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2019-04-09 PIER Vol. 164, 155-166, 2019. doi:10.2528/PIER18101703

Decoupling of Two Closely Located Dipoles by a Single Passive Scatterer for Ultra-High Field MRI

Masoud Sharifian Mazraeh Mollaei, Sergei Alexandrovich Kurdjumov, Anna Hurshkainen, and Constantin Rufovich Simovski

We report decoupling of two closely located resonant dipole antennas dedicated for ultra-high field magnetic resonance imaging (MRI). We show that a scatterer slightly raised over the plane of antennas grants a sufficient decoupling even for antennas separated by very small gap (below 1/30 of the wavelength). We compare the operations of two decoupling scatterers. One of them is a shortcut resonant dipole, and the other is a split-loop resonator (SLR). Previously, we have shown that the SLR offers a wider operational band than the dipole and the same level of decoupling. However, it was so for an array in free space. The presence of the body phantom drastically changes the decoupling conditions. Moreover, the requirement to minimize the parasitic scattering from the decoupling element into the body makes the decoupling dipole much more advantageous than the SLR.

2019-04-01 PIER Vol. 164, 135-153, 2019. doi:10.2528/PIER18102402

Gains Maximization via Impedance Matching Networks for Wireless Power Transfer

Qinghua Wang, Wenquan Che, Marco Dionigi, Franco Mastri, Mauro Mongiardo, and Giuseppina Monti

Wireless Power Transfer (WPT) based on resonant magnetic coupling is an attractive technology for enabling the wireless recharge of electric devices and systems. One of the main drawbacks of this technology is related to the dependence of the efficiency and the power delivered to the load on possible variations of the coupling coefficient and load impedance. In order to alleviate the effects of this dependence, the optimization of appropriate adaptive matching networks is proposed in this paper. The three power gains usually adopted in the context of two-port active networks are assumed as figures of merit in the optimization process. It is theoretically and experimentally demonstrated that the maximum realizable gain of the link is achieved when the conjugate image impedance matching is realized by appropriate matching networks at both the input and output ports of the WPT link.

2019-03-20 PIER Vol. 164, 119-133, 2019. doi:10.2528/PIER18121803

A Numerical Kirchhoff Simulator for GNSS-R Land Applications

Weihui Gu, Haokui Xu, and Leung Tsang

A distinct feature of GNSS-R land reflectometry is that random rough surfaces are superimposed on many levels of elevations. The rms elevations are in tens of meters which are many times larger than the microwave wavelengths at GNSS frequencies. Such multiple elevations were not considered in the coherent model nor the incoherent model. In this paper, we studied the electromagnetic scattering of this new rough surface scattering problem using Kirchhoff integral as first-principle. A numerical Kirchhoff simulator is developed to calculate the electromagnetic scattering and the power ratio in the specular direction. The integration is carried out over a footprint of 10 km by 10 km with the specular point as the center. In integration the surface discretization is as small as 2cm by 2 cm so that a total of 2.5×1011 patches are used. Parallel computing is implemented requiring a moderate amount of computer resources. The results of the power ratio of the numerical Kirchhoff simulator differ from the results of both the coherent model and incoherent model. The results show that the phase of the first Fresnel zone is random, and the power contributed by the first Fresnel zone is a small fraction of that over the 10 km by 10 km. The power ratios of the numerical Kirchhoff simulations are much larger than that of the incoherent model and smaller than the coherent model for small RMS heights. The results show that the multiple elevations in land have large effects on GNSS-R specular reflections.

2019-03-19 PIER Vol. 164, 109-118, 2019. doi:10.2528/PIER18120502

Broadband Plasmonic Circuitry Enabled by Channel Domino Spoof Plasmons

Liangliang Liu, Li Ran, Huadong Guo, Xinlei Chen, and Zhuo Li

Building of compact plasmonic integrated circuits based on domino spoof plasmons (DSPs) is an important requirement and still a challenge. In this work, we report the first demonstration of two kinds of channel domino plasmonic circuitries, which consist of an easy-to-manufacture periodic chain of metallic box-shaped elements inside two finite metallic plates. We reveal that only the channel DSPs itself rather than the hybrid TE10 and DSPs modes is supported in the part of the channel domino plasmonic waveguide with or without the metallic vias on both sides. Two channel domino plasmonic filters based on the efficient transition structures are designed, and the simulated S-parameters and near electric field distributions show excellent transmission performance in broadband. Utilizing the lateral insensitive property of these two channel DSPs, two kinds of broadband plasmonic power dividers/combiners are firstly implemented. Excellent transmission performance validates our optimizations and indicates that the proposed scheme can be easily extended to other bands. This work provides a new route for construction of deep-subwavelength DSP devices in application of high integration of microwave and terahertz circuits.

