JP2015007579A - Magnetic field detection probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic field detection probe configured to improve magnetic field detection sensitivity when being brought close to an object to be measured.SOLUTION: In a magnetic field detection probe 1, positions of a signal conductor 4 and a constant-potential conductor 5 are defined so that the constant-potential conductor 5 may not come closer to an object to be measured than the signal conductor 4 at least, in a sensor unit 2, based on a facing surface 8 facing the object to be measured which generates a magnetic field. A looped transmission line is an unbalanced line where no constant-potential conductor (wider than the signal conductor) is arranged on the outermost side, thereby preventing capacitive coupling between the transmission line and the object to be measured when close to the object to be measured, and preventing change in the magnetic field. Magnetic field detection sensitivity can be improved, accordingly.

Description

  The present invention relates to a magnetic field detection probe using a shielded loop antenna.

  Conventionally, a magnetic field detection probe using a shielded loop antenna is known. In the shielded antenna, a coaxial cable or a semi-rigid cable is formed in a loop shape, and one end of the cable is connected to a detection circuit. The other end of the cable includes a type in which the internal conductor is directly grounded (connected to the external conductor) and a type in which the internal conductor is grounded (connected to the external conductor) via a termination resistor. In either case, a gap using an external conductor is formed in the loop, and an induced voltage generated in the gap by a magnetic field linking the loop is detected by a detection circuit.

  By the way, in recent years, from the viewpoint of electromagnetic noise suppression, so-called EMC (Electro-Magnetic Compatibility), there is a need to measure a magnetic field for a wide variety of electronic devices.

  On the other hand, a transmission line is formed so that the thickness direction of the multilayer substrate having flexibility in the thickness direction is parallel to the loop surface, and for the constant potential on the outermost side and the innermost side of the loop-shaped transmission line, respectively. By placing conductors and placing signal conductors between these outer constant potential conductors and inner constant potential conductors, the multilayer substrate is bent in a direction parallel to the loop surface and closely attached to the measurement target. A shielded loop antenna is known (see, for example, Patent Document 1). In this shielded loop antenna, each of the two constant potential conductors is wider than the signal conductor (with a larger surface area) in order to simulate a known configuration in which the signal conductor is covered with the constant potential conductor. ) Is used.

JP 2012-112675 A

  However, in the prior art of Patent Document 1, the applicant of the present application, for example, when the multilayer substrate is brought into close contact with the measurement target, if the outer constant potential conductor approaches the measurement target, the constant potential conductor and the measurement target There was concern that the magnetic field might change due to electrical coupling with the surface like a capacitor and a part of the current flowing to the measurement target flowing to the constant potential conductor. That is, there is a concern that the magnetic field detection sensitivity may be lowered because a change from the magnetic field that is supposed to be generated depending on the measurement object occurs due to the change of the magnetic field.

  The present invention has been made in view of the above concerns, and an object of the present invention is to provide a magnetic field detection probe capable of improving the magnetic field detection sensitivity when approaching a measurement target.

  The present invention, which has been made to achieve the above object, comprises a signal conductor for transmitting a signal and a constant potential conductor for electromagnetically shielding the signal conductor, and partially exposing the signal conductor. A magnetic field detection probe includes a sensor unit that functions as a shielded loop antenna formed in a loop shape by a transmission line having a unit, and detects an electrical signal corresponding to the magnitude of a magnetic field passing through the sensor unit. In the present invention, in the sensor unit, the signal conductor and the constant potential conductor are positioned at a position where the constant potential conductor is at least closer to the measurement object than the signal conductor with reference to the facing surface facing the measurement target that generates the magnetic field. Each position is defined.

  According to the magnetic field detection probe of the present invention configured as described above, the loop-shaped transmission line is an unbalanced line in which the constant potential conductor (wider than the signal conductor) is not arranged on the outermost side. When approaching the measurement target, capacitive coupling between the transmission line and the measurement target is suppressed, and as a result, a change in the magnetic field is suppressed. Therefore, it is possible to improve the magnetic field detection sensitivity.

The magnetic field detection probe according to the present invention may be configured such that a part of the constant potential conductor is located at the same distance as the signal conductor with respect to the measurement object with reference to the above-described facing surface.
Further, the magnetic field detection probe of the present invention may be arranged such that the signal conductor is closer to the measurement object than the constant potential conductor with reference to the facing surface. That is, the constant potential conductor may be arranged inside the signal conductor in the loop transmission line.

