Suppression Of Waves Research Articles

A Complete System of Wireless Power Transfer Using a Circularly Polarized Retrodirective Array

A complete system of wireless power transfer using a circularly polarized retrodirective array is presented. A dual frequency, active retrodirective array is proposed for a transmitter system. The antenna array uses circularly polarized microstrip patch antenna subarrays with sequential rotation and surface wave suppression. The designed antenna element eliminates undesired coupling between array elements due to surface waves present in conventional microstrip antenna arrays in order to improve array performance. A sequential rotation technique was implemented to improve impedance matching and circular polarization bandwidths. The proposed retrodirective array was designed to operate at about 2.4 GHz for the interrogating signal and about 5.8 GHz for the retransmitted signal. The beam scanning inherent in retrodirective arrays ensures a uniform power level available to the receiving devices, regardless of their location within the angular sector over which retrodirectivity is achieved. A rectenna was designed as a receiver in order to have a complete system the wireless power transfer. A zero bias Schottky diode with high detection sensitivity was used as the rectifying device. The shorting pins used in the antennas to suppress surface waves also act as return paths for the DC current, eliminating the need for an RF chock in the rectifier circuit. The design procedure, simulation results, and experimental measurements are presented.

A study of EEG mu neurofeedback during action observation.

The mirror system is a brain network that gets activated during action performance and observation. Brain mu waves have been used as a mirror system activity index; however, mu rhythm is prone to contamination by occipital alpha wave activity, thus raising a concern regarding its reliability as an index of the mirror system activity. In this study, we investigated whether mu suppression can be used as an index of neurofeedback training, which influences mirror system activities. Participants observed videos of hand movement under three different conditions: central mu feedback (muFB), occipital alpha feedback (aFB), and simple observation without any feedback (OBS). Results showed that at the 4-5min mark, mu wave was most significantly suppressed in the central site at muFB. We thus demonstrated the possibility of increasing mu wave suppression in feedback training using a specific stimulus such as motion observation.

The Impact of Rain on Ocean Surface Waves and Currents

AbstractPrecipitation is an important component of the interaction between Earth's atmosphere and oceans, modifying air‐sea fluxes of momentum, heat, and gas. It has been hypothesized that rain's suppression of ocean surface gravity waves and centimeter‐scale wave enhancement should alter the nature of air‐sea momentum flux, resulting in increased near‐surface current. Here, we use field observations to describe this impact and measure the very near‐surface current response to rainfall. During heavy rain, surface‐roughening ring waves were generated and longer gravity waves were suppressed; immediately following, the magnitude of the near‐surface current increased in response to wind forcing but died as the rain subsided and long waves recovered. These first‐of‐their‐kind field observations indicate that rain reduces ocean wave form drag in favor of tangential stress, resulting in the acceleration of current near the sea surface.

Suppression of Lamb wave excitation via aperture control of a transducer array for ultrasonic clamp-on flow metering.

During ultrasonic clamp-on flow metering, Lamb waves propagating in the pipe wall may limit the measurement accuracy by introducing absolute errors in the flow estimates. Upon reception, these waves can interfere with the up and downstream waves refracting from the liquid, and disturb the measurement of the transit time difference that is used to obtain the flow speed. Thus, suppression of the generation of Lamb waves might directly increase the accuracy of a clamp-on flow meter. Existing techniques apply to flow meters with single element transducers. This paper considers the application of transducer arrays and presents a method to achieve a predefined amount of suppression of these spurious Lamb waves based on appropriate amplitude weightings of the transducer elements. Finite element simulations of an ultrasonic clamp-on flow measurement setting will be presented to show the effect of array aperture control on the suppression of the Lamb waves in a 1-mm-thick stainless steel pipe wall. Furthermore, a proof-of-principle experiment will be shown that demonstrates a good agreement with the simulations.

Modeling and simulation of an antenna with optimized AMC reflecting layer for gain and front-to-back ratio enhancement for 5G applications

A low-profiled microstrip patch antenna for application in the 5G wireless communication systems is backed by a reflecting layer based on an optimized artificial magnetic conductor (AMC) to enhance the gain and the front-to-back ratio. The design and analyses process were carried out using the full-wave commercial simulator CST Microwave Studio in parallel with Matlab, using the embedded CST to Matlab VBA-based interface to create an automated simulation environment and to design both a conventional antenna and the proposed one. A genetic algorithm (GA) is used to optimize the AMC reflecting layer to achieve maximum gain and front-to-back ratio around the frequency band of interest. The results yield an important enhancement in the peak gain and front-to-back ratio, alongside a low side-lobe level (SLL) due to the successful surface waves suppression, thus making this antenna design a good candidate for future wireless communication systems.

