Microwave-band electromagnetic wave-absorbing material and manufacturing method therefor

Abstract

An embodiment of the present invention provides a manufacturing method for an electromagnetic wave-absorbing material containing W-type hexaferrite represented by chemical formula 1, the method comprising the steps of: mixing powders containing one or more selected from the group consisting of a Ca precursor, a Ba precursor, a Sr precursor, a Re precursor, a Me precursor, a Co precursor, and a Fe precursor; performing first heat treatment on the mixed powders; ball-milling the heat-treated powders; and performing second heat treatment on the ball-milled powders. The present invention is made from the research result of a project on the development of a microwave absorber for 5G communication (28 GHz) conducted by the Seoul National University Industry - Academic Cooperation Foundation under the support of Changsung Co., Ltd.

Description

Microwave band electromagnetic wave absorbing material and manufacturing method thereof

[0001] The present invention relates to an electromagnetic wave absorbing material and a method for manufacturing the same, and more specifically, to Fe 2+ The present invention relates to a method for manufacturing an electromagnetic wave absorbing material for the Ka-band (26.5 to 40 GHz range), which is a 5G communication area, comprising W-type hexaferrite containing no ions or only a very small amount of ions.

[0002] With the advancement of information and communication technology, next-generation technologies such as self-driving cars, the Internet of Things (IoT), smartphones, artificial intelligence (AI), and virtual reality are being actively developed.

[0003] Furthermore, electronic devices are becoming smaller, their available operating frequencies are increasing, and the amount of data and communication being processed is rapidly increasing. Consequently, communications between electronic devices are becoming more complex and diverse, raising issues such as communication errors due to frequency interference. Consequently, the need for electromagnetic shielding and absorption is increasing.

[0004] Hexaferrite possesses high magnetic anisotropy, making it a suitable material for electromagnetic wave absorbers in the GHz frequency range. Therefore, for stable communication between electronic devices in the Ka-band (26.5 to 40 GHz), the 5G communication area, electromagnetic interference must be eliminated. Therefore, hexaferrite, which exhibits excellent absorption properties in the tens to tens of GHz frequency range, is increasingly being utilized in 5G communication technology.

[0005] However, in the past, as electronic devices and communication volume increased, interference between signals from peripheral devices occurred, and the problem of electromagnetic interference (EMI) arose, which could degrade functions or cause malfunctions.

[0006] In particular, it can cause serious problems for electronic devices that are closely related to life, such as drones, self-driving cars, and biometric implantable sensors.

[0007] To mitigate these EMI issues, international standards for electromagnetic compatibility (EMC) are being legislated and enforced. Therefore, one of the methods adopted during the product design phase to meet EMC standards is electromagnetic shielding and absorption techniques that block the entry and exit of electromagnetic waves. These techniques are used to minimize unwanted electromagnetic waves in the final product and maximize the device's immunity to unwanted electromagnetic waves.

[0008] However, as the operating frequency gradually moves to a high-frequency band, conventional materials such as Ni-Zn Ferrite, Mn-Zn Ferrite, and Sendust are unsuitable as electromagnetic shielding and absorption materials in the band of several to several tens of GHz due to their low magnetic anisotropy in their crystal structures.

[0009] Currently, with the advent of the fifth generation wireless communication (5G), the need for electromagnetic wave absorbing materials in the 3.5 GHz and 28 GHz bands is increasing. Among these, the need for absorbing materials in the 28 GHz band is increasing, but the supply of appropriate materials is insufficient.

[0010]

[0011] [Prior patent literature]

[0012] Republic of Korea Patent No. 10-2621490

[0013]

[0014] The technical problem to be solved by the present invention is Fe 2+ The present invention provides a method for manufacturing an electromagnetic wave absorbing material for the Ka-band (26.5 to 40 GHz range), which is a 5G communication area, comprising W-type hexaferrite that does not contain ions or contains only a very small amount of ions.

[0015]

[0016] The technical problems to be solved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0017]

[0018] In order to achieve the above technical task, one embodiment of the present invention provides a method for manufacturing an electromagnetic wave absorbing material.

[0019] The method for manufacturing the electromagnetic wave absorbing material according to one embodiment of the present invention is as follows:

[0020] A method for producing a powder, comprising: a step of mixing powders comprising at least one selected from the group consisting of a Ca precursor, a Ba precursor, a Sr precursor, a Re precursor, a Me precursor, a Co precursor, and an Fe precursor; a step of first heat-treating the mixed powder; a step of ball-milling the heat-treated powder; and a step of second heat-treating the ball-milled powder;

[0021] It may be a method for manufacturing an electromagnetic wave absorbing material including W-type hexaferrite expressed by the following chemical formula 1.

[0022] [Chemical Formula 1]

[0023] Ca a Ba b Sr 1-a-b-c Re c Co 2+ x Me 2+ 2-x Fe 3+ 16 O 27

[0024] In the above chemical formula 1, Re is at least one selected from the group consisting of rare earth elements, and Me 2+is at least one selected from the group consisting of divalent transition metals, a is a value of 0.0 or more and 1.0 or less, b is a value of 0.0 or more and 1.0 or less, c is a value of 0.0 or more and 1.0 or less, and x is a value of 0.0 or more and 2.0 or less.

[0025]

[0026] In addition, according to one embodiment of the present invention, there may be a method for manufacturing an electromagnetic wave absorbing material, characterized in that in the chemical formula 1, x is a value of 0.0 or more and 0.3 or less.

