Radiation Modes Research Articles

On Transformation Form-Invariance in Thermal Convection.

Over the past two decades, effective control of physical fields, such as light fields or acoustics fields, has greatly benefited from transforming media. One of these rapidly growing research areas is transformation thermotics, especially embodied in the thermal conductive and radiative modes. On the other hand, transformation media in thermal convection has seldom been studied due to the complicated governing equations involving both fluid motion and heat transfer terms. The difficulty lies in the robustness of form invariance in the Navier-Stokes equations or their simplified forms under coordinate transformations, which determines whether the transformation operations can be executed on thermal convection to simultaneously regulate the flow and thermal fields. In this work, we show that thermal convection in two-dimensional Hele-Shaw cells keeps form-invariance, while its counterpart in general creeping flows or general laminar flows does not. This conclusion is numerically verified by checking the performances of invisible devices made of transformation media in convective environments. We further exploit multilayered structures constituted of isotropic homogeneous natural materials to realize the anisotropic inhomogeneous properties required for transformation media. Our results clarify the long-term confusion about the validation of the transformation method in thermal convection and provide a rigorous foundation and classical paradigm on inspiring various fascinating metadevices in both thermal and flow fields.

Eccentric binary black holes: Comparing numerical relativity and small mass-ratio perturbation theory

The modeling of unequal mass binary black hole systems is of high importance to detect and estimate parameters from these systems. Numerical relativity (NR) is well suited to study systems with comparable component masses, ${m}_{1}\ensuremath{\sim}{m}_{2}$, whereas small mass ratio (SMR) perturbation theory applies to binaries where $q={m}_{2}/{m}_{1}\ensuremath{\ll}1$. This work investigates the applicability for NR and SMR as a function of mass ratio for eccentric nonspinning binary black holes. We produce 52 NR simulations with mass ratios between $1:10$ and $1:1$ and initial eccentricities up to 0.8. From these we extract quantities like gravitational wave energy and angular momentum fluxes and periastron advance, and assess their accuracy. To facilitate comparison, we develop tools to map between NR and SMR inspiral evolutions of eccentric binary black holes. We derive post-Newtonian accurate relations between different definitions of eccentricity. Based on these analyses, we introduce a new definition of eccentricity based on the (2,2)-mode of the gravitational radiation, which reduces to the Newtonian definition of eccentricity in the Newtonian limit. From the comparison between NR simulations and SMR results, we quantify the unknown next-to-leading order SMR contributions to the gravitational energy and angular momentum fluxes, and periastron advance. We show that in the comparable mass regime these contributions are subdominant and higher order SMR contributions are negligible.

Optical Methods for Studying Pre-Breakdown Phenomena in Liquid Dielectrics

Three main groups of non-invasive experimental methods (shadow, spectral, and electro-optical) for studying pre-breakdown processes in liquid dielectrics are reviewed. Each of these methods has its own capabilities and allows a limited set of information about the process under study to be obtained. High-speed shooting makes it possible to record emerging objects and trace the dynamics of the processes occurring in the discharge gap. Shadow methods make it possible, by recording changes in the probing radiation in a real-time mode, to obtain information about the course of processes in a liquid, during which a change in the refractive index occurs. However, neither of these two methods allows the obtained data to be linked to the electrical characteristics of the object under study. Spectral research methods make it possible to consider the effect of high voltage on the physicochemical processes occurring in the discharge gap. To do this, it is advisable to combine them with high-speed shooting methods, but the low intensity of the studied radiation and the high speed of the processes add much difficulty to the use of such methods. If the processes occurring at the molecular and atomic levels are set aside, the electro-optical research method remains the only one that links the electrical parameters of the object under study with the obtained optical picture of the processes. Moreover, with a growth in the field strength, additional features appear in the electro-optical pattern due to the the Kerr effect nonlinearity, as a result of which the characteristic processes that precede the breakdown can be noticed. It is shown, using the electro-optical Kerr effect as an example, how the use of modern computer-aided experimental data processing methods helps obtain additional information that was previously inaccessible.

