| High Intensity Radiated Fields(HIRF) refers to electromagnetic environment which civil aircraft may encounter on their operation with the current guidelines. Electromagnetic environment caused by human activities such as over-the-horizon or warship radar, airport surveillance radar, Am and FM radio stations, VHF TV transmitters has the characteristic of long duration and wide band.With an increase in the complexity, efficiency, power and number of RF emitter devices, and more application of digital avionics and composite materials in modern civil aircraft, HIRF has become a key factor in flight safety. In recent years, impact on flight safety brought by HIRF becomes more apparent.HIRF test is the key verifying project of aircraft in electromagnetic environment(EMC). The EMC effects of HIRF is an EMC research area concerned intensively by aviation circle. One of research methods is analyzing aircraft electromagnetic shielding effectiveness(SE), which is on the start-up phase in our country.In the paper, with the moment method of using Entire Domain Basis Function representing aperture field technology, the interior field intensity is obtained by solving cavity Green function based on the continuous conditions of aperture tangential electromagnetic field. The influence law of SE by the polarization and direction of incident wave, the thickness of cavity wall, the position, number and shape of apertures and the calculating point of SE have been comprehensively analyzed. The main contents are as follows:1. With the thickness of wall is considered, the calculating formula is theoretically derived under the condition that apertures are on both symmetrical wall of shielding cavity. The fuselage has been simplified to a rectangle metal cavity with a certain size and the fuselage windows have been simplified to some rectangle apertures with a certain size distributed on the front and rear symmetrical walls. Taking the wall thickness into consideration, the simplified fuselage model is divided into five areas for analysis by using the picture theory and boundary equivalent principle and replacing the apertures with equivalent magnetic current. With the moment method of using Entire Domain Basis Function representing aperture field technology, the interior field intensity is obtained by solving cavity Green Function based on the continuous conditions of aperture tangential electromagnetic field. And then, shielding effectiveness is obtained.2. The shielding effectiveness of shielding cavity with one aperture is analyzed. A typical cavity made by ideal conductor material with a size of 30cm×12cm×30cm has been selected as the research subject. It is assumed that the thickness of wall is zero, the aperture is on the plane of z=0 and the air in the cavity is ideal. At first, the method presented in this paper is verified. Then, the influence imposed by test point, the polarization mode of incident wave and shape of apertures is analyzed. Finally, the influence on the SE of shielding cavity imposed by the thickness of cavity wall and incident angle of incident wave is analyzed.3. The shielding effectiveness of shielding cavity with multi-appertures is analyzed. Considering the influence on SE of the shielding cavity imposed by factors such as position and shape of aperture, thickness of cavity wall and the polarization mode of incident wave, the changing law of multi-appertures distributed on the same wall of shielding cavity is analyzed.4. Modeling the B757-20 and B737-200 with the ratio of 1:20 and neglecting the seat and baggage holder of fuselage, the fuselage has been simplified into a rectangle metal cavity and windows have been simplified into some apertures with a certain size distributed on both symmetrical sides. The law of the influence of the Electromagnetic shielding properties of fuselage imposed by the number of windows and test position is researched based on the method presented in this paper. |
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