In the last decades, microwave imaging has been a new area of research due to its many advantages over current imaging systems. Microwave imaging system is used for in-depth inspection of biological tissues. The test provides the identification of morphological changes in these biological tissues, as well as their locations. The emerging Ultra-Wideband (UWB) microwave imaging gives better result with the main advantage of using non-ionizing radiation. In these systems, antennas play a very important role, and as such, their optimization has become a very important topic because of the device is placed close to the human body. Thus, many aspects are of great importance in the design of the antennas starting from the material with which it is constructed, its dimensions, operation bandwidth, human body influence on the antenna parameters, short-pulse propagation, etc. Recent research has shown several efforts in improving the electromagnetic sensors used in these systems, either as individual or array elements. In this paper, we provide an overview of the most relevant developments in the field of UWB high directivity sensors used in microwave imaging systems.
Statistics of monthly and diurnal variations in the occurrence of rain fades are needed to give a detailed insight for system design of these services. This paper analyses the performance on three years of rain rate and rain attenuation measurement to study the empirical determination of power law coefficients calculated for monthly distribution of rain attenuation from the knowledge of rain rate at 19.8 GHz link for COMS1 in South Korea. The received signal data for rain attenuation and rain rate were collected at 10 second intervals over a three year period from 2013 to 2015. The comparison of measured data for monthly variation illustrates the suitability for the estimation of signal in Ka-band whose appropriateness is verified through the comparison with prominent rain attenuation models namely ITU-R P. 618-13 and empirically generated regression coefficients values for ITU-R P. 838-3. A monthly variation of the coefficients has been indicated, and the empirical measured data were compared with the ITU-R P. 838-3 derived regression coefficients. Moreover, the statistics analyzed to 6 hour contiguous periods of the day are also shown. Furthermore, the paper presents an overview of the redicted monthly variation of rain attenuation estimation of 2013 year for Ka band in 19.8 and 20.73 GHz from 12.25 GHz link which are obtained from the ITU-R P. 618-13 frequency scaling method, and these predictions are compared with experimentally measured values. These statistics can be useful for communication systems whose service quality and design require seasonal and diurnal variation.
This paper devises a framework of phased array antennas to radiate multiple beams for a fixed coverage. The phased antenna array is chosen so that the beamforming can be fixed in selected coverage area. The antenna arrays are employed with a Butler matrix (BM) to form required phases of excitation coefficients to the radiating elements. Optimally designed 4×4 or 8×8 Butler matrix is utilized at the I/O ports of the phased antenna array. The grating lobes are reduced by using the principle of orthogonality to the feeds of subarray (group of column arrays of phased array). This article also exploits the concept of skirt elements to reach the desired coverage area while reducing the beam overlapping in the restricted area. Simulation studies highlight the proposed claims with elaborated numerical analysis of different case studies.
We theoretically analyze perturbations of ambient magnetic field due to electric currents caused by motion of a dielectric ball in a conductive fluid half-space. The approximate analytical solution of the problem has been derived for the case of arbitrary orientation of the ambient magnetic field and under the requirement that the fluid flow around the ball is laminar and potential in character. We examine spatiotemporal distribution of these perturbations and their dependence on both the depth and distance from the moving ball. The amplitudes of electromagnetic perturbations generated by the fluid flow around the ball have been compared with that resulting from gravity waves in the fluid.
In this paper the equivalent impedance of resonator arrays for wireless power transfer systems is obtained in closed-form from a continued fraction expression. Using the theory of difference equations, the continued fraction is described as the general term of a complex sequence defined by recurrence, and its convergence is analyzed. It is shown that the equivalent impedance can be easily found in closed-form in terms of the system parameters. In this way, the obtained closed-form expressions may help electrical engineers to quickly predict the behaviour of a system with the changes of its parameters. Some numerical examples of the theoretical results are given and discussed. Finally, the analytical formulae obtained in this work are validated with measurements and a good agreement is observed.
