Measurement Technique Study Of Electromagnetic Interference Suppression Performance Of Shielding Materials

With the rapid development of electronic information technology, theelectromagnetic radiation of the surrounding space is growing more and more serious.Electromagnetic interference has brought people much trouble. So, electromagneticshielding materials are widely used in electrical and electronic equipment of aviation,aerospace, medical, automotive, communications and other fields.In the field of electromagnetic wave, the shielding effectiveness is usually used toevaluate the suppression performance of shielding materials acting on electromagneticinterference. According to materials locating at the far-field or near-field of the source,shielding effectiveness is divided into the far-field shielding effectiveness and thenear-field shielding effectiveness. After decades of development, measurement offar-field shielding effectiveness has formed a variety of different test methods. Thesemethods have a high degree of accuracy. The near-field has more components than thefar-field, so, the field structure is more complex than far-field. Because of these twoaspects, plane wave theory can not be applied. Theoretical analysis is difficult. Thesolution of high accuracy of the shielding effectiveness is hard to get.As a part of basic research on the application of electromagnetic shieldingmaterials, accurately measuring electromagnetic interference suppression performance,especially researching the interaction of shielding material and near-field, are thenecessary means of electromagnetic radiation controlling and EMC applied research,and have more and more important practical significance.The thesis is about test methods for near-field shielding effectiveness of material,also the suppression performance acting to conducted interference. The hazards ofelectromagnetic interference, types and application of shielding materials aresummarized. The shielding effectiveness of the material in the case of far-field andnear-field analysis is derived theoretically respectively. Near-field electric field andmagnetic field probes are developed applying to the frequency from10MHz~3GHz.Near-field magnetic field probes have two forms, coaxial line and coplanar waveguide(CPWG). Micro-strip line is fabricated, which is used as the source of electromagnetic field. Two test fixtures, coaxial line and slab line, and corresponding transition structureare developed to test material suppression performance acting on the conduction current.They are used in the frequency from10MHz~18GHz. Test method and thecorresponding calibration method are analyzed, which are applied to test the shieldingeffectiveness of the material acting on the electric field and the magnetic field of thenear field, and the performance suppressing conduction current. According to thesetheory and methods, four sets of test systems are fabricated. Two materials were testedusing these four systems, and good results are achieved. Finally, some improvement tothese four system are described...