BEGINNING OF UKRAINIAN POLITICAL EMIGRATION IN SWITZERLAND IN THE OTHER HALF 1870's

The article analyzes the beginnings of Ukrainian political emigration in Switzerland in the second half of the 1870s, which is related to the activities of prominent Ukrainian political, public and cultural figure M P Drahomanov. The repression by the tsarist authorities, which began after the suppression of the first wave of the populist movement, forced a number of figures of both the Ukrainian and Russian revolutionary movements to leave their homeland in order to continue their struggle in emigration. It was in Switzerland after the end of the revolutions of 1848, as well as the defeat of the Paris Commune in 1871, that people from different countries gather, aiming to analyze the causes of the defeat of the revolutions and to develop measures for the future. M. Drahomanov managed to unite supporters of Ukrainian federalism and start publishing in Geneva both the first free Hromada magazine and literature on current topics of history, culture and major problems of Ukrainian life. At the same time, Drahomanov and his adherents take an active part in the social life of the Geneva colony of emigrants, and he himself becomes one of the most respected figures to be acquainted with by all those who came from Russia. At this time, the revolutionary views of M. Drahomanov and his supporters crystallized as well, which consisted in the need to fight for the federal system of the future of Russia and to abandon the state in general for the benefit of self-governing communities. At the same time, an important component of the activity of Ukrainian political emigration was the promotion of their views among revolutionary figures, especially from Russia. To this end, M. Drahomanov and his supporters spread the ideas of federalism and anarchism through the publishing of literature, the Hromada magazine, and meetings with revolutionaries who came from the Russian Empire. Their views were often incompatible with the ideas of other revolutionaries, as many of them advocated the preservation of Russia as a single state. This has led to misunderstandings and sometimes negative attitudes on the part of Russian figures. Nevertheless, M. Drahomanov did not back down from his ideas, which aroused respect from emigrants and made him a respected figure for all refugees from Russia.

Suppression of a spontaneous dust density wave by modulation of ion streaming

Synchronization of a self-excited dust density wave has been experimentally investigated in a strongly coupled dusty plasma. A dust density wave of frequency ∼78 Hz is spontaneously generated from the dust void boundary due to the ion streaming instability. The electric field in the dust void region is measured, and the electric field force and ion drag force on the dust particles at the void boundary are estimated to explain the mechanism of spontaneous dust density wave excitation. Synchronization occurring through the suppression mechanism is observed by modulating the ion streaming by applying an external sinusoidal signal to the dust void. At sufficiently high modulation amplitude, the onset of period-doubling bifurcation is observed. Fast Fourier transform spectral analysis is done using time-series data obtained from high-speed video imaging. The van der Pol equation with a force term is used to correlate the observed suppression phenomena.

Discrete sliding mode control strategy for a three‐phase Boost‐type VIENNA rectifier with the CB‐PWM

A three‐phase three‐level VIENNA rectifier has been widely used in the data center DC power supply and AC/DC hybrid power supply system with the advantages of without dead‐time, low switch voltage stress and small grid‐current harmonic. However, the performance of grid current strongly depends on the controller parameter, and the unreasonable controller parameter may deteriorate the grid current. To effectively improve the static and dynamic performance of grid current, a new kind of carrier‐based pulse width modulation scheme based on the double closed‐loop discrete sliding mode strategy is put forward. Further, a modified exponential reaching law is presented to effectively improve the shaking shock effect caused by the traditional sliding mode surface and the neutral voltage dc wave suppression strategy is then presented. To verify the correctness and effectiveness of the proposed sliding mode control strategy, a complete simulation model and experimental prototype platform under the digital control is established, the detailed theoretical analysis and design method of the proposed control strategy are presented. The simulation and experimental results show that the steady and the transient performance of the grid current with the proposed control strategy are effectively improved, and the neutral voltage in dc side is kept balanced at the same time. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Suppression of the Detonation Wave with the Aid of a Multi-Component Particle Cloud

Suppression of the Detonation Wave with the Aid of a Multi-Component Particle Cloud

Evaluation of Conditions for Suppression of Combustion and Detonation Waves

Evaluation of Conditions for Suppression of Combustion and Detonation Waves

Double-pulse femtosecond laser ablation for synthesis of ultrasmall carbon nanodots

Carbon nanodots (C-dots) with ultrasmall size possessing large surface-to-volume ratio are expected to improve their performance in sensing and catalytic applications. Here, we present a simple strategy to synthesis ultrasmall C-dots using double-pulse femtosecond laser ablation in solution. The size of C-dots reaches minimum value of ∼1 nm when the delay between the pulses was approaching the electron-ion relaxation time. In this case, the mean sizes of C-dots in double-pulse ablation are even smaller than that obtained in single-pulse ablation with the same laser fluence due to the suppression of rarefaction wave by the shock wave created by the second pulse. Furthermore, abundant functional groups are created on the surface of C-dots in double-pulse ablation because of reheating the nascent ablated materials by the second pulse. These results demonstrate that the double-pulse technique is therefore an effective strategy beyond single-pulse ablation to synthesis ultrasmall C-dots with abundant surface functional groups as well as other nanoparticle for catalytic and sensing applications.

