Band Radiation Research Articles

Terahertz waves dynamic diffusion in 3D printed structures

Applications of metamaterials in the realization of efficient devices in the terahertz band have recently been considered to achieve wave deflection, focusing, amplitude manipulation and dynamical modulation. Terahertz metamaterials offer practical advantages since their structures have typical sizes of hundreds microns and are within the reach of current three-dimensional (3D) printing technologies. Here, we propose terahertz photonic structures composed of dielectric rods layers made of acrylonitrile styrene acrylate realized by low-cost, rapid, and versatile fused deposition modeling 3D-printing. Terahertz time-domain spectroscopy is employed for the experimental study of their spectral and dynamic response. Measured spectra are interpreted by using simulations performed by an analytical exact solution of the Maxwell equations for a general incidence geometry, by a field expansion as a sum over reciprocal lattice vectors. Results show that the structures possess specific spectral forbidden bands of the incident THz radiation depending on their optical and geometrical parameters. We also find evidence of disorder in the 3D printed structure resulting in the closure of the forbidden bands at frequencies above 0.3 THz. The size disorder of the structures is quantified by studying the dynamics diffusion of THz pulses as a function of the numbers of layers of dielectric rods. Comparison with simulations of light diffusion in photonic crystals with increasing disorder allows estimating the size distributions of elements. By using a Mean Squared Displacement model, from the broadening of the pulses’ widths it is also possible to estimate the diffusion coefficient of the terahertz radiation in the photonic structures.

An ultrawideband miniaturized MIMO antenna with split ring Yagi like structures for S and X frequency multiband applications

A miniaturized three split ring-like Multiple-Input Multiple-Output (MIMO) antenna is presented for the S and X frequency band applications. The proposed antenna has been numerically investigated at operating frequency 1-15 gigahertz (GHz). The MIMO antenna is analyzed, and its prototype is measured in five types of structure to identify the effect of the split ring and other physical conditions. This antenna is fabricated on the FR- 4 substrates with a dimension of 25 mm × 40 mm which will provide the miniaturization factor of λ/2. The high gain of 6.61 dBi and an ultrawideband of 3.25 GHz is achieved by using split-ring resonators (SRRs) in the proposed miniaturized MIMO antenna structure. We have also analyzed the effect of the split rings on the overall radiation band and return loss on the S and X frequency band. Furthermore, the prototype measurement confirms the suggested antenna radiation characteristics.

28 GHz and 38 GHz Dual-Band Vertically Stacked Dipole Antennas on Flexible Liquid Crystal Polymer Substrates for Millimeter-Wave 5G Cellular Handsets

Minimizing the size of mobile antennas is necessary for integrating the components inside a mobile device. Wideband and multiband antennas are also required to cover various 5G mobile communication frequency spectra. This article presents a vertically stacked dipole antenna array operating in the 28/38 GHz dual-band. The proposed antenna is small and satisfies the need for wide bandwidth in the form of a dual band. The antenna structure has symmetric 38 GHz band radiators positioned above and below a multilayer substrate, and a 28 GHz band radiator positioned on the middle plane, providing a dual-band antenna structure with small lateral width. Herein, two types of antenna structures are proposed, each with a single-ended and differential feed structure for compatibility with various RF front ends. The single antenna yields −10 dB bandwidth for return loss of 23.9% and 14.4%, and gain of 4.8 and 4.6 dBi at 28 and 38.5 GHz, respectively. The 4-element antenna array yields a gain of 9.0 dBi at 28 GHz and 10.3 dBi at 38.5 GHz. It was fabricated on a flexible substrate and can be bent and inserted into the lateral edge of the terminal. The proposed antenna elements and arrays satisfy the performance factors requisite for millimeter wave 5G communication including compact size, wideband, dual-band, and adequate gain.

