R.E. Diaz

Arizona State University, Phoenix, Arizona, United States

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Publications (39)39.83 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 08/2014; 62(8):4381-4386. DOI:10.1109/TAP.2014.2323435 · 2.18 Impact Factor
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    ABSTRACT: This paper studies the challenging problem of detecting a low radar cross-section target in heavy sea clutter by proposing a physics-based sea clutter generation model. The model includes a process that generates random dynamic sea clutter based on the governing physics of water gravity and capillary waves and a finite-difference time-domain electromagnetics simulations process based on Maxwells equations propagating the radar signal. A subspace clutter suppression detector is considered to remove dominant clutter eigenmodes. The improved detection performance over matched filtering is demonstrated using sea clutter model simulations.
    ICASSP 2014 - 2014 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP); 05/2014
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    R E Diaz · T Sebastian
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    ABSTRACT: The viability of a radiofrequency (RF) telemetry channel for reporting individual neuron activity wirelessly from an embedded antenna to an external receiver is determined. Comparing the power at the transmitting antenna required for the desired Channel Capacity, to the maximum power that this antenna can dissipate in the body without altering or damaging surrounding tissue reveals the severe penalty incurred by miniaturization of the antenna. Using both Specific Absorption Rate (SAR) and thermal damage limits as constraints, and 300 Kbps as the required capacity for telemetry streams 100 ms in duration, the model shows that conventional antennas smaller than 0.1 mm could not support human neuronal telemetry to a remote receiver (1 m away.) Reducing the antenna to 10 microns in size to enable the monitoring of single human neuron signals to a receiver at the surface of the head would require operating with a channel capacity of only 0.3 bps.
    Scientific Reports 12/2013; 3:3535. DOI:10.1038/srep03535 · 5.58 Impact Factor
  • A.H. Panaretos · Rodolfo 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 10/2013; 61(10):5333-5338. DOI:10.1109/TAP.2013.2271311 · 2.18 Impact Factor
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    ABSTRACT: In this paper we demonstrate an efficient conformal broadband dipole antenna made of a lossy magneto-dielectric material. A closed form expression of the radiation efficiency of such a dipole is given which is derived using Schelkunoff's electrically small antenna model and the duality principle. The efficiency equation includes both complex permeability (μ r = μ'-j μ") and permittivity (ε r = ε'-jε") of the magneto-dielectric. A prototypical antenna is fabricated using commercially available NiZn ferrite tiles. The measured performance is shown to be better than a non-conformal conventional whip antenna.
    IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting, Orlando, Florida, USA; 07/2013
  • Zhe Zhang · Derrick Lim · Rodolfo E. Diaz
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    ABSTRACT: We present a quasi-static model of the electromagnetic interaction between dipolar emitting molecule and a Plasmon-metal nano-sphere. Based on the image theory of dielectric sphere, we model the Plasmon nano-spheres by off-centered dipole images. The retardation effect is taken into account by electrodynamical modifications on spherical polarizability and dipole radiation field. The modifications of the radiative rate, total decay rate and the quantum yield for the molecules are derived. The image model indicates the strong distance dependence of the enhancement on both radiative and total decay rates. The comparison with the exact electrodynamical model and other simplified models indicate that the off-center image provide accurate predictions on radiative and total decay rates, even in close distances.
    Proceedings of SPIE - The International Society for Optical Engineering 02/2013; 8595:08-. DOI:10.1117/12.2004164 · 0.20 Impact Factor
  • Tom Sebastian · Sergio A. Clavijo · Rodolfo E. Diaz
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    ABSTRACT: It is shown using full-wave simulations that several of the conventional assumptions made for extracting permeability data from a microstrip permeameter are not justified. In particular, the proportionality between the measured effective permeability in the device and the true permeability of the film is not a constant. It is a function of the permeability of the film, its geometry and the dimensions of the microstrip permeameter. A model exploiting the analyticity of the function relating effective to true permeability is used to derive this proportionality function for our device and the results are confirmed using full-wave simulations. The error incurred by not using this method and employing a reference sample for calibration or by using saturation magnetization “Ms” and anisotropy field “Ha” is shown to be anywhere between 5% and 40% and possibly even more. Our measurement set up is capable of measuring films as thin as 300 nm with a relative permeability as low as 10.
    Journal of Applied Physics 01/2013; 113(3). DOI:10.1063/1.4776715 · 2.18 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.
  • 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. DOI:10.1109/LMWC.2011.2136374 · 1.70 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; DOI:10.1109/TMTT.2008.921656 · 2.24 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.
  • Anastasios H. Panaretos · James T. Aberle · Rodolfo E. Díaz
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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 11/2007; 227(1-227):513-536. DOI:10.1016/j.jcp.2007.08.019 · 2.43 Impact Factor
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    S.A. Clavijo · R.E. Diaz · Eric Caswell
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    ABSTRACT: The goal of this investigation is to obtain mount-independent low profile, tunable antenna operation over VHF and UHF with an omni-directional azimuth radiation pattern for both line-of-sight (LoS) and SATCOM functions thus replacing multiple antennas (including an 8 foot long whip) on current Marine Corps vehicles. The baseline form-factor was an annular slot antenna (ASA) 24" times24" times2.5" with the UHF antenna integrated into the center disk of the ASA. The VHF antenna was to be tunable across two bands of operation, 30 - 88 MHz and 136 - 174 MHz. Thus, at the low end of the band the antenna is extremely small electrically: lambda/14 in diameter and lambda/143 in depth.
    Antennas and Propagation Society International Symposium, 2007 IEEE; 07/2007
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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; 54(12-54):4237 - 4246. DOI:10.1109/TMTT.2006.885900 · 2.24 Impact Factor
  • A. H. Panaretos · R. E. Diaz · J. T. Aberle
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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.
  • S.A. Clavijo · R.E. Diaz
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    ABSTRACT: The EMM of an AMC, reported in (S. A. Clavijo et al, IEEE Trans. Ant. Prop., vol.51, p.2678-2690, 2003), is implemented in FDTD, which allows us to demonstrate the validity of the model. This is done by verifying its surface wave bandwidth. With this model implemented in FDTD then the AMC can easily be treated as a material and its interactions with antennas and other materials can be modeled. Also, the effect of its finiteness can be easily assessed.
    Antennas and Propagation Society International Symposium, 2005 IEEE; 08/2005
  • Rodolfo E. Diaz · Sergio A. Clavijo
    Encyclopedia of RF and Microwave Engineering, 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 02/2005; 203(1):176-190. DOI:10.1016/j.jcp.2004.08.011 · 2.43 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; DOI:10.1109/MAP.2004.1296162 · 1.32 Impact Factor

Publication Stats

377 Citations
39.83 Total Impact Points


  • 1998–2014
    • Arizona State University
      • • Department of Electrical Engineering
      • • School of Electrical, Computer and Energy Engineering
      • • Department of Mechanical Engineering
      Phoenix, Arizona, 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