Device and method for detecting stacking direction of internal electrodes of multilayer capacitor

Abstract

To provide an apparatus for detecting a stacking direction of internal electrodes of a multilayer capacitor and a detecting method thereof.SOLUTION: An apparatus for detecting a stacking direction of internal electrodes of a multilayer capacitor 100 includes a capacitor moving unit 1 having a supply unit 2 to which a plurality of multilayer capacitors are continuously supplied and moving the supplied multilayer capacitors in one direction, a sensor unit 10 including a coil, installed on the capacitor moving unit, and detecting inductance of the coil when each of the multilayer capacitors approaches the coil to determine a stacking direction of internal electrodes of the multilayer capacitor based on the detected inductance of the coil, and a separating unit 5 installed on the capacitor moving unit and separating a multilayer capacitor 100' selected as an unsuitable multilayer capacitor by the sensor unit.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a device and method for detecting the stacking direction of internal electrodes of a multilayer capacitor. [Background technology]

[0002] Multilayer capacitors (MLCCs) may require alignment of the internal electrode direction during PCB mounting to meet customer requirements and improve product characteristics.

[0003] Conventionally, a magnet is used to align the internal electrodes of a multilayer capacitor before packaging it for delivery to customers.

[0004] However, such a method using a magnet has a limited degree of alignment accuracy, and therefore there is an inherent possibility that chips aligned in an undesired direction may be removed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Korean Patent Publication No. 2018-0061001 [Patent Document 2] Japanese Patent No. 6361570 [Patent Document 3] Japanese Patent No. 6107752 Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus and method for detecting the stacking direction of internal electrodes of a multilayer capacitor with improved accuracy. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided an apparatus for detecting a stacking direction of internal electrodes of a multilayer capacitor, the apparatus comprising: a capacitor moving unit having a supply unit to which a plurality of multilayer capacitors are continuously supplied and moving the supplied multilayer capacitors in one direction; a sensor unit including a coil and installed on the capacitor moving unit, for detecting inductance of the coil when each multilayer capacitor approaches each other and determining a stacking direction of internal electrodes of the multilayer capacitors based on a difference in inductance values ​​of the coils; and a separation unit installed on the capacitor moving unit, for separating a multilayer capacitor that has been selected as an unconformable multilayer capacitor by the sensor unit.

[0008] In an embodiment of the present invention, the display device may further include a magnetic member disposed at a position facing the sensor unit with the stacked capacitor interposed therebetween.

[0009] In one embodiment of the present invention, the magnetic member may have a magnetic permeability of 100 to 5,000.

[0010] In an embodiment of the present invention, the sensor may further include a spacing member disposed between the sensor unit and the stacked capacitor, the spacing member being in close contact with one surface of the stacked capacitor to maintain a constant gap between the sensor unit and the stacked capacitor.

[0011] In one embodiment of the present invention, the spacing member may be made of a non-magnetic material.

[0012] In one embodiment of the present invention, the sensor unit has an inner diameter of the coil that is 3.0 times or less the length of the multilayer capacitor, and the number of turns of the coil satisfies the following formula 1: Number of turns (N) ≥ 20 / (length of multilayer capacitor × inner diameter of coil).

[0013] Another aspect of the present invention provides a method for detecting the stacking direction of internal electrodes of a multilayer capacitor by bringing a sensor unit including a coil close to the multilayer capacitor, checking a difference in inductance of the coil depending on the stacking direction of internal electrodes included in the multilayer capacitor, and comparing the checked value with a preset reference inductance value.

[0014] In one embodiment of the present invention, the inductance measurement frequency can be preferably 50 kHz to 5 Mhz.

[0015] In one embodiment of the present invention, a magnetic member may be disposed at a position facing the sensor unit across the multilayer capacitor, thereby increasing the change in inductance of the coil caused by eddy current.

