A hexagonal ferrite high-current magnetic bead and its molding method

Abstract

A high-current hexagonal ferrite bead and its forming method are disclosed. The high-current bead includes a magnetic core and a conductive wire. The magnetic core has a sandwich groove on its side, and the sandwich groove extends through the magnetic core along its length. The conductive wire is embedded in the sandwich groove. The two ends of the magnetic core are coated with end electrode silver paste to form end electrodes. The magnetic core is made of Co2Z type hexagonal ferrite. The forming method utilizes a rotating magnetic field orientation tape casting process and the material properties of hexagonal ferrite to prepare the high-current bead. This invention uses Co2Z type hexagonal ferrite to prepare a patch high-current bead with a bandwidth upper limit of 0.7-3GHz and a Q value greater than 40 within the bandwidth, while the bandwidth upper limit of magnetic beads made of traditional nickel-copper-zinc ferrite is generally no more than 0.2GHz.

Description

Technical Field

[0001] This invention relates to the field of magnetic beads, and more particularly to a hexagonal ferrite high-current magnetic bead and its molding method. Background Technology

[0002] High-current ferrite beads are commonly used in power lines to eliminate high-frequency noise. Surface mount ferrite beads are generally manufactured using nickel-copper-zinc ferrites through casting and low-temperature co-firing processes.

[0003] In existing technologies, nickel-copper-zinc ferrites have the problem of insufficient bandwidth and limited application frequency. Hexagonal ferrites can be used in higher GHz bands, but hexagonal ferrites formed by conventional methods have too low permeability, high bandwidth loss, and a Q value below 20, resulting in severe signal attenuation. Furthermore, their sintering temperature is above 1200℃, making co-firing with any existing electrode paste impossible. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology, which has a low upper limit for the magnetic beads made of nickel-copper-zinc ferrite, which cannot meet the application requirements, and the low magnetic permeability of hexagonal ferrite, which cannot be co-fired with any existing electrode paste. The present invention provides a high-current hexagonal ferrite magnetic bead and a molding method thereof.

[0005] The technical solution adopted by this invention to solve its technical problem is a method for molding hexagonal ferrite high-current magnetic beads, comprising the following steps: S1. Prepare hexagonal ferrite slurry for casting; S2. A magnetizing coil with a rectangular cross-section is wound with copper wire, and a turntable is placed in the middle of the magnetizing coil. An ultrasonic vibration box is installed at the bottom of the turntable, and the plane of the turntable is located in the center of the area surrounded by the magnetizing coil. S3. Drop the prepared hexagonal ferrite slurry into the center of the turntable, and start the turntable to spread the slurry until the slurry covers the turntable. S4. Orientation begins when the hexagonal ferrite slurry is not completely dry. A magnetic field is applied to the magnetizing coil. The applied magnetic field is in pulse form. During the interval between each magnetic field pulse, the turntable rotates at an angle of 90° so that the easily magnetized plane of the thin ferrite particles in the slurry is arranged parallel to the plane of the turntable. After magnetization treatment for 8-10 times, the process is stopped and the slurry is dried. S5. Prepare starch printing paste and print long strip patterns in the same direction on the ferrite thick film formed by air drying the hexagonal ferrite paste. S6. Repeat steps S3 and S4 to cast another layer of hexagonal ferrite paste on the starch film formed by the drying of starch printing paste. S7. Remove the round dough from the turntable and bake it at 50°C for 24 hours to dry it completely. Print multiple equally spaced longitudinal and transverse cutting lines on the center line between the multiple starch films on the dough and in the direction perpendicular to the center line of the channel. Cut the round dough into countless small square pieces along the cutting lines. Discard the dough pieces with rounded edges and keep the small square pieces of the same size. S8. Sinter the small square pieces after cutting, and burn off the starch film in the middle to form a sandwich groove. Polish and deburr the sintered shape, use a square sleeve with a pipe to cover it, connect the pipes at both ends, evacuate air at one end and inject silver paste at the other end to fill the sandwich groove, and then remove the sleeve. S9. Apply silver paste for end electrodes to both ends of the magnetic core blank, then dry it at 10℃ / h, raise the temperature to 700-800℃, and then keep it at that temperature for 20-30 minutes to make the silver and ferrite tightly bonded to form a fixed end electrode. Finally, use an electroplating process to plate a layer of tin on the end surface.