[0027] In addition, according to one embodiment of the present invention, in the chemical formula 1, the Me 2+ is Zn 2+ , Fe 2+ , Ni 2+ , Mn 2+ , and Mg 2+ There may be a method for manufacturing an electromagnetic wave absorbing material characterized by being at least one selected from the group consisting of .

[0028]

[0029] In addition, according to one embodiment of the present invention, in the chemical formula 2, the Me 2+ is Zn 2+ , Fe 2+ , Ni 2+ , Mn 2+ , and Mg 2+ There may be a method for manufacturing an electromagnetic wave absorbing material characterized by being at least one selected from the group consisting of .

[0030]

[0031] In addition, according to one embodiment of the present invention, there may be a method for manufacturing an electromagnetic wave absorbing material, characterized in that the first heat treatment step is performed in a temperature range of 1200°C to 1400°C.

[0032] In addition, according to one embodiment of the present invention, the W-type hexaferrite expressed by the chemical formula 1 contains Fe for 2 moles of the total divalent transition metal included in the chemical formula 1. 2+ There may be a method for manufacturing an electromagnetic wave absorbing material characterized in that the content of ions is 0.5 mol or less.

[0033] In addition, according to one embodiment of the present invention, there may be a method for manufacturing an electromagnetic wave absorbing material, characterized in that the second heat treatment step is performed at a temperature range of 1200°C to 1400°C.

[0034] In addition, according to one embodiment of the present invention, there may be a method for manufacturing an electromagnetic wave absorbing material, characterized in that the second heat treatment step is performed by sintering in the air.

[0035] In order to achieve the above technical task, another embodiment of the present invention provides an electromagnetic wave absorbing material.

[0036] According to one embodiment of the present invention, the electromagnetic wave absorbing material is

[0037] It may be an electromagnetic wave absorbing material characterized by including W-type hexaferrite expressed by the following chemical formula 1.

[0038] [Chemical Formula 1]

[0039] Ca a Ba b Sr 1-a-b-c Re c Co 2+ x Me 2+ 2-x Fe 3+ 16 O 27

[0040] In the above chemical formula 1, Re is at least one selected from the group consisting of rare earth elements, and Me 2+is at least one selected from the group consisting of divalent transition metals, a is a value of 0.0 or more and 1.0 or less, b is a value of 0.0 or more and 1.0 or less, c is a value of 0.0 or more and 1.0 or less, and x is a value of 0.0 or more and 2.0 or less.

[0041]

[0042] That is, the W-type hexaferrite includes a composition that includes both the Ba and Sr elements present in the chemical formula 1.

[0043] In addition, according to one embodiment of the present invention, the W-type hexaferrite expressed by the chemical formula 1 contains Fe for 2 moles of the total divalent transition metal included in the chemical formula 1. 2+ There may be an electromagnetic wave absorbing material characterized by having an ion content of 0.5 mol or less.

[0044] In addition, according to one embodiment of the present invention, there may be an electromagnetic wave absorbing material characterized in that the electromagnetic wave absorbing material has a ferromagnetic resonance (FMR) frequency in a frequency band of 26.5 GHz or more and 40 GHz or less.

[0045] In addition, according to one embodiment of the present invention, there may be an electromagnetic wave absorbing material characterized in that in the chemical formula 1, x is a value of 0.0 or more and 0.3 or less.

[0046]

[0047] In addition, according to one embodiment of the present invention, there may be an electromagnetic wave absorbing material characterized in that the electromagnetic wave absorbing material has a thickness range of 0.97 mm to 1.05 mm.

[0048]

[0049] In addition, according to one embodiment of the present invention, in the chemical formula 1 and the chemical formula 2, the Me 2+ is Zn 2+ , Fe 2+ , Ni 2+ , Mn 2+ , and Mg 2+ There may be a method for manufacturing an electromagnetic wave absorbing material characterized by being at least one selected from the group consisting of .

[0050]

[0051] According to one embodiment of the present invention, Fe 2+ A method for manufacturing an electromagnetic wave absorbing material for the Ka-band (26.5 to 40 GHz) band, which is a 5G communication area, can be provided by including W-type hexaferrite containing only a very small amount of ions.

[0052] According to one embodiment of the present invention, in W-type hexaferrite, Zn 2+ , Co 2+ , Ni 2+ , Mn 2+ , Cu 2+ , Mg 2+ Ions of the back Me 2+ A method for manufacturing an electromagnetic wave absorber including W-type hexaferrite having high complex permittivity and complex permeability in a high-frequency range by substituting a position can be provided.

[0053] According to one embodiment of the present invention, a composition design for adjusting a ferromagnetic resonance frequency to have excellent absorption capability in the Ka-band (26.5 to 40 GHz) band, which is a 5G communication area, can be provided.

[0054]

[0055] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the detailed description of the present invention or the composition of the invention described in the claims.

[0056]

[0057] Figure 1 is a flowchart illustrating a method for manufacturing an electromagnetic wave absorbing material including W-type hexaferrite according to one embodiment of the present invention.

[0058] Figure 2 is an electromagnetic wave absorbing material according to one embodiment of the present invention, Co 2+ This is a graph showing the complex investment rate and complex permittivity (30% powder content volume fraction) according to the change in content.

[0059] Figure 3 is an electromagnetic wave absorbing material according to one embodiment of the present invention, Co 2+ This is a graph showing the results of regression analysis of ferromagnetic resonance frequency according to changes in content.

[0060] Figure 4 is an electromagnetic wave absorbing material according to one embodiment of the present invention, Co 2+ This is a graph showing the absorption characteristics (minimum reflection loss value) of composite sheets according to changes in content.

[0061] Figure 5 is a graph showing the absorption characteristics of a composite sheet according to changes in thickness in an electromagnetic wave absorbing material according to an embodiment of the present invention.

