R.E. Diaz

Arizona State University, Mesa, AZ, United States

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Publications (32)32.59 Total impact

  • A.H. Panaretos, R.E. Diaz
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    ABSTRACT: A computational formulation is presented for the low frequency single-cell finite-difference time-domain (FDTD) modeling of nanospheres. The methodology is developed based on the observation that the electrostatic field inside a dielectric sphere is similar in nature to that of an FDTD cell, or equivalently by considering the electromagnetic correspondence between the single electric field component across an FDTD cell edge, and the electric dipole moment induced in an electrically small dielectric sphere when the latter is excited by a plane wave. By rigorously applying effective medium theory the physical existence of a subcell dielectric sphere in the FDTD grid is translated into an equivalent material, characterized by an effective permittivity that obeys the Clausius-Mossotti (CM) mixing rule, appropriately defined across the cell edge parallel to the excitation plane wave. A circuit based methodology is devised that allows to easily incorporate the effective medium representation of a subcell dispersive dielectric sphere into FDTD update equations. The theoretically derived results are supported by numerical experiments.
    IEEE Transactions on Antennas and Propagation 01/2014; 62(8):4381-4386. · 2.33 Impact Factor
  • A.H. Panaretos, R.E. Diaz
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    ABSTRACT: A computational formulation is presented for the low frequency single-cell finite-difference time-domain (FDTD) modeling of a perfectly electric conducting (PEC) sphere. The approach is based on the fact that the scattered field from electrically small objects can be expressed in terms of an electric and magnetic dipole. These dipoles can be decomposed with respect to the dipole moments that can be defined along the discrete field components that comprise the cell wherein the PEC sphere is inscribed. The dipole moment components couple to each other, and this mechanism is quantified by a quasi analytical coupled dipole approximation (CDA). The quasi-analyticity requires to substitute the involved dyadic Green's function (DGF) terms, in the CDA formula, by their numerically computed, FDTD compatible, equivalents. The material properties of the equivalent electric and magnetic spheres are derived using the quasi-analytical CDA that leads to expressions that resemble the Claussius-Mossotti mixing formula. The theoretically derived results are supported by numerical simulations.
    IEEE Transactions on Antennas and Propagation 01/2013; 61(10):5333-5338. · 2.33 Impact Factor
  • A. H. Panaretos, R. E. Diaz
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    ABSTRACT: A subcell model is presented that mimics the low frequency response of a Drude nanosphere. The approach is based on the observation that the inclusion of a dielectric sphere into a finite-difference time-domain cell requires to appropriately tailor the cell 鈂s material properties utilizing an effective medium approach. A circuit based methodology is employed that allows to easily incorporate the effective medium model in the finite-difference time-domain method. The theoretically derived results are supported by numerical experiments.
    01/2011;
  • A.H. Panaretos, R.E. Diaz
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    ABSTRACT: The stability analysis is presented for the finite-difference time-domain modeling of a Lorentz dielectric. In particular this study is focused on the Young scheme that employs the polarizability and the polarization current for the representation of the Lorentz permittivity, and collocates temporally the magnetic field with the polarization current. The Routh criterion is employed for the stability limit determination. The necessary conditions that ensure stability are thoroughly derived for the general as well as for limiting cases.
    IEEE Microwave and Wireless Components Letters 01/2011; 21(6):283-285. · 1.78 Impact Factor
  • A.H. Panaretos, R.E. Diaz
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    ABSTRACT: We have demonstrated the importance of the group velocity in the case of dispersion optimized FDTD schemes. Our observations constitute a very useful guideline for practical applications, where reliable FDTD results are required over a frequency bandwidth.
    Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE; 08/2008
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    A.H. Panaretos, R.E. Diaz
