Source: https://patents.google.com/patent/US7570225B2/en
Timestamp: 2020-02-19 04:29:14
Document Index: 646935152

Matched Legal Cases: ['§111', 'art 82', 'art 12', 'art 12', 'art 12', 'art 32', 'art 32', 'art 32', 'art 42', 'art.\n7', 'art.\n12', 'Application No. 2006', 'Application No. 04806971']

US7570225B2 - Antenna and non-contact tag - Google Patents
Antenna and non-contact tag Download PDF
US7570225B2
US7570225B2 US11/790,580 US79058007A US7570225B2 US 7570225 B2 US7570225 B2 US 7570225B2 US 79058007 A US79058007 A US 79058007A US 7570225 B2 US7570225 B2 US 7570225B2
US11/790,580
US20070200711A1 (en
2007-04-26 Assigned to FUJITSU LIMITED reassignment FUJITSU LIMITED ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KAI, MANABU, MANIWA, TORU, YAMAGAJO, TAKASHI
2007-08-30 Publication of US20070200711A1 publication Critical patent/US20070200711A1/en
2009-08-04 Publication of US7570225B2 publication Critical patent/US7570225B2/en
An RFID antenna that can be disposed in a space-saving manner. The RFID antenna comprises an outermost peripheral conductive line that is bent in a manner extending along sides of a generally rectangular shape having a predetermined size, and a power-feeding conductive line that is disposed close to an inner periphery of the outermost peripheral conductive line in a manner extending parallel therewith, and is electrically connected to the outermost peripheral conductive line at ends thereof, the power-feeding conductive line including a portion thereof formed with a feeder part. Therefore, the antenna fits into a rectangle having a predetermined size, such as a card size.
This application is a continuing application, filed under 35 U.S.C. §111(a), of International Application PCT/JP2004/018610, filed Dec. 14, 2004.
An RFID system in which non-contact tags (hereinafter referred to as “the RFID tags”) having identification information embedded therein are attached to respective articles or persons, thereby enabling transmission/reception of information between the persons or the articles and RFID reader/writers (hereinafter simply referred to as “the reader/writers”) using a radio signal, is expected to be applied to various fields, such as management of factory production, management of physical distribution, and management of room entrance/exit, and is coming into practical use.
The method of communication therefore is classified into an electromagnetic induction method and a radio-frequency method. The electromagnetic induction method mainly uses electromagnetic waves of 135 kHz or 13.56 MHz, and transmits/receives information by induced voltage caused between the antenna of an RFID tag and the antenna coil of an RFID reader/writer. The communication distance is limited to the maximum of approximately 1 m.
By the way, the radiation resistance of a single dipole antenna is approximately 72 Ω, and hence it is required to increase the radiation resistance so as to achieve impedance matching with an IC chip of the above-mentioned type.
FIG. 15 is a view of the arrangement of the folded antenna.
The illustrated conventional folded antenna 80 comprises two dipole antennas 81 a and 81 b each having a length of approximately 150 mm and arranged close to each other in parallel, with a spacing of e.g. 10 mm therebetween. The dipole antenna 81 a and the dipole antenna 81 b are connected to each other at opposite ends thereof, and electric power is fed via a feeder part 82 formed in the center of the dipole antenna 81 a. With this arrangement, the radiation resistance R2 appearing in FIG. 14 can be made more than four times larger than the radiation resistance (72 Ω) of a single dipole antenna. Further, by changing the ratio of the line width of the dipole antenna 81 b to that of the dipole antenna 81 a as shown in FIG. 15, it is possible to adjust the radiation resistance such that it is increased to approximately 1000 Ω (see e.g. “Antenna Technology Handbook” (Ohmsha Ltd.), the Institute of Electronics, Information and Communication Engineers (IEICE), October, 1980, pp. 112-115).
However, although it is desirable for practical use that an RFID tag has a size not larger than a card size (86 mm×54 mm), for example, the conventional folded antenna requires a length of a longitudinal side thereof of approximately 150 mm for receiving a radio signal in the UHF band. The length is too large for practical use.
