KR930011547B1 - Manufacturing method of radio wave absorber - Google Patents
Manufacturing method of radio wave absorber Download PDFInfo
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- KR930011547B1 KR930011547B1 KR1019910013920A KR910013920A KR930011547B1 KR 930011547 B1 KR930011547 B1 KR 930011547B1 KR 1019910013920 A KR1019910013920 A KR 1019910013920A KR 910013920 A KR910013920 A KR 910013920A KR 930011547 B1 KR930011547 B1 KR 930011547B1
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- 239000006096 absorbing agent Substances 0.000 title description 22
- 238000004519 manufacturing process Methods 0.000 title description 10
- 229910000859 α-Fe Inorganic materials 0.000 claims description 31
- 238000001816 cooling Methods 0.000 claims description 6
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 7
- 229910052760 oxygen Inorganic materials 0.000 description 7
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- 229910018605 Ni—Zn Inorganic materials 0.000 description 4
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- 229910017518 Cu Zn Inorganic materials 0.000 description 2
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
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- Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
- Magnetic Ceramics (AREA)
- Soft Magnetic Materials (AREA)
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Abstract
내용 없음.No content.
Description
제1도는 본 발명 실시예 시편의 전자현미경 사진으로서, 제1a도는 연마면이고, 제1b도는 파단면이다.1 is an electron micrograph of a specimen of an embodiment of the present invention, in which FIG. 1a is a polished surface and FIG. 1b is a fracture surface.
제2도 및 제3도는 각각 본 발명 실시예 시편의 주파수 변화에 대한 감쇠량의 변화거동을 나타낸 그래프.2 and 3 are graphs showing the change behavior of the attenuation with respect to the frequency change of the specimen of the embodiment of the present invention, respectively.
본 발명은 Ni-Zn계 페라이트 전파흡수체의 제조방법에 관한 것으로, 특히 소결시 제반소결 조건을 적절히 제어하여 소결체의 복소투자율 허수부를 증가시킴으로써 박판화와 광대역화를 도모한 전파흡수체의 제조방법에 관한 것이다.The present invention relates to a method for manufacturing a Ni-Zn-based ferrite wave absorber, and more particularly, to a method for manufacturing a wave absorber that is thin and wider by increasing the complex permeability imaginary part of the sintered body by appropriately controlling all sintering conditions during sintering. .
전자 통신기술이 발전함에 따라 전파의 이용이 확대되고 다양한 디지털기기의 사용확대에 수반하여 불필요한 전파의 발생으로 인한 전자장치등의 오동작을 초래하는등의 전파공해 문제가 대두되고 있는데, 일예로 디지털회로의 경우는 본래 방사노이즈 레벨이 높으므로 마이크로 컴퓨터 사이의 평균거리가 짧아지게 되면 입력 임피던스가 높은 MOS형 소자는 노이즈의 영향으로 인해 오동작하는 예가 증가하게 된다.With the development of electronic communication technology, the use of radio waves has expanded and the use of various digital devices has caused radio wave problems such as malfunction of electronic devices due to unnecessary generation of radio waves. In the case of, the emission noise level is high, so when the average distance between the microcomputers is shortened, the MOS type device having a high input impedance increases the number of malfunctions due to the influence of noise.
이같은 불필요한 전파로 인한 문제점을 해결하기 위하여 여러 가지 형태의 전파흡수체가 개발되어 사용되고 있는데, 그 특성에 따라 통상적으로 전파의 전기에너지를 저항체에 의해 열에너지로 변환시키는 저항체형과 실드면에 자성체를 첨부하여 자기손실에 의해 전파를 흡수하는 자성체형 및 이들 두가지 형태를 복합한 복합형의 세가지 종류로 구분된다.In order to solve the problems caused by such unnecessary propagation, various types of radio absorbers have been developed and used. According to the characteristics, magnetic materials are attached to the resistor type and shield surface to convert electric energy of radio waves into heat energy by the resistor. It is divided into three types: magnetic body that absorbs radio waves by magnetic loss and composite type that combines these two forms.