Trajectories and radiation of charged particles in the pulsar magnetosphere

ABSTRACT Trajectories and radiation of the accelerating electrons are studied in the pulsar magnetosphere approximated as the electromagnetic field of the Deutsch’s solutions. Because the electrons are accelerated rapidly to ultra-relativistic velocity near the neutron star surface, the electron velocity vector (and then its trajectory) is derived from the balance between Lorentz force and radiation reaction force, which makes the pitch angle between electron trajectories and magnetic field lines non-zero in most part of the magnetosphere. In such a case, the spectral energy distributions (SEDs) of synchro-curvature radiation for the accelerating electrons with a mono-energetic form are calculated. Our results indicate that: (i) the pitch angle is the function of electron position (r, θ, ϕ) in the open field line regions, and increases with increasing r and θ as well as increasing the inclination angle; (ii) the radius of curvature becomes large along the particle trajectory, and (iii) the SED appears a double peak structure depending on the emission position, where the synchrotron radiation plays an important role in X-ray band and curvature radiation mainly works in GeV band, which is only determined by parameters α and ζ.

Imaging Regional Lung Structure and Function in Small Animals Using Synchrotron Radiation Phase-Contrast and K-Edge Subtraction Computed Tomography.

Synchrotron radiation offers unique properties of coherence, utilized in phase-contrast imaging, and high flux as well as a wide energy spectrum which allow the selection of very narrow energy bands of radiation, used in K-edge subtraction imaging (KES) imaging. These properties extend X-ray computed tomography (CT) capabilities to quantitatively assess lung morphology, and to map regional lung ventilation, perfusion, inflammation, aerosol particle distribution and biomechanical properties, with microscopic spatial resolution. Four-dimensional imaging, allows the investigation of the dynamics of regional lung functional parameters simultaneously with structural deformation of the lung as a function of time. These techniques have proven to be very useful for revealing the regional differences in both lung structure and function which is crucial for better understanding of disease mechanisms as well as for evaluating treatment in small animal models of lung diseases. Here, synchrotron radiation imaging methods are described and examples of their application to the study of disease mechanisms in preclinical animal models are presented.

High-Precision Measurement of Sea Surface Temperature with Integrated Infrared Thermometer.

The sea surface temperature (SST) is a crucial parameter system in climate monitoring. Satellite remote sensing is currently the most common approach for measuring long-term and large-area sea surface temperatures. The SST data measured by the satellite radiometer include the sea surface skin temperature (SSTskin) at a depth of approximately 10 μm. Satellite remote sensing measurement data must be compared and validated with on-site measured data. There are various solutions for on-site measuring instruments; the essential components are usually infrared radiation sensors with radiation output. This paper uses an ordinary integrated infrared thermometer without a radiation output function to remotely measure the sea surface temperature to achieve a high-precision measurement. The scheme of integrating infrared thermometers to measure the sea surface temperature is investigated in this paper. Based on Planck’s formula, the bidirectional conversion relationship between temperature and radiation in a certain band is established. The experimental system introduced in this paper uses an integrated infrared thermometer to measure the small blackbody and the target in a cyclic measurement system. We combine it with the sea surface emissivity characteristics and eliminate the influence of sky background radiation on the sea surface to obtain the actual amount of radiation on the sea surface, from which we obtain the actual radiation amount on the sea surface. Accurate SST can be calculated from the actual amount of radiation at the sea surface. The temperature measurement accuracy can reach 0.1 K, allowing it to meet on-site temperature measurement requirements, as well as the comparison measurement requirements confirmed by satellite remote sensing on-site data. There are relatively few products available for sensors with a temperature measurement accuracy of 0.1 K on the market, and temperature measurement equipment with a temperature measurement accuracy of 0.1 K is relatively expensive. Cost is one of the important factors to consider when using in bulk, especially as global warming increases the need for ocean monitoring. The scheme proposed in this paper is beneficial to reduce the volume and weight of measuring instruments, reduce the cost, and promote the large-scale combined application of sea surface temperature change monitoring.

