Isotropic Radiation Research Articles

A note on estimation of diffuse radiation collected by all‐glass evacuated solar tube collectors

To simplify the estimation of diffuse radiation from the sky and ground collected by all-glass evacuated solar tube collectors (ETCs), four methods were proposed and used in the past. Among them, the one by assuming the directional intensity of diffuse radiation projected on the plane coplanar with cross-section of solar tubes (2-D model) to be isotropic is simpler as mathematical expressions for the estimate of diffuse collectible radiation can be directly derived in this case. However, such assumption is not true for tilted evacuated solar tubes (ET), and the three-dimensional isotropic diffuse radiation (3-D model) should be used. In this note, a trail is made to estimate diffuse radiation collected by tilted-arranged ET collectors (T-type ETC) based on 3-D model and compare with those obtained based on the 2-D model. Results show that the diffuse radiation collected by T-type ETCs estimated based on 2-D and 3-D models are highly in agreement, and the difference between two estimates is dependent on the tilt-angle (β) of ETCs. For the case of β = 0 and 90°, the both estimates are completely identical as expected. For T-type ETCs with ETs sizing 47/58 mm in diameter of inner/outer tubes and spacing (B) between centers of two adjacent ETs less than 80 mm, the relative deviation between two estimates for diffuse radiation from the sky is less than 0.65% and that for diffuse radiation reflecting from the ground is less than 1.7% when β > 20°. This means that the 2-D model is reasonable and advisable for a quick estimation of collectible diffuse radiation of ETCs.

Neuroevolution-Based Adaptive Antenna Array Beamforming Scheme to Improve the V2V Communication Performance at Intersections.

The opportunistic exchange of information between vehicles can significantly contribute to reducing the occurrence of accidents and mitigating their damages. However, in urban environments, especially at intersection scenarios, obstacles such as buildings and walls block the line of sight between the transmitter and receiver, reducing the vehicular communication range and thus harming the performance of road safety applications. Furthermore, the sizes of the surrounding vehicles and weather conditions may affect the communication. This makes communications in urban V2V communication scenarios extremely difficult. Since the late notification of vehicles or incidents can lead to the loss of human lives, this paper focuses on improving urban vehicle-to-vehicle (V2V) communications at intersections by using a transmission scheme able of adapting to the surrounding environment. Therefore, we proposed a neuroevolution of augmenting topologies-based adaptive beamforming scheme to control the radiation pattern of an antenna array and thus mitigate the effects generated by shadowing in urban V2V communication at intersection scenarios. This work considered the IEEE 802.11p standard for the physical layer of the vehicular communication link. The results show that our proposal outperformed the isotropic antenna in terms of the communication range and response time, as well as other traditional machine learning approaches, such as genetic algorithms and mutation strategy-based particle swarm optimization.

A study about signal variation with minor receiver displacement in a meeting room at 60\xa0GHz: measurements and simulations

The aim of this work is to study the impact of small receiver displacement on a signal propagation in a typical conference room environment at a millimeter wave frequency of 60 GHz. While channel measurements provide insights on the propagation phenomena, their use for the wireless system performance evaluation is challenging. Whereas, carefully executed three-dimensional ray tracing (RT) simulations represent a more flexible option. Nevertheless, a careful validation of simulation methodology is needed. The first target of this article is to highlight the benefits of an in-house built three-dimensional RT tool at 60 GHz and shows the effectiveness of simulations in predicting different characteristics of the channel. To validate the simulation results against the measurements, two different transmitter (Tx) positions and antenna types along with ten receiver (Rx) positions are considered in a typical conference room. In first system configuration, an omnidirectional antenna is placed in the middle of the table, while in the second system configuration a directed horn antenna is located in the corner of the meeting room. After validating the simulation results with the measurement data, in the second part of this work, the impact of a small change, i.e., 20 cm in the receiver position, is studied. To characterize the impact, we apply as performance indicators the received power level, root mean square delay spread (RMS-DS) and RMS angular spread (RMS-AS) in azimuth plane. The channel characteristics are considered with respect to the direct orientation (DO), i.e., the Rx antenna is directed toward the strongest incoming path. Different antenna configurations at the Tx and Rx side are applied to highlight the role of antenna properties on the considered channel characteristics. Especially, in the second system configuration the impact of different antenna half power beamwidth on different considered channel characteristics is highlighted through acquired simulation results. The validation of results shows the RMS error of only 2–3 dB between the measured and simulated received power levels for different Tx configurations in the direction of DO. Results indicate that only a small change of the Rx position may result a large difference in the received power level even in the presence of line-of-sight between the Tx and Rx. It is found that the STD of received power level across the room increases with the decrease in HPBW of the antenna. As can be expected, directed antennas offer lower value of RMS-DS and RMS-AS compared with isotropic antenna.

