JP6320974B2 - Loop antenna - Google Patents

Description

  The present invention relates to a loop antenna capable of clearly setting a boundary of a communication area.

  In recent years, there has been an increasing need for wireless communication (area limited wireless) in which a communication area is intentionally limited. For example, the electric field communication system disclosed in Patent Document 1 is a means for realizing area-limited radio.

  On the other hand, a low frequency (approximately 10 MHz) magnetic field has a feature that the interaction with the human body and the surrounding environment is significantly lower than the electric field. For example, the loop antenna disclosed in Patent Document 2 generates a magnetic field in a limited space.

JP 2007-174570 A JP 2013-223117 A

  In electric field communication, only a terminal device existing in an area near an access point device installed in the environment can communicate with the access point device. However, since the electric field distribution in the vicinity of the access point device greatly depends on the installation environment, the posture of the user, and the like, it is difficult to realize a clear nearby area with an electric field. Therefore, there are cases where the terminal device existing at the position to be communicated becomes unable to communicate and vice versa, and it is difficult to construct a stable and highly reliable area limited wireless system.

  Therefore, it is conceivable to use a low-frequency magnetic field as a communication medium as disclosed in Patent Document 2. If it is possible to create a magnetic field portion in which the magnetic field strength rapidly attenuates at the boundary of the communication area, a highly reliable area limited wireless system can be constructed.

  However, since the outer shape of the loop antenna disclosed in Patent Document 2 is a circle, a width greater than the diameter of the circle is required for the installation space. Therefore, there is a problem that it is difficult to install the loop antenna in a narrow space such as a pillar or a groove.

  The present invention has been made in view of this problem, and an object of the present invention is to provide a loop antenna that can be installed even in a narrow space and can clearly set the boundary of a communication area.

The loop antenna according to the present invention includes a first conductor loop and a second conductor loop arranged in the same plane, and the first conductor loop and the second conductor loop are arranged so that their centers of gravity coincide with each other. The same surface has an outer shape having a horizontal dimension larger than a vertical dimension, and the first conductor loop and the second conductor loop have a shape having a horizontal dimension larger than the vertical dimension, and the first conductor loop is The flowing current I ₁ and the current I ₂ flowing through the second conductor loop flow in opposite directions, the sum of the current I ₁ and the current I ₂ is constant, and the area surrounded by the first conductor loop And S ₁ , and the area surrounded by the second conductor loop is S ₂ , the following equation is satisfied , and the area ratio (S ₂ / S ₁ ) is 0.17 to 0.71 .

  According to the loop antenna of the present invention, it is possible to provide a loop antenna that can be installed even in a narrow space and can clearly set the boundary of a communication area.

It is a figure which shows the structural example of the loop antenna 1 of 1st Embodiment. It is a figure which shows the modification of the loop antenna array. It is a figure which shows the modification of the loop antenna array. It is a figure which shows the modification of the loop antenna array. It is a graph which shows the example of a characteristic of an evaluation function. It is a figure which shows the structural example of the loop antenna 2 of 2nd Embodiment. It is a figure which shows the simulation conditions of magnetic field distribution simulation. It is a figure which shows the simulation result of a magnetic field distribution simulation.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same reference numerals are given to the same components in a plurality of drawings, and the description will not be repeated.

[First Embodiment]
In FIG. 1, the structural example of the loop antenna 1 of 1st Embodiment is shown. The loop antenna 1 of this embodiment includes an insulator substrate 10, a first conductor loop 11, a second conductor loop 12, first feeding points 13a and 13b, and second feeding points 14a and 14b. The first conductor loop 11 includes the second conductor loop 12.

  The first feeding points 13 a and 13 b feed the first conductor loop 11. The second feeding points 14a and 14b feed the second conductor loop 12.

  The first feeding point 13 a is a positive electrode (+) and is disposed near the outer edge of the central portion of one long side of the rectangular insulating substrate 10. The first conductor loop 11 extends clockwise from the first feeding point 13a along the outer edge of the insulator substrate 10 and is connected to the first feeding point 13b (-) disposed in front of the first feeding point 13a. It is constituted by a conductive pattern. Note that the distance between the conductive pattern of this example and the outer edge of the insulating substrate 10 varies irregularly. Therefore, the shape of the first conductor loop 11 is a distorted shape. In the first conductor loop 11, a current flows clockwise from the first feeding point 13a toward the first feeding point 13b.

  The second feeding point 14 a is a positive electrode (+) and is disposed inside the first conductor loop 11. The second conductor loop 12 extends from the second feed point 14a in the counterclockwise direction inside the first conductor loop 11 and is disposed at a position in front of the second feed point 14a. It is comprised by the conductive pattern connected to. In the second conductor loop 12, a current flows counterclockwise from the second feeding point 14a toward the second feeding point 14b. That is, the currents flowing through the first conductor loop 11 and the second conductor loop 12 are opposite to each other.