[0062] Fig. 6 is an electromagnetic wave absorbing material according to an embodiment of the present invention, Co 2+ This is a graph showing the absorption characteristics of composite sheets according to changes in content (contour plot of absorption characteristics according to thickness and frequency).

[0063] Fig. 7 is (Fe 2+ , Mg 2+ , Mn 2+ , Ni 2+ )-Co 2+ This is a graph showing the complex investment rate according to the change in the content (epoxy powder content volume fraction 30%).

[0064] Figure 8 shows various divalent transition metals and Co 2+ This is a graph of the regression analysis of the ferromagnetic resonance frequency with respect to the change in ion content.

[0065]

[0066] Hereinafter, the present invention will be described with reference to the attached drawings. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. It should be understood that all modifications, equivalents, and alternatives included within the spirit and technical scope of the present invention are included.

[0067] In addition, in order to clearly explain the present invention in the drawings, parts unrelated to the description are omitted, and similar parts are given similar drawing reference numerals throughout the specification.

[0068] Throughout the specification, when a part is said to be "connected (connected, contacted, coupled)" to another part, this includes not only cases where it is "directly connected" but also cases where it is "indirectly connected" with another part in between.

[0069] In addition, when it is said that a part such as a layer, film, region, or plate is “on” another part, this includes not only the case where it is “directly above” the other part, but also the case where there is another part in between. In addition, in the present specification, when it is said that a part such as a layer, film, region, or plate is formed on another part, the direction in which it is formed is not limited to the upper direction, but also includes the case where it is formed in the side or lower direction. Conversely, when it is said that a part such as a layer, film, region, or plate is “under” another part, this includes not only the case where it is “directly below” the other part, but also the case where there is another part in between.

[0070] In this specification, the terms "upper surface" and "lower surface" are used as relative concepts to facilitate understanding of the technical concepts of the present invention. Therefore, "upper surface" and "lower surface" do not refer to specific directions, locations, or components, and are interchangeable.

[0071] For example, 'upper surface' can be interpreted as 'lower surface', and 'lower surface' can be interpreted as 'upper surface'. Accordingly, 'upper surface' can be expressed as 'first' and 'lower surface' can be expressed as 'second', or 'lower surface' can be expressed as 'first' and 'upper surface' can be expressed as 'second'. However, within one embodiment, 'upper surface' and 'lower surface' are not used interchangeably.

[0072] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0073] Additionally, when a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0074] The terminology used herein is merely used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, it should be understood that the terms "comprises" or "has" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0075]

[0076] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[0077] Figure 1 is a flowchart illustrating a method for manufacturing an electromagnetic wave absorbing material including W-type hexaferrite according to one embodiment of the present invention.

[0078]

[0079] Referring to the above drawing 1, a method for manufacturing an electromagnetic wave absorbing material according to an embodiment of the present invention is described.

[0080]

[0081] As an example of the above embodiment, a method for producing a powder, comprising: a step of mixing powders including at least one selected from the group consisting of a Ca precursor, a Ba precursor, a Sr precursor, a Re precursor, a Me precursor, a Co precursor, and a Fe precursor; a step of first heat-treating the mixed powder; a step of ball-milling the heat-treated powder; and a step of second heat-treating the ball-milled powder;

[0082] There may be a method for manufacturing an electromagnetic wave absorbing material including W-type hexaferrite expressed by the following chemical formula 1.

[0083] [Chemical Formula 1]

[0084] Ca a Ba b Sr 1-a-b-c Re c Co 2+ x Me 2+ 2-x Fe 3+ 16 O 27

[0085] In the above chemical formula 1, Re is at least one selected from the group consisting of rare earth elements, and Me 2+is at least one selected from the group consisting of divalent transition metals, a is a value of 0.0 or more and 1.0 or less, b is a value of 0.0 or more and 1.0 or less, c is a value of 0.0 or more and 1.0 or less, and x is a value of 0.0 or more and 2.0 or less.

[0086]

[0087] At this time, the above hexaferrite is a magnetic material with a hexagonal crystal structure and has high magnetic anisotropy, so it is a material with high potential for application as an electromagnetic wave absorber in the high-frequency region of the GHz band.

[0088] In addition, the above hexaferrite exists in several types depending on the chemical composition, and among them, in the case of W-type hexaferrite, since the magnetic anisotropy exists in the c-axis, it has a high possibility of being applied as an absorber in the high GHz band compared to other hexaferrites.

[0089]

[0090] As an example of the above embodiment, in the chemical formula 1, the Me 2+ is Zn 2+ , Fe 2+ , Ni 2+ , Mn 2+ , and Mg 2+ There may be a method for manufacturing an electromagnetic wave absorbing material characterized by being at least one selected from the group consisting of .

[0091]

[0092] In the above example, in W-type hexaferrite, Zn 2+ , Fe 2+ , Ni 2+ , Mn 2+ , Mg 2+ , etc. ions of Me 2+ A method for manufacturing an electromagnetic wave absorber including W-type hexaferrite having high complex permittivity and complex permeability in a high-frequency range by substituting a position can be provided.

[0093] In addition, it provides a composition design that adjusts the ferromagnetic resonance frequency to have excellent absorption capability in the Ka-band (26.5 to 40 GHz), which is a 5G communication area, and can elucidate the correlation of absorption characteristics according to the ferromagnetic resonance frequency.

[0094]

[0095] The above ferromagnetic resonance phenomenon refers to a phenomenon in which, when a magnetic material is exposed to high-frequency electromagnetic waves, the magnetic spin begins to precess and absorbs electromagnetic waves of a special region, and the ferromagnetic resonance frequency represents the frequency at this time.

