Forward Radiation Research Articles

Advanced directional beam control via holographic acoustic metasurfaces for multibeam scanning

Acoustic multi-beam leaky-wave antennas, designed with holographic metasurfaces, have great potential for beamforming by achieving directional beam control. We propose a planar holographic metasurface for beam steering using multi-beam acoustic radiation serving as high-gain acoustic leaky wave antennas. Based on the principle of holography, we designed a metasurface that adjusts its admittance in a sinusoidal pattern. This surface consists of periodic cylindrical holes with varying depth profiles. A monopole point source is positioned in the middle of the patterned surface, which generates surface waves on the modulated surface and emits acoustic leaky-wave radiation in the desired directions. The holographic admittance surface is designed to radiate an acoustic beam at a frequency of 20 kHz. Additionally, the concept was extended to generate multi-beam scanning for forward leaky-wave radiation in the holographic process. In this research, we employed 3D additive manufacturing to create acoustic holograms, manipulating surface admittance variation at a resolution smaller than the wavelength. The experimental measurements aligned well with both the theoretical and numerical analysis findings, affirming the effectiveness of the proposed technique. The methodology exhibits broad applicability across various domains, including sonar, ultrasound imaging, waveform manipulation, and acoustic communication.

Design of a low-profile bi-directional radiated Fabry-Perot cavity antenna with independent forward and backward radiation based on metasurface technique

This paper introduces a novel Fabry-Perot cavity (FPC) antenna design based on metasurface technique to achieve bi-directional radiation with independent forward and backward beam control capability and a low-profile configuration. Two pieces of partially reflective metasurface (PRMS) based on receiver-transmitter architecture with independent control of transmission and reflection phases are designed to serve as the upper and lower layers of the FPC antenna, respectively. By manipulating the transmission phase distribution of the two pieces of PRMS, designable independent multi-beam bi-directional radiation patterns can be achieved. For validation, two FPC antennas based on the proposed configuration are designed with different bi-directional radiation patterns. Proved by simulated results, Antenna 1 can achieve forward dual-beam and backward single-beam radiation simultaneously with a return loss of less than -10 dB at 10.4 GHz. The two beams of forward radiation point in the -45° and 35° directions, respectively, with gains of 7.42 dBi and 7.70 dBi. The gain of the single beam of backward radiation is 10.82 dBi. Antenna 2 can achieve a four-beam radiation pattern with both forward and backward dual beams. The beam directions of the four beams are -153°, -44°, 37°, and 146°, respectively. The gains in each direction are 5.45 dBi, 6.63 dBi, 5.97 dBi, and 5.22 dBi, respectively. The overall profile is 23.72 mm (0.81 λ) for both antennas. The prototype of Antenna 1 is fabricated and measured. The results are in good agreement with the simulated counterparts, which demonstrates the feasibility of the proposed design methodology.

Jet Structure and Burst Environment of GRB 221009A

We conducted a comprehensive investigation of the brightest-of-all-time GRB 221009A, using new insights from very high-energy (VHE) observations from LHAASO and a complete multiwavelength afterglow data set. Through data fitting, we imposed constraints on the jet structure, radiation mechanisms, and burst environment of GRB 221009A. Our findings reveal a structured jet morphology characterized by a core+wing configuration. A smooth transition of energy within the jet takes place between the core and wing, but with a discontinuity in the bulk Lorentz factor. The jet structure differs from both the case of the short GRB 170817A and the results of numerical simulations for long-duration bursts. The VHE emission can be explained by the forward shock synchrotron self-Compton radiation of the core component, but requiring a distinctive transition of the burst environment from uniform to wind-like, suggesting the presence of complex pre-burst mass ejection processes. The low-energy multiwavelength afterglow is mainly governed by the synchrotron radiation from the forward and reverse shocks of the wing component. Our analysis indicates a magnetization factor of 5 for the wing component. Additionally, by comparing the forward shock parameters of the core and wing components, we find a potential correlation between the electron acceleration efficiency and both the Lorentz factor of the shock and the magnetic field equipartition factor. We discuss the significance of our findings, potential interpretations, and remaining issues.

Comparison of Mammographic Findings after Conventional Radiotherapy and forward Intensity-Modulated Radiation Therapy in Breast Conservative Therapy.

