JP5969371B2 - Near-field antenna - Google Patents

Description

  The present invention relates to an antenna technology using a magnetic field.

  A low-frequency magnetic field of about 10 MHz or less is used as a communication medium for wireless communication in which a communication area is limited because the interaction with the surrounding environment such as a human body or an object is significantly lower than an electric field.

  In general, the magnetic field can be generated by a current loop. By arranging a plurality of current loops having various magnetic moments (current value x inner area of the current loop) appropriately, a sharp magnetic field distribution in which the magnetic field strength rapidly attenuates from the inside to the outside of the communication area is obtained. be able to.

  In the conventional near-field antenna, in order to obtain such a sharp magnetic field distribution, a plurality of current sources are used to supply currents to a plurality of current loops, respectively.

JP 2005-33587 A JP 2001-16025 A JP 2007-174570 A

  On the other hand, it is desirable to supply current to all the current loops using a single current source in order to avoid synchronization processing of alternating currents flowing through each current loop and to further simplify the circuit configuration and reduce the cost.

  However, when one current source is used, (1) a problem that a different current must be supplied for each current loop, and (2) a plurality of currents that connect one current source and all the current loops, respectively. Since the wiring of the input feeder line is complicated, there is a problem that an unnecessary magnetic field is generated from each current input feeder line.

  As one means for solving such a problem, a coil-type antenna as disclosed in Patent Documents 1 and 2 can be considered. Since this coil type antenna has a spiral structure as shown in FIG. 5, it can be assumed that a plurality of equivalent single current loops are formed.

  However, the magnitude and direction of each current flowing through each simulated current loop is equal, and the amount of current and the direction in which the current travels cannot be changed, so in the end it is similar to the magnetic field distribution generated by a single current loop, Although the above two problems are solved, the sharp magnetic field distribution as described above cannot be obtained.

  The present invention has been made in view of the above circumstances. In a near magnetic field antenna using a single current source, the first object is to reduce an unnecessary magnetic field from a feeder line. A second object is to rapidly attenuate the magnetic field.

The near magnetic field antenna according to claim 1 is connected to each one end of a plurality of concentric antennas composed of conducting wires, and one linear current input feeder line for inputting a current to the plurality of antennas, Each one end is connected to each other end of each of the plurality of antennas, and has a plurality of linear current output feeder lines arranged parallel to the current input feeder line within a certain proximity distance, The number of antennas is four, and the plurality of antennas are arranged on the surface of the planar substrate , and the first antenna among the fourth antennas located on the innermost side from the first antenna located on the outermost side The traveling direction of each current flowing through the fourth antenna is the same direction, and the traveling direction of each current flowing through the second antenna and the third antenna is the traveling direction of the current flowing through the first antenna. The current input feeder line and the two current output feeder lines respectively connected to the first antenna and the second antenna are connected to the second antenna. except for the intersection between the first antenna at a current output feeder line, the are arranged in a plane surface of the substrate, the third antenna and the fourth two of said current output feeder respectively connected to the antenna The gist is that the line and the current output feeder line at the intersection are arranged on the back surface of the flat substrate .

According to the present invention, a single linear current input feeder line for inputting current to a plurality of antennas is provided, and a plurality of linear current output feeder lines respectively connected to the plurality of antennas are connected to the current. Since the input feeder lines are arranged in parallel within a certain proximity distance, an unnecessary magnetic field from each feeder line can be reduced. Further, according to the present invention, since the traveling directions of the currents flowing through the plurality of antennas are different, a magnetic field far from the near magnetic field antenna can be rapidly attenuated.

  The near magnetic field antenna according to claim 2 is the near magnetic field antenna according to claim 1, wherein each one end is connected to each other end of each of the plurality of current output feeder wires, and each other end is connected to a ground terminal. The gist of the present invention is to further include a plurality of current adjusting impedance elements for adjusting the values of currents flowing through the antennas.

