Radiation Modes Research Articles

Sound Radiation Characteristics of Acoustically Thick Composite Cylinders and Their Experimental Verification

Cylindrical shells made of composite material form one of the major structural parts in aerospace structures. Many of them are acoustically thick, in which the ring frequencies are much higher than their critical frequencies. In this work, sound radiation behaviour of acoustically thick composite cylinders is presented. Based on the structural and acoustic wave number diagrams, the modal average radiation resistances in the frequency band of interest are theoretically determined. The structural wavenumbers are determined considering transverse shear deformation. The results show lesser sound radiation between the critical and ring frequencies, and significant sound radiation near the ring frequency and beyond. In the absence of the present results the radiation efficiency is considered to be unity at all frequencies beyond the critical frequency, including near the ring frequency. The radiation resistances of the same cylinder are determined experimentally and they are in very good agreement with the theoretical estimates. As part of this investigation, an expression for determining the ring frequency of composite cylinder is also presented.

An Improved MSA Model for Evaluating the Sound Transmission Loss of a Rectangular Plate for Diffuse Field Incidence

This paper presents an approximate analytical model for estimating the transmission loss (TL) of a finite rectangular plate in the low frequency range, which is based on the modal summation approach (MSA) taking into account the modal radiation impedance and fluid loading. The mode-dependent radiation resistance is calculated using the Rayleigh integral. The fluid loading is taken into account through the natural frequency modified by the added mass. The results are compared with the ones of Statistical Energy Analysis (SEA) coupled with FEM and FEM coupled with BEM. In addition, the effects of the various vibration modes and the fluid loading on TL, and a way for reducing the calculation time are discussed.

Two-Wire Power Line Microwave Communication Using Low-Loss Modes

A closed-form solution for the common and differential modal currents induced on a pair of infinitely long parallel conductors by a source, field coupled to a power line, is derived. For lossy conductors, the current consists of a continuous spectrum of radiation modes and (for the common mode) a modified low-loss Sommerfeld–Goubau (SG) mode and (for the differential mode) a quasi-TEM mode. This model is used to investigate the influence of a parallel conductor on microwave power line communication systems. When the complete current spectrum is used, it is shown that the SG mode is not the primary reason why low-loss communication is possible on power lines for distances on the order of 100 m. Nevertheless, and consistent with previous research, microwave communication using power lines has advantages over free space communication, and for typical parameters, the performance of these systems can be enhanced if the power line contains more than one conductor.

Wide-Angle Beam-Scanning Leaky-Wave Antenna Array Based on Hole Array SSPPs

In this letter, a leaky-wave antenna (LWA) array based on hole array spoof surface plasmon polaritons (SSPPs) is proposed, which can realize wide frequency beam scanning angle. By etching periodic hole arrays on the upper metal of the defective ground structure, the SSPP structure is formed and the frequency scanning beam is generated by using its higher-order radiation mode characteristics. The radiation mechanisms of the design are explained by using the dispersion relationship, electric field distributions, and space harmonics. The LWA array is fed by a 1 to 4 power divider and achieves good impedance matching within 6-16 GHz bandwidth. The average peak gain value of the proposed LWA antenna array is about 16.86 dBi and the frequency beam scanning range is 91°. The antenna array has the characteristics of easy fabrication, low cost, and high gain performance, which provides a new design concept for wide-scanning-angle LWA Array and can meet the demand of high gain requirements in radar and other related fields.

Low-Profile Compact Tri-Band Multimode Reconfigurable Antenna Using Characteristic Mode Analysis

A low-profile compact tri-band (2.45/3.5/5.8 GHz) reconfigurable antenna with versatile radiation modes is proposed for portable wireless communication in this paper. The characteristic mode analysis method is used to explain the antenna’s operating principles and reduces the dimension. The antenna primarily comprises a patch radiator with T-shaped cuts, meander-slot defected ground, and shorting pins, resulting in three frequency bands with different radiation patterns. The antenna features a compact volume of 0.24λ0 × 0.24λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.026λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength of 2.45 GHz) and exhibits omnidirectional radiations at 2.45 and 5.8 GHz and unidirectional radiations at 3.5 GHz. In addition, the operating bands can be tuned by applying different DC biases to the varactors. The antenna is fabricated, and the measured results agree reasonably well with the simulations. The miniaturized tri-band antenna can be potentially used in portable wireless services and intelligent transport devices.

