U.S. patent application number 10/756272 was filed with the patent office on 2004-07-29 for electromagnetic wave absorption material and an associated device.
Invention is credited to Fujieda, Tadashi, Hayashibara, Mitsuo, Hidaka, Kishio, Ikeda, Shinzou, Taguchi, Noriyuki.
Application Number | 20040146452 10/756272 |
Document ID | / |
Family ID | 27678159 |
Filed Date | 2004-07-29 |
United States Patent
Application |
20040146452 |
Kind Code |
A1 |
Fujieda, Tadashi ; et
al. |
July 29, 2004 |
Electromagnetic wave absorption material and an associated
device
Abstract
The purpose of the present invention is to provide an
easy-to-manufacture electromagnetic wave absorption material usable
from submillimeter wave region to millimeter wave region with an
excellent radio wave absorbing performance and a variety of usage
thereof. The present invention is characterized by an
electromagnetic wave absorption material comprised of a dispersions
of at least one of the materials: a multi-layer hollow globule of
carbon, a schungite carbon, and the schungite ore; mixed into a
matter having a high electrical resistivity. The invention is
further characterized by an electronic device, an optical
transmission module, an optical reception module, a high frequency
telecommunication equipment, and a stop-free automated tollgate
system, wherein at least a part of their board, electronic element,
and circuit wiring are covered with said electromagnetic wave
absorption material.
Inventors: |
Fujieda, Tadashi; (Mito,
JP) ; Hidaka, Kishio; (Hitachiota, JP) ;
Ikeda, Shinzou; (Tokai, JP) ; Hayashibara,
Mitsuo; (Hitachinaka, JP) ; Taguchi, Noriyuki;
(Yokohama, JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
2101 L STREET NW
WASHINGTON
DC
20037-1526
US
|
Family ID: |
27678159 |
Appl. No.: |
10/756272 |
Filed: |
January 14, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10756272 |
Jan 14, 2004 |
|
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10235711 |
Sep 6, 2002 |
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Current U.S.
Class: |
423/447.2 |
Current CPC
Class: |
H01L 2924/3011 20130101;
H01L 2224/16225 20130101; H01L 2924/3025 20130101; H01L 2924/01079
20130101; H01Q 17/004 20130101; H01L 2924/01012 20130101; H01L
2924/16152 20130101; B82Y 30/00 20130101; H01L 2924/00014 20130101;
H01L 2924/00 20130101; H01L 2224/48091 20130101; H05K 9/0024
20130101; H01L 2224/48091 20130101; H01L 2924/01046 20130101; B82Y
10/00 20130101; H01L 2224/48227 20130101; H01L 2924/1423 20130101;
H01L 2924/01078 20130101; Y10S 977/932 20130101; H05K 9/0083
20130101; H01L 2924/12041 20130101; H01L 2924/1423 20130101; H01L
2924/01025 20130101; H05K 3/284 20130101 |
Class at
Publication: |
423/447.2 |
International
Class: |
C01B 031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 15, 2002 |
JP |
2002-038237 |
Claims
What is claimed is:
1. Electromagnetic wave absorption material comprising a
multi-layer hollow globule of carbon.
2. Electromagnetic wave absorption material comprising a
multi-layer hollow globule of carbon, wherein said globule contains
at least one of a carbon nanotube formed therein, metallic
constituent, and free water.
3. Electromagnetic wave absorption material comprising a schungite
carbon.
4. Electromagnetic wave absorption material comprising a schungite
carbon, wherein said schungite carbon contains at least one of a
carbon nanotube formed therein, metallic constituent, and free
water.
5. Electromagnetic wave absorption material according to claim 4,
wherein said metallic constituent is comprised of one or more
materials selected from the group of materials consisting of
metals, metallic silicates, metallic sulfides, and metallic
oxides.
6. Electromagnetic wave absorption material according to claim 4 or
claim 5, wherein said metallic constituent is comprised of one or
more materials selected from the group of materials consisting of
Cu, Ni, V, Cr, Co, Mn, and Ti.
7. Electromagnetic wave absorption material comprising a schungite
ore.
8. Electromagnetic wave absorption material according to any one of
claims 1 to 7, wherein said electromagnetic wave absorption
material is further comprised of a substance that has an electrical
resistivity higher than that of said multi-layer hollow globule or
said schungite carbon and said electromagnetic wave absorption
material is a composite of said substance.
9. Electromagnetic wave absorption material comprising a
particulate of electromagnetic wave absorbing matter and a
substance that has an electrical resistivity higher than that of
said particulate of electromagnetic wave absorbing matter, wherein
said electromagnetic wave absorption material has the radio wave
return loss of not less than -3.5 dB per 1 GHz of frequency.
