JP2017130918A - Loop antenna array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a loop antenna array capable of forming a boundary of a linear and clear communication area.SOLUTION: The loop antenna array includes two loop antennas 1 and 2. Electric current runs through the loop antennas 1 and 2 in an opposite direction to each other. That is, when viewed from a direction penetrating through each of the loop antennas 1 and 2, at the timing that a signal terminal of an AC power supply E has plus voltage, clockwise electric current runs through the loop antenna 1 and counter-clockwise electric current runs through the loop antenna 2. At the timing that the signal terminal of the AC power supply E has minus voltage, on the contrary, counter-clockwise electric current runs through the loop antenna 1 and clockwise electric current runs through the loop antenna 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a loop antenna array capable of forming a linear and clear communication area boundary.

  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 below is one means for realizing area-limited radio.

JP 2007-174570 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 user's posture, and the like, it is difficult to realize a linear and clear boundary of the communication area by the electric field. Therefore, the terminal device existing at the position to be communicated cannot communicate, or vice versa, and a stable and highly reliable area limited wireless system cannot be constructed.

  One of the causes of such difficulty is considered to be the use of an electric field as a communication medium. This is because the electric field distribution is strongly influenced by conductors and dielectrics existing around it.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a loop antenna array that can form a linear and clear boundary of a communication area.

  In order to solve the above problems, a loop antenna array of the present invention includes two loop antennas through which currents in opposite directions flow, and the linear distance between the centers of the two loop antennas is a midpoint between the centers. Is less than twice the distance from the communication area boundary away in the direction penetrating the loop antenna.

  According to the loop antenna array of the present invention, since two loop antennas through which currents flow in opposite directions are provided, a linear and clear boundary of the communication area can be formed.

It is a figure which shows an example of the loop antenna array of 1st Embodiment. It is a figure which shows the magnetic field area which the loop antenna array of FIG. 1 forms. It is a figure which shows an example of the loop antenna array of 2nd Embodiment. It is a figure which shows the magnetic field area which the loop antenna array of FIG. 3 forms. It is a figure which shows an example of the loop antenna array which is a modification of 2nd Embodiment. It is a figure which shows an example of the loop antenna array of 3rd Embodiment. It is explanatory drawing which shows the effect | action in the loop antenna array of each embodiment. It is a figure which shows the loop antenna which is a comparative example of the loop antenna array of this Embodiment. It is a figure which shows the magnetic field area which the loop antenna shown in FIG. 8 forms.

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

  The loop antenna array of the present embodiment is a magnetic field antenna. For example, a low-frequency (approximately 10 MHz or less) magnetic field has a feature that the interaction with the human body and the surrounding environment is significantly lower than the electric field. Therefore, it is conceivable to use a low-frequency magnetic field as a communication medium as one means for solving the problem. If a “sharp magnetic field distribution” in which the magnetic field intensity rapidly attenuates at the boundary of the communication area can be created, a highly reliable area limited wireless system can be constructed.

  However, in the loop antenna (FIG. 8) generally used for forming the magnetic field area, the attenuation factor of the magnetic field is 60 dB / dec and the magnetic field to be formed is shown in FIG. The shape of the area becomes a curved surface. For this reason, it is difficult to form a straight and clear boundary of the communication area.

[First Embodiment]
FIG. 1 is a diagram illustrating an example of a loop antenna array according to the first embodiment. FIG. 2 is a diagram showing a magnetic field area formed by the loop antenna array of FIG.

  As shown in FIG. 1, the loop antenna array includes two loop antennas 1 and 2. Each of the loop antennas 1 and 2 has a conductor formed in a loop shape, and is formed, for example, on a substrate (not shown) (same plane). The loop antennas 1 and 2 have, for example, the same shape (circle), the area of the area surrounded by the loop antennas is the same, and the number of turns is one.

  The loop antennas 1 and 2 are formed by, for example, a continuous conducting wire LN. The + terminal which is one end of the conducting wire LN is connected to the signal terminal of the AC power supply E, and the − terminal which is the other end of the conducting wire LN is connected to the GND terminal of the AC power supply E.

  In the loop antennas 1 and 2, currents in opposite directions flow. That is, when the signal terminal of the AC power supply E is a positive voltage when viewed in the direction penetrating the loop antennas 1 and 2 (z direction), a clockwise current flows through the loop antenna 1 and counteracts at the loop antenna 2. A clockwise current flows. Conversely, when the signal terminal of the AC power source E is at a negative voltage, a counterclockwise current flows through the loop antenna 1 and a clockwise current flows through the loop antenna 2.

  Each loop antenna 1, 2 is provided with a + terminal and a − terminal, that is, not formed by a continuous conductor, and the + terminal of the loop antenna 1 and the − terminal of the loop antenna 2 are connected to the signal terminal of the AC power source E. By connecting the negative terminal of the loop antenna 1 and the positive terminal of the loop antenna 2 to the GND terminal of the AC power supply E, currents in opposite directions may flow.

