<CMC Beads as a New EM Absorber >

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Page 1 of 2 - Mechanism of Electromagnetic Wave Absorption - < Conventional Electromagnetic Wave Absorber> In general, the materials used for absorbing the electromagnetic(em) waves are classified;

1 Page 1 of 2 - Mechanism of Electromagnetic Wave Absorption - < Conventional Electromagnetic Wave Absorber> In general, the materials used for absorbing the electromagnetic(em) waves are classified; (1) High resistive materials, such as carbon particles (2) High permeability materials,such as ferrite materials (3) High dielectric loss materials,such as foam with carbon particles dispersed The EM wave consists of two parts;electric field and magnetic field. And the high resistive materials and high dielectric loss materials(above (1) and (3) ) absorb the electric energy and convert it to thermal energy, while the high permeability materials (above(2)) works for the magnetic energy and convert it to thermal energy. Note that some people confuse the difference between the EM shielding and EM absorption. The shield materials reflect the electric field or prevent the EM wave from coming in or out while absorption means transferring energy to heat and attenuating EM energy. < Mechanism of Carbon Micro Coil(CMC) EM Absorption> CMC beads is the new type material which contains the CMC and have the marvelous EM absorption performance. This function is based on the two principles;(1) the electromagnetic induction effect causing by the inductance(l), capacitance (C), and resistance(r) of CMC and (2) the increased loss of electric and magnetic field due to the chiral effect of CMC. CMC is the carbon material with the conductivity and its shape is double helix coil with the diameter of a few micrometers. The helical shape means that this material has no symmetrical axis and is called as chirality. These features realize the remarkable EM absorption characteristics. (1) Absorption due to electromagnetic induction CMC is the conductive material and has three electrical parameters,i.e. inductance(l), capacitance(c), and resistance(r). These three components act as the resonance circuit and resonate the specific frequency decided by LCR. This means the resonant EM wave is transferred into resonant circuit and consumed by the resistance to heat. (See Fig.1) (2) Enhanced absorption capability by Chirality CMC as a chiral material acts both the electrical field and magnetic field and combines them in the CMC and it results in the increase of the effective permittivity and permeability. This leads to the enhancement of the EM absorption caused by dielectric loss and magnetic permeability. Therefore, CMC can absorb the energy of both electric and magnetic field. (See Fig.2) Such a chiral effect of CMC is more significant in the higher frequency range of over GHz. The chiral material of CMC has also a characteristics of scattering EM wave, and such a characteristics enforces EM absorbing efficiency. <CMC Beads as a New EM Absorber > CMC beads are the new EM absorbing materials which utilize CMC characteristics. Especially, it shows the good performance in GHz band. EM wave absorber without the reflection metal can be assembled by CMC beads. (See Fig. 3 and 4.)

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3 - Feature and Application of CMC Beads - Features Compared to the existing EM absorbing materials,cmc beads have remarkable characteristics and are applicable to various products. Major features are as follows; *Resonance Absorption Material due to Electromagnetic induction *Chiral characteristics increases the effective permittibity, permeabilty, which results in the high attenuation. *Marvelously light weight compared to the existing absorber like ferrite materials *Volume reduction can be achieved. No pyramidal configuration required. Applicable to any shape. Application <Sample Ordered CMC Beads> CMC beads can be used in various fields of EM absorbers, for example, the composite materials for the formed plastic product, resin filler, or complementary use of the existing electromagnetic absorber. Formed Products: CMC beads are made from the acryl resin(polymethyl methacrylate). So these can be formed to sheets, panels, bars, etc. of plastic products. The arbitrary shaped plastic products, such as EM absorber panels, PC enclosure, building walls, etc., which absorb the electromagnetic energy, can be formed. You can mix CMC beads with the other EM absorbing materials like carbon particle, carbon fibers, ferrite particles, etc. when the products are formed so that you can achieve the required EM absorption characteristics. You have a good advantage of light weight, it would be good application that the EM absorber panel for the high tower or building to prevent the electromagnetic interference to TV ghost. If you use the panel made from CMC beads as the interior wall panels, partition boards, or, utensils like closets, you can improve the interior electromagnetic environment for the microwave LAN network for PC. Based on the fundamental data of CMC beads, you can design the desirable electromagnetic absorber with center frequency, frequency band, and attenuation to be realized. Stand alone usages: So the CMC beads have the shape of small particles, you can fill them into the various places such as boxes, grooves, gaps, etc.. For example, when you want to decrease the noise level emitted from the motors, etc. to investigate the electromagnetic interference, or when you want to enforce the noise immunity temporarily, CMC beads are very useful and effective to be applied. When the electrical wires are rooted in the closed section like the conduit pipes, you can decrease the mutual electromagnetic interference between wires by filling CMC beads as fillers. Besides, CMC beads can be mixed into the other electromagnetic absorption composites to enhance the original absorption characteristics. <Custom Order> Now, we start providing CMC beads as a sample product. It can be applied to the very high frequency absorbers of over several GHz, and made of the acryl plastic material(pmma) containing the suitable sized CMC of a few percentage in weight. The kinds of matrix material, size of CMC beads, containing percentage, etc. can be available, according to the customer s order.