2019-03-06 PIER Vol. 164, 97-107, 2019. doi:10.2528/PIER18120408

Internal Magnetic Induction Tomography Using a Single Coil

Joe R. Feldkamp and Stephen Quirk

Most imaging modalities image an object's interior while all instrumentation, including sources and receivers, is externally located. One notable exception is ultra-sound (US), which can be miniaturized sufficiently to locate a US transducer within an object and gather data for image reconstruction. Another is cross-borehole geophysical imaging. The goal of any internal imaging modality is to provide images of greater fldelity while avoiding interfering structures. Due to the bulkiness of multi-coil magnetic induction tomography (MIT), transmitting and receiving coils are never placed within small targets (e.g., a human body). Here, we demonstrate a novel implementation of single-coil MIT that performs a scan all while the coil is located within the interior of a small, lab-created phantom consisting of salt-doped agarose. Phantom geometry is annular, consisting of a 6.0 cm diameter channel of depth 5.5 cm surrounded by a 3.0 cm thick cylindrical wall. A centrally located agarose gel annulus, 2.0 cm thick, is doped with sucient NaCl to elevate its conductivity above that of surrounding agarose. The resulting nearly axisymmetric phantoms consist of material having conductivity ranging from 0.11 to 10.55 S/m. A scan is accomplished robotically, with the coil stub-mounted on the positioning head of a 3-axis controller that positions the planar circular loop coil into 360 or 720 pre-programmed internal positions. Image reconstruction from gathered data is shown to correctly reveal the location, size and conductivity of the approximately axisymmetric inclusion.

2019-03-06 PIER Vol. 164, 75-95, 2019. doi:10.2528/PIER18102903

Broadband Green’S Function with Higher Order Low Wavenumber Extractions for an Inhomogeneous Waveguide with Irregular Shape

Tien-Hao Liao, Kung-Hau Ding, and Leung Tsang

The method of broadband Green's functions with low wavenumber extractions (BBGFL) is used to calculate Green's function for inhomogeneous waveguides filled with different dielectrics and with irregular boundaries. To construct the BBGFL modal solutions, we derive governing equations of the linear eigen-matrix problem and orthonormalization condition. In BBGFL, the Green's function is represented in modal expansions with convergence accelerated by higher order low wavenumber extractions. To obtain a linear eigenvalue problem for the modes, we use two BBGFLs of rectangular waveguides with two dielectric wavenumbers. The orthonormalized mode functions are used to construct the Green's function. Current wavenumber derivatives and Green's function wavenumber derivatives are computed by a single low wavenumber MoM impedance matrix. The wavenumber derivatives are used to accelerate the convergence of modal summations to 6th order. Numerical results are illustrated and compared with the direct MoM method of using free space Green's function. Results show accuracies and computation efficiencies for broadband simulations of Green's functions.

2019-01-28 PIER Vol. 164, 63-74, 2019. doi:10.2528/PIER18102001

Efficient Broadband Evaluations of Lattice Green's Functions via Imaginary Wavenumber Components Extractions

Shurun Tan and Leung Tsang

A novel and systematic method is developed to evaluate periodic Green's functions on empty lattices through extractions of an imaginary wavenumber component of the lattice Green's function and its associated derivatives. We consider cases of volumetric periodicity where the dimensionality of the periodicity has the same dimensionality as the physical problem. This includes one-dimensional (1D) problem with 1D periodicity, two-dimensional (2D) problem with 2D periodicity, and three-dimensional (3D) problem with 3D periodicity, respectively. The remainder of the Green's function is put in spectral series with high-order power-law convergence rates, while the extracted imaginary wavenumber parts are put in spatial series with super-fast and close-to exponential convergence rate. The formulation is free of transcendental functions and thus simple in implementation. It is especially efficient for broadband evaluations of the Green's function as the spatial series are defined on fixed wavenumbers that take small CPU to compute, and the spectral series have simple and separable wavenumber dependences. Keeping only a few terms in both the spatial and spectral series, results of the lattice Green's function are in good agreement with benchmark solutions in 1D, 2D, and 3D, respectively, demonstrating the high accuracy and computational efficiency of the proposed method. The proposed method can be readily generalized to deal with Green's functions including arbitrary periodic scatterers.

