Dipole Frequency Research Articles

Adaptive adjustment method of segment linear frequency modulation excitation for wideband dipole logging

Abstract Wideband dipole signal is the basis for dipole dispersion correction and near-borehole imaging. Segment linear frequency modulation (SLFM) sound source signal is an effective method to broaden the dipole frequency band. In the actual logging process, the formation environment changes in real time, and the SLFM sound source with fixed parameters cannot compensate the bending wave excitation intensity curve at any time, which affects the quality of logging. This paper presents a method for adaptive adjustment of the SLFM sound source signal. Adaptive parameter adjustment can be made according to the change of downhole environment, so that the signal can be adapted to the changing downhole geological environment.

Numerical simulation of RHIC polarized proton run 17 spin flipper experiments

RHIC nine-magnet spin flipper has been operated successfully during RHIC polarized proton Run 17, with 97% spin flip efficiency achieved. The results show the importance of mirror resonance removal, small spin tune spread, and proper spin flipper driving tune sweep speed. Detailed spin tracking simulations, based on a Lorentz force and Thomas-BMT differential equation numerical solver code for accuracy, have been carried out to understand the experimental results. Agreement within measurement accuracy is obtained at injection energy, 23.8 GeV. It is not as tight at 255 GeV, reasons for that are exposed. These measurements and numerical studies allow to determine the sensitivity of spin-flip efficiency to the dispersion slopes at the two Siberian snakes and to the ac dipole frequency sweep speed. They also provide guidance for future developments at BNL’s electron-ion collider. Published by the American Physical Society 2024

Modeling of a linear ion trap with driving rectangular waveforms.

We consider the operation of a digital linear ion trap with resonant radial ejection. A sequence of rectangular voltage pulses with a dipole resonance signal is applied to the trap electrodes. The periodic waveform is piecewise constant, has zero mean, and is determined by an asymmetry parameter : one value is taken on interval and another on , where is the RF period. Ion mass scanning is performed by varying the asymmetry parameter and amplitude of the negative pulse part with time. The ion oscillation frequencies and acceptance of the linear trap are calculated. The dependence of the ion mass to charge ratio on the parameter is . The maximum value is about kDa for typical parameters of the linear trap: frequency 0.5 MHz, rod radius 4 mm, and negative pulse amplitude 1 kV. The dipolar excitation frequency is 0.125 MHz at which the LIT acceptance is maximal.

Control of excitation selectivity in pulse EPR on spin-correlated radical pairs with shaped pulses.

Spin-correlated radical pairs generated by photoinduced electron transfer are characterised by a distinctive spin polarisation and a unique behaviour in pulse electron paramagnetic resonance (EPR) spectroscopy. Under non-selective excitation, an out-of-phase echo signal modulated by the dipolar and exchange coupling interactions characterising the radical pair is observed and allows extraction of geometric information in the two-pulse out-of-phase electron spin echo envelope modulation (ESEEM) experiment. The investigation of the role of spin-correlated radical pairs in a variety of biological processes and in the fundamental mechanisms underlying device function in optoelectronics, as well as their potential use in quantum information science, relies on the ability to precisely address and manipulate the spins using microwave pulses. Here, we explore the use of shaped pulses for controlled narrowband selective and broadband non-selective excitation of spin-correlated radical pairs in two model donor-bridge-acceptor triads, characterised by different spectral widths, at X- and Q-band frequencies. We demonstrate selective excitation with close to rectangular excitation profiles using BURP (band-selective, uniform response, pure-phase) pulses and complete non-selective excitation of both spins of the radical pair using frequency-swept chirp pulses. The use of frequency-swept pulses in out-of-phase ESEEM experiments enables increased modulation depths and, combined with echo transient detection and Fourier transformation, correlation of the dipolar frequencies with the EPR spectrum and therefore the potential to extract additional information on the donor-acceptor pair geometry.

2.5D switchable metasurfaces

Nowadays, two-dimensional metasurfaces are widely used to control the amplitude, phase, and direction of light. However, such structures do not provide sufficient degrees of freedom, and thus, the fine adjustment of their optical properties is limited. To solve this problem, phase change materials such as GeSbTe are used. This family of materials is attractive for engineering tunable optical elements because of their non-volatile reversible phase transition and pronounced changes of the dielectric permittivity. Besides, the so-called two and a half dimensional (2.5D) metasurfaces introduce an additional degree of freedom. A fabrication of metasurface combining these two approaches and a detailed study of its photonic properties was reported. The arrangement in 2.5D geometry was tailored to match the lattice resonances to the frequency of the magnetic dipoles supported by the metasurface elements to demonstrate the effects related to the interaction between resonances of different origin. The phase change material enables the on/off switching behavior of the complex resonance effect.