Design and Development of a Near Isotropic Printed Arc Antenna for Direction of Arrival (DoA) Applications

This research presents an easy to fabricate isotropic printed arc antenna element to be used for direction of arrival (DoA) arrays. The proposed antenna exhibits a total gain variation of 0.5 dB over the entire sphere for 40 MHz impedance bandwidth at 1 GHz, which is the best design isotropy reported in literature so far. In addition, the isotropic bandwidth of the antenna for total gain variation of ≤3 dB is 225 MHz with 86% efficiency. The isotropic wire antenna is first designed and simulated in Numerical Electromagnetic code (NEC). An equivalent printed antenna is then simulated in CST, where single (short circuited) stub is integrated with the antenna for input matching and the results of NEC simulations are verified. The planar antenna is then manufactured using FR4 substrate for measurements. Good agreement between the measured and simulated results is observed, however the total gain variation is increased to 2 dB for the fabricated antenna. This is because of the unavoidable field scattering from the antenna substrate, the feed cables, and the antenna testing platform.

A detailed simulation study on the effect of energy and angle of incidence for low energy protons on Single Event Upsets induced in nanometer CMOS SRAM

Low-energy proton-induced single event upsets (SEUs) are a significant threat to the reliability of nanometer technologies, which are used in radiation environments. In this paper, through a developed program using Geant4 simulation toolkit, the effect of proton energies (<10 MeV) and angles of incidence (0∘ to 60∘), as well as isotropic radiation field on the SEU cross-section in a 65 nm CMOS SRAM, is studied. Furthermore, we have investigated the role of dominant physical mechanisms contributing to inducing SEUs. To analyze the responsible mechanisms for the upsets, proton interactions with BEOL of the device are considered to determine which particles could cause the upsets.The results show that for all investigated cases, the SEU cross-sections first increase for protons with incident energies of less than about 1 MeV and then decrease for higher energy protons. It is also observed that with increasing the tilt angle up to 45∘, the SEU cross-section increases, and the SEU peak shifts to higher energies, while for larger angles, the cross-section decreases. The results for the isotropic proton field show that the SEU peak occurs in lower energies compared to the fixed angle cases. We have also observed that for the proton energies corresponding to the SEU cross-section peak, the energy spectrum of the protons entering the sensitive volume confirms the occurrence of the Bragg peak inside the sensitive volume. Regarding the physical mechanisms responsible for SEU, the results show that for protons with energies of less than 1 MeV, direct ionization and for energies between 2 MeV and 10 MeV, recoiled Si ions due to elastic scattering of protons in the sensitive volume are dominant in inducing upsets. Our findings have also revealed that for proton energies of more than 5 MeV, other particles produced in BEOL such as oxygen and alpha particles also play a role to induce upsets, but have less contribution. These results indicate that the structures of the BEOL in advanced CMOS technologies can play an important role in inducing upsets for the upper limit of low energy protons. These considerations can be useful for designing advanced technologies more hardened against radiation. In general, we have found that for low energy protons, the proton-induced SEU cross-section of the device is a strongly correlated function of energy and direction of the incident protons.

