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One of the best methods to protect electronic circuits against high-altitude electromagnetic pulse (HEMP) is using a metallic shield enclosure, which usually has apertures and slots for venting and passing power and data cables. In this article, we investigate the effect of the rise time of HEMP-like pulses on time-domain shielding effectiveness (TD-SE). The rise time of the electromagnetic pulse is one of the essential characteristics that depend on the mechanism of pulse production in pulse generators. Since the dimensions and location of aperture, the wall thickness of enclosure, and the enclosure dimension are important factors in coupling the electromagnetic pulse with circuits inside the enclosure shield, the effect of these factors on TD-SE will be checked. Finite difference delay modeling (FDDM) is used as a new method in the computation of transient field in perforated metallic enclosure and SE. Results of FDDM is verified by comparing with finite integration technique (FIT) method results (CST-Microwave Studio). [ABSTRACT FROM AUTHOR]

High-power electromagnetic (HPEM) pulse affects electronic devices that have linear/nonlinear characteristics. To protect the electronic circuit board, the use of metallic enclosure as an electromagnetic shield is one of the best methods. Apertures and slots in the body of metallic enclosure is the path of coupling HPEM fields to electronic board and equipment. In this article, we are following to evaluate the effect of HPEM fields on the microstrip line with nonlinear load that is enclosed by perforated metallic enclosure. For this purpose, a method has been proposed that uses the benefits of the time domain analysis and frequency domain analysis. The whole electromagnetic system of the problem is decomposed into linear and nonlinear subsystems. Thevenin’s equivalent circuit of the linear subsystem from the connection point to nonlinear load has been evaluated by using finite difference delay modeling (FDDM) in the frequency domain. By vector fitting method and by using rational functions, Thevenin’s equivalent circuit is converted to circuits with RLC elements and the time domain voltage source. This circuit can be analyzed in Spice. Results obtained from this model are well adopted with those that are calculated by CST-Microwave studio for linear and nonlinear load and have better time efficiency. [ABSTRACT FROM AUTHOR]

With the advancement of the electromagnetic (EM) launcher and the idea of the launch of smart equipment by railgun, one cannot ignore the EM compatibility issues of the railgun. Large acceleration values, varying strong magnetic and electric fields and the existence of electric arcs specialized EM launchers. Future applications of railguns include the launch of small satellites or launch of smart meteorological parts to space. Such applications necessarily involve the acceleration of complex electronic circuitry and a reliable communication channel to the outer world. Moreover, during the accelerating run of the railgun, the radiated EM fields can compromise the life of electronic devices, can influence the signal to noise ratio, and can generate electrical shock. The short duration pulse signal, such as a current pulse of the railgun, switching and arcing between components of railgun is typically rich in frequency spectral contents. All these effects might affect any electronic circuitry that the projectile is being equipped with. It should be noted that the propulsive force of the current pulse in each time push the armature in motion direction and changes the parameters of the railgun. As a result, the strong EM field varies versus time. In this study, it is investigated the magnetic field from the current pulse in the environment of the railgun by considering the change in armature position and it is discussed about the best location of the electronic equipment inside the barrel. Furthermore, the presence of the earth as a good conductor near railgun can affect the EM fields around it. In this study, the effect of the earth on the fields, which is due to the transient flow of current, is obtained theoretically. The calculations done by using the Maxwell equations and image theory have shown that the earth presence can affect the performance of noise-sensitive equipment. [ABSTRACT FROM AUTHOR]

A novel augmented railgun using multilayer magnets and sabots is proposed in this paper, in which the rails have dc constant currents. Using dc constant currents for the rails generates the constant acceleration for the projectile. The augmentation with multilayer permanent magnets increases the length of passing current, which improves the railgun efficiency. Furthermore, the proposed railgun does not require the high power supplies because each sabot carries only low current. In addition, the iron structure has been located at the top and bottom of the whole structure to produce a homogeneous magnetic field. Accurate analytical expressions have been derived for the Lorentz force and the velocity of the proposed structure in this paper. The railgun structure has been simulated in Maxwell software for various rail currents, and the analytical results have good agreement with simulation results. The amplitude of the Lorentz force in the z-direction has been calculated for various sabot materials to investigate the effect of the sabot materials on the performance of the railgun. Our results indicate that the velocity of the projectile can achieve to 300 m/s for the projectile mass of 2 kg in our proposed railgun. This makes the railgun a good candidate for the heavy projectiles in the launcher technology. [ABSTRACT FROM AUTHOR]