[0006] Furthermore, in step S1, the preparation of the hexagonal ferrite slurry includes the following steps: Chemically pure raw materials such as BaO, CoO, and Fe2O3 powders were mixed in a mol ratio of 3:2:12. All powder raw materials were mixed with deionized water in a 1:1 ratio and ball-milled for 1-3 hours. The discharged material was dried and passed through a 40-mesh sieve. The powder was calcined at 1250℃ in air for 2 hours, then mixed with water in a 1:1 ratio and ball-milled again until D50 = 0.7~1.0μm. The powder was then dried and passed through a 40-mesh sieve for later use. The powder from the previous step is mixed with 1.0 wt% Triton, 15-20 wt% PVB or acrylic resin, 80 wt% toluene or anhydrous ethanol, and 2 wt% dibutyl phthalate. The mixture is ball-milled for 24 hours and filtered through a 200-mesh sieve to form a castable hexagonal ferrite slurry.

[0007] Furthermore, in step S3, the rotation speed of the turntable is controlled at 80-140 rpm, and when the slurry just covers the entire turntable, the rotation speed is reduced to 10-15 rpm.

[0008] Furthermore, in step S4, before the magnetic field orientation, the ultrasonic vibration box first emits an ultrasonic pulse with a pulse width of 0.6-0.8 seconds. 0.2-0.4 seconds before the ultrasonic pulse disappears, the magnetizing coil begins to apply a magnetic field with a magnetic field strength in the range of 200-500 mT.

[0009] Furthermore, in step S5, the preparation of the starch printing paste includes the following steps: Starch is mixed with 15-20wt% ethyl cellulose, 40-60wt% terpineol, and 2wt% dibutyl phthalate, ball-milled for 24 hours, and filtered through a 200-mesh sieve to obtain starch printing paste.

[0010] Furthermore, in step S8, sintering is performed in the following manner: The temperature was increased to 300°C at 3°C / minute at room temperature, held for 600 minutes, then increased to 1250°C at 3°C / minute, held at 1250°C for 120 minutes, and finally cooled naturally.

[0011] The present invention further solves the technical problem by providing a hexagonal ferrite high-current magnetic bead prepared based on the above-mentioned hexagonal ferrite high-current magnetic bead molding method, comprising a magnetic core and a wire. The magnetic core has a sandwich groove on its side, and the sandwich groove penetrates the magnetic core along its length. The wire is embedded in the sandwich groove. The two ends of the magnetic core are coated with end electrode silver paste to form end electrodes. The magnetic core is made of Co2Z type hexagonal ferrite.

[0012] Furthermore, in the cross-section of the magnetic core, the center of the interlayer groove coincides with the center of the magnetic core.

[0013] Furthermore, after the two ends of the magnetic core are coated with end electrode silver paste, they are subjected to high-temperature silver burning to achieve a tight bond, thereby forming end electrodes.

[0014] Furthermore, both the sandwich groove and the magnetic core are rectangular in shape, and the conductor is a silver sheet. The present invention has the following beneficial technical effects: Using Co2Z type hexagonal ferrite, patch high-current magnetic beads with a passband upper limit of 0.7-3GHz can be prepared, with a Q value greater than 40 within the passband, while the passband upper limit of magnetic beads made of traditional nickel-copper-zinc ferrite is generally no more than 0.2GHz.

