Multi-band electromagnetic wave-absorbing composite material and method for manufacturing same

Abstract

The present disclosure relates to an electromagnetic wave-absorbing composite material and a method for manufacturing same, wherein the absorption of electromagnetic waves can be maximized while minimizing the amount of reflected electromagnetic waves in frequency bands suitable for 5G communication bands, thereby ensuring excellent electromagnetic shielding efficiency and enabling the control of electromagnetic shielding capability for multiple frequencies. Also, the electromagnetic wave-absorbing composite material has a thickness of less than a millimeter and thus can maximize the utilization in electronic products trending toward miniaturization / lightweight design.

Description

Multi-band electromagnetic wave absorbing composite material and method for manufacturing the same

[0001] The present invention relates to an electromagnetic wave absorbing composite material and a method for manufacturing the same, which can maximize the amount of electromagnetic waves absorbed while minimizing the amount of electromagnetic waves reflected in a frequency band suitable for a 5G communication band, thereby ensuring excellent electromagnetic wave shielding efficiency and enabling control of electromagnetic wave shielding ability for multiple frequencies, and which can maximize the usability in electronic products, etc., which are trending toward miniaturization / thinness, due to having a thickness of less than a millimeter.

[0002] Recent advancements in electrical and electronic components and next-generation information and communication devices have led to an increase in circuit operating frequencies into the GHz (gigahertz) frequency band. While current 4G LTE (Long Term Evolution) communications operate in the 2.1 GHz frequency band, 5G communications typically require a frequency band at least ten times higher. In particular, 5G communications require electronic and communication devices that operate in high-frequency and multi-frequency bands. As devices become increasingly multifunctional and miniaturized, the minute electromagnetic waves generated by these electronic components can cause malfunctions due to electromagnetic interference between each other, leading to serious problems such as reduced signal quality, harmful electromagnetic waves to the human body, and electromagnetic pollution.

[0003] For example, in the recently emerging autonomous vehicles, electromagnetic interference (EMI) from radars can cause false detections or misdetections of targets, potentially leading to serious accidents. Therefore, demand is growing for EMI shielding materials for 5G frequency bands with wideband / multiband shielding capabilities. Accordingly, diverse research is being conducted on EMI shielding materials that absorb and shield EMI to address EMI issues and improve the stability of electronic components.

[0004] However, the electromagnetic shielding materials reported so far are electromagnetic wave-reflecting shielding materials including metal, carbon, and MXene-based materials, which can effectively reflect more than 90% of external electromagnetic waves due to their high conductivity and have the advantage of minimizing transmission even in thin films with a thickness of less than 20 μm. However, the reflected electromagnetic waves can generate additional overlap and interference with electromagnetic waves, which can be more problematic due to the short wavelength of the 5G communication frequency band and the narrow gap between components of the integrated 5G mobile module, which limits their application in the 5G communication frequency band.

[0005] There have been various attempts to solve these problems and develop electromagnetic wave absorbing shielding materials that operate in the 5G communication frequency band. However, most of them have limited the operating frequency to the 26 GHz 5G band or the thickness of the electromagnetic wave absorbing composite material cannot be controlled, so no absorbing shielding materials have been reported for the 5G communication frequency band above 40 GHz.

[0006] Accordingly, the present applicant has completed an invention for an electromagnetic wave absorbing composite material that can maximize the amount of electromagnetic waves absorbed while minimizing the amount of electromagnetic waves reflected in a frequency band suitable for 5G communication bands, thereby ensuring excellent electromagnetic wave shielding efficiency while enabling control of electromagnetic wave shielding ability for multiple frequencies, and can maximize utilization in electronic products that are trending toward miniaturization / thinness due to its thickness of less than a millimeter.

[0007] The present invention has been devised to overcome the above-described problem, and the problem to be solved by the present invention is to provide an electromagnetic wave absorbing composite material that absorbs multiple band frequencies of 20 GHz or more, and an electromagnetic wave absorbing composite material having a thickness of less than a millimeter that can maximize electromagnetic wave absorption ability while simultaneously minimizing electromagnetic wave reflection ability for efficient shielding of electromagnetic waves in a target frequency range, and a method for manufacturing the same.

[0008] Meanwhile, it is disclosed that the present invention was made possible with the support of the following national research and development project.

[0009] [National Research and Development Project 1]

[0010] [Project ID] 1711154112 (PNCB980) [Project ID] 2019M3D1A2104156

[0011] [Ministry Name] Ministry of Science and ICT [Project Management (Specialized) Institution Name] National Research Foundation of Korea

[0012] [Research Project Name] Nanomaterial Technology Development [Research Project Name] Millimeter-Wave Absorption / Shielding / Heat Dissipation Characteristics Customized Composite Material Process Technology Development [Contribution Ratio] 70 / 100 [Project Implementing Organization Name] Korea Institute of Materials Science

[0013] [Research Period] January 1, 2022 - December 31, 2022

[0014] [National Research and Development Project 2]

[0015] [Project ID] 1711158279 (PNCC020) [Project ID] 2020M3H4A3081843

[0016] [Ministry Name] Ministry of Science and ICT [Project Management (Specialized) Institution Name] National Research Foundation of Korea

[0017] [Research Project Name] Nanomaterial Technology Development [Research Project Name] Ultra-high Frequency Loss Control Magnetic Materials and Composite Material Technology for RF Filters [Contribution Ratio] 30 / 100 [Project Implementing Organization] Korea Institute of Materials Science

[0018] [Research Period] January 1, 2022 - December 31, 2022

[0019] The present invention provides an electromagnetic wave absorbing composite material that absorbs multi-band frequencies of 20 GHz or higher in order to solve the above-described problem, comprising a magnetic composite material layer including a magnetic material and a conductive layer formed on at least one surface of the magnetic composite material layer, and a multi-band electromagnetic wave absorbing composite material in which electromagnetic waves reflected at multi-band frequencies of 20 GHz or higher are less than 5%.