To accomplish the above object, the present invention provides an antenna for RFID. This antenna comprises an outermost peripheral conductive line that is bent in a manner extending along sides of a generally rectangular shape having a predetermined size, and a power-feeding conductive line that is disposed close to an inner periphery of said outermost peripheral conductive line in a manner extending parallel therewith, and is electrically connected to said outermost peripheral conductive line at ends thereof, said power-feeding conductive line including a portion formed with a feeder part.
FIG. 2 is a view of the arrangement of an RFID tag to which is applied the antenna according to the first embodiment.
FIG. 5 is a diagram showing calculated values of a reflection coefficient between an antenna and an IC chip. The abscissa represents frequency.
FIG. 6 is a diagram showing a radiation pattern of the antenna according to the first embodiment.
FIG. 7 is a view of the arrangement of an RFID antenna according to a second embodiment.
FIG. 9 is a diagram illustrating a result of an electromagnetic field simulation, which shows the relationship between the length of an inductor and the value of inductance.
FIG. 10 is a diagram showing calculated values of a reflection coefficient between an antenna and an IC chip. The abscissa represents frequency.
FIG. 11 is a diagram showing a radiation pattern of the antenna according to the second embodiment.
FIG. 13 is a view showing a case where some of bent portions of the antenna according to the first embodiment are formed in a curved manner.
FIG. 14 is a view of an equivalent circuit of an RFID tag.
FIG. 15 is a view of the arrangement of a folded antenna.
The antenna 10 according to the first embodiment is formed by bending the folded antenna, shown in FIG. 15, into a rectangular shape, and comprises an outmost peripheral conductive line (hereinafter simply referred to as the outermost peripheral line) 11 bent in a manner extending along the sides of a rectangle having a size of approximately 72 mm×42 mm, for example, and a power-feeding conductive line (hereinafter simply referred to as the feeder line) 13 disposed close to the inner periphery of the outermost peripheral line 11 in a manner extending parallel therewith. The feeder line 13 is electrically connected to the outermost peripheral line 11 at ends thereof, and includes a portion formed with a feeder part 12. In the antenna 10 according to the first embodiment, the outermost peripheral line 11 and the feeder line 13 are formed in a manner extending bilaterally symmetrically with respect to the feeder part 12.
Further, the antenna 10 has an impedance-adjusting inductor 14 for performing impedance matching with an IC chip (not shown) connected to the feeder part 12. The inductor 14 is disposed in an area inside the rectangle. In the first embodiment, the inductor 14 has two bent portions, and is connected to one side of a rectangular shape into which the feeder line 13 is bent.
An antenna for receiving an electromagnetic wave of a predetermined frequency basically needs to have a length of a half wavelength λ/2. Therefore, in order to receive an electromagnetic wave of 953 MHz, an antenna needs to have a length of approximately 150 mm. In the case of the antenna 10, the outermost peripheral line 11 is formed to have a length large enough to receive the electromagnetic wave of 953 MHz. However, when the line is bent into a rectangular shape as shown in FIG. 1, it is actually required to have a length larger than 150 mm so as to cause resonance. For this reason, lines 11 a for adjusting the length are added to the outermost peripheral line 11. It should be noted that the lines 11 a may be formed by extending the outermost peripheral line 11 and the feeder line 13 in parallel similarly to the other part of the antenna 10 (in this case, however, the feeder line 13 is required to be connected to the outermost peripheral line 11 at ends thereof).
By configuring the antenna 10 as described above, it is possible to reduce the size of the folded antenna capable of obtaining a high radiation resistance e.g. to a card size (86 mm×54 mm).
The antenna 10 has a size of approximately 72 mm×42 mm and a thickness of approximately 0.02 mm, for example. The sheet 21 is formed e.g. of paper or PET (polyethylene terephthalate) film. The sheet 21 has a size of approximately 86 mm×54 mm and a thickness of approximately 0.1 mm, for example.
