JP4644357B2 - Magnetic detection antenna - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic detection antenna that detects a minute magnetic field.
[0002]
[Prior art]
Conventionally, there is a method for detecting a magnetic field generated by the current in analysis of a current flowing in a line pattern formed on an electronic substrate, and this method uses a magnetic detection antenna that outputs a detection signal corresponding to the magnetic field. It is done. As shown in FIG. 8, there are magnetic detection antennas in which an air core bobbin 900 is wound with a coil 901, and a magnetically permeable material core is inserted into the bobbin 900 to increase sensitivity. .
[0003]
[Problems to be solved by the invention]
However, in a relatively low frequency, for example, in the medium wave (MF) band (300 kHz to 3 MHz), the detection sensitivity is insufficient, and the coil diameter must be increased to ensure a certain amount of magnetic flux. As a result, it is difficult to detect the magnetic field in the minute region, and the magnetic field distribution cannot be measured with high resolution.
[0004]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a magnetic detection antenna capable of detecting a magnetic field with high accuracy.
[0005]
[Means for Solving the Problems]
In the invention according to claim 1, a core member formed of a magnetically permeable material in a substantially ring shape and forming a closed magnetic path therein,
A coil for detection formed by winding a conducting wire around a part of the core member to form a closed circuit;
An output coil formed by winding a conductive wire around the other part of the core member;
The core member is formed into an elongated substantially ring shape, and the half of the longitudinal direction thereof is formed into an elongated shape having two substantially straight side surfaces facing each other and having a U-shaped one end portion connecting these substantially linear portions, The detection coil is provided at the one end, and the other half of the longitudinal direction of the core member is shaped so as to spread in a gentle arc, and the output coil is provided in a part of the arc. ,
Forming the detection coil in a size with a gap between the core member,
The gap is used as a detection region that receives an external magnetic field, and when the external magnetic field penetrates the detection region, a detection signal of the external magnetic field is output from the line end of the output coil.
[0006]
Since the detection coil and the output coil are magnetically coupled by the core member, when an external magnetic field penetrates the detection region and an induced electromotive force is generated in the detection coil, the detection output is output to the output coil. Can be taken out from. Here, the detection sensitivity is defined by the turn ratio between the detection coil and the output coil. Therefore, it is not necessary to take a method of ensuring sensitivity by increasing the diameter of the detection coil close to the detection site such as an electronic substrate, and high resolution can be obtained by reducing the detection area.
The magnetic field can be easily detected by touching the one end side of the magnetic detection antenna even in a narrow place where electronic parts are densely packed.
[0007]
According to a second aspect of the present invention, in the configuration of the first aspect of the present invention, a core piece of a magnetically permeable material is provided in the detection region.
[0008]
By increasing the magnetic permeability of the detection region, the magnetic flux contributing to the induced electromotive force of the detection coil is increased, and the detection sensitivity is improved.
[0009]
According to a third aspect of the present invention, in the configuration of the first or second aspect of the present invention, a resistor is connected in series with the detection coil.
[0010]
By selecting the resistance value of the resistor, impedance matching with the device that receives the detection output of the output coil can be easily achieved.
[0011]
According to a fourth aspect of the present invention, in the configuration of the first to third aspects of the invention, in the other half of the core member in the longitudinal direction, the opposing side surfaces following the two substantially linear side surfaces of the half portion are gently expanded. Thus, the arc-shaped portion is formed .
[0013]
According to a fifth aspect of the present invention, in the configuration of the first to fourth aspects of the invention, the core member around which the detection coil and the output coil are wound is made of a conductive material or a magnetically permeable material. Covered with a shield member,
The shield member has a configuration in which a portion of the detection coil surrounding the detection region protrudes outside the shield member.
[0014]
Since the inside is electromagnetically shielded by the shield member, erroneous detection and noise can be reduced.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
1A and 1B show a magnetic detection antenna according to a first embodiment of the present invention. The magnetic detection antenna includes two types of cores 1 and 2 and two types of coils 3 and 4.
