Large Phase Shift Research Articles

Suppression of High-Frequency Circulating Current Caused by Asynchronous Carriers for Parallel Three-Phase Grid-Connected Converters

The parallel three-phase grid-connected converters sharing dc and ac bus can increase the system power level effectively. However, the circulating current will occur inevitably. The existing studies primarily focus on dc, fundamental, and low-frequency circulating current. The high-frequency circulating current (HFCC) caused by asynchronous carriers is studied emphatically in this paper, which is based on the analysis of the change of circulating current in one control cycle. A novel method to suppress HFCC caused by asynchronous carriers of modules is proposed. In this method, the carrier period of slave module is adjustable and the carrier period of the master module is constant. When a large phase shift between modules occurs, an adjusting cycle is inserted to carrier of slave module to realize resynchronizing with master module. It is noted that there is no other commutation between the two modules (expect the dq current reference), such as the carrier information. Finally, the feasibility and effectiveness of the proposed method are verified by experiments.

On the evolution of planetary‐scale fields and genesis of monsoon depressions over the Indian region

Daily composite Fourier coefficients of height, zonal, meridional and vertical velocity, temperature, vorticity and divergence for zonal wave numbers 0–4, during 7 days of pre‐ and 4 days of post‐depression, from 1000 to 200 hPa in the latitude belt 0–30°N are obtained for six monsoon depressions formed over the Bay of Bengal in the years 2006–2008. The planetary‐scale fields zonally averaged over the Indian region (75–96°E) are examined. Consistent with the quasi‐geostrophic approximation, in the northern sector (15–30°N) the monsoon trough, the low‐level westerlies and the vorticity are strongly intensified and progressively extended upward to 400 hPa preceding depressions. Wave number 1 is the dominant contributor towards the strengthening and vertical upward expansion of these entities linked to an increase of its amplitude in the lower‐ and a large westward phase shift in the mid‐troposphere, respectively. The cyclonic shear zone in the lower troposphere is developed to the north of 15°N due to the combined effect of intensification and sharp decrease of meridional scale of the westerlies. Different northward speeds of the zonal wind reversal and westerly maximum creates a strong cyclonic zone 2 days before depressions at 400 hPa. The planetary‐scale zonal flow in the troposphere satisfies the necessary condition for barotropic instability. The northward (westward) movement of wave number 1 at 400 hPa is 0.73° latitude (5.6° longitude) day−1. An intensification of direct thermal meridional circulation is associated with a southward and upward shift of the primary rising motion zone.The planetary waves have captured the main characteristics of observed vertical and latitudinal profiles of unstable background zonal flow, used earlier for instability studies. It is concluded that wave number 1 is the main contributor to genesis of a depression. The planetary fields weakened in the presence of depressions mainly due to wave numbers 3 and 4.

Single Self-Injection-Locked Radar With Two Antennas for Monitoring Vital Signs With Large Body Movement Cancellation

This paper presents a novel self-injection-locked radar with two antennas to transmit and retransmit a continuous wave to opposite sides of a human body for monitoring vital signs in real time with large body movements. The system can prevent the nonlinear effects of large Doppler phase shifts on the cancellation of body motion artifacts, to extract accurate vital signs from the received Doppler-shifted signal. However, the effectiveness of the cancellation is limited by the received clutter echoes in this system. Therefore, the system also has a clutter effect elimination circuit to improve substantially the detection of vital signs in an examinee at various positions between the two antennas even when the examinee moves often by more than one wavelength.

Distortion-free propagation in a chiral medium using the coherent superposition of atomic states

We propose a scheme for distortion free left/right circularly polarized beams in a chiral atomic medium in a tripod-type configuration using the superposition of atomic states. We measure and control the group index, group velocity and delay and advance times for left/right circularly polarized beams in a transparent chiral atomic medium by varying the population distribution probability in the superposition states. For the left and right circularly polarized beams of the probe field, delay and advance times have been observed at resonance and away from resonance. A negligible distortion and large phase shift in the left/right circularly polarized beams is theoretically investigated in the system. The results show potential applications in telecommunication, cloaking base technology and information processing.