Dual-Polarized Multiresonant Metantenna for Quasi-Independent Radiation and In-Band Scattering Manipulation

A dual-polarized multi-resonant metantenna (MRMTA) is proposed for quasi-independent radiation and multiple in-band <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> -polarized scattering manipulations using characteristic mode analysis. The MRMTA unit cells in radiation and scattering modes have different resonance behaviors around meandering edges and inner slots, respectively. Moreover, tuning the inner slots of MRMTA unit cells can alter the reflection phase distributions for MRMTA’s different scattering functions but leave a weak influence on the radiation mode resonance, which enables dual-polarized radiation quasi-independent of multiple in-band <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> -polarized scattering manipulations. To verify the quasi-independence, the MRMTA’s top layout is designed based on 2-bit coding for two examples of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> -polarized in-band low scattering and scattered-beam deflection. Fed by three stacked substrate integrated waveguides, the MRMTAs with different layouts can reduce the radar cross section by 16 dB, steer scattered beams near the desired deflection direction, and maintain stable in-band dual-polarized radiation properties across experiments and simulations.

Generations of Multiple Orbital Angular Momentum Modes by 2-D Fisheye-Lens-Based Beamformer Excited Antenna Arrays in a Spiral Configuration

This paper presents the generations of multiple orbital angular momentum (OAM) modes in a spiral antenna array configuration. The feeds to the antenna elements are produced from a Fisheye-lens-based beamforming circuit (FL-BFC), where relatively linear phase variations of different slopes are generated. By selecting proper slope values, the feeding to planar circular arrays results in orthogonal OAM modes. Besides, selecting proper output port positions on the circumference of the FL-BFN may produce phases to excite the antenna array in various configurations to reduce the nulling regions of radiation by different OAM modes. This paper presents the characteristics of FL-BFC in its implementation to excite a planar array of antennas for OAM mode radiations. The orthogonality characteristics are quantized using an envelope correlation coefficient (ECC) for accounting for the mutual interaction. An orthogonalization procedure is also examined to obtain the orthogonal OAM modes. The radiation characteristics are compared to demonstrate the feasibility. Both full-wave simulation and measurement results are shown to validate the design concept.

Investigation of the mechanism of noise radiation reduction from an ABH-cavity under interior acoustic excitation considering multistage coupling

The acoustic black hole (ABH) structure exhibits superior vibration and sound radiation control capability compared to its flat counterpart. However, for a coupled plate-cavity system under interior acoustic excitation, the underlying suppression mechanism of noise radiation has not been explored, especially below the critical frequency of the structure. In this paper, the noise suppression mechanism of an ABH-cavity system under interior acoustic excitation is investigated both theoretically and numerically. Based on the theoretical analysis, the noise radiation depends on both the structural modes and the cavity modes, which can be suppressed in two ways. One is to lower the magnitude of structural transfer functions. The other is to change the mapping matrix which maps the structural modal amplitude to the amplitude of radiation modes. For the former, numerical analysis based on FEM demonstrates that a lower structural transfer function is obtained in the ABH-cavity system compared to its flat counterpart because of the damping enhancement characteristic of the ABH structure. Therefore, attenuated flexural vibrations and reduced sound radiation are achieved at corresponding modal frequencies. For the latter, ABH-cavity systems with varying numbers of ABHs are constructed to demonstrate a simple solution of manipulating the mapping matrix to achieve the reduced radiation efficiency of structural panels and the enhanced suppressing effect of noise radiation. The study in this paper indicates a feasible direction for the further optimization analysis of noise radiation suppression of the ABH-cavity system.

Random Laser Based on Materials in the Form of Complex Network Structures

The theory of a random laser with an interface in the form of random or scale-free networks whose nodes are occupied by microcavities with quantum two-level systems has been proposed for the first time. The microcavities are coupled to each other through light-guiding channels forming edges of the network. It has been shown that such a laser has a number of spectral features associated with the statistical properties of the network structure. Among them are the existence of a topologically protected Perron eigenvalue caused by the presence of a strong mean field at the node of maximum influence located in the central part of the network and the delocalization/localization of radiation modes depending on the probability of coupling between arbitrary microcavities. The results obtained in this work open prospects for the fabrication of new low-threshold laser sources.