Smith–Purcell radiation improved by multi-grating structure

The photonic crystal structure has attracted much attention due to its ability to confine light. In this paper, we present our study on an improved Smith–Purcell radiation from a simple metal photonic crystal excited by moving electrons. Different from the wide-band Smith–Purcell radiation from a single metal grating, the results show that the injected electrons could induce more dipole oscillations inside the multi-grating structure, and it leads to the enhancement of the radiation intensity. In addition, there are strong resonances in metal multi-grating structure, and the resonance characteristics may narrow the radiation band, which leads to a radiation with an obvious peak in the spectrum. Therefore, the multi-grating structure has the ability to enhance the radiation intensity and shape the radiation frequency band. By optimizing the structure parameters, coherent and tunable Smith–Purcell radiation can be realized, and it provides a potential way to develop band-controllable light or THz radiation source.

Performance analysis of double-face logarithmic spiral metamaterial superstrate for full enhancement of circularly polarized 5G spiral patch antenna investigated using characteristic mode analysis

AbstractIn this article, a novel double-face logarithmic spiral metamaterial (LSMTM) superstrate-inspired multiple-input multiple-output (MIMO) for fully enhanced circularly polarized (CP) antenna system is examined for 5G wireless communications. This novel double-face LSMTM superstrate acts as a planar concave-concave lens. Initially, the antenna is designed with a circular spiral patch to generate CP radiation in the frequency band of interest. Then, at a height of 6.5 mm (0.606 λo) above the MIMO antenna, which has a 0.8 mm (0.075 λo) edge-to-edge separation, the LSMTM superstrate is employed for isolation, gain, and bandwidth improvement. The proposed superstrate enhances the isolation, gain, and bandwidth of the antenna by about 32 dB, 3.47 dB, and 900 MHz, respectively. In contrast to the conventional technique of verifying operation with a simulated surface current distribution, characteristic mode analysis (CMA) is used to provide a better explanation of the proposed antenna's different modes and the creation of circular polarization. Additionally, the CMA supports the development of an effective technique that can predict whether or not the isolation can be further improved. The simulated results align with the measured results and are well adapted for 5G wireless communication devices.

Particle Acceleration in Mildly Relativistic Outflows of Fast Energetic Transient Sources

Recent discovery of fast blue optical transients (FBOTs)—a new class of energetic transient sources—can shed light on the long-standing problem of supernova—long gamma-ray burst connections. A distinctive feature of such objects is the presence of modestly relativistic outflows which place them in between the non-relativistic and relativistic supernovae-related events. Here we present the results of kinetic particle-in-cell and Monte Carlo simulations of particle acceleration and magnetic field amplification by shocks with the velocities in the interval between 0.1 and 0.7 c. These simulations are needed for the interpretation of the observed broad band radiation of FBOTs. Their fast, mildly to moderately relativistic outflows may efficiently accelerate relativistic particles. With particle-in-cell simulations we demonstrate that synchrotron radiation of accelerated relativistic electrons in the shock downstream may fit the observed radio fluxes. At longer timescales, well beyond those reachable within a particle-in-cell approach, our nonlinear Monte Carlo model predicts that protons and nuclei can be accelerated to petaelectronvolt (PeV) energies. Therefore, such fast and energetic transient sources can contribute to galactic populations of high energy cosmic rays.