[0096] At this time, the reason for adjusting the ferromagnetic resonance frequency as described above is that it is possible to create an electromagnetic wave absorbing material with excellent absorption characteristics in the required frequency band.

[0097]

[0098] The composition of the above W-type hexaferrite is generally Sr(or Ba)Me2Fe 16 O 27 , where Me is Mn 2+ , Zn 2+ , Mg 2+ , Ni 2+ , Co 2+ , Cu 2+ It represents a divalent metal ion such as .

[0099]

[0100] Referring to FIG. 1, a process for manufacturing an electromagnetic wave absorbing material including W-type hexaferrite expressed by the chemical formula 1 can be confirmed through a step (S10) of mixing powders including at least one selected from the group consisting of a Ca precursor, a Ba precursor, a Sr precursor, a Re precursor, a Me precursor, a Co precursor, and a Fe precursor; a step (SS20) of first heat-treating the mixed powder; a step (S30) of ball-milling the heat-treated powder; and a step (S40) of second heat-treating the ball-milled powder.

[0101]

[0102] At this time, as an example of the above embodiment, SrCO3 may be used as the Sr precursor, Fe2O3 may be used as the Fe precursor, CoO may be used as the Co precursor, and MeO may be used as the Me precursor.

[0103]

[0104] Referring to the above Figure 1, the process of manufacturing W-type hexaferrite substituted with a divalent transition metal ion using precursor powders such as SrCO3, Fe2O3, CoO, and MeO can be confirmed.

[0105] At this time, the manufacturing process used is a solid-state reaction.

[0106] When performing the first heat treatment step (S20), the sample may be in either a powder form or a pellet form.

[0107] In the step (S30) of ball milling the above heat-treated powder, a conventional grinding mill using beads can be used for ball milling.

[0108]

[0109] Basically, in the above chemical formula 1, x may be a value greater than or equal to 0.0 and less than or equal to 2.0,

[0110] More preferably, there may be a method for manufacturing an electromagnetic wave absorbing material, characterized in that the above x is a value of 0.0 or more and 0.3 or less.

[0111]

[0112] As can be seen from the following experimental examples, the Co 2+ As the content increases, the ferromagnetic resonance frequency gradually shifts to a lower frequency band, and when the value of x is in the range of 0.0 to 0.3, a ferromagnetic resonance frequency value near 28 GHz can be confirmed.

[0113] Most preferably, there may be a method for manufacturing an electromagnetic wave absorbing material, characterized in that the above x is a value of 0.25 or more and 0.3 or less.

[0114] When the above x range is 0.25 or more and 0.3 or less, the absorption characteristics for the target frequency of 28 GHz are the best.

[0115]

[0116] As an example of the above embodiment, the Re (rare earth element) may be at least one selected from the group consisting of La, Ce, and Y.

[0117]

[0118] As an example of the above embodiment, in the step of forming the powder, when only the Ba precursor, Me precursor, Co precursor, and Fe precursor powders are mixed, an electromagnetic wave absorbing material including W-type hexaferrite expressed by the following chemical formula 2 instead of the chemical formula 1 can be manufactured.

[0119] [Chemical Formula 2]

[0120] BaCo 2+ x Me 2+ 2-x Fe 3+ 16 O 27

[0121] In the above chemical formula 2, the Me 2+ is at least one selected from the group consisting of divalent transition metals, and x is a value of 0.0 or more and 2.0 or less.

[0122] As another example of the above embodiment, when only the Sr precursor, Me precursor, Co precursor, and Fe precursor powders are mixed in the step of forming the powder, an electromagnetic wave absorbing material including W-type hexaferrite expressed by the following chemical formula 3 can be manufactured instead of the chemical formula 1.

[0123] [Chemical Formula 3]

[0124] SrCo 2+ x Me 2+ 2-x Fe 3+ 16 O 27

[0125] In the above chemical formula 3, the Me 2+ is at least one selected from the group consisting of divalent transition metals, and x is a value of 0.0 or more and 2.0 or less.

[0126]

[0127] As an example of the above embodiment, in the chemical formula 2, the Me 2+ There may be a method for manufacturing an electromagnetic wave absorbing material characterized in that it is at least one selected from a group consisting of divalent transition metals.

[0128]

[0129] Unlike the above chemical formulas 2 and 3, the W-type hexaferrite expressed by the above chemical formula 1 includes a composition in which not only the Sr element and the Ba element but also Ba and Re (rare earth elements) are present.

[0130] In the above chemical formula 1, when a, c, and b are 0, it becomes the same as the above chemical formula 3,

[0131] In the above chemical formula 1, when a and c are 0 and b is 1, it becomes the same as the above chemical formula 2.

[0132]

[0133] The above a may more preferably be a value greater than or equal to 0 and less than or equal to 0.5.

[0134] The above b may more preferably be a value greater than or equal to 0 and less than or equal to 1.0.

[0135] The above c may more preferably be a value greater than or equal to 0 and less than or equal to 0.5.

[0136]

[0137] As an example of the above embodiment, there may be a method for manufacturing an electromagnetic wave absorbing material, characterized in that the first heat treatment step is performed in a temperature range of 1200°C to 1400°C.

[0138] The above first heat treatment step can be performed by calcination.

[0139] Additionally, the first heat treatment step may be performed in air and may be performed for a time period ranging from 5 hours to 7 hours.

[0140]

[0141] At this time, if the first heat treatment step is performed at a temperature lower than 1200°C, there is a problem in that crystal phases of W type hexaferrite, M type hexaferrite, and spinel ferrite are formed in a mixed manner.