Electromagnetic force on rails of railgun is the effective factor which impacts on input current pulse, rails and armature geometry, dimensions, and materials. This paper investigates how the stimulated current form affects the electromagnetic force on rails. A transient analysis with a finite-element method is discussed to simulate a 3-D railgun in this paper. In the first section, we consider the effect of flat-top length of stimulated current pulse on electromagnetic force distribution on rail and armature velocities. In the second section, we consider the effect of stimulated currents that have the same areas but have various amplitudes and flat-top lengths and at the last section, the flat-top length and amplitude of current are exactly the same, but the flat-top part replaces during time. Consequences are shown in several figures. [ABSTRACT FROM AUTHOR]

Nowadays lunching masses to faraway distances is an important issue. One of important electromagnetic launcher for this purpose is duble-projectil railgun because it can launch synchronously two separated projectiles. It has been obtained before that two-turn railgun have better inductance gradient and performance than simple railgun. Also, self-inductance gradient and mutual-inductance gradient in two-turn railgun depend on the initial position of armatures. In this paper, we want to calculate the inductance gradient of a new structure that we named it plus railgun. The plus railgun has one barrel between two-pair rails by two separated armatures and two pairs of rails are powered by one pulse power at the same time. A 3-D finite-element method is applied to the transient analysis of the magnetic field, current distribution, and the inductance gradient of railguns. Finally, we will compare the parameters of two-turn and plus railguns. [ABSTRACT FROM PUBLISHER]

Electromagnetic (EM) interference and its suppression are one of the major issues in most current systems design. The electric device such as railgun generates the EM fields that unintentionally propagate away from the structure. Railgun that have significant amounts of radiated emissions may interfere with the normal operation of other devices in close proximity. Also during the accelerating run of rail launchers, and particularly during the ignition of the armature, the radiated EM fields can compromise the life of electronic devices, can influence the signal to noise ratio, and can generate electrical shock hazard. The short duration pulse signal, such as current pulse of railgun, switching and arcing between components of railgun is typically rich in frequency spectral contents. It should be noted that the propulsive force of current pulse in each time push the armature in motion direction and change the propagation parameters of railgun as a time varying antenna and can affect on the radiation pattern in the various frequency ranges. Furthermore, in each component of current pulse, armature is in special position in direction of motion along the barrel and the impedance of railgun that power source see in front is different with previous stage and radiation pattern is different too. In this paper, the relationship between pulse form of input current and electric field around railgun are analyzed and simulated with finite-element method, then by attention of the armature position in each time it will be investigated the radiation pattern of railgun. [ABSTRACT FROM PUBLISHER]

This paper proposed a railgun with sector of circular rails. The center of the sector of circular rails is located at the outside of the railgun bore. The distance between the sectors of two circles is s , opening angle facing outward \theta , the inner and outer radius are also assumed to be Ri and Ro , respectively. The influence of internal curvature of the rails, the rail thickness and the distance between rails on the current density, magnetic flux density, and inductance gradient ( L' ) have been studied and analyzed using finite-element method. First of all, the different values of \theta , s , , and R_{o} are calculated for various values of the area of the railgun bore ( S_{C}) and cross section of the rails ( SR) . The current density, magnetic flux density, and L' have been calculated for different values. The area of the railgun bore is assumed to be 9 and 10 cm ^2 and the area of rails are assumed to be 9, 6, 3, and 1 cm ^2 . In next section, L' is found as a function of s , Ri , and Ro for \theta =90 ^\circ , 120°, 150°, and 180°. Finally, $L'$ is compute for rail thickness equals to one-tenth of bore size and $\theta $ on the interval [180°, 360°]. According to the achieved results it can be observed the behavior of $L'$ in terms of railgun dimensions changes and it is compared with other geometries. [ABSTRACT FROM PUBLISHER]

The electromagnetic force on rails is one of the most important factors that restrict the improvement of railgun performance by deforming, damaging, and reducing its life span. This force is generated by the current flowing through the rail and a magnetic field that is established in the space between the rails that acts as an outward mutually repulsive load. For decreasing the electromagnetic force on rails, we have a few options, such as changing the geometry and dimension of the armature and rails or changing the stimulated current. This paper has two parts. In the first part, we defined graded laminated armature, in which the electrical resistivity of each lamination is constant but different from that of other laminations in the whole armature. In the second part, laminated rails with various electrical resistivities and homogenous rectangular cube armatures are considered. The purpose of the calculation is to find a suitable assembly of conductors to form a laminated armature and rails to decrease the electromagnetic force on rails and obtain an appropriate performance for railgun. It is shown that we can decrease the maximum electromagnetic force on rails with rail’s resistivity change and investigate an appropriate resistivity profile to increase armature muzzle velocity. The results are significant for the design and optimization of the railgun. [ABSTRACT FROM PUBLISHER]