The area surrounded by the first conductor loop 11 is S ₁ , and the current flowing through the first conductor loop 11 is I ₁ . Further, the area surrounded by the second conductor loop 12 is S ₂ , and the current flowing through the second conductor loop 12 is I ₂ . Then, adjusted to the conditions are satisfied _{I 1} and _{I 2} shown in the following equation.

  According to the equation (1), the sum of the magnetic dipole moments of the loop antenna constituted by the first conductor loop 11 and the second conductor loop 12 is made zero, so that the far magnetic field of the loop antenna 1 is rapidly attenuated. A sharp magnetic field distribution can be formed. The condition of Expression (1) can be easily satisfied by adjusting the signal voltage at the first feeding point 13a and the second feeding point 14a.

  The shape of the magnetic field distribution of the loop antenna 1 hardly depends on the shapes of the first conductor loop 11 and the second conductor loop 12. Specific magnetic field distribution will be described later.

  Thus, by using the first conductor loop 11 and the second conductor loop 12 arranged in the same plane of the rectangular insulator substrate under the condition of the expression (1), the width of the pillars, grooves, etc. is narrow. The loop antenna 1 that can be installed in a space and can create a sharp magnetic field distribution can be realized.

[Modification]
In FIG. 2, the structure of the modification of the loop antenna 1 of 1st Embodiment is shown. FIG. 2A shows a rectangular shape of the first conductor loop 11 and the second conductor loop 12. FIG. 2B shows the first conductor loop 11 having a rectangular shape and the second conductor loop 12 having an elliptical shape.

  As described above, the loop conductor 1 can be easily manufactured by forming the first conductor loop 11 and the second conductor loop 12 in a shape having regularity or symmetry such as a rectangle or an ellipse.

  FIG. 3 shows another modification of the loop antenna 1 of the first embodiment. FIG. 3 shows the first conductor loop 11 and the second conductor loop 12 having the same center of gravity. The center of gravity may be rephrased as the center.

  FIG. 3A shows an example in which the first conductor loop 11 and the second conductor loop 12 are rectangular and the centers of gravity of the respective loops are matched. FIG. 3B shows an example in which the first conductor loop 11 is rectangular and the second conductor loop 12 is elliptic. In this way, by making the centroids of the first conductor loop 11 and the second conductor loop 12 coincide with each other, it is possible to obtain a magnetic field rapid attenuation characteristic at a closer distance from the loop antenna 1.

  FIG. 4 shows another modification of the loop antenna 1 of the first embodiment. FIG. 4 shows the first conductor loop 11 and the second conductor loop 12 in a similar shape. FIG. 4A shows a rectangular similar shape of the first conductor loop 11 and the second conductor loop 12. FIG. 4B shows the first conductor loop 11 and the second conductor loop 12 having an elliptical similarity.

  As shown in FIG. 4, the two conductor loops have a similar relationship, so that a configuration with higher symmetry than the above modification can be obtained. Further, by making the distance between the first conductor loop 11 and the second conductor loop 12 closer, it is possible to obtain a magnetic field abrupt attenuation characteristic at a closer distance from the loop antenna 1.

Note that there is an area ratio λ (λ = S ₂ / S ₁ ) that maximizes the magnetic field strength at a distance. By setting the area ratio to maximize the magnetic field strength, the current consumption can be minimized. Next, conditions for minimizing the current consumption will be described.

  The magnetic field H (z) generated far away by the loop antenna 1 in which the centers of gravity of the first conductor loop 11 and the second conductor loop 12 shown in FIGS. 3 and 4 coincide with each other can be approximately expressed by the following equation.

Here, z is the distance from the center of gravity to the observation point. c ₁ = 1 / 2π, c ₂ = 3 / 4π ² . The area ratio λ of the conductor loop is defined by the following equation.

Furthermore, placing the sum of the currents flowing through the two conductor loops and I _t.

  In order to obtain the rapid decay characteristic, the current may be adjusted so that the first term on the right side of Equation (2) becomes zero.

  The following equation is obtained from equations (3) to (5).

  Practically, it is desirable to maximize the far magnetic field while satisfying the rapid decay characteristics. Therefore, it is desirable to maximize the second term while satisfying zero in the first term of the formula (2). Substituting Equation (3) and Equation (6) into the second term on the right side gives the following equation.

Therefore, when a constant and I _t and S _1, to maximize second term of equation (2) may be maximized evaluation function f (lambda) which is defined by the following equation.

  Let λc be λ that maximizes the evaluation function f (λ). To obtain λc, the following equation should be solved.

  Solving equation (9) yields:

  Further, the range of the area ratio λ for obtaining the value of the evaluation function f (λ) within 3 dB from the maximum value is obtained by the following equation.

  When equation (11) is solved, the area ratio λ range within 3 dB can be determined as shown in the following equation.

That is, when a constant I _t, the area ratio λ of (S ₂ / S ₁₎ by the range of 0.17 to 0.71, the value of the magnetic field H (z) of the loop antenna 1 is generated in the distance, the maximum The value can be in the range of -3dB.