10. Electromagnetic wave absorption material comprising a
particulate of electromagnetic wave absorbing matter and a
substance that has an electrical resistivity higher than that of
said particulate of electromagnetic wave absorbing matter, wherein
said electromagnetic wave absorption material has the radio wave
return loss of not less than -20 dB at a frequency of 6 GHz.
11. Electromagnetic wave absorption material according to any one
of claims 8 to 10, wherein said high electrical resistivity
substance contains at least one of rubber, insulating polymeric
material, and inorganic insulating material.
12. Electromagnetic wave absorption material according to any one
of claims 8 to 11, wherein the content of said multi-layer hollow
globule, said schungite carbon, a schungite carbon included in said
schungite ore, and said particulate of electromagnetic wave
absorbing matter is 5 to 50 weight-% of the whole weight of said
electromagnetic wave absorption material.
13. Electromagnetic wave absorption material according to any one
of claims 8 to 12, wherein content of said multi-layer hollow
globule, said schungite carbon, and said particulate of
electromagnetic wave absorbing matter are graded to plural degrees
so that characteristic impedance may reduce toward inside from the
incident plane of electromagnetic wave.
14. Electromagnetic wave absorption material according to any one
of claims 8 to 13, wherein said absorption material further
includes any one of: a magnetic metal of which main constituent is
at least one of Fe, Co, and Ni; a compound selected from the group
consisting of an oxide, a nitride, and a carbide, in which their
main constituent is at least one of Fe, Co, Ni, Al, Si, Ti, Ba, Mn,
Zn, and Mg; or a carbon-based substance which contains at least one
of carbon black, graphite, coke, and carbon micro-coil.
15. A printed wiring board comprising an insulated board having a
circuit wiring thereon, said circuit wiring being at least partly
covered with an insulating layer, wherein at least one of surfaces
of said insulated board, one surface having said wiring circuit
thereon and the other the reverse surface thereof, has a layer
comprised of an electromagnetic wave absorption material, which is
the electromagnetic wave absorption material described in any one
of claims 1 to 14.
16. An electronic device comprising an electronic element mounted
on a printed wiring board, said electronic element being covered
with a metal cap, wherein at least a part of internal surface of
said metal cap is provided with an electromagnetic wave absorption
material, which is the electromagnetic wave absorption material
described in any one of claims 1 to 14.
17. An electronic device comprising a printed wiring board, an
electronic device mounted on said printed wiring board, said
printed wiring board and said electronic device being covered with
a metal casing, wherein at least a part of internal surface of said
metal casing is provided with an electromagnetic wave absorption
material, which is the electromagnetic wave absorption material
described in any one of claims 1 to 14.
18. A metal casing having an opening, wherein at least a part of
internal surface of said metal casing is provided with the
electromagnetic wave absorption material described in any one of
claims 1 to 14.
19. A module of optical transmission or of optical reception
comprising a circuit board having at least either a light emitting
element or a photo acceptance element and having at least either a
transmission circuitry or a reception circuitry thereon, wherein at
least a part of said circuit board, said element, and said
circuitry are covered with the electromagnetic absorption material
described in any one of claims 1 to 14.
20. A module of optical transmission or of optical reception
comprising a circuit board having at least either a light emitting
element or a photo acceptance element and having at least either a
transmission circuitry or a reception circuitry thereon, wherein at
least a part of said circuit board, said elements, and said
circuitry are covered with a metal cap, and at least a part of
internal surface of said metal cap is formed by an element having
the electromagnetic absorption material described in any one of
claims 1 to 14.
21. A module of optical transmission or of optical reception
comprising a circuit board having at least either a light emitting
element or a photo acceptance element and having at least either a
transmission circuitry or a reception circuitry thereon, wherein at
least a part of said circuit board, said elements, and said
circuitry are covered with an element having the electromagnetic
absorption material described in any one of claims 1 to 14, and
external surface of said element is covered with a metal cap.
22. A module of optical transmission or of optical reception
according to any one of claims 18 to 20, wherein at least a part of
said circuit board, said elements, and said circuitry are covered
with an insulating resin, the surface of said insulating resin is
provided with said electromagnetic absorption material.
23. An automated tollgate comprising a roofed tolling gate, an
entrance antenna arranged at the entrance of said tolling gate and
faced to a transit vehicle approaching said tolling gate, an exit
antenna arranged at the exit of said tolling gate and faced to a
transit vehicle leaving said tolling gate, and an automated toll
collection system that exchanges information between a roadside
communication equipment and an on-vehicle equipment carried by said
transit vehicle, wherein the surface of a structural member in said
tolling gate and its vicinity which reflects electromagnetic wave,
the surface of facing-to-vehicle side of the roof of said tolling
gate, and at least a part of the surface of a supporting column for
said entrance antenna and said exit antenna are provided with the
electromagnetic wave absorption material described in any one of
claims 1 to 14.