SH Wavelet Propagation Through the Random Distribution of Aligned Line Cracks Based on the Radiative Transfer Theory

This paper studies the propagation of SH wavelet intensity through the random distribution of aligned line cracks in a two-dimensional (2-D) homogeneous medium as the simplest mathematical model of the heterogeneous Earth medium. The scattering process of a single line crack is described by Mathieu functions. The random distribution of cracks is well represented by the scattering coefficient, that is, the scattering power per unit area. Two methods are proposed for the derivation of the space–time distribution of the intensity Green function for the unit isotropic radiation from a point source: one is the single scattering approximation and the other is the Monte Carlo simulation. The former and the latter are deterministic and stochastic methods, respectively. In the case that the wavenumber is larger than the reciprocal of the crack length, synthesized time traces show that direct wavelets near the ray direction parallel to the line cracks decrease according to the geometrical decay with increasing travel distance as if there exists a transparent channel along the crack line direction; however, those near the direction normal to the line cracks decrease more rapidly because of strong scattering attenuation. At large lapse times, multiple scattering produces a swelling around the source location, which is prolonged to the crack line direction. Those characteristics well reflect the anisotropy of the line crack scattering. The Monte Carlo simulation presented here could be a fundamental base for the study of more realistic crack scattering problems.

Lineal energy calibration of a mini-TEPC via the proton-edge technique

PurposeThe possibility to calibrate microdosimetric spectra using the proton- and electron-edge was proposed many years ago. It consists of two steps: first identifying the edge and a marker point on it and then ascribing the correct lineal energy value to the position of the edge in the event size spectrum. The purpose of this work is to study rigorously the marker identification for the proton-edge in the mini-TEPC spectra measured in neutron and in clinical proton fields, and the correspondent lineal energy value to assign to it. Materials and methodsMicrodosimetric measurements were performed with a cylindrical miniaturized tissue-equivalent proportional-counter (mini-TEPC) in neutron and gamma rays radiation fields at the CN accelerator of the Legnaro National Laboratories of the Italian National Institute for Nuclear Physics (LNL-INFN) and in the clinical 62 MeV proton beam of the Southern National Laboratories of INFN (LNS-INFN). The fitting of the proton-edge region of the microdosimetric spectra with a Fermi-like function was studied in both neutron and proton fields to identify the most precise marker point. The lineal energy value to ascribe to it was determined starting from the maximum energy deposit in protons obtained in FLUKA simulations. ResultsBoth in neutron radiation field and in clinical proton beams the flex and the intercept of the tangent through the inflection point are determined with similar precision. The flex was chosen as the most suitable marker of the proton-edge in sealed detectors because it is known to be less sensitive to pressure variations. The lineal energy value to ascribe to the flex position for 0.75 μm of propane depends on the irradiation geometry: 194 keV/μm for isotropic radiation fields and 165 keV/μm for mono-directional radiation fields orthogonal to the axis of the cylinder. The calibration values for the proton-edge have been converted in water by means of the mean stopping power ratio of water and propane for protons obtaining 171 keV/μm for isotropic radiation fields and 145 keV/μm for mono-directional radiation fields.

What is the radiation before 5G? A correlation study between measurements in situ and in real time and epidemiological indicators in Vallecas, Madrid

BackgroundExposure of the general population to electromagnetic radiation emitted by mobile phone base stations is one of the greater concerns of residents affected by the proximity of these structures due to the possible relationship between radiated levels and health indicators. ObjectivesThis study aimed to find a possible relationship between some health indicators and electromagnetic radiation measurements. MethodsA total of 268 surveys, own design, were completed by residents of a Madrid neighborhood surrounded by nine telephone antennas, and 105 measurements of electromagnetic radiation were taken with a spectrum analyzer and an isotropic antenna, in situ and in real – time, both outside and inside the houses. ResultsIt was shown statistically significant p - values in headaches presence (p = 0.010), nightmares (p = 0.001), headache intensity (p < 0.001), dizziness frequency (p = 0.011), instability episodes frequency (p = 0.026), number of hours that one person sleeps per day (p < 0.001) and three of nine parameters studied from tiredness. Concerning cancer, there are 5.6% of cancer cases in the study population, a percentage 10 times higher than that of the total Spanish population. Discussion: People who are exposed to higher radiation values present more severe headaches, dizziness and nightmares. Moreover, they sleep fewer hours.

