Coupling Of Electromagnetic Fields From Intentional High Power Electromagnetic Sources With A Buried Cable And An Airborne Vehicle In Flight

Abstract

Society’s dependence on electronic and electrical systems has increased rapidly over the past few decades, and people are relying more and more on these gadgets in their daily life because of the efficiency in operation that these systems can offer. This has revolutionized many areas of electrical and electronics engineering including the power sector, telecommunication sector, transportation, and many other allied areas. With progress in time, the sophistication in the systems has also increased. As the system size has reduced from micro?level to nano?level, the compactness of the systems has increased. This paved the way for developments in digital electronics leading to new and efficient ICs that came into existence. The power sector also faced a resurgence in its technology. Most of the analog meters are now replaced by digital meters. The increased sophistication and compactness in digital system technology made it susceptible to electromagnetic interference, especially from High?Power Electromagnetic (HPEM) sources. Communication, data processing, sensors, and similar electronic devices are vital parts of the modern technological environment. Damage or failures in these devices could lead to technical or financial disasters as well as injuries or loss of life. Electromagnetic Interference (EMI) can be explained as any malicious generation of electromagnetic energy introducing noise or signals into electric and electronic systems, thus disrupting, confusing, or damaging these systems. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. These effects can range from simple data degradation to total data loss. The source may be any object, artificial or natural, that carries rapidly changing electrical currents, such as an electrical circuit. The sources of electromagnetic interference can be either unintentional or intentional. The sources producing electromagnetic interference can be of different power levels, different operating frequencies, and different field strengths. One such classification of these sources is High?Power Electromagnetic Sources (HPEM). A High?Power Electromagnetic environment refers to sources producing very high peak electromagnetic fields at very high power levels. These power levels, coupled with the extremely high magnitude of the fields, are sufficient to cause disastrous effects on electrical and electronic systems. There have been extensive developments in the source technology of HPEM sources such that they are now among the strongest sources of electromagnetic interference. HPEM environments are categorized based on the source characteristics such as peak electric field (also called threat level), frequency coverage or bandwidth, average power density, and energy content. Unintentional sources include increased use of electromagnetic spectrum generating disturbance to systems operating in that frequency band, poor design of systems without considering nearby systems, and lightning. Intentional sources are High?Altitude Electromagnetic Pulse (HEMP) or Nuclear Electromagnetic Pulse (NEMP) due to nuclear detonations, Ultra?Wideband (UWB) fields from Impulse Radiating Antennas (IRA), narrowband fields from High?Power Microwaves (HPM), and High?Intensity Radiated Fields (HIRF). Of these, lightning is natural and all other sources are man?made. The significant progress in intentional HPEM source and antenna technologies and the easy access to simple HPEM systems for anyone necessitate determining the susceptibility of electronic equipment as well as the coupling of these fields with systems such as cables (buried and aerial), airborne vehicles, etc., to these types of threats. Buried cables are widely used in the communication and power sectors due to their efficient functioning in urban cities and towns. These cables are more prone to electromagnetic interference from HPEM sources. The buried communication cables or buried data cables are connected to sensitive equipment, and hence even a slight rise in the voltage or current at the terminals of the equipment can become a serious problem for the smooth operation of the system. In the first part of the thesis, the effect of electromagnetic fields due to these sources on cables laid underground has been studied. The second part of this thesis deals with the study of the interaction of the EM field from the above?mentioned HPEM sources with an airborne vehicle. Airborne vehicles and their payload are extremely expensive so that any destruction to these as a result of the voltages and currents induced on the vehicle on account of the incoming HPEM fields can be quite undesirable. The incoming electromagnetic fields illuminate the vehicle along its axis, resulting in induction of currents and voltages. These currents and voltages get coupled to internal control circuits that are extremely sensitive. If the induced voltage/current magnitude happens to be above the damage threshold level of these circuits, it will result in malfunction or permanent damage, both detrimental to the mission’s success. This may even result in mission abortion or degradation of vehicle performance. Hence, it is worthwhile to study the influence of an incoming HPEM electromagnetic field on the airborne vehicle with and without the presence of an exhaust plume. In this work, the HPEM sources considered are NEMP, IRA, and HPM. The electromagnetic fields produced by the EMP can induce large voltage and current transients in electrical and electronic circuits which can lead to possible malfunction or permanent damage of the systems. The electric field at the earth’s surface can be modelled as a double exponential pulse as per the IEC standard 61000?2?9. The NEMP field incident on the earth’s surface is considered to be from a distant source; hence a plane?wave approximation has been used. Impulse radiating antennas are major sources of ultrawideband radiation. These high?power antennas use a pulsed power source conditioned to obtain an extremely sharp rise?time pulse. The field due to the aperture of the parabolic reflector antenna is computed using aperture distribution methods. The IRA considered is one of the most powerful IRAs reported in literature, with an input voltage of 1.025 MV. The far?field electric field measured at the boresight (at r = 85 m) is 62 kV/m with an uncorrected pulse rise time (10%–90%) of 180 ps. HPM sources are usually electromagnetic radiators with a reflector and a horn antenna. They generally operate in single mode at tens or hundreds of Hz repetition rates. In this thesis, a WR?975 waveguide?fed HPM antenna assembly is studied. The waveguide has a 1 GHz cutoff frequency and power level of 10 GW. The field pattern shows a definite peak at its cutoff frequency of 1 GHz. Electromagnetic fields from HPEM sources propagate with less attenuation in air due to the lower resistance offered for wave propagation. Hence, systems in air will be under strong illumination. In the second part of this thesis, the influence of the fields on an airborne vehicle in flight is analyzed, with and without plume. The plume conductivity is computed based on ionic species present in the exhaust. The induced current is computed using Method of Moments and depends on the interference source, plume properties, and vehicle characteristics. HPM induces the maximum current because plume conductivity is higher at these frequencies. IRA and NEMP follow thereafter. The presence of plume enhances induced current.