24. A high frequency communication equipment comprising a high
frequency circuit element mounted and accommodated inside a casing,
wherein at least the inner wall of said casing and at least a part
of said inner wall are provided with the electromagnetic wave
absorption material described in any one of claims 1 to 14.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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.
[0003] 2. Description of the Prior Art
[0004] 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.
[0005] 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.
[0006] 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)
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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
[0011] 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.
[0012] 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.
[0013] 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.sub.2, 3 to 5% AlO.sub.3, 1 to 3%
Fe.sub.2O.sub.3+FeO, 0.5 to 2% K.sub.2, 0.2 to 1.0% sulfur, 0.2 to
0.5% free water, and 0.3% or less for each of TiO.sub.2, MgO, CaO,
Na.sub.2O, and MnO.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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 consisting of an oxide, a nitride, and a
carbide, in which their main constitution is at least one of iron
(Fe), cobalt (Co), nickel (Ni), aluminum (Al), silicon (Si),
titanium (Ti), barium (Ba), manganese (Mn), zinc (Zn), and
magnesium (Mg); and a carbon-based substance which contains at
least one of carbon black, graphite, coke, and carbon microcoil.
Thereby the absorbing performance of the electromagnetic wave
absorption material is more improved.
[0018] The present invention is characterized by an electromagnetic
wave absorption material comprising an electromagnetic wave
absorbing particulate and a substance that has an electrical
resistivity higher than said electromagnetic wave absorbing
particulate, wherein the return loss (reflection coefficient) of
said electromagnetic wave absorption material is -3.5 dB or more
(in absolute value) at a radio wave frequency of 1 GHz and the
return loss of the same is -20 dB or more at a radio wave frequency
of 6 GHz. Said electromagnetic wave absorbing particulate prefers
to be comprised of said electromagnetic wave absorption material.
Such return loss levels can be attained by regulating combination
of thickness of said electromagnetic wave absorption material and
content of said electromagnetic wave absorbing particulate in a
composite.
[0019] The electromagnetic wave absorption material by the present
invention can be applied to a broad range of articles typically
listed below through various suited methods depending on each
article. Said absorption material is applied in a form of
dispersions mixed in said insulating material for coating or for
sheeting to glue, or in a style of a near net shape by injection
molding.
[0020] (1)A printed wiring board in which all or a part of at least
one of surfaces of said wiring board, one wired surface and the
other the reverse surface thereof which has no circuit wiring, is
covered with a layer of direct coating or a sheet-formed film each
comprised of the electromagnetic wave absorption material by the
present invention.
[0021] (2)An electronic device in which an electronic element
mounted thereon is covered with a cap that has the electromagnetic
wave absorption material by the present invention.
[0022] (3)An electronic device in which a printed wiring board
thereof and an electronic element mounted on said printed wiring
board is covered with a casing having the electromagnetic wave
absorption material by the present invention, or in which the
internal surface of a metal casing having an opening is provided
with the electromagnetic wave absorption material by the present
invention.
[0023] (4)A module for optical transmission or optical reception in
which at least either a light emitting element thereof or a photo
acceptance element thereof, each of which has an opt-electric
conversion device for use in a high-speed telecommunication
networks, and at least either a transmission circuitry therein or a
reception circuitry therein are covered with the member that is
equipped with the electromagnetic absorption material described by
the present invention.
[0024] (5)An automated tollgate comprising a roofed tolling gate,
an entrance antenna arranged at the entrance of said tolling gate
and faced to a transit vehicle approaching said tolling gate, an
exit antenna arranged at the exit of said tolling gate and faced to
a transit vehicle leaving said tolling gate, and an automated toll
collection system that exchanges information between a roadside
communication equipment and an on-vehicle equipment carried by said
transit vehicle, wherein the surface of a structural member in said
tolling gate and its vicinity which reflects electromagnetic wave,
the surface of facing-to-vehicle side of the roof of said tolling
gate, and at least a part of the surface of a supporting column for
said entrance antenna and said exit antenna are provided with the
electromagnetic wave absorption material described by the present
invention.
[0025] (6)A high frequency communication equipment comprising a
mounted high frequency circuit element and an antenna both
accommodated inside a casing, wherein at least the inner wall of
said casing, and at least a part said inner wall, are provided with
the electromagnetic wave absorption material described by the
present invention.
[0026] According to the present invention, it is practicable to
provide an economical electromagnetic wave absorption material
having far more excellent performance in absorbing property than
that in a dielectric loss type electromagnetic wave absorbing
material in the prior art comprised of carbon-based material.