  The near-field antenna according to claim 3 is the near-field antenna according to claim 2, wherein the near-field antenna is inserted between the plurality of current adjusting impedance elements and the ground terminal, and current values flowing through the plurality of antennas are respectively determined. It further includes a plurality of current monitoring resistors having the same resistance value for monitoring, and a plurality of monitor terminals for monitoring voltage values generated between both ends of the plurality of current monitoring resistors, respectively. And

The near magnetic field antenna according to claim 4 is the near magnetic field antenna according to any one of claims 1 to 3 , wherein an absolute value of a current flowing through the first antenna and an area of the portion surrounded by the first antenna And the multiplication value of the absolute value of the current flowing through the third antenna and the area of the portion surrounded by the third antenna are the same, and the absolute value of the current flowing through the second antenna The product of the value and the area of the portion surrounded by the second antenna, and the product of the absolute value of the current flowing through the fourth antenna and the area of the portion surrounded by the fourth antenna. The gist is that they are the same.

The near magnetic field antenna according to claim 5 is the near magnetic field antenna according to any one of claims 1 to 4 , wherein the plurality of antennas are concentric loop antennas.

  According to the present invention, in a near magnetic field antenna using one current source, an unnecessary magnetic field from a feeder line can be reduced, and a magnetic field far from the near magnetic field antenna can be rapidly attenuated.

It is a figure which shows the structure of a double loop antenna. It is a figure which shows electric field strength distribution on a double loop antenna central axis. It is a figure which shows the structure of a quadruple loop antenna. It is a figure which shows the electric field strength distribution on a quadruple loop antenna central axis. It is a figure which shows the basic structure of the conventional loop antenna.

  Hereinafter, an embodiment for carrying out the present invention will be described with reference to the drawings. However, the present invention can be implemented in many different modes and should not be construed as being limited to the description of the present embodiment.

[First Embodiment]
In the first embodiment, a case of a double loop antenna using two loop antennas will be described as an example.

  FIG. 1 is a diagram showing a structure of a near magnetic field antenna 1 according to the present embodiment. The near magnetic field antenna 1 outputs two loop antennas 11a and 11b, one current input feeder line 12 for inputting a current to each loop antenna 11a and 11b, and a current flowing through each loop antenna 11a and 11b. Two current output feeder lines 13a and 13b are provided.

  The first loop antenna 11a and the second loop antenna 11b are each configured by an arc-shaped conductor, so that the first loop antenna 11a having a large diameter is outside the second loop antenna 11b having a small diameter. They are arranged concentrically on the same plane.

  Further, in order to make the traveling directions of the currents flowing in opposite directions to each other, the terminal in which the current flows in the clockwise direction in the first loop antenna 11a is the current input terminal 11a_in, and the terminal in the second loop antenna 11b is in the opposite direction. The terminal that supplies current in the clockwise direction is defined as a current input terminal 11b_in.

  Since the current input feeder line 12 supplies the current from one current source (signal source) to all the loop antennas 11a and 11b, it is one linear shape that is commonly used for all the loop antennas 11a and 11b. It is comprised by the conducting wire.

  Both ends thereof are connected to a current source connection terminal T_in for connecting a current source and a current input terminal 11b_in of the second loop antenna 11b. Further, an arbitrary part on the current input feeder line 12 is connected to the current input terminal 11a_in of the first loop antenna 11a.

  Since the two current output feeder lines 13a and 13b output the currents flowing through the two loop antennas 11a and 11b, respectively, one ends are connected to the current output terminals 11a_out and 11b_out of the two loop antennas 11a and 11b, respectively. ing.

  The current input feeder line 12 and the two current output feeder lines 13a and 13b are arranged on the same plane as the two loop antennas 11a and 11b. However, the second current output feeder line 13b is arranged on the back plane parallel to the plane only at the portion intersecting with the outer first loop antenna 11a.

  Here, the two current output feeder lines 13a and 13b are configured by linear conductors like the current input feeder line 12, but are not arbitrarily wired on a plane, but are connected to the current input feeder line 12. They are arranged so as to be parallel and close to each other within a certain distance.

  Thus, since the current input feeder line 12 and the two current output feeder lines 13a and 13b are arranged in parallel and close to each other, an unnecessary magnetic field from these feeder lines can be reduced.