[0016] In an embodiment of the present invention, a spacing member made of a non-magnetic material may be disposed between the sensor unit and the multilayer capacitor, and one surface of the multilayer capacitor may be in close contact with one surface of the spacing member, thereby maintaining a constant gap between the sensor unit and the multilayer capacitor. [Effects of the Invention]

[0017] According to one embodiment of the present invention, a coil is used to detect the direction of the internal electrodes included in the multilayer capacitor, and a difference in inductance of the coil depending on the stacking direction (horizontal / vertical) of the internal electrodes of the capacitor body is detected, thereby providing an effect of easily and accurately grasping the alignment state of the internal electrode direction of the multilayer capacitor. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a perspective view illustrating a first stacked capacitor being detected by a sensor unit according to an embodiment of the present invention; [Figure 2] 10 is a perspective view illustrating a second stacked capacitor being detected by a sensor unit according to an embodiment of the present invention; FIG. [Figure 3]1 is a plan view schematically illustrating a detection device according to an embodiment of the present invention; [Figure 4] 2 is a diagram illustrating an operation principle of a sensor unit in a detection device according to an embodiment of the present invention; [Figure 5] 10 is a diagram illustrating a method for detecting a lamination direction of internal electrodes according to another embodiment of the present invention; [Figure 6] 10(a) and 10(b) are views schematically illustrating a method for detecting the lamination direction of internal electrodes according to still another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into several other forms, and the scope of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those having average knowledge in the art. Therefore, the shapes and sizes of elements in the drawings may be enlarged or reduced (or highlighted or simplified) for clearer explanation.

[0020] In addition, components having the same function within the same concept shown in the drawings of each embodiment will be described with the same reference numerals.

[0021] Furthermore, throughout the specification, "comprising" an element means that it may further include other elements, rather than excluding other elements, unless specifically stated to the contrary.

[0022] Hereinafter, to clearly explain the embodiments of the present invention, the directions of the stacked capacitor will be defined as follows: X, Y, and Z shown in the drawings may be defined as the length direction, width direction, and thickness direction of the stacked capacitor, respectively.

[0023] As multilayer capacitors are becoming increasingly thinner and smaller, there is an increasing need for technology that can easily detect the orientation of the internal electrodes contained therein.

[0024] The present invention relates to an apparatus for detecting the lamination direction of internal electrodes contained in a multilayer capacitor, and a method for detecting the lamination type of a multilayer capacitor using the apparatus.

[0025] The multilayer capacitor applied to one embodiment of the present invention is classified into a first multilayer capacitor and a second multilayer capacitor according to the lamination direction of the internal electrodes, which will be described later.

[0026] Here, the first multilayer capacitor has a structure in which a plurality of internal electrodes are stacked in a direction horizontal to the mounting surface, and the second multilayer capacitor has a structure in which a plurality of internal electrodes are stacked in a direction vertical to the mounting surface.

[0027] FIG. 1 is a perspective view schematically illustrating a first stacked capacitor being detected by a sensor unit according to an embodiment of the present invention, and FIG. 2 is a perspective view schematically illustrating a second stacked capacitor being detected by a sensor unit according to an embodiment of the present invention.

[0028] Referring to FIG. 1, a first multilayer capacitor 101 according to an embodiment includes a capacitor body 110, a first external electrode 131, and a second external electrode 132.

[0029] The capacitor body 110 is formed by stacking multiple dielectric layers 111 in the Z direction and then firing them, and the boundaries between adjacent dielectric layers 111 of the capacitor body 110 may be so integrated that they are difficult to identify without using a scanning electron microscope (SEM).

[0030] In this case, the capacitor body 110 may have a substantially hexahedral shape, but the present invention is not limited thereto. In addition, the shape and size of the capacitor body 110 and the number of laminated dielectric layers 111 are not limited to those shown in the drawings of this embodiment.

[0031] In this embodiment, for convenience of explanation, both surfaces of the capacitor body 110 facing each other in the Z direction are defined as a first surface and a second surface, both surfaces connected to the first and second surfaces and perpendicular to the Z direction and facing each other in the X direction are defined as a third surface and a fourth surface, and both surfaces connected to the first and second surfaces and the third and fourth surfaces and perpendicular to the Z direction and facing each other in the Y direction are defined as a fifth surface and a sixth surface.

[0032] The mounting surface of the first multilayer capacitor 101 may be the first surface of the capacitor body 110 .

[0033] The capacitor body 110 includes a dielectric layer 111, a first internal electrode 121, and a second internal electrode 122, and may include an active area that contributes to forming the capacitance of the capacitor, and upper and lower cover areas that are disposed above and below the active area in the Z direction as upper and lower margin areas.