Suppression of the Detonation Wave with the Aid of a Multi-Component Particle Cloud

The aim of this study is to investigate the effect of diversity of particles in the downstream cloud on detonation wave suppression. The multi-component two-phase model for a reacting compressible flow field including clouds of chemically inert solid particles is utilized here. The detonation wave is simulated in a stoichiometric hydrogen and oxygen mixture using a detailed full chemistry model. The finite volume scheme is used in the developed numerical program, where the advection upstream splitting method is used in addition to the Saurel method for the multi-particle cloud in order to compute the particle-phase and gas-phase fluxes. The impact of the detonation wave on the rigid wall is investigated, and the magnitude of the resulting pressure rise is accurately predicted in the case of a head-on collision of two similar waves instead of direct simulation of the wall reflection. The results demonstrate that the impact pressure rise is rather strong and destructive, and using a multi-component particle cloud may have better attenuating features for both short and long action times and require a shorter required propagation length for detonation wave suppression than using a single-component particle cloud.

Integration of a Via-Loaded Annular-Ring Reduced-Surface-Wave Antenna and a Branch-Line Coupler

This study proposes a dual-circularly polarized Reduced-Surface-Wave (RSW) antenna which has a compact and simple structure by the integration of a via-loaded annular-ring (VLAR)-RSW antenna with a branch-line coupler. The fundamental characteristics of a VLAR-RSW antenna are analyzed through simulations in detail. In general, stronger mutual coupling between RSW antennas occurs in comparison with conventional patch antennas when the element spacing is small, since the effect of the close physical distance becomes larger than the effect of surface wave suppression. It is shown that the VLAR antenna can reduce the mutual coupling than the conventional antenna by selecting the appropriate radius at each element spacing, even when the element spacing is small. A matching circuit is generally required for an annular-ring antenna because of the high input impedance when exciting the TM11 mode. In contrast, for the VLAR-RSW antenna, impedance matching is feasible without a matching circuit by adjusting the distance between the feed position and the shorting vias. Measured results show the performance of the developed dual-circularly polarized antenna is in agreement with the simulation. At 5.8GHz, the measured axial ratios of both polarizations are smaller than 0.6dB and the measured isolation between ports is about 29 dB. Moreover, it is shown that the developed antenna reduces mutual coupling than the conventional patch antenna because of the effect of suppressing surface waves.

Laser-driven high-velocity microparticle launcher in atmosphere and under vacuum

This paper presents a novel approach to launch single microparticles at high velocities under low vacuum conditions. In an all-optical table-top method, microparticles with sizes ranging from a few microns to tens of microns are accelerated to supersonic velocities depending on the particle mass. The acceleration is performed through a laser ablation process and the particles are monitored in free space using an ultra-high-speed multi-frame camera with nanosecond time resolution. Under low vacuum, we evaluate the current platform performance by measuring particle velocities for a range of particle types and sizes, and demonstrate blast wave suppression and drag reduction under vacuum. Showing an impact on polyethylene, we demonstrate the capability of the experimental setup to study materials behavior under high-velocity impact. The present method is relevant to space applications, particularly to rendezvous missions where velocities range from tens of m/s to a few km/s, as well as to a wide range of terrestrial applications including impact bonding and impact-induced erosion.

Multiple wave prediction and suppression based on L0-norm sparsity constraint

Multiple wave is one of the important factors affecting the signal-to-noise ratio of marine seismic data. The model-driven-method (MDM) can effectively predict and suppress water-related multiple waves, while the quality of the multiple wave contribution gathers (MCG) can affect the prediction accuracy of multiple waves. Based on the compressed sensing framework, this study used the sparse constraint under L0 norm to optimize MCG, which can not only reduce the false in the prediction and improve the image accuracy, but also saves computing time. At the same time, the MDM-type method for multiple wave suppression can be improved. The unified prediction of multiple types of water-related multiple waves weakens the dependence of conventional MDM on the adaptive subtraction process in suppressing water-related multiple waves, improves the stability of the method, and simultaneously, reduces the computational load. Finally, both theoretical model and practical data prove the effectiveness of the present method.

