JP2009130560A - Parasitic sensor with antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a parasitic sensor with an antenna capable of preventing sensitivity deterioration even though a metal body approaches in a parasitic sensor using an antenna. <P>SOLUTION: The parasitic sensor with an antenna is configured so as to have a vibration sensor element 31 in which impedance between two terminals changes due to the application of a vibration from the outside, and an antenna connected to the two terminals, to reflect an electromagnetic wave emitted from an interrogator installed at a separate place by the antenna and to detect vibrations that cause a change in the impedance between the two terminals by receiving the reflected wave by the interrogator. The antenna comprises a plate-like dipole antenna part 36 respectively connected to the two terminals of the vibration sensor element 31 and made of two rectangular metal film patterns 32 and 33 placed side by side on the same plane at a fixed interval, the length L being 0.3λ to 3λ and the width being ≥0.3L, and a metal film 34 installed in parallel with the plate-like dipole antenna part 36. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sensor including an antenna, and more particularly to a parasitic sensor with an antenna that can detect physical information at a remote location without supplying power to the sensor.

  Sensors corresponding to various physical information such as vibration sensors, impact sensors, strain sensors, submersion sensors, proximity sensors, etc. for structural abnormality diagnosis, security security applications, and abnormality detection for equipment and machine tool maintenance, etc. Is used. There are many cases where power cannot be easily supplied to the environment in which these sensors are installed, and it is considered that the range of application of these sensors will expand if sensors that do not require power supply become possible.

  As a sensor system that does not require such power supply, Patent Document 1 discloses a vibration detection method and a vibration sensor using radio. A schematic diagram of this conventional vibration sensor system is shown in FIG. In FIG. 4, the vibration sensor element 20 having the impedance between the two terminals that changes due to external vibration and the antenna 13 connected to the two terminals is separated from the parasitic vibration sensor 100. An interrogator 18 is installed at a location, an electromagnetic wave 16 emitted from an antenna 19 of the interrogator 18 is reflected by the antenna 13, and the reflected wave 17 is received by the interrogator 18, thereby changing impedance between the two terminals. It is configured to detect vibrations to be generated.

  Here, the vibration sensor element 20 includes a piezoelectric single crystal substrate 15 having a cantilever structure that is deformed by external vibrations, and a comb electrode 14 for exciting surface acoustic waves formed on the piezoelectric single crystal substrate 15. The two electrode terminals of the comb electrode 14 are connected to the antenna 13.

  A part of the electric power of the electromagnetic wave 16 having a specific frequency radiated from the antenna 19 of the interrogator 18 is scattered and reflected by the antenna 13 of the vibration sensor 100, and a part of the electric power of the reflected wave 17 is reflected by the antenna of the interrogator 18. 19 is received. At this time, the intensity and phase information of the reflected wave 17 depend on the impedance characteristics between the two electrode terminals of the comb electrode 14 of the vibration sensor element 20 connected to the antenna 13. That is, the piezoelectric single crystal substrate 15 having a cantilever structure is deformed and strained in accordance with external vibration, and the comb-tooth electrode 14 for exciting the surface acoustic wave formed on the piezoelectric single crystal substrate 15 along with the deformation. Impedance characteristics vary. Therefore, the interrogator 18 can detect the vibration generated in the vibration sensor 100 from the information of the reflected wave 17.

  FIG. 5 is a perspective view showing an example of a specific structure of the conventional vibration sensor 100. In FIG. 5, the vibration sensor element 20 is installed on the substrate 40, and two rectangles that are installed so as to sandwich the two terminals 42 connected to the comb-teeth electrodes of the vibration sensor element 20 and are respectively connected to the two terminals 42. A plate-shaped dipole antenna 10 composed of conductors 11 and 12 is installed.

  Conventionally, the vibration sensor as shown in FIG. 5 is used by being installed at various places to be measured. When a metal body is present near the vibration sensor, the sensor may be used depending on the position and size. This greatly affects the impedance characteristics and reflected wave characteristics of the antenna, and causes deterioration in sensitivity detected by the interrogator.

  As a method for reducing the influence of such an adjacent metal body, a high permeability material such as ferrite or a means for arranging a metal body so as to surround a part of the antenna is used. For example, in Patent Document 2, a battery serving as a conductor is arranged on the back side of an antenna in a transponder for a data transmission wireless communication device, and its shielding effect is used, and electromagnetic waves generated from the antenna are affected by a nearby metal body. I do not accept it.

Japanese Patent Laid-Open No. 2007-232708 JP-A-5-83173

  The means disclosed in Patent Document 2 described above is that the antenna is a coil antenna and the resonance frequency of the antenna is adjusted so that it matches the frequency of the communication device with the battery installed to prevent sensitivity deterioration. The technical idea cannot be applied to the plate-shaped dipole antenna used in the sensor of the present invention. Further, since the present invention relates to a non-powered sensor, no battery is used.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a parasitic sensor with an antenna that can prevent sensitivity deterioration even when a metal body is close to the parasitic sensor using an antenna.