자성체형의 일종인 페라이트 전파흡수체는 자유공간과 임계결합을 하고 있는 광대역 공진기로서 이같은 광대역 성능은 강자성체 고유의 자연공명현상에 의한 것으로 알려지고 있는바, 이같은 페라이트를 카본등을 이용한 저항손실재료와 조합하여 복합형 전파흡수체로 제작하게 되면 VHF대역 이상의 광대역을 커버하게 된다.Ferrite wave absorber, a type of magnetic body, is a broadband resonator with critical coupling with free space. Such broadband performance is known to be due to the natural resonance phenomenon of ferromagnetic materials. If the composite wave absorber is manufactured, it covers a wide bandwidth over the VHF band.
이와같은 복합형 전파흡수체는 파장이 긴 저주파 영역은 주로 페라이트의 자기손실이, 그리고 파장이 짧은 고주파영역은 카본을 사용한 도전재료의 저항손실이 분담하는 주파수 분담형의 전파흡수체로서, 저항체 형이나 자성체형에 비해 비교적 넓은 주파수 범위에 걸쳐 전파감쇠특성을 발휘함에 반해 그 두께가 두꺼운 단점이 있어 실용화에 문제점으로 지적되고 있다.Such a composite wave absorber is a frequency-sharing wave absorber in which the low frequency region with a long wavelength is mainly a magnetic loss of ferrite, and the resistance loss of a conductive material using carbon is a frequency sharing type electromagnetic wave absorber. Compared to the body shape, the radio wave attenuation characteristic is exhibited over a relatively wide frequency range, but the thickness thereof has a disadvantage of being thick.
전파흡수체를 이용한 전파 차폐기술은 EMI대책의 한 방법으로서 또는 불요전파의 억제대책면에서 전자회로 및 전파전송의 기술과 병행하여 새로운 전파흡수재료의 개발에 관한 종합적인 연구가 행해지고 있는데 전자파 간섭의 방지를 위한 재료로서는 반사에 의한 전자파의 방사를 방지할 뿐만 아니라 흡수와 함께 반사파 및 투과파도 감소시키는 효과를 갖는 페라이트 전파흡수 및 전자실드 재료에 대한 연구가 행해지고 있다.Radio wave shielding technology using radio wave absorber is a comprehensive research on the development of new wave absorbing material as a method of EMI countermeasures or in parallel with the technology of electronic circuit and radio wave transmission in order to suppress unwanted radio waves. As a material for the research, studies have been conducted on ferrite wave absorption and electron shielding materials having the effect of preventing radiation of electromagnetic waves due to reflection as well as reducing reflection and transmission waves as well as absorption.
특히, 전자부품내에서의 노이즈에 대한 불요모드의 발생에 의해서 기기의 성능을 저하시키거나 이상공진을 일으키는 현상을 방지하기 위한 방편으로서 페라이트 복합재료를 회로케이스 및 회로의 일부에 부착하게 되면 방사노이즈의 흡수 내지는 자기손실에 의한 댐핑효과를 통해서 불필요한 모드의 제어와 동시에 전자기로부터의 불요복사 방지 및 누수방지를 기할 수 있다.In particular, as a means of preventing the phenomenon of device degradation or abnormal resonance caused by the generation of an unnecessary mode for noise in electronic components, when the ferrite composite material is attached to the circuit case and part of the circuit, radiation noise The damping effect caused by absorption or magnetic loss of can prevent unnecessary modes and prevent unnecessary radiation from leaking and leakage.
일반적으로 모든 전파흡수체는 투자율 및 유전율로 재료자체의 고유정수로 나타낼 수 있으며, 이같은 전파흡수체의 설계에는 투자율(실수,허수), 유전율(실수,허수), 주파수 및 두께등과 더불어 페라이트의 원료, 조성, 제조공정변수 및 소결온도(가열속도, 최고온도유지시간, 냉각속도)등의 적절한 조절이 요구되며, 나아가 컴퓨터 시뮬레이션(computer simulation)을 통하여 최적의 두께를 찾아내도록 하여야 하는등의 많은 변수가 존재하기 때문에 정밀한 제어 및 적절한 변수조절을 필요로 한다.In general, all the radio absorbers can be expressed as the intrinsic constant of the material itself with permeability and permittivity. Such design of the radio absorber includes ferrite raw materials, real permeability (imaginary, imaginary), permittivity (real, imaginary), frequency and thickness. Proper adjustment of composition, manufacturing process variables and sintering temperature (heating rate, maximum temperature holding time, cooling rate) is required, and many variables such as finding the optimum thickness through computer simulation. Presence requires precise control and proper parameter adjustment.