[0142] As the above heat treatment temperature increases, the M type and spinel ferrite phases can be synthesized into the W type hexaferrite phase around 1300°C.

[0143]

[0144] Conversely, if the second heat treatment step is performed at a temperature exceeding 1400°C, it exists in a liquid phase with Magnetite and is not easily compatible.

[0145]

[0146] As an example of the above embodiment, W-type hexaferrite expressed by the chemical formula 1 contains Fe for 2 moles of the total divalent transition metal included in the chemical formula 1. 2+ There may be a method for manufacturing an electromagnetic wave absorbing material characterized in that the content of ions is 0.5 mol or less.

[0147] At this time, the second heat treatment step may be performed at a temperature range of 1200°C to 1400°C, and the second heat treatment step may be performed by sintering in air.

[0148]

[0149] At this time, if the second heat treatment step is performed at a temperature lower than 1200°C, there is a problem in that crystal phases of W type hexaferrite, M type hexaferrite, and spinel ferrite are formed in a mixed manner.

[0150] As the above heat treatment temperature increases, the M type and spinel ferrite phases can be synthesized into the W type hexaferrite phase around 1300°C.

[0151]

[0152] Conversely, if the second heat treatment step is performed at a temperature exceeding 1400°C, a problem arises in that it exists in a liquid phase with Magnetite and is not easily compatible.

[0153]

[0154] In addition, the above-mentioned secondary heat treatment step can be performed in an air atmosphere by sintering.

[0155] In conventional cases, generally W-type is stable at high temperature and Fe in air 2+ The ion is Fe 3+ Since it is easily oxidized into ions and causes phase decomposition, there was a need to conduct heat treatment at low oxygen partial pressure.

[0156] However, in the case of the above example, Fe is used for 2 moles of the total 2-valent transition metals included in the above chemical formula 1. 2+ Since the ion content is less than 0.5 mol, there is an advantage in that heat treatment can be performed in the air.

[0157]

[0158] For the total 2 moles of divalent transition metals included in the above chemical formula 1, Fe 2+ When the ion content is 0.5 mol or more, a stable W-type hexaferrite phase can be synthesized without phase decomposition if accompanied by gas control or quenching. Compared to cases where oxygen partial pressure control is required, the secondary heat treatment step has the advantage of reducing process costs because additional gas control is not required.

[0159]

[0160] An electromagnetic wave absorbing material according to another embodiment of the present invention is described.

[0161] Since the above electromagnetic wave absorbing material is an invention of a different category with virtually the same technical characteristics as the electromagnetic wave absorbing material manufacturing method described above,

[0162] The above-described content in the description of the method for manufacturing the above electromagnetic wave absorbing material can be applied as is.

[0163]

[0164] As an example of the above embodiment, there may be an electromagnetic wave absorbing material characterized by including W-type hexaferrite represented by the following chemical formula 1.

[0165] [Chemical Formula 1]

[0166] Ca a Ba b Sr 1-a-b-c Re c Co 2+ x Me 2+ 2-x Fe 3+16 O 27

[0167] In the above chemical formula 1, Re is at least one selected from the group consisting of rare earth elements, and Me 2+ is at least one selected from the group consisting of divalent transition metals, a is a value of 0.0 or more and 1.0 or less, b is a value of 0.0 or more and 1.0 or less, c is a value of 0.0 or more and 1.0 or less, and x is a value of 0.0 or more and 2.0 or less.

[0168]

[0169] As an example of the above embodiment, there may be an electromagnetic wave absorbing material characterized by including W-type hexaferrite expressed by the following chemical formula 2.

[0170] [Chemical Formula 2]

[0171] BaCo 2+ x Me 2+ 2-x Fe 3+ 16 O 27

[0172] In the above chemical formula 2, the Me 2+ is at least one selected from the group consisting of divalent transition metals, and x is a value of 0.0 or more and 2.0 or less.

[0173] As another example of the above embodiment, there may be an electromagnetic wave absorbing material characterized by including W-type hexaferrite represented by the following chemical formula 3.

[0174] [Chemical Formula 3]

[0175] SrCo 2+ x Me 2+ 2-x Fe 3+ 16 O 27

[0176] In the above chemical formula 3, the Me 2+ is at least one selected from the group consisting of divalent transition metals, and x is a value of 0.0 or more and 2.0 or less.

[0177]

[0178] Unlike the above chemical formulas 2 and 3, the W-type hexaferrite expressed by the above chemical formula 1 includes a composition in which not only the Sr element and the Ba element but also Ba and Re (rare earth elements) are present.

[0179] In the above chemical formula 1, when a, c, and b are 0, it becomes the same as the above chemical formula 3,

[0180] In the above chemical formula 1, when a and c are 0 and b is 1, it becomes the same as the above chemical formula 2.

[0181]

[0182] The above a may more preferably be a value greater than or equal to 0 and less than or equal to 0.5.

[0183] The above b may more preferably be a value greater than or equal to 0 and less than or equal to 1.0.

[0184] The above c may more preferably be a value greater than or equal to 0 and less than or equal to 0.5.

[0185]

[0186] As an example of the above embodiment, W-type hexaferrite expressed by the chemical formula 1 contains Fe for 2 moles of the total divalent transition metal included in the chemical formula 1. 2+ There may be an electromagnetic wave absorbing material characterized by having an ion content of 0.5 mol or less.

[0187] As an example of the above embodiment, there may be an electromagnetic wave absorbing material characterized in that the electromagnetic wave absorbing material has a ferromagnetic resonance frequency in the range of 26.5 GHz to 40 GHz.

