Microwave absorbing materials

Microwave-absorbing materials are currently in high demand for many expanded EMI shielding and radar cross section reduction applications with both commercial and defense purposes. The nanostructured materials have attraction for microwave radiation absorbing and shielding materials in the high-frequency range due... 

MAJOR PRODUCT APPLICATIONS plastic magnets, xerographic materials, filters, fibers, energy attenuating powders, microwave absorbing materials... 

The wind wave tank of the University of Hamburg is 26 m long and 1 m wide. It is filled with lfesh water with a mean water depth of 0.5 m. The wind-tunnel height is 1 m, and the effective (maximum) fetch is 19 m. All measurements reported herein were performed at a fetch of 14.5 m and at wind speeds between 2 and 10 m s"1 generated by a radial blower. In the measurement and rain area, the metallic plates of the tank s roof were removed and, on the leeward side, replaced by Styrofoam panels to ensure the unattenuated transmission of the microwaves (Figure 2). At the windward side of the rain area plates of microwave absorbing material were vertically mounted in the direction of the specular-reflected radar beams. 

From the point of view of understanding the properties, conductivity is the only main parameter which controls the performance. It is not the case for microwave absorbing materials as shown below. 

Due to their unusual dielectric properties, conducting polymers belong to a new class of microwave absorbing material [97]. In order to optimise the use of such... 

The results obtained are supposed to make possible a choice between different materials in agreement with the requested concept for the manufacturing of microwave absorbing materials. For instance, in the case of a Salisbury screen (resistive layer of 377 Q/D), it is better to use materials with a low e, lower than e". While, in the case of a Dallenbach screen, the best solution would be a high f/, higher than f". 

Olmedo, L., R Hourquebie, and F. Jousse. 1993. Microwave absorbing materials based on conducting polymers. Adv Mater 5 373. 

J. Tang, M. Radosz, Y. Shen, (2008) "Poly(ionic liquid)s as optically transparent microwave-absorbing materials." Macromolecules, 41,493-4%. 

Spriggs, R. M., Ceramic Sintering, Proceedings of the Workshop on Microwave-Absorbing Materials for Accelerators, CEBAF, Newport News, Va (1993)... 

Figure 2.3. Dielectric spectrum for a microwave absorbing material...

Electroactive network membranes as artificial muscles, direct methanol fuel cells Electrochemical actuators, micromechanical systems, on-demand devices, chemical sensors, antibacterial nanocomposite materials, dye sensitized solar cells, microwave absorbing materials... 

The unusual dielectric properties of conducting polymers make them a unique new class of microwave absorbing materials (1). We have previously studied the links between structural (crystal structure, counter-anion size, molar mass, length of the alkyl chain on the substituted monomer) and electrical properties (Cdc and values) (2). The key parameters affecting conduction properties are clearly the interchain distance and the delocalization length as it was proposed by Wang et. al. a few years ago (3). These parameters are closely related to the method by which the polymer is synthesized, and doped. 

As an extension of our earlier work we have studied soluble conductive polymers (sulfonic acids doped polyaniline (4), poly(3-alkyl thiophenes) (5)) for the design of a new generation of microwave absorbing materials (6). These studies have own that microwave properties were very dependent on minor changes in e q)erimental procedures. Therefore it was necessary to determine how synthetic conditions effects influence structural parameters of polymers, and how these structural parameters influence electrical, optical properties and stability over time. In the case of poly(a]kylthiophene)s, solubility of polymers permits a complete structural characterization and then a better understanding of links between... 

Soluble conducting polymers are very attractive materials in order to realize microwave absorbing materials. However, structural parameters of the polymer and details of preparation techniques have to be severely controlled in order to get reproducible and expected values. More specifically, DBSA doped polyaniline based materials are promising materials if two major problems are fixed homogeneity of properties after extrusion and stability over time. Work is in progress now in order to increase properties stability of the polymer. 

T. C. P. Wong, B. Chambers, A. P. Anderson, and P. V. Wright, Large area conducting polymer composites and their use in microwave absorbing material. Electron. Lett. 25 1651 (1992). 

However, many investigations indicate that a shielding effectiveness value of 30 dB is required to protect electronic equipment in most of the cases [118]. In this regard, multicomponent nanocomposites containing also titanium dioxide nanoparticles have been evaluated as microwave absorbing material because the Ti02 has... 

Several consequences of single-mode cavity design must be appreciated. First, microwave-absorbing materials placed inside such a cavity will absorb microwaves and as a consequence, the material is heated. The second consequence is more important. There are some specific positions inside the single-mode cavity, where items are placed so that the sample is heated. On the other hand, there are certain positions in the single-mode cavity, where no heating will occiu. 

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