Field Amplitude Research Articles

Influence of ionospheric resonators on daily dynamics of the first Schumann resonance spectral parameters according to data from a meridional chain of ULF magnetometers

We have experimentally studied the influence of the local ionosphere, namely the ionospheric Alfvén resonator (IAR) and the lower ionospheric resonator at altitudes 80–300 km (sub-IAR) on the amplitude and polarization of the first Schumann resonance. The study is based on spectral analysis of data from simultaneous monitoring of ULF magnetic noise components at a meridional chain of stations: high-latitude stations Barentsburg and Lovozero, mid-latitude observatory NNGU NIRFI (NL, Nizhny Novgorod Region), a low-latitude station in Israel. We have also used monitoring data from the Borok and Crete observatories. At the stations in dark conditions, significant variations were found in the spectrum of the polarization parameter ε at the frequency of the first Schumann resonance (SR). Moreover, these variations had different character at different observatories. Analysis of the daily dynamics of the parameter ε has shown that these variations are associated with the influence of local sub-IAR having different optical thickness and quality factor at these observatories. The influence of sub-IAR on polarization in the SR band was found to depend on the ratio of the boundary frequency fb (the frequency that separates the negative and positive polarization of ULF magnetic noise) to the frequency of the first SR. The IAR influence on the polarization and amplitude of magnetic fields in the frequency band of the first Schumann resonance was discovered only at the NL and Lovozero stations: a high-quality Alfvén resonator in the ionosphere above the NL station could cause the SR frequency band to change and its central frequency to shift. Analysis of low-frequency data from the observatories separated by distances of 400 km has revealed that the influence of local ionospheric resonators can lead to a difference in the amplitude characteristics of the first SR even at such distances. It has also been shown that the influence of the IAR and sub-IAR resonators on the azimuthal angle of the magnetic field vector in the frequency band of the first SR is less noticeable and can generate variations in this parameter by 10°–20°. Numerical calculations performed for the spherical waveguide model made it possible to adequately interpret the features of the daily dynamics of the parameter ε in the frequency range of the first SR.

Влияние ионосферных резонаторов на суточную динамику спектральных параметров первого шумановс-кого резонанса по данным меридиональной сети УНЧ-магнито-метров

We have experimentally studied the influence of the local ionosphere, namely the ionospheric Alfvén resonator (IAR) and the lower ionospheric resonator at altitudes 80–300 km (sub-IAR) on the amplitude and polarization of the first Schumann resonance. The study is based on spectral analysis of data from simultaneous monitoring of ULF magnetic noise components at a meridional chain of stations: high-latitude stations Barentsburg and Lovozero, mid-latitude observatory NNGU NIRFI (NL, Nizhny Novgorod Region), a low-latitude station in Israel. We have also used monitoring data from the Borok and Crete observatories. At the stations in dark conditions, significant variations were found in the spectrum of the polarization parameter ε at the frequency of the first Schumann resonance (SR). Moreover, these variations had different character at different observatories. Analysis of the daily dynamics of the parameter ε has shown that these variations are associated with the influence of local sub-IAR having different optical thickness and quality factor at these observatories. The influence of sub-IAR on polarization in the SR band was found to depend on the ratio of the boundary frequency fb (the frequency that separates the negative and positive polarization of ULF magnetic noise) to the frequency of the first SR. The IAR influence on the polarization and amplitude of magnetic fields in the frequency band of the first Schumann resonance was discovered only at the NL and Lovozero stations: a high-quality Alfvén resonator in the ionosphere above the NL station could cause the SR frequency band to change and its central frequency to shift. Analysis of low-frequency data from the observatories separated by distances of 400 km has revealed that the influence of local ionospheric resonators can lead to a difference in the amplitude characteristics of the first SR even at such distances. It has also been shown that the influence of the IAR and sub-IAR resonators on the azimuthal angle of the magnetic field vector in the frequency band of the first SR is less noticeable and can generate variations in this parameter by 10°–20°. Numerical calculations performed for the spherical waveguide model made it possible to adequately interpret the features of the daily dynamics of the parameter ε in the frequency range of the first SR.

