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2012-02-14 PIER B Vol. 38, 387-403, 2012. doi:10.2528/PIERB11121313

Modified DOA Estimation Methods with Unknown Source Number Based on Projection Pretransformation

Qing-Chen Zhou, Huotao Gao, Fan Wang, and Jie Shi

In this paper, our purpose is to develop methods that have high resolution and robustness in the presence of unknown source number, array error, snapshot deficient, and low SNR. The DOA (Direction-Of-Arrival) estimation with unknown source number methods referred as MUSIC-like and SSMUSIC-like methods have shown high resolution in the snapshot deficient and low SNR scenario. However, they need to take several times of fine search on the full space, which bring about high computational complexities. Thus, modified methods are proposed to reduce computational complexities and improve performances further. In the modified methods, we priori use conventional beamforming to get the rough distribution of signals' angle, which helps to reduce computational complexity and connect the technique of projection pretransformation. Then through projection pretransformation, original methods are further simplified and improved. As demonstrated in computer simulations, the modified DOA estimation with unknown source number methods shows not only higher resolution in the snapshot deficient and lower SNR scenario, but also more robustness against array errors. Although the proposed methods cannot replace the array calibration completely, they reduce the requirement of calibration accuracy. Combined with these advantages, it has been shown that the new methods are more suitable in engineering.

2012-02-10 PIER B Vol. 38, 367-385, 2012. doi:10.2528/PIERB11111802

Efficient Circular Array Synthesis with a Memetic Differential Evolution Algorithm

Ankush Mandal, Hamim Zafar, Swagatam Das, and Athanassios V. Vasilakos

In this article, we introduce an improved optimization based technique for the synthesis of circular antenna array. The main objective is to achieve minimum side lobe levels, maximum directivity and null control for the non-uniform, planar circular antenna array. The design procedure utilizes an improved variant of a prominent and efficient metaheuristic algorithm of current interest, namely the Differential Evolution (DE). An efficient classical local search technique called Solis Wet's algorithm is incorporated with the competitive Differential Evolution. While the competitive DE is used for the global exploration, Solis Wet's algorithm is employed for local search. Combining the capability of both techniques the hybrid algorithm exhibits improved performance for circular array design problem. Three examples of circular array design problems are considered to illustrate the effectiveness of the hybrid algorithm cDESW (Competiteve Differential Evolution with Solis Wet's technique). The design results obtained using cDESW has comfortably outperformed the results obtained by other state-of-the-art metaheuristics like CLPSO, JADE.

2012-02-09 PIER B Vol. 38, 351-365, 2012. doi:10.2528/PIERB11121407

Towards the Detection of Multiple Reflections in Time-Domain EM Inverse Scattering of Multi-Layered Media

Salvatore Caorsi and Mattia Stasolla

In this paper, a new theoretical approach for the classification of multiple reflections in time-domain e.m.~inverse scattering of multi-layered media is presented. The existence of multiples limits the capabilities of inversion algorithms, thus suitable identification and suppression techniques should be applied to reduce this undesired effect. Assuming a scenario composed of loss-less and non-dispersive media, and providing an accurate time delay estimation (TDE) of backscattered signals, the proposed method allows not only to evaluate the presence of multiples and discriminate them from primary reflections, but also to determine their propagation paths. Preliminary tests performed on FDTD simulated data have shown its potentialities to effectively handle multiple reflections and therefore to enhance the e.m. signals backscattered by primary reflectors.

2012-02-09 PIER B Vol. 38, 333-349, 2012. doi:10.2528/PIERB12011501

Magnetic Force Between Inclined Circular Loops (Lorentz Approach)

Slobodan Babic and Cevdet Akyel

This paper presents a new general formula for calculating the magnetic force between inclined circular loops placed in any desired position. This formula has been derived from the Lorentz force equation. All mathematical procedures are completely described to define the coil positions that lead to a relatively easy method for calculating the magnetic force between inclined circular loops in any desired position. The presented method is easy to understand, numerically suitable and easily applicable for engineers and physicists. The obtained formula is given in its simplest form from the already existing formulas for calculating the magnetic force between inclined circular loops. We validated the new formula through a series of examples, which are presented here.

