Radiation Quality Factor Research Articles

Prediction of Resonant Frequency of an Equilateral Triangular Microstrip Antenna Using Conformal Mapping Technique

In this manuscript, Conformal Mapping Technique (CMT) is applied to predict the resonant frequency of an Equilateral Triangular Microstrip Antenna (ETMA). The ETMA is mapped into a simple circular geometry with the aid of CMT. The wave equation is solved in the transformed domain using Galerkin technique to obtain the approximate solution of eigenfunction and eigenvalue. Twenty-three measured data are collected from the open literature to validate our theory. Our theoretical results are also compared with several CAD models to show the effectiveness of the present theory. It is found that our proposed theory can predict the resonant frequency of the ETMA with an error of less than 1.5%, whereas those CAD models can produce a large error (sometimes, 10-19% error). Internal field patterns, input impedance, far-field radiation patterns, quality factor, bandwidth gain, and directivity of the ETMA for the dominant mode are also investigated using CMT.

Design and fabrication of a coupled high-Q photonic nanocavity system with large coupling coefficients.

In a previous work, we demonstrated a coupled cavity system where photons in one storage cavity can be transferred to another storage cavity at an arbitrary time by applying a voltage pulse to a third cavity placed in a p-i-n junction. In this work, we demonstrate methods to improve the transfer efficiency and photon lifetimes of such a coupled system. Firstly, we designed a photonic-crystal structure that achieves a large coupling coefficient without reducing the radiation quality factor compared to the previously proposed structure: The photonic-crystal design was changed to a more symmetric configuration to suppress radiation losses and then optimized using an automatic structure tuning method based on the Covariance Matrix Adaptive Evolutional Strategy (CMAES). Here we added two improvements to achieve an evolution toward the desired direction in the two-dimensional target parameter space (spanned by the coupling coefficient and the inverse radiation loss). Secondly, to improve the experimental cavity quality factors, we developed a fabrication process that reduces the surface contamination associated with the fabrication of the p-i-n junction: We covered the photonic structure with a SiO2 mask to avoid the contamination and the electrode material was changed from Al to Au/Cr to enable cleaning by a weak acid. Owing to these improvements of the cavity design and the fabrication process, the obtained system provides coupling strengths that are about three times stronger and photon lifetimes that are about two times longer, compared to the previously reported system.

Tissue-specific dose equivalents of secondary mesons and leptons during galactic cosmic ray exposures for mars exploration

During a human mission to Mars, astronauts would be continuously exposed to galactic cosmic rays (GCR) consisting of high energy protons and heavier ions coming from outside our solar system. Due to their high energy, GCR ions can penetrate spacecraft and space habitat structures, directly reaching human organs. Additionally, they generate secondary particles when interacting with shielding materials and human tissues. Baryon secondaries have been the focus of many previous studies, while meson and lepton secondaries have been considered to a much lesser extent. In this work, we focus on assessing the tissue-specific dose equivalents and the effective dose for males of secondary mesons and leptons for the interplanetary cruise phase and the surface phase on Mars. We also provide the energy distribution of the secondary pions in each human organ since they are dominant compared to other mesons and leptons. For this calculation, the PHITS3.27 Monte Carlo simulation toolkit is used to compute the energy spectra of particles in organs in a realistic human phantom. Based on the simulation data, the dose equivalent has been estimated with radiation quality factors in ICRP Publication 60 and in the latest NASA Space Cancer Risk model (NSCR-2022). The effective dose is then assessed with the tissue weighting factors in ICRP Publication 103 and in the NSCR model, separately. The results indicate that the contribution of secondary mesons and leptons to the total effective dose is 6.1 %, 9.1 %, and 11.3 % with the NSCR model in interplanetary space behind 5, 20, and 50 g/cm2 aluminum shielding, respectively, with similar values using the ICRP model. The outcomes of this work lead to an improved understanding of the potential health risks induced by secondary particles for exploration missions to Mars and other destinations.

