy resin coating to a desired shape, and heat-curing the epoxy resin.
The receiving antenna 10 with such structure can receive magnetic flux coming from outside the casing 21 substantially in all directions in an XY plane. In addition, because the additional coil 6 for receiving magnetic flux flowing in the axial direction (Z-axis direction) of the circular-ring-shaped, magnetic core 1 is disposed inside the circular-ring-shaped, magnetic core 1, radiowaves in all directions in XYZ axes can be received in the metal casing 21.
a) and 13(b) schematically show examples of key bodies for a keyless entry system, one of RFID tags containing the receiving antenna 10 of the present invention.
The substantially oval-shaped key body comprises a metal casing 74, a key-opening button 73, a printed circuit board 71 having various devices, and the receiving antenna 10. The receiving antenna 10 comprises a circular-ring-shaped, magnetic core 1 along an inner surface of the casing 74, two coils 2a, 2b disposed near the gap 4a(4) of the circular-ring-shaped, magnetic core 1, and capacitors 3a, 3b each connected to each coil 2a, 2b. The arrangement of the receiving antenna 10 along an inner surface of the casing 74 prevents the key body from becoming larger. Also arranged inside the circular-ring-shaped, magnetic core 1 are an additional coil 6, and a means (not shown) for measuring voltage induced by a magnetic flux passing through that coil.
The circular-ring-shaped, magnetic core 1 was produced by laminating pluralities of ribbons of a Co-based, amorphous alloy (ACO5) each having a width of 1 mm, a thickness of 18 μm and a predetermined length and a 2-μm-thick epoxy resin coating to a desired shape, and heat-curing the epoxy resin.
The receiving antenna 10 with such structure can receive magnetic flux coming from outside the casing 74 substantially in all directions in an XY plane. In addition, because the additional coil 6 for receiving magnetic flux flowing in the axial direction (Z-axis direction) of the circular-ring-shaped, magnetic core 1 is disposed inside the circular-ring-shaped, magnetic core 1, radiowaves in all directions in XYZ axes can be received in the metal casing 74.
The resonance-type, receiving antenna of the present invention comprising a circular- or rectangular-ring-shaped, magnetic core for forming a closed magnetic path having one gap has high detection sensitivity not only in the axial direction of the coil, but also in directions perpendicular to the axial direction.
With two coils, even one circular-ring-shaped, magnetic core provides an antenna with high detection sensitivity in all directions in an XY plane whose origin is a geographical center of the core. In the case of a rectangular-ring-shaped, magnetic core, the arrangement of two coils perpendicular to each other provides an antenna with high detection sensitivity in all directions in an XY plane.
The arrangement of circuit devices inside the circular-ring-shaped, magnetic core provides a receiving apparatus with less influence on the circuit devices by radiowaves, and with less noise even at high output voltage. The circular-ring-shaped, magnetic core made of high-strength, soft-magnetic materials such as ribbons or thin wires of soft-magnetic alloys is suitable for arrangement along an inner surface of the metal casing.
Less restricted by the shape of the casing, the resonance-type, receiving antenna of the present invention is suitable for small radiowave watches (particularly radiowave wristwatches) having various shapes for users' preference, keyless entry systems, RFID tag systems, etc.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-323826 | Dec 2008 | JP | national |
| 2009-081365 | Mar 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/070777 | 12/11/2009 | WO | 00 | 8/19/2011 |
