Sensor tag and manufacturing method for sensor tag

• US 9,958,333 B2
• Filed: 08/11/2015
• Issued: 05/01/2018
• Est. Priority Date: 02/22/2013
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Ito, Yoshihiro
• Primary Examiner(s): Lau, Hoi
• Application Number:
  US14/823,594
• Publication Number:
  US 20150349400A1
• Time in Patent Office: 994 Days
• Field of Search: 3405721, 3405725, 3405727, 340 104, 340 101, 343702, 343741, 343870
• CPC Class Codes: G01K 1/024 for remote indication
• CPC Class Codes: G01K 7/32 using change of resonant frequency of a crystal
• CPC Class Codes: G06K 19/0672 with resonating marks
• CPC Class Codes: G06K 19/0717 the sensor being capable of sensing environmental conditions such as temperature history or pressure
• CPC Class Codes: H01Q 1/085 Flexible aerials; Whip aerials with a resilient base
• CPC Class Codes: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
• CPC Class Codes: H04Q 2209/47 using RFID associated with sensors
• CPC Class Codes: H04Q 9/00 Arrangements in telecontrol or telemetry systems for selectively calling a substation from a main station, in which substation desired apparatus is selected for applying a control signal thereto or for obtaining measured values therefrom
• CPC Class Codes: Y10T 29/4902 Electromagnet, transformer or inductor

Abstract

A sensor tag (10) includes a crystal vibrator (110) and an antenna (102). The antenna (102) is composed of a radiating conductor (121) and connection conductors (122). A crystal vibrator (110) is mounted on land conductors (120) provided at an end portion of the connection conductors (122) on the opposite side to the antenna (121). The antenna (102) is formed in a shape such that an amount of shift (ΔF) of a radiation frequency of the sensor tag (10) falls within an acceptable range in accordance with a resonant frequency (Fxs) and an equivalent inductance (Lxs) of the crystal vibrator (110) and a self-resonant frequency (Fant) and an equivalent inductance (Lant) of the antenna (102).

Claims

1. A sensor tag comprising:

a resonator having a resonant frequency corresponding to a sensed physical quantity; and

an antenna that radiates a signal generated by resonance of the resonator to the outside;

wherein the antenna is formed such that a resonant frequency ratio between the resonant frequency of the resonator and a self-resonant frequency of the antenna falls within a ratio range, the ratio range being selected based on an inductance ratio between an equivalent inductance of the resonator and an equivalent inductance of the antenna.

2. The sensor tag according to claim 1,

wherein the resonant frequency ratio is expressed by a function of the inductance ratio, and

the antenna is formed such that the resonant frequency ratio is equal to or less than a value obtained by inputting the inductance ratio into the function.

3. The sensor tag according to claim 1,

wherein the resonant frequency ratio is expressed by a function of the inductance ratio, and

the antenna is formed such that the resonant frequency ratio is equal to or more than a value obtained by inputting the inductance ratio into the function.

4. The sensor tag according to claim 2,

wherein the function is expressed by a quadratic function of the inductance ratio.

5. The sensor tag according to claim 2,

wherein a coefficient of the function is determined on the basis of an acceptable range of frequency shifting.

6. The sensor tag according to claim 1,

wherein the antenna includes a radiating conductor and a connection conductor connecting the radiating conductor and the resonator, and

a shape of the antenna is determined by a shape of the radiating conductor or the connection conductor.

7. The sensor tag according to claim 1,

wherein the resonator is a crystal vibrator.

9. The sensor tag according to claim 3,

wherein the function is expressed by a quadratic function of the inductance ratio.

10. The sensor tag according to claim 3,

wherein a coefficient of the function is determined on the basis of an acceptable range of frequency shifting.

11. The sensor tag according to claim 4,

wherein a coefficient of the function is determined on the basis of an acceptable range of frequency shifting.

12. The sensor tag according to claim 2,

wherein the antenna includes a radiating conductor and a connection conductor connecting the radiating conductor and the resonator, and

a shape of the antenna is determined by a shape of the radiating conductor or the connection conductor.

13. The sensor tag according to claim 3,

wherein the antenna includes a radiating conductor and a connection conductor connecting the radiating conductor and the resonator, and

a shape of the antenna is determined by a shape of the radiating conductor or the connection conductor.

14. The sensor tag according to claim 4,

wherein the antenna includes a radiating conductor and a connection conductor connecting the radiating conductor and the resonator, and

a shape of the antenna is determined by a shape of the radiating conductor or the connection conductor.

15. The sensor tag according to claim 5,

wherein the antenna includes a radiating conductor and a connection conductor connecting the radiating conductor and the resonator, and

a shape of the antenna is determined by a shape of the radiating conductor or the connection conductor.

16. The sensor tag according to claim 2,

wherein the resonator is a crystal vibrator.

17. The sensor tag according to claim 3,

wherein the resonator is a crystal vibrator.

18. The sensor tag according to claim 4,

wherein the resonator is a crystal vibrator.

19. The sensor tag according to claim 5,

wherein the resonator is a crystal vibrator.

20. The sensor tag according to claim 6,

wherein the resonator is a crystal vibrator.

8. A manufacturing method for a sensor tag including a resonator having a resonant frequency corresponding to a sensed physical quantity and an antenna that radiates a signal generated by resonance of the resonator to the outside, the manufacturing method comprising:

a step of preparing a plurality of antennas;

a step of measuring a self-resonant frequency and an equivalent inductance of each of the antennas;

a step of measuring a resonant frequency and an equivalent inductance of a crystal vibrator; and

a step of connecting one of the antennas to the crystal vibrator, the antenna being selected from the plurality of antennas such that a resonant frequency ratio between the resonant frequency of the resonator and the self-resonant frequency of the antenna falls within a ratio range, the ratio range being selected based on an inductance ratio between the equivalent inductance of the resonator and the equivalent inductance of the antenna.