Source Localization of EM Waves in the Near‐Field of Spherical Antenna Array in the Presence of Unknown Mutual Coupling

To obtain an antenna array with isotropic radiation, spherical antenna array (SAA) is the right array configuration. The challenges of locating signals transmitted within the proximity of antenna array have been investigated considerably in the literature. However, near‐field (NF) source localization of signals has hitherto not been investigated effectively using SAA in the presence of mutual coupling (MC). MC is another critical problem in antenna arrays. This paper presents an NF range and direction‐of‐arrival (DoA) estimation technique via the direction‐independent and signal invariant spherical harmonics (SH) characteristics in the presence of mutual coupling. The energy of electromagnetic (EM) signal on the surface of SAA is captured successfully using a proposed pressure interpolation approach. The DoA estimation within the NF region is then calculated via the distribution of pressure. The direction‐independent and signal invariant characteristics, which are SH features, are obtained using the DoA estimates in the NF region. We equally proposed a learning scheme that uses the source activity detection and convolutional neural network (CNN) to estimate the range of the NF source via the direction‐independent and signal invariant features. Considering the MC problem and using the DoA estimates, an accurate spectrum peak in the multipath situation in conjunction with MC and a sharper spectrum peak from a unique MC structure and smoothing algorithms are obtained. For ground truth performance evaluation of the SH features within the context of NF localization, a numerical experiment is conducted and measured data were used for analysis to incorporate the MC and consequently computed the root mean square error (RMSE) of the source range and NF DoA estimate. The results obtained from numerical experiments and measured data indicate the validity and effectiveness of the proposed approach. In addition, these results are motivating enough for the deployment of the proposed method in practical applications.

Frequency-Dependent Feeding Methods for Broadband Vivaldi Arrays With Minimum Half-Power Beamwidth (HPBW) Variation

This paper reports on the design of frequency-dependent feed networks for linear antenna arrays with minimum half-power beamwidth (HPBW) variation in more than one octave of the frequency spectrum. The proposed approach is based on: i) frequency-dependent power dividers that gradually shift the RF power from the outer elements of the array to the inner ones with the increase of frequency and ii) uniformly or non-uniformly-spaced directive antenna elements. The operating principles and design trade-offs of the concept are presented through ideal simulations of four- and six-element antenna arrays shaped by isotropic or directive radiators. It is shown that by employing directive antenna elements and non-uniform spacing, minimum HPBW variation can be obtained in a broad bandwidth (BW, e.g., 3:1). For physical verification purposes, two frequency-dependent feed networks and Vivaldi antenna elements were designed, manufactured, and measured. The first network feeds a uniformly-spaced four-element array of Vivaldi antennas and demonstrates a 58% HPBW variation in a 3:1 of BW. The second network feeds a non-uniformly-spaced six-element Vivaldi array and results in a 67% HPBW variation in a 2.5:1 of BW.

Low-Power Radar System for Noncontact Human Respiration Sensor

The development of a radar system for human respiration noncontact sensor will contribute to the healthcare field, particularly in the monitoring of patients’ respiration for a long period with all the while providing more advantages, such as hygiene and comfort. The radar system must be able to detect the small displacement with millimeters or centimeters scale on the human body associated with the respiratory activity. The minimum power of electromagnetic wave radiation is also needed to avoid unsafe usability in patients’ respiration monitoring. To attain low power operation and efficient frequency spectrum usage, the multifrequency continuous-wave (MFCW) radar system is proposed in this article as a noncontact sensor for human respiration. The simulation study and laboratory experiment of the MFCW radar system in detecting human respiration were performed, and the comparison study with frequency-modulated continuous-wave (FMCW) radar was discussed in this article. The simulation shows that the effective isotropic radiation power (EIRP) of MFCW is 9 dBm lower than FMCW at a 2-m measurement distance. The result also demonstrates that the proposed MFCW performs well under amplitude and phase noise. The laboratory experiments were conducted by implementing the proposed system using the software-defined radio device. The experiment results also confirm that the proposed MFCW was able to reduce the EIRP and spectrum occupation compared to the FMCW. The MFCW system is then recommended as a radar system in developing a noncontact sensor for respiration monitoring in healthcare.

Simulation Comparison of Directional Antenna and Isotropic Antenna Used in Projectile-carried Communication Jammer

From the aspect of appearance size, gain and directivity, the simulation analysis of isotropic antenna and directional antenna is carried out by HFSS software. The simulation results show that isotropic antenna is suitable for projectile-carried communication jammer.