[0027] Further according to the present invention, electromagnetic
wave interference within an electronic device is efficiently
suppressed by use of a light weight electromagnetic wave absorption
material having an absorbing property usable from submillimeter
wave region to millimeter wave region. Thus, it becomes practicable
to provide equipment acceptable for use in a high speed
telecommunication network, such as semiconductor device, an optical
transmission module, an optical reception module, or an optical
transmission-reception module, and high frequency telecommunication
equipment; thanks to their capability rendered from the absorbing
material of suppressing internal noise interference and noise
emission to outside, of achieving small-sizing and
weight-reduction, of working under high speed transmission, and of
having high sensitivity.
[0028] Moreover according to the present invention, it also becomes
practicable to provide an automated tollgate capable of exchanging
information between a roadside communication equipment and an
on-vehicle equipment free from suffering electromagnetic wave
interference.
BRIEF DESCRIPTION OF DRAWINGS
[0029] FIG. 1 is a pattern diagram for schungite carbon that
comprises the electromagnetic wave absorption material by the
present invention.
[0030] FIG. 2 is a graph to show complex relative dielectric
constants of electromagnetic wave absorption materials by the
present invention and by a comparative example, and the conforming
range of a complex relative dielectric constant.
[0031] FIG. 3 is a graph to show calculation results for return
losses for various materials at the same center frequency in return
loss examination when they are metal-backed.
[0032] FIG. 4 is a graph to show calculation results for return
losses for various thicknesses when they are metal-backed.
[0033] FIG. 5 is a cross sectional view of the printed wiring board
equipped with an electromagnetic wave absorbing layer comprised of
the electromagnetic wave absorption material by the present
invention.
[0034] FIG. 6 is a cross sectional view of the electromagnetic wave
absorbing cap arranged on a printed wiring board so that a
semiconductor element that will generate noises may be enveloped
thereby.
[0035] FIG. 7 is a cross sectional view of the casing for an
electronic device comprised of the electromagnetic wave absorption
material by the present invention.
[0036] FIG. 8 is a cross sectional view of the optical transmission
module in one embodiment of the present invention.
[0037] FIG. 9 is a cross sectional view of the optical transmission
module, with its casing removed, in the embodiment of the present
invention.
[0038] FIG. 10 is a cross sectional view of the 2-layer
construction optical transmission module in the other embodiment of
the present invention.
[0039] FIG. 11 is a plan view of the optical transmission-reception
module in the first configuration of an optical
transmission-reception module.
[0040] FIG. 12 is a cross sectional view to show figuration of the
automated tollgate equipped with an electronic toll collection
system (ETC), wherein the ceiling of the gate roof and supporting
columns are applied with the electromagnetic wave absorption
material by the present invention.
[0041] FIG. 13 is a cross sectional view of the
multi-layer-structured radio wave absorber by the present
invention.
[0042] FIG. 14 is a cross sectional view of the millimeter wave
transmission-reception apparatus in one embodiment of a high
frequency communication equipment applied with the electromagnetic
wave absorption material by the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Embodiment 1
[0043] FIG. 1 is a pattern diagram of the schungite carbon, being
contained in a natural schungite ore, which is composed of a
multi-layer small hollow sphere of carbon called a globule. As
shown in FIG. 1(b), the globule contains, inside thereof, a small
quantity of a carbon nanotube (CNT), metals (Cu, Ni, V, Cr, Co, Mn,
and Ti), and free water. These metals exist there in a form of
silicate, sulfide, and oxide. The natural schungite ore contains 28
to 32% of the schungite carbon in weight ratio together with 57 to
66% of SiO.sub.2, 3 to 5% of Al2 O3, 1 to 3% of
Fe.sub.2O.sub.3+FeO, 0.5 to 2% of K.sub.2O, 0.2 to 1.0% of sulfur,
0.2.about.0.5% of free water, and 0.3% or less for the lump of
TiO.sub.2, MgO, CaO, Na.sub.2O, and MnO.
[0044] FIG. 2 graphs the relative dielectric constant of the
sheet-shaped electromagnetic wave absorption material for a range
of frequencies. Said sheet of absorbing material was prepared
using: a carbon black (hereinafter abbreviated to CB) and a carbon
nanotube (hereinafter abbreviated to CNT), each 20-part by weight
to a binder resin, and a natural schungite ore, ground into powders
of 1 to 30 .mu.m in sizes (hereinafter referred to as a schungite)
70-part by weight to a liquid binder resin (wherein the weight
ratio of the schungite to the binder resin is about 20-part). These
materials are mixed and kneaded into a paste, then sheeted by the
doctor blade method or by the roll-forming method. The schungite
carbon is 3 nm in internal diameter of its hollow and about 22.5 nm
in external diameter.