Nanoscale refractive index sensor with ultrahigh figure of merit based on toroidal dielectric metasurfaces

Dielectric metasurfaces exhibiting low intrinsic loss and strong localized field are an emergent platform in light manipulation and sensing. Toroidal dipole, a new eigenmode distinct to the common electric and magnetic multipoles, expands the toolbox of nonlinear optics, filters, and multi-channel biosensors. Here, we propose a dielectric metasurface with two semicircle disks, which supports the high Q-factor toroidal dipole for the refractive index sensing. The performance of toroidal dipole is sensitive to the parameters of two semicircle disks. Via optimizing the geometrical parameters, we realize a Q-factor up to 69000. Moreover, the corresponding sensitivity and figure of merit can reach up to 70nm/RIU and 2970/RIU, respectively. The figure of merit is substantially higher than the previous works in near-infrared region. The enhancement of electric field located in the gap of two semicircles enables the strong interaction of light and the analyte. The introduction of the analyte will introduce the redshift of the resonant frequency of toroidal dipoles. Our findings expand the scope of toroidal dipoles and may serve as a new platform for high sensitivity sensing.

Microwave resonant absorption of SARS-CoV-2 viruses

Low power microwave can effectively deactivate influenza type A virus through the nonthermal structure-resonant energy transfer effect, at a frequency matching the confined-acoustic dipolar mode frequency of the virus. Currently, aerosol is considered the major route for SARS-CoV-2 transmission. For the potential microwave-based sterilization, the microwave-resonant frequency of SARS-CoV-2 must be unraveled. Here we report a microwave absorption spectroscopy study of the SARS-CoV-2 and HCoV-229E viruses through devising a coplanar-waveguide-based sensor. Noticeable microwave absorption can be observed, while we identified the resonant frequencies of the 1st and 2nd dipolar modes of SARS-CoV-2 virus as 4 and 7.5 GHz respectively. We further found that the resonant frequencies are invariant to the virus titer, and we also studied the microwave absorption of HCoV-229E in weak acidity medium to simulate the common pH value in fluid secretion. Our results suggest the possible radiation frequency for the recently proposed microwave sterilization devices to inactivate SARS-CoV-2 virus through a nonthermal mechanism so as to control the disease transmission in the post-pandemic era.

Adaptation and operation of a quadrupole/time-of-flight tandem mass spectrometer for high mass ion/ion reaction studies

A commercial quadrupole/time-of-flight tandem mass spectrometer has been modified and evaluated for its performance in conducting ion/ion reaction studies involving high mass (>100 kDa) ions. Modifications include enabling the application of dipolar AC waveforms to opposing rods in three quadrupole arrays in the ion path. This modification allows for resonance excitation of ions to effect ion activation, selective ion isolation, and ion parking. The other set of opposing rods in each array is enabled for the application of dipolar DC voltages for the purpose of broad-band (non-selective) ion heating. The plates between each quadrupole array are enabled for the application of either DC or AC (or both) voltages. The use of AC voltages allows for the simultaneous storage of ions of opposite polarity, thereby enabling mutual storage ion/ion reactions. Ions derived from nano-electrospray ionization of GroEL and β-galactosidase under native conditions were used to evaluate limits of instrument performance, in terms of m/z range, ion isolation, and ion storage. After adjustment of the pulser frequency, ions as high in m/z as 400,000 were detected. Significant losses in efficiency were noted above m/z 250,000 that is likely due to roll-over in the ion detector efficiency and possibly also due to limitations in ion transfer efficiency from the collision quadrupole to the pulser region of the mass analyzer. No measurable decrease in the apparent mass resolving power was noted upon charge state reduction of the model ions. Resonance ejection techniques that employ the dipolar AC capabilities of the quadrupoles allow for ion isolation at m/z values much greater than the RF/DC limitation of Q1 of m/z = 2100. For example, at the highest low-mass cutoff achievable in the collision quadrupole (m/z = 500), it is possible to isolate ions of m/z as high as 62,000. This is limited by the lowest dipolar AC frequency (5 kHz) that can be applied. A simple model is included to provide for an estimate of the ion cloud radius based on ion m/z, ion z, and ion trap operating conditions. The model predicts that singly charged ions of 1 MDa and thermal energy can be contained in the ion trap at the maximum low-mass cutoff, although such an ion would not be detected efficiently. Doubly charged GroEL ions were observed experimentally. Collectively, the performance characteristics at high m/z, the functionality provided by the standard instrument capabilities, the modifications described above, and highly flexible instrument control software provide for a highly versatile platform for the study of high mass ion/ion reactions.

How accurately defined are the overtone coefficients in Gd(III)-Gd(III) RIDME?