현재까지 개발되어 적용되고 있는 전파흡수재료로는 전파암실 및 건축용 재료인 페라이트 소결체로 제조된 전파흡수타일, 페라이트 및 고무의 복합페라이트, 도전성 섬유에 발포 스티롤을 혼합하여서 된 시트상 전파흡수체, 카보닐철에 고무를 혼입한 시트상 자성체, 페라이트에 카보닐철과 하이파론 고무를 섞어서 제조한 액상 전파흡수재료 및 페라이트에 에폭시 수지 계통을 혼합하여 이루어진 복합페라이트등 그 용도 및 형상이 매우 다양하다.The radio wave absorbing materials that have been developed and applied to date are radio wave absorbing tiles made of a ferrite sintered body, a radio darkroom and a building material, a composite ferrite of ferrite and rubber, and a sheet-like wave absorber obtained by mixing foamed styrol with conductive fibers and carbonyl iron. There are various uses and shapes such as a sheet-like magnetic material in which rubber is mixed, a liquid wave absorbing material made by mixing carbonyl iron and hyparon rubber in ferrite, and a composite ferrite made by mixing epoxy resin with ferrite.
페라이트계 전파흡수재료는 공진형이기 때문에 사용가능 주파수 대역이 매우 좁다는 특성에 기인하여 대개 UHF대역에서만이 사용가능한 Ni-Zn계와, VHF대역에서만 사용가능한 Mn-Zn계의 두가지 형태가 알려져 있는데, 이들 Ni-Zn, Mn-Zn계 페라이트는 조성에 따라 다소의 차이가 있긴하나, 약 1200-1300℃에서 소결이 이루어지며 특히 Mn-Zn계 페라이트의 경우 자기특성을 발휘하기 위해서는 소결시 산소분압을 적절히 유지시켜야 된다.Because ferrite-based wave-absorbing materials are resonant, two types of Ni-Zn and Mn-Zn, which can be used only in the UHF band, are known due to the very narrow usable frequency band. Although these Ni-Zn and Mn-Zn ferrites have some differences depending on their composition, the sintering is performed at about 1200-1300 ° C. Particularly in the case of Mn-Zn ferrites, the partial pressure of oxygen is increased during sintering. Should be maintained properly.
공지의 페라이트계 전파흡수체의 구체적인 일예로 미국특허 제3,720,951호에는 판상페라이트의 이면에 금속재질의 반사파를 접착시킨 페라이트 전파흡수벽에 관한 기술이 나타나 있는데, 그 명세서상에 기재된 바에 따르면 Ni-Zn계 페라이트인 Ni-Cu-Zn 페라이트 조성의 경우 5.3㎜의 두께로 130-540MHz 범위의 주파수 대역에서 전파흡수특성을 나타내어 20dB 이상의 밴드폭이 410MHz이고, Mn-Zn계 페라이트인 Mn-Cu-Zn계 페라이트 조성의 경우 12.1mm의 두께로 74-185MHz의 주파수대역에서 전파흡수 특성을 나타내어 20dB 이상의 밴드폭은 111MHz에 불과하여 전체적으로 20dB 이상의 전파감쇠량을 보이는 밴드폭이 좁고 두께가 비교적 두껍다는 단점이 있다.As a specific example of a known ferrite wave absorber, U.S. Patent No. 3,720,951 discloses a technology of a ferrite wave absorption wall in which a reflection wave made of a metal is adhered to a back surface of a plate ferrite. Ni-Cu-Zn ferrite, ferrite, has a thickness of 5.3mm and exhibits radio wave absorption characteristics in the frequency range of 130-540MHz.A bandwidth of 20dB or more is 410MHz, and Mn-Cu-Zn-based ferrite is Mn-Zn ferrite. In the case of the composition, the thickness of 12.1mm shows the radio wave absorption characteristics in the frequency band of 74-185MHz, and the bandwidth of 20dB or more is only 111MHz, which has the disadvantage that the overall bandwidth is narrow and the thickness is relatively thick.