[0020] In addition, according to one embodiment of the present invention, it can be characterized by exhibiting an electromagnetic wave absorption rate of 95% or more at a multi-band frequency of 20 GHz or more.

[0021] In addition, the multi-band frequency of 20 GHz or more may be characterized by being determined by the magnetic composite material layer and the conductive layer.

[0022] Additionally, it can be characterized by exhibiting an electromagnetic shielding efficiency of 99% or more at 30 to 90 GHz.

[0023] In addition, the magnetic material may be characterized as a magnetic material that causes ferromagnetic resonance (FMR).

[0024] Additionally, the magnetic composite material layer may be characterized by including a ferrite series material doped with a transition metal.

[0025] Additionally, the magnetic composite material layer may be characterized by further including a dielectric material and a heat dissipation material.

[0026] In addition, the conductive layer may include at least one or more of a conductor that is an iron (Fe)-based, cobalt (Co)-based, nickel (Ni)-based, molybdenum (Mo)-based, manganese (Mn)-based, neodymium (Nd)-based, gold (Au)-based, silver (Ag)-based, copper (Cu)-based, aluminum (Al)-based, platinum (Pt)-based, carbon nanotube, carbon nanofiber, carbon black, carbon fiber, and graphene or palladium (Pd)-based metal or an alloy thereof, MXene or a conductive polymer that is polypyrrole, polyaniline, polyacetylene, polyparaphenylenevinylene, polythiophene, polyethylenedioxythiophene, polyphenylene sulfide or a composite thereof, and may be characterized in that it is in the form of a film, a plate, a mesh or a grid.

[0027] Additionally, the thickness of the magnetic composite material layer may be characterized as being 10 to 1000 μm.

[0028] In addition, it may be characterized in that the frequency peak determined by the magnetic composite material layer and the frequency peak determined by the conductive layer are controlled by controlling the thickness of the magnetic composite material layer or the electromagnetic impedance of the conductive layer.

[0029] In addition, the magnetic material may be characterized as being a material expressed by the following chemical formula 1 that causes ferromagnetic resonance (FMR).

[0030] [Chemical Formula 1]

[0031] AFe x-y M y O 19

[0032] At this time, A is Sr or Ba,

[0033] wherein the above x is 9 to 12, the above y is 0 to 3,

[0034] The above M is Al, a transition metal of the 4th period, a transition metal of the 5th period, or a metal material synthesized thereof.

[0035] In addition, the present invention provides a method for manufacturing a multi-band electromagnetic wave absorbing composite material, which comprises a first step of forming a magnetic composite material layer including a magnetic material and a second step of forming a conductive layer on at least one surface of the magnetic composite material layer, and in which electromagnetic waves reflected at a multi-band frequency of 20 GHz or higher are less than 5%.

[0036] In addition, the first step may be characterized by including a step of preparing a composite solution by mixing the synthesized magnetic material and the polymer solution in a weight ratio of 1:0.1 to 1.

[0037] In addition, the present invention provides an electromagnetic wave absorbing circuit module including a circuit board on which an element is mounted and the above-described electromagnetic wave absorbing composite material provided on the circuit board so as to cover at least one surface of the element.

[0038] In addition, the present invention provides an electronic device including the electromagnetic wave absorption circuit module described above.

[0039] The present invention is an electromagnetic wave absorbing composite material that exhibits an electromagnetic wave shielding effect in the frequency band required for 5G communication and absorbs multiple frequency bands, and can maximize the amount of electromagnetic waves absorbed while minimizing the amount of reflected electromagnetic waves, thereby ensuring excellent electromagnetic wave shielding efficiency. At the same time, since it has a thickness of less than a millimeter, it can minimize electromagnetic interference between electronic components that are trending toward miniaturization / thinness, and thus can greatly increase its usability in fields where electronic and communication devices operating in high frequency and multiple frequency bands are used.

[0040] FIGS. 1A to 1C are drawings of an electromagnetic wave absorbing composite material according to an embodiment of the present invention, wherein FIG. 1A is a conceptual diagram of an electromagnetic wave absorbing composite material, FIG. 1B is a cross-sectional image of an implemented electromagnetic wave absorbing composite material (the area between the black areas indicated at the top / bottom of the drawing is a cross-section of the electromagnetic wave absorbing composite material, and the dotted line in contact with the lower black area is a conductive layer which is a Cu grid, and the remaining area of ​​the cross-section of the electromagnetic wave absorbing composite material excluding the dotted line represents a magnetic composite material layer), and FIG. 1C is a planar photograph of the implemented electromagnetic wave absorbing composite material.