2012-02-09 PIER B Vol. 38, 315-331, 2012. doi:10.2528/PIERB11122404

A Monopole Microstrip Antenna with Enhanced Dual Band Rejection for UWB Applications

Pramendra Tilanthe, Pramod Chandra Sharma, and T. K. Bandopadhyay

In this paper, a compact, planar ultrawideband (UWB) monopole microstrip antenna is proposed which offers dual band notch characteristics with enhanced rejection at frequency bands centered at 3.4 GHz and 5.5 GHz. To realize enhanced band notched characteristics at 3.4 GHz, a pair of filters is incorporated which includes an inverted `L' shaped slot and a twisted `J' shaped slot in the patch element. Another pair of filters comprises of a spur line filter in the feed line and `U' shaped slot in the patch are used to get a strong frequency band rejection centered at 5.5 GHz. Step by step development of the antenna with its analysis in frequency and time domain is presented. The prototype is fabricated and the measured results are presented which are in close similarity to the simulated results.

2012-02-08 PIER B Vol. 38, 297-314, 2012. doi:10.2528/PIERB11121601

Analysis of Frequency Selective Surfaces for Radar Absorbing Materials

Dharmendra Singh, Abhishek Kumar, Shivram Meena, and Vijaya Agarwala

Nowadays, applications of Frequency Selective Surfaces (FSS) for radar absorbing materials (RAM) are increasing, but it is still a challenge to select a proper FSS for a particular material as well as the dimensions of FSS for optimized absorption. Therefore, in this paper an attempt has been made to optimize the dimensions of FSS for microwave absorbing application using Genetic Algorithm (GA) approach. The considered frequency selective surfaces are composed of conducting patch elements pasted on the ferrite layer. FSS are used for filtration and microwave absorption. In this work, selection and optimization of FSS with radar absorbing material has been done for obtaining the maximum absorption at 8-12 GHz frequency. An equivalent circuit method has been used for the analysis of different FSS, which is further used to design fitness function of GA for optimizing the dimensions of FSS. Eight different available ferrite materials with frequency dependant permittivities and permeabilities have been used as material database. The GA optimization is proposed to select the proper material out of eight available materials with proper dimensions of FSS. The optimized results suggest the material from database and dimensions of FSS. The selected material is then mixed with epoxy and hardener, and coated over the aluminium sheet. Thereafter, all five FSS were fabricated on ferrite coated Al sheets using photolithographic method followed by wet etching. The absorption was measured for all FSS using absorption testing device (ATD) method at X-band. Absorption results showed that significant amount of absorption enhanced with the addition of proper FSS on radar absorbing coating.

2012-02-06 PIER B Vol. 38, 281-296, 2012. doi:10.2528/PIERB11121210

Equivalent Circuit Model of Coaxial Probes for Patch Antennas

Yusheng Hu, Yao Jiang Zhang, and Jun Fan

An equivalent circuit model of coaxial probes is derived directly from the intrinsic via circuit model. As all the higher-order evanescent modes have been included analytically in the parasitic circuit elements, only the propagating mode needs to be considered by the simplest uniform-current model of a coaxial probe in numerical solvers such as finite element method (FEM) or finite difference time domain (FDTD). This avoid dense meshes or sub-gridding techniques and greatly reduces the computational efforts for accurate calculation of the probe input impedance. The derived equivalent circuit model and the new feeding technique have been validated by both analytical formulas and numerical simulations.

2012-01-27 PIER B Vol. 38, 261-279, 2012. doi:10.2528/PIERB11111105

A Flexible Integrated Photonic True Time Delay Phaser for Phased Array Antennas

Amedeo Capozzoli, Claudio Curcio, and Giuseppe D'Elia

An integrated photonic True Time Delay phaser for phased array, based on an innovative technology, is here presented. The module versatility is showed by presenting more driving strategies matching different antenna features. The phaser insertion loss, the fluctuations of the excitation coefficients corresponding to the various driving configurations and the statistical modeling of the realization defects are also discussed.

