Analysis Of Electromagnetic Railgun Projectile Fuze’s High Magnetic Field Environment And Its Shield Design And Utilization

Electromagnetic railgun launch can be used in anti-missile system and launching nano satellite with its hyper-velocity feature. The projectile launched in electromagnetic railgun is transformed from the traditional kinetic-energy projectile to intelligent ammunition, which means an electromagnetic railgun fuze is required. The severe electromagnetic environment that railgun projectile fuze suffered, may interfere, disable even destroy the electronic devices and units in intelligent ammunition. In this dissertation, a research based on such background, has been made on analysis of high magnetic field environment which railgun projectile fuze suffered and the shield design and utilization of such magnetic field.First, based on the theory of magnetic diffusion, the Velocity Skin Effect during railgun launch is analysed. Surface current geometry model and thin rail model are built, and the time-frequency characteristics of railgun pulsed current is evaluated. The surface current geometry model is used to estimate the spatial distribution of the in-bore pulsed magnetic field which is around fuze electronic devices and the magnetic field’s time-frequency characteristics. The thin rail model is used to estimate the strong recoil force environment during railgun launch.Then, passive shielding and semi-active shielding design are applied to the railgun in-bore pulsed high magnetic field. The passive shielding utilizes the one-side open hollowed cylinder. Optimizations of the shielding materials, the relative distance from the bottom of projectile and the shield thickness are necessary due to the low frequency and high magnetic flux density features of in-bore magnetic field. The combined passive shielding with multi-layers alternative high conductivity materials and high permeability materials has the expected shielding effectiveness only at two calibers from the bottom of projectile. The flux density after shield is less than0.01T in these points of interest, and the averaged shielding effectiveness of the plane of interest is25.79dB. Semi-active shielding adopts the impedance-optimized inductive coil. With the phase delay of the induced current in the inductive coil, a out-of-phase magnetic field is generated, which cancels the original railgun magnetic field. Limited by the geometrical dimensions of railgun projectile, the semi-active shielding only has good shielding effectiveness in some local points.With1Tesla magnitude static magnetic field generated by a electromagnet, the high magnetic field during the plat part of pulsed railgun current is simulated to observe the effect on typical electronic devices usd in fuze. The failure modes are built for resistors, inductors, capacitors, crystal oscillator, diodes, Zener diodes, MOSFETs, Single-Chip Microcomputer and FRAM, and all these devices are exposed to the magnetic field. Experiment result shows1Tesla static magnetic field has little effect on the devices above.Finally, with the in-bore high magnetic field and recoil force environment, a preliminary schematic design of fuze safety and arming device(S&A) is shown, and this work will be useful for the future work on electromagnetic railgun fuze design.