Relative surface wave amplitude and phase anomalies from the Democratic People's Republic of Korea announced nuclear tests

AbstractWe performed relative locations of six event pairs based on surface wave (SW) and body wave (BW) differential traveltimes of the 9 September 2016, 6 January 2016, 12 February 2013, and 25 May 2009 announced North Korea nuclear explosions. The SW relative locations for the 25 May 2009 and 12 February 2013 events were inconsistent with the BWs when paired with other events, and only the 6 January 2016/9 September 2016 pair was consistent. Apparent SW phase shift is investigated with respect to the BW relative locations. The pairs formed with the 25 May 2009 and 12 February 2013 events, beneath the southeast slope of Mount Mant'ap, have the largest phase shifts and amplitude ratio deviations, whereas the least deviation was from the 6 January 2016 and 9 September 2016 event pair beneath the mountain peak. Regional moment tensors (MTs) predict the amplitude ratios but do not resolve the relative phase. We find that MTs with 10% difference in isotropic and rotated +CLVD can fit both relative phase and amplitude ratios. SW relative locations of highly isotropic and correlated explosion clusters can be affected by topography and small differences in MT.

Very large phase shift of microwave signals in a 6 nm HfxZr1−xO2 ferroelectric at ±3 V

In this letter, we report for the first time very large phase shifts of microwaves in the 1–10 GHz range, in a 1 mm long gold coplanar interdigitated structure deposited over a 6 nm HfxZr1−xO2 ferroelectric grown directly on a high resistivity silicon substrate. The phase shift is larger than 60° at 1 GHz and 13° at 10 GHz at maximum applied DC voltages of ±3 V, which can be supplied by a simple commercial battery. In this way, we demonstrate experimentally that the new ferroelectrics based on HfO2 could play an important role in the future development of wireless communication systems for very low power applications.

A Novel Optoelectronic Oscillator Based on Brillouin-Induced Slow Light Effect

A novel optoelectronic oscillator (OEO) using a phase modulator is proposed and experimentally demonstrated. A carrier phase shift technique based on Brillouin-induced slow light effect is used to realize a conversion from phase modulation to intensity modulation. Two kinds of pump structures for producing large nonlinear phase shifts, a single-pump structure and a dual-pump structure, are investigated. As a comparison, the single-sideband phase noises of the single-pump and dual-pump OEOs are measured, respectively. The experimental results indicate that the single-pump OEO exhibits better phase noise performance near carrier than the dual-pump OEO. The maximum fractional frequency deviation of both types of OEOs is about ±0.85 ppm over 5000 s. The proposed scheme can be widely used in stable microwave or millimeter wave generation.

Large optical phase shifts in hydrogels written with femtosecond laser pulses: elucidating the role of localized water concentration changes

We describe the treatment of new hydrogels with nine different chemical compositions by femtosecond laser writing. The phase change induced in the wavefront when passing through the written areas was measured in all of these materials. The induced phase change is negative, which is attributed to the higher presence of water in the written regions and confirmed via Raman spectroscopy. The largest induced change in a single layer at 100 mm/s was −3.69 waves at 543 nm. These results show a strong dependence of the phase change on the concentration of some components and their molar ratio. We propose that some components are essential for the nonlinear energy absorption (“dopants”), while other components (“quenchers”) are essential in redirecting the absorbed energy to cause chemical reactions that profoundly change the polymer structure.

High-resolution, on-chip RF photonic signal processor using Brillouin gain shaping and RF interference

Integrated microwave photonics has strongly emerged as a next-generation technology to address limitations of conventional RF electronics for wireless communications. High-resolution RF signal processing still remains a challenge due to limitations in technology that offer sub-GHz spectral resolution, in particular at high carrier frequencies. In this paper, we present an on-chip high-resolution RF signal processor, capable of providing high-suppression spectral filtering, large phase shifts and ns-scale time delays. This was achieved through tailoring of the Brillouin gain profiles using Stokes and anti-Stokes resonances combined with RF interferometry on a low-loss photonic chip with strong opto-acoustic interactions. Using an optical power of <40 mW, reconfigurable filters with a bandwidth of ~20 MHz and an extinction ratio in excess of 30 dB are synthesized. Through the concept of vector addition of RF signals we demonstrate, almost an order of magnitude amplification in the phase and delay compared to devices purely based upon the slow-light effect of Brillouin scattering. This concept allows for versatile and power-efficient manipulation of the amplitude and phase of RF signals on a photonic chip for applications in wireless communications including software defined radios and beam forming.