AN IMPROVED SOLUTION FOR SHIELDING OF THERMAL RADIATION FROM FIRES USING MIST CURTAINS OF PURE WATER OR SEAWATER

An improved theoretical model for shielding of thermal radiation from large-scale fires using pure water or seawater mists is presented. It is a continuation of a recent study and takes into account both the reabsorption of radiation in the absorption bands of gases and the variations of the radiative flux along the flame. The combined heat transfer problem consists of the radiative transfer, droplet evaporation kinetics, and convective heat transfer along the curtain. Previously suggested spectral models for the optical properties of water droplets and salt particles are used in the calculations. Radiative heat losses to the nozzle head and the floor below the curtain, as well as a decrease in the downward velocity near the floor, are taken into account for the first time. It is shown that these heat losses are insignificant even for thick curtains. The use of smaller droplets in the second layer of the mist curtain has been confirmed to reduce the required total water supply flow rate. It is also shown that the protection provided by a seawater curtain is almost the same as that obtained with pure water. Seawater is even preferable for better protection against fire radiation in the lower part of the curtain, where pure water droplets evaporate completely, whereas hollow sea salt particles remain in the lower part of the seawater mist curtain. The study confirms that seawater can be used in coastal areas, offshore platforms, and maritime transportation ships.

Spark Sensor Based on Lithium-Potassium-Aluminophosphate Borate Glass Doped with Eu

We demonstrate the concept of a spark sensor operating in UV range of the electromagnetic spectrum. The design of the device and the results of measurements of its most important characteristics are presented. Response time of the sensor is 3.8 ms and response threshold is 0.4 mW/m2. For the sensing element of the device glass material with the composition 10Li2O-15K2O-15Al2O3-35B2O3-25P2O5 doped with 5 at.% Eu is used. The peak of luminescence of the material corresponds to 611 nm when excited by a wide band (with wavelengths from 300 to 400 nm) of UV radiation that guarantees the high operation ability of the designed sensor.

ИСПОЛЬЗОВАНИЕ РАДИОЛОКАЦИОННЫХ СИГНАЛОВ С ОРТОГОНАЛЬНЫМИ ПОЛЯРИЗАЦИЯМИ В ЗАДАЧЕ ОБНАРУЖЕНИЯ НАХОДЯЩИХСЯ ЗА ПРЕГРАДОЙ БИОЛОГИЧЕСКИХ ОБЪЕКТОВ

In recent decades, there has been a great interest in the use of ultra-wideband (UWB) radar methods for detecting living biological objects hidden behind various barriers. The wide frequency band of the UWB radiation makes it possible to provide a high penetrating power along with a spatial resolution sufficient to detect oscillations characteristic of the respiration of a living organism. This article considers a model of an ultra-wideband radar for detecting a living biological object located behind an optically-nontransparent obstacle. The considered radar model consists of two channels, each of which has two independent antennas with orthogonal polarizations, that supports implement processing orthogonal polarization echo signals. A method is proposed to increase the information content by using the amplitude, phase and polarization characteristics of the reflected signals. This is done in order to isolate the signals reflected from biological objects against the background of interfering reflections. The use of the proposed method leads to reduce amount of processed data and a decrease the probability of false detection.

A weather-resistant daytime radiative cooler based on fluorocarbon resin

Daytime radiative cooling (DRC) technology is used for cooling by reflecting sunlight and radiating the heat to outer space. It does not require energy for cooling, and there is no pollution. In this study, a double-layer DRC structure was prepared using the doctor's blade method. The upper layer was a fluorocarbon resin (FEVE), while the bottom layer was a silver layer. The average reflectivity in the solar radiation band and the average emissivity in the atmospheric window were 0.933 and 0.945, respectively. Without considering non-radiative heat transfer, the cooling power was calculated as 128.75 W/m2 under direct sunlight and for the ambient temperature of 27 °C. When the material was used as a radiative cooler in Tianjin, China, the average temperature drop from 10:00 a.m. to 2:00 p.m. was 5.1 °C. The proposed polymer cooler is cost-efficient, easy to fabricate and commercially feasible. In addition, its good weather resistance makes it possible for radiative coolers to be used outdoors for a long time, which will greatly promote the wider practical application of DRC.