[0016]
The first type of core 1 that is a core member is formed by forming a magnetically permeable material into an elongated substantially ring shape, and has a closed magnetic path formed therein. The shape of the core 1 is configured so that there is no discontinuity in the curvature of each part, and the leakage magnetic flux is suppressed. Further, the slightly half portion in the longitudinal direction of the core 1 has a substantially straight shape in which the opposite side surfaces are close to each other, and one end portion 11 in the longitudinal direction of the core 1 where the substantially straight portions gather is bent in a U-shape. ing. R is given to the bent part. The remaining half of the length of the core is slightly arcuate with the opposite side surfaces expanding (hereinafter this core is referred to as the main core). As the magnetic permeable material for the main core 1, a material having high magnetic permeability and low frequency loss is desirable, and ferrite, iron, or the like is used. From the viewpoint of formability, an amorphous magnetic material is preferable. The structure may be a structure in which a magnetically permeable material is formed into a sheet shape having the above-described shape and a plurality of sheets are laminated to reduce eddy current loss.
[0017]
The second type of core 2 that is a core piece is formed by forming a magnetically permeable material into a cylindrical shape having a thickness substantially the same as that of the main core 1, and its length is one end of the main core 1 that is close to the opposite side surface. The interval between the opposing side surfaces of the portion 11 is about the same (hereinafter, this core is called a sense core). The magnetically permeable material for the sense core 2 is preferably a material having high magnetic permeability and low high-frequency loss, such as ferrite. The sense core 2 is attached to the outer side surface of the main core 1 with an adhesive or the like along the U-shaped one end portion 11 of the main core 1.
[0018]
The first type coil 3 that is a detection coil is formed by winding a conductive wire together with the U-shaped one end portion 11 of the main core 1 and the sense core 2 and is linked to the main core 1 ( Hereinafter, this coil is referred to as a sense coil). The sense coil 3 has a closed circuit in which wire ends (not shown) are connected to each other by soldering or the like.
[0019]
In the second type coil 4 that is an output coil, a conducting wire is wound around the other end portion 12 in the longitudinal direction of the main core 1, and a detection signal Vo is extracted from the line ends 401 and 402. (Hereinafter, this coil is referred to as an output coil).
[0020]
This magnetic detection antenna is used with the side on which the sense core 2 and the sense coil 3 are provided close to the electronic substrate to be measured. If there is a magnetic field penetrating the cylindrical sense core 2 in the axial direction in a state where a magnetic field oscillating due to a current flowing through a line pattern formed on the electronic substrate is generated, the magnetic field in the sense core 2 depends on the magnitude of magnetic flux. An induced electromotive force is generated in the sense coil 3 and an induced current flows. Since the induced magnetic field penetrates the inner region defined by the sense coil 3 by this induced current, a magnetic flux appears in a closed magnetic path inside the main core 1 that is linked to the sense coil 3.
[0021]
Then, an induced electromotive force is generated in the output coil 4 by this magnetic flux, and a magnetic field generated near the surface of the electronic substrate or the like can be detected from this.
[0022]
The output signal of the magnetic detection antenna is extracted from the line end 41 of the output coil 4 that is separate from the sense coil 3, and the magnetic field is detected by changing the turns ratio of the sense coil 3 and the output coil 4. Since the sensitivity can be selected, a good sensitivity can be obtained without adopting a high sensitivity by increasing the diameter of the coil through which the magnetic field to be detected penetrates. Therefore, the resolution is improved by reducing the cross-sectional area of the sense core 2 through which the detected magnetic field passes.
[0023]
Further, since the main core 1 has an elongated shape, and particularly the one end 11 side where the sense core 2 and the sense coil 3 are provided, the sense core 2 and the sense coil 3 can be handled in a narrow space, and the electronic component It becomes an excellent probe for detecting a magnetic field corresponding to a recent electronic substrate having a high mounting density.