Response characteristics and detectability of pegmatitic rare-metal deposits using different grounded-wire configurations

The differential electrical dipole (DED) and differentially normalized electromagnetic method (DNME) have a stronger transverse magnetic field than the horizontal electric dipole (HED) and, thus, have been successfully used for resource exploration in conductive ocean environments. However, which of these two is more suitable for the exploration of resistive targets on land, such as pegmatite veins and ore-related mafic and ultramafic intrusions in mineral deposits, remains unknown. Thus, we conduct a comparative study of the DED, DNME, and HED based on forward modeling and application to a field survey. The signal amplitude of the horizontal electric field measured using the DED and DNME is substantially weaker than that obtained via the HED with the same source length and transmitting current. The lateral variation in the horizontal electric field response observed via the DNME reflects the change in the shallow electrical structure, indicating the spatial distribution of pegmatite veins, as verified by the 3D simulation results and data obtained in a field survey of pegmatitic rare-metal deposits in Lushi County, China. The DED and DNME exhibit similar abilities for detecting resistive targets. Both methods show higher detectability than HED based on 3D synthetic modeling. Our results indicate that the DNME, with its higher responses and better lateral resolution, is a better choice in field surveys on land than the DED.

Printed Liquid Crystal Optical Vortex Beam Generators

AbstractThis study presents an innovative application of inkjet printing technology in the construction of a switchable optical vortex beam generator. The fabrication process involves drop‐on‐demand printing of liquid crystal (LC) droplets that can generate an optical vortex beam in the far‐field with the application of a voltage. Notably, this vortex beam can be activated and deactivated by manipulating the amplitude of the electric field. Both simulations and experiments are used to determine the optical characteristics of the printed LC devices and the resulting far‐field patterns for different polarizations of light. The study showcases the versatility of the generator in that it can produce both vortex and vector beams, the choice of which is simply determined by the polarization of the input light. This highlight the potential of this printed LC technology for integration into a multitude of optical systems.

Tunable acoustic vortex generation by a compact rotating disk

Acoustic vortices (AVs) carry orbital angular momentum (OAM), showing great promise in advancing communication, biomedicine, and metrology. An ideal OAM generation method that realizes the tunability of AV topological charge and working frequency in a compact way is strongly desired. Here, we utilize aerodynamic dipole sources from a rotating disk to generate AV. This method generates AVs with different topological charges through the interference of these dipole sources at the angular rotation frequency and its multiples. These AVs exhibit high purity, and their three-dimensional characteristics are explored. Furthermore, our experiment demonstrates that the generated AVs significantly enhance the sound field amplitude at their working frequency, which is the product of the topological charge and angular frequency. The results also verify that this amplitude enhancement effect is positively correlated with the AV’s stability and achieves the contactless detection of disk rotation information. The demonstrated method provides expanded versatility for OAM-based applications.

Evaluating the motional timescales contributing to averaged anisotropic interactions in MAS solid-state NMR