This study aimed to determine and compare mammographic findings after conventional radiotherapy and forward intensity-modulated radiation therapy for breast conservation. Eighty-six patients with BCT (373 mammograms) were included between 2010-2015 and had post-treatment mammograms available for review. All mammograms were taken with an 18 × 24 cm detector and 0.070 mm pixel size (Selenia Dimensions, Hologic, Marlborough, Massachusetts, US). We documented the radiation technique, dose, and mammographic findings (e.g., edema, thickening, scarring, and calcification). We tracked the stability duration for each patient and grouped mammographic findings into 1-, 2, and 3 years post-treatment. SPSS version 26 and Stata version 18 were used for analysis. The FIMRT group received a lower total radiation dose (p=0.030), a higher dose per fraction (p=0.030), and a lower maximum skin dose (p<0.001). The time to stable was shorter in the FIMRT group (975 days for CRT vs. 478 days for FIMRT; p=0.001). Among the 86 patients, the FIMRT group showed less breast parenchymal edema and noticeable scarring at 1, 2, and 3 years post-treatment than the CRT group, although the difference was not statistically significant. In the FIMRT group, post-BCT mammographic findings, including breast parenchymal edema and marked scar appearance, were fewer than those in the CRT group, and the duration to stable was significantly reduced.

Directional microwave emission from femtosecond-laser illuminated linear arrays of superconducting rings

We examine the electromagnetic emission from two photo-illuminated linear arrays composed of inductively charged superconducting ring elements. The arrays are illuminated by an ultrafast infrared laser that triggers microwave broadband emission detected in the 1–26 GHz range. Based on constructive interference from the arrays a narrowing of the forward radiation lobe is observed with increasing element count and frequency demonstrating directed GHz emission. Results suggest that higher frequencies and a larger number of elements are achievable leading to a unique pulsed array emitter concept that can span frequencies from the microwave to the terahertz (THz) regime.

2–18 GHz dual‐polarised tightly coupled dipole array with ±75° scanning range

AbstractThe authors proposed an ultrawideband (UWB) dual‐polarised tightly coupled dipole array (TCDA). A split X‐shaped resistive frequency selective surface (FSS) is utilised, which can get more admirable impedance matching. The proposed antenna can achieve active voltage standing wave ratio (VSWR) below 2.9 when scanning up to ±75° and ±60° in the E and H planes from 2 to 18 GHz, respectively. Furthermore, two rectangular patches served as directors are designed, which can provide stronger forward radiation to reduce the loss of resistive FSS for radiation efficiency. As a result, the average radiation efficiency is above 84% and the lowest radiation efficiency is 70%. Moreover, the overall antenna profile is 15 mm (0.1λ at the largest working wavelength). To validate the design method, a 16 × 16 array prototype is fabricated and measured. Good agreement is achieved between the simulations and measurements.

Assessing the marginal costs of radiation therapy and antiestrogen therapy for post-lumpectomy, early-stage breast cancer across Medicaid and Medicare plans.

529 Background: With recent Level I evidence (FAST FORWARD) supporting radiation therapy (RT) duration as short as one week and Level I evidence (CALGB9343) supporting RT omission in favor of antiestrogen endocrine therapy (ET) alone in select patients, the necessity of both RT and ET, adjuvantly, in early-stage breast cancer (BC) has been questioned. Evidence providing granular details on the role of insurance in the aggregate cost of RT and ET is lacking. This project disaggregates costs by insurance plan to increase transparency of out-of-pocket (OOP) cost estimates. Methods: National Comprehensive Cancer Network guidelines were utilized to determine the proper treatments, with FAST FORWARD radiation dose/fractionation (26 Gy in 5 fractions) representing RT. Treatments were identified using Current Procedural Terminology and Healthcare Common Procedure Coding System codes. OOP costs, deductibles, and copay/coinsurance were calculated for Medicaid, Original Medicare, Medigap Plan G, and Medicare Part D Rx. The medicare.gov, medicaid.oh.gov, aarpmedicareplans.com, and cms.gov were used to determine pricing. Price estimates reflect actual costs per insurance plan rather than costs estimated from claims data. All procedures were considered to be performed in an Ohio hospital setting, insurance coverages were based on the zip code 44106, and total expenses were based on all treatments plus a 5-year follow-up (not adjusted for inflation). Results: Treatment charges for ET include medical oncology initial consultation, biannual medical oncology follow-up, baseline bone density study, and Anastrozole cost (5-years). Treatment charges for RT include initial consultation, treatment planning, dosimetry calculations, treatment device, simulation and verification, RT delivery, on-treatment visits, and medical physics consultation. Original Medicare beneficiaries face an OOP cost of 20% for Medicare Part B claims with no cost cap for approved procedures after the deductible. Medications are covered under Medicare Part D with copays. This results in a marginal OOP treatment charge (after 5-year follow-up) of $767.54 for ET alone and $1,416.78 for ET + RT. Medigap Plan G beneficiaries face a marginal OOP charge of $1,225 for both ET alone and ET + RT, assuming the $226 Medicare Plan B deductible is met by the cost of lumpectomy during the year of RT. For Medicaid beneficiaries (assuming all treatments are approved by Medicaid), all expenses are covered without limit, resulting in no OOP expense for either treatment plan. Conclusions: Discussions of adding RT to ET for post-lumpectomy early-stage BC often involves considerations of treatment costs. This model (based on actual cost estimates per insurance plan rather than claims data) can help to enhance cost transparency by comparing expenses between Medicare and Medicaid plans.