[0034] The first internal electrode 121 and the second internal electrode 122 are electrodes to which different polarities are applied, and are alternately arranged along the Z direction with the dielectric layer 111 sandwiched therebetween, and one end can be exposed through the third and fourth surfaces of the capacitor body 110, respectively.

[0035] At this time, the first internal electrode 121 and the second internal electrode 122 may be electrically insulated from each other by the dielectric layer 111 disposed therebetween.

[0036] In this manner, the ends of the first internal electrode 121 and the second internal electrode 122 alternately exposed through the third and fourth surfaces of the capacitor body 110 can be electrically connected to the first external electrode 131 and the second external electrode 132, respectively, disposed on the third and fourth surfaces of the capacitor body 110, which will be described later.

[0037] With the above configuration, when a predetermined voltage is applied to the first external electrode 131 and the second external electrode 132, charges are accumulated between the first internal electrode 121 and the second internal electrode 122.

[0038] At this time, the capacitance of the first multilayer capacitor 101 is proportional to the overlapping area of ​​the first internal electrode 121 and the second internal electrode 122 that overlap each other along the Z direction in the active region.

[0039] Furthermore, the material for forming the first internal electrode 121 and the second internal electrode 122 is not particularly limited, and may be formed using a conductive paste made of one or more of precious metal materials such as platinum (Pt), palladium (Pd), palladium-silver (Pd-Ag) alloy, nickel (Ni), and copper (Cu).

[0040] The first external electrode 131 is disposed at one end of the capacitor body 110 in the X direction.

[0041] In addition, the first external electrode 131 may include a first connection portion arranged on the third surface 3 of the capacitor body 110, and a first band portion extending from the first connection portion toward portions of the first, second, fifth and sixth surfaces of the capacitor body 110.

[0042] The second external electrode 132 is provided with a voltage of a polarity different from that of the first external electrode 131 and is disposed at the other end of the capacitor body 110 in the X direction.

[0043] In addition, the second external electrode 132 may include a second connection portion disposed on the fourth surface of the capacitor body 110, and a second band portion extending from the second connection portion toward portions of the first surface, the second surface, the fifth surface, and the sixth surface of the capacitor body 110.

[0044] Referring to FIG. 2, the second multilayer capacitor 102 has a dielectric layer 111, a first internal electrode 123, and a second internal electrode 124 stacked in the Y direction. Except for this, the remaining structure is similar to that of the first multilayer capacitor 101 of FIG. 1 described above, and therefore, detailed description thereof will be omitted to avoid redundancy.

[0045] FIG. 3 is a plan view schematically illustrating a detection device according to an embodiment of the present invention.

[0046] 3 and 4, a device for detecting the stacking direction of internal electrodes of a multilayer capacitor according to an embodiment of the present invention includes a capacitor moving unit 1, a sensor unit 10, and a separating unit 5.

[0047] The capacitor moving unit 1 has a supply unit 2 to which a plurality of stacked capacitors 100 are successively supplied one by one, and serves to move the supplied stacked capacitors 100 in one direction. Here, reference numeral 100 indicates a first or second stacked capacitor before the stacking direction is confirmed.

[0048] The sensor part 10 includes a coil 11 and is placed on the capacitor moving part 1 .

[0049] The sensor unit 10 detects the inductance of the coil 11 when each multilayer capacitor 100 approaches, and determines whether the direction in which the internal electrodes of the corresponding multilayer capacitor 100 are stacked is vertical or horizontal to the mounting surface based on the difference in the inductance value of the coil 11.

[0050] At this time, if the size of the multilayer capacitor is too small, the change in inductance measured by the sensor unit 10 is small, making it difficult to detect the change in inductance, and it may be difficult to distinguish the multilayer type.

[0051] To solve this problem, it is advantageous to reduce the size of the coil 11 included in the sensor unit 10.

[0052] In this case, the inner diameter of the coil 11 may preferably be 3.0 times or less the length in the X direction of the multilayer capacitor 100. For example, if the length in the X direction of the multilayer capacitor 100 is 0.6 mm, the inner diameter of the coil 11 may be 1.8 mm or less.