Abstract. Dynamic processes in molecules can occur on a wide range of timescales, and it is important to understand which timescales of motion contribute to different parameters used in dynamics measurements. For spin relaxation, this can easily be understood from the sampling frequencies of the spectral-density function by different relaxation-rate constants. In addition to data from relaxation measurements, determining dynamically averaged anisotropic interactions in magic-angle spinning (MAS) solid-state NMR allows for better quantification of the amplitude of molecular motion. For partially averaged anisotropic interactions, the relevant timescales of motion are not so clearly defined. Whether the averaging depends on the experimental methods (e.g., pulse sequences) or conditions (e.g., MAS frequency, magnitude of anisotropic interaction, radio-frequency field amplitudes) is not fully understood. To investigate these questions, we performed numerical simulations of dynamic systems based on the stochastic Liouville equation using several experiments for recoupling the dipolar coupling, chemical-shift anisotropy or quadrupolar coupling. As described in the literature, the transition between slow motion, where parameters characterizing the anisotropic interaction are not averaged, and fast motion, where the tensors are averaged leading to a scaled anisotropic quantity, occurs over a window of motional rate constants that depends mainly on the strength of the interaction. This transition region can span 2 orders of magnitude in exchange-rate constants (typically in the microsecond range) but depends only marginally on the employed recoupling scheme or sample spinning frequency. The transition region often coincides with a fast relaxation of coherences, making precise quantitative measurements difficult. Residual couplings in off-magic-angle experiments, however, average over longer timescales of motion. While in principle one may gain information on the timescales of motion from the transition area, extracting such information is hampered by low signal-to-noise ratio in experimental spectra due to fast relaxation that occurs in the same region.

Effect of magnetic field on macroscopic hysteresis and microscopic magnetic domains for different ferromagnetic materials

The macroscopic hysteresis of ferromagnetic materials is influenced by their microscopic magnetic domains, establishing a correspondence between the two that enables a fundamental understanding of the magnetization process of ferromagnetic materials. Based on this, this study employs the phase field method to investigate the macroscopic hysteresis and microscopic magnetic domain evolution of soft, hard, and rectangular ferromagnetic materials. The hysteresis loops of the three materials present narrow, wide and rectangular characteristics respectively, which are quantitatively consistent with the experimental data. Subsequently, the influence of the magnetic field on the macroscopic hysteresis is analyzed. The results show that the hysteresis loop area increases when the magnetic field amplitude increases. Furthermore, the proportion of each type of energy under different magnetic fields is discussed, the dominant energy terms are generally consistent for the same category of ferromagnetic materials. Additionally, the corresponding magnetic domain evolution under different magnetic field is displayed, with soft magnetic materials exhibiting no vortex structures, hard ferromagnetic materials presenting a 45° vortex structure, and rectangular magnetic material showcasing a 90° vortex structure. Finally, the asymmetric characteristics of the major hysteresis loop and minor hysteresis loops are discussed. The change of the magnetic field path leads to the corresponding change of the major and minor hysteresis loops. At the same magnetic field, distinctions in magnetic domain configurations between the major and minor hysteresis loops are evident.

Abnormal Global Cortical Responses in Drug-Naïve Patients With Schizophrenia Following Orbitofrontal Cortex Stimulation: A Concurrent Transcranial Magnetic Stimulation–Electroencephalography Study

BackgroundAbnormalities in cortical excitability and plasticity have been considered to underlie the pathophysiology of schizophrenia. Transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) can provide a direct evaluation of cortical responses to TMS. Here, we employed TMS-EEG to investigate cortical responses to orbitofrontal cortex (OFC) stimulation in schizophrenia. MethodsIn total, we recruited 92 drug-naïve patients with first-episode schizophrenia and 51 age- and sex-matched healthy individuals. For each participant, one session of 1-Hz repetitive TMS (rTMS) was delivered to the right OFC, and TMS-EEG data were obtained to explore the change in cortical-evoked activities before and immediately after rTMS during the eyes-closed state. The MATRICS Consensus Cognitive Battery was used to assess neurocognitive performance. ResultsThe cortical responses indexed by global mean field amplitudes (i.e., P30, N45, and P60) were larger in patients with schizophrenia than in healthy control participants at baseline. Furthermore, after one session of 1-Hz rTMS over the right OFC, the N100 amplitude was significantly reduced in the healthy control group but not in the schizophrenia group. In the healthy control participants, there was a significant correlation between modulation of P60 amplitude by rTMS and working memory; however, this correlation was absent in patients with schizophrenia. ConclusionsAberrant global cortical responses following right OFC stimulation were found in patients with drug-naïve first-episode schizophrenia, supporting its significance in the primary pathophysiology of schizophrenia.