[0024]
FIG. 2 shows the result of measuring the magnetic field in the vicinity of a single wire with this magnetic detection antenna. With a signal of about 300 kHz flowing through the single wire, the magnetic detection antenna is moved in a direction perpendicular to the single wire at a position 1 mm from the single wire, The detection result of the near magnetic field component in this moving direction is shown. Since the magnetic field around the single line is inversely proportional to the distance from the single line and is orthogonal to the direction facing the single line, the magnetic field component in the direction of movement decreases as the distance from the antenna increases. According to the present magnetic detection antenna, if the position of the magnetic detection antenna is different by about 2 mm, it changes by 10 dB or more, and the resolution is extremely high. This is recognized as an effect of being able to sufficiently reduce the size of the detection region of the sense coil 3, that is, the size of the cross section of the sense core 2.
[0025]
Further, the output coil 4 functions as a balun that realizes balanced / unbalanced conversion, and the coaxial wire 5 is connected to the line ends 401 and 402 of the output coil 4 as shown in FIG. When the balanced output is received by the unbalanced line, the common mode current I flowing in the output coil 4 in the same phase can be canceled out.
[0026]
(Second Embodiment)
4A and 4B show a magnetic detection antenna according to a second embodiment of the present invention. In the figure, the same number is attached | subjected about the part which carries out substantially the same operation | movement as 1st Embodiment, and it demonstrates centering around difference with 1st Embodiment. Both line ends 301 and 302 of the sense coil 3 are connected by a resistor 6, and the sense coil 3 and the resistor 6 form a closed circuit.
[0027]
By providing the resistor 6, it is possible to easily match the impedance with the device that receives the output signal of the magnetic detection antenna. The impedance matching can be further improved by adjusting the turns ratio of the sense coil 3 and the output coil 4.
[0028]
(Third embodiment)
5 and 6 show a magnetic detection antenna according to a third embodiment of the present invention. In the figure, the same number is attached | subjected about the part which carries out substantially the same operation | movement as 1st Embodiment, and it demonstrates centering around difference with 1st Embodiment.
[0029]
The main core 1 is housed in a flat dropper-shaped shield case 7 that is a shield member that covers substantially the whole. The shield case 7 is composed of case members 7a and 7b having substantially the same shape, which are divided in half. The notches 701a and 701b in which the sense core 2 attached to the one end 11 of the main core 1 is exposed. And notches 702a and 702b for drawing out the wire ends of the output coil 4. The case members 7a and 7b have a laminated structure of a high magnetic permeability material layer 71 and a conductive material layer 72, and the shield case 7 is shielded magnetically and electrically. For example, ferrite or the like can be used as the high magnetic permeability material, and copper or the like can be used as the conductive material.
[0030]
Due to the shielding effect of the shield case 7, a magnetic detection antenna with good noise resistance can be obtained.
[0031]
The shield case 7 does not necessarily have a two-layer structure, and may be made of iron (silicon steel plate) having both high magnetic permeability and conductivity.
[0032]
(Fourth embodiment)
FIG. 7 shows a magnetic detection antenna according to a fourth embodiment of the present invention. In the figure, the same number is attached | subjected about the part which carries out substantially the same operation | movement as 1st-3rd embodiment, and it demonstrates centering around difference with 1st-3rd embodiment.
[0033]
In this magnetic detection antenna, in the configuration of the third embodiment, the coaxial line 5 </ b> A that receives the output of the output coil 4 has the same double shield structure as the shield case 7. In the coaxial line 5A, an inner conductor 51, an insulator 52, an outer conductor 53, and a magnetic shield body 54 are formed coaxially from the center side, and the inner conductor 51 and the outer conductor 53 are connected to the line ends 401 and 402 of the output coil 4. Conduction is conducted in a one-to-one correspondence. The outer conductor 53 is also in electrical communication with the conductive material layer 72 of the shield case 7.
[0034]
Thereby, it can be set as a magnetic detection antenna with better noise resistance.
[0035]
The coaxial line 5A does not necessarily need to have the outer conductor 53 and the magnetic shield 54 separated, and may be made of iron (silicon steel plate) having both high magnetic permeability and conductivity.