  In the magnetic field detection probe of the present invention, a transmission line may be formed by using a loop-shaped multilayer substrate in the sensor unit, or a constant potential may be formed on the inner surface of a non-multi-layered loop substrate (single-layer substrate). A conductor may be disposed and a signal conductor may be disposed on the outer surface.

  In the magnetic field detection probe of the present invention, the sensor unit may be configured using a flexible substrate, and the transmission line may be a strip line configured on the substrate.

It is a perspective view which shows the external appearance of a magnetic field detection probe. It is sectional drawing which showed typically the internal structure of the magnetic field detection probe. It is the III-III sectional view in FIG. It is a graph which shows the measurement result of magnetic field detection sensitivity. It is a graph which shows the measurement result of a magnetic field detection sensitivity and an electric field detection sensitivity, (a) is a thing of a magnetic field detection probe, (b) is a thing of a comparative example. It is explanatory drawing which shows the structure of a measurement system. It is sectional drawing which showed typically the internal structure of the shielded loop antenna used as a comparative example. It is III-III sectional drawing in FIG. It is the 1st sectional view for explaining the variation of the conductor for constant potentials. It is the 2nd sectional view for explaining the variation of the conductor for constant potentials. It is the 3rd sectional view for explaining the variation of the conductor for constant potentials. It is sectional drawing for demonstrating the variation of a transmission line.

Embodiments of the present invention will be described below with reference to the drawings.
<Overall configuration>
As shown in FIG. 1, the magnetic field detection probe 1 includes a sensor unit 2 that generates an electrical signal corresponding to the magnitude of the magnetic field, and a connection unit 3 that extracts an electrical signal from the sensor unit 2. .

The connecting portion 3 includes a center conductor 31 and a cylindrical outer conductor 32 formed around the center conductor 31, and is formed of a well-known SMA connector having a characteristic impedance of 50Ω.
The sensor unit 2 is configured using a flexible multilayer substrate having flexibility formed in a loop shape, and includes a sealed dead loop antenna formed using a strip line printed on the multilayer substrate.

  As shown in FIG. 2, the multilayer substrate constituting the sensor unit 2 includes three dielectric layers 21 (211 to 213) and two conductor layers 22 (221) formed between the dielectric layers 21. To 222). Hereinafter, the innermost dielectric layer of the loop is referred to as a first layer 211, the outermost dielectric layer is referred to as a third layer 213, and the dielectric layer positioned therebetween is referred to as a second layer 212. . The signal conductor 4 is formed in the signal conductor layer 222, which is a conductor layer located between the second layer 212 and the third layer 213, and is located between the first layer 211 and the second layer. A constant potential conductor 5 is formed on the constant potential conductor layer 221 which is a conductor layer.

  However, as shown in FIG. 3, the constant potential conductor 5 has a line width (in the Y-axis direction in the figure) so that the transmission line formed by the signal conductor 4 and the constant potential conductor 5 functions as a strip line. Width) is formed to have a sufficiently wide width compared to the line width of the signal conductor 4. That is, assuming that the width of the signal conductor 4 is W, the thickness of the signal conductor 4 is L, the distance between the signal conductor 4 and the constant potential conductor 5 is H, and the relative dielectric constant of the dielectric layer 21 is ε. By appropriately setting these parameters, the impedance of the transmission line (strip line) composed of the signal conductor 4 and the constant potential conductor 5 can be set to an arbitrary magnitude.

  Returning to FIG. 2, the signal conductor 4 is wired so as to form a loop along the shape of the multilayer substrate. One end of the signal conductor 4 is connected to the central conductor 31 constituting the connection portion 3, and the other end is connected to the external conductor 32 constituting the connection portion 3 via the termination resistor 6.

  The constant potential conductor 5 is formed so as to make one round of the loop along the shape of the multilayer substrate. A gap (a break of the constant potential conductor 5) is provided at a portion facing the formation portion of the connection portion 3 across the hollow portion of the loop formed by the multilayer substrate. The part of the sensor part 2 provided with this gap is hereinafter referred to as a gap part 7. The constant potential conductor 5 is connected to an external conductor 32 that constitutes the connection portion 3.