  Further, as shown in FIG. 1, the near-field antenna 1 according to the present embodiment includes two current adjustment variable resistors 14a and 14b corresponding to the two loop antennas 11a and 11b, and two current monitors. Fixed resistors 15a and 15b.

  The variable resistor for current adjustment 14a has one end connected to the other end of the current output feeder line 13a and the other end connected to the ground side. Similarly, the current adjusting variable resistor 14b has one end connected to the other end of the current output feeder line 13b and the other end connected to the ground side.

  These two current adjustment variable resistors 14a and 14b are used to adjust the current values flowing through the two loop antennas 11a and 11b, respectively. Although one resistor may be used as in this embodiment, for example, a capacitor, an inductor, or any combination thereof including a resistor may be used.

  One end of the current monitoring fixed resistor 15a is connected to the ground side of the current adjusting variable resistor 14a, and the other end is connected to the ground connection terminal T_gnd and the ground. Similarly, the current monitoring fixed resistor 15b has one end connected to the ground side of the current adjusting variable resistor 14b and the other end connected to the ground.

  These two current monitoring fixed resistors 15a and 15b have the same resistance value and are used to monitor the current values flowing through the two loop antennas 11a and 11b, respectively.

  Further, a conducting wire is connected to a connection end of the current monitoring fixed resistor 15a with the current adjusting variable resistor 14a, and the other end of the conducting wire is used as a first monitor terminal T_mon_a. Similarly, another conducting wire is connected to the connecting end of the current monitoring fixed resistor 15b with the current adjusting variable resistor 14b, and the other end of the conducting wire is used as a second monitor terminal T_mon_b.

  These two monitor terminals T_mon_a and T_mon_b are used to monitor voltage values generated between both ends of the two current monitoring fixed resistors 15a and 15b, respectively.

  Next, functions and effects of the near magnetic field antenna 1 according to the present embodiment will be described based on the flowing current. However, it is assumed that a signal line and a ground line of an appropriate current source are connected to the current source connection terminal T_in and the ground connection terminal T_gnd of the near magnetic field antenna 1, respectively.

  The current supplied from the current source is supplied to the first loop antenna 11a and the second loop antenna 11b by the current input feeder line 12, respectively. Here, when viewed from the current source connection terminal T_in, a current is supplied to the left current input terminal 11a_in of both ends of the first loop antenna 11a, and a current is supplied to the right current input terminal 11b_in of both ends of the second loop antenna 11b. Therefore, the traveling directions of the currents flowing through the two loop antennas 11a and 11b are opposite to each other.

  Thus, since the traveling directions of the currents flowing through the first loop antenna 11a and the second loop antenna 11b are opposite to each other, a magnetic field far from the near magnetic field antenna 1 can be rapidly attenuated.

  Here, the reason why such an effect is obtained will be described. In general, the strength of the magnetic field generated by the loop antenna at a distance is proportional to the magnetic moment vector (current value × current loop area).

  Here, the direction of the vector is assumed to be a right-handed direction with respect to the direction of current perpendicular to the loop surface. Then, when the traveling directions of the currents flowing through the two loop antennas 11a and 11b arranged on the same plane are opposite to each other and the magnitudes of the magnetic moments are approximately the same, the magnetic moments cancel each other out. Therefore, the magnetic field strength in the distance is extremely small.

  On the other hand, the magnetic field strength in the vicinity is not necessarily proportional to the magnetic moment, and the magnetic field distribution in the vicinity changes in a complicated manner on a case-by-case basis. For example, in the vicinity of the center point of the loop antenna of FIG. 1, the magnetic moments of the two loop antennas 11a and 11b cancel each other because they are strongly influenced by the current flowing through the inner current loop rather than the outer current loop. Even if there is a relationship, the magnetic field near the center point does not become extremely small. The above is the attenuation effect of the magnetic field.

  Returning to the description of the function and the like of the near magnetic field antenna 1. The currents returned from the two loop antennas 11a and 11b pass through the current output feeder wires 13a and 13b, pass through the current adjusting variable resistors 14a and 14b and the current monitoring fixed resistors 15a and 15b, respectively, and then are grounded. Return to the current source from the connection terminal T_gnd.

