| Electromagnetic environment is the sum of all electromagnetic phenomena existing in a given place.At present,the vast majority of instruments,sensitive devices and sensors are in some form of electrically large shielding cavity.The threats to the electronic system are more from the "electromagnetic environment in the cavity" formed by multiple reflections of radiation sources in the cabin.Because of the resonance in cavity,the coupling energy is much stronger than that between equipments,which challenges the EMC design.In this paper,an effective electromagnetic environment assessment method is proposed by using the theory of reverberation chamber in a well shielded cavity.1.The basic theory of reverberation chamber is analyzed based on the deterministic cavity theory and the statistical theory of electically large cavities.Based on the Maxwell equation,the concept of the number of modes and the bandwidth of quality factor(Q)in reverberation chamber is analyzed;The distribution law of electric field,the probability distribution function of electric field strength,the uncertainty of field distribution and the theory of generalized extreme value distribution are analyzed by plane wave integral principle of Hill so as to the exreme value distribution function.2.Analyze that the cavity meets the basic conditions for establishing the reverberation field,determine the similarities and differences between the electromagnetic environment of the cavity and that of the reverberation chamber,and determine to use the reverberation chamber theory to analyze the electromagnetic environment of the cavity above 200 MHz.3.The field uniformity in the loaded and unloaded cavity in accordance with GB/T 17626.21 was tested,and the results showed that the field uniformity met the requirements under the loading of three absorbing materials;the electric field distribution of the cavity was fitted with the Rayleigh distribution of the theoretical electric field component,and passed the K-S test under the 95% confidence interval;the anisotropy coefficient of the cavity was analyzed,and the results showed that it reached the "good" level;the shape parameter k was analyzed by the generalized extreme value distribution theory,and the results show that the cavity reaches the ideal overmold state above 400 MHz.The test results show that the field formed in the cavity meets the requirements of electromagnetic reverberation field.4.The high frequency structure simulator(HFSS)was used to simulate and analyze the influence of loading degree and loading methods on the cavity,and compared with the loading test,the Q value of the cavity was determined as the characterization of the loading amount.The Q-value of the cavity under various loading conditions is tested by using the frequency-domain Q-value test method,and the experimental results agree with the simulation results.5.the Q value of EUT is analyzed by using the parameters of absorption cross section,and the Q value of loading cavity with known EUT is estimated based on theoretical derivation.The feasibility of using equivalent absorption section to analyze the Q value of loading cavity is verified by experiments.6.The relationship between the Q value of the cavity and the field distribution inside the cavity is analyzed theoretically.Based on the Q value of the loading cavity,the maximum electric field and the average electric field formed by the given input power in the cavity are predicted.The verification experiment shows that the maximum electric field is within the 95% confidence interval of the theoretical derivation,and the mean field strength is basically the same.Finally,the field strength of the edge field is predicted. |
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