[0041] FIG. 2 is a graph showing the frequency-dependent permeability and permeability characteristics of SrM (M-type strontium ferrites) materials included in an electromagnetic wave absorbing composite material according to one embodiment of the present invention. In FIG. 2 a and b, the solid line represents the real part (μ') of the complex permeability, the dotted line represents the imaginary part (μ''), and the dotted line in FIG. 2 a represents the imaginary part of the complex permeability of five overlapping SrM (M-type strontium ferrites) materials.

[0042] FIG. 3 is a schematic diagram of an electromagnetic wave shielding system using an electromagnetic wave absorbing composite material according to one embodiment of the present invention.

[0043] Figures 4 to 6 are graphs showing the electromagnetic wave shielding effect in a specific band of an electromagnetic wave absorbing composite material according to one embodiment of the present invention.

[0044] Figures 7 to 9 are graphs showing the electromagnetic shielding effect in another specific band of an electromagnetic wave absorbing composite material according to one embodiment of the present invention.

[0045] FIG. 10 is a graph showing the electromagnetic wave shielding effect in three different frequency bands of an electromagnetic wave absorbing composite material according to one embodiment of the present invention.

[0046] Fig. 11 is a graph showing the control of the distance between frequency peaks of an electromagnetic wave absorbing composite material according to one embodiment of the present invention.

[0047] Figures 12 and 13 are graphs showing the electromagnetic wave shielding effect of an electromagnetic wave absorbing composite material according to a comparative example of the present invention.

[0048] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0049]

[0050] As described above, there is an urgent need for research on electromagnetic shielding materials for the frequencies required in the recent 5G band, multi-band frequency absorption materials, and composite materials with a thickness of less than a millimeter.

[0051] Accordingly, the present invention seeks to solve the above-described problem by providing an electromagnetic wave absorbing composite material that absorbs a multi-band frequency of 20 GHz or higher, comprising a magnetic composite material layer including a magnetic material and a conductive layer formed on at least one surface of the magnetic composite material layer, and a multi-band electromagnetic wave absorbing composite material in which electromagnetic waves reflected at a multi-band frequency of 20 GHz or higher are less than 5%.

[0052] This allows for the maximization of absorbed electromagnetic waves while minimizing the amount of electromagnetic waves reflected in the frequency band suitable for 5G communication bands, ensuring excellent electromagnetic shielding efficiency while enabling control of electromagnetic shielding for multiple frequencies. Furthermore, with a thickness of less than a millimeter, it can maximize its usability in electronic products that are trending toward miniaturization and thinning.

[0053]

[0054] The present invention will be described in detail with reference to the drawings below.

[0055] Multiband electromagnetic wave absorbing composite material

[0056] A multi-band electromagnetic wave absorbing composite material according to the present invention includes a magnetic composite material layer including a magnetic material and a conductive layer formed on at least one surface of the magnetic composite material layer.

[0057] As described above, there is a high demand for electromagnetic shielding materials with superior electromagnetic wave absorption for 5G millimeter wave (mmWave) frequencies. However, most existing electromagnetic shielding materials are based on electromagnetic wave-reflecting conductive materials. Consequently, stability issues due to electromagnetic interference (EMI) in the high-frequency band of 5G communications are expected to be exacerbated, driving a growing demand for EMI shielding materials based on superior electromagnetic wave absorption and conductive materials.

[0058] Moreover, 5G communications have the characteristic of operating in multiple frequency bands, such as mobile phones (26, 39, 52 GHz) and autonomous vehicles (60, 77 GHz), and the demand for electromagnetic shielding materials with both broadband and multi-band shielding functions to suit the multiple bands used by each electronic component is also increasing.

[0059] Accordingly, the present invention provides an electromagnetic wave absorbing composite material capable of controlling electromagnetic wave absorption in a multi-band band by changing the design of the magnetic composite material layer and the conductive layer, while aiming at electromagnetic wave shielding in a frequency band of 20 GHz or higher to be suitable for 5G communication as shown in FIG. 1, and through this, the present invention can implement a multi-band electromagnetic wave absorbing composite material in which less than 5% of electromagnetic waves are reflected in a multi-band frequency of 20 GHz or higher.

[0060] More specifically, the present invention allows a specific frequency among multiple band frequencies of 20 GHz or more to be determined through the magnetic composite material layer.

[0061] While soft magnetic materials typically exhibit low resonance frequencies below a few GHz, ferromagnetic materials such as M-ferrite can induce ferromagnetic resonance above 45 GHz due to their higher magnetic anisotropy than other magnetic materials. Since the ferromagnetic resonance frequency of such ferromagnetic materials is proportional to the magnitude of their magnetic anisotropy, studies have reported on modifying their magnetic anisotropy to control the frequency band. However, since ferromagnetic resonance occurs within a specific frequency band, it is difficult to achieve broadband or multi-band electromagnetic shielding performance using only ferromagnetic materials such as M-ferrite.

[0062] Accordingly, the present invention provides a methodology for the effects of ion substitution, magnetic anisotropy change, and FMR frequency shift of a frequency band of such a ferromagnetic material, thereby enabling the determination of a specific frequency suitable for use in a desired electronic component among multi-band frequencies.

[0063] To this end, the present invention can determine a specific frequency among multi-band frequencies of 20 GHz or more by including a ferrite series material doped with a transition metal in the magnetic composite material layer, and in particular, the magnetic material can be a magnetic material that causes ferromagnetic magnetic resonance (FMR). More preferably, the magnetic material can be SrM (M-type strontium ferrites) synthesized by doping Co-Ti or Al into an M-type ferrite series material that causes ferromagnetic magnetic resonance as shown in the following chemical formula 1.