Detection of planar subsurface defects in fiberglass plastic composite panels by optical-acoustic method

An optical-acoustic method for detecting subsurface defects in laminated composite structures is considered. The method is based on a new approach to detecting such defects by forming and visualizing the mode structure of oscillations of a thin layer of material (region of interest (ROI)) located directly above the defect. The oscillations of the ROI occur at frequencies corresponding to the resonant frequencies of an edge-clamped thin membrane excited by flexural ultrasonic (US) waves. To technically implement the method, an experimental breadboard of a hybrid optical-digital system was created, in which laminated composite specimens are excited by harmonic US radiation in the frequency sweep mode in the range of 5-150 kHz. For research, laminated fiberglass panels with square and round planar subsurface defects were used. A series of experiments was carried out to detect square defects with dimensions of 20x20 mm2 located in composite panels at different depths. It is shown that spatial responses from defects correspond to the mode structure of the nodes of a rectangular membrane at its fundamental and multiple resonant frequencies. Dependences between the depth of the defects and their resonant frequencies are obtained. They indicate a monotonous increase in resonant frequencies with an increase in the depth of the defect. The main reasons for the deviations of the experimental results from the values of calculating the fundamental and multiple frequencies for the planar square subsurface defect using known formulas are analyzed.

Wideband band-notched monopulse antenna design utilizing differential mode and common mode radiations

This letter proposes a dual-port wideband monopulse Vivaldi antenna based on a new perspective of common mode and differential mode radiations. To realize the sum and difference patterns utilizing the differential and common mode radiations, a metallic wedge is introduced in the center of the Vivaldi antenna, the effect of the virtual magnetic wall disappears, and the realistic electric wall plays the dominant role, fulfilling the boundary condition for difference beam under common mode excitation. Meanwhile, the sum beam is kept unchanged under differential mode excitation. The desired sum and difference radiation patterns are realized in a single Vivaldi antenna under differential mode and common mode excitations, respectively. Moreover, a notched band is introduced for interference suppression, and the notched frequency can be easily controlled by adjusting the microstrip feeding stub without loading an extra resonator. Measured results show that the proposed monopulse antenna exhibits 101 % fractional bandwidth from 2.2 GHz to 6.7 GHz, in which a notched band is from 3.75 GHz to 4.3 GHz. Across the operational band, the average gain of the sum pattern is 8 dBi, and the null depth of the difference pattern is below −15 dB. Measured results agree well with the simulated ones.

Exploring Quantum Geometry Created by Quantum Matter

Exactly soluble models can serve as excellent tools to explore conceptual issues in non-perturbative quantum gravity. In perturbative approaches, it is only the two radiative modes of the linearized gravitational field that are quantized. The goal of this investigation is to probe the ‘Coulombic’ aspects of quantum geometry that are governed entirely by matter sources. Since there are no gravitational waves in three dimensions, 3-dimensional (3-d) gravity coupled to matter provides an ideal arena for this task. The analysis presented here reveals novel aspects of quantum gravity that bring out limitations of classical and semi-classical theories in unforeseen regimes: non-linearities of general relativity can magnify small quantum fluctuations in the matter sector to large effects in the gravitational sector. Finally, this analysis leads to thought experiments that bring out rather starkly why understanding of the nature of physical reality depends sensitively on the theoretical lens with which it is probed. As theories become richer, new scales emerge, triggering novel effects that could not be imagined before. The model provides a concise realization of this well-known chain.

Radiation modes and loudspeaker arrays for close-listening: Experimental verification

In personal audio systems, the loudspeaker array for enhancing the near field is designed based on the theory of generalized radiation modes. These modes are formulated as a generalized eigenvalue problem associated with acoustic transfer functions on the surface of the loudspeaker array. The eigenvectors, i.e., the modal shapes, represent combinations of the amplitude and polarity of individual loudspeakers. The eigenvalues indicate the reactive-to-active ratio of the acoustic power generated by the loudspeaker array. Hence, the loudspeaker array is designed according to the eigenvector with the largest eigenvalue to maximize the reactive-to-active ratio. In this study, a planar array consisting of nine loudspeakers is constructed, and the acoustic radiation characteristics are experimentally investigated.

