Study On Anti-EMI Suppression Materials Used For RFID System

The aim of this dissertation was to provide theoretical and experimental evidence for anti-EMI suppression material used for radio frequency identification system (RFID). Aimed at the problem of tag can't used to metallic environment in RFID system, the reason was analyzed. The practicable plan will be given base on measure method and preparation method.At first, according to the theory of electromagnetism, transmission-line and antenna, the reason which tag can't used to metallic environment in RFID system was analyzed, and determined the corresponding countermeasure.On the basis of deducing impedance calculation, the measuring principle of the relative complex permeability was analyzed.The reason which tag can't use to metallic environment in RFID system is electromagnetic induction changed the electromagnetic field distribution around tag and indirectly changed input impedance of the tag antenna.On the basis of deducing impedance calculation,"One circle inductance"physical model on magnetic ring samples was perfected.Secondly, suppression material is prepared in order to solve problem which tag should not apply to metal in the environment.With the combination of theoretical analysis and foreign suppression material analysis, design appropriate process of anti-EMI suppression material used for RFID system.Suppression material was successfully prepared through the reasonable process which flattened alloy powder after the vacuum annealing mixed organic compound and pressed into suppression material.Using X-ray diffraction,scanning electron microscopy and Agilent4396B network analyzer, the effects of milling time, annealing temperature, powder content and material thickness on the alloy powder micro-structure and suppression material properties have been studied.With the milling time from 0 hours to 50 hours, the aspect ratio of milled powder from 1.18 increases to 7.01 while particle size from 50.36μm decreases to 33.31μm,the average grain size from 79.7 nm decreases to 49.7 nm while internal strain from 0.4252% increases to 0.5974%;The real and imaginary part of suppression material's complex permeability improves simultaneously after alloys powder by attrition milling;With the increase of milling time, the real and imaginary part of suppression material's complex permeability at the same frequency increased respectively.With the annealing temperature from 550℃to 900℃, the ordering degree of DO3 superlattice structure from 0.38 increases to 0.66,the average grain size from 36.93nm increases to 71.41nm,the real and imaginary part of suppression material's complex permeability at the same frequency increased respectively.With the increase of powder content, suppression material's complex permeability and dielectric constant modulus︱ε︱increased.With the increase of the material thickness, permeability modulus︱μ︱and dielectric constant modulus︱ε︱into a nonlinear change.With the increase in milling time, read and write distance of RFID system is also gradually increasing but a smaller increase.The read and write distance of RFID system have no apparent regularity with annealing temperature, the powder content, material thickness change.After comprehensive analysis, the read and write distance of RFID system for suppression material have higher distance while process parameters is milling time 50h, annealing temperature 650℃, powder content 80%, material thickness 2.0mm.