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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 raft, 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 raft. Tolerable current is bonded for Lagrange's equations. Index Terms--Lagrange's equations, optimization, railgun, 2-D finite-element method (FEM).

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. Index Terms--Formula, inductance gradient, intelligent estimation method (IEM), interpolation function, railgun.

When the tissue is changing from normal to abnormal, the distribution of tissue liquids between intra 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. Index Terms--Current distribution, finite element analysis (FEA), normal and malignant bladder tissue.

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. Index Terms--Current density, finite-element method (FEM), inductance gradient, railgun.

The aim of this paper is proposing a new fast designing method for planar graphene leaky‐wave antennas without periodical changes. Thus, Floquet theory cannot be used for designing, an optimization in numerical EM solver is needed. Since leaky‐wave antennas are electrically long, their simulation using commercial EM simulators needs a large number of meshes, also the optimization of the large number of parameters (slot lengths and their distances) needs huge amount of memory and computation time. To resolve this problem, the method of Moments, implemented in MATLAB, which has been accelerated by applying some techniques, has been used in the design procedure. The antenna comprises a slotted graphene micro ribbon with a specific pattern, which is placed on two dielectric substrates and a PEC reflector. Graphene is used in the proposed LWA, instead of the electric conductor, because of its wonderful properties. The suitable pattern of slots on the graphene microstrip, is obtained using optimization by MATLAB Genetic algorithm tool. The usefulness and performance of the proposed designing approach, is verified in one example. It has been shown that the presented antenna, compared with one of the new successful similar antennas, has a better gain, radiation efficiency, and a wider range of beam scanning. [ABSTRACT FROM AUTHOR]

A new reconfigurable band-notched ultra-wideband (UWB) dielectric resonator antenna (DRA) has been designed and fabricated for cognitive radio (CR) applications. The UWB antenna design comprises a dielectric resonator as a radiation element, a ground plane, and a microstrip feed line. The frequency band's rejection mechanism is achieved by cutting two slots and adding an L-shaped stub on the ground plane. The reconfigurable function is created by PIN diode switches to change the current distribution path on the ground plane. A preliminary model of the DRA was fabricated, and its efficiency was verified. The proposed antenna occupies an area of 40 × 40 × 7.3 mm. The simulated and measured results have demonstrated suitable radiation patterns attained by the proposed antenna, which operates within the UWB frequency range of 3–11 GHz. Moreover, the antenna has shown an ability by rejecting switchable bands to achieve the WiMAX (3.2–3.65 GHz), WLAN 5 GHz (4.8–6 GHz), and ITU 8 GHz (8–8.3 GHz). Also, this antenna can be operated as dual and triple band-notched antennas. [ABSTRACT FROM AUTHOR]

A new ultra-wideband (UWB) dielectric resonator antenna (DRA) integrated with a reconfigurable narrowband (NB) antenna is designed and analyzed for cognitive radio (CR) applications. The UWB antenna consists of a rectangular dielectric resonator which is fed by a microstrip line. The NB antenna composes of a rectangular ring patch and three stubs which is fed by a microstrip line. The UWB and reconfigurable NB antennas provide 2:1 VSWR bandwidth from 3 to 11 GHz and from (3.25 to 3.7 GHz, 5.5 to 6.5 GHz, and 8 to 8.4 GHz), respectively. There is a reasonable isolation between the antennas. The narrowband reconfigurability is achieved by two p-i-n diode switches within the antenna structure. A prototype of the integrated antenna was fabricated and its performance was verified. The dimensions of the antenna are 65 mm × 40 mm × 6.5 mm. The antenna represents good radiation characteristics. Also, in order to reduce mutual coupling, the space between the ground planes is 10 mm. [ABSTRACT FROM AUTHOR]

This paper presents a new analytical method based on mode matching technique for a waveguide full of anisotropic material with rods. It is proved that mode matching technique is applicable for the waveguide with anisotropic materials. The problem is considered as a 2D electromagnetic problem assuming no field variation normal to the waveguide length. Incident and scattered fields from circular cylinder rods in ferrite medium are expanded with cylindrical modes, and the fields in the waveguide ports are expanded using progressive and regressive modal summations. In both regions, extraordinary wave number is considered for the fields. Finally, the hybrid mode matching between guided and cylindrical modes is done by projecting continuity equations in the circular boundary containing the rod. The fast Fourier transform is used to solve the matching in the presented method. It is shown, that the new method runs faster than commercial software packages, with very good accuracy. [ABSTRACT FROM AUTHOR]