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    ABSTRACT: A two-stage simple and accurate methodology is presented for the dispersion error minimization of parameter-dependent finite-difference time-domain schemes over a useful bandwidth. The methodology is rigorously developed for both 2-D and 3-D schemes. First, the anisotropy error is treated by expanding the spatial part of the numerical dispersion relation in a cosine-Fourier series, and eliminating the contribution of the angle-dependent terms. The dispersion error is then corrected by employing a modified single-frequency accurate temporal finite-difference operator. This modification can be translated into the parameters of the updating equations, which greatly simplifies its programming. The theoretically derived results are further supported by numerical experiments.
    IEEE Transactions on Microwave Theory and Techniques 06/2008; · 2.23 Impact Factor
  • A. H. Panaretos, R. E. Diaz
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    ABSTRACT: Numerical modeling of silver cylinders is examined using the finite-difference time-domain (FDTD) technique.Numerical experiments are performed and the scattering cross section of a single cylinder is predicted and compared to the analytical solution. It is demonstrated how the coarseness of the model can affect the quality of the results. The same experiments are performed in the case of an array consisting of three cylinders. The response of the structure is examined, and the significance of the cell size for the accurate prediction of the plasmon resonance red shift is demonstrated.
    01/2008;
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    ABSTRACT: In this paper, a three-dimensional finite-difference time-domain (FDTD) scheme is presented with improved isotropy characteristics and higher Courant number than the standard Yee scheme. The basic idea is to transversely extend the curl operator in order to improve the transverse Laplacian representation of the curl-curl operator. A stability analysis is performed, and the dispersion characteristics of the proposed scheme are investigated. It is shown that the latter is significantly more isotropic than the regular FDTD scheme. Additionally, it is proved that under certain conditions a unity Courant number can be achieved, and the resulting scheme is characterized by dispersion characteristics complementary to those of the regular FDTD scheme. Numerical simulations are performed that validate the theoretically derived results
    IEEE Transactions on Microwave Theory and Techniques 01/2007; · 2.23 Impact Factor
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    ABSTRACT: A sixth order isotropic FDTD algorithm has been described. The algorithm can be of great importance in cases where high global isotropy is required such as radiation and cavity related problems. The algorithm is also very attractive for single frequency problems where dispersion can be easily eliminated by introducing correcting artificial material dispersion.
    01/2007;
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    ABSTRACT: The behavior of the finite-difference time-domain method (FDTD) is investigated with respect to the approximation of the two-dimensional Laplacian, associated with the curl–curl operator. Our analysis begins from the observation that in a two-dimensional space the Yee algorithm approximates the Laplacian operator via a strongly anisotropic 5-point approximation. It is demonstrated that with the aid of a transversely extended-curl operator any 9-point Laplacian can be mapped onto FDTD update equations. Our analysis shows that the mapping of an isotropic Laplacian approximation results in an isotropic and less dispersive FDTD scheme. The properties of the extended curl are further explored and it is proved that a unity Courant number can be achieved without the resulting scheme suffering from grid decoupling. Additionally, the case of a 25-point isotropic Laplacian is examined and it is shown that the corresponding scheme is fourth order accurate in space and exhibits isotropy up to sixth order. Representative numerical simulations are performed that validate the theoretically derived results.
    Journal of Computational Physics 01/2007; · 2.14 Impact Factor
  • Rodolfo E. Diaz, Sergio A. Clavijo
    04/2005; , ISBN: 9780471654506
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    Rodolfo E. Diaz, Igor. Scherbatko
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    ABSTRACT: In [Electromagnetics 23 (2003) 187], a technique for injecting perfect plane waves into finite regions of space in FDTD was reported. The essence of the technique, called Field Teleportation, is to invoke the principle of equivalent sources using FDTDs discrete definition of the curl to copy any field propagating in one FDTD domain to a finite region of another domain. In this paper, we apply this technique of Field Teleportation to the original domain itself to create a transparent boundary across which any outward traveling FDTD field produces an exact negative copy of itself. When this copied field is teleported one cell ahead and one cell forward in time it causes significant self-cancelation of the original field. Illustrative experiments in two-dimensions show that a two-layer (10-cell thick) multi-stack Radiation Boundary Condition (RBC) with a simplest Huygens’s termination readily yields reflection coefficients of the order of −80 dB up to grazing incidence for all the fields radiated by a harmonic point source (λ=30 cells) in free space located 20 cells away from the boundary. Similarly low levels of artificial reflection are demonstrated for a case in which the RBC cuts through five different magnetodielectric materials.