  That is, the transmission line formed by the signal conductor 4 and the constant potential conductor 5 is formed in a loop shape, and in a portion other than the gap portion 7, the constant potential conductor 5 generates a magnetic field against the electric field. The gap portion 7 also has a shielding effect against the electric field, but the magnetic field has a structure in which the signal conductors 4 are linked.

  Further, the impedance formed by the signal conductor 4 and the constant potential conductor 5 and the impedance of the termination resistor 6 are the same as the characteristic impedance of the connection portion 3 (and hence the input impedance of the detection circuit connected to the connection portion 3). This value is set to 50Ω in this embodiment. In particular, the impedance of the transmission line is 50Ω by using a substrate with ε = 3.5 and designing H = 0.2 mm, t = 0.018 mm, and W = 0.43 mm.

  The sensor unit 2 configured as described above uses a strip line formed on a multilayer substrate instead of a coaxial cable or a semi-rigid cable as a transmission line forming a loop.

  The loop formed by the transmission line of the sensor unit 2 is formed on the XZ plane in the figure (see FIGS. 1 and 2). That is, the magnetic field detection probe 1 is configured to output a detection signal corresponding to the magnitude of the component along the Y-axis direction of the magnetic flux passing through the sensor unit 2 (particularly the hollow portion of the loop).

  Then, an induced voltage is generated between the gaps according to the magnitude of the magnetic flux (and hence the magnetic field) passing through the sensor unit 2 (the loop antenna formed by the transmission line), and the induced voltage is converted to the characteristic impedance (detection of the connection unit 3). A detection signal having a magnitude divided by the input impedance of the circuit and the impedance of the termination resistor 6 is input to the detection circuit.

<Experiment>
The measurement results of the magnetic field detection sensitivity and the electric field detection sensitivity are shown in FIGS. However, as shown in FIG. 6, the magnetic field detection probe 1 is arranged on the substrate on which the microstrip line is formed as a measurement system, and a signal is supplied from the port 1 of the network analyzer to the microstrip line. The connection is made so that the detection signal output from the connection unit 3 is input to the port 2 of the network analyzer.

  However, the sensor unit 2 in the magnetic field detection probe 1 is formed such that the size Lx in the X-axis direction is 35.4 mm, the size Ly in the Y-axis direction is 10 mm, and the size Lz in the Z-axis direction is 5.4 mm (see FIG. 1 and 2) and arranged so that the X-axis direction is along the wiring direction of the microstrip line.

  FIG. 4 is a graph showing magnetic field detection sensitivity. Specifically, the microstrip line is formed on the opposing surface 8 on the XY plane in the magnetic field detection probe 1 with the same signal supplied to the microstrip line via the port 1 by the network analyzer. When approaching the surface of the substrate (measurement target) within a range of 10 mm to 0.1 mm, the S parameter from port 1 to port 2 (S21: passage loss) was calculated by simulation.

However, in the magnetic field detection probe 1, the signal conductor 4 is arranged closer to the measurement object than the constant potential conductor 5 with reference to the opposing surface 8 (see FIGS. 2 and 3).
As a comparative example, as shown in FIG. 7, four dielectric layers 21 a (211 a to 214 a) and three conductor layers 22 a (221 a to 223 a) formed between the dielectric layers 21 are used. The signal conductor 4a is formed on the signal conductor layer 222a located between the second layer 212a and the third layer 213a, and the inner conductor layer 221a located between the first layer 211a and the second layer 212a, and Measurements were similarly performed on the shielded loop antenna 1a in which the constant potential conductors 5a (51a, 52a) were respectively formed on the outer conductor layer 223a located between the third layer 213a and the fourth layer 214a. In this shielded loop antenna 1a, as shown in FIG. 8, the impedance of the transmission line is such that a substrate with ε = 3.5 is used, the interval between the constant potential conductors 51a, 52a is h, and h = 50Ω is realized by designing 0.418 mm, t = 0.018 mm, and W = 0.2 mm.

  As shown in FIG. 4, even when the shielded loop antenna 1a of the comparative example is brought close to the surface of the measurement object, the magnetic field detection probe 1 is measured while the magnetic field detection sensitivity does not increase so much when the distance becomes 1 mm or less. When approaching the surface of the object, the magnetic field detection sensitivity continues to increase to a distance of about 0.1 mm, and the difference is 7 dB or more compared to the comparative example.