Novel periodic pile barrier with low-frequency wide bandgap for Rayleigh waves

This paper aims to investigate the propagation of low-frequency seismic surface waves in periodic in-filled barriers from the viewpoint of bandgaps. Based on Bloch-Flouquet theory, four configurations of periodic pile barriers with the same filling rate but different cross sections are studied. The periodic boundary conditions are imposed to derive the characteristics equation. Simultaneously, the finite element method is used to calculate the numerical dispersion relation and vibration modes of four types of periodic pile barriers with various inclusions. The sound cone and the energy parameter method are introduced to identify the surface wave modes further. Additionally, the mitigation effectiveness of a finite number of periodic barriers is evaluated using a three-dimensional transmission model. The results show that the initial frequency and bandwidth of the surface bandgaps are sensitive to the shape of the cross-section and mechanical parameters of the inclusions. The surface wave bandgaps within 9.64 ∼ 13.92 Hz are observed for the periodic barrier composed of cross-like polyfoam sections. Moreover, the radiation modes formed by the leakage of some surface waves into the sound cone are expected to widen the attenuation zones of the periodic barriers. The numerical results in frequency and time domains further validate the attenuation effect of finite barrier in the bandgap and the attenuation widening phenomenon caused by the dissipation of the leak modes into the bulk. This study provides new insights into the design of periodic pile barriers. In the future, it is expected to mitigate the low-frequency ground motion by fully designing the section shape and filling materials of pile barriers.

Self-Decoupled MIMO Antenna Realized by Adjusting the Feeding Positions

This paper proposes a novel decoupling technique achieved by adjusting the position of feeding probes of antennas. Two inherent radiation modes (patch mode and monopole mode), with different patterns and polarizations, are simultaneously excited by the same feeding probe. High isolation is realized based on manipulating the relationship of two-mode couplings by moving the feeding positions. Since the two radiation modes are generated by the same antenna element, the proposed MIMO antenna features a simple structure and compact size. For verification, a two-element array with center-to-center spacing of 0.404 λ0 (λ0 is the wavelength in the air) is prototyped and characterized. Simulation and experimental results show that the proposed novel technique can offer higher port isolation (>18.1 dB), increased efficiency (>70%), and a lower envelope correlation coefficient (ECC < 0.1) in the operating frequency band (11.61–12.49 GHz).

Electromagnetic-Model-Driven Twin Delayed Deep Deterministic Policy Gradient Algorithm for Stealthy Conformal Array Antenna

Conformal array antennas (CAAs) can effectively broaden the beam scanning range and improve radiation flexibility. Unfortunately, confirmation will increase the difficulty of analysis and synthesis, and the stealth of CAAs is arduous. In this article, we propose an innovative array optimization algorithm for stealthy CAAs based on the twin delayed deep deterministic policy gradient (TD3) algorithm, which combines the advantages of deep learning and reinforcement learning. Furthermore, we characterize the CAA as an electromagnetic model (EMM) and embed it into the TD3 algorithm as the environment to improve its stability and efficiency. Additionally, we independently excite the radiation and absorption modes to integrate radiation and stealth characteristics into the CAA. The simulated and measured results indicate that the designed CAA with EMM-TD3 algorithm features high-flexibility beam scanning within ±50° around 6 GHz and 10 dB radar cross section reduction in the frequency bands of 3.1–5.3 and 6.5–11.2 GHz.