A reflective acoustic meta-diffuser based on the coding meta-surface

The acoustic coding metasurfaces have attracted much attention recently for their unique and flexible control of wavefronts by arranging the binary elements in special sequences with antiphase responses. In this paper, we investigate the application of coding metasurfaces to manipulate the scattering features found under plane-wave illumination. Different coding strategies are considered to realize multibeam generation and construct meta-diffusers that can disperse incoming energy in various directions, leading to considerable suppression of acoustic waves traveling in specular directions. Both simulated and measured results demonstrate the powerful capability of wave manipulation by the coding metasurfaces, offering a new method for noise control in the future.

Microstrip patch back radiation reduction using metamaterial superstrate

The capability of the capacitively loaded loop (CLL) metamaterial (MTM) superstrate to attenuate surface waves thereby reducing the back radiation of microstrip patch antennas is examined. To understand the surface wave suppression mechanism, theoretical approaches of a grounded dielectric slab waveguide is provided. Both theoretical and numerical analyses show that the proposed superstrate causes a drastic attenuation of surface wave propagation. To confirm the numerical simulations, the proposed antenna is fabricated and tested. The dimensions of the CLL-MTM covered patch antenna are 0.6λ × 0.8λ × 0.14λ. The radiated gain and efficiency are measured at 7.8 dB and 95%, respectively. Measurements show that the front-to-back ratio is enhanced by more than 12 dB. In comparison with the patch antenna without the CLL-MTM superstrate, the proposed antenna reduces the gain and efficiency by less than 0.1 dB and 2%, respectively.

Ion intercalation engineering of electronic properties of two-dimensional crystals of2H−TaSe2

Ion intercalation was recently used to explore two-dimensional (2D) transition metal dichalcogenides (TMDs) with precise tuning of ion concentration in a field-effect-transistor configuration. However, how to systematically change the properties of 2D TMDs, e.g., superconductivity and charge density waves, by ion intercalation has not been explored. We report in this paper results of electrical transport measurements on 2D crystals of $2\text{H}\text{\ensuremath{-}}{\mathrm{TaSe}}_{2}$ intercalated with Li ions that is tuned continuously by ionic gating. Shubnikov--de Haas magnetoconductance oscillation and Hall coefficient measurements on crystals of $2\text{H}\text{\ensuremath{-}}{\mathrm{TaSe}}_{2}$ revealed an ion intercalation induced multi- to single-band change in the Fermi surface (FS) topology, deep in the charge density wave phase, resulting in a reduction of the number of independent channels for electronic conduction. A remarkable crossover from weak antilocalization to weak localization tuned by gate voltage or temperature was found and attributed to the ion intercalation induced variations in the spin-orbital coupling and electron-phonon interaction. These observations provide new insight into the enhancement of superconductivity and the suppression of charge density waves in 2D $2\text{H}\text{\ensuremath{-}}{\mathrm{TaSe}}_{2}$ induced by ion intercalation and demonstrate furthermore the great potential of ion intercalation for engineering electronic properties of 2D TMDs.

Direct wave suppression technology of passive radar system

This work studies the direct wave suppression technology of passive radar system based on ‘global system for mobile (GSM)’ communication. In order to suppress direct waves, this study proposes an adaptive suppression algorithm based on NLMS criterion. Achieves great suppression of the strong interference signal, and finally realised target positioning and velocity measurement to the actual measured GSM signal.

A Low-Profile Wideband Hybrid Metasurface Antenna Array for 5G and WiFi Systems

A hybrid metasurface (HMS) is proposed to form a low-profile wideband antenna array. The antenna element is an array of $4\,\,\times4$ square metal patches and fed by a $50~\Omega $ microstrip line through an H-shaped coupling slot on the ground plane. Only are the edge patches of HMS antenna element grounded by shorting pins for the suppression of surface waves and cross-polarization levels as well as the enhancement of the gain. With the HMS antenna element, a compact $2\times 2$ array with an overall size of $1.58\lambda _{0} \times 1.58\lambda _{0} \times 0.068\lambda _{0}$ ( $\lambda _{0}$ is the free-space wavelength at 5.0 GHz) is designed, where the adjacent elements share the edge patches of the elements. The measurement shows the impedance bandwidth of 28% (4.41–5.85 GHz) for $\vert \text{S}_{11}\vert \le -10$ dB is obtained, and the boresight gain is greater than 8.4 dBi across the operating band, covering both fifth-generation (5G) sub 6 GHz and WiFi bands.