[0036]
In each of the above embodiments, the sense core 2 is provided to increase the magnetic flux density, but depending on the required detection performance, this may be omitted and the gap between the sense coil 3 and the main core 1 will be detected as an air core. It can also be an area.
[0037]
Further, the sense core 2 may be a rectangular shape, a curved shape or the like instead of a cylindrical shape.
[0038]
Further, in each of the above examples in plan view, the axial direction of the sense core 2 that is the direction of the detectable magnetic field is configured to be horizontal and transverse to the paper surface, but in the longitudinal direction of the main core 1. By providing a twisted portion or a bent portion in the middle, the direction of the detectable magnetic field can be directed in a convenient direction.
[0039]
In addition, the main core 1 and the sense core 2 are in contact with each other, but the lengths of the end portions 11 of the main core 1 do not reach the notches 701a and 701b by extending the notches 701a and 701b of the case members 7a and 7b. The sense core 2 located outside the core 1 and the case 7 may be separated.
[0040]
Further, the shape of the main core is not limited to the dropper shape shown in the figure, and a simple, generally elongated shape can be used without providing a gently curved portion. On the contrary, if it is not necessary to touch a narrow place, the shape may be rounded as a whole.
[Brief description of the drawings]
FIG. 1A is a plan view of a magnetic detection antenna according to a first embodiment of the present invention, and FIG. 1B is an enlarged perspective view of a tip portion of the magnetic detection antenna.
FIG. 2 is a graph illustrating the operation of the magnetic detection antenna.
FIG. 3 is a plan view of a modified example of the magnetic detection antenna.
4A is a plan view of a magnetic detection antenna according to a second embodiment of the present invention, and FIG. 4B is an enlarged perspective view of a tip portion of the magnetic detection antenna.
FIG. 5 is a plan view of a magnetic detection antenna according to a third embodiment of the present invention.
FIG. 6 is an exploded perspective view of the magnetic detection antenna.
FIG. 7 is a plan view of a magnetic detection antenna according to a fourth embodiment of the present invention.
FIG. 8 is a front view of a typical example of a conventional magnetic detection antenna.
[Explanation of symbols]
1 Main core (core member)
2 Sense core (core piece)
3 Sense coil (coil for detection)
301, 302 Line end 4 Output coil (coil for output)
401, 402 Line end 5, 5A Coaxial line 6 Resistor 7 Shield case (shield member)

Claims (5)

A core member formed of a magnetically permeable material in a substantially ring shape and forming a closed magnetic path therein;
A coil for detection formed by winding a conducting wire around a part of the core member to form a closed circuit;
An output coil formed by winding a conductive wire around the other part of the core member;
The core member is formed into an elongated substantially ring shape, and the half of the longitudinal direction thereof is formed into an elongated shape having two substantially straight side surfaces facing each other and having a U-shaped one end portion connecting these substantially linear portions, The one end portion is provided with the detection coil, and the other half of the core member in the longitudinal direction is expanded in a gentle arc, and the output coil is provided in a part of the arc-shaped portion,
Forming the detection coil in a size with a gap between the core member,
The magnetic detection antenna according to claim 1, wherein a detection signal of an external magnetic field is output from a line end of the output coil when the external magnetic field penetrates the detection region with the gap as a detection region for receiving an external magnetic field.   The magnetic detection antenna according to claim 1, wherein a core piece made of a magnetically permeable material is provided in the detection region.   3. The magnetic detection antenna according to claim 1, wherein a resistor is connected in series with the detection coil. 4. The magnetic detection antenna according to claim 1, wherein the other half portion of the core member in the longitudinal direction has an opposite side surface that extends gradually from two substantially straight side surfaces of the half portion, and the arc-shaped portion. Forming a magnetic detection antenna. 5. The magnetic detection antenna according to claim 1, wherein the core member around which the detection coil and the output coil are wound is covered with a shield member made of a conductive material or a magnetically permeable material. ,
And the magnetic detection antenna which made this shield member the structure where the part surrounding the said detection area | region among the said coils for a detection protrudes outside the shield member.

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