This paper introduces a tensorial analysis of networks (TAN) applied to a tree asymmetrical structure. To illustrate the TAN concept easily, the present investigation is applied to a three-port structure represented by a Y-tree topology. The unfamiliar method of TAN circuit modelling is elaborated from the graph topology. The fast formulation of the Y-matrix model of the structure is established from branch and mesh space TAN analyses. The TAN model is validated with commercial tool simulation and measurements from DC up to 0.5 GHz in the frequency domain and two different waveform signals in the time domain. The proof of concept circuit is implemented in microstrip technology on an FR4-epoxy dielectric substrate. Mapping sensitivity analysis with respect to the Y-tree RLC-parameters is realized by showing that local variations around initial set of R, L, and C do not equally influence reflection and transmission coefficients over the frequency bandwidth. If a similar impact is observed at the lowest frequency, maximum variations up to 250% show the importance of parameters ranking to improve both microstrip design and modelling.
We provide an explicit geometric generalisation of the antenna current Green's function (ACGF) formalism from the perfect electric conducting (PEC) to generic coupled N-body systems composed of arbitrarily shaped coupled PEC and dielectric objects, with the main emphasis on the mathematical foundations and the rigorous construction of the Green's function using distributional limits. Starting from mainly reciprocity, surface equivalence theorems, and other typical regularity conditions, we carefully construct the current Green's function by employing a combination of methods including Riemannian geometry, distribution theory, and functional analysis. The formalism outlined here for composite domains turns out to be more complicated than the PEC-only formulation due to the former's need to explicitly account for the coupling interaction between the magnetic and electric degrees of freedom. The approach is developed for extremely general systems, and use is made of Riemannian geometry to avoid working with specific or concrete configurations, hence retaining high generality in our final conclusions. While the ACGF tensor's matrix representations depend on the coordinate system on the manifolds supporting the electromagnetic boundary conditions, we focus here on providing coordinate-independent integral expressions for the induced current. With the ACGF it is possible to theoretically treat arbitrary N-body coupled PEC-dielectric configurations as space-frequency linear systems with an exact and rigorous response function being the current Green's function itself. While the derivation is very general, it still leaves open questions regarding whether the ACGF can be constructed for nonreciprocal systems or using volume integral equations.
A problem of electromagnetic wave diffraction by a longitudinal slot cut in a waveguide wide wall is solved by a generalized method of induced electro-magneto-motive forces (EMMF). The slot radiates in a half-space above a perfectly conducting plane where two vertical impedance monopoles are arbitrarily located. To control electrodynamic characteristics of the radiator, a passive impedance monopole is placed in the waveguide. The paper is aimed at the study of the electrodynamic characteristics of waveguide vibrator-slot structures, analogous to the known Clavin element, with two identical impedance monopoles on both sides of the narrow half-wave slot. The influence of the geometric structure parameters on the directional characteristic of Clavin type element: relative level of sidelobes in the E-plane and the RP width differences in the main polarization plane at 3 dB level was analyzed. It was shown that the directional and energy characteristics of the radiators: radiation and reflection coefficients, antenna directivity, and gain can be varied within wide limits by changing the electrical length and/or distributed surface impedance of the vibrators.
In this paper we show a procedure to measure the impedance mismatch of antennas by exploiting the Time Domain (TD) option available in usual VNAs. The procedure can be applied even in the presence of reflecting obstacles in the measurement scenario surrounding the antenna under test (AUT). It is shown that effective application of the procedure requires to fulfill a reduced number of constraints basically involving the distance of the AUT from the nearest obstacle, the response resolution to be set through the TD option of the VNA, and the length of the gating aperture to be applied to the received signal. The proposed measurement procedure is in principle applicable to any antenna. However, it is very easy and advantageous for antennas having short responses in the time domain, such as horn antennas, where the method can likely be applied to frequencies less than 500 MHz. Comparison between the results obtained from measurements performed inside an anechoic chamber (that is, in the absence of reflecting obstacles around the AUT), outside the anechoic chamber, and even inside a reverberation chamber, demonstrate the effectiveness of the proposed measurement procedure.
With the increasing number of mobile phone users, new services and mobile applications, the proliferation of radio antennas has raised concerns about human exposure to electromagnetic waves. This is now a challenging topic to many stakeholders such as local authorities, mobile phone operators, citizen, and consumer groups. Thus, the prediction of exposure map at urban scale is a very important requirement to find a relevant indicator of the real exposure. In this paper, we propose a monitoring solution for electromagnetic field (EMF) exposure based on a numerical modeling of the radio wave propagation radiated by mobile telephony base stations. The accuracy of this tool directly depends on the input data precision, such as location of base station antennas or their radiation pattern, which are often poorly known. These data are therefore refined by an optimization algorithm fed by a lot of information, such as the indication of the received signal strength (RSSI) measured directly from users' smartphones, which are used as probes. Results show that this method significantly improves the precision of unknown data concerning mobile base stations and the accuracy of exposure maps at urban scale.