Carrier signal injection‐based sensorless control for permanent magnet synchronous machine drives with tolerance of signal processing delays

In the case of high precision A/D converters, carrier signal injection based position estimation methods can adopt a relatively higher injection frequency (>1/10 pulse width modulation (PWM) switching frequency), which can lead to enhanced system bandwidths. However, simultaneously, signal processing delay effects (e.g., PWM duty ratio updating delay, etc.) become prominent, resulting in large phase shifts of carrier currents. On the other hand, the high frequency (HF) resistance effects may also be enlarged. Consequently, large oscillating position estimation errors will arise for the pulsating injection method due to carrier signal distortions induced by the delay and HF resistance effects. In order to suppress the undesirable position errors, based on the theoretical analyses, a new compensation strategy of maximizing the useful inductive saliency part and minimising the resistive saliency components using a PI regulator is proposed. The proposed position error suppression method is very easy and simple to implement, and moreover can significantly improve the sensorless control performance. Furthermore, the similar compensation strategy can also be applied for the position error compensation for rotating injection method as will also be discussed in this paper. Finally, the theoretical analyses and compensation effectiveness are validated by experiments on a laboratory interior permanent magnet machine.

Controllable double electromagnetically induced transparency in a closed four-level-loop cavity–atom system**Project supported by the National Natural Science Foundation of China (Grant No. 11174109).

We present a theoretical study of an optical cavity coupled with single four-level atoms in closed loop formed via applied control lasers. The transmitted probe field from the cavity is analyzed. We show that the electromagnetically induced transparency (EIT) in the cavity and the normal mode splitting will be very different with changing the closed interaction phase and the intensity of the free-space control laser. This coupled cavity–atom system presents a variational double-EIT that comes from modulating the splitting of the dark state, which means that we could realize the gradual transfer between one EIT peak and two EIT peaks by adjusting the applied control lasers, and the normal mode splitting sidebands will shift slightly by changing the free-space control laser. This means that we could control the output cavity probe field more freely and it is easer to realize optical switch controlled by more parameters. We also depict the angular dispersion of the intracavity probe field in different free-space control laser. The large phase shift () of the reflected intracavity probe field will be very useful for optical temporal differentiation and quantum phase gate.

Terahertz artificial birefringence and tunable phase shifter based on dielectric metasurface with compound lattice

A dielectric metasurface with line-square compound lattice structure has been fabricated and demonstrated in the terahertz (THz) regime by the THz time-domain spectroscopy and numerical simulation. A polarization dependent electromagnetically induced transparency (EIT) effect is achieved in this metasurface due to the mode coupling and interference between the resonance modes in line and square subunits of the metasurface. Accompany with the EIT effect, a large artificial birefringence effect between two orthogonal polarization states is also observed in this compound metasurface, of which birefringence is over 0.6. Furthermore, the liquid crystals are filled on the surface of this dielectric metasurface to fabricate an electrically tunable THz LC phase shifter. The experimental results show that its tunable phase shift under the biased electric field reaches 0.33π, 1.8 times higher than the bare silicon, which confirms the enhancement role of THz microstructure on the LC phase shift in the THz regime. The large birefringence phase shift of this compound metasurface and its LC tunable phase shifter will be of great significance for potential applications in THz polarization and phase devices.

Evolution of diffraction and self-diffraction phenomena in thin films of Gelite Bloom/Hibiscus Sabdariffa

In this work, we present a study of non-linear optical response in thin films elaborated with Gelite Bloom and extract of Hibiscus Sabdariffa. Non-linear refraction and absorption effects were studied experimentally (Z-scan technique) and numerically, by considering the transmittance as non-linear absorption and refraction contribution. We observe large phase shifts to far field, and diffraction due to self-phase modulation of the sample. Diffraction and self-diffraction effects were observed as time function. The aim of studying non-linear optical properties in thin films is to eliminate thermal vortex effects that occur in liquids. This is desirable in applications such as non-linear phase contrast, optical limiting, optics switches, etc. Finally, we find good agreement between experimental and theoretical results.