The IC chip 22 has a size of approximately 1 mm×1 mm and a thickness of approximately 0.2 mm, for example.
When frequency f=953 MHz holds, the reflection coefficient S11 is below −20 dB, which shows that the impedance matching is sufficiently achieved.
Similarly to the antenna according to the first embodiment, the antenna 30 according to the second embodiment comprises an outermost peripheral line 31 that is bent in a manner extending along the sides of a rectangle having a size of approximately 72 mm×42 mm, for example, and a feeder line 33 that is disposed close to the inner periphery of the outermost peripheral line 31 in a manner extending parallel therewith, and is electrically connected to the outermost peripheral line 31 at ends thereof, the feeder line 33 including a portion formed with a feeder part 32. However, the antenna 30 according to the second embodiment is different from the antenna 10 according to the first embodiment in that the outermost peripheral line 31 and the feeder line 33 are formed in a manner extending bilaterally asymmetrically with respect to the feeder part 32.
Further, the antenna 30 has an impedance-adjusting inductor 34 for performing impedance matching with an IC chip (not shown) connected to the feeder part 32. The inductor 34 is disposed in an area inside the rectangle. In the antenna 30 according to the second embodiment, the inductor 34 has a single bent portion, and is connected to two of the sides of a rectangular shape into which the feeder line 33 is bent. Compared with the inductor 14 of the antenna 10 according to the first embodiment, the inductor 34 has only one bent portion, so as to reduce loss due to current concentration.
In the antenna 30 according to the second embodiment as well, lines 31 a for adjusting length are added to the outermost peripheral line 31. Although the lines 31 a are formed as solid traces each having a width obtained e.g. by adding together the line widths of the outermost peripheral line 31 and the feeder line 33 and the width of a space between the lines 31 and 33, so as to increase the antenna area, the lines 31 a may be formed by extending the outermost peripheral line 31 and the feeder line 33 in parallel similarly to the other part of the antenna 30 (in this case, however, the feeder line 33 is required to be connected to the outermost peripheral line 31 at ends thereof).
For example, assuming that the resistance is 1000 Ω and the capacitance is 0.9 pF in the equivalent circuit of the IC chip 22 (see FIG. 14), it is required to set the radiation resistance Rr2 of the antenna 30 to 1000 Ω and the inductance value Lp2 to 31 nH so as to achieve impedance matching. Therefore, as can be understood from FIGS. 8 and 9, by selecting the line width w2 of the outermost peripheral line 31 as approximately 2 mm, and the length d2 of the inductor 34 as approximately 14.5 mm, the impedance matching between the IC chip 22 and the antenna 30 is achieved, whereby power received by the antenna 30 is sufficiently supplied to the IC chip 22. The reflection coefficient between the antenna and the IC chip at this time is as follows:
Similarly to the case of the antenna 10 according to the first embodiment, when frequency f=953 MHz holds, the reflection coefficient S11 is below −20 dB, which shows that the impedance matching is sufficiently achieved.
Although in the above-described first and second embodiments, the description is given of the antennas 10 and 30 which can be received within the card size (86 mm×54 mm), it is possible to further reduce the antenna size.
The antenna 40 according to the third embodiment comprises an outermost peripheral line 41 that is bent in a manner extending along the sides of a rectangle having a size of approximately 42 mm×42 mm, for example, and a feeder line 43 that is disposed close to the inner periphery of the outermost peripheral line 41 in a manner extending parallel therewith, and is electrically connected to the outermost peripheral line 41 at ends thereof, the feeder line 43 including a portion formed with a feeder part 42. If the size of the antenna is reduced as in the case of the antenna 40 according to the third embodiment, the outermost peripheral line 41 suffers from a length shortage by which the outer periphery of the rectangle having a size of 42 mm×42 mm, for example, is short of a length required for receiving radio waves of 953 MHz, and hence a length corresponding to the shortage is formed by bending the outermost peripheral line 41 into the inside of the rectangle, as illustrated by lines 41 a.