[0064] [Chemical Formula 1]

[0065] AFe x-y M y O 19

[0066] At this time, the above A can be Sr or Ba,

[0067] The above x may be 9 to 12, and preferably 0 to 1.

[0068] The above y may be 0 to 3, and preferably 0 to 2.

[0069] The above M may be Al, a transition metal of the 4th period, a transition metal of the 5th period, or a metal material synthesized thereof.

[0070]

[0071] More specifically, referring to FIG. 2, the frequency-dependent magnetic permeability and permeability characteristics of SrM (M-type strontium ferrites) synthesized by doping Co-Ti or Al as a material that induces ferromagnetic resonance according to an embodiment of the present invention can be known. Here, the solid line and the dotted line represent the real and imaginary parts of the permeability, respectively. As can be seen in FIG. 2b, all synthesized samples show clear FMR peaks of the real part (μ') and imaginary part (μ'') permeability, but the ferromagnetic resonance (FMR) frequency varies depending on the doping element and concentration. That is, it can be seen that the doping of Co-Ti shifts the FMR frequency to a lower frequency band, whereas the doping of Al shifts the FMR frequency to a higher frequency band. In addition, it can be confirmed that the degree of frequency shift increases depending on the doping concentration, and through this, it can be deduced that the FMR resonance frequency of the M-type ferrite according to one embodiment of the present invention is closely related to magnetic anisotropy, and that the FMR frequency (fr) is proportional to the anisotropy field (Ha) as in mathematical expression 1.

[0072] [Mathematical Formula 1]

[0073]

[0074] The above γ is the gyromagnetic ratio and the above g is the Lande coefficient. From the above mathematical expression 1 and Fig. 2, it can be expected that the substitution of Co-Ti decreases Ha, while the substitution of Al increases Ha.

[0075]

[0076] Next, the present invention can determine another specific frequency among the multi-band frequencies of 20 GHz or more by the conductive layer.

[0077] More specifically, referring to FIG. 3, the amount of reflected electromagnetic waves or the reflection coefficient Γ when an incident electromagnetic wave is directed toward a shielding system can be defined as follows.

[0078] [Equation 2]

[0079]

[0080] The above Z o is the electromagnetic impedance of air and Z in is the input impedance of the shielding system. Therefore, it is important to minimize the impedance difference between the air and the shielding system to minimize the amount of electromagnetic wave reflection, and the present invention implements the shielding system with a conductive layer and a magnetic composite material layer, thereby Z in can be derived as follows.

[0081] [Equation 3]

[0082]

[0083] The above Z c is the electromagnetic impedance of the magnetic composite layer, and Z L is the electromagnetic impedance of the conductive layer, d is the thickness of the magnetic composite layer, μ and ε are the permeability and permittivity of the magnetic composite layer, respectively, f is the EMI frequency, and c is the speed of light in free space. Consequently, it can be sufficiently expected that the electromagnetic wave absorbing composite material according to the present invention can control the ferromagnetic resonance frequency in multiple bands by adjusting each given variable through the above mathematical equations 1 to 3, and can control the impedance of the conductive layer by changing the width and spacing of the conductive layer.

[0084]

[0085] In this way, the present invention can determine a specific frequency among frequencies of 20 GHz or higher by including a ferrite series material doped with a transition metal in the magnetic composite material layer, and can also control electromagnetic wave absorption capacity in the multi-band frequency required for 5G communication by determining another specific frequency among frequencies of 20 GHz or higher by changing the design of the conductive layer.

[0086] More specifically, referring to FIG. 4, it can be seen that the electromagnetic wave absorbing composite material according to an embodiment of the present invention exhibits a very low electromagnetic wave reflectivity of less than 5% (less than 0.1 dB) at 39 GHz and 52 GHz, and shields more than 30 dB over the entire frequency range. At this time, the first frequency (0.009 dB at 38.9 GHz) is determined by the FMR frequency of the doped SrM, and the other frequency (0.055 dB at 52.5 GHz) is determined by the magnetic composite material layer, and it can be seen that it has a high peak in the 40-50 GHz band due to the high magnetic loss around the FMR frequency. In addition, the reflection shielding effectiveness (SER) and absorption shielding effectiveness (SEA) values ​​predicted through the above-described mathematical formulas indicated by dotted lines in FIGS. 5 and 6 are in very good agreement with the measured actual experimental values ​​(solid lines), which shows that the accuracy of the electromagnetic wave absorbing design theory of the present invention is excellent.

[0087] Finally, it can be seen through FIGS. 4 to 6 that the electromagnetic wave absorbing composite material according to one embodiment of the present invention reflects only 0.2% of electromagnetic waves and absorbs only 99.7% at 39 GHz, which is set as a specific band among frequencies above 20 GHz, reflects only 1.6% of electromagnetic waves and absorbs 98.3% at 52 GHz, and has an ultra-low reflectivity of less than 5% in both bands and a low reflectivity of less than 20% in a wide frequency band (34.5-58.5 GHz).