    Journal of Computational Physics 01/2005; 203(1):176-190. · 2.14 Impact Factor
  • R.E. Diaz, I. Scherbatko
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    ABSTRACT: The fundamental properties of a new re-radiating boundary condition (rRBC) for terminating the grid in the finite-difference time-domain (FDTD) method are examined. It is shown that because it is based on the field teleportation principle of [M.E. Watts et al., February-March 2003], this rRBC generates exact negative copies of the outgoing time-domain fields in FDTD, independently of the angle of incidence, polarization, field impedance, or material properties. The effect of the rRBC is to differentiate the outgoing signal and reduce it approximately by a factor of 10 in the time domain. Several rRBC boundaries can be stacked, one after the other, to continually decrease the level of the outgoing signal. Termination of the rRBC stack with a one cell Huygen's condition further reduces the signal, and minimizes the integration feedback as the faint echoes cross backwards through the rRBCs. It is shown that the net result is a boundary that is more efficient than a PML of similar total thickness (especially at shallow angles of incidence) and is trivial to program, requiring no special treatment for corners or material properties.
    IEEE Antennas and Propagation Magazine 03/2004; · 1.18 Impact Factor
  • I. Scherbatko, R. Diaz
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    ABSTRACT: Not Available
    Mathematical Methods in Electromagnetic Theory, 2004. 10th International Conference on; 02/2004
  • R. Diaz, I. Scherbatko
    [Show abstract] [Hide abstract]
    ABSTRACT: A technique for injecting perfect plane waves into finite regions of space in FDTD has been reported. The essence of the technique, called field teleportation, is to invoke the principle of equivalent sources using FDTD's discrete definition of the curl to copy any field propagating in one FDTD domain to a finite region of another domain. In this paper we apply this technique of field teleportation to the original domain itself to create a boundary across which any outward traveling FDTD field produces an exact negative copy of itself. Repeated application of this radiation boundary and termination of the domain with a moderate absorbing boundary condition readily yields reflection coefficients of the order of -80 dB up to grazing incidence onto the boundary.
    Microwave Symposium Digest, 2003 IEEE MTT-S International; 07/2003
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    ABSTRACT: This paper presents the theoretical design of an artificial dielectric exhibiting narrowband frequency selective properties in the bulk without relying on periodic placement of elements. In this manner, it initiates a novel approach that bypasses the drawbacks of the traditional frequency selective surfaces (FSS), namely, unwanted passbands, dependence on excitation angle and polarization, and difficulties in conversion from planar to curved geometries. The key design elements are the concentric geometry of the inclusions and the use of Lorentzian resonant media. A discussion of physical resonant materials is presented, substantiating the credibility of the theoretical design. To illustrate the approach, a novel complex medium is synthesized as an ensemble of spherical particles composed of a lossy core coated with a highly resonant dielectric layer and embedded into a dielectric host. The resulting structure is an amorphous substance, lossy over its entire spectrum except for two narrow-band transparency windows, where it may become as lossless as desired. The parameter space of the system is thoroughly analyzed which determines the type of constitutive materials and geometries for tailor-designing the windows according to specifications (shape, positioning and overall normalization). In this sense, the lossy concentric structure forms an ideal candidate for thin absorbing films (TAFs) with extensive applications in antenna systems, RF absorbers, and anechoic chambers
    IEEE Transactions on Antennas and Propagation 02/2000; · 2.33 Impact Factor
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    ABSTRACT: This paper presents the application of nonempirical effective medium theories to describe composite mixtures of spherical inclusions within a host continuum. It is shown that the most common effective medium theories collapse into Bruggeman's (1935) asymmetric formula when they are implemented in an iterative scheme to extend their validity to higher volume fractions. Comparisons of DC and 4-GHz data show that of all the formulas Bruggeman's asymmetric formula corresponds best with experiment for large differences between the complex permittivities of the host and inclusion materials. Permeability values are also formulated and compared with experiment and a simple scheme is considered to extend the effective medium theories herein to a description of the diamagnetic effect of induced current in metal spherical inclusions
