Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
2002-09-06
2004-11-16
Ngo, Hung V. (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C361S816000, C174S036000
Reexamination Certificate
active
06818821
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel electromagnetic wave absorption material and associated devices. The invention relates to various articles particularly, such as, an electromagnetic wave absorption material for millimeter wave of 1 to 300 GHz band, a printed wiring board that uses such absorbing material, an electronic device, a casing for an electronic device, a module for optical transmission or reception, automated tollgate, and high frequency communication equipment.
2. Description of the Prior Art
In late years, the high speed processing in electronic devices is spreading at an accelerating pace together with rapidly raised operating frequency of ICs and LSIs in microprocessors. This raised frequency allows such devices to easily emit undesired noise.
Moreover, in the telecommunications field, the next-generation multimedia mobile communication (on 2 GHz), the wireless LAN (on 2 to 30 GHz), and the high-speed telecommunication network on the optical fiber are presently in use. Further, 5.8 GHz in ETC (an automated Electronic Toll Collection) system in ITS (Intelligent Transport System), 76 GHz in AHS (an advanced cruise-assist highway system) are also in use. Therefore, a rapid expansion of use-range toward higher frequencies is continuously anticipated.
Rise in frequency of a radio wave causes more eased emission in a form of noise. At the same time, narrowed noise margin in the recent electronic device because of lowered power consumption therein, together with poor quality in noise-ambient inside an apparatus because of miniaturization and dense mounting in the electronic device, brings a malfunctioning problem due to EMI (Electro-Magnetic Interference).
Under these circumstances, a measure such that a radio wave absorbing material is installed inside an electronic device is typically adopted to reduce EMI that will appear inside the device. One of radio wave absorbing materials so far used is a composite sheet of electrically insulating organic matters, such as rubber and resin, and magnetically lossy material, like soft magnetic metal oxides having spinel crystal structure and soft magnetic metals. These techniques were disclosed by Japanese Patent application laid-open No. 7-212079, 9-111421, 11-354973, 11-16727, etc.
However, the relative permeability of a soft magnetic metal oxide of spinel crystal structure sharply reduces in the GHz-band according to the Snoek's law of threshold This means that the usable frequency range for such metal oxide as an electromagnetic wave absorption material is up to several-GHz. In a soft magnetic metal on the other hand, its marginal frequency usable as a electromagnetic wave absorption material can be expanded up to about 10 GHz by use of eddy current suppression effect and shape-dependent magnetic anisotropy effect both yielded from making the particle therein into a flat-shape having a thickness thinner than the skin depth. However, such magnetic material prevents realization of light-weight electromagnetic wave absorber because of its inherent weightiness.
Japanese Patent application laid-open No. 2001-358493 has disclosed an integrated electromagnetic wave absorption material composed of particulate magnetic metal and ceramic, and those articles or facilities, which use said integrated absorption material, such as a printed wiring board, an electronic device, a casing for electronic device, an optical transmission or reception module, an automated tollgate, a high frequency telecommunication equipment, etc.
However, said magnetic material is still unsatisfactory in its electromagnetic wave absorption performance. Thus, development of an electromagnetic wave absorption material having an excellent performance in the extended use up to millimeter wave region is continuously desired. Although the electromagnetic wave absorption material according to said Japanese Patent application laid-open No. 2001-358493 is satisfactory for sub-millimeter wave region up to 5.8 GHz, the use in the millimeter wave region over such frequency does not satisfy with the performance of said material.
SUMMARY OF THE INVENTION
The purpose of the present invention is to provide an electromagnetic wave absorption material having an excellent radio wave absorbing performance usable spanning from sub-millimeter wave region to millimeter wave region in which radio wave frequency ranges from 1 to 300 GHz, and the one being easy to manufacture and light in weight. The purpose further includes to provide various appliances of and systems with said electromagnetic wave absorption material particularly an electronic device, an optical transmission or reception module, a high frequency telecommunication equipment, and a stop-free tollgate system which is prevented from malfunctioning due to electromagnetic wave interference.
The inventors of the present invention found that an electromagnetic wave absorption material comprised of a dispersions of multi-layer hollow globule of carbon mixed into electrical insulating organic material has a far more excellent performance as the electromagnetic wave absorption material available for use in millimeter wave region compared to an electromagnetic wave absorbing material relying on dielectric loss, i.e. a dispersions of carbon-based substance, such as carbon black particulate, graphite, coke, carbon microcoil, and carbon nanotube, mixed into electrical insulating organic material like rubber and resin. Since said multi-layer hollow globule of carbon or a multi-layer hollow globule of carbon existing in a natural schungite ore (hereinafter referred to as a schungite carbon) is contained in natural schungite ore, the use such material for the electromagnetic wave absorption material sees little difficulty. Particularly, the present invention is devised based on the finding that such globule has a high absorption property in millimeter wave region of which frequencies are 30 to 300 GHz.
The schungite carbon for this purpose is preferred to have 1.5 to 45% of porosity, 0.15 to 0.25 nm of thickness, and to have a shape being spherical or flat, or their mix. As for the natural schungite ore, preferred contents is 25 to 35% of the schungite carbon, 57 to 67% SiO
2
, 3 to 5% AlO
3
, 1 to 3% Fe
2
O
3
+FeO, 0.5 to 2% K
2
, 0.2 to 1.0% sulfur, 0.2 to 0.5% free water, and 0.3% or less for each of TiO
2
, MgO, CaO, Na
2
O, and MnO.
The present invention is characterized by an electromagnetic wave absorption material that includes: one of a multi-layer hollow sphere (globule) of carbon and a schungite carbon; or one of a multi-layer hollow sphere and a schungite carbon, said multi-layer hollow sphere containing at least one of a carbon nanotube, a metallic component, and free water; or a schungite ore otherwise.
The electromagnetic absorption material in the present invention is preferred to be a dispersions mixed into a substance that has a higher electrical resistance than that of multi-layer hollow globule or the schungite carbon. In this dispersing, the quantity of the multi-layer hollow globule and the schungite carbon is preferred to be in a range of 5 to 50% of the weight of such high-resistance substance. This high-resistance substance is preferred to be selected among from rubber, insulation high polymer, and insulating inorganic material.
The electromagnetic wave absorption material in the present invention prefers a configuration wherein content of the multi-layer hollow globule or the schungite carbon is graded to plural degrees so that characteristic impedance may reduce toward inside from the incident plane of electromagnetic wave. Thereby, the electromagnetic wave absorbing performance for an oblique incidence of electromagnetic wave is improved or becomes being capable of accommodating electromagnetic wave of wide range of frequencies.
Material having a high electrical resistivity can contain at least one of: a magnetic metal of which main constituent is at least one of iron (Fe), cobalt (Co), and nickel (Ni); a compound selected from the group co
Fujieda Tadashi
Hayashibara Mitsuo
Hidaka Kishio
Ikeda Shinzou
Taguchi Noriyuki
Dickstein , Shapiro, Morin & Oshinsky, LLP
Hitachi , Ltd.
Ngo Hung V.
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