Dependent scattering and absorption by densely packed discrete spherical particles: Effects of complex refractive index

Due to the dependent scattering and absorption effects, the radiative transfer equation (RTE) may not be suitable for dealing with radiative transfer in dense discrete random media. This paper continues previous research on multiple and dependent scattering in densely packed discrete particle systems, and puts emphasis on the effects of particle complex refractive index. The Mueller matrix elements of the scattering system with different complex refractive indexes are obtained by both electromagnetic method and radiative transfer method. The Maxwell equations are directly solved based on the superposition T-matrix method, while the RTE is solved by the Monte Carlo method combined with the hard sphere model in the Percus-Yevick approximation (HSPYA) to consider the dependent scattering effects. The results show that for densely packed discrete random media composed of medium size parameter particles (equals 6.964 in this study), the demarcation line between independent and dependent scattering has remarkable connections with the particle complex refractive index. With the particle volume fraction increase to a certain value, densely packed discrete particles with higher refractive index contrasts between the particles and host medium and higher particle absorption indexes are more likely to show stronger dependent characteristics. Due to the failure of the extended Rayleigh-Debye scattering condition, the HSPYA has weak effect on the dependent scattering correction at large phase shift parameters.

P098 Cortical layer-specific distribution of TES electric fields

Introduction Cellular targets of transcranial electric stimulation (TES) are not well understood. Due to a number of factors including size, packing, myelination and orientation of predominant cell types and related variations in conductivity across layers, some cortical layers may be more susceptible to stimulation than others. Current biophysical models of TES do not account for laminar specific differences in the electric field distribution. Objectives In this study we systematically mapped the electric field distribution during TES across cortical layers as a function of electrode montage, stimulation frequency and cortical depth. Methods Using laminar multielectrode recordings (100 μm spacing, 24 contacts, implanted in V1) in an anesthetized cebus monkey we recorded TES induced potentials for two montages: 1. Anterior-Posterior current direction, electrodes placed over V1 and forehead. 2. Left–Right current direction, electrodes placed over bilateral temples. Stimulation intensity was 100 μA applied through round (3.14 cm2) Ag/AgCl electrodes. Measurements were performed using alternating currents with frequencies from 1–150 Hz for different depths (from dura through GM and WM). Electric fields were computed as the first spatial derivative of recorded potentials. Results We found a marked influence of the laminar structure on the electric field distribution ( Download : Download high-res image (624KB) Download : Download full-size image Fig. 1A) with locally increased field strengths (Layer IV/V). This effect was dependent on current direction (Fig. 1B). The amplitude and phase of recorded potentials varied in a frequency and spatially dependent manner ( Download : Download high-res image (444KB) Download : Download full-size image Fig. 2). Conclusion Our results highlight differential effects of electric field propagation across cortical layers. Locally enhanced electric fields are likely due to currents passing across conductivity mismatches between layers. This effect is dependent on current orientation. Magnitude and phase of recorded potentials varied across the depth of cortex demonstrating changes in local electric properties of brain tissue. Larger phase shifts in deeper WM regions could be related to stronger capacitive influences from myelinated axons. In summary our results show previously unreported laminar specific effects of TES electric fields making a first step in the identification of cell specific targets for TES.

Freestanding transparent terahertz half-wave plate using subwavelength cut-wire pairs.

We designed a cut-wire-pair metasurface that works as a transparent terahertz half-wave plate, by matching the electric and magnetic resonances of the structure. Due to the impedance matching nature of the resonances, a large transmission phase shift between the orthogonal polarizations was achieved, while permitting a high transmission. The electric and magnetic responses of the proposed structure were confirmed by evaluating the electric admittance and magnetic impedance. The structure was fabricated on a flexible film and its helicity-conversion function in the terahertz frequency range was experimentally demonstrated. The thickness of the device is less than 1/10 of the working vacuum wavelength, and a high amplitude helicity conversion rate over 80 % was achieved. Finally, using simulations, we demonstrate the feasibility of the gradually rotating cut-wire-pair array in terahertz wave-front control.