Numerical Simulation of Liulin-MO Instrument for Measuring Cosmic Radiation Onboard ExoMars Trace Gas Orbiter

We present the results from numerical simulation of Liulin-MO instrument for measurement of the space radiation on board Trace Gas Orbiter (TGO) satellite of ExoMars-2016 mission during its transit to Mars in April-September 2016 [Semkova J., T. Dachev, St. Maltchev, B. Tomov, Yu. Matviichuk} et al. (2015) Radiation environment investigations during ExoMars mission to Mars – objectives, experiments and instrumentation, C. R. Acad. Bulg. Sci., 68 (4), 485–496] [Semkova J., R. Koleva, V. Benghin, T. Dachev, Yu. Matviichuk et al. (2018) Charged particles radiation measurements with Liulin-MO dosimeter of FREND instrument aboard ExoMars Trace Gas Orbiter during the transit and in high elliptic Mars orbit, Icarus, 303, 53–66], using the Geant4 package. The methodology for calculating galactic cosmic rays (GCR) linear energy transfer (LET) is described. A methodology for screening false signals in the deposited energy spectra in the Liulin-MO detectors and correspondingly LET spectra is proposed. The contribution of the individual components of the spectrum of GCR in the LET spectrum is estimated. The calculated average radiation quality factor of GCR using the cleaned from false signals LET spectrum is compared with the experimental results obtained during the transit to Mars and a reasonable agreement is observed.

European astronaut radiation related cancer risk assessment using dosimetric calculations of organ dose equivalents

An illustrative sample mission of a Mars swing-by mission lasting one calendar year was chosen to highlight the application of European risk assessment software to cancer (all solid cancer plus leukaemia) risks from radiation exposures in space quantified with organ dose equivalent rates from model calculations based on the quantity Radiation Attributed Decrease of Survival (RADS). The relevant dose equivalent to the colon for radiation exposures from this Mars swing-by mission were found to vary between 198 and 482 mSv. These doses depend on sex and the two other factors investigated here of: solar activity phase (maximum or minimum); and the choice of space radiation quality factor used in the calculations of dose equivalent. Such doses received at typical astronaut ages around 40 years old will result in: the probability of surviving until retirement age (65 years) being reduced by a range from 0.38% (95%CI: 0.29; 0.49) to 1.29% (95%CI: 1.06; 1.56); and the probability of surviving cancer free until retirement age being reduced by a range from 0.78% (95%CI: 0.59; 0.99) to 2.63% (95%CI: 2.16; 3.18). As expected from the features of the models applied to quantify the general dosimetric and radiation epidemiology parameters, the cancer incidence risks in terms of surviving cancer free, are higher than the cancer mortality risks in terms of surviving, the risks for females are higher than for males, and the risks at solar minimum are higher than at solar maximum.

Merging and Band Transition of Bound States in the Continuum in Leaky‐Mode Photonic Lattices

AbstractBound states in the continuum (BICs) theoretically have the ability to confine electromagnetic waves in limited regions with infinite radiative quality (Q) factors. However, in practical experiments, resonances can only exhibit finite Q factors due to unwanted scattering losses caused by fabrication imperfections. Recently, it has been shown that ultrahigh‐Q guided‐mode resonances (GMRs), which are robust to fabrication imperfections, can be realized by merging multiple BICs in momentum space. This study analytically and numerically investigates the merging and band transition of accidental BICs in planar photonic lattices. Accidental BICs can merge at the edges of the second stop band, either with or without a symmetry‐protected BIC. The results show that as the thickness of the photonic lattice gradually increases, the merged state of BICs transitions from the upper to the lower band edge. Using coupled‐mode analysis, the analytical merging thickness at which multiple accidental BICs merge at the second‐order Γ point is presented. The coupled‐mode analysis can be beneficial for achieving ultrahigh‐Q GMRs in various photonic lattices composed of materials with different dielectric constants.

