Research On Effect Of Aircraft Cable Damaged-shield On Shielding Effectiveness

Aircraft cable is the main body of the electrical wiring interconnection system of the more electric aircraft,which is responsible for the effective transmission of information and energy between various systems.The electromagnetic environment of the more electric aircraft is extremely complex.Shielded cable is often used to suppress electromagnetic interference to ensure the electromagnetic compatibility of aircraft cable.Various natural and man-made factors in the actual environment can easily lead to the damage of the aircraft cable shield.The ability of the shield to suppress electromagnetic coupling will be greatly reduced,resulting in poor transmission signal quality.It will affect the normal operation of other electronic equipment,and in serious cases may even cause system-level failures of aircraft and fatal safety accidents.It can be seen that in order to ensure the safety and reliability of aircraft flight,the research on broken shielded cable has important practical significance and implemented value.In this paper,the transfer impedance of the aircraft cable’s shield is taken as the research object,and the methods of theoretical analysis,numerical simulation and experimental test are adopted.Firstly,based on the mechanism of shielding coupling,according to different shielding structures and common types of damage,the analytical expressions of transfer impedance for spherical damage of thin-walled tubular shield,static and dynamic damage of braided-shield are proposed respectively;Secondly,the three-dimensional geometric models of the shielded cable and different damaged shield structures were established in SolidWorks,which were imported into ANSYS HFSS for finite element analysis of electromagnetic field,and the numerical simulation results of the transfer impedance of the damaged-shield were obtained;Finally,the quantitative relationship between shielding effectiveness of the shielded cable and transfer impedance was derived using the electromagnetic radiation model and transmission line theory.The RG58 shielded cable was used as an example to perform the line injection test of transfer impedance.The results show that when spherical damage occurs to the thin-walled tubular shield,if damaged-area exceeds 30% at low frequency,the transfer impedance will increase by more than 3dB.If damaged-area exceeds the thickness of shield at high frequency,the transfer impedance will increase by tens of d B.When static damage occurs to the braided shield,more than 25% of damaged-braided wire at low frequency will lead to the increase of transfer impedance by more than 3dB.The change of transfer impedance of same damaged-braided wire is larger at high frequency.When dynamic damage occurs,the transfer impedance increases by several dB,and the shielding effectiveness decreases significantly.The maximum error between the numerical simulation results of the damaged shield model’s transfer impedance in ANSYS HFSS and the theoretical calculation is within 1dB.The practical measurement results of RG58 transfer impedance are basically consistent with the theoretical calculation results,which verifies the validity of the analytical model of damaged-shieldThe research results of this subject have certain engineering application value that can provide theoretical support for the optimization and improvement of the relevant parameters in the aircraft cable shield termination process standard in the design stage.