[0088] In addition, as another embodiment of the electromagnetic wave absorbing composite material according to the present invention, FIGS. 7 to 9 show that electromagnetic waves in the frequency bands of 60 GHz and 77 GHz corresponding to the automotive radar band can be efficiently absorbed and shielded. That is, referring to FIGS. 7 to 9, as in the above-described embodiment, the first frequency (0.065 dB at 59.3 GHz) is determined as the FMR frequency, and the other frequency (0.12 dB at 74.8 GHz) is determined by the magnetic composite material layer, and it can be seen that the values ​​derived through mathematical expressions 1 to 3 and the measured experimental values ​​match very well. In addition, it can be seen through FIG. 9 that it has an ultra-low reflectivity of less than 5% in two bands (56.3-60.8 GHz and 72.7-80.4 GHz) and a low reflectivity of less than 20% in a wide frequency band (53.8-91.8 GHz).

[0089]

[0090] In summary, it can be seen that the electromagnetic wave absorbing composite material according to the present invention can exhibit less than 5% of electromagnetic waves reflected at multi-band frequencies of 20 GHz or higher, an electromagnetic wave absorption rate of 95% or higher at multi-band frequencies of 20 GHz or higher, and preferably an electromagnetic wave shielding efficiency of 99% or higher at 30 to 90 GHz, through appropriate design changes of the magnetic composite layer and conductive layer described above, so as to be suitable for electronic products targeting electromagnetic interference problems in the 5G communication band.

[0091] At this time, the conductive layer includes at least one or more of a conductor that is an iron (Fe)-based, cobalt (Co)-based, nickel (Ni)-based, molybdenum (Mo)-based, manganese (Mn)-based, neodymium (Nd)-based, gold (Au)-based, silver (Ag)-based, copper (Cu)-based, aluminum (Al)-based, platinum (Pt)-based, carbon nanotube, carbon nanofiber, carbon black, carbon fiber, and graphene or palladium (Pd)-based metal or an alloy thereof, MXene or a conductive polymer that is a polypyrrole, polyaniline, polyacetylene, polyparaphenylenevinylene, polythiophene, polyethylenedioxythiophene, polyphenylene sulfide or a composite thereof, and may be in the form of a film, a plate, a mesh or a grid.

[0092] In addition, the thickness of the magnetic composite material layer may be 10 to 1000 μm. In this case, if the thickness of the magnetic composite material layer is less than 10 μm, there may be a problem of difficulty in forming the composite material layer, and further, if the thickness of the magnetic composite material layer exceeds 1000 μm, the accuracy of predicting actual experimental values ​​through the mathematical formula of the intended multi-band frequency design may decrease, and the usability in electronic products that are trending toward miniaturization / thickness may be hindered.

[0093] In addition, according to one embodiment of the present invention, the magnetic composite material layer may further include a dielectric material and a heat-dissipating material, and may further include a known conventional functional material, without being limited thereto, so as to be suitable for the intended use of the electronic component.

[0094]

[0095] Meanwhile, in the present invention, the distance between the frequency peak determined by the magnetic composite material layer and the frequency peak determined by the conductive layer can be controlled by controlling the thickness or electromagnetic impedance of the magnetic composite material layer.

[0096] More specifically, referring to FIG. 11, when using a ferromagnetic resonance magnetic material corresponding to 40 GHz according to one embodiment of the present invention, it can be seen that the distance between the first peak and the second peak can be adjusted by changing the thickness of the magnetic composite material layer. That is, the first peak is determined around the magnetic material frequency (40 GHz), and the second peak depends on the thickness of the magnetic composite material layer, and it can be seen that the distance between the first peak and the second peak changes as the thickness of the magnetic composite material layer decreases.

[0097] More specifically, referring to the above mathematical expression 3, the first peak is determined around the magnetic material frequency, and the second peak is determined by the input impedance of the system, so the position of the second peak can be adjusted by changing the thickness of the magnetic composite material layer or the electromagnetic impedance of the conductive layer, thereby adjusting the distance between the first peak and the second peak.

[0098]

[0099] Method for manufacturing multi-band electromagnetic wave absorbing composite materials

[0100] The following describes a method for manufacturing a multi-band electromagnetic wave absorbing composite material according to the present invention. However, to avoid duplication, descriptions of parts that share the same technical concept as the multi-band electromagnetic wave absorbing composite material described above are omitted.

[0101]

[0102] A method for manufacturing a multi-band electromagnetic wave absorbing composite material according to the present invention includes a first step of forming a magnetic composite material layer including a magnetic material, and a second step of forming a conductive layer on at least one surface of the magnetic composite material layer.

[0103] The first step of the method for manufacturing a multi-band electromagnetic wave absorbing composite material according to the present invention is a step of forming a magnetic composite material layer including a magnetic material, which may include a step of manufacturing a ferrite series material doped with a transition metal by a solid-state method or a molten salt method, and preferably a step of synthesizing the magnetic material by a citrate sol-gel method.