Space radiation quality factor for Galactic Cosmic Rays and typical space mission scenarios using a microdosimetric approach

Space radiation exposure from omnipresent Galactic Cosmic Rays (GCRs) in interplanetary space poses a serious carcinogenic risk to astronauts due to the—limited or absent—protective effect of the Earth’s magnetosphere and, in particular, the terrestrial atmosphere. The radiation risk is directly influenced by the quality of the radiation, i.e., its pattern of energy deposition at the micron/DNA scale. For stochastic biological effects, radiation quality is described by the quality factor, Q, which can be defined as a function of Linear Energy Transfer (LET) or the microdosimetric lineal energy (y). In the present work, the average Q of GCR for different mission scenarios was calculated using a modified version of the microdosimetric Theory of Dual Radiation Action (TDRA). NASA’s OLTARIS platform was utilized to generate the radiation environment behind different aluminum shielding (0–30 g/cm2) for a typical mission scenario in low-earth orbit (LEO) and in deep space. The microdosimetric lineal energy spectra of ions (Zge 1) in 1 μm liquid water spheres were calculated by a generalized analytical model which considers energy-loss fluctuations and δ-ray transport inside the irradiated medium. The present TDRA-based Q-values for the LEO and deep space missions were found to differ by up to 10% and 14% from the corresponding ICRP-based Q-values and up to 3% and 6% from NASA’s Q-model. In addition, they were found to be in good agreement with the Q-values measured in the International Space Station (ISS) and by the Mars Science Laboratory (MSL) Radiation Assessment Detector (RAD) which represent, respectively, a LEO and deep space orbit.

A filtering waveguide aperture antenna based on all‐resonator structures

AbstractIn recent years, there has been a large amount of attention focused on the design of filtering antennas to reduce the front‐end size of modern wireless communication systems. Although numerous design approaches are presented in the literature, they are usually applicable to a certain microwave circuit structure. Additionally, their implementations demand extra matching circuits or a structure which leads to an increase in the filtering antenna size. In this paper, the design of a 3rd‐order filtering antenna operating at the X‐band frequencies is presented utilizing the coupling matrix approach. It is based on 3rd order coupled‐resonators filter without employing any extra structure. For the physical configuration, three inline coupled rectangular waveguide cavity resonators operating at TE101 mode are employed. The output of the last resonator is coupled to free space via a rectangular aperture. The dimensions of the aperture are manipulated to control the radiation quality factor (Qr). To validate the simulated results, the design has been fabricated using the Computer Numerical Control technique. Excellent agreement between the simulation and measurement results has been obtained. The fractional bandwidth (FBW) is more than 10% when the reflection coefficient S11 = −20 dB. The gain response is very flat (7.54 0.2 dBi) from 9.5 to 10.5 GHz. The proposed filtering antenna is compact and low profile which may be of interest in radar applications.

Terahertz ultrasensitive biosensor based on wide-area and intense light-matter interaction supported by QBIC

A quasi-bound state in the continuum (QBIC) has unique attraction in optical switch, nonlinearity, communication, and sensing due to its ultrahigh radiation quality (Q) factor. The QBIC observed in metasurfaces also provides a feasible platform to achieve in-plane strong light-matter interaction, as well as to develop ultrasensitive biosensor. However, the existing metasurface designs are difficult to realize highly efficient excitation and high-performance sensing of QBIC in terahertz (THz) band. Here, we manipulate the interference coupling between electric quadrupole and magnetic dipole by introducing an asymmetry α into the metallic metasurface structure, which excites ultrahigh quality QBIC resonance with Q factor of up to 503. Correspondingly, light field energy constrained by the metasurface and effective sensing area achieved enormous increases of about 400% and 1300%, respectively, which greatly expands the spatial extent and intensity of light-matter interaction. Simulations and experiments show that the proposed QBIC metasurface deliver a high refractive index sensitivity reaching 420 GHz/RIU, where RIU is the refractive index unit, and its direct limit of detection (LoD) for trace homocysteine (Hcy) molecules is 12.5 pmol/μL. Its performance is about 40-times better than that of the classical Dipole mode. This work provides a new avenue to achieve rapid, precise, and nondestructive sensing of trace molecules, and has potential applications in the fields of biochemical reaction monitoring, photocatalysis and photobiomodulation.