Aretakis hair for extreme Kerr black holes with axisymmetric scalar perturbations

We study the evolution of axially symmetric scalar field perturbations on an extreme Kerr spacetime for initial data with multipole moments ${\ensuremath{\ell}}^{\ensuremath{'}}$ higher than the least radiative mode, and we measure modes $\ensuremath{\ell}$---and, for the first time, also horizon charges---that are excited by mode-coupling interactions. We then find the Ori-Sela prefactors, a certain quantity that can be evaluated at finite distances, and the Aretakis constant along the event horizon of the extreme Kerr black hole for a sequence of initial data preparations that differ only by their distance from the event horizon. We find that for initial data in the near field there is a linear relationship of the Aretakis constant and the Ori-Sela prefactor. For initial data farther than these, the linear relationship is not universal, and we propose that stronger numerical simulations would be needed to regain linearity. The linear relationship suggests that the Aretakis charge along the event horizon can be measured at a finite distance, thereby extending this type of violation of the no-hair theorems from the least radiative axisymmetric mode also to situations that involve mode coupling.

A phase 1 dose-escalation study of RiMO-301 with palliative radiation in advanced tumors.

2527 Background: Nanoscale metal−organic frameworks (MOFs) are a new class of organic−inorganic hybrid nanomaterials constructed from metal centers and organic ligands. Preclinical studies have shown that nanoscale MOFs can enhance the antitumor effects of ionizing radiation via a unique radiotherapy-radiodynamic therapy mode of action, and MOFs plus radiation can enhance the immunotherapeutic effects of immune checkpoint inhibitors. RiMO-301 is a hafnium-based MOF which enhances radiotherapy and checkpoint blockade immunotherapy without showing systemic toxicity in preclinical models. RiMO-301 is the first MOF to enter clinical trials on human patients. Methods: This is a multicenter, open-label, first-in-human dose-escalation phase I trial of RiMO-301 [NCT03444714]. The primary objective is to determine the maximum tolerated dose (MTD) of locally injected RiMO-301 with or without the PD-1 inhibitor pembrolizumab in patients treated with concurrent palliative doses of radiation (20 Gy in 5 fractions or 30 Gy in 10 fractions) using a 3+3 design. The MTD is defined as the dose associated with dose-limiting toxicity (DLT) in less than 33% of patients. The secondary objective is to evaluate antitumor response (objective response rate, ORR) using RECIST and itRECIST criteria. Results: A total of 25 patients were enrolled and treated with escalating doses of RiMO-301 (relative to tumor volumes). No protocol defined DLT was reported. The observed possibly treatment related adverse events included mild dermatitis radiation, mild dysgeusia, diarrhea, mild hypotension (30 days post treatment) and mild dizziness (30 days post treatment). One patient each experienced a Grade 2 alanine aminotransferase increase 45 days post treatment, a Grade 2 dry mouth, and a Grade 3 pain at the injection site. Nineteen patients were evaluable, with 13 and 6 patients, respectively, for RiMO-301 without and with pembrolizumab treatments. By itRECIST criteria, RiMO-301 without pembrolizumab demonstrated 38.5% (5/13) ORR (1 complete response and 4 partial responses) with 2 additional patients experiencing 20-30% tumor size reduction. RiMO-301 with pembrolizumab exhibited 66.7% (4/6) ORR with the 2 remaining patients showing 15-20% tumor size reduction. Preliminary pharmacokinetic analysis indicated that the hafnium concentrations in the systemic circulation were either below or barely above the level of detection. Conclusions: RiMO-301 with or without pembrolizumab was well tolerated and demonstrated promising signs of efficacy in patients with advanced tumors when treated with concurrent palliative radiotherapy. The results support the use of RiMO-301 as a potential radio-enhancer and will prompt further phase 2 studies in the development of RiMO-301 for patients undergoing radiotherapy. Clinical trial information: NCT03444714 .

Random Laser Based on Materials in the Form of Complex Network Structures

The theory of a random laser with an interface in the form of random or scale-free networks whose nodes are occupied by microcavities with quantum two-level systems has been proposed for the first time. The microcavities are coupled to each other through light-guiding channels forming edges of the network. It has been shown that such a laser has a number of spectral features associated with the statistical properties of the network structure. Among them are the existence of a topologically protected Perron eigenvalue caused by the presence of a strong mean field at the node of maximum influence located in the central part of the network and the delocalization/localization of radiation modes depending on the probability of coupling between arbitrary microcavities. The results obtained in this work open prospects for the fabrication of new low-threshold laser sources.