  That is, in the magnetic field detection probe 1, the signal conductor 4 is arranged closer to the measurement object than the constant potential conductor 5 with respect to the opposing surface 8 (see FIGS. 2 and 3). It was verified that the magnetic field detection sensitivity was improved because capacitive coupling between the transmission line and the measurement object was suppressed when 8 was brought close to the measurement object, and the change in the magnetic field was suppressed.

  Next, FIG. 5 is a graph showing magnetic field detection sensitivity and electric field detection sensitivity. Specifically, the output voltage of the connection part 3 when the plane wave swept in the range of 0.1 MHz to 100 MHz was irradiated was calculated by simulation. In FIG. 5, (a) is a case where a plane wave is irradiated to the magnetic field detection probe 1 installed in the space, and (b) is a plane wave irradiated to the shielded loop antenna 1a of the comparative example installed in the space. Indicates the case. However, the plane wave to be radiated is formed of a perpendicular magnetic field and an electric field, and the magnetic field is in the Y-axis direction (solid line in the figure) and Z-axis direction (see FIG. Set in the X-axis direction (broken line in the figure), and the electric field in the X-axis direction (dark solid line and dotted line in the figure) and Z-axis direction (light solid line and broken line in the figure), respectively It is set.

  As shown in FIG. 5A, when the magnetic field is set in the Y-axis direction with respect to the magnetic field detection probe 1, the output voltage is compared with the case where the magnetic field detection probe 1 is set in other directions (Z-axis direction, X-axis direction). Becomes the largest state. In this setting state (magnetic field: Y-axis direction), even if the plane wave base condition is changed from the X-axis direction (dark solid line in the figure) to the Z-axis direction (thin solid line in the figure), the output voltage Hardly changed.

  Further, as shown in FIG. 5 (a), with the electric field set to the X-axis direction with respect to the magnetic field detection probe 1, the magnetic field is changed from the Y-axis direction (dark solid line in the figure) to the Z-axis direction (in the figure). Change the plane wave base condition to the dotted line) or set the magnetic field from the Y axis direction (thin solid line in the figure) to the X axis direction (dashed line in the figure) with the electric field set in the Z axis direction. Or changing the output voltage, the output voltage decreases by at least 30 dB or more.

  For these reasons, in the magnetic field detection probe 1, the magnetic field in the Y-axis direction, which is the original purpose, is most easily detected without being affected by the electric field (a state in which only the magnetic field in the Y-axis direction is easily detected). Therefore, it was confirmed to have a shielding effect against the electric field.

  As shown in FIG. 5B, the above experimental results have also been confirmed for the shielded loop antenna 1a of the comparative example, and the shielding effect of the electric field in the magnetic field detection probe 1 is the seal of the comparative example. It has been verified that it has an effect equivalent to or better than that of the dead loop antenna 1a.

  As described above, in the magnetic field detection probe 1, the constant potential conductor 5 is at least closer to the measurement object than the signal conductor 4 with reference to the opposing surface 8 facing the measurement object that generates the magnetic field in the sensor unit 2. The positions of the signal conductor 4 and the constant potential conductor 5 are defined in the positions.

  Specifically, in the magnetic field detection probe 1, the constant potential conductor 5 is a loop-shaped transmission line so that the signal conductor 4 is closer to the measurement object than the constant potential conductor 5 with respect to the facing surface 8. In FIG. 4, the signal conductor 4 is disposed on the inner side.

  Thereby, according to the magnetic field detection probe 1, the loop-shaped transmission line is brought close to the measurement object by making the constant potential conductor (wider than the signal conductor) not disposed on the outermost side. Sometimes, the capacitive coupling between the transmission line and the measurement target is suppressed, and consequently the change in the magnetic field is suppressed, so that it is possible to improve the magnetic field detection sensitivity.

  Specifically, in the magnetic field detection probe 1, the constant potential conductor 5 is moved away from the surface of the measurement target by one layer of the multilayer substrate from the outer constant potential conductor 52a of the comparative example. Compared with the shielded loop antenna 1a, the capacitive coupling between the transmission line and the measurement object can be suppressed.

  In the magnetic field detection probe 1, the sensor unit 2 is configured using a flexible substrate, and the transmission line is formed of a strip line formed on the substrate. The magnetic field can be measured for a wide variety of electronic devices.

<Other embodiments>
As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, In the range which does not deviate from the summary of this invention, it is possible to implement in various aspects.