[0104] In the first step, if the ferrite series material doped with the transition metal according to a preferred embodiment of the present invention is SrM (M-type strontium ferrites) synthesized by doping with Co-Ti or Al, a mixed solution of strontium nitrate, iron nitrate nonahydrate, cobalt nitrate hexahydrate, titanium isopropoxide, aluminum nitrate and citric acid monohydrate can be used, in which case Sr 2+ The concentration of ions can be 0.005 to 0.2 M, and Sr 2+ The molar ratio of ions and citric acid monohydrate may be 1: 0.5 to 2. Thereafter, the mixed solution is heated and dried to produce a gel using the citrate sol-gel method, and then dried to produce a magnetic material. The magnetic material produced in this way can be mixed with a known polymer solution to form a magnetic composite material layer having a thickness of 10 to 1000 μm. At this time, the magnetic material and the polymer solution are mixed in a weight ratio of 1: 0.1 to 1 to produce a composite solution, which can then be cast through bar coating.

[0105]

[0106] Next, the second step of the method for manufacturing a multi-band electromagnetic wave absorbing composite material according to the present invention is a step of forming a conductive layer on at least one surface of the magnetic composite material layer. At this time, the conductive layer includes at least one or more of a conductor that is an iron (Fe)-based, cobalt (Co)-based, nickel (Ni)-based, molybdenum (Mo)-based, manganese (Mn)-based, neodymium (Nd)-based, gold (Au)-based, silver (Ag)-based, copper (Cu)-based, aluminum (Al)-based, platinum (Pt)-based, carbon nanotube, carbon nanofiber, carbon black, carbon fiber, and graphene or palladium (Pd)-based metal or an alloy thereof, MXene or a conductive polymer that is a polypyrrole, polyaniline, polyacetylene, polyparaphenylenevinylene, polythiophene, polyethylenedioxythiophene, polyphenylene sulfide or a composite thereof, and may be in the form of a film, a plate, a mesh or a grid. In addition, the method for forming such a conductive layer is not particularly limited, but preferably, it is manufactured by pressing at 5 to 20 MPa at 100 to 150°C for 10 to 30 minutes, thereby easily manufacturing it to a thickness suitable for the intended electronic product.

[0107]

[0108] Electromagnetic wave absorbing circuit module and electronic device including the same

[0109] The present invention provides an electromagnetic wave absorbing circuit module including a circuit board on which an element is mounted and the electromagnetic wave absorbing composite material according to the present invention provided on the circuit board so as to cover at least one surface of the element, and also provides an electronic device including such an electromagnetic wave absorbing circuit module.

[0110] According to one embodiment of the present invention, the electronic device may be a mobile phone utilizing a multi-band frequency of 26, 39, and 52 GHz, and further, the electronic device may be an autonomous vehicle utilizing a multi-band frequency of 60 and 77 GHz. However, these are merely examples to aid understanding of the present invention, and the electronic device may be an electronic and communication device operating in 5G high-frequency and multi-frequency bands.

[0111] Hereinafter, the present invention will be described in more detail through examples, but the following examples do not limit the scope of the present invention, and should be interpreted as helping to understand the present invention.

[0112]

[0113] Preparation example

[0114] The precursors used in the doped SrM were strontium nitrate (Sr(NO3)2), iron nitrate anhydride (Fe(NO3)3·9H2O), cobalt nitrate hexahydrate (Co(NO3)2·6H2O), titanium isopropoxide (Ti(OCH(CH3)2)4), aluminum nitrate (Al(NO3)3), and citric acid monohydrate, which were purchased from Sigma-Aldrich and used without further purification. In addition, a thermoplastic polyurethane (TPU) solution of 30 wt% TPU in n,n-dimethylformamide (DMF) from Songwon Industrial Co., Ltd., Korea was used as a polymer binder for the magnetic composite layer, and the conductive layer was fabricated by electroforming at Samwon Act Co., Ltd., Korea.

[0115]

[0116] Example 1

[0117] Co-Ti doped SrMs powder (SrFe 10.9 Co 0.55 Ti 0.55 O 19) was synthesized using the citrate sol-gel method. First, stoichiometric amounts of strontium nitrate, iron nitrate nonahydrate, cobalt nitrate hexahydrate, titanium isopropoxide, aluminum nitrate, and citric acid monohydrate were dissolved in deionized water. Sr 2+ The concentration of ions is 0.05M, Sr 2+ The molar ratio of ions and citric acid monohydrate was 1:1. The mixed solution was then heated to 90°C for 24 h to completely evaporate the water. The dried gel was gently crushed by hand using a mortar containing 40 wt% NaCl and calcined at 1250°C for 3 h. Finally, the calcined powder was washed five times with deionized water to remove residual NaCl and dried at 80°C for 24 h to produce a magnetic material.

[0118] Next, the TPU solution and the magnetic material were mixed at a weight ratio of TPU:SrMs=3:7 at 2000 rpm for 5 minutes using a planetary mixer (ARE-310, Thinky). The mixed composite solution was cast into a 100 μm thick layer through bar coating, and the cast layer was dried at 110°C for 30 minutes to evaporate unnecessary DMF solvent. Afterwards, a conductive layer having a Cu grid was formed by pressing at 10 MPa at 120°C for 20 minutes as shown in Fig. 1b, and finally, as shown in Fig. 1c, it consists of a magnetic composite material layer (layer between the upper / lower black marked areas) and a conductive layer (dotted line indicated at the bottom of the layer between the upper / lower black marked areas), and an electromagnetic wave absorbing composite material that absorbs electromagnetic waves in the final 40 GHz and 52 GHz bands was manufactured.