Low-Cost Distributed Acoustic Sensor Network for Real-Time Urban Sound Monitoring

Continuous exposure to urban noise has been found to be one of the major threats to citizens’ health. In this regard, several organizations are devoting huge efforts to designing new in-field systems to identify the acoustic sources of these threats to protect those citizens at risk. Typically, these prototype systems are composed of expensive components that limit their large-scale deployment and thus reduce the scope of their measurements. This paper aims to present a highly scalable low-cost distributed infrastructure that features a ubiquitous acoustic sensor network to monitor urban sounds. It takes advantage of (1) low-cost microphones deployed in a redundant topology to improve their individual performance when identifying the sound source, (2) a deep-learning algorithm for sound recognition, (3) a distributed data-processing middleware to reach consensus on the sound identification, and (4) a custom planar antenna with an almost isotropic radiation pattern for the proper node communication. This enables practitioners to acoustically populate urban spaces and provide a reliable view of noises occurring in real time. The city of Barcelona (Spain) and the UrbanSound8K dataset have been selected to analytically validate the proposed approach. Results obtained in laboratory tests endorse the feasibility of this proposal.

Exciton Transport in Molecular Semiconductor Crystals for Spin-Optoelectronics Paradigm.

Organic semiconductors with long-range exciton diffusion length are highly desirable for optoelectronics but currently remain rare. Here, the estimated diffusion length of singlet excitons (LD ) in 2,6-diphenyl anthracene (DPA) crystals grown by solvent evaporation was shown to be up to approximately 124 nm. These crystals showed a previously unseen parallelogram morphology with layer-by-layer edge-on molecular stacking, isotropic optical waveguiding, radiation rate and non-radiation rate constants of 0.15 and 0.26 ns-1 respectively, as well as good field-effect transistor hole mobility and theoretically computed strong electronic couplings as high as 109 meV. Photoresponse experiments revealed that the photoconductivity of DPA crystals is surprisingly not related to the radiative pathway but associated with rapid exciton diffusion to the crystal surface for charge separation and carrier bimolecular recombination. Taken together, DPA was shown to be a promising semiconducting material for a new organic optoelectronics paradigm.

Error Inherent in Simulating Planetary Thermal Effect on the Spacecraft Surface by using Isotropic Planetary Radiation Intensity Field Model Instead of Anisotropic

In order to mathematically simulate the thermal effect that radiation emitted by planets has on spacecraft, two intensity field models describing planetary radiation may be used depending on the emitter specifics: isotropic and anisotropic. The isotropic model is based on the assumption that the local surface density of outgoing radiation flux is the same for all surface regions visible from orbit. In the case of the anisotropic model this value is assumed to be proportional to the zenith angle cosine for each surface element on the side of the planet that is illuminated by the Sun. Published results of studies concerning developing planetary radiation field simulators indicate that thermal vacuum installations where the working volume is comparable to the total installation volume can only reproduce the sotropic planetary radiation intensity field model. It is a pressing issue to determine whether and when it is possible to replace the anisotropic model with an isotropic one when physically simulating the effect that the solar radiation reflected from a planet and intrinsic radiation flows generated by planets with no atmosphere have on spacecraft. The investigation that we conducted regarding this issue was based on comparing the results of computing the irradiance of spacecraft elements using the models under consideration. These computation results allowed us to conclude that it is possible to physically simulate the effect of solar radiation flows reflected from planets combined with intrinsic (infrared) radiation flows generated by planets with no atmosphere by means of using simulators reproducing isotropic radiation fields in their working volumes

Invariance property in inhomogeneous scattering media with refractive-index mismatch

The mean path length invariance property is a very important property of scattering media illuminated by an isotropic and homogeneous radiation. Here we investigate the case of inhomogeneous media with refractive index mismatch between the external environment and also among their subdomains. The invariance property remains valid by the introduction of a correction, dependent on the refractive index, of the mean path length value. It is a consequence of the stationary solution of the radiative transfer equation in a medium subjected to an isotropic and homogeneous radiance. The theoretical results are in agreement with the reported results for numerical simulations for both the three-dimensional and the two-dimensional media.