[0015] The magnetic core made by using Co2Z-type hexagonal ferrite, combined with rotating magnetic field orientation tape casting and printing processes, involves creating a starch film interlayer within the hexagonal ferrite during the printing process. After sintering, a magnetic core with interlayer grooves is formed, thus avoiding co-firing with the electrode paste. This allows for the direct formation of a core with holes. Furthermore, the rotating magnetic field orientation tape casting process increases the permeability. Afterward, silver paste is injected through a sleeve, and end electrode silver paste is applied to both ends as usual. After silver firing and electroplating, the firing temperature is much lower than that of hexagonal ferrite, thus avoiding the problem of co-firing with the silver electrode at the same temperature. Finally, a magnetic bead made of hexagonal ferrite is formed. Based on the rotating magnetic field orientation tape casting process and the material characteristics of hexagonal ferrite, the upper limit of the bandwidth of the high-current magnetic bead prepared is higher than that of the conventional method. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the magnetizing coil in an embodiment of the molding method of a hexagonal ferrite high-current magnetic bead according to the present invention. Figure 2This is a schematic diagram of the magnetizing coil and turntable in an embodiment of the molding method of a hexagonal ferrite high-current magnetic bead of the present invention. Figure 3 This is a schematic diagram of the hexagonal ferrite slurry bottom layer after orientation, according to an embodiment of the molding method of hexagonal ferrite high-current magnetic beads of the present invention. Figure 4 This is a schematic diagram of printing paste molding according to an embodiment of the molding method of hexagonal ferrite high-current magnetic beads of the present invention; Figure 5 This is a schematic diagram of the top layer of hexagonal ferrite slurry after orientation, according to an embodiment of the molding method of hexagonal ferrite high-current magnetic beads of the present invention. Figure 6 This is a schematic diagram of the formation of a magnetic core after cutting the green blank according to an embodiment of the molding method of a hexagonal ferrite high-current magnetic bead of the present invention; Figure 7 This is a schematic diagram of the magnetic core after sintering, according to an embodiment of the molding method of hexagonal ferrite high-current magnetic beads of the present invention. Figure 8 This is a schematic diagram of the sleeve and magnetic core of an embodiment of the molding method of a hexagonal ferrite high-current magnetic bead of the present invention; Figure 9 This is a schematic diagram of the magnetic core injection silver paste according to an embodiment of the molding method of hexagonal ferrite high-current magnetic beads of the present invention; Figure 10 This is a schematic diagram of the magnetic core and wire structure of an embodiment of the molding method of a hexagonal ferrite high-current magnetic bead of the present invention; Figure 11 This is a schematic diagram of the magnetic bead structure of an embodiment of a hexagonal ferrite high-current magnetic bead according to the present invention.

[0017] Explanation of reference numerals in the attached figures: 1. Magnetic core; 11. Sandwich groove; 2. Wire; 3. End electrode; 4. Starch film; 5. Magnetizing coil; 6. Turntable; 7. Sleeve. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0019] Reference Figure 6 and Figure 7 This embodiment includes a magnetic core 1 and a wire 2. The magnetic core 1 has a sandwich groove 11 on its side for placing the wire 2.

[0020] Reference Figure 6 As shown in the figure, specifically, both the magnetic core 1 and the interlayer groove 11 are rectangular. The interlayer groove 11 is located on the side of the magnetic core 1 and completely penetrates the magnetic core 1 along its length. From the cross-section of the magnetic core 1, the center point of the interlayer groove 11 coincides with the center point of the magnetic core 1, that is, the magnetic core 1 has a symmetrical structure in all directions.

[0021] The magnetic core 1 is made of Co2Z type hexagonal ferrite and is formed by a rotating magnetic field orientation casting process during the manufacturing process. It should be noted that the rotating magnetic field orientation casting process is derived from the invention patent of a ferrite raw material sheet forming equipment and forming method with application number CN201911110135.2. The rotating magnetic field orientation casting process needs to be combined with a printing process to form the interlayer groove 11 during the manufacturing process.

[0022] Reference Figure 6 , Figure 7 and Figure 10 The conductor 2 is made of silver sheet, and the end electrode silver paste is applied to the surface of the silver sheet and then embedded in the interlayer groove 11. Then, the end electrode silver paste is applied to both ends of the magnetic core 1, and after high temperature silver burning and electroplating, the end electrode 3 is formed, thereby realizing the production of hexagonal ferrite high current magnetic beads.