  In order to solve the above problems, a parasitic sensor with an antenna according to the present invention includes a vibration sensor element in which impedance between two terminals changes according to physical information from the outside, and an antenna connected to the two terminals. The physical information that causes the impedance change between the two terminals by receiving the reflected wave generated by reflecting the electromagnetic wave emitted from the interrogator installed at a distant place by the antenna. In a parasitic sensor with an antenna configured to detect, the antenna is connected to each of the two terminals, and a plate-shaped dipole antenna unit including two rectangular conductors juxtaposed on the same plane at a constant interval and the plate In the case where the wavelength of the center frequency of the electromagnetic wave is λ The length of the plate-shaped dipole antenna portion in the direction across the fixed interval is 0.3λ to 3λ, and the width of the plate-shaped dipole antenna portion in the direction orthogonal to the length direction is the length. L is 0.3L or more, and the conductor has a rectangular shape with a length greater than or equal to the length and width of the plate-shaped dipole antenna portion, and the distance between the plate-shaped dipole antenna portion and the conductor is λ / 12 to λ.

  In the present invention, the vibration sensor element may be a vibration sensor in which the impedance changes due to vibration. The vibration sensor includes a piezoelectric single crystal substrate having a cantilever structure that is deformed by external vibration, and the piezoelectric single crystal. You may comprise from the comb-tooth electrode for exciting the surface acoustic wave formed on the board | substrate.

  The present invention forms a composite antenna by installing a conductor at a certain interval on a plate-shaped dipole antenna used in a conventional sensor, and the shape of the plate-shaped dipole antenna and the conductor, and the above-mentioned distance By setting to a specific value, it is based on the finding that the sensitivity equivalent to the conventional one can be obtained and that the sensitivity of the sensor does not deteriorate even if the metal object is placed close to the antenna. .

  According to the present invention, even when a metal body is provided in the vicinity of the antenna, it is possible to suppress a significant decrease in the gain of the antenna, and a predetermined sensitivity can be obtained without increasing the antenna shape in a wider environmental condition. It is done. Therefore, by using this antenna, it is possible to obtain a vibration sensor that is small and lightweight and can detect mechanical external vibrations far away by radio, and enables highly accurate vibration measurement without constraining the conditions of the object to be measured as in the past. It becomes. In addition, since the vibration sensor can be reduced in size and weight like a tag shape, there are few restrictions on the location of attachment to the measurement object. Further, in addition to the conventional feature that a power source is unnecessary, there are few environmental restrictions as described above, so that it can be used for a wide range of applications.

  According to the present invention, in a parasitic sensor using an antenna, a parasitic sensor with an antenna that can prevent deterioration in sensitivity even when a metal body is in proximity can be obtained.

  Hereinafter, embodiments will be described based on examples of the present invention with reference to the drawings.

  FIG. 1 is a perspective view showing a vibration sensor as an embodiment of a parasitic sensor with an antenna according to the present invention, and FIG. 2 is a perspective view showing a specific example of a vibration sensor element used in the vibration sensor of this embodiment. is there.

  The vibration sensor of this embodiment also has a vibration sensor element 31 in which the impedance between the two terminals changes when vibration is applied from the outside, and an antenna connected to the two terminals. Similarly, the electromagnetic wave emitted from the antenna of the interrogator installed at a distant place is reflected by the antenna of the vibration sensor, and the reflected wave is received by the interrogator, thereby causing an impedance change between the two terminals. It is configured to detect vibration.

  In FIG. 1, the vibration sensor of the present embodiment includes a vibration sensor element 31 and two rectangular metal film patterns 32 and 33 connected to two terminals of the vibration sensor element 31 and juxtaposed on the same plane at a constant interval. And an antenna composed of a metal film 34 disposed in parallel with the plate-like dipole antenna unit 36. Here, in the present embodiment, the center frequency of the electromagnetic wave used for communication is 2.45 GHz, the wavelength λ is about 120 mm, and the length L of the plate-shaped dipole antenna portion in the direction sandwiching the predetermined interval is about 60 mm. (0.5λ) and its width W is about 40 mm (0.67 L).

  The plate-shaped dipole antenna portion 36 is formed on the upper surface of a rectangular substrate 35 on which the vibration sensor element 31 is mounted, and a metal film 34 is formed on the entire back surface of the substrate 35. The shape of the substrate 35 is about 80 mm × 80 mm, and the distance between the plate-shaped dipole antenna portion 36 and the metal film 34, that is, the thickness t of the substrate 35 is about 1.6 mm (0.133λ).

  In FIG. 1, the substrate 35 can be constituted by a printed board with copper foil made of glass epoxy resin. In this case, the plate-shaped dipole antenna portion 36 can be formed by a known mechanical cutting technique or photo etching technique. The copper foil on the back surface is used as the metal film 34 as it is. After the antenna pattern is formed, it can be cut into a desired size, and then the vibration sensor element 31 can be mounted to easily manufacture the antenna pattern. The thickness of the copper foil is about 36 μm. In addition, the rectangular apexes of the rectangular metal film patterns 32 and 33 are formed such that the corners are dropped by a curve having a radius of curvature R of about 10 mm in order to prevent the efficiency of the antenna from decreasing due to disturbance of the current flowing in the metal film. Has been.