2019-01-23 PIER Vol. 164, 27-61, 2019. doi:10.2528/PIER18112810

On the Convergence of Numerical Computations for Both Exact and Approximate Solutions for Electromagnetic Scattering by Nonspherical Dielectric Particles (Invited Review)

Ping Yang, Jiachen Ding, Richard Lee Panetta, Kuo-Nan Liou, George Kattawar, and Michael I. Mishchenko

We summarize the size parameter range of the applicability of four lightscattering computational methods for nonspheric dielectric particles. These methods include two exact methods - the extended boundary condition method (EBCM) and the invariant imbedding T-matrix method (II-TM) and two approximate approaches - the physical-geometric optics method (PGOM) and the improved geometric optics method (IGOM). For spheroids, the single-scattering properties computed by EBCM and II-TM agree for size parameters up to 150, and the comparison gives us confidence in using IITM as a benchmark for size parameters up to 150 for other geometries (e.g., hexagonal columns) because the applicability of II-TM with respect to particle shape is generic, as demonstrated in our previous studies involving a complex aggregate. This study demonstrates the convergence of the exact II-TM and approximate PGOM solutions for the complete set of single-scattering properties of a nonspherical shape other than spheroids and circular cylinders with particle sizes of ~48λ, specifically a hexagonal column with a size parameter of length as kL=300, where k=2π/λ and L is the column length. IGOM is also quite accurate except near the exact 180º backscattering direction. This study demonstrates that a synergetic combination of the numerically-exact II-TM and the approximate PGOM can seamlessly cover the entire size parameter range of practical interest. To demonstrate the applicability of the approach, we compute the optical properties of dust particles with a downstream application to the retrieval of dust aerosol optical thickness and effective particle size from polarimetric observations.

2019-01-08 PIER Vol. 164, 17-25, 2019. doi:10.2528/PIER18061804

Design and Experimental Validation of Multifunction Antenna with Direct Modulation for Radar and Communication

Samir Ouedraogo, Israel David Hinostroza Sáenz, Régis Guinvarc'h, and Raphael Gillard

A multifunction antenna system providing a radar function and a communication function simultaneously is proposed. The system is composed of a horn antenna whose feeding waveguide is loaded with slots. The horn radiation is used for the main radar function. The slotted waveguide radiation is controlled independently from the horn radiation to perform a direct binary phase shift keying (BPSK) communication provided that each radiating slot is equipped with a simple switching mechanism. Then, the antenna system provides two different functions using orthogonal polarizations and directions. Measured results show 9.1 dB and 32 dB isolation between the two functions at the working frequency. In addition, the proposed system can be integrated with the existing radars which use horns by replacing only the feeding waveguide.

2018-11-20 PIER Vol. 164, 1-15, 2019. doi:10.2528/PIER18071704

A Method for Effective Permittivity and Conductivity Mapping of Biological Scenarios via Segmented Contrast Source Inversion

Martina Bevacqua, Gennaro G. Bellizzi, Tommaso Isernia, and Lorenzo Crocco

Quantitative estimation of both conductivity and permittivity of biological tissues is essential in many biomedical applications, ranging from therapeutic treatments to safety assessment of medical devices and dosimetry. Typically, the electromagnetic field distribution inside the body is predicted based on available ex-vivo measured electrical properties. Unfortunately, these values may be quite different from the ones measured in-vivo and cannot account for the differences among individuals. As a result, their use can introduce significant errors affecting therapeutic treatments and dose estimation. To cope with this problem, in this paper a new approach for estimation of effective electrical properties of human tissues is introduced. The proposed strategy is based on the solution of an inverse scattering problem (by means of a contrast source inversion scheme) and the use of an effective representation of the unknowns based on spatial priors derived by magnetic resonance imaging or computed tomography. The approach is tested in controlled conditions against simulated single frequency data and realistic and anthropomorphic head and neck phantoms. Moreover, the inherent advantages have been assessed in the framework of hyperthermia treatment planning.