Perfect excitation and attenuation-free propagation of graphene surface polaritons under optical admittance matching.

Graphene supports both transverse magnetic and electric modes of surface polaritons due to the intraband and interband transition properties of electrical conductivity. Here, we reveal that perfect excitation and attenuation-free propagation of surface polaritons on graphene can be achieved under the condition of optical admittance matching. With both vanished forward and backward far-field radiation, incident photons are fully coupled to surface polaritons. This requires an exact match between the admittance difference of sandwiching media and the conductivity of graphene, resulting in no decay of propagating surface polaritons. The dispersion relation has a completely different line shape for structures that support compared to those that do not support admittance matching. This work promotes complete comprehension of the excitation and propagation behaviors of graphene surface polaritons and may further inspire ideas for research on surface waves on two-dimensional materials.

The afterglow of GRB 070707 and a possible kilonova component

ABSTRACTGRB 070707 was the first short gamma-ray burst (GRB) detected by INTEGRAL and the optical afterglow was attributed to the prolonged activity of the central engine in the literature. Here, we reanalyse the afterglow data and examine the physical origin of the emission. The redshift of this burst is uncertain and in this work we assume an association with a galaxy at the redshift of 0.2394 for a chance coincidence probability Pcc = 0.046. It is found that the sole forward shock radiation cannot well reproduce the data, while including a kilonova component similar to AT2017gfo is very helpful in reproducing the multiwavelength afterglow emission. The properties of the candidate host galaxy have been studied in detail; its high metallicity, low star formation rate, and old stellar population age are similar to the host galaxies of other GRBs associated with kilonovae. In view of the facts that a kilonova signal was identified in the first short GRB with detected optical emission (i.e. GRB 050709) and the first short GRB with gravitational wave detection (i.e. GRB 170817A), and now the identification of a kilonova signature in the first INTEGRAL short GRB strongly indicates that kilonovae are rather common among the neutron star merger events.

An SIW Pillbox-Based Compact Dual-Polarized Multibeam Antenna With Passive 2-D Beam Scanning Capability

In this brief, a dual-polarized multi-beam antenna is proposed based on substrate integrated waveguide (SIW) pillbox beamforming networks (BFNs). By using a rotationally symmetrical frequency scanning leaky-wave antenna (LWA) array and four SIW pillbox BFNs, the 2-D beam steering capability is realized for two polarizations. Due to the rotationally symmetrical geometric characteristic of the LWA, the orthogonally placed BFNs can excite orthogonally polarized beams. A stable gain with a wide beam scanning range in the limited bandwidth is realized, where only the backward to broadside scanning region of the LWA is used, and the forward radiation is compensated by the axisymmetric BFN. Moreover, the stacked layout of the multi-layer antenna structure greatly helps realize miniaturization. The proposed antenna can provide ±35° beam scanning range by switching 7 ports in the multi-beam plane and ±31° frequency beam scanning range within the bandwidth of 21 GHz to 27.5 GHz. The advantages of the proposed antenna, including dual-polarization, 2-D beam scanning, low profile, compact size, and low cost, make it a very appropriate choice in millimeter-wave multi-beam radars systems.

The Late Afterglow of GW170817/GRB 170817A: A Large Viewing Angle and the Shift of the Hubble Constant to a Value More Consistent with the Local Measurements

The multimessenger data of neutron star merger events are promising for constraining the Hubble constant. So far, GW170817 is still the unique gravitational wave event with multiwavelength electromagnetic counterparts. In particular, its radio and X-ray emission have been measured in the past ∼3–5 yr. In this work, we fit the long-lasting X-ray, optical, and radio afterglow light curves of GW170817/GRB 170817A, including the forward shock radiation from both the decelerating relativistic gamma-ray burst outflow and the subrelativistic kilonova outflow (though whether the second component contributes significantly is still uncertain), and find out a relatively large viewing angle (∼0.5 rad). Such a viewing angle has been taken as a prior in the gravitational wave data analysis, and the degeneracy between the viewing angle and the luminosity distance is broken. Finally, we have a Hubble constant , which is more consistent with that obtained by other local measurements. If rather similar values are inferred from multimessenger data of future neutron star merger events, it will provide critical support to the existence of the Hubble tension.