Microstrip antennas on 3D-printed magneto-dielectric substrates: fabrication and efficiency study

AbstractMagneto-dielectric antennas (MDAs) provide small sizes, enhanced bandwidths, and frequency/polarization agility. We describe the fabrication and efficiency characterization at 0.4–0.8 GHz of five microstrip MDAs, whose gradually thicker substrates were 3D-printed using an off-the-shelf polylactic acid (PLA) filament doped with ferromagnetic particles. It was experimentally discovered that efficiency increases monotonically from 12% (−9.2 dB) to 37% (−4.3 dB) as substrate thickness goes from 1.6 to 4.3 mm; the rate is faster than expected for microstrip antennas. Numerical analysis indicated that the apparent magnetic loss tangent of the MD substrate experiences a threefold decrease as the 3D printer deposits more layers of iron-doped PLA. The MDAs exhibit radiation quality factors that are 3.7–7.2 times better than the dielectric counterparts. Moreover, a simple optimization of ground plane size could increase efficiency to 55% (−2.6 dB). The reduction in magnetic loss is attributed to a reduction in eddy current loss due to the separation of agglomerate iron particles. Therefore, despite the inherently lossy material used, the potential of 3D-printed MD substrates in providing acceptable antenna efficiencies is demonstrated together with unprecedented design freedom and fabrication flexibility.

Wideband planar coupled patch antennas with enhanced radiation pattern stability

This article tries to address the unstable radiation pattern issue of the planar-coupled patch antennas with two different methods. First, characteristic mode analysis (CMA) reveals that the coupled patch antennas generate three characteristic modes with distinctive radiation patterns. A slot-loading scheme is proposed to reshape the current distribution of the higher mode and reduce its sidelobe level significantly. Then a 13.4% bandwidth with consistent radiation patterns and high gain is achieved by exciting modes 1 and 3 while suppressing unwanted modes with an aperture-coupled feeding. Second, the radiation pattern stability of the coupled patch antennas is further improved by employing shorted parasitic patches. The presented antenna can be equivalent as the same magnetic current array model under the in-phase and out-of-phase modes, and thus the radiation patterns hardly get changed. Moreover, the non-radioative nature and high radiation quality factor of the higher mode improve the radiation performance in a new principle. It not only enhances the bandwidth up to 18.5% but also results in a sharp filtering edge of gain response.

Novel Cavity-Backed Filtering Antennas Based on Radiant Metal Block Structure

In this article, a radiant metal block structure is proposed for designing reduced-size cavity-backed filtering antenna. The method of characteristic mode analysis is used to investigate the characteristic current modes of the cubic metal block, one of which can maintain a high inherent radiation capacity over a wideband. In addition, the radiation quality factor of the utilized mode is described in detail. Based on this characteristic current mode, metal block antennas with different bandwidths can be designed to realize broadside radiation. The proposed metal block antenna element can maintain stable radiation characteristics in the passband and the realized gain is greater than 9 dBi. To design the filtering antennas, the proposed metal block is cascaded with traditional resonant cavities. A third-order metal block filtering antenna array is fabricated for verification. The measurement results are basically consistent with the simulated ones. The maximum measurement gain is 12.85 dBi and the gain in the passband is flat.

Substrate-supported nano-objects with high vibrational quality factors

Recent optical time-resolved experiments on single supported nano-objects (gold nanodisks with various diameter over thickness ratios) have demonstrated a marked enhancement of their vibrational quality factors for specific nano-object morphologies, resulting from the near-suppression of radiative vibrational damping associated with the emission of acoustic waves in the nano-object environment. This paper clarifies the origin of this phenomenon, which is ascribed to the creation of a “quasi-bound state in the continuum” vibrational mode by radiative coupling between two nano-object modes whose frequencies become close for specific nano-object shapes. The symmetry breaking induced by the presence of a substrate, which limits nanodisk acoustic emission to a half-space, is shown to play an essential role in enabling such radiative coupling. The impact of the acoustic mismatch between the nano-object and the substrate is explored, and it is shown that a moderate acoustic mismatch can still enable the creation of near-localized vibrational modes with high radiative quality factors, while allowing radiative coupling effects to occur over a broad range of nano-object geometries. Although this paper focuses on the situation of a substrate-supported gold nanodisk, which has already been the object of experimental investigations, the effects that it describes are general and constitute a promising approach to enhance the vibrational quality factors of nano-objects.

Medical Countermeasure Requirements to Meet NASA's Space Radiation Permissible Exposure Limits for a Mars Mission Scenario.