[0023] An embodiment of the present invention discloses a method for molding hexagonal ferrite high-current magnetic beads, comprising the following steps: S1. Mix chemically pure raw materials such as BaO, CoO, and Fe2O3 in a mol ratio of 3:2:12. Mix all the powder raw materials with deionized water in a 1:1 ratio and ball mill for 1-3 hours. Then, dry the discharged material and pass it through a 40-mesh sieve. Calcine the powder at 1250℃ in air for 2 hours. Then mix it with water in a 1:1 ratio and ball mill it again until D50 = 0.7~1.0μm. Dry the powder and pass it through a 40-mesh sieve for later use. The powder from the previous step is mixed with 1.0 wt% Triton or other type of dispersant, 15-20 wt% PVB or acrylic resin, 80 wt% toluene or anhydrous ethanol, and 2 wt% dibutyl phthalate. The mixture is ball-milled for 24 hours and filtered through a 200-mesh sieve to form a cast hexagonal ferrite slurry. S2. Make a magnetizing coil 5 with a rectangular cross-section using thick, flat copper wire, such as... Figure 1 As shown; a turntable 6 is placed inside the magnetizing coil 5, with the plane of the turntable 6 positioned exactly in the center of the area enclosed by the wire frame. The turntable 6 is made of non-magnetic aluminum or copper, such as... Figure 2 As shown, a pair of ultrasonic vibration boxes (not shown in the figure) are symmetrically mounted on the bottom of the turntable 6. S3. During the casting process, the hexagonal ferrite slurry prepared in step 2 is first dripped vertically into the center of turntable 6 from the upper part of the center through a pipe. Then, turntable 6 is started, and its rotation speed is controlled at 80-140 rpm. The hexagonal ferrite slurry spreads on turntable 6 as it rotates. When the slurry just covers the entire turntable 6, the rotation speed is reduced to 10-15 rpm, and the solvent begins to gradually evaporate and dry. Figure 3 As shown; S4. Orientation begins when the solvent is not completely dry (a liquid luster appears on the surface of the turntable 6 when it stops rotating, and disappears when it starts rotating). Before magnetic field orientation, the ultrasonic vibration box first emits an ultrasonic pulse with a pulse width of 0.6-0.8 seconds. 0.2-0.4 seconds before the ultrasonic pulse disappears (ultrasound has an auxiliary orientation effect, weakening the interaction force between powders and making them easier to orient), a magnetic field is applied to the magnetizing coil 5. The magnetic field is also applied in the form of pulses, with the magnetic field size in the range of 200-500mT. The rotation angle of the turntable 6 is controlled to be 90° during each magnetic field pulse interval. In this way, under the continuous vertical magnetic field orientation in the plane, the easily magnetized plane of the thin-film ferrite particles in the slurry will be arranged parallel to the plane of the turntable 6. After rotating magnetization 8-10 times, stop applying the pulsed magnetic field, maintain the rotation speed at 10-15 revolutions per minute, and start blowing the surface of the turntable with a unidirectional wind at 35-40°C until a thick ferrite film is formed and basically dried. S5. Mix starch with 15-20wt% ethyl cellulose, 40-60wt% terpineol and 2wt% dibutyl phthalate, ball mill for 24 hours, and filter through a 200-mesh sieve to obtain printing paste. Multiple elongated patterns are printed onto the ferrite thick film formed by air-drying the hexagonal ferrite paste using the starch printing paste from the previous step. These elongated patterns are spaced evenly on turntable 6 and face the same direction. Figure 4 As shown, it is dried by unidirectional airflow without rotation; S6. Repeat steps 3 and 4 on top of the printed starch paste pattern, and then cast another layer of hexagonal ferrite paste oriented by a rotating pulse magnetic field onto the printed starch film 4, such as... Figure 5 As shown; S7. Remove the formed round blank from turntable 6 and bake at 50℃ for 24 hours to dry it completely. Print multiple equally spaced longitudinal and transverse cutting lines along the center line between the multiple elongated shapes on the green blank, as well as perpendicular to this center line. Then, cut the circular green blank into numerous small squares along these cutting lines. Discard the green blanks with rounded edges, and keep the small squares of the same size. Figure 6 As shown; S8. Sinter the cut small square pieces according to the following sintering curve: under air atmosphere, at room temperature, raise the temperature to 300℃ at 3℃ / min, hold for 600 minutes, then raise the temperature to 1250℃ at 3℃ / min, hold at 1250℃ for 120 minutes, and finally cool naturally. The starch film in the middle is etched away in four parts, forming the sandwich groove 11. Figure 7 As shown; After the sintering of the magnetic core 1 is completed, the bevel is polished and the burrs are removed by blowing the middle interlayer groove 11 with high-speed airflow. Use a square sleeve 7 with a pipe to cover it, such as Figure 8 As shown, pipes are connected to both ends; one end is used for evacuation, and the other for injecting silver paste. Figure 9 As shown, fill the intermediate interlayer groove 11, then remove the sleeve 7, as... Figure 10 As shown; S9. Then, apply silver paste of suitable end electrode area to both ends of the magnetic core blank, such as... Figure 11 As shown, the temperature is then increased to 700-800℃ at 10℃ / h and then kept warm for 20-30 minutes to allow the silver and ferrite to bond tightly and form a fixed end electrode 3; a layer of tin is plated on the end surface using an electroplating process.