Chemical Effects of Light and Photography

Abstract: This article discusses the chemical and biological effects of light and photography. Light is a form of energy known as electromagnetic radiation, and its expression at wavelengths and the unit of measurement, nanometer, is considered a separate characteristic. It ranges from very short wavelength to long wavelength radiation. Visible (normal / sunlight) light is the band of radiation that our eyes can see. Under the influence of light, the following processes can occur: the attachment of atoms to molecules, dissociation, photochemical reaction, synthesis reaction. This article discusses light and its chemical effects, as well as photography. Keywords: Photosynthesis. Photography, electromagnetic radiation, synthesis, photography, xerography, photography, photochemistry, eosin, erythrosine, methylene film.

Precoded SLM and PTS Scheme for Reduced PAPR in OFDM for Wireless Communications

Orthogonal Frequency Division Multiplexing (OFDM) contribute high data rates in current as well as future wireless communication systems but it aches from high Peak to Average Power Ratio (PAPR). But this high PAPR makes the High-Power Amplifier (HPA) complex which increases the cost of it and leads to the drawbacks like Inter Carrier Interference (ICI) and rise in out of band radiation. Even though many techniques are there to decrease the complexity of HPA by reducing the PAPR, Selected Mapping (SLM) and the Partial Transmit Sequence (PTS) provides less PAPR with low complexity. In this paper, both PTS and SLM are combined with Discrete Sine Transform (DST) and their PAPR and efficiencies are also compared with OFDM signal. The proposed hybrid DST-PTS and DST-SLM provides less PAPR compared to OFDM, SLM and PTS techniques with low complexity. Also, the bit error rate for DST-SLM and DST-PTS techniques are compared for different values of SNR. In future wireless communication systems, these proposed techniques can be used as they provide less bit error rate and less PAPR with low complexity

Фотолюмінесценція нанокристалічного CdTe, впровадженого в пористий кремній

A method of colloidal synthesis of monodisperse nanocrystals (NC) with high stability, narrow bands of photoluminescence (PL) and high quantum yield has been developed. The process of colloidal synthesis took place at room temperature and for the passivation of NC used a variety of surfactants. The surface of NC CdTe was modified by introducing them into a matrix, organic or crystalline. In our case, the matrix was porous Silicon (PS), that is a composite structure was formed on the basis of the matrix and NC semiconductor. Nanocomposite structures of PS – NC CdTe were obtained by introducing colloidal solutions of NC CdTe into the solid matrix of PS and subsequent processing at a certain temperature regime. The photoluminescent properties of a composite system in which the matrix is microcrystalline PS and the second component is NC CdTe deposited from a colloidal solution of NC CdTe have been studied. The peculiarity of this system is that both components have PL of different intensities.The large difference in PL intensities and different positions of the radiation bands allowed, comparing the PL spectra of the colloidal solution of NC CdTe, PS and NC CdTe – PS at different stages of introduction of CdTe nanoparticles into the porous Silicon surface, to identify the interaction and mutual influence of the two constituent materials. The main disadvantages of the method are its relative novelty, which leads to the need for empirical selection of some parameters of the synthesis. The planned change of properties of PS and colloidal solutions of NC CdTe by variation of technological methods of synthesis and processing methods will allow to control the physical properties of this composite system and use it to develop new principles of design and creation of new generation sensor devices.

Study on the optoelectronic properties of Zn and Mg doped CuGaO2 nanoplates

In this study, significant optoelectronic performance boost was observed after Mg and Zn doping of hexagonal CuGaO2 (CGO) nanoplates (NPs) by the hydrothermal method. Details effects of dopant are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), absorption spectra, and photoluminescence (PL)spectrum. There is a sharp peak at 700 nm in the PL spectrum of pure CGO NPs ascribed to the intrinsic defect caused by Cu vacancy (VCu) and the peak increases dramatically in intensity as elements doping. To deeply understand the enhancement mechanism in PL intensity of Zn-doped CGO (ZCGO) NPs and Mg-doped CGO (MCGO) NPs, the band diagram and radiation transition of divalent ions doped CGO NPs are investigated in detail. These results reveal that the divalent element doping (ZCGO especially) could increase the carrier concentration of CGO material effectively and form stable and high-intensity PL emission. In addition, photodetection performance of pure CGO NPs and doping CGO NPs has been demonstrated, which could be enhanced by constructing non-planar heterojunction of nanoplate and ZnO nanowire arrays. And Zn doping has a significantly better effect than Mg doping in absorption, photoluminescence and ultraviolet (UV) detection. The findings can play an important role in the regard of optoelectronic performance enhancement of CGO NPs, which common used in optoelectronic devices such as red light emitters and ultraviolet (UV) detectors.