The space radiation environment consists of a complex mixture of ionizing particles that pose significant health risks to crew members. NASA currently requires that an astronaut's career Risk of Exposure Induced Death (REID) for cancer mortality should not exceed 3% at the upper 95% confidence level. This career radiation limit is likely to be exceeded for even the shortest round-trip mission scenario to Mars. As such, NASA has begun to pursue more vigorously approaches to directly reduce radiation risks, despite the large uncertainties associated with such projections. A recent study considered cohort studies of aspirin and warfarin as possible medical countermeasures (MCMs) acting to reduce background cancer mortality rates used in astronaut risk projections. It was shown that such MCMs can reduce the REID for specific tissues in restricted time intervals over which the drugs were administered; however, the cumulative effect on total lifetime REID was minimal. As an extension, the present work addresses more general MCM requirements that would be needed to meet current NASA radiation limits for a Mars mission scenario. A sensitivity analysis is performed within the major components of the NASA cancer risk model that would likely be modified by MCM interventions. This includes the background cancer incidence and mortality rates, epidemiologically based hazard rates derived from acute terrestrial exposures, and radiation quality factors used to translate terrestrial exposures to space radiation. Relationships between possible MCMs and each of these components are discussed. Results from this study provide important information regarding MCM requirements needed to meet NASA limits for planned Mars missions. Insight into the types of countermeasures expected to yield greatest reductions in crew risk is also gained.

Flying without a Net: Space Radiation Cancer Risk Predictions without a Gamma-ray Basis.

The biological effects of high linear energy transfer (LET) radiation show both a qualitative and quantitative difference when compared to low-LET radiation. However, models used to estimate risks ignore qualitative differences and involve extensive use of gamma-ray data, including low-LET radiation epidemiology, quality factors (QF), and dose and dose-rate effectiveness factors (DDREF). We consider a risk prediction that avoids gamma-ray data by formulating a track structure model of excess relative risk (ERR) with parameters estimated from animal studies using high-LET radiation. The ERR model is applied with U.S. population cancer data to predict lifetime risks to astronauts. Results for male liver and female breast cancer risk show that the ERR model agrees fairly well with estimates of a QF model on non-targeted effects (NTE) and is about 2-fold higher than the QF model that ignores NTE. For male or female lung cancer risk, the ERR model predicts about a 3-fold and more than 7-fold lower risk compared to the QF models with or without NTE, respectively. We suggest a relative risk approach coupled with improved models of tissue-specific cancers should be pursued to reduce uncertainties in space radiation risk projections. This approach would avoid low-LET uncertainties, while including qualitive effects specific to high-LET radiation.

A practical approach for continuous in situ characterization of radiation quality factors in space

The space radiation environment is qualitatively different from Earth, and its radiation hazard is generally quantified relative to photons using quality factors that allow assessment of biologically-effective dose. Two approaches exist for estimating radiation quality factors in complex low/intermediate-dose radiation environments: one is a fluence-based risk cross-section approach, which requires very detailed in silico characterization of the radiation field and biological cross sections, and thus cannot realistically be used for in situ monitoring. By contrast, the microdosimetric approach, using measured (or calculated) distributions of microdosimetric energy deposition together with empirical biological weighting functions, is conceptually and practically simpler. To demonstrate feasibility of the microdosimetric approach, we estimated a biological weighting function for one specific endpoint, heavy-ion-induced tumorigenesis in APC1638N/+ mice, which was unfolded from experimental results after a variety of heavy ion exposures together with corresponding calculated heavy ion microdosimetric energy deposition spectra. Separate biological weighting functions were unfolded for targeted and non-targeted effects, and these differed substantially. We folded these biological weighting functions with microdosimetric energy deposition spectra for different space radiation environments, and conclude that the microdosimetric approach is indeed practical and, in conjunction with in-situ measurements of microdosimetric spectra, can allow continuous readout of biologically-effective dose during space flight.

Оптимизация спектральных и геометрических параметров параметрического генератора света среднего ИК-диапазона

The results of computational and experimental studies of the parameters of a parametric light generator in the mid-IR range are presented. One of the main problems of OPO in the near and mid-IR range (1-8 μm) is the high divergence of the output radiation. The purpose of this study is to improve the spectral and amplitude-spatial characteristics for the out-of-cavity scheme of the IR-OPO ring resona-tor. In an in vitro experiment simulating the radiation of an IR parametric laser, the dependences of the spectral width and quality factor of the radiation of a tunable laser frequency on the wavelength were obtained. It is shown that the improved optical-geometrical parameters of the out-of-zone OPO scheme made it possible to achieve high values of the spectral radiation width (≤ 1 cm-1) and quality factor (≥ 4.106). It is shown that such a developed scheme of an out-of-cavity OPO based on new chalcogenide crystals will expand its application in the mid- and far-IR ranges.