[0024] It should be noted that the solvents in steps S3 and S4 refer to the toluene or anhydrous ethanol in step S1, which are used to dissolve the PVB resin that acts as an adhesive. After casting, a certain amount of solvent remains in the thick film formed. At the beginning of casting, the solvent content in the slurry is relatively high, and a liquid gloss can be seen, similar to freshly sprayed paint. When there is airflow on the surface of the thick film, the solvent on the outermost layer evaporates rapidly and temporarily loses its liquid gloss. If the airflow stops, the solvent inside the thick film quickly replenishes the surface layer, and the surface layer will have gloss again. When the cast film is completely dried, the liquid gloss will no longer be visible on the surface.

[0025] In step S4, the frequency of the magnetic field pulse depends on the rotation speed. The frequency is four pulses per revolution, with a frequency of 2 / 3 to 1, a time width of 0.3 to 0.5 seconds, and a magnetic field strength of 160 to 400 kA / m, so that the magnetic induction intensity is within the range of 200 to 500 mT. Since two intersecting lines in a plane determine a plane, during the magnetic field pulse interval, the rotating disk 6 is rotated 90°, and the sheet-like magnetic powder can be oriented in both directions, so its radial plane will inevitably be arranged parallel to the plane of the rotating disk. For the above reasons, the rotating disk 6 rotates 90° during the magnetic field pulse interval, so that the magnetic field is always perpendicular to the magnetic powder in the slurry. As the rotating disk 6 rotates continuously, the easily magnetized plane of the thin sheet-like ferrite particles in the slurry will be arranged parallel to the plane of the rotating disk 6.

[0026] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Identical components are represented by the same reference numerals. It should be noted that the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, while the terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component. Therefore, all equivalent changes made to the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for molding hexagonal ferrite high-current magnetic beads, characterized in that, Includes the following steps: S1. Prepare hexagonal ferrite slurry for casting; S2. A magnetizing coil (5) with a rectangular cross-section is wound with copper wire, and a turntable (6) is placed in the middle of the magnetizing coil (5). An ultrasonic vibration box is installed at the bottom of the turntable (6), and the plane of the turntable (6) is located in the center of the area surrounded by the magnetizing coil (5). S3. Drop the prepared hexagonal ferrite slurry into the center of the turntable (6), start the turntable (6) to spread the slurry until the slurry covers the turntable (6); S4. Orientation begins when the hexagonal ferrite slurry is not completely dry. A magnetic field is applied to the magnetizing coil (5). The applied magnetic field is in pulse form. During the interval between each magnetic field pulse, the turntable (6) rotates at an angle of 90° so that the easily magnetized plane of the thin ferrite particles in the slurry is arranged parallel to the plane of the turntable (6). After magnetization treatment for 8-10 times, the process is stopped and the slurry is dried. S5. Prepare starch printing paste and print long strip patterns in the same direction on the ferrite thick film formed by air drying the hexagonal ferrite paste. S6. Repeat steps S3 and S4 to cast another layer of hexagonal ferrite paste on the starch film (4) formed by the drying of starch printing paste. S7. Take the round blank out of the turntable (6) and bake it at 50°C for 24 hours to dry it completely. Print multiple equally spaced longitudinal and transverse cutting lines on the center line of the passage between multiple starch films (4) on the blank and in the direction perpendicular to the center line of the passage. Cut the round blank into countless small square pieces along the cutting lines. Discard the blanks with rounded edges and keep the small square pieces of the same size. S8. Sinter the small square pieces after cutting, and burn off the starch film (4) in the middle to form a sandwich groove (11). Polish and deburr the sintered pieces, and use a square sleeve (7) with a pipe to cover them. Connect the pipes to both ends, evacuate one end and inject silver paste into the other end to fill the sandwich groove (11), and then remove the sleeve (7). S9. Apply silver paste to both ends of the magnetic core (1) blank, then dry it at 10℃ / h, raise it to 700-800℃ and keep it heated for 20-30 minutes to make the silver and ferrite tightly bonded to form a fixed end electrode (3). Finally, use electroplating process to plate a layer of tin on the end surface.