[0045] In the figure, (a) is for property at 6 GHz and (b) is for
the one at 10 GHz; each frequency belongs to the millimeter wave
region. Shaded area in the graph shows a range such that the return
loss of a complex relative dielectric constant is -20 dB or more.
As can be understood from these, the complex relative dielectric
constant of the schungite falls in a conforming range at every
frequency examined. In contrast to this, CB and CNT show the
imaginary part of the complex dielectric constant (.epsilon.') is
too large compared with the real part of that (.epsilon.") to fall
in the conforming range and some return losses (reflection
coefficients) of them are less than -20 dB. The range of complex
relative dielectric constant that satisfies the return loss being
not Less than -20 dB which characterizes the present invention is
the range such that, at both the frequencies of 6 GHz and 10 GHZ, a
value of 10 in the real part (.epsilon.') corresponds to values of
4 to 6 in the imaginary part (.epsilon.") and such that values of
75 in the real part (.epsilon.') correspond to values of 10 to 13
in the imaginary part (.epsilon.).
[0046] For the use as a paint form, application methods by
spraying, dipping, and casting may be applicable for forming after
preparation of said paste.
[0047] Usable materials as the binders are: polyester-based resin,
polyvinyl chloride-based resin, polyvinyl butyral resin,
polyurethane resin, cellulose-based resin, and copolymer of these
resin; epoxy resin, phenol resin, amide-based resin, imide-based
resin, nylon, acrylic resin, synthetic rubber, and other similar
polymeric insulating material; and inorganic insulating material of
which main constituent is alumina, silica, or the like. In this
embodiment, a resin-mix of acrylic and polyamide is used as the
binder.
[0048] A refined schungite carbon alone may be used, wherein said
refined carbon is obtained by dissolving mineral constituents other
than the schungite carbon contained in the natural schungite ore
using such as hydrofluoric acid. Contrary to this manner, it is
acceptable, for improved electromagnetic wave absorbing
performance, to make the schungite carbon support magnetism
metallic particle which includes at least one of Fe, Co, and
Ni.
[0049] The schungite carbon contained in a ground powder of the
natural schungite has a structure of a broken globule having a
sport-like shape as shown in FIG. 1; matters such as CNT, usually
found inside the structure, exist independently of the globule.
Artificially produced carbon being given the same structure as the
natural schungite may bring the same effects. It is also acceptable
to heat treat the ground powder of the natural schungite in inert
gas atmosphere to alter the complex relative dielectric constant
thereof for improved electromagnetic wave absorption performance.
The preferred temperature in such treatment is 500 to 1000.degree.
C.
[0050] The complex relative dielectric constant was measured with a
measuring system comprised of the network analyzer (by HP 8720C)
and a coaxial line. Calibrating the system so that both the
measured permeability and dielectric constant of the free space may
equal to 1, placing the test specimen in the coaxial line, and
measuring parameters S.sub.11 and S.sub.21 using two ports; then
the relative dielectric constant was obtained using Nicolson-Ross
and Weir Method.
[0051] The absorption mechanism in a metal-backed electromagnetic
wave absorber of a matched type may include a multi-path reflection
effect produced by the critical coupling between the surface
reflected wave and the multiple reflected wave generated in the
absorber, and attenuation effect caused from the dielectric loss
within the absorber. Generally, the return loss (R.L., in dB) for a
normal incidence is expressed by the below described equations (1)
and (2).
R.L.=-20 log .vertline.Z.sub.in-1/Z.sub.in+1.vertline. (1)
[0052] (where Z.sub.in: characteristic impedance of the
absorber)
Z.sub.in=(1/.epsilon..sub.r).sup.0.5 tan
h(j2.pi.ft.epsilon..sub.r.sup.0.5- ) (2)
[0053] (where .epsilon..sub.r: complex dielectric constant
(.epsilon..sub.r=.epsilon.'+j.epsilon."), f: frequency (Hz), t:
thickness (m) of the absorber)
[0054] FIG. 3 is a graph to show comparison of thickness dependency
of return losses in various electromagnetic wave absorption
materials at the same center frequency in the figure is 6 GHz in
(a) and 10 GHz in (b). The thickness of each electromagnetic wave
absorption material is also shown in the figure. In FIG. 3(a), at 6
GHz, CNT shows -6 dB of return loss, CB -13 dB, the schungite
carbon -21 dB; and in FIG. 3(b), at 10 GHz, CNT shows -6 dB, CB -17
dB, the schungite carbon -40 dB. This shows that the schungite
carbon has the largest return loss, i.e. the most excellent
electromagnetic wave absorbing performance among these materials at
both frequencies. In millimeter wave region, CNT and CB may be
usable either they alone or in combination with the material by the
present invention since they show acceptable performance in such
region.
