Hazards of electromagnetic radiation to ordnance (HERO) assessment of electro-explosive devices and validation of extrapolation method for estimation of the safety margin at HERO electromagnetic environments

HERO is one of the critical electromagnetic environmental effects as defined in the MIL-STD-464A. The HERO electromagnetic environment is very severe for the ship born systems, as it contains the sources of Electromagnetic environments (Radars, HF Transmitters and VHF communication systems etc.) and ordnance systems on the same platforms. Necessarily most of the ordnance system contains the EEDs/EIDs, and these are fired as and when the operation of the ordnance system is desired. HERO environment has the potential threat to cause an inadvertent actuation or firing of these ordnance systems by inducing the sufficient current in the EEDs/EIDs circuits. This results into a disaster and causing the loss of ordnance system along with collateral effects, platform, cost and human being. So now it has become essential to certify every ordnance system to be HERO safe and reliable, when it is on board or when it moving in the stock-pile to safe operation. The HERO environment defined in MIL-STD-464A calls for generation of very high field strength (i.e. 2620 V/m @ 2.7-3.6 GHz), which is really a challenge to generate inside the laboratory. So to overcome this practical difficulty the MIL HDBK-240 suggested to use extrapolation method for high fields, provided the bridge wire should exhibit the linear characteristics. The aim of this paper is to demonstrate the extrapolation method (MIL-HDBK-240) for assessing the induced current on the bridge wires at very high fields. The induced current measurement system on bridge-wire consists of Fibre-optic temperature (FOT-HERO) sensor and the signal conditioner, which works on the principle of Fabry-Perot Interferometery (FPI). To verify the extrapolation FOT-HERO sensor mounted bridge-wire will be exposed to the different electromagnetic field levels at specified spot HERO test frequencies. The measured induced currents at the lower field levels will be extrapolated to higher field level to compute the induced currents at high field levels, and then it will be compared to the actual measured results and finally with the safety margin (i.e. 15% of the Maximum No Fire Current (MNFC)) of the ordnance system.