2. The method for forming hexagonal ferrite high-current magnetic beads according to claim 1, characterized in that, In step S1, the preparation of the hexagonal ferrite slurry includes the following steps: Chemically pure raw materials such as BaO, CoO, and Fe2O3 powders were mixed in a mol ratio of 3:2:

12. All powder raw materials were mixed with deionized water in a 1:1 ratio and ball-milled for 1-3 hours. The discharged material was dried and passed through a 40-mesh sieve. The powder was calcined at 1250℃ in air for 2 hours, then mixed with water in a 1:1 ratio and ball-milled again until D50 = 0.7~1.0μm. The powder was then dried and passed through a 40-mesh sieve for later use. The powder from the previous step is mixed with 1.0 wt% Triton, 15-20 wt% PVB or acrylic resin, 80 wt% toluene or anhydrous ethanol, and 2 wt% dibutyl phthalate. The mixture is ball-milled for 24 hours and filtered through a 200-mesh sieve to form a castable hexagonal ferrite slurry.

3. The method for forming hexagonal ferrite high-current magnetic beads according to claim 1, characterized in that, In step S3, the rotation speed of the turntable (6) is controlled at 80-140 rpm. When the slurry just covers the entire turntable (6), the rotation speed drops to 10-15 rpm.

4. The method for forming hexagonal ferrite high-current magnetic beads according to claim 1, characterized in that, In step S4, before the magnetic field orientation, the ultrasonic vibration box first emits an ultrasonic pulse with a pulse width of 0.6-0.8 seconds. 0.2-0.4 seconds before the ultrasonic pulse disappears, the magnetizing coil (5) starts to apply a magnetic field with a magnetic field size in the range of 200-500mT.

5. The method for forming hexagonal ferrite high-current magnetic beads according to claim 1, characterized in that, In step S5, the preparation of the starch printing paste includes the following steps: Starch is mixed with 15-20wt% ethyl cellulose, 40-60wt% terpineol, and 2wt% dibutyl phthalate, ball-milled for 24 hours, and filtered through a 200-mesh sieve to obtain starch printing paste.

6. The method for forming hexagonal ferrite high-current magnetic beads according to claim 1, characterized in that, In step S8, sintering is performed in the following manner: The temperature was increased to 300°C at 3°C / minute at room temperature, held for 600 minutes, then increased to 1250°C at 3°C / minute, held at 1250°C for 120 minutes, and finally cooled naturally.

7. A hexagonal ferrite high-current magnetic bead manufactured based on the hexagonal ferrite high-current magnetic bead molding method according to any one of claims 1-6, characterized in that, The magnetic core (1) includes a magnetic core (1) and a wire (2). The magnetic core (1) has a sandwich groove (11) on its side and the sandwich groove (11) extends through the magnetic core (1) along its length. The wire (2) is fitted into the sandwich groove (11). The two ends of the magnetic core (1) are coated with end electrode silver paste to form end electrodes (3). The magnetic core (1) is made of Co2Z type hexagonal ferrite.

8. A hexagonal ferrite high-current magnetic bead according to claim 7, characterized in that, On the cross-section of the magnetic core (1), the center of the interlayer groove (11) coincides with the center of the magnetic core (1).

9. A hexagonal ferrite high-current magnetic bead according to claim 7, characterized in that, After the two ends of the magnetic core (1) are coated with end electrode silver paste, they are subjected to high temperature silver burning to achieve tight bonding, thereby forming end electrodes (3).

10. A hexagonal ferrite high-current magnetic bead according to claim 7, characterized in that, The sandwich groove (11) and the magnetic core (1) are both rectangular in shape, and the wire (2) is a silver sheet.

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