Zhao Yang Zeng

Property Analysis for Microwave Absorbing Material Based on Effective Medium Model

In order to predict the absorbing properties of absorbing material effectively in theory, effective media theory was applied to reduce the effective electromagnetic parameters of several composite absorbing agents under different volume ratio. The comparison with experimental data shows that this method can well forecast the absorbing properties of absorbing material. For practical absorbing agent and penetrating agent, this method can compute the optimal proportioning and material thickness.

Input Impedance Adjustment and Property Optimization for Microwave Absorbing Slabs

It is generally believed that materials with high imaginary permeability and high imaginary permittivity are effective absorbers. For specific samples, however, the adjustment of input impedance is still necessary for the sample property optimization. By analyzing the relation between the diffraction rate and the input impedance, a method of absorption maximization for slab sample are presented in this sample. Medium choosing and volume rate controlling is the key of this method.

Investigation on Microwave Property of Fe/Co Mixed Powders

For the purse of improving the microwave absorption ability of carbonyl iron, Co power was chosen as additions to add into the sample. Both analyze and measurement proved that the addition of Co power effectively decreased the conductivity, while not obviously destroyed the magnetic property of the sample. In this way, the addition of Co power improved the sample surface matching effect, and correspondingly, the absorption ability is increased.

Influence of Lamellar Graphite Additions on the Electro-Magnetic Properties of Carbonyl Iron

For the purpose of investigating the influence of graphite addition on the property of carbonyl iron absorber, some samples were made by mixing graphite and carbonyl iron powders. The electro-magnetic parameters were then measured and compared between samples containing different graphite mass ratio. Microstructures of these samples were observed to make sure that additions were uniformly distributed in these samples. By this way, the influence of graphite addition was systematically analyzed.

Usability of Effective Medium Model for Microwave Absorbing Ceramics

For the purpose of describing the microwave properties of microwave absorbing ceramics, the usability of effective-medium theory for this kind of materials was investigated. Different equations deduced from effective-medium theory were first discussed and then compared with the measured data of microwave absorbing sample. It was found that the theory could not explain the measured data well only if some empirical exponent were used.

Investigation on the Representation Method for Microwave Absorbing Coat

Based on the transmission line theory, influence factors of microwave absorbing ability for slab coat were analyzed and calculated. It was found that the parameter absorption rate could not effectively describe the different influence from material character, geometry dimension and microwave. As a solution, the matching property and absorption property needed to be discussed simultaneously. According to the new representation, matching property of coat depends only on the material character, whereas the absorbing ability resulted from the interaction between different interfaces within the sample. The influence of microwave frequency is reflected by interfere between different interfaces. Relatively, in the new representation, the influence from different factors was clear and intuition, which means the applicability of the new representation.

Study on Chemical Plating and Shielding Effectiveness for Electromagnetic Shielding Fabric

For the purpose of investigating the influence of different process condition on alkali reduce rate and mass increase rate, the techniques of polyester fiber pretreatment, electroless copper plating, and electroless silver plating were carefully analyzed and compared. It was found that the best coursing condition was: 5.5 mol/L concentration, 65°C temperature, 30 minutes reaction time, 1:200 bath ratio. Under these conditions, the alkali reduction rate was 11.38%. As for copper plating liquid concentration of 0.08 mol/L, pH value 9.5, 80°C temperature, liquid silver plated concentration 0.02 mol/L, the coating weight gain rate was 52.1%. Microcosmic morphology on coating surface and surface resistance test show that the fabric was evenly coated with Cu, Ag, metal ions, which resulting in excellent electric conductivity and good electromagnetic shielding performance.

Scheme Selection of Camouflage Screen Design Based on Hierarchical Grey Relational Analysis

As many influence factors and technical problems should be taken into account in the scheme selection decision of multi-band camouflage screen design, a method based on hierarchical grey relational analysis combing analytic hierarchy process (AHP) and grey relational analysis (GRA) was developed. The hierarchy model was constructed firstly, and the judging matrixes were established through analytic hierarchy process. The weight value for each index which effects the evaluation was determined accordingly. The relational degree between an individual alternative scheme and the ideal alternative and the worst alternative are calculated by grey correlation degree, and the evaluation degree is calculated according the grey correlation degree and weight value. Based on the relational degree a quality order for the alternative schemes can be obtained. Experiment was carried out, which proved that the method mentioned in this paper had both strict mathematical theory basis and good practical utility. This method can be also used in scheme selection decision of other camouflage designs.

Property Improvement for Microwave Absorbing Slabs by Adding Conductive Grains

The possibility of improving microwave absorption ability for magnetic slabs by adding conductive grains was analyzed within the theory of effective medium. It was found that pure magnetic slabs cannot mediate the contradiction between high absorption ability and high reflection property. Gradient magnetic structure cannot improve the absorption either. Adding conductive grains, however, can simultaneously improve the matching effect and absorption ability of slabs. This result means some methods for fabricating high absorption slabs.

Describing Method for Information Protecting Composite Materials

For the purpose of discussing the potentiality of composite materials in information protecting, the microwave transmitting properties of epoxy-based carbonyl iron composite material was systematically analyzed in this report. The effective medium approximation (EMA) model was used to calculate the electro-magnetic parameters of the material, while the transmission line model was used to calculate the absorption ability of the composite material. Good agreement between calculation and experiments was obtained, which means the rationality of the describing method in this paper.