  As described above, since the two current monitoring fixed resistors 15a and 15b are provided on the current lines of the two loop antennas 11a and 11b, the two current monitoring fixed resistors are used by using the monitor terminals T_mon_a and T_mon_b. By monitoring the voltage generated between both ends of 15a and 15b, the current flowing through the two loop antennas 11a and 11b can be indirectly monitored.

  Since the current adjusting variable resistors 14a and 14b are respectively inserted between the current monitoring fixed resistors 15a and 15b and the loop antennas 11a and 11b, the values of these two variable resistors can be set while performing the above monitoring. By adjusting, the value of the current flowing through the loop antennas 11a and 11b can be set appropriately.

FIG. 2 is a diagram showing the distribution of the magnetic field strength on the central axis of the double loop antenna. Magnetic field intensity distributions by the conventional loop antenna and the double loop antenna according to the present embodiment are shown by a broken line and a solid line, respectively. The horizontal axis is the relative position (= z / r _a ) on the center axis of the loop antenna, and the vertical axis is the magnetic field strength (strength normalized with the value at the loop center). However, where the r _a is the outermost radius of the loop antenna, z is the position on the loop antenna center axis.

  As can be seen from the figure, since it has a steep magnetic field attenuation characteristic, a magnetic field far from the near magnetic field antenna can be rapidly attenuated, and a sharper magnetic field distribution can be generated than in the prior art.

  When such a double loop antenna is used, it is desirable to appropriately set the radius r and current value I of each loop antenna according to the purpose, but when plotting the solid line in FIG. As an example, the following relationship is established. However, the subscripts a and b of r and I are identifiers of the first and second loop antennas, respectively.

r _a = 2r _b Formula (1)
I _b = 4I _a Formula (2)
[Second Embodiment]
In the second embodiment, a case of a quadruple loop antenna using four loop antennas will be described as an example.

  FIG. 3 is a diagram showing the structure of the near magnetic field antenna 1 according to the present embodiment. The near magnetic field antenna 1 outputs four loop antennas 11a to 11d, one current input feeder line 12 for inputting a current to each of the loop antennas 11a to 11d, and a current flowing through each of the loop antennas 11a to 11d. 4 current output feeder wires 13a to 13d for carrying out the operation.

  The four loop antennas 11a to 11d are each constituted by an arcuate conductor, and are concentrically arranged on the same plane, as in the first embodiment. Here, the first loop antenna 11a to the fourth loop antenna 11d are set in order from the loop antenna having the largest diameter.

  Further, the first loop antenna 11a, the fourth loop antenna 11d, the second loop antenna 11b, and the third loop antenna 11c have the first loop antenna to reverse the traveling directions of the currents flowing in the first loop antenna 11a and the fourth loop antenna 11d, The terminals through which current flows in the clockwise direction in 11a and the fourth loop antenna 11d are defined as current input terminals 11a_in and 11d_in, and the current in the counterclockwise direction in the second loop antenna 11b and the third loop antenna 11c. The terminals through which current flows are designated as current input terminals 11b_in and 11c_in.

  Since the current input feeder line 12 supplies the current from one current source to all the loop antennas 11a to 11d as in the first embodiment, it is commonly used for all the loop antennas 11a to 11d. It is comprised by one linear conducting wire.

  Both ends thereof are connected to a current source connection terminal T_in for connecting a current source and a current input terminal 11d_in of the fourth loop antenna 11d. Further, in any part on the current input feeder line 12, the current input terminal 11a_in of the first loop antenna 11a, the current input terminal 11b_in of the second loop antenna 11b, and the current input terminal of the third loop antenna 11c. 11c_in.

  Since the four current output feeder lines 13a to 13d output the currents flowing through the four loop antennas 11a to 11d, respectively, as in the first embodiment, each one end of each of the four loop antennas 11a to 11d The current output terminals 11a_out, 11b_out, 11c_out, and 11d_out are respectively connected.

  The current input feeder line 12 and the two current output feeder lines 13a and 13b are arranged on the same plane as the four loop antennas 11a to 11d. However, the second current output feeder line 13b is arranged on the back plane parallel to the plane only at the intersection of the outer first loop antenna 11a. The remaining two current output feeder lines 13c and 13d are arranged on the back plane.