[0053] However, if the inner diameter of the coil 11 is small, the generated inductance will decrease, so it is necessary to increase the number of turns of the coil 11 (the number of times the coil is wound) to achieve an appropriate level of inductance.

[0054] In this case, the preferred number of turns of the coil can be calculated using the following formula 1. Formula 1) Number of windings (N) ≥ 20 / (length of multilayer capacitor in X direction x inner diameter of coil)

[0055] The separating unit 5 is installed on the capacitor moving unit 2 and serves to separate the stacked capacitor 100′ that has been identified as an unsuitable stacked capacitor by the sensor unit 10. Here, reference numeral 4 denotes the point where the separating unit 5 is connected to the capacitor moving unit 2.

[0056] Reference numeral 7 denotes a discharge unit that discharges the stacked capacitor 100 selected as a suitable stacked capacitor 100 by the sensor unit 10 as a commodity when the stacked capacitor 100 reaches the position indicated by reference numeral 6 .

[0057] FIG. 4 is a diagram illustrating the operation principle of a sensor unit in a detection device according to an embodiment of the present invention.

[0058] The principle of detecting the lamination direction of the internal electrodes according to the present invention will be described with reference to FIG.

[0059] When the plane of the Ni electrodes IE (first and second internal electrodes in the present invention) made of conductive material and the plane of the measuring coil are horizontal, the magnetic field MF2 induced in the coil C generates an eddy current EC in the Ni electrodes IE, and the eddy current EC generated in the Ni electrodes IE forms an eddy current magnetic field MF1.

[0060] The eddy current magnetic field MF1 thus generated causes interference with the magnetic field MF2 of coil C, causing a change in the inductance of coil C. By measuring and detecting this, it is possible to determine whether the state of the Ni electrode IE is horizontal or vertical.

[0061] For example, in the case of horizontal mounting as shown in FIG. 1, the plane of the coil 10 and the first and second internal electrodes 121 and 122 are horizontal, which is a condition where eddy currents are easily generated, resulting in a large decrease in inductance.

[0062] On the contrary, in the case of vertical mounting as shown in FIG. 2, the formation of eddy currents due to the first internal electrode 123 and the second internal electrode 124 is small, so the decrease in inductance is relatively small compared to the case of horizontal mounting.

[0063] Using the above principle, by bringing a coil through which current flows close to a multilayer capacitor and measuring the inductance value of the coil generated at that time, it is possible to distinguish whether the stacking direction of the internal electrodes of the multilayer capacitor is horizontal or vertical to the mounting surface.

[0064] At this time, the inductance measurement frequency may preferably be 50 kHz to 5 MHz. If the measurement frequency is lower than 50 kHz, the sensitivity of the sensor may be low when measuring a small-sized multilayer capacitor, resulting in inaccurate measurement, and if the measurement frequency is higher than 5 MHz, current may flow only on the surface, making it difficult to measure the inductance change depending on the direction of the internal electrodes of the multilayer capacitor.

[0065] Table 1 below shows the measured ΔL of the first horizontally stacked type multilayer capacitor and the second vertically stacked type multilayer capacitor in multilayer capacitors having lengths, widths, and heights of 2.0 mm, 1.25 mm, and 1.2 mm.

[0066] Here, ΔL is defined as the difference between the inductance value measured in the coil when there is no stacked capacitor, which is called Ref, and the inductance value measured in the coil when current is passed through the coil to generate eddy currents, as ΔL.

[0067] [Table 1]

[0068] From Table 1, it can be seen that ΔL is negative (-) for the first stacked capacitor and positive (+) for the second stacked capacitor, and that the stacking direction of the internal electrodes of the stacked capacitor can be distinguished through the change in inductance.

[0069] Table 2 shows the measured ΔL of the first and second multilayer capacitors in multilayer capacitors having lengths, widths, and heights of 1.6 mm, 0.8 mm, and 0.8 mm.

[0070] [Table 2]

[0071] From Table 2, it can be seen that ΔL is negative (-) for the first stacked capacitor and positive (+) for the second stacked capacitor, and that the stacking direction of the internal electrodes of the stacked capacitor can be distinguished through the change in inductance.