Origin of Large Phase Shift and Magnetoelectric Resonance in Magnetoelectric Laminate Composite

Magnetoelectric composites enjoy large magnetoelectric transfer efficiency at resonance frequency, accompanying a large phase shift. We prepared two magnetoelectric laminate composites to research the origin of large phase shift and magnetoelectric characteristics by electric-field-induced strain and magnetic-field-induced strain. The piezoelectric part plays a dominant role in both the direct and converse magnetoelectric resonances. The electromechanical resonance inspires direct and converse magnetoelectric resonant peaks, and results in the magnetoelectric phase shift of near $\pi $ around the resonance frequency. However, the magnetostrictive part is difficult to inspire the magnetoelectric resonance and phase shift.

Propagation of light through small clouds of cold interacting atoms

We demonstrate experimentally that a cloud of cold atoms with a size comparable to the wavelength of light can induce large group delays on a laser pulse when the laser is tightly focused on it and is close to an atomic resonance. Delays as large as -10 ns are observed, corresponding to "superluminal" propagation with negative group velocities as low as -300 m/s. Strikingly, this large delay is associated with a moderate extinction owing to the very small size of the cloud and to the light-induced interactions between atoms. It implies that a large phase shift is imprinted on the continuous laser beam, and opens interesting perspectives for applications to quantum technologies.

Circadian rhythms of European and African-Americans after a large delay of sleep as in jet lag and night work.

Jet travel and night shift work produce large changes in when people sleep, work and eat; a challenge that was not encountered during most of our evolution. Successful adaptation would require the internal, master, circadian clock to make large phase shifts to reduce the circadian misalignment between circadian rhythms and the times for sleep, work and meals. We compared African-Americans and non-Hispanic European-Americans in how much their circadian clocks shifted after a 9 hour phase delay of the light/dark, sleep/wake and meal schedule, which has similarities to flying west or sleeping in the daytime after night shifts. We also measured their free-running circadian periods using a forced desynchrony protocol with a 5-h day. European-Americans had longer free-running periods and larger phase delays than African-Americans. Correlations (among all subjects, just African-Americans and just European-Americans) showed that longer circadian periods were associated with larger phase delays. Larger phase delays, facilitated by longer circadian periods, reduce jet lag after westward travel and make it easier to work night shifts and sleep during the daytime after night work. On the other hand, a shorter circadian period, which makes one more of a morning-type person, is better for most people given our early-bird dominated society.

Observations and simulations of midlatitude ionospheric and thermospheric response to the January 2013 stratospheric sudden warming event

AbstractUsing observations from midlatitudes, we examine the ionospheric and thermospheric responses to the 2013 stratospheric sudden warming event by comparing data with four simulations performed by the Whole Atmosphere Community Climate Model eXtended (WACCM‐X), Thermosphere‐Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM), and Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIEGCM). The WACCM‐X simulation was nudged by the GEOS‐5 data. The two TIMEGCM simulations were nudged by the Modern‐Era Retrospective analysis for Research and Applications data and by the aforementioned WACCM‐X outputs, respectively. The standard TIEGCM simulation was also performed. These four simulations were compared with Millstone Hill (42.6°N, 71.4°W) incoherent scatter radar data, Millstone Hill and Boulder (40.1°N, 105.2°W) upper and lower thermospheric wind data. The meteor radar data from Collm (51.3°N, 13°E) were also used to examine the zonal wave number of the semidiurnal tide (SD). We evaluate the model simulations of the mesospheric and thermospheric responses to the 2013 SSW. The TIMEGCM simulation nudged with the WACCM‐X output has suitable stratospheric input and ionospheric dynamics and can reproduce a sharp rise of hmf2 on January 12 observed by the Millstone Hill radar. The comparison of different models with the lower thermospheric SD tide yielded mixed results. The SD tide maintained mostly as a migrating tide for most of the time and matched the TIEGCM simulation very well. The WACCM‐X appeared to perform better when the observed SD tide displays the large phase shift. It also has larger and more variable SD tide amplitude. The two TIMEGCM simulations have smaller SD amplitudes in general. Observations showed complex SD tide patterns after 20 January, which was difficult to characterize as a migrating tidal mode.