Side lobe level reduction of thinned concentric elliptical array antenna in vertical and horizontal plane for a desired peak directivity

AbstractThis study, describes the design problem of a thinned multiple concentric elliptical arrays of uniformly excited isotropic antennas using meta‐heuristic optimization algorithms; Teaching Learning Based Optimization (TLBO), Crow Search Algorithm (CSA) and Moth Flame Optimization (MFO) algorithm. Two simulations are performed here. In simulation 1, the synthesis of the thinned array structure is presented in the vertical plane at a scanning angle 30° and in simulation 2, the synthesis is performed in the horizontal plane. In both cases, our objective is to minimize side lobe level (SLL) to the extent possible and at the same time maximize the peak directivity to a level higher than the desired value. Here, all the optimization algorithms are applied to obtain the optimum number of switched on and off elements in every concentric ellipse that will meet the above objective. A comparative analysis of all three algorithms is performed using peak directivity, SLL and first null beam width (FNBW) as well as statistical parameters such as mean, SD, best cost function value and run time. To assess the enhanced outcome of the proposed optimization design comparison is also made with the results of a fully populated concentric elliptical array antenna (CEAA) for both the cases separately. This paper shows a measure of effectiveness and potential of all the algorithms mentioned above, for designing a thinned concentric elliptical array.

Direction-independent and self-reconfigurable spherical-cap antenna array beamforming technique for massive 3D MIMO systems

Massive 3D MIMO beamforming is very important for 5G and beyond networks to improve the system performance and capacity. However, 3D beamforming capabilities are limited by the antenna array configuration. Therefore, in this paper, an efficient self-reconfigurable spherical-cap antenna array and 3D beamforming technique are proposed to provide direction-independent symmetrical beam patterns with low sidelobe and backlobe levels. The symmetric beam generation is achieved by forming electronically steerable spherical-cap array which is extracted from a uniform spherical antenna array and is continuously reconfigured so that its axis of symmetry is maintained the same as the mainlobe direction. On the other hand, the antenna elements in the spherical-cap array are further processed to minimize the sidelobe and backlobe levels by using an optimized exponential decaying feeding profile in the form of $$e^{{ - \alpha \left( \rho \right)^{\beta } }}$$ . Assuming isotropic antenna elements with negligible mutual coupling, the generated beam power patterns are examined where simulation results show that a sidelobe level of − 30 dB and backlobe level of less than − 16 dB relative to the mainlobe level can be achieved. Also, the variation in the 3 dB beamwidth with the mainlobe direction has been examined for 10,000 uniformly random generated mainlobe directions at different array sizes where it is found that the beamwidth is almost constant with less than 1% variation especially for large sized arrays.

Analogue beamforming solution for beam‐alignment problem

Analogue only beamforming generally refers to a structure of analogue phase shifters that have no control over the amplitude of the signals and are utilised in millimetre-wave massive multi-input multi-output systems to reduce the cost and power consumption. Conventional analogue only beamforming methods are based on beam-training and subspace sampling where the transmitter and receiver select the best beamformer and combiner from a list of predefined beam patterns to maximise the beamforming gain. In this study, first, the beam-alignment problem is formulated as a quadratic optimisation problem with quadratic constraints. Then, a practical solution for analogue only beamforming is proposed to maximise beamforming gain. The proposed method has no assumption on the array structure or isotropic antenna elements in the array. Also, a new method is proposed to design sub-codebooks to reduce the construction time of the codebook. Simulation results also corroborate the analytical results and performance of the proposed method.

Synthesis of Linear, Planar, and Concentric Circular Antenna Arrays Using Rao Algorithms

The aim of this paper is to display the efficacy of three newly proposed optimization algorithms named as Rao-1, Rao-2, and Rao-3 in synthesizing antenna arrays. The algorithms are applied to three different antenna array configurations. Thinned arrays with isotropic radiators are considered and the main objective is to find the optimal configuration of ON/OFF elements that produce low side lobe levels. The results of Rao-1, Rao-2, and Rao-3 algorithms are compared with those of improved genetic algorithm (IGA), hybrid Taguchi binary particle swarm optimization (HTBPSO), teaching-learning-based optimization (TLBO), the firefly algorithm (FA), and biogeography-based optimization (BBO). The Rao-1, Rao-2, and Rao-3 algorithms were able to realize antenna arrays having lower side lobe levels (SLL) when compared to the other optimization algorithms.