  In FIG. 2, the vibration sensor element 31 used in the vibration sensor of the present embodiment includes a piezoelectric single crystal substrate 22 having a cantilever structure and a comb for exciting surface acoustic waves formed on the piezoelectric single crystal substrate 22. It comprises a tooth electrode 23 and a surface acoustic wave reflector 24 for constituting a resonator. Since the piezoelectric single crystal substrate 22 has a cantilever structure, it bends and deforms in response to external vibration. Due to this bending deformation, the comb-tooth electrode 23 formed on the piezoelectric single crystal substrate 22 is distorted, and the impedance characteristics of the surface acoustic wave resonator at the resonance frequency change. The two terminals 25 of the comb-tooth electrode 23 formed on the piezoelectric single crystal substrate 22 are electrically connected to the rectangular metal film patterns 32 and 33 (FIG. 1) by solder mounting or aluminum wire bonding.

  The vibration sensor of this example was prototyped and subjected to a field strength test by the 3 m method in an anechoic chamber. As a result, the gain of the antenna was 2 (dBi), which is equivalent to that of a normal dipole antenna.

  FIG. 3 is a diagram illustrating an example of a measurement result of the vibration sensor according to the present embodiment, and reception of vibration information received by the interrogator with respect to a distance between the interrogator and the vibration sensor when a metal body is brought close to the antenna. Indicates power. For comparison, FIG. 3 also shows the received power of the conventional dipole antenna when the metal body is approached and the conventional dipole antenna when the metal body is not approached.

  Here, the shape of the conventional dipole antenna used for comparison is approximately 60 mm in length and approximately 20 mm in width. The transmission power from the interrogator is 10 dBm, and the frequency is 2.45 GHz. When the metal body approaches the antenna, the reception power of the conventional antenna rapidly decreases with respect to the distance from the interrogator, and the propagation distance capable of receiving the vibration signal is reduced to 1 m or less. On the other hand, in the vibration sensor of the present embodiment, even when the metal body approaches the antenna, the propagation distance capable of receiving the vibration signal is not significantly reduced unlike the conventional case.

  As described above, according to the present invention, even when a metal body is provided in the vicinity of the antenna, it is possible to suppress a significant decrease in the gain of the antenna.

  Needless to say, the present invention is not limited to the above-described embodiments, and the design can be changed depending on the purpose and application of the sensor. For example, in addition to the vibration sensor, the present invention can be applied to any sensor that causes an impedance change between terminals connected to an antenna, and even when the communication frequency is different, the frequency is defined by the present invention. The effect of the present invention can be obtained by providing the antenna having the shape. In addition, various materials can be selected for the rectangular conductor and the conductor constituting the antenna.

The perspective view which shows the vibration sensor which is one Example of the parasitic sensor with an antenna by this invention. The perspective view which shows a specific example of the vibration sensor element used for the vibration sensor of a present Example. The figure which shows an example of the measurement result of the vibration sensor of a present Example. The schematic diagram of the conventional vibration sensor system which does not require power supply. The perspective view which shows an example of the specific structure of the conventional vibration sensor.

Explanation of symbols

10 Dipole antenna 11, 12 Rectangular conductor 13, 19 Antenna 14, 23 Comb electrode 15, 22 Piezoelectric single crystal substrate 16 Electromagnetic wave 17 Reflected wave 18 Interrogator 20, 31 Vibration sensor element 24 Reflector 25, 42 Terminals 32, 33 Rectangular Metal film pattern 34 Metal films 35 and 40 Substrate 36 Plate-shaped dipole antenna unit 100 Vibration sensor

Claims (3)

A sensor element whose impedance between two terminals changes according to physical information from the outside and an antenna connected to the two terminals, and an electromagnetic wave emitted from an interrogator installed at a remote location is caused by the antenna. In a parasitic sensor with an antenna configured to detect the physical information that causes an impedance change between the two terminals by receiving a reflected wave generated by reflection with the interrogator,
The antenna is composed of a plate-shaped dipole antenna portion made of two rectangular conductors connected to the two terminals and juxtaposed on the same plane at regular intervals, and a conductor installed in parallel with the plate-shaped dipole antenna portion. When the wavelength of the center frequency of the electromagnetic wave is λ, the length of the plate-shaped dipole antenna unit in the direction of sandwiching the constant interval is 0.3λ to 3λ, and the plate-shaped dipole antenna unit The width in the direction perpendicular to the length direction is 0.3 L or more, where L is the length, and the conductor has a rectangular shape that is larger than the length and width of the plate-shaped dipole antenna portion. A parasitic sensor with an antenna, wherein a distance between the plate-shaped dipole antenna portion and the conductor is λ / 12 to λ.   The parasitic sensor with an antenna according to claim 1, wherein the sensor element is a vibration sensor in which the impedance is changed by vibration applied from outside.   The vibration sensor includes a piezoelectric single crystal substrate having a cantilever structure that is deformed by external vibration, and a comb electrode for exciting surface acoustic waves formed on the piezoelectric single crystal substrate. The parasitic sensor with an antenna according to claim 2.

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