This paper describes an experiment in a wind-wave pool in Brest, France, to characterize surface films when observed at moderate incidence from X-to-K radar bands. Measurements of the radar backscattered field were carried out for various seawater surface states and incidence angles. From this meaningful database (mainly lying in simultaneous acquisitions in X-, Ku-, and K-bands), an inversion method is proposed to characterize the elasticity modulus of the surface film. This process is based on the minimization of the cost function correlating the values given by a physical model of the damping ratio and the measured ones. The resulting oil parameters are found in overall good agreement - but still qualitative - with the various released oils. Nonetheless, the inversion method does not work properly for the rapeseed oil slick when higher wind speeds are considered, and this failure is explained. In addition, it can be seen that the results can be applied in an ocean context by comparing the modeled normalized radar cross section (NRCS) in an ocean context (given by the Bragg scattering and the Elfouhaily spectrum) and the measured NRCS.
Microwave imaging (MWI) is a non-ionizing, non-invasive and an upcoming affordable medical imaging modality. Over the last few decades, MWI has invited active research towards bio-medical imaging, with special focus on breast tumor detection. After long years of intense research and clinical trials, a breast tumour monitoring unit based on MWI is finally entering clinical imaging scenarios. In this manuscript, the vast literature in MWI to date has been consolidated, and an in-detail study of the state-of-the-art for breast tumor detection has been presented. The hurdles faced during clinical trials are discussed, and their possible solutions and future directions for a fast transition into clinical imaging have been presented. It is hoped that this paper can serve as a guide for MWI researchers and practitioners, especially those new to the field to comprehend the potential of MWI as a viable imaging tool for breast imaging.
In this paper, we present the design and fabrication of a novel class of emerging waveguide filters based on chained-functions at the millimeter-wave band. The derivation of chained-functions by chaining of prescribed generalized Chebyshev seed functions based on the partition theory is presented in details, and the implementation to waveguide technology is proposed and evaluated. The waveguide filter is fabricated through two different technologies, namely the Computer Numerical Control (CNC) milling technology and the Direct Metal Laser Sintering (DMLS) based additive manufacturing technology. The chained-function filters, which lie in between the Butterworth and Chebyshev filters, inherit the salient properties of both Butterworth and Chebyshev filters. Therefore, the chained-function waveguide filter exhibits filtering responses that have a superior rejection property and a lower loss with reduced sensitivity to fabrication tolerance than the standard Chebyshev waveguide filter. The efficiency of the proposed waveguide filter is confirmed both theoretically and empirically, using the CNC and DMLS processes. The issues of a higher manufacturing tolerance and apparent surface roughness associated with the DMLS method are found to be electrically insignificant when the chained-function concept is adopted in waveguide filter design. In general, the measured results of all the realized waveguide filters agree well to those of the simulation models. These results positively demonstrate that the chained-function concept has robust properties for rapid, high-performance, low-cost, and sustainable filter design and implementation, particularly for higher millimeter-wave frequency bands and for narrow-band applications.
This paper proposes a four-port rectangular monopole antenna for ultra-wideband multiple-input multiple-output (UWB-MIMO) applications. The proposed antenna was designed by using step etching on the ground plane and arrow-shaped slot etching on a radiating patch to enhance bandwidth and improve performances. The homogeneous elements and angular variation techniques were applied to reduce mutual coupling between multiple antenna elements. The structural simulation technique used Computer Simulation Technology (CST) program to analyze the antenna characteristics such as reflection coefficient, group delay, mutual coupling, envelope correlation coefficient, and radiation patterns. The measured results were found to cover a frequency range of 3.1-10.6 GHz for UWB communications. The envelope correlation coefficient for the MIMO system was obtained under 0.001 which is less than the specific parameters of UWB-MIMO antennas. The radiation pattern was bi-directional. Also, the efficiency of the four-port antenna was more than 85.70%.
Magnetic nanoparticle (MNP) based thermal therapies have shown importance in clinical applications. However, it lacks a compromise between its robustness and limitations. We developed theoretical strategies to enhance the heating efficiency, which could be utilized in thermal therapies and calculated parameter dependence for superparamagnetic MNPs (approximative ellipsoid-shaped) within a sphere-shaped ball. Then we calculated specific loss power (SLP) for magnetic particles in a magnetic ball. The dependency of features of the nanoparticles (such as mean particle size, a number of particles, frequency and the amplitude of the exposed field, relaxation time, and volume gap between particles and a sphere-shaped ball) on the SLP or the heating effect in superparamagnetic MNPs was analyzed. In this study, optimal parameter values were calculated using Kneedle Algorithm as the optimization technique to represent the accurate heating efficiency. The influence of a number of particles in a sphere-shaped ball shows that SLP of magnetic particles increases with the increasing number of particles (N); however, after N = 10 particles, the SLP increment is insignificant. The most remarkable result arising from this analysis is that when particles are more closer together (less volume gap of a sphere-shaped ball), high SLP is found for the same number of particles. This model also predicts that the frequency dependency on the SLP is negligible when the frequency is higher than 10 kHz depending on the size of a sphere-shaped ball and nanoparticle parameters. This analysis has shown that the SLP of MNPs in a sphere-shaped ball strongly depends on magnetic parameters and properties of the particles. In brief, we have demonstrated, for the first time, impact on SLP of the accumulation of ellipsoid-shaped superparamagnetic nanoparticles into a sphere-shaped ball. This finding has essential suggestions for developing links between heating properties with loose aggregate and dense aggregate scenarios in the superparamagnetic condition.