We consider the accuracy improvement of the high frequency scattered fields from 3-D convex scatterers. The Fock currents from the convex scatterers are carefully studied. Furthermore, we propose the numerical contour deformation method to calculate the Fock currents with frequency independent workload and error controllable accuracy. Then, by adopting the Fock currents and the incremental length diffraction coefficient (ILDC) technique, the scattered fields are clearly formulated. Compared to physical optics (PO) scattered fields from 3-D convex sphere, numerical results demonstrate significant accuracy enhancement of the scattered field via the Fock current approach.
This paper presents non-coil sources to improve the wireless power transfer efficiency for implantable device used in various medical applications --- cardiovascular devices, endoscope in the small intestine, and neurostimulator in the brain. For each application, a bound on the power transfer efficiency and the optimal source achieving such bound are analytically solved. The results reveal that depending on the depth of the implantable devices, power can be transferred to a sub-millimeter scaled receiver with the efficiency ranging from -57 dB to -33 dB, which is up to 6.6 times higher than the performance of existing coil-based source systems. The technique introduced in this paper can be broadly applied to other medical applications.
In this paper, a 79 GHz microstrip antenna subarray, optimized for operation in a Phase Modulated Continuous Wave (PMCW) MIMO radar demonstrator is presented. The antenna combines all necessary features for this very specific type of applications. First of all, the spillover between transmit and receive channels in such a system is reduced by the combined effect of a microvia cage and the arraying of two elements. Second, it shows a wide band of 13.5%. Third, a wide beam in the E-plane (136 degrees), necessary for scanning, and a much smaller beamwidth in H-plane (36 degrees), advantageous to reduce mutual coupling, are realized. Finally, it has been fabricated with the advanced so-called ``Any-Layer'' technology. This technology is as accurate as other advanced technologies in the millimeter wave bands, but at a much lower cost, and thus very suited for mass production. The gain and radiation efficiency were simulated to be 7.27 dBi and 83%, respectively.
We aim to estimate the average dielectric properties of centimeter-scale volumes of biological tissues. A variety of approaches to measurement of dielectric properties of materials at microwave frequencies have been demonstrated in the literature and in practice. However, existing methods are not suitable for noninvasive measurement of in vivo biological tissues due to high property contrast with air, and the need to conform with the shape of the human body. To overcome this, a method of antenna calibration has been adapted and developed for use with an antenna system designed for biomedical applications, allowing for the estimation of permittivity and conductivity. This technique requires only two calibration procedures and does not require any special manufactured components. Simulated and measured results are presented between 3 to 8 GHz for materials with properties expected in biological tissues. Error bounds and an analysis of sources of error are provided.
In this conceptual study, all-optical amplification of the light pulses in two weakly coupled nonlinear photonic crystal waveguides (PCWs) is proposed. We consider two adjacent PCWs, which consist of line defects in a 2D square lattice of periodically distributed circular rods made from dielectric material with Kerr-type nonlinearity. Dispersion diagrams of the PCW's symmetric and antisymmetric modes are analyzed using a recently developed analytical formulation. The operating frequency is properly chosen to be located at the edge of the PCW's dispersion diagram (i.e. adjacent to the photonic crystals low-energy band edge), where in the linear case no propagation modes are excited. However, in case of a nonlinear medium when the amplitude of the injected signal is above some threshold value, solitons are formed propagating inside the coupled nonlinear PCWs. The near field distributions of the propagating light pulse inside the coupled nonlinear PCWs and the output power of the received signal are numerically studied in a detail. A very good agreement between the analytic soliton solution based on the nonlinear Schrödinger equation and numerical result is obtained. Amplification coefficients are calculated for the various amplitudes of the input signals. The results vividly demonstrate the effectiveness of the weakly coupled nonlinear PCWs as an all-optical digital amplifier.
The radiation characteristics of a cylindrical array antenna for Multifunction Phased Array Radar (MPAR) and Terminal MPAR (TMPAR) applications are presented. A probe-fed stacked microstrip patch antenna is used for array elements. In calculations, the embedded element pattern of the patch antenna is obtained by simulation of a 5×5 element planar array. The radiation pattern of the TMPAR- and MPAR-sized cylindrical array antenna is calculated using the coherent addition method which is veried with full-wave simulation. For cross-polarization suppression, the array elements are arranged with identical 2×2 element subarrays. The radiation patterns of MPAR and TMPAR cylindrical array antennas with and without image conguration are calculated and compared. It is shown that the low cross-polarization level and azimuthally scan invariant beam characteristics can be achieved by the cylindrical array with image arrangement.
A new approach for position and shape reconstruction of both penetrable and impenetrable objects from the measurements of the scattered fields is introduced and described. The approach takes advantage of the fact that for perfect electric conductors the induced currents are localized on the boundary, and equivalent sources also placed on the surface of the scatterers can be considered in the case of dielectric targets by virtue of the equivalence theorem. Starting from these considerations, a new inversion approach is formulated in order to retrieve the location and the boundary of unknown objects. Examples with both numerical and experimental data are given to demonstrate and assess the effectiveness of the method.
Diffraction tomography (DT) from limited projection data has been an active research topic for over three decades. The interest has been steadily fueled due to its application in multiple disciplines including medical imaging, structural health monitoring and non-destructive evaluation to name a few. This paper explores the applicability of compressed sensing to recover complex-valued objective functions (e.g., complex permittivity in microwave tomography). Generally, compressed sensing based tomographic reconstruction has been studied under full angular access. In this paper, the effect of lowering the angular access in addition to highly limited number of projection data is explored. The effectiveness of the reconstruction methods is tested with severely limited dataset which would render reconstruction impossible by traditional iterative approximation methods. Furthermore, results show that complex-valued phantoms can be reconstructed from as few as 15 projections from 120˚ coverage, a significant finding. In this study, the Total Variation (TV) has been used as the l1 norm within the compressed sensing framework. The robustness of the algorithm in presence of noise is discussed. Use of multiple sparse domains has also been explored briefly. The results show the effectiveness of TV as a regularization parameter even for complex-valued images under the compressed sensing regime. This is a pertinent observation as TV is a simple norm to implement. For a large class of images, especially in medical imaging, this implies the availability of a steady l1 norm for easy implementation of compressed sensing reconstruction for complex-valued images.
In this paper we develop a higher order extraction method to accelerate the convergence in the computation of broadband Green's function for an arbitrary shaped waveguide. This is applied to a homogeneous waveguide of arbitrary shape. The broadband Green's function is based on modal expansion in which the modal fields are frequency independent. The higher order extraction is obtained by using three low wavenumbers for extraction. It gives a modal expansion of Broadband Green's Function with Low Wavenumber Extraction (BBGFL) with 6th order convergence requiring much fewer evanescent modes for convergence. Numerical results are illustrated for homogeneous waveguides for both lossless and lossy dielectric cases. The accuracy of results are validated with direct method of moment (MoM) and HFSS. The BBGFL method is computationally efficient for broadband simulations.
By reductio ad absurdum, we show that a perfect power combiner of single-mode waveguides is impossible for incoherent input waves of the same frequency and same polarization as it is against the law of conservation of energy. The inevitable 3 dB loss of a three-port power combiner is explained physically. An incoherent power combiner of nearly 100% efficiency can be realized only if the two input fields have different wavelengths, have different polarizations, or are of orthogonal modes.