Coherently Driven Quantum Harmonic Oscillator Battery

AbstractRecently, quantum harmonic oscillator (QHO) battery models have been studied with importance because these experimentally realizable batteries have high ergotropy and capacity to store more than one quanta of energy. However, the following fundamental questions are not yet answered: Do these models have any benefit? Are these models stable against the environment? These questions are answered both numerically and analytically by considering a model that allows a laser to shine on a QHO charger, which interacts with a QHO battery. The laser frequency is tuned with the local frequencies of the charger and battery (off‐resonance) or the frequency of the global charger‐battery system (on‐resonance). It is shown that for a fixed laser field amplitude, in the off‐resonance (on‐resonance) charging process, the maximum energy stored in a battery depends on the detuning and coupling strength (charger dissipation constant). The charging process of the open QHO, which is a simplified model, is also discussed. Further, the charging process of QHO in the simplified model is observed to be faster than the same for the catalytic and non‐catalytic batteries. The self‐discharging process is found to be almost doubly faster than the charging process, implying that the QHO batteries are unstable against the environment.

Loss of Coherence and Change in Emission Physics for Radio Emission from Very Inclined Cosmic-Ray Air Showers.

Next-generation radio experiments such as the radio detector of the upgraded Pierre Auger Observatory and the planned GRAND and BEACON arrays target the detection of ultra-high-energy particle air showers arriving at low elevation angles. These inclined cosmic-ray air showers develop higher in the atmosphere than vertical ones, enhancing magnetic deflections of electrons and positrons inside the cascade. We evidence two novel features in their radio emission: a new polarization pattern, consistent with a geosynchrotron emission model and a coherence loss of the radio emission, both for showers with zenith angle θ≳65° and strong enough magnetic field amplitude (typical strength of B∼50 μT). Our model is compared with both ZHAireS and CoREAS MonteCarlo simulations. Our results break the canonical description of a radio signal made of Askaryan and transverse current emission only, and provide guidelines for the detection and reconstruction strategies of next-generation experiments, including cosmic-ray or neutrino discrimination.

ON THE PROPERTIES OF A FAST ALGORITHM FOR SOLVING A THREE-DIMENSIONAL INVERSE PROBLEM OF SCALAR ACOUSTICS

t Theinverse single-frequency problem of scalar acoustics in three-dimensional space is considered. It consists in determining the characteristics of acoustic inhomogeneities lying in a flat layer from the distribution of the complex amplitude of the acoustic field in a flat recording layer. To effectively solve it, a special numerical algorithm is used, previously proposed and justified by the authors. As its component part, the algorithm uses solutions to special one-dimensional Fredholm equations of the 1st kind, and in the case of ambiguity in the solution of the latter, their normal solutions (solutions with a minimum norm) are sought. To regularize this ill-posed inverse problem, Tikhonov regularization and the TSVD method are used. A systematic numerical study is carried out of the influence of various parameters in the data recording scheme on the accuracy of the approximate solutions obtained using the algorithm. In particular, we study the dependence of this accuracy on the position of point sources and composite sources that cause sound vibrations, its dependence on the position of the data recording layer, and on the number of planes in which the recording sensors lie. It is shown that acceptable accuracy of approximate solutions can be obtained even with two such layers. In addition, an approach to the numerical study of the ambiguity of the solution to the inverse problem under consideration is proposed. It is based on special theoretical statements given in the article, and on the same numerical algorithm for solving the inverse problem. The approach is focused on comparing several normal solutions of one-dimensional integral equations from the problem under consideration. These normal solutions are calculated with respect to various elements. An example of using this theory to numerically estimate the non-uniqueness of a solution is given.