Dual-Band Dual-Mode Patch Antenna With High-Gain and Wide-Beam Radiations in Two Respective Bands

In this article, a novel dual-band dual-mode (DBDM) patch antenna is proposed with flexible radiation coverage and a simple structure. Distinct radiation properties with high-gain in the lower band and wide-beam in the upper band could be attained under a small frequency ratio and a single element. The working principle of the wide-beam radiation is, for the first time, proposed and theoretically analyzed based on the electric current calculation, providing a good insightful understanding of the radiation of the inverse currents. The high-gain radiation in the lower band is realized by introducing the shunt inductive effect while maintaining a negligible influence on the upper band. In terms of realization, a pair of stubs and shorting pins are properly loaded on a square patch to achieve the conditions required in the theoretical analysis. It indicates that the proposed method could be easily achieved with the simple structure of a single layer and a single element. Additionally, further discussion on the size reduction of the patch is provided with good cross-polarization. Two prototypes are finally designed, fabricated, and tested. The simulated and measured results exhibit good agreement with each other, certifying the validity of the proposed method. All these attractive merits, such as flexible coverage with high-gain and wide-beam radiations, simple structure with a single element, small achievable frequency ratio, and low profile, demonstrate that the proposed antenna could be a good potential candidate in the modern wireless systems.

A model and thermal loss evaluation of a direct-absorption solar collector under the influence of radiation

A complete two-wavelength band radiation model of a direct-absorption solar collector (DASC) is proposed herein. The model considers not only the absorption but also the emission and scattering effects in the heat transfer fluid. In previous studies, the emission and scattering effects are generally ignored because of the complex solution of the radiative transport equation in the participant medium. This work also improves the evaluation of heat loss and analyzes the effects of fluids on the radiative heat loss of two-wavelength bands. The results show that the DASC has both advantages and drawbacks compared with the traditional surface absorption solar collector (SASC). Also, this study realizes the regression of the radiative heat loss and effective emissivity using response surface methodology (RSM) with a maximum error of 5.6%. When measurement errors of 2% were introduced into the numerical model, the maximum deviation between the calculated results and the reference values corresponding to no error still met the accuracy requirements. This work demonstrates the necessity of considering the effects of emission and scattering in the DASC photothermal conversion, and provides a robust method to evaluate the heat loss of the DASC.

Gas discharge sustained by powerful THz and sub-THz gyrotrons in the mixtures of noble gases with nitrogen

The discharge propagation velocity towards electromagnetic radiation of sub-THz and THz bands was measured in various noble gases (argon, krypton) mixtures with nitrogen in the wide pressure range (0.1 – 2 atm) for various field intensities into the focal spot (from dozen of kW/cm2 to several MW/cm2). In the experimental setups two different gyrotrons were used. In case of 263 GHz it was CW gyrotron with power up 1 kW, in case of 670 GHz – pulsed gyrotron (20 μs) with power up to 40 kW. In both cases the focusing system provided the size of the focal spot of (2–3)·λ, which ensured the investigation of discharge phenomena in a wide pressure range (0.1 – 2 atm). In both cases discharge appeared in the focal spot spread towards heating radiation into the area with the field intensity much less than one in the focal spot. Velocity of the discharge propagation was measured by using photos from speed camera with small exposure (down to 20 ns) and streak camera. It was demonstrated that discharge velocity increase along with pressure decrease and drops with electric field decrease as it moves away from the focal spot.