RF tag

Abstract

There is provided an RF tag that can be mounted in a cavity of a member formed of a conductor having the cavity therein, and has high communication performance. An RF tag 1 of the present invention is an RF tag that is mounted in a cavity 101 of a conductor-made member 100 having the cavity 101 therein, and includes at least a free space antenna 10, a resonance circuit 20, an IC chip 30, a closed space antenna 40, and a substrate 50 for supporting the closed space antenna, a portion of the free space antenna is exposed from the cavity to the outside, and the substrate supports the closed space antenna so that the closed space antenna is not in contact with the inner surface of the conductor-made member. The closed space antenna, the substrate and the conductor-made member forms a capacitor portion C2.

Claims

1. An RF tag that can be mounted in a cavity of a conductor-made member having the cavity therein including: at least a free space antenna; a resonance circuit; an IC chip; a closed space antenna; and a substrate for supporting the closed space antenna, wherein a part of the free space antenna is exposed from the cavity to an outside, and the substrate supports the closed space antenna so that the closed space antenna is not in contact with an inner surface of the conductor-made member.

2. The RF tag according to claim 1, wherein the free space antenna is a helical antenna.

3. The RF tag according to claim 1, wherein when a wavelength of a reception electric wave is , an electrical length of a portion of the free space antenna which is exposed to the outside is equal to /4.

4. The RF tag according to claim 1, further including a cap for covering the exposed portion of the free space antenna to the outside, wherein the cap is made of a material that transmits electric waves therethrough.

5. The RF tag according to claim 1, wherein the closed space antenna, the substrate, and the conductor-made member constitute a capacitor portion, and a resonance frequency is adjusted by adjusting a capacitance of the capacitor portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram showing the inside of a conductor-made member with an RF tag attached thereto.

(2) FIG. 2 is an enlarged view showing a structure of a free space antenna.

(3) FIG. 3 is a perspective view showing the conductor-made member with an RF tag attached thereto.

(4) FIG. 4 is an equivalent circuit diagram of the RF tag.

(5) FIG. 5 is a diagram schematically showing a reception state of electric waves and a capacitor portion.

(6) FIG. 6 is a diagram showing another configuration example of the RF tag.

DESCRIPTION OF EMBODIMENT

(7) An embodiment of an RF tag of the present invention will be described with reference to the drawings.

(8) As shown in FIGS. 1 to 3, an RF tag 1 is mounted in a cavity 101 of a conductor-made member 100 having the cavity 101 therein to perform various managements such as identification of the conductor-made member 100.

(9) In the present embodiment, it is assumed that a pipe made of metal is used as the conductor-made member 100 having the cavity 101 therein. The conductor-made member 100 may be a member having a cavity 101 therein, and the cross-sectional shape on a plane orthogonal to a longitudinal direction is not limited to a circle, but may be a polygon.

(10) The RF tag 1 is generally configured by a free space antenna 10, a resonance circuit 20, an IC chip 30, a closed space antenna 40, a substrate 50 and a cap 60. In FIG. 3, the cap 60 is omitted from the illustration.

(11) The free space antenna 10 is generally configured by first conductors 11 and second conductors 12.

(12) Two arrays of multiple through-holes 13 are provided along a front-and-rear direction on right and left sides on the substrate 50 to be spaced from each other at a regular interval.

(13) The first conductors connect the right and left through-holes 13 on the front surface side of the substrate 50 while inclined with respect to the right-and-left direction of the substrate 50.

(14) The second conductors connect the right and left through-holes 13 on the back surface side of the substrate 50 while inclined with respect to the right-and-left direction of the substrate 50.

(15) A coil having a predetermined length is configured as a whole by electrically connecting the first conductors 11 and the second conductors 12 via the through-holes 13.

(16) Lands 14 are provided in the vicinity of the through-holes 13 provided on the rear side of the substrate 50. The lands 14 are electrically connected to one another to be set as a jumper wire 15, which enables fine adjustment of the resonance frequency of the free space antenna 10.

(17) A portion of the free space antenna 10 is exposed to the outside from the cavity 101 of the conductor-made member 100, and the electrical length of the exposed portion is equal to one fourth of a use frequency .

(18) A helical antenna or a bar antenna may be also used as the free space antenna 10.

(19) The resonance circuit 20 and the IC chip 30 are formed on the surface of the substrate 50.

(20) FIG. 4 is an equivalent circuit diagram of the RF tag 1 of the present embodiment. Reference sign L represents a coil, and constitutes the resonance circuit 20 with a first capacitor C1. It is to be noted that the resonance circuit 20 may be constituted by using a capacitor in the IC chip 30 without providing the first capacitor C1.

(21) The IC chip 30 rectifies a part of a carrier wave W (see FIG. 5) transmitted from a reader/writer to generate a power supply voltage which is necessary for the IC chip 30 to operate. Then, a memory in which a logic circuit for control, etc. are stored, a communication circuit for transmitting/receiving data to/from the reader/writer, and the like in the IC chip 30 are operated with the generated power supply voltage. It is to be noted that an external power supply may be input to the IC chip 30 to operate the IC chip 30.

(22) The closed space antenna 40 extends in the front-and-rear direction on the substrate 50 while one end portion thereof is connected to the IC chip 30.

(23) The substrate 50 supports the closed space antenna 40 so that the closed space antenna 40 is not in contact with the inner surface of the conductor-made member 100.

(24) As shown in FIG. 5, the closed space antenna 40, the substrate 50, and the conductor-made member 100 constitute a second capacitor C2. As a result, the closed space antenna 40 and the conductor-made member 100 are electrically connected to each other, so that the entire conductor-made member 100 can be used as an antenna. Furthermore, the capacitance of the second capacitor C2 can be adjusted by changing the length of the closed space antenna 40, whereby the resonance frequency can be adjusted.

(25) It is to be noted that the closed space antenna 40 may be configured in a meandering shape or a coil-like shape in addition to a rod-like shape.

(26) Furthermore, as shown in FIG. 6, a spacer 16 may be interposed between the substrate 50 and the inner surface of the conductor-made member 100 so as to prevent the closed space antenna 40 from being in contact with the inner surface of the conductor-made member 100.

(27) The cap 60 is a member for covering a portion of the free space antenna 10 which is exposed to the outside, and is made of a material for transmitting electric waves therethrough. By using the cap 60, the RF tag 1 can obtain waterproof/dustproof performance.

(28) In the present embodiment, the RF tag 1 itself is fixed to the conductor-made member 100 by fixing the substrate 50 to the inside of the cap 60 and fixing the cap 60 to the conductor-made member 100. It is to be noted that the RF tag 1 itself may be fixed to the conductor-made member 100 by fixing the side surface of the free space substrate 50 to the inner surface of the conductor-made member 100.

INDUSTRIAL APPLICABILITY

(29) The present invention relates to an RF tag that can be mounted in a cavity of a member made of a conductor having the cavity therein and has a high communication performance, and has an industrial applicability.

REFERENCE SIGNS LIST

(30) C1 first capacitor C2 second capacitor L coil W carrier wave 1 RF tag 10 free space antenna 11 first conductor 12 second conductor 13 through-hole 14 land 15 jumper wire 16 spacer 20 resonance circuit 30 IC chip 40 closed space antenna 50 substrate 60 cap 101 cavity 100 conductor-made member