1λ Spaced Dual Radiating Modes Based Phased Array Antenna Using Silicon RFICs With Grating Lobe Cancellation

A dual radiating modes (TM11 and TM21)-based phased array antenna with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\lambda $ </tex-math></inline-formula> interelement spacing at Ku-band is demonstrated using silicon beamforming RFICs, which offers grating lobe cancellation. The radiating element consists of concentric microstrip circular patch antennas supporting TM11 and TM21 modes. Excitation of both modes (TM11 and TM21), with the proper amplitude and phase values, allows for the suppression of grating lobe present in the array radiation pattern. The array utilizes Anokiwave RFICs (AWMF-0117), which provides flat panel integration of the beamforming network with the antenna aperture. A suitable beamforming network consisting of wideband Wilkinson power dividers was used to feed the RFICs from a single input. We demonstrate a grating lobe suppression ability of up to 30.8 dB with a first sidelobe level (SLL) of 15.2 dB. We also confirm the grating lobe mitigation technique through the demonstration of an over-the-air (OTA) link using digitally modulated signals and observing the error vector magnitude (EVM) of the received signal.

Low-Profile Dual-Wideband Dual-Polarized Antenna for 5G Millimeter-Wave Communications

This letter presents a dual-wideband dual-polarized antenna that fully covers the fifth-generation (5G) millimeter-wave (mm-wave) bands of n257−n261 (24.25–29.5 GHz and 37–43.5 GHz), and that shows a low-profile feature and a band-stop filtering response. For each polarization, the low-band and high-band radiation modes are, respectively, achieved by the two pairs of U-shaped dipole arms which are distributed along the co- and cross-polarized directions. Meanwhile, a radiation null is generated by the radiating cancellation effect of the two pairs of dipole arms, suppressing the unwanted frequency between the two operating bands. Moreover, an extra high-band resonant mode is introduced by the parasitic patches, enhancing the bandwidth of the proposed antenna. Furthermore, a vertical balun structure connecting each dipole arm with the ground is bent to reduce the antenna profile. In the fabrication, high-density interconnect printed circuit board process is employed to meet the antenna-in-package consideration. Under the constrained substrate thickness of 1 mm, the proposed antenna achieves a dual-wideband operation of 24–30 GHz (22%) and 37–43.5 GHz (16%). These merits make the proposed antenna suitable for 5G mm-wave communications.

Modal Performance Analysis of Compressor for Active Control of Acoustic Radiation

Compressor has a complex internal structure and contains various kinds of motion mechanism. At present, research on compressor’s vibration and sound radiation characteristics is insufficient. In this paper, structure and sound radiation modes of control objects are analysed by mode analysis. Explore the mode distribution law and correspond the structure mode to the sound radiation mode. On this basis, by suppressing the vibration mode, the influence is transmitted to the acoustic domain to realize the active control of sound radiation of the structure as a whole.

Analysis and Design of Filtering Series-Feed Omni-Directional Antenna for V2X Application

In general, the vehicle-to-everything (V2X) series-feed antenna excites the spurious mode radiation in the adjacent bands and thus causes the strong mutual coupling between the vehicle antennas. To solve this problem, this article proposes a method to realize a filtering series-feed V2X antenna. This antenna consists of two radiators connected to a double-sided parallel strip line (DSPSL). The DSPSL operates as the series-feed structure and the first resonator. The radiators function as the second resonator. An equivalent filtering network is analyzed and derived. Then, based on the filter synthesis, the initial design parameters are obtained to realize a second-order bandpass response. However, the synthesis method only involves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11}$ </tex-math></inline-formula> and efficiency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{21}$ </tex-math></inline-formula> ). The radiation performances are not concerned and satisfied. To solve this problem, the antenna currents are manipulated to generate the taper exciting. Thus, the upper sidelobe and the gain are improved. Moreover, to further enhance the out-of-band suppression level, three radiation zeros are generated by manipulating the current distribution on the DSPSL. The fabrication prototype demonstrates that the out-of-band suppression of the proposed antenna is better than 8.8 dB, which significantly reduces the mutual coupling.

Inverse Design of Whispering-Gallery Nanolasers with Tailored Beam Shape and Polarization.

Control over the shape and polarization of the beam emitted by a laser source is important in applications such as optical communications, optical manipulation and high-resolution optical imaging. In this paper, we present the inverse design of monolithic whispering-gallery nanolasers which emit along their axial direction with a tailored laser beam shape and polarization. We design and experimentally verify three types of submicron cavities, each one emitting into a different laser radiation mode: an azimuthally polarized doughnut beam, a radially polarized doughnut beam and a linearly polarized Gaussian-like beam. The measured output laser beams yield a field overlap with respect to the target mode of 92%, 96%, and 85% for the azimuthal, radial, and linearly polarized cases, respectively, thereby demonstrating the generality of the method in the design of ultracompact lasers with tailored beams.