[0188] As an example of the above embodiment, there may be an electromagnetic wave absorbing material characterized in that in the chemical formula 1, x is a value of 0.0 or more and 0.3 or less.

[0189] As an example of the above embodiment, there may be an electromagnetic wave absorbing material characterized in that the electromagnetic wave absorbing material has a thickness range of 0.97 mm to 1.05 mm.

[0190] As an example of the above embodiment, in the chemical formula 1, the Me 2+ is Zn 2+ , Fe 2+ , Ni 2+ , Mn 2+ , and Mg 2+ There may be an electromagnetic wave absorbing material characterized by being at least one selected from the group consisting of:

[0191]

[0192] As an example of the above embodiment, the Re (rare earth element) may be at least one selected from the group consisting of La, Ce, and Y.

[0193]

[0194] The characteristics of the electromagnetic wave absorbing material according to the above embodiment are described in detail through the following experimental examples.

[0195]

[0196] Manufacturing Example 1. Electromagnetic wave absorbing material (SrCo) according to one embodiment of the present invention x Zn 2-x Fe 16 O 27 ).

[0197]

[0198] The process for manufacturing W-type hexaferrite substituted with divalent transition metal ions using precursor powders of SrCO3, Fe2O3, CoO, and ZnO is illustrated. The manufacturing process used is a solid-state reaction, and the sample for calcination can be in powder or pellet form.

[0199]

[0200] The ball mill used a grinding mill using conventional beads.

[0201]

[0202] 1. 1 mol of SrCO3, x mol of CoO, (2-x) mol of ZnO, and 8 mol of Fe2O3 precursor powder are ball milled for 24 hours.

[0203] The total amount of the above materials is 20g, and each was manufactured while adjusting the value of x, and the numerical values ​​applied to the x value are described below.

[0204] 2. Calcined in air at 1250℃ for 6 hours.

[0205] 3. Afterwards, ball mill again for 24 hours.

[0206] 4. Again, sinter at 1300℃ in air for 2 hours.

[0207]

[0208] For the balls used for crushing, zirconia balls were used, and the zirconia balls weighed 20 times as much as 20 g of the precursor, which was 240 g.

[0209] The types of balls used were three types with diameters of 1 mm, 0.5 mm, and 0.3 mm, and 80 g of each diameter ball was used.

[0210] Ball milling temperature and rpm were based on 150 rpm at room temperature.

[0211] Through the above process, SrCo x Zn 2-x Fe16 O 27 Hexaferrite powder is manufactured.

[0212]

[0213] By adjusting the amount of the precursor used above, the values ​​of x were manufactured to be 0.0, 0.1, 0.2, 0.225, 0.250, 0.275, and 0.3, respectively.

[0214]

[0215] Experimental Example 1. Co 2+ Analysis of the characteristics of electromagnetic wave absorbing materials according to their content and material thickness.

[0216] Figure 2 is an electromagnetic wave absorbing material according to one embodiment of the present invention, Co 2+ This is a graph showing the complex investment rate and complex permittivity (30% powder content volume fraction) according to the change in content.

[0217] Figure 3 is an electromagnetic wave absorbing material according to one embodiment of the present invention, Co 2+ This is a graph showing the results of regression analysis of ferromagnetic resonance frequency according to changes in content.

[0218] Figure 4 is an electromagnetic wave absorbing material according to one embodiment of the present invention, Co 2+ This is a graph showing the absorption characteristics (minimum reflection loss value) of composite sheets according to changes in content.

[0219] Figure 5 is a graph showing the absorption characteristics of a composite sheet according to changes in thickness in an electromagnetic wave absorbing material according to an embodiment of the present invention.

[0220] Fig. 6 is an electromagnetic wave absorbing material according to an embodiment of the present invention, Co 2+ This is a graph showing the absorption characteristics of composite sheets according to changes in content (contour plot of absorption characteristics according to thickness and frequency).

[0221] The experimental example is explained through the above figures 2 to 6.

[0222]

[0223] In Figure 2, SrCo according to one embodiment of the present invention x Zn 2-x Fe 16 O 27 (0≤x≤0.3) To evaluate the absorption characteristics in the hexaferrite composition, composite sheets were manufactured by mixing epoxy solid resin according to the content.

[0224] The above resin can be manufactured using various types of materials such as epoxy, acrylic, silicone, urethane, and paraffin wax, depending on the need.

[0225] To evaluate the absorption of the manufactured composite sheet, the complex permeability and complex permittivity values, which are material constants, were obtained using a network analyzer.

[0226] The ferromagnetic resonance frequency is usually expressed as the complex permeability (μ r =μ'- jμ'') can be confirmed as the area of ​​the inflection point of the real part investment rate (μ') and the maximum point of the imaginary part investment rate (μ'').

[0227] Referring to Figure 2, Co 2+ As the content of Co increases, the ferromagnetic resonance frequency gradually shifts to a lower frequency band, and 2+ It can be confirmed that the content (x value) has a ferromagnetic resonance frequency value near 28 GHz in the content range of 0.25 to 0.3.

[0228]

[0229] This can also be confirmed through Table 1 below.

[0230]

[0231]

[0232]

[0233] As mentioned above, through the values ​​in Table 1, Co 2+ As the content of Co increases, the ferromagnetic resonance frequency gradually shifts to a lower frequency band, and 2+It can be confirmed that the content (x value) has a ferromagnetic resonance frequency value near 28 GHz in the content range of 0.25 to 0.3.