이와같이 기존의 페라이트계 전파흡수체 대부분이 그 구조상 판상 페라이트의 이면 금속판이 부착된 단층형으로 이루어지고 VHF대역이나 UHF대역중 어느 하나의 대역에 대해서만 전파흡수특성을 나타내는 대역폭의 협소함을 해결하기 위하여 페라이트의 이면에 유전체층을 복층화하여 광대역화를 도모한 전파흡수체가 알려지고 있으나, 이 경우의 전파흡수체는 유전체층의 복층화에 따른 두께의 증가를 가져오기 때문에 실용적이지 못하다는 문제점을 지니고 있다.As described above, most of the existing ferrite-based radio absorbers are formed in a single layer type with a metal plate attached to the back side of the plate-shaped ferrite, and in order to solve the narrowness of the bandwidth of the radio wave absorption characteristics in only one of the VHF band and the UHF band. Background Art [0002] A radio wave absorber in which a dielectric layer is doubled and a wider band is known on the back side, but the radio wave absorber in this case has a problem in that it is not practical because the thickness of the dielectric layer increases.
따라서, 본 발명은 상기 종래의 전파흡수재료가 지니고 있는 문제점을 감안하여 페라이트 소결체의 제조시 가능한한 모든 손실을 활성화하도록 제조조건을 제어하여 복소투자율의 허수부를 증대시켜 전파흡수체의 박판화와 광대역화를 도모한 전파흡수체의 제조방법을 제공하는데에 그 목적이 있다.Therefore, in view of the problems of the conventional radio wave absorbing material, the manufacturing conditions are controlled to activate all possible losses in the manufacture of the ferrite sintered body, thereby increasing the imaginary part of the complex permeability to increase the thickness and width of the radio wave absorber. It is an object of the present invention to provide a method for producing a radio wave absorber.
즉, 본 발명은 동일한 페라이트 조성인 경우라도 소결온도, 최고온도유지시간, 승온/냉각속도 및 소결체의 미세구조 등의 제반 제조공정의 차이에 따라 복수투자율이 변화하게 되고, 이같은 복소투자율의 변화에 따라 전파흡수특성이 변화하게 된다는 사실에 기초하여 상기 소결공정시 제반조건을 적절하게 제어함으로서 박판화와 광대역화가 달성토록 한 전파흡수체의 제조방법에 관한 것이다.That is, in the present invention, even in the case of the same ferrite composition, the multiple permeability is changed according to various manufacturing processes such as sintering temperature, maximum temperature holding time, temperature / cooling rate, and microstructure of the sintered body. Accordingly, the present invention relates to a method for manufacturing a radio wave absorber to achieve thinner and wider bands by appropriately controlling various conditions in the sintering process based on the fact that the radio wave absorption characteristics change.
특히, 본 발명에 의해서 제조된 전파흡수체는 20dB 이상의 반사감쇠량을 나타내는 주파수의 범위가 확대되어 박형인 6-7mm의 두께에서 VHF(90-222MHz)대역과 UHF(470-770MHz)대역을 동시에 만족시켜 TV고스트(ghost)장애방지재료, 전파암실용재료 및 방사노이즈 전파흡수용 재료를 비롯한 다양한 용도에 실용적으로 사용될 수 있다.In particular, the radio wave absorber manufactured by the present invention has a wide range of frequencies indicating a reflection attenuation of 20 dB or more, and simultaneously satisfies the VHF (90-222 MHz) band and the UHF (470-770 MHz) band at a thin thickness of 6-7 mm. It can be practically used in various applications including ghost obstacle preventing materials, radio darkroom materials and radiation noise electric wave absorption materials.
본 발명의 전파흡수체 제조방법은 다음과 같다.Radio wave absorber manufacturing method of the present invention is as follows.
먼저, Fe2O3, ZnO, NiO, MnO2, Co3O4및 CuO를 평량하여 혼합, 건조 및 분쇄공정을 거친 뒤 900℃에서 2시간 정도 하소하고 다시 분쇄하여 성형한 다음 전기로에서 소결을 행하게 되는데, 이때 승온속도는 2-12℃/분으로하여 1250℃까지 가열한 상태에서 2-6시간 정도 유지한 다음 2-12℃/분의 냉각속도로 냉각함으로써 본 발명의 소결체가 얻어지게 된다.First, Fe 2 O 3 , ZnO, NiO, MnO 2 , Co 3 O 4 and CuO are weighed, mixed, dried and pulverized, calcined at 900 ° C. for about 2 hours, crushed and molded again, followed by sintering in an electric furnace. At this time, the temperature increase rate is 2-12 ℃ / min and maintained for 2-6 hours in the state heated to 1250 ℃ and then cooled to a cooling rate of 2-12 ℃ / min to obtain the sintered body of the present invention .