2012-01-26 PIER B Vol. 38, 241-259, 2012. doi:10.2528/PIERB11121412

Direction of Arrival Estimation for Nonuniform Planar Array Based on Piecewise Interpolation Method

Wael Elshennawy, Ahmed Attiya, , Essam Hashish, and Islam A. Eshrah

The problem of direction-of-arrival (DOA) estimation by using spectral search for a non-uniform planar array is addressed. New search methods for DOA estimation based on piecewise interpolation are proposed. The relationships between these methods and Fourier-Domain (FD) root-MUSIC are discussed. The proposed methods are based on dividing the multiple signal classification (MUSIC) null-spectrum function into a number of equal subintervals. These subintervals are interpolated by using low-degree polynomials. Piecewise interpolation methods based on elementary functions are used to reduce the required computations of MUSIC null-spectrum function. This property reduces the computational complexity compared with line-search methods for DOA estimation. The Cramér Rao Lower Bound (CRB) is used as a benchmark to check the accuracy and validity of the proposed methods.

2012-01-22 PIER B Vol. 38, 225-239, 2012. doi:10.2528/PIERB11121504

Characterization of Open Cell SiC Foam Material

Irena Zivkovic and Axel Murk

This paper presents characterization and modeling of microwave characteristics of SiC foam material. Transmission and reflection measurements are performed in X, K and Ka band for the samples of two different pore sizes and three different thicknesses. Effective and frequency dependent dielectric permittivity is extracted for 50PPI 10 mm sample, while for the other samples it was not possible because of density gradient in the samples. By calculation of Mie scattering efficiencies approximate magnitude of dominant loss mechanism (scattering or absorption) at certain frequencies is predicted.

2012-01-20 PIER B Vol. 38, 205-223, 2012. doi:10.2528/PIERB11102304

Modeling Terahertz Diffuse Scattering from Granular Media Using Radiative Transfer Theory

Kyung M. Nam, Lisa Marie Zurk, and Scott Schecklman

Terahertz (THz) spectroscopy can potentially be used to probe and characterize inhomogeneous materials. However, identification of spectral features from diffuse scattering by inhomogeneous materials has not received much attention until now. In this paper, THz diffuse scattering from granular media is modeled by applying radiative transfer (RT) theory for the first time in THz sensing. The diffuse scattered field from compressed polyethylene (PE) pellets containing steel spheres was measured in both transmission and reflection modes using a THz time domain spectroscopy (THz-TDS) system. The RT model was validated by successfully reproducing qualitative features observed in experimental results. Diffuse intensity from granular media containing lactose was then simulated using RT theory. In the results, spectral features of lactose were observed in the diffuse intensity spectra from the granular media.

2012-01-20 PIER B Vol. 38, 189-203, 2012. doi:10.2528/PIERB11111004

Electromagnetic Interference Impact on Front-End Receivers Outside the Antenna Bandwidth

François Caudron, Achour Ouslimani, Rene Vezinet, and Abed-elhak Kasbari

Impact of electromagnetic interference on front-end receiver behaviour is theoretically and experimentally studied outside the bandwidth of the antennas. Microwave chaotic generation is observed. Under certain conditions, reflected waves combined to the non linearity of the front-end receiver leads to a chaotic signal generation between the antenna and the front-end receiver. Different antennas, such as patch, loop, monopole and horn, are tested. Theoretical and experimental results are presented for each antenna.