On-chip non-uniform geometric metasurface for multi-channel wavefront manipulations.

Metasurfaces integrated with waveguides have been recently explored as a means to control the conversion between guided modes and radiation modes for versatile functionalities. However, most efforts have been limited to constructing a single free-space wavefront using guided waves, which hinders the functional diversity and requires a complex configuration. Here, a new, to the best of our knowledge, type of non-uniformly arranged geometric metasurface enabling independent multi-channel wavefront engineering of guided wave radiation is ingeniously proposed. By endowing three structural degrees of freedom into a meta-atom, two mechanisms (the Pancharatnam-Berry phase and the detour phase) of the metasurface are perfectly joined together, giving rise to three phase degrees of freedom to manipulate. Therefore, an on-chip polarization demultiplexed metalens, a wavelength-multiplexed metalens, and RGB-colored holography with an improved information capacity are successively demonstrated. Our results enrich the functionalities of an on-chip metasurface and imply the prospect of advancements in multiplexing optical imaging, augmented reality (AR) holographic displays, and information encryption.

Miniaturized Pattern-Reconfigurable Multimode Antennas With Continuous Beam-Steering Capability

In this paper, two miniaturized multi-mode pattern steering antennas for Internet of Things (IoTs) applications are proposed. A compact multi-mode cavity functions both the hybrid and radiator. A continuous 360° pattern scanning in the azimuth plane is controlled by the amplitude and phase of three excitation ports. The first design achieves the smallest size with TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> modes. In contrast, the second design has improved impedance bandwidth and mode isolation by introducing TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> and high-order TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> modes. Eight dipole chokes are attached to the cavity for surface current suppression. This approach eliminates the unwanted patch mode radiation. The antennas support multibeam applications with digital beamforming and analog beamforming with the 0°/180° phase switch and variable gain amplifier (VGA). The direction of arrival (DOA) can be estimated by directly measuring the amplitude and phase of the receiving signal. No full phase shifter and signal classification algorithm are required. The prototypes are fabricated and measured at 2.4 GHz. The diameters of the two antennas are 0.4 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and 0.9 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . The achieved antenna size is very miniature as shown by the literature comparison. The radiation and DOA performance is evaluated. The peak system efficiency is better than 60% after calibration and a good DOA estimation result is obtained.

Vibro-Acoustic Performance of a Fluid-Loaded Periodic Locally Resonant Plate

The vibro-acoustic performance of a fluid-loaded periodic locally resonant (LR) plate was examined in this research, with a specific focus on the effect of water fluid on the vibration and sound radiation of the LR structure. The analytical models of the fluid-loaded LR plate’s band gap, vibration, and acoustic radiation were theoretically derived with closed-form solutions, which can be used to predict the general vibro-acoustic rules of underwater LR structure. The results show that the LR band-gap width and Bragg frequency are significantly reduced when water fluid is considered. Besides, the frequency range that can be tuned to control the vibration and sound radiation for the LR plate with fluid is much narrower than that without fluid. The reason for inducing the above effects was also given in this research, which can be physically explained by the attached mass caused by the water fluid. In addition, the reason for the enhanced radiation efficiency close above the band gap was also discussed, which is caused by the change of radiation mode from corner or edge radiation to monopole radiation. Furthermore, adding small damping into the resonator could reduce the vibration and sound radiation in the frequency range above or close below the band gap, inducing the attenuation zone to be significantly broadened. Thus, designing the periodic resonators with proper damping could be an efficient method to make the LR plate more beneficial for vibration and noise reduction in water-surrounding applications.