일반적으로 Ni-Zn계 페라이트의 평형산소분압은 1000-1400℃에서 증가하게 되고 1250℃에서의 페라이트의 평형산소분압은 대기중의 산소분압보다 높은 것으로 알려져 있으므로 본 발명에서는 소결시 최고온도를 1250℃로 유지하여 고온에서 페라이트내의 산소부족(스피넬 페라이트상과 산소 사이의 평행)으로 인해 과다 Fe+2의 생성을 유도하고, 낮은 온도에서 평형산소분압의 감소로 이차상으로서의 Fe2O3가 석출되도록 한다. 이때 상기 고온에서 생성된 과다 Fe+2는 자기응력계수(magnetocryst alline anisotropy)를 양의 값으로 되게 하여 초투자율을 감소시키며, 저온에서 생성된 Fe2O3의 이차상석출은 자벽이동을 방해하여 낮은 투자율의 원인으로 되고 또한 Fe+2의 존재는 일렉트론 호핑(electron hopping)에 의해 비저항을 감소시켜 와전류 손실을 일으키게 되어 결과적으로 전파흡수능력을 증가시키게 된다.In general, the equilibrium oxygen partial pressure of Ni-Zn-based ferrite is increased at 1000-1400 ° C., and the equilibrium oxygen partial pressure of ferrite at 1250 ° C. is known to be higher than the oxygen partial pressure in the atmosphere. At low temperature to induce excess Fe +2 due to lack of oxygen in the ferrite (parallel between the spinel ferrite phase and oxygen) and to precipitate Fe 2 O 3 as a secondary phase at a lower temperature by reducing the equilibrium oxygen partial pressure. do. At this time, the excessive Fe +2 generated at high temperature decreases the super-permeability by making the magnetoresistance (magnetocryst alline anisotropy) positive, and the secondary phase precipitation of Fe 2 O 3 generated at low temperature impedes the movement of the wall. The presence of low permeability and the presence of Fe +2 also reduces the resistivity by electron hopping, resulting in eddy current loss, which in turn increases the radio absorption capability.
그리고, 본 발명은 최고온도유지시간을 연장시키고 냉각속도를 낮추어서 소결후의 결정립크기(grainsize)를 크고 불균일하게 성장시켜 소결체 조직의 불균일을 초래하여 미세조직의 변화를 가져옴으로써 손실을 극대화시키고 있다.In addition, the present invention maximizes the loss by extending the maximum temperature holding time and lowering the cooling rate to grow the grain size after sintering large and non-uniformly, resulting in non-uniformity of the sintered body structure resulting in a change in the microstructure.
이하 본 발명의 실시예는 다음과 같다.Examples of the present invention are as follows.
[실시예]EXAMPLE
Fe2O366.1g, ZnO 23.1g, NiO 8.8g, MnO20.5g, Co3O40.5g 및 CuO 1.0g을 스틸볼과 함께 폴리에틸렌 쟈(Jar)에 넣고 탈이온수를 분산매로 하여 상기 원료와 볼 및 탈이온수의 무게비를 1 : 1 : 1.5로 유지한 상태에서 80RRM으로 10시간동안 혼합한 후 감압여과하여 110℃의 전기오븐에서 24시간 건조시켰다. 건조된 시료를 분쇄하여 전기로에서 900℃의 온도로 2시간 하소한 다음 하소한 원료를 분쇄하여 감압여과한 후 110℃의 전기오븐에서 12시간동안 건조시켰다.66.1 g of Fe 2 O 3 , 23.1 g of ZnO, 8.8 g of NiO, 0.5 g of MnO 2, 0.5 g of Co 3 O 4 and 1.0 g of CuO were placed together with a steel ball in a polyethylene jar with deionized water as a dispersion medium. The ball and deionized water were mixed at 80 RRM for 10 hours while maintaining the weight ratio of 1: 1: 1.5, and then filtered under reduced pressure and dried in an electric oven at 110 ° C for 24 hours. The dried sample was pulverized and calcined at 900 ° C. in an electric furnace for 2 hours, and then the calcined raw material was pulverized and filtered under reduced pressure, followed by drying at 110 ° C. in an electric oven.