Relaxation-induced dipolar modulation enhancement (RIDME) is a pulse EPR technique that is particularly suitable to determine distances between paramagnetic centers with a broad EPR spectrum, e.g. metal-ion-based ones. As far as high-spin systems (S > ½) are concerned, the RIDME experiment provides not only the basic dipolar frequency but also its overtones, which complicates the determination of interspin distances. Here, we present and discuss in a step-by-step fashion an r.m.s.d.-based approach for the calibration of the overtone coefficients for a series of molecular rulers doubly labeled with Gd(III)-PyMTA tags. The constructed 2D total-penalty diagrams help revealing that there is no unique set of overtone coefficients but rather a certain pool, which can be used to extract distance distributions between high-spin paramagnetic centers, as determined from the RIDME experiment. This is of particular importance for comparing RIDME overtone calibration and distance distributions obtained in different labs.

Experimental and simulation studies of localization and decoding of single and double dipoles

Objective. Electroencephalography is a technique for measuring normal or abnormal neuronal activity in the human brain, but its low spatial resolution makes it difficult to locate the precise locations of neurons due to the volume conduction effect of brain tissue. Approach. The acoustoelectric (AE) effect has the advantage of detecting electrical signals with high temporal resolution and focused ultrasound with high spatial resolution. In this paper, we use dipoles to simulate real single and double neurons, and further investigate the localization and decoding of single and double dipoles based on AE effects from numerical simulations, brain tissue phantom experiments, and fresh porcine brain tissue experiments. Main results. The results show that the localization error of a single dipole is less than 0.3 mm, the decoding signal is highly correlated with the source signal, and the decoding accuracy is greater than 0.94; the location of double dipoles with an interval of 0.4 mm or more can be localized, the localization error tends to increase as the interval of dipoles decreases, and the decoding accuracy tends to decrease as the frequency of dipoles decreases. Significance. This study localizes and decodes dipole signals with high accuracy, and provides a technical method for the development of EEG.

Dielectric properties, polarization process, and charge transport in granular (FeCoZr)x(Pb(ZrTi)O3)(100−x) nanocomposites near the percolation threshold

This paper presents the research of dielectric properties of (FeCoZr)x(Pb(ZrTi)O3)(100−x) granular metal–dielectric nanocomposites below the percolation threshold. Tested materials have been prepared by using the ion beam sputtering technique in the atmosphere of argon and oxygen. The impedance spectroscopy method has been used to investigate the polarization processes and dielectric relaxation mechanism in the granular nanocomposites. AC measurements in the frequency region of 50 Hz to 1 MHz and measuring temperature range of 81–293 K have been performed. Interfacial, in the low frequency region, and dipolar, in intermediate and high frequency regions, types of polarization processes were observed. The interfacial relaxation process testifies to charge accumulation at the interfaces (grain boundaries) between conductive nanoparticles surrounding an insulative matrix, as well as the space charge region around the contact area between the measurement probes and tested sample. Dipolar polarization corresponds to electric dipole formation after applying to the material an external electric field. The conduction mechanism in the tested material is considered to be hopping carrier exchange and takes place between metallic phase nanograins. It corresponds to the exponential frequency dependence of conductivity. The relaxation mechanism in the (FeCoZr)x(Pb(ZrTi)O3)(100−x) layer has been estimated as a near-Debye process with relaxation time distribution. The nanocomposite exhibits dielectric type and capacitive characteristics in the whole measuring frequency range.

Coupling of plasmonic nanoparticles on a semiconductor substrate via a modified discrete dipole approximation method.

Understanding the plasmonic coupling between a set of metallic nanoparticles (NPs) in a 2D array, and how a substrate affects such coupling, is fundamental for the development of optimized optoelectronic structures. Here, a simple semi-analytical procedure based on discrete dipole approximation (DDA) is reported to simulate the far-field and near-field properties of arrays of NPs, considering the coupling between particles, and the effect of the presence of a semiconductor substrate based on the image dipole approach. The method is validated for Ag NP dimers and single Ag NPs on a gallium nitride (GaN) substrate, a semiconductor widely used in optical devices, by comparison with the results obtained by the finite element method (FEM), indicating a good agreement in the weak coupling regime. Next, the method is applied to square and random arrays of Ag NPs on a GaN substrate. The increase in the surface density of NPs on a GaN substrate mainly results in a redshift of the dipolar resonance frequency and an increase in the near-field enhancement. This model, based on a single dipole approach, grants very low computational times, representing an advantage to predict the optical properties of large NP arrays on a semiconductor substrate for different applications.

Non-neutral plasma manipulation techniques in development of a high-capacity positron trap.

Preliminary experiments have been performed toward the development of a multi-cell Penning-Malmberg trap for the storage of large numbers of positrons (≥1010 e+). We introduce the master-cell test trap and the diagnostic tools for first experiments with electrons. The usage of a phosphor screen to measure the z-integrated plasma distribution and the number of confined particles is demonstrated, as well as the trap alignment to the magnetic field (B = 3.1 T) using the m = 1 diocotron mode. The plasma parameters and expansion are described along with the autoresonant excitation of the diocotron mode using rotating dipole fields and frequency chirped sinusoidal drive signals. We analyze the reproducibility of the excitation and use these findings to settle on the path for the next generation multi-cell test device.