[0055] FIG. 4 is a graph to show calculation results of return
losses for various electromagnetic wave absorption material in
variety of thicknesses. Although the center frequencies of return
losses differ each from other, the schungite shows the most
excellent absorbing performance at every thickness. In each figure,
(a) corresponds to thickness of 1.5 mm, (b) 2.0 mm, and (c) 2.5
mm.
[0056] The figure shows that, in (a) for the thickness of 1.5 mm,
the return loss of CNT is -6 dB, CB -17 dB, the schungite carbon
-40 dB; in (b) for 2.0 mm, CNT -6 dB, CB -17 dB, the schungite
carbon -27 dB; and in (c) for 2.5 mm, CNT -6 dB, CB -14 dB, the
schungite carbon -22 dB. These show that the schungite carbon has
the largest return loss at every frequency indicating it has the
most excellent electromagnetic wave absorbing performance. In
millimeter wave region, CNT and CB may be usable either they alone
or in combination with the material by the present invention since
they show acceptable performance in such region.
[0057] Further, it is known from these that the material by the
present invention which includes the schungite carbon has the
return loss (reflection coefficient) of -3.5 dB per 1 GHz at 6 GHz
of the radio wave frequency, and -4.0 dB at 10 GHz; and has the
return loss of -20 dB or more at 6 GHz.
Embodiment 2
[0058] FIG. 5 is a cross sectional view of the printed wiring board
equipped with an electromagnetic wave absorbing layer comprised of
the electromagnetic wave absorption material by the present
invention. A printed wiring board 3 comprised of a circuit wiring 2
formed on an insulator board has an insulting layer 4 on its one
side of surface where said circuit wiring 2 is formed; and the
other side, the reverse side thereto, has no wiring. On a part of
said insulating layer 4 and on a part of said reverse side, or all
of the both, a material comprised of ground powder of the natural
schungite ore and a binder resin is applied to provide an
electromagnetic wave absorbing layer thereon. This application is
performed either by a direct coating of painting of said material
or by providing a sheet of said material. The thickness of said
coating or sheet is preferred to be 0.1 to 1.0 mm, though it may be
designed otherwise depending on the frequency generated and the
absorbing rate for electromagnetic wave. Thereby, generation of
noise such as crosstalk phenomenon due to electromagnetic wave
emitted from a printed wiring circuit is suppressed. Especially,
high-density and high-integration will be realized with highly
reliable manner in a multi-layer circuit wiring board which is
comprised of a first wiring layer formed on at least one main side
of surfaces of a semiconductor board, an insulating skin formed on
the surface of said first wiring layer, and a second wiring layer
electrically connected to said first wiring layer through a
conducting hole on said insulating skin, said second layer being
stacked repeatedly onto said first wiring layer. Arranging a
conductive layer every outside of the electromagnetic wave
absorbing layer will improve the absorption efficiency against
electromagnetic and shielding effect against incoming
electromagnetic wave from outside.
Embodiment 3
[0059] FIG. 6 is a cross sectional view of the electromagnetic wave
absorbing cap for semiconductors arranged on a printed wiring board
so that a semiconductor element that will generate noises may be
enveloped thereby. This is to show a configuration of an
arrangement of an electromagnetic wave absorbing cap, to which the
present invention concerns, that is placed on a printed wiring
board so that a possible noise generating source, such as a
microprocessor or a system LSI, may be enveloped by said cap. FIG.
6(a) shows a configuration in which the electromagnetic wave
absorbing layer by the present invention is arranged inside a metal
cap 5 for shielding against electromagnetic wave coming from
outside and for absorbing electromagnetic wave emitted from inside.
The metal cap 5 uses copper plated material, copper and gold plated
material, or stainless steel. FIG. 6(b) show a cap made by
injection molding using electromagnetic wave absorption material by
the present invention. An electromagnetic wave absorption material
1 formed into a cap is fixed on the printed wiring board 3 in
hermetically, in glued, or in similar manner.
[0060] By these mounting practice, electromagnetic wave emitted
from a semiconductor element is efficiently absorbed with
suppressed inner interference.
Embodiment 4
[0061] FIG. 7 is a cross sectional view of the electronic device,
in which an IC 6 mounted on the printed wiring board 3 is sealed
with an electronic device casing comprised of the electromagnetic
wave absorbing material by the present invention. FIG. 7(a) shows
an example wherein inside of a metal casing for an electronic
device is provided with a layer of the electromagnetic wave
absorption material by the present invention by coating or
injection molding. FIG. 7(b) shows the electronic device casing
formed by injection molding using the electromagnetic wave
absorption material by the present invention. Thus, electromagnetic
wave interference within an electronic device can be suppressed by
giving the casing of devices an absorbing function against
electromagnetic wave as shown in these examples.