Experimental Investigation on Vibro-Acoustic Characteristics of Stiffened Plate Structures with Different Welding Parameters

Varied welding process parameters result in different welding energy inputs and welding residual stresses, significantly impacting the vibro-acoustic characteristics. This work investigated the influence of different welding energy inputs on the vibro-acoustic characteristics of the stiffened plate structure. Several experiments on the stiffened plate structure with different welding energy inputs were conducted regarding modal, underwater vibration, and acoustic radiation. The results revealed that welding energy input had the most significant impact on the first-order natural frequency, and the impact first becomes higher and subsequently decreases as welding energy input increases. The welding energy input had relatively little effect on the peak point distribution of vibration and acoustic radiation curves but could affect the peak point amplitude. With the increase in welding energy input, the overall vibration acceleration level and sound radiation level in each frequency band decreased and then increased. The best result was obtained when the welding energy input was 167 J/cm with a welding current of 200 A, a welding voltage of 25 V, and a welding speed of 3.02–3.06 mm/s. Based on construction technology, this research can provide some instructive insights for enhancing the acoustic stealth performance of ships and marine structures.

A High-Efficiency Microstrip Antenna Pair with Similar Pi-Shaped Decoupling Structure for 3.5 GHz 5G Ultrathin Smartphones

In this paper, a low profile and high-efficiency decoupling antenna pair for multiunit smartphones is proposed using a similar π-shaped feed structure that can excite the dipole radiation mode of microstrip antenna. Ordinarily, symmetrical single-port T-shaped microstrip antennas can only excite monopole modes of bilateral radiation. This paper changes the vertical feeding microstrip structure into two oblique, similar π-shaped feeding structures. This oblique feeding structure can excite the dipole mode of unilateral radiation of the microstrip antenna. Using this method, the antenna design can be simplified, and the low-coupling independent radiation on both sides of the microstrip antenna can be freely controlled without the need for additional structures. Considering the ultra-thin characteristics of 5G smartphone devices, the parameters of the antenna are further optimized: the optimized antenna profile is only 3.7 mm. The measured results show that the 2 × 2 microstrip antenna pairs can effectively cover the 3.5 GHz band (3.4–3.6 GHz), with a coupling that varies from −16.14 dB to −11.01 dB and an efficiency that varies from 80% to 94.1%. The 8 × 8 MIMO smartphone antenna results show that the coupling varies from −20.1 dB to −12.17 dB, the efficiency varies from 79.72% to 93.7%, and the envelope correlation coefficient (ECC) is lower than 0.05. The microstrip antenna decoupling pair with a similar π-shaped feed structure proposed in this paper has high efficiency and low-profile characteristics have important application value in the decoupling design of 3.5 GHz 5G ultra-thin smartphone antennas.

Design of a 5G Sub-6 GHz Vehicular Cellular Antenna Element with Consistent Radiation Pattern Using Characteristic Mode Analysis.

A cellular 5G sub-6 GHz vehicle antenna design with a consistent radiation pattern across the frequency bands in 0.617-5 GHz is demonstrated via characteristic mode analysis. The design focuses on maintaining monopole first-order mode radiation pattern over cellular frequency bands and avoiding higher-order modes out of the operational frequency bands to provide optimal performance for automotive requirements. Rather than using an empirical design method, the design procedure in this paper uses the calculated modal significance, characteristic current, modal radiation pattern, and reflection coefficient to define the antenna structure dimensions. The proposed design was simulated, a prototype was measured, and the performance was evaluated on a 1-m ground plane. The antenna has perfect omnidirectionality with a high and stable gain across the frequency range in the 30° area above the horizon.