  For example, in the magnetic field detection probe 1 of the above-described embodiment, the impedance of the termination resistor 6 is matched with the impedance of the transmission line that constitutes the sensor unit 2, and these impedances are used as the input impedance of the detection circuit (the characteristics of the connection unit 3). Although it is set to the same value as (impedance), it is not limited to this.

  Specifically, in the magnetic field detection probe 1, the impedance of the termination resistor 6 is matched with the impedance of the transmission line that constitutes the sensor unit 2, and these impedances are used as the input impedance of the detection circuit (the characteristic impedance of the connection unit 3). ) It may be set smaller. In this case, since the voltage dividing ratio on the detection circuit side becomes larger than when the impedance of the transmission line and the impedance of the termination resistor 6 are matched (matched) with the input impedance of the detection circuit, the detection sensitivity can be further improved. it can.

  Specifically, by setting the input impedance of the detection circuit to 50Ω and setting the impedance of the termination resistor 6 and the transmission line to 10Ω, it is possible to suppress a decrease in the input voltage with respect to the induced voltage.

  In the magnetic field detection probe 1 of the above embodiment, the transmission line is formed by using a loop-shaped multilayer substrate in the sensor unit 2, but the present invention is not limited to this. The constant potential conductor 5 may be disposed on the inner surface of the substrate (single layer substrate), and the signal conductor 4 may be disposed on the outer surface.

  Moreover, in the magnetic field detection probe 1 of the said embodiment, although the sensor part 2 is comprised using the stripline which comprised on the multilayer substrate, it is not limited to this, For example, instead of a stripline, A modified coplanar line having a cross-sectional view taken along the line III-III in FIG. 2 may be used.

  Further, in the magnetic field detection probe 1 of the above embodiment, the constant potential conductor 5 is arranged for one layer of the multilayer substrate. However, the present invention is not limited to this, and a sectional view taken along line III-III in FIG. As shown in FIG. 10, a part of the constant potential conductor 5 is extended to the layer (outer layer) of the signal conductor 4 in the multilayer substrate, and the extended part and the constant potential conductor 5 are connected by vias. Also good. Further, as shown in FIG. 11 in the cross-sectional view taken along the line III-III in FIG. You may connect.

  In the magnetic field detection probe 1 of the above embodiment, the constant potential conductor 5 is arranged on the inner side of the signal conductor 4 in the loop-shaped transmission line. However, as shown in FIG. A configuration in which a part of the conductor 5 is located at the same distance as the signal conductor 4 with respect to the measurement object with respect to the facing surface 8 may be employed.

  Further, the loop-shaped multilayer substrate or single-layer substrate is not limited to a flexible substrate bent in a loop shape, but vias between multilayers of the rigid substrate so that the II-II sectional view in FIG. May be used to form a transmission line in a loop shape, or the structure shown in FIGS.

  DESCRIPTION OF SYMBOLS 1 ... Magnetic field detection probe, 2 ... Sensor part, 3 ... Connection part, 4 ... Signal conductor, 5 ... Constant potential conductor, 6 ... Termination resistor, 7 ... Gap part, 8 ... Opposite surface, 21 ... Dielectric layer, 22 ... conductor layer, 31 ... center conductor, 32 ... outer conductor, 211 ... first layer, 212 ... second layer, 213 ... third layer, 21221 ... constant potential conductor layer, 222 ... signal conductor layer.

Claims (3)

The gap portion (7) is composed of a signal conductor (4) for transmitting a signal and a constant potential conductor (5) for electromagnetically shielding the signal conductor, and partially exposing the signal conductor. A sensor unit (2) functioning as a shielded loop antenna formed in a loop shape by a transmission line having,
A magnetic field detection probe (1) for detecting an electrical signal corresponding to the magnitude of a magnetic field passing through the sensor unit,
The signal conductor is located at a position where the constant potential conductor is at least closer to the measurement object than the signal conductor with reference to the facing surface (8) facing the measurement object that generates the magnetic field. And a position of each of the constant potential conductors is defined.   The magnetic field detection probe according to claim 1, wherein the constant potential conductor is arranged inside the signal conductor in the loop transmission line.   3. The magnetic field detection according to claim 1, wherein the sensor unit is configured using a flexible substrate, and the transmission line includes a strip line configured on the substrate. probe.

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