Embodiment 5
[0062] FIG. 8 is a cross sectional view of composition of the
optical transmission module by the present invention. An optical
transmission module 8 is comprised of a jacketed optical fiber 9, a
light guide 13, an LD 10, a transmission circuit 11, and a circuit
board 12. The transmission circuit 11 is further comprised of an LD
driver, which drives the LD 10 as a light emitting diode, a laser
output control unit, and a flip-plop circuitry. In practice, such
configuration is accompanied by lead-frames and wires, which are
omitted in the figures however. As the transmission speed
increases, the clock frequency of electrical signal to excite the
LD 10 becomes high causing emission of high-frequency
electromagnetic wave inside the optical transmission module. This
electromagnetic wave leads to noise, which adversely affects other
elements and parts in the module.
[0063] In this embodiment, an optical transmission module is placed
in a mold and is set by a resin-mix poured in a metal casing 14,
then is metal-capped to provide a complete sealing over outside of
said module with the metal casing 14, wherein said resin-mix is
comprised of ground powder of said natural schungite ore equal to
40 to 80 wt-% of a resin being regulated depending on the
above-mentioned frequency and the electromagnetic wave absorbing
rate of said resin-mix. Thereby, not only protection of the element
and board against moisture and gas but also absorbing and shielding
of electromagnetic wave have been realized therein contributing
suppression of noise interference in the transmission module
together with complete prevention of noise emission to outside the
module.
[0064] FIG. 9 is a cross sectional view of an optical transmission
module. Since the metal casing 14 is not always required, a
structure that is complete, as shown in FIG. 9, in being sealed
with the resin-mix formed by a transfer molding is acceptable. This
structure brings an advantage for lowered cost although absorbing
and shielding effects against electromagnetic wave may be slightly
degraded.
[0065] FIG. 10 is a cross sectional view of an optical
transmission-reception module. For assured prevention of short
circuit between wirings, a 2-layer construction, as shown in FIG.
10, is useful. The wiring part alone is first sealed with a resin
that does not contain any of ground powder of the natural schungite
ore; over which sealing by resin-mix containing ground powder of
the natural schungite ore is provided to form said 2-layer
construction.
[0066] In this embodiment, the LD 10 and the transmitter circuit 11
are shown. However, an optical reception module is also realized by
replacing these units with a photo acceptance circuitry and a
receiver circuitry respectively.
Embodiment 6
[0067] FIG. 11 is a plan view of the optical transmission-reception
module in which an optical transmission module and an optical
reception module are formed on the circuit board 12. An optical
transmission-reception module 17 works both as an optical
transmission module and an optical reception module. The optical
transmission part is comprised of the jacketed optical fiber 9, the
light guide 13, the LD 10, the transmitter circuit 11, and the
circuit board 12. The transmitter circuit is comprised of an LD
driver to drive a laser, a laser output control unit, and a
flip-flop circuitry. The optical reception part is comprised of the
jacketed optical fiber 9, the light guide 13, a PD 19, a receiver
circuit 18, and the circuit board 12. The receiver circuit is
comprised of the PRE-IC that has a pre-amplifying function, the
CDRLSI composed of a clock extraction part and an equalizing
amplifier, a SAW narrow band filter, and an AOD bias controlling
circuitry. In practice, these configuration is accompanied by
lead-frames and wires, which are omitted in the figures
however.
[0068] As has been mentioned, the transmission-reception module,
when a transmission module and a reception module are integrated
therein, raises the inner noise interference problem caused from
emitting-and-suffering of noise between its optical transmission
unit and optical reception unit.
[0069] To prevent noise interference, the conventional optical
transmission-reception module uses a metal shielding plate placed
between the optical transmission unit and the optical reception
unit or uses encapsulation of each module in a metal package to
separate one into a transmission module and the other into a
reception module. However, these constructions connect not only to
a large and weighty module by the gross but also to being expensive
because of use of a costly metal package. The construction
according to the present invention not only prevents the noise
interference within a module but also realizes miniaturization and
price-reduction.
[0070] According to the present embodiment, it becomes practicable
to provide equipment acceptable for use in a high speed
telecommunication network, such as an optical transmission module,
an optical reception module, or an optical transmission-reception
module composed of an optical transmission unit and an optical
reception unit; thanks to their capability rendered from the
absorbing material to suppress internal noise interference and
noise emission to outside, to achieve small-sizing and
weight-reduction, to work under high speed transmission, and to
have high sensitivity.