Due to changes in global security requirements attention is turning to new means by which anomalies on the human body might be identified. For security screening systems operating in the millimeter wave band anomalies can be identified by measuring the emissivities of subjects. As the interaction of millimeter waves with the human body is only a fraction of a millimeter into the skin and clothing has a small, but known effect, precise measurement of the emission and reflection of this radiation will allow comparisons with the norm for that region of the body and person category. A technique to measure the human skin emissivity in vivo over the frequency band 80 GHz to 100 GHz is developed and described. The mean emissivity values of the skin of a sample of 60 healthy participants (36 males and 24 females) measured using a 90 GHz calibrated radiometer was found to range from 0.17±0.005 to 0.68±0.005. The lower values of emissivity are a result of measuring particularly thin skin on the inner wrist, volar side of the forearm, and back of hand, whereas higher values of emissivity are results of measuring thick skin on the outer wrist, dorsal surface of the forearm, and palm of hand. The mean differences in the emissivity between Asian and European male participants were calculated to be in the range of 0.04 to 0.11 over all measurement locations. Experimental measurements of the emissivity for male and female participants having normal and high body mass index indicate that the mean differences in the emissivity are in the range of 0.05 to 0.15 for all measurement locations. These results show the quantitative variations in the skin emissivity between locations, gender, and individuals. The mean differences in the emissivity values between dry and wet skin on the palm of hand and back of hand regions were found to be 0.143 and 0.066 respectively. These results confirm that radiometry can, as a non-contact method, identify surfaces attached to the human skin in tens of seconds. These results indicate a route to machine anomaly detection that may increase the through-put speed, the detection probabilities and reduce the false alarm rates in security screening portals.
This paper focuses on the cognitive design of transmitting waveform to improve target detection capability in the presence of signal-dependent modulated jamming (e.g., chopping and interleaving (C&I) jamming). In particular, we reasonably assume that the modulation mode of signal-dependent jamming is available based on cognitive paradigm. The first design criterion is to minimize the integrated cross-correlation energy (ICE) between the transmitting waveform and jamming signal. In this way, the received jamming signal can be suppressed after matched filter processing is performed using the optimized waveform. The second design criterion is to minimize the integrated auto-correlation sidelobe level (IASL) for maintaining good range compression property. The practical constant modulus constraint is imposed on the transmitting waveform. Finally, to deal with the resulting non-convex problem, an iterative algorithm based on the majorization-minimization framework is developed. Numerical examples for specific signal-dependent modulated jammings are provided to demonstrate the effectiveness of the proposed methodology.
Two alternative approaches to the spatial spectral integral equation method are proposed. The first enhancement comprises a Hermite interpolation as the set of basis functions instead of the Gabor frame. The continuity, differentiability, equidistant spacing, and small support of these basis functions allows for an efficient and accurate numerical implementation. The second approach encompasses a method to transform between the spatial domain and the deformed path in the complexplane spectral domain. This method allows for more general path shapes, thereby removing the need to decompose the complex-plane spectral-domain path into distinct straight sections. Both enhancements are implemented for the case of TE polarization, and the results are validated against the finite element method and the rigorous coupled-wave analysis.
This paper presents the power density evaluation and power mapping performance of a novel magnetic geared double-stator permanent magnet generator (DSPMG) which is proposed to address problems of mechanical geared generators for low-speed power generation applications. The operating principle is based on three PM rotors consisting of prime permanent-magnet (PM) poles in the middle rotor and field PM poles in the inner and outer rotors respectively. To evaluate the power density performance, a 2-D finite-element method (FEM) is used to predict the performance of the generator, and a demonstrator prototype is fabricated and evaluated experimentally. The power density characteristics of the proposed generator are analyzed and reported. The measured results agree closely with the simulated ones to verify the validity of the magnetic geared generator design. Finally, a measurable comparison is conducted with other published prototype magnetic gear machines to demonstrate its benefits of higher power density and smaller volume size.
An alternative formulation of the Small Perturbation Method (SPM) in solving electromagnetic scattering from multi-layer random rough surfaces to resolve singularities in spectral integrals is presented. Non-monotonic permittivity changes will allow a multi-layer structure with flat interfaces to support guided modes. The presence of these guided modes translates to poles in the zeroth order Green's function of the media for the surface fields. The poles appear in the first and second order perturbation solutions based on a iterative procedure. Thus, evaluating the spectral integrals to obtain the spatial fields becomes problematic. The Sommerfeld integration path instead of real line integrals is introduced by analytic continuation of the integrand into complex spectral space. It is verified that this alternative spectral integration method is valid for both monotonic and non-monotonic cases.