2012-01-18 PIER B Vol. 38, 165-188, 2012. doi:10.2528/PIERB11102506

High Frequency Scattering by a Second-Order Generalized Impedance Discontinuity on a Cylindrically Curved Surface

Gokhan Cinar and Alinur Buyukaksoy

The aim of the present paper is to obtain explicit asymptotic expressions for the "transfer (diffraction) coefficients" related to the diffraction of high frequency cylindrical waves from the discontinuity occurred in the material properties as well as in the thicknesses of a coated cylindrically curved metallic sheet characterized by the second order GIBCs. Relying on the locality of the high frequency diffraction phenomenon, the angular interval φ∈(-π;π) is extended to the abstract in nite space φ∈(-∞;∞) wherein the diffracting structure is replaced by a two-part cylindrically curved second order impedance sheet ρ = a extending from φ = -∞ to φ = ∞. The resulting boundary value problem is formulated as a Hilbert equation which is solved asymptotically in the high frequency limit. Some graphical results showing the e ects of various parameters on the transfer coecients are presented.

2012-01-13 PIER B Vol. 38, 135-164, 2012. doi:10.2528/PIERB11111107

Subcell Method for Modeling Metallic Resonators in Metamaterials

Larry Kevin Warne, William A. Johnson, Lorena I. Basilio, William L. Langston, and Michael B. Sinclair

This paper describes a subcell modeling technique for metallic resonators where the actual metal traces are replaced by a thin wire having equivalent magnetic and electric radii, as well as an impedance per unit length. The formulas for these quantities in the case of rectangular traces are given. In addition, the gap of a split-ring resonator is replaced by a lumped load. The response of the resonator can then be modeled using thin-wire algorithms in an integral equation code. It is demonstrated that the number of unknowns and runtime can be reduced by factors of a thousand using the subcell models. This is particularly important in cases where metamaterial designs with tapered properties are encountered and periodic boundary conditions are not applicable, because with this simplification larger numbers of resonator cells can be handled.

2012-01-13 PIER B Vol. 38, 107-134, 2012. doi:10.2528/PIERB11112607

Combining Advances in EM Induction Instrumentation and Inversion Schemes for Uxo Characterization

Charles Oden

Several experimental time-domain EM induction instruments have recently been developed for unexploded ordnance (UXO) detection and characterization that use multiple transmitting and receiving coil combinations. One such system, the US Geological Survey's ALLTEM system, is unique in that it measures both the electro-dynamic response (i.e., induced eddy currents) and the magneto-static response (i.e., induced magnetization). This allows target characterization based on the dyadic polarizability of both responses. This paper examines the numerical response of the ALLTEM instrument due to spheroidal, conductive, and permeable UXO targets; and to conductive and optionally viscous magnetic earth. An inversion scheme is presented for spheroidal targets that incorporates fully polarimetric measurements for both magneto-static and electro-dynamic excitations. The performance of the inversion algorithm is evaluated using both simulated and surveyed data. The results are examined as a function of the number of coil combinations, number of instrument locations, and uncertainty in sensor location and orientation. Results from the specific cases tested (prolate spheroids lying horizontally) show that 1) that collecting data from more than 12 sensor locations or from more than four coil combinations reduced the chances that inversion solutions would be from a local minimum, and 2) that uncertainties in position greater than 3 cm or in orientation greater than 10 degrees cause errors in the estimated spheroid principal lengths of greater than 100%. Soil conductivities less than 1 S/m contribute negligible interference to the target response, but viscous magnetic soils with permeabilities greater than 10-6 MKS units do cause detrimental interference.

2012-01-13 PIER B Vol. 38, 71-105, 2012. doi:10.2528/PIERB11112606

Closed Analytical Formulae for Multi-Pole Magnetic Rings

Udo Ausserlechner

Multi-pole permanent magnetic encoders are used for wheel speed sensing in automotive systems. This paper discusses rings and discs magnetized along axial direction. The vector field is calculated analytically in 3D as sums over all poles. For the case of discs with vanishing inner and infinite outer diameter the summation is done in closed form with a new summation formula. The results are discussed and several plots of field patterns are given in normalized form: At very small air-gap the field shows an overshoot. At moderate and large air-gaps it is a sine-function with exponentially decaying amplitude. The amplitude versus air gap, reading radius, thickness of the magnetic layer, and number of poles is studied and excellent agreement with measurements is found. The effect of a steel-back on the field is explained. It is also shown how to maximize the torque transmitted in axially magnetized couplings.