  Here, all the current output feeder lines 13a to 13d are configured by linear conductors as in the case of the current input feeder line 12, but are not arbitrarily wired on each plane, but the first embodiment. Similar to the embodiment, the current input feeder line 12 is arranged so as to be parallel and close to each other within a certain distance.

  Thus, since the current input feeder line 12 and the four current output feeder lines 13a to 13d are arranged in parallel and close to each other, an unnecessary magnetic field from these feeder lines can be reduced.

  In addition, the two current output feeder lines 13c and 13d are arranged behind the plane on which the current input feeder line 12 and the two current output feeder lines 13c and 13d are arranged. Since the distance to the feeder line can be made closer, the unnecessary magnetic field from the feeder line can be further reduced.

  Further, as shown in FIG. 3, the near-field antenna 1 according to the present embodiment includes four current adjustment variable resistors 14a to 14d corresponding to the four loop antennas 11a to 11d and four current monitors. Fixed resistors 15a to 15d. The purpose of use of these resistors and the connection relationship with other components are the same as those in the first embodiment as can be understood from the configuration shown in FIG. Omitted.

  Next, functions and effects of the near magnetic field antenna 1 according to the present embodiment will be described based on the flowing current. However, it is assumed that a signal line and a ground line of an appropriate current source are respectively connected to the current source connection terminal T_in and the ground connection terminal T_gnd of the above-described near-field antenna 1.

  The current supplied from the current source is supplied to all the loop antennas 11 a to 11 d by the current input feeder line 12. Here, when viewed from the current source connection terminal T_in, a current is supplied to the left current input terminals 11a_in and 11d_in of both ends of the first loop antenna 11a and the fourth loop antenna, and the second loop antenna 11b and the second loop antenna 11b. Since current is supplied to the current input terminals 11b_in and 11c_in on the right side of both ends of the third loop antenna 11c, the first loop antenna 11a, the fourth loop antenna 11d, the second loop antenna 11b, and the third loop are supplied. The traveling directions of the currents flowing through the antenna 11c are opposite to each other.

  As described above, since the traveling directions of the currents flowing through the first loop antenna 11a and the fourth loop antenna 11d and the second loop antenna 11b and the third loop antenna 11c are opposite to each other, the near magnetic field antenna The magnetic field far from 1 can be attenuated rapidly.

  The currents returned from the four loop antennas 11a to 11d pass through the current output feeder lines 13a to 13d, respectively, and pass through the current adjustment variable resistors 14a to 14d and the current monitoring fixed resistors 15a to 15d, respectively. Return from the ground connection terminal T_gnd to the current source.

  As described above, the four current monitoring fixed resistors 15a to 15d are provided on the current lines of the four loop antennas 11a to 11d. By monitoring the voltage generated across each of the fixed monitoring resistors 15a to 15d, the current flowing through the four loop antennas 11a to 11d can be monitored indirectly.

  Since the current adjusting variable resistors 14a to 14d are inserted between the current monitoring fixed resistors 15a to 15d and the loop antennas 11a to 11d, the values of these four variable resistors are set while performing the above monitoring. By adjusting, the value of the current flowing through the loop antennas 11a to 11d can be set appropriately.

Here, it is considered that there are an infinite number of current values suitable for obtaining a sharp magnetic field distribution. For example, | I _a × S _a | = | I _c × S _c | and | I _b × S _b | = By setting each current value I so as to satisfy the relationship | I _d × S _d |, a sharp magnetic field distribution that cannot be obtained with a single loop antenna can be obtained. Here, I and S are the absolute value of the current of the loop antenna and the area of the portion surrounded by the loop antenna, respectively. The subscripts a to d are identifiers of the first to fourth loop antennas, respectively.