Robust Prediction of the Bandwidth of Metamaterial Antenna Using Deep Learning

The design of microstrip antennas is a complex and time-consuming process, especially the step of searching for the best design parameters. Meanwhile, the performance of microstrip antennas can be improved using metamaterial, which results in a new class of antennas called metamaterial antenna. Several parameters affect the radiation loss and quality factor of this class of antennas, such as the antenna size. Recently, the optimal values of the design parameters of metamaterial antennas can be predicted using machine learning, which presents a better alternative to simulation tools and trial-and-error processes. However, the prediction accuracy depends heavily on the quality of the machine learning model. In this paper, and benefiting from the current advances in deep learning, we propose a deep network architecture to predict the bandwidth of metamaterial antenna. Experimental results show that the proposed deep network could accurately predict the optimal values of the antenna bandwidth with a tiny value of mean-square error (MSE). In addition, the proposed model is compared with current competing approaches that are based on support vector machines, multi-layer perceptron, K-nearest neighbors, and ensemble models. The results show that the proposed model is better than the other approaches and can predict antenna bandwidth more accurately.

Analysis of an electrically reconfigurable metasurface for manipulating polarization of near-infrared light

Integrating plasmonic metasurfaces with transparent conductive oxide (TCO) materials provides a new, to the best of our knowledge, opportunity to dynamically manipulate all degrees of freedom of light beams. Applying external stimuli to TCOs changes the plasmonic response of the nanostructure as a result of establishing an inhomogeneous optical property with deeply subwavelength films of epsilon-near-zero media, which is a challenge for better theoretical understanding of the dynamical tuning functionality. In this paper, we propose a dynamically reconfigurable reflective metasurface with the capability of electrical manipulation of the polarization state of near-infrared light. The structure behavior is investigated by numerical analysis and described based on the coupled-mode theory concept using the parameters of resonance wavelength, absorption, and radiation quality factors, altered by an external voltage. Variation of the applied bias voltage from − 0.7 to 4.2 V for p -polarized light leads to a wide range of absorption quality factors from 43 to two. This change causes a dramatic decrease in the equivalent surface impedance of the metasurface in the ratio 4.9:0.2, which may pave the way to tailor polarization-manipulating functions such as circular-to-linear polarization conversion and cross-polarization conversion.

New Design Approach of “3rd - Order Dipole Antenn” Based on Direct Coupled Resonator Bandpass Filter

ABSTRACT In ultra-wideband (UWB) antennas used with the applications of wireless communication systems (WCS), the following five antenna parameters; radiation patterns, directivity, bandwidth, efficiency and antenna gain should be well optimized. A new design approach-based on coupling matrix theory of synthesis antenna has been presented. The most important parameters of this matrix are; external normalized quality factor, normalized un-loaded quality factor, radiation quality factor and coupling coefficients between the resonators. Accuracy in calculating these parameters will greatly facilitate control of the antenna bandwidth to be designed. The design approach included a BPF which was also expanded to become an antenna arrays-filter in the hope of increasing the gain and bandwidth of the antenna. Further, a matching unit is placed between the designed BPF and the antenna, to overcome the mismatching situation, and to achieve a high transmission power. The paper presented a new design approach for an active BPF at frequency “2.45 GHz” and then its integration with a 3rd-order dipole antenna [1]. This design is followed by the creation of another efficient couple-resonant filter (CRF), in which each resonant grid is represented by a radiator. Moreover, a lossless two-port dipole antenna was introduced. Here, each of the poles is integrated with an inductor, to sure that the bipolar antennas can exploit as a resonator. The scores of the simulation-sketches and the computed results were convincing. Finally, the performance efficiency of the designed filter at the resonant frequency 2.45 GHz and for both “H-plane” and “E-plan” were summarized in Table 1.