In this paper, the railgun is assumed to be an antenna and simulated with the finite element method (FEM) and the finite difference time domain (FDTD) method. For FEM analysis, the caliber of the railgun is 10\,\times\,10 mm, rail thickness is 10 mm, and rail length is 400 mm. At first, the H-field on the cross section of the rails is computed. Next, power radiation and the maximum value of the E-field in the near and far field are obtained as a function of frequency. Polar radiation patterns versus frequency (1 kHz-1 MHz) in the near and far-field regions are calculated as a function of the angle. For FDTD, we assume that the railgun operates in the far-field region, and radiation patterns are computed in this region. The caliber of the railgun is 15\,\times\,19 mm, rail thickness is 10 mm, and length is 1000 mm. Directivity has been computed versus frequency (100 Hz-1 MHz) in the far-field region. The H-field is calculated versus frequency and the energy is computed as a function of time. For both methods, the railgun included copper rails and an aluminum projectile. [ABSTRACT FROM PUBLISHER]

The use of a multiturn railgun is a method for decreasing the current without reducing the electromagnetic force on the projectile. The objective of this paper is to study a novel multiturn railgun that can launch several separated projectiles launching synchronously or asynchronously. In addition to distributing the force on the projectiles, this method prepares the projectiles to be launched in time. The railgun has two barrels stacked in series and is powered by one pulse power supply. In this paper, by using a finite-element method, we simulate a 3-D railgun. The projectiles are in different positions. It is investigated by obtaining the self-inductance gradient and mutual inductance gradient for each position of armatures by which time of launch can be regulated through changing the configuration of the launcher. In addition, we explore how the launching time is directly proportional to the propulsive force, their relation and its limitation by the rails and armatures geometry, armatures initial positions, and armatures mass and material. Finally, with simulation results, we conclude that a two-turn railgun has a higher effective inductance gradient than a simple railgun. [ABSTRACT FROM PUBLISHER]

Two different geometries of the rail in an electromagnetic launcher are rectangular and circular. In this paper, rectangular and circular railguns are simulated and compared using the finite-element method. Rectangular and circular railguns are formed by two parallel copper rails. The surface area of the railgun bore is 9 cm^2 and the surface area of the rail cross-section is 6 and 18 cm^2. Current distribution (J), magnetic field intensity (H), and inductance gradient (L^\prime) are computed for the two aforementioned bore geometries, and the results are compared together. In the circular railgun, L^\prime is a function of the opening angle of the rails (\theta), inner radius (Ri), and outer radius (Ro). Different values for \theta, Ri, and Ro, in practical range, are used to compute L^\prime. By analyzing the numerical and theoretical results, it can be shown that the magnetic flux density in the middle of the circular railgun is a descending function according to the central angle. Finally, strengths and weaknesses of the rectangular railgun in comparison with the circular railgun are discussed. [ABSTRACT FROM PUBLISHER]

Thermal energy in railgun is unwanted and generated by ohmic losses that are dependent to the current implied, rail dimensions, electrical conductivity (\sigma), and specific heat (CP). \sigma and CP are functions of temperature. Using achievement L^\prime formula by intelligent estimation method, the current density and ohmic losses on the cross section of the rail are computed. Ohmic losses are the source heat and utilized heat equation that are used to compute thermal distribution and temperature that are compared with other results in some papers. This paper chose h = 30\ \mm, w = 10\ \mm, and copper for the rail material and a method to compute the thermal distribution on the surface of the rail and side rail edges. Effects of rail dimensions on the temperature in time domain are calculated and shown in the figures. Rail materials are investigated with copper and aluminum in which the average temperature of both materials on the rail surface is calculated and compared. [ABSTRACT FROM AUTHOR]

The intelligent estimation method (IEM) is based on approximations which can be described by the configuration and behavioral characteristic of the problem. This paper used the IEM in time domain (IEM-TD) which can be utilized to predict the current distribution and maximum current density. A detailed IEM technique to compute the current distribution over the surface of a rail, current profile around the rail, and maximum current density ( J\max) formula will be presented in this paper. The current distribution is computed for rectangular and circular rails that are shown in color figures. Finally, this paper considers the effect of the rail dimensions and material on these parameters that are shown in several figures. The results of this paper are compared to other published studies and FEM simulation. [ABSTRACT FROM AUTHOR]

The inductance gradient is one of the important parameters on the design and evaluation of railgun performance. The size, shape, and material of rails have effects on the inductance gradient. In 2-D analysis, the length of rails assumed to be infinite and then the effect of the armature ignored and a constant inductance gradient is obtained. In 3-D simulations, with assuming a fixed position for the armature (usually in the middle of rail), the inductance gradient can be determined. However, with the moving of the armature along rail length and the increasing of the current path, the applied force on the projectile will be different when it is constant and in the middle of the structure. Therefore, inductance gradient in the structure length will be changed. In this paper, with considering a railgun with copper rails with 1-m length, according to the input current and the resultant force of the aluminum armature in the rail length it was displaced in every step, the inductance gradient was determined. The results show that the amount of inductance gradient is not constant and will be increased with armature movement toward the muzzle. [ABSTRACT FROM AUTHOR]