4 Absorption of Electromagnetic Field or Noise required, not a shielding nor suppression Differences between EM Absorbers and EM Shields <Electromagnetic Shield> To prevent the unexpected electromagnetic interference, the EM shielding has been used. Usually,two kinds of EM shields are used, one is the electrical shielding and another is the magnetic shielding. *Electrical shield The equipments or units to be protected are enclosed by the electrically conductive material such as the metals. The conductive enclosure reflects the electrical field and prevents the electrical field from coming inside of the equipments. The enclosure is usually made of the metal sheet, metal foils, and metal plates etc.. *Magnetic shield The equipments or units to be protected are enclosed by the high permeability materials. The high permeability enclosure deflects and concentrates the magnetic flux inside of the shield enclosure and prevents the magnetic flux from penetrating into the internal space. The materials which contains the considerable percents of ferrites are usually used. Both the electrical shields and magnetic shields are used to prevent the EM waves coming in or out and never absorb and attenuate the electromagnetic energy. EM Wave (Electrical Field) (reflection) -- Electrical Shielding -- Unit (reflection) Shielding Enclosure (Conductive material: metal etc.) -- Magnetic Shielding -- Unit EM Wave (Magnetic Field) Grounding <Electromagnetic Absorber> The electromagnetic absorbers absorb the electromagnetic energy and transform it to the thermal energy. The absorbers attenuate the undesirable EM waves and substantially solve EM interference. < EM Wave Absorption> (1) The existing absorbers consist of absorbing materials with a reflection metal. The EM wave coming into the surface of a absorbing material are attenuated by multiple reflections. The EM wave from opposite side are reflected and never absorbed.*1) (1) The existing Absorber EM absorbing material 1 st Reflected Wave EM Wave Thermal loss due to high frequency current Unit Reflector(metal sheet,foil,etc.) Magnetic Flux EM Absorber (2) Ideal Absorber Shielding Enclosure (High permeability material:ferrite etc.) (2) The ideal absorber can absorb the incident EM wave from both side without the reflector. (The absorbers which made of CMC beads can be the ideal EM absorbing materials.) EM absorbing material Attenuation/Consumption 2 nd reflected Wave Reflected Wave(Full reflection) (One side absorption) (Both sides absorption)

5 Electromagnetic Induction and EM Absorption of Carbon Micro Coil(CMC) Carbon Micro Coil(CMC) has the helical configuration of micrometers, i.e. micro-coil shape, and is a electrically conductive carbon material. It has been confirmed that CMC also has three electrical parameters, resistance(r), capacitance(c), inductance(l). In general, the inductance takes effects in the magnetic behavior, so dose the capacitance in the dielectric behavior, and the resistance is responsible for the electrical conductivity of materials. So, those three electrical parameters,l,c,r of CMC constructs the resonant circuit by itself. CMC can be modeled as follows; or The LCR circuit can be resonated at the resonance frequency and generate the largest electrical current in the circuit. This electrical current flows through the coil resistance and is converted to the thermal energy. By this mechanism, CMC absorbs and consumes the electromagnetic energy and transfers to the thermal energy. As mentioned above, a CMC is the self-active electromagnetic absorption material. Compared to the existing EM absorber materials, CMC will be able to give you a new concept of EM absorber. The figures below show this EM absorbing mechanism of CMC and CMC beads. The EM absorber made from CMC beads shows the multiple of sharp fall curves over the broad bandwidth of GHz in the electromagnetic absorption graphs. This is the result of the resonance absorption caused by the electromagnetic induction. In addition to the effects mentioned above, the chiral characteristics of CMC, which is explained in another technical note, amplify the EM absorption capability of CMC beads.

6 Carbon Micro Coil(Chiral object) Interaction with Electromagnetic Field The Carbon Micro Coil(CMC) has the special shape of double helical coil, which has no symmetrical axis, which is called as chiral object. The optical activity is well-known effect of the chiral object. And so is the electromagnetic activity. The chiral object can react the electromagnetic fileld as follows; D: electric displacement, B: magnetic displacement, E: electric field strength, H: magnetic field strength: permitivity, : permeability, : conductivity, : chirality parameter, xa : curl of vector A In General, the electromagnetic filed acts the object as follows; the electric displacement(d) is determined by the electrical field strength(e) with permitivity of and so is the magnetic displacement(b) with the permeability of. But in the case of the chiral objects, additional term of xe, xb are contributed respectively. This means that the interaction between the chiral objects and the electromagnetic field increases by xe, xb.this results in the increase of effective permitivity and permeability and consequently more electromagnetic fluxes is concentrated in the chiral object and then electromagnetic fluxes areattenuated. It is also well-known that the polarization of EM wave in chiral object is rotated. When the linearly polarized wave is incident, this wave is divided to two polarized wave; right handed circular polarization and left handed circular polarization. The cross section of chiral objects are larger than that of the achiral. The electrical and magnetic field are concentrated near reign of the chiral objects. So, the incident wave energy are distributed near the chiral objects and attenuated, then scattered to neighbor ones, and get more attenuated repetitively. These effects realize the electromagnetic energy are more attenuated in the chiral objects.

Technique for the electric and magnetic parameter measurement of powdered materials

Computational Methods and Experimental Measurements XIV 41 Technique for the electric and magnetic parameter measurement of powdered materials R. Kubacki,. Nowosielski & R. Przesmycki Faculty of Electronics,