Ultrahigh-Amplitude Isolated Attosecond Pulses Generated in the Transmission Regime from Ultrathin Foil

A coherent-synchrotron-emission regime of forward high-order harmonics generation (HHG) is proposed for the emission of an isolated unipolar half-cycle attosecond pulse by a three-color laser pulse impinging on ultrathin foil. A theoretical model is proposed for the electron nanobunching mechanism and the forward radiation, which is consistent with the numerical-simulation results. As the forward HHG does not need to penetrate from the front to the rear side of the target, the spectrum of the forward HHG has no low-frequency cutoff. The robustness of this regime is verified with different laser and foil plasma conditions as well as the two-dimensional effects. The robustness is also checked with similarity theory, which confirms that isolated attosecond pulses can be efficiently generated when the plasma density and the laser amplitude change simultaneously such that their ratio remains unchanged.

Forward and Backward Multibeam Scanning Controlled by a Holographic Acoustic Metasurface

Acoustic metasurfaces have great potential in the field of beam-forming acoustic antennas due to their thin, two-dimensional, and miniature artificial materials that can freely control sound waves. Here, we propose an acoustic metasurface, with multibeam acoustic radiation serving as leaky-wave antennas used for acoustic beam steering. Based on the holographic principle, we pattern a sinusoidal modulated admittance surface, which is designed as a periodic arrangement of cylindrical holes with varying depth profiles. An omnidirectional sound generated from a tiny hole located at the center of the patterned plate creates acoustic surface waves on the modulated surface while simultaneously generating leaky-wave radiation. For multibeam steering, the holographic admittance surfaces are designed with multiple subregions of the metasurface, with each subregion emitting single-beam radiation in the desired direction. Furthermore, the holographic metasurfaces are programmed separately to have forward and backward leaky-wave radiation. In this study, we use three-dimensional additive fabrication to print acoustic holograms to craft the surface-admittance variation at subwavelength resolution. Experimental results on these printed holograms show multidirectional acoustic beam steering in close agreement with the theoretical analysis and numerical results. Forward and backward multibeam frequency scanning is also demonstrated by frequency variation. Thus, we expect that this planar surface can be used in applications such as acoustic communications, levitation, and imaging.

A beam‐formed leaky‐wave antenna array with power‐recycling feeding network

A substrate integrated waveguide leaky-wave antenna array using power-recycling feeding network to achieve beamforming radiation pattern is investigated in this article. The antenna array consists of three elements represented by An1, An2, and An3 on two kinds of radiation mechanism. An1 and An2 are working on the -1th spatial harmonic mode with broadside and backward radiation directions, respectively, and An3 is working on the fundamental wave mode with forward radiation direction. The open-stopband due to broadside radiation design in An1 is suppressed by arranging two similar slots in one radiation unit. By using power-recycling feeding network, the traveling wave directions in An2 and An3 are opposite, which partially compensates the opposite radiation directions of these two elements. Therefore, by adjusting the sizes of radiation slots appropriately, the proposed antenna array can achieve a cosecant–distribution radiation pattern within the range from 0° to 50°.

Design of compact multiple‐input and multiple‐output antenna based on slow‐wave corrugated strips

A method of designing two-element compact multiple-input and multiple-output (MIMO) antennas with good isolation based on slow-wave corrugated strips (CSs) is presented in this paper. Using the slow-wave characteristic, a pair of CSs is applied as arms of each dipole antenna element to realise the compact design. A metal plane is placed between the two dielectric boards serving as the reflector so that the antenna can achieve good forward radiation. There are two coupling paths between the closely placed antennas: the coupling between the adjacent antenna arms and the coupling with the reflector. By adjusting the phase constants of the two coupling paths, good isolation is achieved in the operating frequency band without any additional de-coupling structures. A sample of a two-element MIMO antenna is fabricated at the centre frequency of 5.1 GHz with a bandwidth of 330 MHz. Measured results show good performance to support the design method. As each arm is about 1/8λ0 (λ0 is wavelength in free space), the edge-to-edge distance is 0.04λ0, and the isolation in the operating frequency is 15 dB.