[0119]

[0120] Example 2

[0121] Manufactured in the same manner as in Example 1 above, but using Al-doped SrMs powder (SrFe 10.5 Al 1.5 O 19) was used to manufacture an electromagnetic wave absorbing composite material that absorbs electromagnetic waves in the 60 GHz and 77 GHz bands.

[0122]

[0123] Example 3

[0124] The Co-Ti doped SrMs powder (SrFe) of Example 1 above 10.9 Co 0.55 Ti 0.55 O 19 ) and the Al-doped SrMs powder (SrFe) of the above Example 2 10.5 Al 1.5 O 19 ) was used to manufacture an electromagnetic wave absorbing composite material that absorbs electromagnetic waves in the 40 GHz, 55 GHz, and 68 GHz bands.

[0125]

[0126] Examples 4 to 6

[0127] An electromagnetic wave absorbing composite material was manufactured in the same manner as in Example 1, but the thickness of the magnetic composite material layer was changed to 600 μm, 500 μm, and 450 μm, respectively.

[0128]

[0129] Comparative Example 1

[0130] An electromagnetic wave absorbing composite material was manufactured in the same manner as in Example 1 above, but without forming a conductive layer.

[0131]

[0132] Comparative Examples 2 to 4

[0133] An electromagnetic wave absorbing composite material was manufactured in the same manner as in Examples 4 to 6 above, but with a thinner magnetic composite layer, to confirm that it does not operate effectively in multiple bands if the spacing between the first and second peaks is not appropriate.

[0134]

[0135]

[0136] Experimental Example 1 - Measurement of Electromagnetic Shielding Effectiveness

[0137] After scattering the electromagnetic wave absorbing composite materials according to Examples 1 to 3 and Comparative Example 1 using a vector network analyzer (Keysight N5291A) and a spatial measurement system (EMLabs FS-110), the electromagnetic wave shielding effect was measured in three frequency bands of Q (33-50 GHz), V (50-75 GHz), and W (75-110 GHz), and the results are shown in FIGS. 4 to 10 and FIG. 12.

[0138] Referring to FIGS. 4 to 6, it can be seen that the electromagnetic wave absorbing composite material according to Example 1 of the present invention exhibits a very low electromagnetic wave reflectivity of less than 5% (less than 0.1 dB) at 39 GHz and 52 GHz, and shields more than 30 dB over the entire frequency range. At this time, the first frequency (0.009 dB at 38.9 GHz) is determined by the FMR frequency of the doped SrM, and the other frequency (0.055 dB at 52.5 GHz) is determined by the magnetic composite layer, and it can be seen that it has a high peak in the 40-50 GHz band due to the high magnetic loss around the FMR frequency. In addition, the predicted value through the above-described mathematical formula indicated by the dotted line in FIGS. 5 and 6 is in very good agreement with the measured actual experimental value (solid line), which shows that the accuracy of the electromagnetic wave absorbing design theory of the present invention is excellent. Finally, it can be seen through FIGS. 4 to 6 that the electromagnetic wave absorbing composite material according to one embodiment of the present invention reflects only 0.2% of electromagnetic waves and absorbs only 99.7% at 39 GHz, which is set as a specific band among frequencies above 20 GHz, reflects only 1.6% of electromagnetic waves and absorbs 98.3% at 52 GHz, and has an ultra-low reflectivity of less than 5% in both bands and a low reflectivity of less than 20% in a wide frequency band (34.5-58.5 GHz).

[0139] Referring to FIGS. 7 to 9, it can be seen that the electromagnetic wave absorbing composite material according to Example 2 of the present invention can efficiently absorb electromagnetic waves in the frequency bands of 60 GHz and 77 GHz and shield the electromagnetic waves. That is, referring to FIGS. 7 to 9, as in Example 1 described above, the first frequency (0.065 dB at 59.3 GHz) is determined by the FMR frequency, and the other frequency (0.12 dB at 74.8 GHz) is determined by the magnetic composite material layer, and it can be seen that the values ​​derived through mathematical expressions 1 to 3 and the measured experimental values ​​match very well. In addition, it can be seen from FIG. 9 that it has an ultra-low reflectivity of less than 5% in two bands (56.3-60.8 GHz and 72.7-80.4 GHz) and a low reflectivity of less than 20% in a wide frequency band (53.8-91.8 GHz).

[0140] Also, referring to FIG. 10, it can be seen that the electromagnetic wave absorbing composite material according to Example 3 of the present invention can exhibit an ultra-low reflectivity of less than 5% in not only two frequency bands but also three or more frequency bands and a low reflectivity of less than 20% in a wide frequency band.

[0141] In contrast, referring to FIG. 12, in the case of Comparative Example 1, it can be seen that the electromagnetic wave absorbing composite material having only a magnetic composite material layer without forming a conductive layer not only fails to exhibit electromagnetic wave absorption and shielding effects in multiple bands, but also the electromagnetic wave absorption and shielding effects are significantly reduced.

[0142]

[0143] Experimental Example 2 - Peak-to-peak distance analysis

[0144] As in Experimental Example 1 above, the electromagnetic shielding effect of the electromagnetic wave absorbing composite materials according to Examples 4 to 6 and Comparative Examples 2 to 4 was measured in three frequency bands, and the results are shown in Figs. 11 and 12, respectively.