다음, 5% PVA 수용액을 원료무게에 대해 5-8% 첨가하여 충분히 혼합한 다음 50메쉬의 체를 통과시켜 과립형태로 형성한 후 측정용 지그에 적합하도록(외경7㎜,내경3㎜) 조립한 분말을 넣고 2ton/㎠의 압력으로 성형하여 시편을 제조하였다. 이어서 대기중의 전기로에서 2-12℃/분의 승온속도로 1250℃로 가열하여 2-6시간 정도 유지한 다음 2-12℃/분의 냉각속도로 냉각하여 아래의 표1에 나타나 있는 바의 소결조건으로 시편을 제조하였다. 소결후 시편을 정밀하게 연마하여 가공한 다음 동축형 측정장치(HP85051-60007)와 네트워크 애널라이저(Network analyzer)를 사용하여 각 시편의 복소투자율, 복소유전율 및 감쇠량에 대한 측정을 하였다.Next, 5-8% aqueous PVA solution was added to the raw material weight by 5-8%, and the mixture was sufficiently mixed and then passed through a 50 mesh sieve to form granules, and then assembled to fit the measuring jig (outer diameter 7mm, inner diameter 3mm). One powder was added and molded at a pressure of 2ton / cm 2 to prepare a specimen. Subsequently, it is heated at 1250 ° C. at a heating rate of 2-12 ° C./minute in an electric furnace in the atmosphere and maintained for about 2-6 hours, and then cooled at a cooling rate of 2-12 ° C./minute as shown in Table 1 below. Specimens were prepared under sintering conditions. After sintering, the specimens were precisely ground and processed, and then the complex permeability, complex dielectric constant, and attenuation of each specimen were measured using a coaxial measuring device (HP85051-60007) and a network analyzer.
[표 1]TABLE 1
제1도는 위 표1의 시편 8에 대한 전자현미경 확대 사진으로서, 제1a도는 연마면의 조직이고,제1b도는 파단면의 조직인 바, 사진에서 군데군데 눈송이처럼 흰점으로 나타난 부분이 Fe2O3이차상이며, 전체적으로 볼 때 결정립의 크기가 비교적 크며, 결정립간의 크기가 5μm 내지 30μm에 이르기까지 상당한 차이를 보여 조직이 불균일함과 아울러 결정립 내부에 기공(pore)등을 비롯한 내부결함이 많이 존재함을 알 수 있다.First turning an electron microscope picture is taken in a sample 8 in the above Table 1, the first 1a and the organization of turning the grinding surface, the 1b-watering wave bar, shown with white point as patches of snowflakes in a photo part organization of the section Fe 2 O 3 Secondary phase, the grain size is relatively large in overall, and the grain size varies considerably from 5μm to 30μm, resulting in uneven organization and many internal defects including pores in the grain. It can be seen.
아래의 표 2는 본 발명 실시예 시편들이 두께변화에 대한 20dB이상의 반사감쇠량을 나타내는 주파수 범위를 나타낸 것이다.Table 2 below shows the frequency range in which the specimens of the present invention exhibit a reflection attenuation of 20 dB or more with respect to the thickness change.
[표 2]TABLE 2
×는 20dB 이상의 반사감쇠량을 나타내지 않은 경우× denotes no more than 20 dB of reflection attenuation
☆는 VHF, UHF 대역 모두에서 20dB이상의 반사감쇠량을 나타낸 경우☆ indicates the amount of reflection attenuation of 20 dB or more in both the VHF and UHF bands.
제2도 및 제3도는 각각 7㎜ 두께에서 시편 및 시편 6의 주파수 변화에 대한 감쇠량 효과를 나타낸 도표로서 두 시편 모두 VHF대역 및 UHF대역을 동시에 커버함을 알 수 있다.2 and 3 are diagrams showing the attenuation effects on the frequency change of the specimen and specimen 6 at 7 mm thickness, respectively, and it can be seen that both specimens simultaneously cover the VHF band and the UHF band.
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| KR1019910013920A KR930011547B1 (en) | 1991-08-13 | 1991-08-13 | Manufacturing method of radio wave absorber |
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