[0072] Table 3 shows the results of measuring ΔL of the first and second multilayer capacitors in multilayer capacitors having lengths, widths, and heights of 1.0 mm, 0.5 mm, and 0.5 mm.

[0073] [Table 3]

[0074] From Table 3, it can be seen that ΔL is negative (-) for the first stacked capacitor and positive (+) for the second stacked capacitor, and that the stacking direction of the internal electrodes of the stacked capacitor can be distinguished through the change in inductance.

[0075] Table 4 shows the results of measuring ΔL of the first and second multilayer capacitors in multilayer capacitors having lengths, widths, and heights of 0.6 mm, 0.3 mm, and 0.3 mm.

[0076] [Table 4]

[0077] From Table 4, it can be seen that ΔL is negative (-) for the first stacked capacitor and positive (+) for the second stacked capacitor, and that the stacking direction of the internal electrodes of the stacked capacitor can be distinguished through the change in inductance.

[0078] According to one embodiment of the present invention, the lamination direction of the internal electrodes of a multilayer capacitor is detected using eddy currents generated in a coil, which can be expected to have little effect on the appearance or shape of the product, a fast measurement speed, and high repeatability. Here, high repeatability means that there is little deviation in the measurement values ​​when the same product is measured multiple times.

[0079] Also, as can be seen from Tables 1 to 4, this method is applicable to all stacked capacitors that use metal electrodes inside the capacitor body, and the difference in ΔL between the horizontal and vertical directions can be increased by changing the coil size and the current flowing through the coil, thereby further improving the detection power.

[0080] A method for detecting the lamination direction of the internal electrodes of the multilayer capacitor of the present invention using the detection device configured as above will now be described in detail.

[0081] According to an embodiment of the present invention, a sensor unit including a coil is brought close to the multilayer capacitor, a difference in inductance of the coil depending on the stacking direction of the internal electrodes included in the multilayer capacitor is checked, and the checked value is compared with a preset reference inductance value, thereby detecting the stacking direction of the internal electrodes of the multilayer capacitor.

[0082] FIG. 5 is a diagram illustrating a method for detecting the lamination direction of internal electrodes according to another embodiment of the present invention.

[0083] Referring to FIG. 5, in order to increase the sensitivity of the sensor unit 10 to inductance changes, a magnetic member 200 may be disposed on the opposite side of the multilayer capacitor 100 facing the coil of the sensor unit 10 .

[0084] In this case, the magnetic member 200 may be made of a material having a high magnetic permeability, for example, iron (Fe), and the magnetic member 200 may have a preferable magnetic permeability of 100-5000.

[0085] By positioning the magnetic member 200 made of a material with high magnetic permeability on the opposite side of the sensor unit 10 in this manner, the magnetic field generated by the coil of the sensor unit 10 is prevented from dispersing and is concentrated on the magnetic member 200 side, thereby increasing the inductance change of the coil generated by eddy currents and increasing the sensitivity of the sensor unit 10.

[0086] In this case, it is effective when the size of the magnetic member 200 is 100 to 400% of the size of the multilayer capacitor 100 to be measured, and preferably the best results are obtained when the size is 100 to 200% of the size of the multilayer capacitor to be measured.

[0087] 6(a) and 6(b) are diagrams schematically illustrating a method for detecting the lamination direction of internal electrodes according to still another embodiment of the present invention.

[0088] In one embodiment, the sensor unit 10 may change the measured inductance value according to the change in the measurement distance.

[0089] Referring to FIG. 6(a), even if the stacked capacitors 100a and 100b have the same specifications, there may be slight differences in size. In this case, if the distances d1 and d2 between the sensor unit 10 and the stacked capacitor are different from each other, an error will occur in the measured inductance value, which may make it difficult to accurately distinguish whether the stacking direction of the internal electrodes of the stacked capacitors 100a and 100b is vertical or horizontal.

[0090] Referring to FIG. 6(b), in one embodiment of the present invention, a spacing member 300 may be disposed between the sensor unit 10 and the stacked capacitors 100a and 100b having size deviations.