Reflections of High-Frequency Pulsed Ultrasound by Underwater Acoustic Metasurfaces Composed of Subwavelength Phase-Gradient Slits

We numerically and experimentally investigated the behavior of high-frequency underwater ultrasounds reflected by gradient acoustic metasurfaces. Metasurfaces were fabricated with a periodic array of gradient slits along the surface of a steel specimen. The finite element method was adopted for the acoustics–structure interaction problem to design the metasurfaces and simulate the reflected fields of the incident ultrasound. Our metasurfaces yielded anomalous reflection, specular reflection, apparent negative reflection, and radiation of surface-bounded modes for ultrasonic waves impinging on the metasurfaces at different incident angles. The occurrence of these reflection behaviors could be explained by the generalized Snell’s law for a gradient metasurface with periodic supercells. We showed that at some incident angles, strong anomalous reflection could be generated, which could lead to strong retroreflection at specific incident angles. Furthermore, we characterized the time evolution of the reflections using pulsed ultrasound. The simulated transient process revealed the formation of propagating reflected ultrasound fields. The experimentally measured reflected ultrasound signals verified the distinct reflection behaviors of the metasurfaces; strong anomalous reflection steering the ultrasound pulse and causing retroreflection was observed. This study paves the way for designing underwater acoustic metasurfaces for ultrasound imaging and caustic engineering applications using pulsed ultrasound in the high-frequency regime.

How do axisymmetric black holes grow monopole and dipole hair?

We study the dynamical formation of scalar monopole and dipole hair in scalar Gauss-Bonnet theory and dynamical Chern-Simons theory. We prove that the spherically symmetric mode of the dipole hair is completely determined by the product of the mass of the spacetime and the value of the monopole hair. We then show that the dynamics of the $\ensuremath{\ell}=1$ mode of the dipole hair is intimately tied to the appearance of the event horizon during axisymmetric collapse, which results in the radiation of certain modes that could have been divergent in the future of the collapse. We confirm these analytical predictions by simulating the gravitational collapse of a rapidly rotating neutron star in the decoupling limit, both in scalar Gauss-Bonnet and dynamical Chern-Simons theory. Our results, combined with those in Hegade K. R. et al. [Phys. Rev. D 105, 064041 (2022)], provide a clear physical picture of the dynamics of scalar monopole and dipole radiation in axisymmetric and spherical gravitational collapse in these theories.

Tuning the Luminescence Response of an Air-Hole Photonic Crystal Slab Using Etching Depth Variation.

Detailed studies of the luminescent properties of the Si-based 2D photonic crystal (PhC) slabs with air holes of various depths are reported. Ge self-assembled quantum dots served as an internal light source. It was obtained that changing the air hole depth is a powerful tool which allows tuning of the optical properties of the PhC. It was shown that increasing the depth of the holes in the PhC has complex influences on its overall photoluminescence (PL) response due to the simultaneous influences of counteracting factors. As a result, the maximal increase in the PL signal of more than two orders of magnitude was obtained for some intermediate, but not full, depth of the PhC's air holes. It was demonstrated that it is possible to engineer the PhC band structure in such a way as to construct specific states, namely bound states in continuum (BIC), with specially designed dispersion curves being relatively flat. In this case, such states manifest themselves as sharp peaks in the PL spectra, and have high Q-factors which are larger than those of radiative modes and other BIC modes without such a flat dispersion characteristic.

Scattering theory with matter fields of classical gravitons in the null surface formulation

Using a set of field equations in the null surface formulation we obtain the linearized coupling between the gravitational and matter fields. We first derive a formula for the metric of the space time and then we use this formula to study the scattering of incoming gravitational waves when matter is present, obtaining explicit formulae relating the radiation modes at past and future null infinity for a general asymptotically flat spacetime. An example application is made at the end of this work when the matter field is a massless real scalar field. The relevance of this result for a perturbation procedure is discussed.

Terahertz topological photonic crystals with dual edge states for efficient routing.

Topological photonic crystals with robust pseudo-spin and valley edge states have shown promising and wide applications in topological waveguides, lasers, and antennas. However, the limited bandwidth and intrinsic coupling properties of a single pseudo-spin or valley edge state have imposed restrictions on their multifunctional applications in integrated photonic circuits. Here, we propose a topological photonic crystal that can support pseudo-spin and valley edge states simultaneously in a single waveguiding channel, which effectively broadens the bandwidth and enables a multipath routing solution for terahertz information processing and broadcasting. We show that distorted Kekulé lattices can open two types of bandgaps with different topological properties simultaneously by molding the inter- and intra-unit cell coupling of the tight-binding model. The distinct topological origins of the edge states provide versatile signal routing paths toward free space radiation or on-chip self-localized edge modes by virtue of their intrinsic coupling properties. Such a powerful platform could function as an integrated photonic chip with capabilities of broadband on-chip signal processing and distributions that will especially benefit terahertz wireless communications.