[0145]

[0146] First, referring to FIG. 11, when using a ferromagnetic resonance magnetic material corresponding to 40 GHz according to Examples 4 to 6 of the present invention, it can be seen that the distance between the first peak and the second peak can be adjusted by changing the thickness of the magnetic composite material layer. That is, the first peak is determined around the magnetic material frequency (40 GHz), and the second peak depends on the thickness of the magnetic composite material layer, and it can be seen that the distance between the first peak and the second peak changes as the thickness of the magnetic composite material layer decreases.

[0147] In contrast, referring to FIG. 13, in the case of Comparative Examples 2 to 4, if the distance between the first peak and the second peak is too wide, not only is the electromagnetic wave absorption and shielding effect not exhibited in multiple bands, but the electromagnetic wave absorption and shielding effect is also significantly reduced.

[0148] In summary, it can be seen that the electromagnetic wave absorbing composite material according to the present invention can exhibit less than 5% of electromagnetic waves reflected at multi-band frequencies of 20 GHz or higher, an electromagnetic wave absorption rate of 95% or higher at multi-band frequencies of 20 GHz or higher, and preferably an electromagnetic wave shielding efficiency of 99% or higher at 30 to 90 GHz, through appropriate design changes of the magnetic composite layer and conductive layer described above, so as to be suitable for electronic products targeting electromagnetic interference problems in the 5G communication band.

Claims

As an electromagnetic wave absorbing composite material that absorbs multi-band frequencies of 1.20 GHz or higher, A magnetic composite layer comprising a magnetic material; and A multi-band electromagnetic wave absorbing composite material comprising a conductive layer formed on at least one surface of the magnetic composite material layer; wherein less than 5% of electromagnetic waves are reflected at multi-band frequencies of 20 GHz or higher.

2. In paragraph 1, A multi-band electromagnetic wave absorbing composite material characterized by exhibiting an electromagnetic wave absorption rate of 95% or more at multi-band frequencies of 20 GHz or higher.

3. In paragraph 1, A multi-band electromagnetic wave absorbing composite material, characterized in that the multi-band frequency of 20 GHz or higher is determined by the magnetic composite material layer and the conductive layer.

4. In paragraph 1, A multi-band electromagnetic wave absorbing composite material characterized by an electromagnetic wave shielding efficiency of more than 99% in the range of 30 to 90 GHz.

5. In paragraph 1, A multi-band electromagnetic wave absorbing composite material characterized in that the above magnetic material is a magnetic material that causes ferromagnetic resonance (FMR).

6. In paragraph 1, A multi-band electromagnetic wave absorbing composite material, characterized in that the above magnetic composite material layer includes a ferrite series material doped with a transition metal.

7. In paragraph 1, A multi-band electromagnetic wave absorbing composite material, characterized in that the above magnetic composite material layer further includes a dielectric material and a heat-radiating material.

8. In paragraph 1, The conductive layer comprises at least one or more of a conductor selected from the group consisting of iron (Fe)-based, cobalt (Co)-based, nickel (Ni)-based, molybdenum (Mo)-based, manganese (Mn)-based, neodymium (Nd)-based, gold (Au)-based, silver (Ag)-based, copper (Cu)-based, aluminum (Al)-based, platinum (Pt)-based, carbon nanotubes, carbon nanofibers, carbon black, carbon fibers, and graphene or palladium (Pd)-based metals or alloys thereof, MXene or a conductive polymer selected from the group consisting of polypyrrole, polyaniline, polyacetylene, polyparaphenylenevinylene, polythiophene, polyethylenedioxythiophene, polyphenylene sulfide or a composite thereof, and is characterized by being in the form of a film, a plate, a mesh or a grid.

9. In paragraph 1, A multi-band electromagnetic wave absorbing composite material, characterized in that the thickness of the magnetic composite material layer is 10 to 1000 μm.

10. In paragraph 3, A multi-band electromagnetic wave absorbing composite material, characterized in that the distance between the frequency peak determined by the magnetic composite layer and the frequency peak determined by the conductive layer is controlled by controlling the thickness of the magnetic composite layer or the electromagnetic impedance of the conductive layer.

11. In paragraph 1, The above magnetic material is a multi-band electromagnetic wave absorbing composite material characterized by being a material expressed by the following chemical formula 1 that causes ferromagnetic resonance (FMR): [Chemical Formula 1] AFe x-y M y O 19 At this time, A is Sr or Ba, wherein the above x is 9 to 12, the above y is 0 to 3, The above M is Al, a transition metal of the 4th period, a transition metal of the 5th period, or a metal material synthesized thereof.

12. A first step of forming a magnetic composite material layer including a magnetic material; and A method for manufacturing a multi-band electromagnetic wave absorbing composite material, comprising: a second step of forming a conductive layer on at least one surface of the magnetic composite material layer; wherein the multi-band electromagnetic wave absorbing composite material has less than 5% of electromagnetic waves reflected at a multi-band frequency of 20 GHz or higher.

13. In Article 12 A method for producing a multi-band electromagnetic wave absorbing composite material, characterized in that the first step includes a step of producing a composite solution by mixing a synthesized magnetic material and a polymer solution in a weight ratio of 1:0.1 to 1.

14. Circuit board on which the component is mounted; and An electromagnetic wave absorbing circuit module comprising an electromagnetic wave absorbing composite material according to claim 1, which is provided on the circuit board so as to cover at least one surface of the element.

15. An electronic device including an electromagnetic wave absorbing circuit module according to Article 14.

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