  FIG. 4 is a diagram showing the distribution of the magnetic field strength on the central axis of the quadruple loop antenna. As can be seen from this figure, it has a steeper magnetic field attenuation characteristic than the double loop antenna, so it can attenuate the magnetic field far away from the nearby magnetic field antenna more abruptly and generate a sharper magnetic field distribution can do. Note that when the solid line in FIG. 4 is plotted, the following relationship is established as an example.

r _a : r _b : r _c : r _d = 10: 8: 5: 4 (3)
I _a : I _b : I _c : I _d = 1: 2: 4: 8 Formula (4)
As mentioned above, according to each embodiment, since the current input feeder line 12 and all the current output feeder lines 13 are arranged in parallel within a certain proximity distance, the unnecessary magnetic field from these feeder lines can be reduced. Can do.

  Moreover, according to each embodiment, since the traveling directions of the currents flowing through the plurality of loop antennas 11 are different from each other, a magnetic field far from the near magnetic field antenna 1 can be rapidly attenuated.

  Furthermore, according to each embodiment, since the current adjusting variable resistor 14 is inserted between the current monitoring fixed resistor 15 and the loop antenna 11, the magnetic field distribution intended by the user can be generated.

  Finally, in each of the embodiments, a concentric loop antenna has been described as an example, but in addition to such an arc-shaped loop antenna, a regular dodecagonal antenna that is close to an arc or an arc that is so close to an arc Similar effects can be obtained even when non-square or rectangular antennas are arranged concentrically.

  Moreover, such a near magnetic field antenna 1 can be used for an antenna of an electric field communication system as disclosed in Patent Document 3, for example.

DESCRIPTION OF SYMBOLS 1 ... Near magnetic field antenna 11 ... Loop antenna 12 ... Current input feeder line 13 ... Current output feeder line 14 ... Variable resistance for current adjustment 15 ... Fixed resistance for current monitoring T_in ... Current source connection terminal T_gnd ... Ground connection terminal T_mon ... Monitor terminal

Claims (5)

One linear current input feeder line connected to each end of a plurality of concentric antennas composed of conducting wires, and for inputting a current to the plurality of antennas;
Each one end is connected to each other end of each of the plurality of antennas, and has a plurality of linear current output feeder lines arranged in parallel to the current input feeder line within a certain proximity distance, and
The number of the plurality of antennas is four, and the plurality of antennas are disposed on the surface of the planar substrate,
Among the fourth antennas located on the innermost side from the first antenna located on the outermost side, the traveling directions of the respective currents flowing in the first antenna and the fourth antenna are the same direction, and the second antenna and the third antenna The traveling direction of each current flowing through the antenna is opposite to the traveling direction of the current flowing through the first antenna,
The current input feeder line and the two current output feeder lines respectively connected to the first antenna and the second antenna are:
Except for the intersection between the first antenna at a current output feeder line connected to the second antenna, it is disposed on a surface of the planar substrate,
The two current output feeder lines connected to the third antenna and the fourth antenna, respectively, and the current output feeder line at the intersection,
A near magnetic field antenna, wherein the near magnetic field antenna is disposed on a back surface of the flat substrate .   Each one end is connected to each other end of the plurality of current output feeder wires, each other end is connected to a ground terminal, and a plurality of current adjustment impedance elements for adjusting the current values flowing through the plurality of antennas are respectively provided. The near magnetic field antenna according to claim 1, further comprising: A plurality of current monitoring resistors, each inserted between the plurality of current adjusting impedance elements and the ground terminal, each having a same resistance value for monitoring a current value flowing through each of the plurality of antennas;
A plurality of monitor terminals for respectively monitoring voltage values generated between both ends of the plurality of current monitoring resistors;
The near magnetic field antenna according to claim 2, further comprising: Surrounded by the multiplication value of the absolute value of the current flowing through the first antenna and the area of the portion surrounded by the first antenna, and the absolute value of the current flowing through the third antenna and the third antenna. The multiplication value of the area of the selected part is the same,
The multiplication value of the absolute value of the current flowing through the second antenna and the area of the portion surrounded by the second antenna, and the absolute value of the current flowing through the fourth antenna and the fourth antenna. The near magnetic field antenna according to claim 1, wherein a multiplication value of the area of the adjacent portion is the same. The plurality of antennas are:
The near magnetic field antenna according to claim 1, wherein the near magnetic field antenna is a concentric loop antenna.

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