  Alternatively, each of the loop antennas 1 and 2 is provided with a + terminal and a − terminal, two AC power supplies are provided, and the + terminal and the − terminal of the loop antenna 1 are respectively connected to the signal terminal and the GND terminal of one AC power supply, By connecting the + terminal and the − terminal of the loop antenna 2 to the signal terminal and the GND terminal of the other AC power supply, respectively, currents in opposite directions may flow. In this case, when the signal terminal of one AC power supply is a positive voltage, the signal terminal of the other AC power supply may be synchronized so as to be a negative voltage.

  As shown in FIG. 2, in the loop antenna array composed of two loop antennas, the boundary of the communication area can be flattened compared to the case of a single loop antenna (FIG. 9).

  Preferably, a point Pa separated by a predetermined distance a from the middle point PL of the center-to-center line segment L connecting the center 1c of the loop antenna 1 and the center 2c of the loop antenna 2 in the direction penetrating the loop antenna (z direction). When there is a condition that the contour line of the passing magnetic field intensity does not intersect the center-to-center line segment L, if the length of the center-to-center line segment L (the distance between the centers 1c and 2c) is d, then d / 2 <a. It has become. That is, d is less than twice a (d <2a).

  As shown in FIG. 2, the contour line of the magnetic field intensity passing through the point Pa ′ separated from the midpoint PL by a predetermined distance d / 2 (<a) in the z direction does not intersect the center-to-center straight line segment L. Therefore, by setting d <2a, the condition that the contour line of the magnetic field strength passing through the point Pa farther from the midpoint PL than the point Pa ′ can be satisfied without crossing the straight line segment L between the centers.

  The contour line of the magnetic field intensity passing through the point Pa has a portion substantially parallel to the center-to-center straight line segment L. That is, the contour lines of the parallel magnetic field strength can be used as a linear and clear boundary of the communication area.

  In general, the amplitude of the magnetic field generated by the loop antenna in the distance is proportional to the magnitude of the magnetic dipole moment vector m. m is given by the following equation.

m = N ・ I ・ S
N is the number of turns of the loop antenna, I is the current value flowing through the loop antenna, S is the area of the area surrounded by the loop antenna, and the direction of m (vector) is the direction of the right screw with respect to the current rotation direction It is.

  In the first embodiment, current flows in the opposite direction. For example, if the shape, area, and number of turns of the loop antennas 1 and 2 are the same, the sum of m considering the direction becomes zero.

  That is, as shown in FIG. 7, the loop antenna array according to the first embodiment can be regarded as a quadrupole obtained by arranging loop antennas having one turn (with an attenuation factor of 60 dB / dec) in the reverse direction. The attenuation factor of the magnetic field is 80 dB / dec.

  That is, according to the first embodiment, it is possible to form a magnetic field area (communication area) that is sharper than a loop antenna having one turn.

  The shape of the magnetic field area does not depend on the shape of the loop antenna. Therefore, the shape is not a circle, but may be a square, a rectangle, an ellipse, a fan, a triangle, a semicircle, a spiral, or a string winding. However, the shape is not limited to these. The shape may be any shape as long as a magnetic dipole moment vector is formed when a current is passed.

  Further, the number of turns is not limited to one. Further, the N × S (the number of turns × the area) of each of the loop antennas 1 and 2 may be made equal and the shapes may be different.

[Second Embodiment]
FIG. 3 is a diagram illustrating an example of a loop antenna array according to the second embodiment. FIG. 4 is a diagram showing a magnetic field area formed by the loop antenna array of FIG.

  The loop antenna array of the second embodiment includes a plurality (two) of loop antenna arrays (FIG. 1) of the first embodiment. That is, two loop antennas 1 and 2 are provided. All the loop antennas are arranged on the same plane. For convenience, one loop antenna 1 is called a loop antenna 3, and one loop antenna 2 is called a loop antenna 4.

  In the loop antenna array, the total number of loop antennas is 2 to the nth power (n = 2) = 4.

  The centers of all the loop antennas 1 to 4 are arranged on the same straight line LL.

  Further, when a group of 2 (n−1) power (= 2) loop antennas is used as a unit loop antenna array, the loop antennas 1 and 2 constitute one unit loop antenna array A, and the loop antenna 3 4 constitutes another unit loop antenna array B.

  In one unit loop antenna array A, the direction of current flowing in the loop antenna 1 located on one end side (for example, the left side of the drawing) of the same straight line LL and the one end side (for example, in the other unit loop antenna array B, for example, The directions of currents flowing through the loop antenna 3 located on the left side of the drawing are opposite to each other.

  The loop antenna array of the second embodiment includes a plurality of the loop antenna arrays of the first embodiment, and preferably, each loop antenna array has d <2a (see FIG. 2). The contour line of the magnetic field strength separated from the straight line LL by the distance a has a portion substantially parallel to the same straight line LL. That is, the contour lines of the parallel magnetic field strength can be used as a linear and clear boundary of the communication area.