Insights into the dynamic induction in FOWT surge motion using an actuator-line model

This research investigates the impact of surge motion on Floating Offshore Wind Turbines (FOWTs) through dynamic inflow analyses using an in-house Actuator Line Model (ALM). The study explores surge reduced frequencies in the range from 1 to 10 to analyse the returning wake phenomenon occurring at blade passage frequency. The findings highlight the dampening effect of the rotor thrust and torque by 25% due to induction field inertia. Noteworthy observations include the filter-like effect on the span-wise induced velocity trends: with the frequency increment, the induction field is ’synchronised’ with the apparent wind and forces. The results of the analyses evidence the suitability of the induction parsed in the absolute reference frame to capture the induction field features, amplitude and phase shift, at increasing surge frequencies.

Phase space representation of sound field excited by a noise source in underwater acoustic waveguide.

The analysis of the field excited in a waveguide by a point noise source is performed using the phase space representation of this field given by the distribution of its amplitude in the depth-angle-time space. The transition from the traditional description of the field amplitude as a function of depth and time to phase space representation is performed using the coherent state expansion developed in quantum mechanics. In this paper, the correlation function of noise signals arriving at different points of the phase plane depth-angle is investigated. Numerical simulation data show that measurements of signal correlations in phase space, performed with the help of a receiving vertical antenna, can be used as input data in solving the problem of source localization and reconstruction of unknown parameters of the sound speed profile. It is shown that in phase space there is an analog of the classical interference pattern observed in the distribution of sound intensity in the distance-frequency plane. The slopes of striations in this interference pattern, as in the conventional one, are given by the Chuprov waveguide invariant.

Femtosecond Drift Photocurrents Generated by an Inversely Designed Plasmonic Antenna.

Photocurrents play a crucial role in various applications, including light detection, photovoltaics, and THz radiation generation. Despite the abundance of methods and materials for converting light into electrical signals, the use of metals in this context has been relatively limited. Nanostructures supporting surface plasmons in metals offer precise light manipulation and induce light-driven electron motion. Through the inverse design optimization of a gold nanostructure, we demonstrate enhanced volumetric, unidirectional, intense, and ultrafast photocurrents via a magneto-optical process derived from the inverse Faraday effect. This is achieved through fine-tuning the amplitude, polarization, and gradients in the local light field. The virtually instantaneous process allows dynamic photocurrent modulation by varying optical pulse duration, potentially yielding nanosources of intense, ultrafast, planar magnetic fields and frequency-tunable THz emission. These findings open avenues for ultrafast magnetic material manipulation and hold promise for nanoscale THz spectroscopy.

All-optical complex field imaging using diffractive processors.

Complex field imaging, which captures both the amplitude and phase information of input optical fields or objects, can offer rich structural insights into samples, such as their absorption and refractive index distributions. However, conventional image sensors are intensity-based and inherently lack the capability to directly measure the phase distribution of a field. This limitation can be overcome using interferometric or holographic methods, often supplemented by iterative phase retrieval algorithms, leading to a considerable increase in hardware complexity and computational demand. Here, we present a complex field imager design that enables snapshot imaging of both the amplitude and quantitative phase information of input fields using an intensity-based sensor array without any digital processing. Our design utilizes successive deep learning-optimized diffractive surfaces that are structured to collectively modulate the input complex field, forming two independent imaging channels that perform amplitude-to-amplitude and phase-to-intensity transformations between the input and output planes within a compact optical design, axially spanning ~100 wavelengths. The intensity distributions of the output fields at these two channels on the sensor plane directly correspond to the amplitude and quantitative phase profiles of the input complex field, eliminating the need for any digital image reconstruction algorithms. We experimentally validated the efficacy of our complex field diffractive imager designs through 3D-printed prototypes operating at the terahertz spectrum, with the output amplitude and phase channel images closely aligning with our numerical simulations. We envision that this complex field imager will have various applications in security, biomedical imaging, sensing and material science, among others.