The Effective Vector Boson Approximation in high-energy muon collisions

Due to the inclination for forward gauge radiation, lepton colliders beyond a few TeV are effectively electroweak (EW) boson colliders, suggesting the treatment of EW bosons as constituents of high-energy leptons. In the context of a muon collider, we revisit the validity of W and Z parton distribution functions (PDFs) at leading order in 2 → n process. We systematically investigate universal and quasi-universal power-law and logarithmic corrections that arise when deriving (polarized) weak boson PDFs in the collinear limit. We go on to survey a multitude of 2 → n processes at sqrt{s} = 2–30 TeV via polarized and unpolarized EW boson fusion/scattering. To conduct this study, we report a public implementation of the Effective W/Z and Weizsäcker-Williams Approximations, which we collectively call the Effective Vector Boson Approximation, into the Monte Carlo event generator MadGraph5_aMC@NLO. This implementation lays the groundwork for developing matrix-element matching prescriptions involving EW parton showers and renormalized EW PDFs. To further with this agenda, we give recommendations on using W/Z PDFs.

Frequency Reconfigurable Near-Zero Refractive Index Material for Antenna Gain Enhancement Applications

In this paper, a planar near-zero refractive index material (NZRIM) consisting of an outer loop with four symmetrical quarter-rings is proposed. The quarter-rings are connected to the outer loop by two symmetrical microstrip lines on the opposite side. The backside of the substrate has mutually central split microstrip lines. By loading adjustable capacitor between the split in the center of the backside of the substrate, the resonance frequencies of the proposed NZRIM can be controlled and thus the epsilon-near-zero (ENZ) frequency bands change correspondingly. According to the specific frequency bands of its metamaterial characteristics, the proposed NZRIM can be mounted above the surface of different antennas with different operation bands for 5G applications. Results show that the proposed NZRIM can enhance the forward radiation gain of antennas.

Tunable Cherenkov radiation based on a van der Waals semiconductor α-MoO3 and graphene hybrid

In this Letter, we explore the Cherenkov radiation properties of α-phase molybdenum trioxide (α-MoO3). We demonstrate that the asymmetric, forward, and reverse Cherenkov radiation can simultaneously exist by rotating the α-MoO3 slab at the same working frequency and structure. In addition, thanks to the tunable functionalities of graphene, the conversion of forward and reverse Cherenkov radiation can be actualized by altering the Fermi level of graphene. These dynamically adjustable features provide a novel, to the best of our knowledge, and intuitive way for tunable Cherenkov radiation in the mid-infrared range, which opens up new opportunities in designing and manufacturing tunable radiation sources in future.

Optical amplification and gain dynamics of cavity-free lasing of argon pumped by ultraviolet femtosecond pulses.

Argon gas excited by resonant femtosecond ultraviolet pulses gives rise to cavity-free lasing emission in the near-infrared (NIR) range. Here we reported on a pump-probe study of the optical gain of this lasing phenomenon. With the injection of an external seeding pulse, the forward signal was significantly enhanced, confirming the existence of optical gain. The temporal dynamics of the optical gain were characterized by a time-resolved measurement. It was found that the optical gain decays on a time scale of ∼ 10 ps and it does not present a significant dependence on the gas pressures. Moreover, the intensity of the forward NIR emission signal shows a linear dependence on the gas pressure. These features suggest that the nature of this forward NIR radiation is amplified spontaneous emission, not superradiance when multiple-photon resonant excitation is involved.

Machine learning approach to predict the heat transfer coefficients pertaining to a radiant cooling system coupled with mixed and forced convection

Mixed convection phenomenon over radiant cooled surfaces with displacement ventilation in living environments is becoming a popular issue due to the airborne viruses and energy economy. Artificial neural networks are one of the machine learning methods that are widely evaluated as an engineering tool. In the current study, heat transfer coefficients for a radiant wall cooling system coupled with mixed and forced convection have been predicted by a machine learning approach. This approach should be noted as a first experimental investigation couple with an artificial neural network analysis in the open sources in which mixed convection systems in real sized living environments is examined. Experimentally obtained heat transfer coefficients have been used in the development of the feed forward back propagation multi-layer perceptron network structure. So as to analyze the impact of the input factors on the prediction performance, two neural network structures with dissimilar input parameters such as various temperatures, velocities, and heat transfer rates have been developed. By means of feed forward back propagation multi-layer perceptron neural network algorithms, convection, radiation, and total heat transfer coefficients have been predicted using the experimentally acquired dataset including 35 data points belonging to the mixed and forced convection conditions. Training, validation, and test data groups include 70%, 15%, and 15% of the dataset, in turn. Training algorithm has been computed via Levenberg-Marquardt one with 10 neurons in the hidden layer. The findings obtained from the computational solution have been evaluated as a result of the contrast with the target data with in the ±5% deviation band for all heat transfer coefficients. The performance factors have been computed and the estimation precision of the numerical models has been thoroughly examined.