  In the second embodiment, since the current direction is as described above, for example, if the shape, area, and number of turns of each of the loop antennas 1 to 4 are the same, the sum of m considering the direction becomes zero. .

  That is, as shown in FIG. 7, the loop antenna array of the second embodiment can be regarded as an octupole obtained by arranging the quadrupoles in the opposite direction, and the attenuation factor of the magnetic field is 100 dB / dec. Become.

  That is, according to the second embodiment, a magnetic field area (communication area) sharper than that of the first embodiment can be formed.

  In the second embodiment, the shape of the loop antenna is not limited to a circle. It may be different for each loop antenna and for each unit loop antenna array. The number of turns is not limited to one. The loop antennas 1 and 2 do not have to be formed of continuous conducting wires. Moreover, the loop antennas 2 and 3 may be formed with continuous conducting wires. That is, even if it is a different loop antenna array, the group of adjacent loop antennas may be formed with continuous conducting wires.

  Moreover, as shown in FIG. 5, the loop antennas 1-4 may be formed with the continuous conducting wire.

[Third embodiment]
FIG. 6 is a diagram illustrating an example of a loop antenna array according to the third embodiment.

  The loop antenna array of the third embodiment includes a plurality (four) of the loop antenna array (FIG. 1) of the first embodiment. That is, four loop antennas 1 and 2 are provided. All the loop antennas are arranged on the same plane. For convenience, the loop antennas 1 other than one loop antenna 1 are referred to as loop antennas 3, 5, and 7, and the loop antennas 2 other than one loop antenna 2 are referred to as loop antennas 4, 6, and 8.

  In the loop antenna array, the total number of loop antennas is 2 to the nth power (n = 3) = 8.

  Further, the centers of all the loop antennas 1 to 4 are arranged on the same straight line (not shown).

  Further, when a group of 2 (n−1) power (= 4) loop antennas is used as a unit loop antenna array, the loop antennas 1 to 4 constitute one unit loop antenna array AB, and the loop antenna 5 ˜8 constitute another unit loop antenna array CD.

  In one unit loop antenna array AB, the direction of current flowing in the loop antenna 1 located on one end side (for example, the left side of the drawing) of the same straight line LL and the one end side (for example, in the other unit loop antenna array CD, for example) The directions of currents flowing through the loop antenna 5 located on the left side of the drawing are opposite to each other.

  The loop antenna array according to the third embodiment includes a plurality of the loop antenna arrays according to the first embodiment. Preferably, each loop antenna array satisfies d / 2 <a (d <2a) ( Therefore, the contour lines of the magnetic field strength separated by the distance a from the same straight line passing through the center of each loop antenna have a portion substantially parallel to the same straight line. That is, the contour lines of the parallel magnetic field strength can be used as a linear and clear boundary of the communication area.

  In the third embodiment, since the direction of the current is as described above, for example, if the shape, area, and number of turns of each of the loop antennas 1 to 8 are the same, the sum of m considering the direction becomes zero. .

  That is, as shown in FIG. 7, the loop antenna array of the third embodiment can be regarded as a 16-pole element obtained by arranging octupoles in the opposite direction, and the attenuation factor of the magnetic field is 120 dB / dec. Become.

  That is, according to the third embodiment, a magnetic field area (communication area) sharper than that of the second embodiment can be formed.

  In the third embodiment, the shape of the loop antenna is not limited to a circle. It may be different for each loop antenna and for each unit loop antenna array. The number of turns is not limited to one. Further, each set of loop antennas 2 and 3, loop antennas 4 and 5, and loop antennas 6 and 7 may be formed of continuous conductors. That is, even if it is a different loop antenna array, the group of adjacent loop antennas may be formed with continuous conducting wires. Moreover, the loop antennas 1-8 may be formed with the continuous conducting wire.

  Further, as shown in FIG. 7, n (= k) may be 4 or more. By setting k to 4 or more and arranging the loop antennas in a straight line, a (k + 1) -th power multipole is formed, and an attenuation factor of 20 (k + 3) dB / dec can be obtained. That is, a sharper magnetic field area (communication area) can be formed as n (= k) is larger.

1-8 Loop antenna A, B, AB, CD Unit loop antenna array

Claims (6)

It has two loop antennas in which currents in opposite directions flow,
The loop antenna array according to claim 1, wherein a linear distance between the centers of the two loop antennas is less than twice a distance from a midpoint between the centers to a communication area boundary separated in a direction penetrating the loop antenna.   The loop antenna array according to claim 1, wherein the two loop antennas are arranged on the same plane.   The loop antenna array according to claim 1 or 2, wherein the two loop antennas have a total magnetic moment of zero.   The loop antenna array according to claim 1, wherein the two loop antennas have the same shape.   5. The loop antenna according to claim 1, wherein the loop antenna array is any one of a square, a circle, a rectangle, an ellipse, a fan, a triangle, a semicircle, a helix, and a chord winding. array.   6. The loop antenna according to claim 1, wherein one loop antenna and the other loop antenna are formed of continuous conductors in a loop antenna array including the two adjacent loop antennas. array.

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