2012-01-11 PIER B Vol. 38, 57-70, 2012. doi:10.2528/PIERB11102505

Reconfigurable Fishnet Metamaterial Using Pneumatic Actuation

Iryna Khodasevych, Wayne Rowe, and Arnan Mitchell

The design, fabrication and measurement of a reconfigurable fishnet metamaterial based on a new method of tuning by changing unit cell geometry is reported. Retractable elements are added to the unit cell utilizing pneumatically actuated switching. It is shown that the pneumatic actuation approach can unite a number of metallic elements into a complex conducting structure. Experimental demonstration confirms that the structure operates at two different frequencies in the GHz range in distinct actuation states. The measured results also show good agreement with numerical simulations.

2012-01-09 PIER B Vol. 38, 39-56, 2012. doi:10.2528/PIERB11120510

Improved Shift-Operator FDTD Method for Anisotropic Magnetized COLD Plasmas with Arbitrary Magnetic Field Declination

Xiong Yin, Hou Zhang, Hai-Yang Xu, and Xian-Feng Zeng

In this paper, a recently improved SO-FDTD (shift-operator finite difference time-domain) method is proposed and applied to the numerical analysis of the anisotropic magnetized plasma with arbitrary magnetic declination. By using the constitutive relation between polarized current density vector J and electric vector E and bringing the shift operators, the difference iteration equations of field components for Maxwell equations are derived in detail. Furthermore, the memory requirement is decreased significantly through incorporating a memory-minimized algorithm into the FDTD iterative cycles. The reflection and transmission coefficients of electromagnetic wave through a magnetized plasma layer are calculated by using this method. It is shown that the new method not only improves accuracy but also produces speed and memory advantages over the SO-FDTD method in kDB coordinates system proposed in the recent reference. In addition, the recursion formulae of the improved SO-FDTD method are deduced and programmed easily and they involve no complex variables, so the computations for the magnetized plasma become very simple.

2012-01-09 PIER B Vol. 38, 23-37, 2012. doi:10.2528/PIERB11112202

"Natural" Definition of the Modal Impedances in Non-Homogeneous Dielectric Loaded Rectangular Waveguide

Leonardo Zappelli

In this paper, the definition of the modal impedances of the electromagnetic field in a nonhomogeneously filled waveguide is discussed. The presence of TM modal impedances, which are functions of the transverse coordinate, does not permit us to obtain a unique Z matrix of these guides. Hence, the evaluation of the scattering matrix can be involved. The introduction of a {``natural" EM} expansion overcomes this problem leading to the definition of a unique modal impedance and a unique Z matrix. This approach is applied to the simulation of the effect of a block of dielectric in an empty waveguide by ``cascading" the $S$ matrices of the existing junctions. Finally, this {``natural" EM} expansion is applied to the junction between an empty waveguide and a completely filled waveguide, obtaining an equivalent circuit which better represents the physics of this problem, and to the optical fibers.

2012-01-08 PIER B Vol. 38, 1-22, 2012. doi:10.2528/PIERB11112111

Computationally Efficient Model for UWB Signal Attenuation Due to Propagation in Tissue for Biomedical Implants

Paul Theilmann, M. Ali Tassoudji, E. Harrison Teague, Donald F. Kimball, and Peter M. Asbeck

An analytical model which predicts the attenuation of ultrawide-band (UWB) signals as they traverse various inhomogeneous tissues is presented. The model provides a computationally efficient method of determining the frequency-dependent losses encountered by electromagnetic radio frequency (RF) signals used to communicate with biomedical implants. Classic transmission line theory is employed to generate an analytical representation which models the inhomogeneous tissue using layers of homogeneous material. The proposed model was verified experimentally with tests of both single and multilayer samples. A realistic abdominal implant scenario was also modeled and the predictions were verified using a commercially available 3D electromagnetic (EM) simulator. The results of this study indicate that for deep implants the higher frequency portion of the UWB spectrum is attenuated much more strongly than the lower end of the band. This implies that for robust communication UWB signals targeting biomedical implants should be limited to the lower portion of the spectrum.