High-frequency diffraction contribution by planar metallic–DNG metamaterial junctions

AbstractThe plane wave diffraction by a planar junction consisting of a thick metallic sheet and a lossy double-negative metamaterial slab is studied by using the Uniform Asymptotic Physical Optics approach. This approach assumes the radiation integral as a starting point and uses the physical optics surface currents as sources to be integrated. The integral is manipulated by taking advantage of useful approximations and evaluations, and re-formulated in order to apply an asymptotic procedure able to generate a closed-form approximate solution in the framework of the Uniform Geometrical Theory of Diffraction. Accordingly, advantages and drawbacks result from the application of the proposed solution. The jumps of the geometrical optics field are compensated. Implementation and handling of the computer code are facilitated by the evaluation of well-known functions and parameters. No differential/integral equations or special functions must be computed

Application of Nonredundant Sampling Representations of Electromagnetic Fields to NF-FF Transformation Techniques

An overview of the application of the band-limitation properties and nonredundant sampling representations of electromagnetic fields to NF-FF transformations is presented. The progresses achieved by applying them to data acquired on conventional NF scanning surfaces are discussed, outlining the remarkable reduction in the number of needed NF samples and measurement time. An optimal sampling interpolation expansion for reconstructing the probe response on a rotational scanning surface from a non-redundant number of its samples is also discussed. A unified theory of the NF-FF transformations with spiral scannings, which allow a remarkable reduction of the measurement time, is then reviewed by describing a sampling representation of the voltage on a quite arbitrary rotational surface from its nonredundant samples collected on a proper spiral wrapping it. Some numerical and experimental results assessing the effectiveness of the considered NF-FF transformations are shown too

Communication on the World Wide Web: Designing an Effective Homepage

The purpose of this study was to examine the content and structural features of a World Wide Web homepage with the explicit goal of making recommendations for how a homepage should be designed

Near-Field/Far-Field Transformation with Helicoidal Scanning from Irregularly Spaced Data

A fast and accurate technique for the compensation of the probe positioning errors in the near-field/far-field transformation with helicoidal scanning is proposed in this paper. It relies on a nonredundant sampling representation using a spherical modelling of the antenna under test and employs an iterative scheme to evaluate the near-field data at the points fixed by the helicoidal nonredundant representation from the acquired irregularly distributed ones. Once these helicoidal data have been recovered, those required by a classical cylindrical near-field/far-field transformation are efficiently determined by using an optimal sampling interpolation algorithm. Some numerical tests assessing the effectiveness of the proposed approach and its stability with respect to random errors affecting the near-field data are shown

Measurements Performance of a Bioradar for Human Respiration Monitoring

Abstract Breathing pattern monitoring of humans is very important especially during long isolation in space missions. In particular, several factors can induce some breathing anomalies during the sleep, which may cause apnea episodes; an early diagnosis of such episodes is crucial for the application of an efficient therapy. Continuous wave bioradars operating in the microwave frequency range are effective contactless tools for monitoring the respiratory activity. These active systems emit a low power electromagnetic wave at a single frequency, which is reflected by the human chest. Based on the phase difference between the incident and reflected signals, it is possible to estimate and monitor the respiratory rate. In this paper, a metrological characterization of the bioradar methodology is presented. To this end, bioradar results are compared with the ground truth data recorded by a spirometer, which is a standard medical device that measures the air volume inhaled and exhaled by the subject

An Innovative Direct NF-FF Transformation Technique with Helicoidal Scanning

A direct near-field-far-field transformation with helicoidal scanning is developed. It is based on the nonredundant sampling representation of electromagnetic fields and uses a spherical antenna modelling to determine the number of helix turns. Moreover, the number of voltage samples on each of them is fixed by the maximum transverse dimension of the antenna, both to simplify the mechanical scanning and to reduce the computational effort. This technique allows the evaluation of the antenna far field directly from a minimum set of near-field data without interpolating them. Although the number of near-field data employed by the developed technique is slightly increased with respect to that required by rigorously applying the nonredundant sampling representation on the helix, it is still remarkably smaller than that needed by the standard near-field-far-field transformation with cylindrical scanning. The effectiveness of the technique is assessed by numerical and experimental results

Monitoring the breath through mechanical movements of the chest using continuous wave bioradar system

In space missions, during the long isolation at extreme condition for human health is most important monitoring vital signs. One of these is the breathing detection. Indeed several factors can induce some breathing anomalies during the sleep, which may cause apnea episodes. In order to act timely with the right therapy, an early diagnosis is required. A new, innovative, way to perform this kind of measurement is continuous wave bioradar, shown in Figure 1, operating in the microwave frequency. This is effective contactless tool for monitoring the respiratory activity through the measurement of chest deformation due to inhalation and exhalation. This system emit a low power electromagnetic wave at a single frequency, which is reflected by the human chest. Through to measuring of the phases shift between the incident and reflected wave is possible discovering and monitoring the respiratory rate. In this paper, the continuous wave bioradar measurement technique and test campaign experimental results are presented. Furthermore, to this end, bioradar results are compared with data recorded by a spirometer, which is a standard and noted medical device that measures the air volume inhaled and exhaled by the subject. Finally, the measurement standard uncertainty of the bioradar system is defined, and the system performance is evaluated. Please click Additional Files below to see the full abstract

Two efficient procedures to correct the positioning errors in the plane-polar scanning

Two techniques to effectively compensate known positioning errors in a plane-polar near-field–far-field (NF–FF) transformation, using a minimum number of NF data and adopting an oblate ellipsoid to shape the considered antenna, are proposed and validated through experimental proofs. The former makes use of the singular value decomposition method to recover the voltage samples which would be acquired by the probe at the points fixed by the non-redundant sampling representation from the collected positioning error affected ones, whereas the latter employs an iterative scheme. The NF data required by the classical NF–FF transformation with plane-rectangular scanning are then efficiently evaluated via a two-dimensional optimal sampling interpolation formula. The effectiveness of the proposed techniques is assessed by experimental tests performed at the Antenna Characterisation Lab of the University of Salerno