[0234]

[0235] In Fig. 3, Co 2+ You can check the results of the regression analysis of the ferromagnetic resonance frequency according to the change in the content.

[0236] Referring to Figure 3, Co 2+ As the content of Co increases, the ferromagnetic resonance frequency gradually shifts to a lower frequency band, and the Co 2+ It can be confirmed that the content (x value) has a ferromagnetic resonance frequency value near 28 GHz in the content range of 0.25 to 0.3.

[0237]

[0238] In Fig. 4, Co 2+ In order to evaluate the absorption characteristics of the composite sheet according to the change in content, first, the impedance value is obtained through the following [Mathematical Formula 1] according to the transmission line theory.

[0239] Afterwards, the reflection loss (RL) value expressed as an absorption characteristic was calculated by substituting it into [Mathematical Equation 2] below.

[0240]

[0241] [Mathematical Formula 1]

[0242]

[0243] [Equation 2]

[0244]

[0245]

[0246] Referring to Figure 4, Co 2+ As the substitution content increases, the frequency showing the maximum absorption capacity (the lowest RL) shifts to a lower frequency band, which is consistent with the behavior of the ferromagnetic resonance frequency shift.

[0247] In the composition x=0.3, where the ferromagnetic resonance frequency is 26.9 GHz,

[0248] It exhibited maximum absorption at a frequency of 27.7 GHz, and excellent absorption of over 99.99% at a frequency of 28 GHz.

[0249] Therefore, Co 2+ Wow Zn 2+ It can be confirmed that excellent absorbers can be developed not only in the 28 GHz band but also in other bands of Ka frequency by controlling the content.

[0250]

[0251] In Figure 5, the absorption characteristics of the composite sheet can be confirmed according to the change in thickness of the absorbent material.

[0252] Referring to Figure 5, Z according to the above mathematical formula 1 in / Z0 shows the best absorption capacity in an absorbent with a thickness of 1.01 mm, which satisfies the condition of 1, and it can be confirmed that the absorption capacity decreases as the thickness changes.

[0253] In actual commercialization, there may be a thickness deviation of about 5%, and even if there is a difference in the range of + or - 0.04 mm from the standard thickness of 1.01 mm, the absorption capacity of 99.0% or more is maintained at a frequency of 28 GHz.

[0254]

[0255] In Fig. 6, Co 2+ You can check the absorption characteristics of the composite sheet according to the change in content (absorption characteristics contour plot according to thickness and frequency).

[0256] Referring to Fig. 6, Co 2+ As the content increases, the absorption peak gradually shifts to lower frequency bands. This is consistent with the shift in the ferromagnetic resonance frequency discussed above.

[0257]

[0258] Table 2 below compares absorption characteristics according to reflection loss.

[0259]

[0260]

[0261]

[0262] Table 2 above is a conversion table for reflection loss and absorption expressed in decibel units.

[0263] At this time, if the reflection loss (RL) is -20 dB, it means that 99.0% of the electromagnetic waves incident on the absorber sample from the outside are absorbed inside the absorber, and only 1.0% are reflected to the outside.

[0264]

[0265] Table 3 below shows Co 2+ This table summarizes the ferromagnetic resonance frequency, volume fraction, maximum absorption peak frequency and thickness, and frequency range over 99% absorption (-20 dB) according to the substitution amount.

[0266]

[0267]

[0268]

[0269] To summarize the above, Co 2+ As the content increases, the C-axis magnetic anisotropy decreases, and the ferromagnetic resonance frequency gradually decreases.

[0270] The above ferromagnetic resonance frequency is the Co 2+ It was confirmed that the content moved to the target frequency of 28 GHz around 0.25 to 0.3.

[0271]

[0272] According to the transmission line theory, the reflection loss value represented by the absorption characteristic was calculated.

[0273] As a result, Co 2+ When the content is 0.25 to 0.3 and the thickness is 0.97 mm to 1.05 mm,

[0274] It was confirmed that excellent absorption characteristics of -65.5 dB at 27.7 GHz and -50.3 dB at 28.0 GHz were obtained.

[0275]

[0276] Also, Co 2+ When the content is 0.3 and the volume fraction is 30%,

[0277] It was confirmed that excellent absorption properties were obtained between 0.97 mm and 1.05 mm in thickness.

[0278] The characteristics at this time showed a value of less than -20dB, absorbing more than 99%.

[0279]

[0280] Through this, excellent absorption characteristics can be obtained by setting the ferromagnetic resonance frequency 1.0 to 1.5 GHz lower than the target frequency.

[0281] In addition, it can be confirmed that the ferromagnetic resonance frequency can be efficiently adjusted by changing the substitution ion and powder content, and thus it can be applied equally not only to the Ka-band (26.5 to 40 GHz), which is the 5G communication area, but also to other utilization frequencies.

[0282]

[0283]

[0284] Experimental Example 2. Changes in ferromagnetic resonance frequency due to changes in transition metals.

[0285]

[0286] SrCo 2+ x Me 2+ 2-x Fe 3+ 16 O 27 In Co 2+ Fix the ion and the above Me 2+ In place, Zn 2+ We confirmed the change in ferromagnetic resonance frequency by substituting it with a divalent transition metal that can be applied in addition to ions.

[0287] Fe each2+ , Mg 2+ , Mn 2+ , and Ni 2+ By replacing it with , the change in ferromagnetic resonance frequency was confirmed, and through this, a magnetic composite sheet with excellent absorption characteristics at the target frequency can be manufactured.

[0288]

[0289] Fig. 7 is (Fe 2+ , Mg 2+ , Mn 2+ , Ni 2+ )-Co 2+ This is a graph showing the complex investment rate according to the change in the content (epoxy powder content volume fraction 30%).