[0091] The spacing member 300 serves to keep the distances d1 and d2 between the sensor unit 10 and the multilayer capacitors 100a and 100b constant by bringing one side of the multilayer capacitors 100a and 100b into close contact with the sensor unit 10. Therefore, even if the sizes of the multilayer capacitors 100a and 100b vary, the inductance value can be measured stably.

[0092] In this case, the spacing member 300 may be made of a non-magnetic, non-conductive material, such as a PET film or glass.

[0093] On the other hand, the sensor portion of the embodiment of the present invention may be disposed below the capacitor moving portion.

[0094] In this case, the stacked capacitor is supported on the support surface of the capacitor moving part, and the sensor part is located below the support surface, so that even if there is a size deviation between the stacked capacitors, the distance between the stacked capacitor and the sensor part can always be maintained constant.

[0095] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments and the accompanying drawings, but is limited only by the appended claims. Therefore, various substitutions, modifications, and changes may be made by a person skilled in the art without departing from the technical spirit of the present invention as set forth in the claims, and these also fall within the scope of the present invention. [Explanation of symbols]

[0096] 1: Capacitor moving part 5: Separation part 10: Sensor section 100: Multilayer capacitor 200: Magnetic material 300: Spacing member

Claims

1. a capacitor moving unit having a supply unit to which a plurality of stacked capacitors are continuously supplied and moving the supplied stacked capacitors in one direction; a sensor unit including a coil, the sensor unit being installed on the capacitor moving unit, the sensor unit detecting the inductance of the coil when each of the multilayer capacitors approaches each other and determining the direction in which the internal electrodes of the multilayer capacitors are stacked based on a difference in the inductance values ​​of the coils; a separating unit disposed on the capacitor moving unit and configured to separate the multilayer capacitors selected as non-conforming multilayer capacitors by the sensor unit.

2. 2. The device for detecting the stacking direction of internal electrodes of a multilayer capacitor according to claim 1, further comprising a magnetic member disposed at a position facing the sensor unit across the multilayer capacitor.

3. 3. The device for detecting the lamination direction of the internal electrodes of a multilayer capacitor according to claim 2, wherein the magnetic member has a magnetic permeability of 100 to 5000.

4. 4. The device for detecting a stacking direction of internal electrodes of a multilayer capacitor according to claim 1, further comprising a spacing member disposed between the sensor unit and the multilayer capacitor, the spacing member being in close contact with one surface of the multilayer capacitor to maintain a constant gap between the sensor unit and the multilayer capacitor.

5. 5. The device for detecting the stacking direction of the internal electrodes of a multilayer capacitor according to claim 4, wherein said spacing member is made of a non-magnetic material.

6. 2. The device for detecting a stacking direction of internal electrodes of a multilayer capacitor according to claim 1, wherein the sensor unit has an inner diameter of the coil that is 3.0 times or less the length of the multilayer capacitor, and the number of windings of the coil satisfies the following formula 1: Equation 1) Number of windings (N) ≥ 20 / (length of multilayer capacitor × inner diameter of coil)

7. A method for detecting the stacking direction of the internal electrodes of a multilayer capacitor by bringing a sensor unit including a coil close to the multilayer capacitor and checking the difference in inductance of the coil depending on the stacking direction of the internal electrodes included in the multilayer capacitor, and comparing the checked value with a preset reference inductance value.

8. 8. The method for detecting the lamination direction of the internal electrodes of a multilayer capacitor according to claim 7, wherein the inductance is measured at a frequency of 50 kHz to 5 Mhz.

9. 8. The method for detecting the lamination direction of the internal electrodes of a multilayer capacitor according to claim 7, further comprising: disposing a magnetic member at a position facing the sensor unit across the multilayer capacitor, thereby increasing a change in inductance of a coil generated by eddy current.

10. 10. The method for detecting the lamination direction of the internal electrodes of a multilayer capacitor according to claim 9, wherein the magnetic member has a magnetic permeability of 100 to 5000.

11. 11. The method for detecting the stacking direction of the internal electrodes of a multilayer capacitor according to claim 7, further comprising: disposing a spacing member made of a non-magnetic material between the sensor unit and the multilayer capacitor; and bringing one surface of the multilayer capacitor into close contact with one surface of the spacing member, thereby maintaining a constant distance between the sensor unit and the multilayer capacitor.

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