The interplay between imprint, wake-up, and domains in ferroelectric Al0.70Sc0.30N

This paper investigates wake-up and imprint in ferroelectric Al0.70Sc0.30N films. The study employs a series of electrical measurements with varying field amplitudes and waveforms to understand the origin and underlying principle of wake-up and imprint as well as their relation. It is shown that the material can be considered wake-up free. However, inherent imprint and imprint variation of the polarization-electric field hysteresis in combination with minor loops result in a wake-up like effect. This effect is most likely related to the formation of persistent inversion domain nuclei—a mechanism that is discussed in detail and compared with alternative explanations based on charged defects. Investigations using unipolar fields are conducted to explore the reversibility of imprint and ways to program it, while partial switching is applied to investigate domain propagation and support the aforementioned explanation for the evolution of the polarization-electric field hysteresis. It is concluded that after an energetically more demanding domain nucleation, domain wall motion can switch the majority of polarization in Al1−xScxN. As a consequence, the presence of initial domains reduces the coercive field with respect to unipolar films.

An impurity model in a random magnetic field

We explore the destruction of the Kondo interaction due to a random magnetic field. Using entanglement measures, the Kondo length and the impurity entropy are analyzed. We identify a critical magnetic field amplitude hc at which the destruction happens. We find that hc scales with the Kondo temperature of the model.

Hybrid architectures for terahertz molecular polaritonics

Atoms and their different arrangements into molecules are nature’s building blocks. In a regime of strong coupling, matter hybridizes with light to modify physical and chemical properties, hence creating new building blocks that can be used for avant-garde technologies. However, this regime relies on the strong confinement of the optical field, which is technically challenging to achieve, especially at terahertz frequencies in the far-infrared region. Here we demonstrate several schemes of electromagnetic field confinement aimed at facilitating the collective coupling of a localized terahertz photonic mode to molecular vibrations. We observe an enhanced vacuum Rabi splitting of 200 GHz from a hybrid cavity architecture consisting of a plasmonic metasurface, coupled to glucose, and interfaced with a planar mirror. This enhanced light-matter interaction is found to emerge from the modified intracavity field of the cavity, leading to an enhanced zero-point electric field amplitude. Our study provides key insight into the design of polaritonic platforms with organic molecules to harvest the unique properties of hybrid light-matter states.

Calculation of RF pulse evolution due to dispersion in travelling wave linacs using Fourier methods

An rf pulse propagating through a travelling wave linac can be seen to evolve due to dispersion. To accurately predict the field amplitude experienced by electron bunches travelling through the cavity, this pulse evolution must be well known. Here we present an method to predict the pulse evolution using Fourier methods. The method requires two inputs to calculate the dispersion: the group velocity as a function of cell number, and the phase advance. Attenuation is included in the model with the addition of a third input: the cavity Q0. The method is faster and more simple than 3D modelling, and allows subtle details of the pulse evolution to be revealed, without the need to know the exact dimensions of the structure. A synchronism condition can be added to predict the voltage experienced by a particle beam. The model is tested on the first CLARA linac, and shows good agreement both with measurements of the rf pulse and with measurements of the beam momentum as the time of beam injection is varied.

An improvement of the Jiles-Atherton model at various magnetic field amplitudes using the example of Terfenol-D material

Jiles-Atherton (JA) model has been widely used to describe the magnetic hysteresis property of Terfenol-D material. However, the accuracy of the classic JA model is not convincing any more when it is employed to predict the magnetizations under various amplitudes of the applied magnetic fields. This paper measures the magnetic field and magnetization indirectly and approximates the measured results to the best of the classic static JA model. Then it shows that the JA model fails to describe the magnetic hysteresis effectively, especially in computing the hysteresis width. The high computational error is caused from inappropriate value of the pinning parameter to quantify the average energy required to break pinning site. Then the parameter is modified from the constant value to an independent variable on the field amplitude. From the comparisons on the results of the maximum magnetization, maximum magnetization, residual magnetization and coercivity, the performance in describing the hysteresis property of Terfenol-D is obviously promoted by the improved model apparently compared to the classic one.