    IEEE Transactions on Antennas and Propagation 02/1999; · 2.33 Impact Factor
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    ABSTRACT: Synthetic materials in which new electromagnetic properties are obtained from the combination of two or more materials have been of theoretical and practical interest for nearly a century. The ability to explain and predict the properties of these materials has traditionally relied on combining physicomathematical models of the effective environment seen by the various constituents of the mixture with some assumptions about the way these microscopic properties should translate into macroscopic homogeneous parameters. Thus, even in the simplest case of the binary mixture, with every new set of assumptions, a new effective medium theory (EMT) results, and, with each new theory, stronger claims of correctness and applicability are made. This issue of correctness becomes critical when the properties of one of the constituents is unknown a priori and the claim is made that by inverting a fit of experimental results to the EMT model those properties can be ascertained. For this inverse procedure to be possible, the EMT theory should not only be correct, it should be unique in the analytic sense. In this article, a generalized framework is developed through which the analytic properties of all binary mixture EMTs can be deduced and compared. In the process it is shown that in the complex plane of the variable u = i/(ϵeff−1), it is straightforward to separate the morphology dependent properties of the EMT from its dependence on the susceptibilities of the components. The frequency dependence of the EMT model as a function of the arbitrary complex properties of the filler is easily summarized as a compact sum of the poles of a complex function. This process is demonstrated for a number of common EMTs. © 1998 American Institute of Physics.
    Journal of Applied Physics 12/1998; 84(12):6815-6826. · 2.21 Impact Factor
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    ABSTRACT: We present an alternative vector potential formulation of Maxwell's equations derived upon introduction of a quantity related to the Hertz potential. Once space and time are discretized, within this formulation the electric field and vector potential components are condensed in the same point in the elementary cell. In three dimensions the formulation offers an alternative to finite-difference time-domain (FDTD) method; when reduced to a two-dimensional (2-D) problem, only two variables, instead of three, are necessary, implying a net memory saving of 1/3 with respect to FDTD
    IEEE Microwave and Guided Wave Letters 10/1998;
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    ABSTRACT: We present the design of a dispersive medium with a permittivity regime less than unity and investigate the radiation characteristics of elementary printed antennas within such a grounded substrate. The study is motivated by the possibility of minimization or elimination of surface waves in this permittivity region irrespective of the substrate thickness. The novel material is resynthesized as an amorphous ensemble of spherical particles composed of a low-loss dielectric core coated with a highly resonant dielectric layer and embedded into a dielectric host. The resulting complex structure is transparent over its entire spectrum except of two narrow-band opaque windows of adjustable depth, shape and positioning. The effective permittivity function is obtained according to the classical theory of effective media and exhibits a characteristic region with the real permittivity function ε<sup>r </sup><sub>eff</sub><1. We discuss the non-local but causal character of wave propagation in this permittivity region and examine the application of the novel medium in printed circuit antennas. A horizontal elementary microstrip dipole is pieced on a grounded substrate layer composed of this complex medium. The radiation pattern is examined within the region ε<sup>r</sup><sub>eff</sub><1 as a function of the constitutive media parameters and the of the inclusions geometry
    Antennas and Propagation Society International Symposium, 1998. IEEE; 07/1998

Publication Stats

188 Citations
32.59 Total Impact Points

Institutions

  • 1998–2008
    • Arizona State University
      • • School of Electrical, Computer and Energy Engineering
      • • Department of Mechanical Engineering
      Mesa, AZ, United States
    • University of California, Irvine
      • Department of Electrical Engineering and Computer Science
      Irvine, CA, United States
  • 1997–2000
    • University of California, Los Angeles
      • Department of Electrical Engineering
      Los Angeles, CA, United States
    • Northrop Grumman
      Falls Church, Virginia, United States