Study of Generation of Singlet Oxygen in Human Saliva &lt;i&gt;in vitro&lt;/i&gt; Under the Action of Nanosecond Pulsed Laser Radiation

Background. The development of new laser devices for use in the treatment of complex dental pathology and microsurgery of the oral cavity with unique parameters with the ability to generate nanosecond pulsed radiation in a quasi-monochromatic radiation band is necessary. The high peak output power per pulse allows laser light to penetrate deeper into biological media without significant heating. The possibility of excitation of singlet oxygen without the use of endogenous photosensitizers is an indisputable advantage of such laser generators.&#x0D; Aims study of singlet oxygen generation in human oral fluid in vitro depending on the parameters of nanosecond pulsed laser radiation with a wavelength of ~1265 nm.&#x0D; Methods. We used a laser device with a main infrared (IR) emitter with a wavelength approximately corresponding to the oxygen absorption maximum (~1265 nm) with the generation of nanosecond pulsed radiation. A study was carried out to study the generation of singlet oxygen in the human oral fluid and the washing out of the oral fluid by the fading of the trap in solutions under the action of laser radiation before irradiation, after 30 and 60 min. The laser radiation parameters were set as follows: power 1 W, nanosecond pulsed radiation with a pulse duration of 400 ns and a frequency of 0.5, 1.0, 1.5 and 2.0 MHz in comparison with the continuous radiation mode.&#x0D; Results. It has been established that nanosecond laser radiation leads to the oxidation of a chemical singlet oxygen trap solubilized with sodium dodecyl sulfate (0.05 M SDS) detergent in the oral fluid and saliva flushing from the oral cavity. In pulsed nanosecond modes, laser radiation is more efficient than in continuous mode. With an increase in the repetition frequency, an increase in the effect by an average of 10% compared to a lower frequency was observed and the effect with a maximum frequency of 2.0 MHz was almost 50% higher than when using continuous radiation in all studies. A decrease in optical density at 414 nm was reliably observed in samples with oral fluid washing, the effect was 0.07 0.01 for 60 min of exposure. In the oral fluid, the effect with the same parameters was slightly lower and amounted to 0.05 0.03.&#x0D; Conclusions. The rate of fading of the trap in the saliva wash turned out to be 1.3 times faster than in water with detergent, which may indicate the activation of photoacceptors and their oversaturation with oxygen when using aqueous dilution of the oral fluid. The maximum effect was observed when using laser radiation with a pulse repetition rate of 2.0 MHz.

Real-Time Phaseless Microwave Frequency-Diverse Imaging with Deep Prior Generative Neural Network

The millimeter-wave frequency-diverse imaging regime has recently received considerable attention in both the security screening and synthetic aperture radar imaging literature. Considering that the minor systematic errors and alignment errors could still produce heavily corrupted images, these complex-based imaging reconstructions rely heavily on the precise measurement of both phase and amplitude of radiation field patterns and echo signals. In the literature, it is shown that by leveraging phase-retrieval techniques, salient reconstruction images can still be acquired, even in the presence of significant phase errors, which could ease the phase error calibration pressure to a large extent in practical imaging applications. In this paper, in the regime of phaseless frequency-diverse imaging, with the powerful feature inference and generation power of unsupervised generative models, an end-to-end deep prior generative neural network is designed to achieve near real-time imaging. The harsh imaging reconstruction with both the high radiation mode correlations and extremely low scene compression sampling ratio, which are extremely troublesome to tackle for generally applied matched-filter and compressed sensing approach in the current frequency-diverse imaging literature, can still be preferably handled with our reconstruction network. The well-trained reconstruction network is constituted by prior inference and deep generative modules with excellent generative capabilities and significant prior inference abilities. Using simulation experiments with radiation field data, we verify that the integration of phase-free frequency-change imaging with deep learning networks can effectively improve reconstruction capabilities and improve robustness to systematic phase errors. Compared with existing imaging methods, our imaging method has high imaging performance and can even reconstruct targets under low compression ratio conditions, which is somewhat competitive with current state-of-the-art algorithms. Moreover, we find that the proposed method has good anti-noise and stability.