The FDTD method has emerged as one of the easiest and versatile computational tools for solving electromagnetic problems involving complex geometries. In most books and papers, it has become a common practice to assume a time-harmonic variation; however, there appears to be a growing interest in time-domain solutions also in the present literature. This paper discuses the reflection of an electromagnetic pulse (EMP) from a dielectric slab and presents a visual display of the same at different snapshots of time. The problem is formulated directly from Maxwell's equations and solved via the FDTD method. With the aid of a perfectly matched layer, this technique may be extended to tackle the wave-structure interaction problems that arise in the context of EMI/EMC.
Advanced technology, high density and increased complexity of electronics equipment calls for a detailed EMI evaluation of a missile ground support system. A missile ground support system is most vulnerable to both intra-system and inter-system EMI. To attain success of the mission, it is very important to harden all the subsystems of the missile ground support system individually and take the necessary steps to ensure the total electromagnetic compatibility (EMC) of the system. The authors describe various problems encountered during the EMI performance evaluation of the subsystems and also after integrating the subsystems into a vehicle. They also discuss various control techniques used in the subsystem level as well as in the system level to overcome the problems.
In recent trends, DC-DC power converters are now used in mostly all subsystems for deriving single or multiple output voltages from a single power supply module. Though it gives a distinct advantage to the system designer, it has a serious drawback from an EMI point of view which most of the time goes unnoticed in the design level. The authors have evaluated different subsystems of aerospace systems and found that one of the main culprits for high conducted emissions from subsystems is the DC-DC power converter, the levels of which are sometimes so high that they affect the system itself. So as to achieve success of a mission, it is very important to know the EMI performance of DC-DC power converters used in these subsystems. This paper presents some of the problems the authors have come across which are explicitly due to DC-DC power converters of different makes and the methods used to mitigate them. The paper also suggests general EMC design guidelines which can be followed in the design and development stages to control the emissions from DC-DC power converters in order to save the cost and time of hardening at a later date.
The effect of growth of the electronics industry and the widespread use of electronic equipment in communications, computation, automation, biomedicine, space and other areas has led to many electromagnetic interference (EMI) problems for the designers as their systems/subsystems operate in close proximity. It is likely to become more severe in the future, unless designers follow EMI control methodology/techniques to meet the EMC requirements during the design stage itself. The elimination or suppression of EMI should be a prime objective of the designer. In this paper the authors have made an attempt to present technical data/details of various EMI suppression materials/devices available in the market and simplified the job of designers in verifying different catalogues which may be directly applied to the problem and harden the system/subsystem in compliance with EMC standards. As the design and development proceeds, the number of available noise reduction techniques also decreases and at the same time the cost of the mitigating noise goes up. Hence selecting the right component at the right time is essential. This paper gives a quick reference to the designer to reduce the noise at source level in the system during the design and development stages by choosing the appropriate component/device and fixing it correctly into the problem.
This paper discusses typical electromagnetic interference (EMI) problems encountered in airborne/ground subsystems during EMI/EMC performance evaluation for conducted emission, radiated emission and conducted susceptibility tests. It also highlights different suppression techniques, followed in hardening the units by selecting proper EMI power line filters, using appropriate shielding aids, good grounding practices and transient protection devices to achieve electromagnetic compatibility (EMC) in all the equipment to meet the test requirements. Finally the test results along with the specification limits are also given.
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.
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