1. An antenna for RFID, comprising:
an outermost peripheral conductive line that is bent in a manner extending along sides of a generally rectangular shape having a predetermined size; and
a power-feeding conductive line that is disposed close to an inner periphery of said outermost peripheral conductive line in a manner extending parallel therewith, and is electrically connected to said outermost peripheral conductive line at ends thereof, said power-feeding conductive line including a portion formed with a feeder part, wherein a ratio between a line width of the power-feeding conductive line and a line width of the outermost peripheral conductive line is adjusted, such that radiation resistance is adjusted as desired.
2. The antenna according to claim 1, wherein said outermost peripheral conductive line is formed to have a sufficient length for receiving radio waves in a UHF band.
3. The antenna according to claim 1, wherein an impedance-adjusting inductor for performing impedance matching with an IC chip connected to said feeder part is disposed in an area inside the generally rectangular shape.
4. The antenna according to claim 3, wherein a bent portion of said inductor is bent in a curved manner.
5. The antenna according to claim 3, wherein said inductor is linearly connected to two opposite sides of a generally rectangular shape into which said power-feeding conductive line is bent.
6. The antenna according to claim 1, wherein said outermost peripheral conductive line and said power-feeding conductive line are formed asymmetrically with respect to said feeder part.
7. The antenna according to claim 1, wherein a portion of said outermost peripheral conductive line is formed by being bent into an inside of the generally rectangular shape, said portion having a length by which an outer periphery of the generally rectangular shape thereof is short of a length required for receiving electromagnetic waves of a predetermined frequency.
8. The antenna according to claim 1, wherein said outermost peripheral conductive line or said power-feeding conductive line has bent portions thereof bent at an angle of 90 degrees.
9. The antenna according to claim 1, wherein said outermost peripheral conductive line or said power-feeding conductive line has bent portions thereof bent in a curved manner.
10. An antenna for RFID, comprising:
an outermost peripheral conductive line that is bent in a manner extending along sides of a generally rectangular shape having a predetermined size;
a power-feeding conductive line that is disposed close to an inner periphery of said outermost peripheral conductive line in a manner extending parallel therewith, and is electrically connected to said outermost peripheral conductive line at ends thereof, said power-feeding conductive line including a portion formed with a feeder part; and
an impedance-adjusting inductor for performing impedance matching with an IC chip connected to said feeder part, wherein the impedance-adjusting inductor is disposed in an area inside the generally rectangular shape surrounded by the outermost peripheral conductive line; wherein the power-feeding conductive line is bent in a manner extending along the inner peripheral of the outermost peripheral conductive line.
11. A non-contact tag for RFID, comprising:
an antenna including an outermost peripheral conductive line that is bent in a manner extending along sides of a generally rectangular shape having a predetermined size, and a power-feeding conductive line that is disposed close to an inner periphery of said outermost peripheral conductive line in a manner extending parallel therewith, and is electrically connected to said outermost peripheral conductive line at ends thereof, said power-feeding conductive line including a portion formed with a feeder part, wherein a ratio between a line width of the power-feeding conductive line and a line width of the outermost peripheral conductive line is adjusted, such that radiation resistance is adjusted as desired; and
an IC chip connected to said feeder part.
12. The antenna according to claim 10, wherein the impedance-adjusting inductor is disposed in the area surrounded by the power-feeding conductive line.
US11/790,580 2004-12-14 2007-04-26 Antenna and non-contact tag Active US7570225B2 (en)
PCT/JP2004/018610 Continuation WO2006064540A1 (en) 2004-12-14 2004-12-14 Antenna and noncontact tag
US20070200711A1 US20070200711A1 (en) 2007-08-30
US7570225B2 true US7570225B2 (en) 2009-08-04
US11/790,580 Active US7570225B2 (en) 2004-12-14 2007-04-26 Antenna and non-contact tag
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US9979426B2 (en) * 2016-01-27 2018-05-22 Lg Electronics Inc. Watch-type mobile terminal including antenna
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:KAI, MANABU;MANIWA, TORU;YAMAGAJO, TAKASHI;REEL/FRAME:019292/0084