FIG. 5 shows the relationship between the area ratio λ and the evaluation function f (λ). The horizontal axis in FIG. 5 is the area ratio λ, and the vertical axis is the evaluation function f (λ). The area ratio λ of the magnetic field strength in the distance to the maximum in the case where the I _t is constant, is approximately 0.41. The area ratio in the range of the maximum magnetic field intensity of −3 dB is in the range of λ = 0.17 to 0.71.

[Second Embodiment]
FIG. 6 shows a configuration example of the loop antenna 2 of the second embodiment. The loop antenna 2 of the present embodiment is one in which the number of turns of the first conductor loop 11 and the second conductor loop 12 of the loop antenna 1 shown in FIG.

When the number of turns of the first conductor loop 11 is N ₁ and the number of turns of the second conductor loop 12 is N ₂ , the above equation (1) is expanded to the following equation.

FIG. 6 shows an example in which N ₁ = 3 and N ₂ = 2. As is clear from the equation (13), the current values I ₁ and I ₂ can be made smaller than when the number of turns is one. That is, the loop antenna 2 can generate a magnetic field with the same strength as the magnetic field generated by the loop antenna 1 when N ₁ = 1 and N ₂ = 1.

[Simulation of magnetic field distribution]
In order to confirm the effect of the present invention, a magnetic field distribution was simulated. The simulation result will be described with reference to FIG. 7 and FIG.

  FIG. 7 is a diagram showing simulation conditions. The simulation was performed for another modification of the loop antenna 1 of the first embodiment shown in FIG.

  The first conductor loop 11 was an ellipse having a major axis of 0.4 m and a minor axis of 0.1 m. The second conductor loop 12 was an ellipse having a major axis of 0.2 m and a minor axis of 0.05 m. In FIG. 7, the notation of the insulator substrate is omitted, but as is apparent from the shape of the first conductor loop 11, the shape is, for example, a rectangle that is long in the major axis direction of an ellipse.

  Further, the center positions of the first conductor loop 11 and the second conductor loop 12 were matched. Then, a magnetic field generated by feeding an alternating current having the same phase to the first conductor loop 11 and the second conductor loop 12 was simulated.

  FIG. 8 shows the simulation result of the zx plane. The unit of numerical values in the figure is dBμA / m, and one contour line represents a difference of 10 dB.

  The intensity of the magnetic field at the coordinates (x = 0.0, z = −0.5) is about 70 dBμA / m, which is 60 dB down at a position 0.5 m away from the strongest part near the origin. This attenuation is about 22 dB greater than the conventional single loop antenna.

  Thus, the loop antenna of the present invention can generate a sharp magnetic field portion that can clearly set the boundary of the communication area. In the loop antenna of the present invention, the shape of the insulator substrate on which the first conductor loop 11 and the second conductor loop 12 are arranged is, for example, a rectangle. Therefore, it can be installed even in a narrow space.

  Although the contents of the present invention have been described according to the embodiments, the present invention is not limited to these descriptions, and it is obvious to those skilled in the art that various modifications and improvements can be made. For example, the shapes of the first conductor loop 11 and the second conductor loop 12 may be different.

  Further, the first conductor loop 11 and the second conductor loop 12 may have irregular shapes. That is, the shape may not be symmetrical from the center. In the above embodiment, the direction of the current flowing through the first conductor loop 11 is shown as the clockwise direction, and the direction of the current flowing through the second conductor loop 12 is shown as the counterclockwise direction. It does not matter.

  Further, the insulator substrate 10 shown in the rectangular example is not limited to the rectangular shape. The shape may be anything as long as the outer shape has a larger horizontal dimension than the vertical dimension. In short, the shape of the insulator substrate 10 may be any shape as long as the substrate shape matches the shape in which the loop antenna can be arranged. As described above, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the gist thereof.

1, 2: Loop antenna 10: Insulator substrate 11: First conductor loop 12: Second conductor loops 13a, 13b: First feed points 14a, 14b: Second feed points

Claims (1)

A communication area boundary setting method using a loop antenna in which a first conductor loop and a second conductor loop are arranged in the same plane,
The first conductor loop includes the second conductor loop having a shape different from that of the first conductor loop so that the centers of gravity of the first conductor loop coincide with each other, and the same surface has an outer shape having a larger horizontal dimension than a vertical dimension, the first conductor loop and the second conductor loop is larger shape lateral dimension than longitudinal dimension, the area in which the first conductor loop surrounds S _1, the area of the second conductor loop surrounds a case of the S ₂ In the loop antenna whose area ratio (S ₂ / S ₁ ) is 0.17 to 0.71,
The current I ₁ flowing through the first conductor loop, said current I ₂ flowing through the second conductor loop, the reverse flow to each other and a constant sum of the currents I ₁ and the current I _2, the loop antenna setting the communication area boundary using a loop antenna, characterized in that electric current I ₁ and the current I ₂ flowing through the Suyo meet the following equation.

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