The increasing of projectile final velocity and the uniformity of current density in the special regions of the armature and rail such as the root of the armature which is in melting are some of the purposes of the railgun design. In railgun, the applied force to run an armature is resulted from the interaction of the current passing from the armature with the magnetic field in that place. Therefore, to increase the running force and gain bigger projectile velocities, we have to increase the input current or the magnetic field between two rails per a constant current. The increasing of input current can cause more heat losses in the structure of the railgun and may cause failing of the projectile procedure because of the melting of some points of the armature or rail. High magnetic fields between rails without input stimulation increasing are possible with the application of the geometrical and structural variations in rails. The current paths in rails will be closer to each other (increasing the amount of magnetic fields between them), and so, narrowing the rail using a constant current, the current density will be bigger in the cross section of the rail. We will evaluate the effect of rail narrowing in the projectile path length with consideration of a rail length of 1 m. The narrowing procedure of the rail is defined as decreasing its cross section in the projectile path length until, in the output gate, its amount reaches zero (the height of the rail is constant). The result of simulation shows that the gradient inductance will be increased with the narrowing of the cross section of the rail in the projectile path length, and this will increase the amount of the final projectile velocity. [ABSTRACT FROM AUTHOR]

One of the methods that are used for increasing accelerator force of projectile in the railgun is the increasing of inductance gradient. Essentially, the inductance gradient is determined by current density in rails and projectile. If we change geometry of the rail, the current density and inductance gradient will be changed. One of the factors that restricts variation domain of rails geometry is the tolerable current of rails. In this paper, we have obtained analytical formulas for the maximum current density and the inductance gradient in terms of rail dimensions using the results that have been obtained by 2-D finite-element method. By these formulas and Lagrange's optimization equations, we determined the optimum dimensions of rail. Tolerable current is bonded for Lagrange's equations. [ABSTRACT FROM AUTHOR]

The efficiency of a railgun can be defined as the exchanged transferred electrical energy to the kinetic energy of the armature. According to the good relation between the applied force to the armature and the inductance gradient (L′), the importance of this parameter calculation is obviously clear. There are several researchers who calculated L′ using different numerical and analytical methods in these years. The analytical method to solve the simple problems is suitable, and numerical methods include sufficient coding time and programmer performance time. A method will be introduced in this paper to extract a formula or formulas of L′ using structural railgun parameters which can cause the results similar to the results of the numerical methods. This method has not any time problem, and so, there is a good accuracy of data analysis. In this technique, which is called intelligent estimation method, according to the behavior of the railgun magnetism and its geometrical structure, an equation with unknown multiplications for L′ formula is defined. Then, by applying the reported data in different studies for L′, these equations can be found. Finally, the proposed method introduces a closed formula for a given structure of railgun. A rectangular configuration is investigated as a case study in this paper. [ABSTRACT FROM AUTHOR]

When the tissue is changing from normal to abnormal, the distribution of tissue liquids between ultra and extra cellular space will be changed and then the measured conductivity and impedivity will also be changed. Therefore, it will cause a different current distribution inside the human bladder tissue in normal and malignant cases. By knowing the amount of electrical impedance inside the bladder tissue and the morphological parameters of the different layers of this tissue, the current distribution inside the bladder tissue (surface fluid, superficial urothelium, intermediate urothelium, basal urothelium, basement membrane, and connective tissue) was modelled and calculated in different frequencies using the finite element analysis. The model results showed that very little of the current actually flows through the urothelium and much of the injected current flows through the connective tissue beneath the urothelium (in normal cases). However, most of the current flows through the surface fluid in the low frequency range in normal tissue. Furthermore, for the high frequencies, the tight junctions are short-circuited, so the current penetrates deeper, flowing through the connective tissue beneath the urothelium, while, in the malignant cases, at least 50% of the injected current flows beneath transformed urothelium across the frequency range modelled. [ABSTRACT FROM AUTHOR]

The railgun is one of the most important electromagnetic launchers that can accelerate a projectile to hypervelocity. Current distribution in railgun structure is the effective factor that determines its efficiency. Current density is affected by rails and armature geometry and dimensions. This paper investigates how the rails dimensions and spaces affect the current density distribution, magnetic flux density, and inductance gradient (L'). L' plays an important role in the performance of an electromagnetic launcher (EML), and it determines directly the force that accelerate projectile. Finally, L' for various dimensions are tabulated and compared with values obtained from other methods. A finite-element method is discussed to simulate a two-dimensional railgun in this study. [ABSTRACT FROM AUTHOR]