Embodiment 7
[0071] FIG. 12 is a cross sectional view to show a basic
configuration of a tollgate equipped with an electronic toll
collection system (ETC) that exchanges information between a
roadside communication equipment and an on-vehicle equipment
carried by a transit vehicle passing said tollgate.
[0072] As shown in FIG. 12, information required for toll
collection is exchanged on a frequency 5.8 GHz among an entrance
antenna 21, an exit antenna 22, and an on-vehicle equipment 23. A
spread of the radio wave (a direct wave 27) transmitted from the
exit antenna 22 broadens due to a multi-path reflection phenomenon
caused by a road surface 24 and a ceiling or a supporting column of
a gate roof 25. This causes a problem in discrimination of chained
vehicles, wherein a reflected wave 28 reflected from the road
surface 24 is received by other on-vehicle equipment carried by a
following vehicle B 30 as shown in FIG. 12 although the radio wave
transmitted form the exit antenna 22 (the direct wave 27) is
received by the on-vehicle equipment carried by a vehicle A 29.
Malfunctioning attributable to radio wave disturbance like
interference to a vehicle on adjacent traffic lane is also further
anticipation. These problems are solved by application of an
electromagnetic wave absorption material on the surface of
structural members, such as the ceiling of the gate roof 25 and
supporting column that may reflect electromagnetic wave, so that
the reflected wave 28 may be absorbed thereby. In this application,
said electromagnetic wave absorption material is prepared and
applied in a manner: i.e. a resin-mix containing ground powder of
said natural schungite ore equal to 50 to 85 wt-% of the resin is
made into either a liquid state using a solvent or a sheet, then
the liquid state material is applied on the desired structural
members and the sheeted material is glued on the same.
[0073] The radio wave absorbing material for ETC in the
conventional technique is of a type integrated into one panel
having a thickness of several tens of centimeters measuring much.
This feature invites problems in installation such as difficulty in
applying onto complicated shapes, which demands a paint type of or
a flexible sheet type of thin electromagnetic wave absorption
material layer. An electromagnetic wave absorption material 1 by
the present invention is comprised of a resin-mix which contains
ground powder of the natural schungite ore, which permits supplying
in a paint or a flexible sheet depending on choice of resin to be
used therein.
[0074] A radio wave absorber 31 comprised of a resin-mix which
contains ground powder of natural schungite ore should be formed in
single layer or multi-layer structure as shown in FIG. 13. The
multi-layer structure effectively improves absoring performance for
an oblique incidence when layers are formed so that the
characteristic impedance of the radio wave absorber to an incident
wave 32 may gradually reduce toward a metal plate 33, a perfect
reflector, from the incident plane of the radio wave. To realize
this grading, a gradual increase of the complex relative dielectric
constant toward the metal plate 33 from the incident plane of the
radio wave is enough; this is attained by changing the filling
ratio of ground powder of natural schungite ore to the resin. When
the object to be applied is metal, the metal plate is not required.
The radio wave absorber 31 shown in FIG. 13 is 3-layer.
[0075] If the filling ratio of the multi-layer hollow globule of
carbon to resin in each layer is 5 weight-% or less, the complex
relative dielectric constant is too small to obtain acceptable
electromagnetic wave absorbing performance. Therefore, in
conjunction with the viewpoint of securing the fluidity of
resin-mix, this ratio in each layer is preferred to be 50 weight-%
at the maximum or less.
Embodiment 8
[0076] FIG. 14 is a cross sectional view of the millimeter wave
transmission-reception apparatus as an embodiment of a high
frequency communication equipment. The flat-face-side of a
semiconductor device 34 such as MMIC for transmission-reception use
and a flat circuit board 35 that connects such semiconductor
devices are mounted on a metallic base-plate 36, which is the
bottom of a casing, to form a transmission-reception circuitry; an
input-output signal is connected to an antenna (not illustrated)
though a coaxial line 37. A metallic lid 38, being separated from
the base-plate 36 by a sidewall 39 of the casing, forms a ceiling
of the casing. The material of the sidewall of the casing can be
any of metal, glass, alumina, and other nonmetals. The base-plate
36 is made of nonmetal like plastic or alumina, but a portion of
the surface thereof on which the MMIC and the flat circuit board
are mounted may be covered with metal formed by plating or
deposition. The ceiling of the lid 38 that faces inside the casing
is applied with a resin-mix containing ground powder of the natural
schungite ore being prepared in a paint formula or in a sheet. The
resin-mix in a paint formula is applied on said ceiling, and the
one in a sheet is glued on the same. Thereby, undesirable emission
from the transmission side of the transmission-reception circuitry
straying within the casing is prevented from invading the reception
side reducing mutual interference between transmission side and
reception side.
* * * * *