[0290] Figure 8 shows various divalent transition metals and Co 2+ This is a graph of the regression analysis of the ferromagnetic resonance frequency with respect to the change in ion content.

[0291] Table 4 below summarizes the change in ferromagnetic resonance frequency according to the change in transition metal.

[0292]

[0293]

[0294]

[0295] The above experimental example 2 is described with reference to FIG. 7, Table 4, and FIG. 8.

[0296]

[0297] Referring to Figure 7 and Table 4, SrCo 2+ x Me 2+ 2-x Fe 3+ 16 O 27 In Co 2+ Fix the ion and the above Me 2+ In place, Zn 2+ Fe, a divalent transition metal that can be applied in addition to ions 2+ , Mg 2+ , Mn 2+ , and Ni 2+Even when replacing with , it can be confirmed that the ferromagnetic resonance frequency gradually shifts within the Ka band region according to the composition change.

[0298] This suggests that the specific ferromagnetic resonance frequency can be tuned by various compositions, and that it can be applied as a filler as an absorber in applications that operate at the corresponding frequency.

[0299]

[0300] Referring to Fig. 8, Co 2+ -Me 2+ (Fe 2+ , Zn 2+ , Mg 2+ , Mn 2+ , Ni 2+ ) The results of regression analysis of the measured ferromagnetic resonance frequency values ​​according to the substitution composition can be confirmed.

[0301] Through the above figure 8, Co is used to obtain the desired ferromagnetic resonance frequency value for each material. 2+ You can check the content range.

[0302]

[0303] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single entity may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined manner.

[0304] The scope of the present invention is indicated by the claims described below, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims

1. A step of mixing powders including at least one selected from the group consisting of a Ca precursor, a Ba precursor, a Sr precursor, a Re precursor, a Me precursor, a Co precursor, and a Fe precursor; A step of first heat treating the above mixed powder; A step of ball milling the above heat-treated powder; and Including a step of performing a second heat treatment on the ball-milled powder; A method for manufacturing an electromagnetic wave absorbing material comprising W-type hexaferrite represented by the following chemical formula 1: [Chemical Formula 1] Approx a Ba b Sr 1-a-b-c Re c Co 2+ x Along with 2+ 2-x Feb 3+ 16 O 27 In the above chemical formula 1, Re is at least one selected from the group consisting of rare earth elements, Me above 2+ is at least one selected from the group consisting of divalent transition metals, The above a is a value greater than or equal to 0.0 and less than or equal to 1.0, The above b is a value greater than or equal to 0.0 and less than or equal to 1.0, The above c is a value greater than or equal to 0.0 and less than or equal to 1.0, The above x is a value greater than or equal to 0.0 and less than or equal to 2.

0.

2. A method for manufacturing an electromagnetic wave absorbing material, characterized in that in the first paragraph, in the chemical formula 1, x is a value of 0.0 or more and 0.3 or less.

3. In the first paragraph, in the chemical formula 1, the Me 2+ is Zn 2+ , Fe 2+ , Ni 2+ , Mn 2+ , and Mg 2+ A method for manufacturing an electromagnetic wave absorbing material, characterized in that at least one selected from the group consisting of:

4. A method for manufacturing an electromagnetic wave absorbing material, characterized in that in the first paragraph, the first heat treatment step is performed at a temperature range of 1200°C to 1400°C.

5. In the first paragraph, the W-type hexaferrite expressed by the chemical formula 1 is Fe for 2 moles of the total divalent transition metal included in the chemical formula 1. 2+ A method for manufacturing an electromagnetic wave absorbing material, characterized in that the content of ions is 0.5 mol or less.

6. A method for manufacturing an electromagnetic wave absorbing material, characterized in that in the first paragraph, the second heat treatment step is performed at a temperature range of 1200°C to 1400°C.

7. A method for manufacturing an electromagnetic wave absorbing material, characterized in that in the first paragraph, the second heat treatment step is performed by sintering in air.

8. An electromagnetic wave absorbing material characterized by including W-type hexaferrite represented by the following chemical formula 1: [Chemical Formula 1] Approx a Ba b Sr 1-a-b-c Re c Co 2+ x Along with 2+ 2-x Feb 3+ 16 O 27 In the above chemical formula 1, Re is at least one selected from the group consisting of rare earth elements, Me above 2+ is at least one selected from the group consisting of divalent transition metals, The above a is a value greater than or equal to 0.0 and less than or equal to 1.0, The above b is a value greater than or equal to 0.0 and less than or equal to 1.0, The above c is a value greater than or equal to 0.0 and less than or equal to 1.0, The above x is a value greater than or equal to 0.0 and less than or equal to 2.

0.

9. In the 8th paragraph, the W-type hexaferrite expressed by the chemical formula 1 is Fe for 2 moles of the total divalent transition metal included in the chemical formula 1. 2+ An electromagnetic wave absorbing material characterized by having an ion content of 0.5 mol or less.

10. In the 8th paragraph, the electromagnetic wave absorbing material is characterized in that it has a ferromagnetic resonance frequency in a frequency band of 26.5 GHz or more and 40 GHz or less.

11. An electromagnetic wave absorbing material according to claim 8, characterized in that in the chemical formula 1, x is a value of 0.0 or more and 0.3 or less.

12. In the 8th paragraph, in the chemical formula 1, the Me 2+ is Zn 2+ , Fe 2+ , Ni 2+ , Mn 2+ , and Mg 2+ An electromagnetic wave absorbing material characterized by being at least one selected from the group consisting of:

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