Adiabatic quantum decoherence in many non-interacting subsystems induced by the coupling with a common boson bath

This work addresses adiabatic quantum decoherence of many-body spin systems coupled with a boson field in the framework of open quantum systems theory. We generalize the traditional spin-boson model by considering a system–environment interaction Hamiltonian that represents a partition of non-interacting subsystems and highlights the collective correlation that appears exclusively due to the coupling with a common environment. Remarkably, this simple, exactly solvable model encompasses relevant aspects of a many-body open quantum system and features the subtle quantum effects that arise when the size scales up to a macroscopic level. We derive an analytical expression for the time dependence of the density matrix elements (in the preferred basis) without assuming coarse-graining. The resulting decoherence function is eigen-selective and is a complex exponential whose exponent has a real part that introduces a decay similar to that in the spin-boson model. On the contrary, the imaginary part depends on the quantum numbers and geometry of the whole partition and does not reflect the system temperature. Motivated by decoherence in solid-state NMR, and in search of realistic numerical estimations, we apply the theoretical results to a partition of dipole-coupled spin pairs in contact with a common phonon bath, using typical parameters of hydrated salts. The proposal allows estimating the decoherence time scale in terms of the system physical constants: sound velocity and eigenvalue distribution width. As a significant novelty, the decoherence function phase depends on the eigenvalue distribution throughout the sample. It plays the leading role, overshadowing the mechanism associated with the bath thermal state. Finally, we apply the formalism to describe decoherence in the “magic echo” NMR reversal experiment. We find that the system–environment correlation explains the origin of irreversibility, and both the decoherence rate value and its dependence on the dipolar frequency, are remarkably similar to the experiment.

Study of Properties of Metamaterial Screen for Isolation Increase Between Antennas

The theoretical and experimental researches of influence of metamaterial screen on antenna isolation in order to provide for electromagnetic compatibility (EMC) of compact radio-electronic equipment groups have been conducted. It is shown that the metamaterial screen has special characteristics, namely, at a natural frequency of dipole radiation the screen is almost transparent for electromagnetic radiation, while at the second dipole frequency it becomes ill-transparent and acts as a reflector.

Dipole-Dipole Frequency Shifts in Multilevel Atoms.

Dipole-dipole interactions lead to frequency shifts that are expected to limit the performance of next-generation atomic clocks. In this work, we compute dipolar frequency shifts accounting for the intrinsic atomic multilevel structure in standard Ramsey spectroscopy. When interrogating the transitions featuring the smallest Clebsch-Gordan coefficients, we find that a simplified two-level treatment becomes inappropriate, even in the presence of large Zeeman shifts. For these cases, we show a net suppression of dipolar frequency shifts and the emergence of dominant nonclassical effects for experimentally relevant parameters. Our findings are pertinent to current generations of optical lattice and optical tweezer clocks, opening a way to further increase their current accuracy, and thus their potential to probe fundamental and many-body physics.

Floquet Dynamics in a One-Dimensional Chain in the Multipulse Spin Locking of Nuclear Magnetic Resonance

The dynamics of a one-dimensional chain that consists of 10–14 dipolar-coupled nuclear spins, is placed in an external magnetic field, and is irradiated by a periodic sequence of resonant π/n pulses (n is a natural number) with the same time delay 2τ between them has been studied. The numerical calculation has shown that thermodynamic equilibrium, which is determined by the common temperature of the Zeeman and dipole reservoirs, is established in the spin system at the average pulse field π/(2nτ) ∼ ωloc (where ωloc is the dipole frequency and n > 2) and times t ∼ ω loc −1 . The relaxation of the magnetization in the system irradiated by (π/2)x pulses at π/4τ ≫ πlocis due to a four-spin resonant process, and the relaxation rate is proportional to τ4.

On attempting to automate the identification of mixed dipole modes for subgiant stars

Context. The existence of mixed modes in stars is a marker of stellar evolution. Their detection serves for a better determination of stellar age. Aims. The goal of this paper is to identify the dipole modes in an automatic manner without human intervention. Methods. I used the power spectra obtained by the Kepler mission for the application of the method. I computed asymptotic dipole mode frequencies as a function of the coupling factor and dipole period spacing, as well as other parameters. For each star, I collapsed the power in an echelle diagramme aligned onto the monopole and dipole mixed modes. The power at the null frequency was used as a figure of merit. Using a genetic algorithm, I then optimised the figure of merit by adjusting the location of the dipole frequencies in the power spectrum. Using published frequencies, I compared the asymptotic dipole mode frequencies with published frequencies. I also used published frequencies to derive the coupling factor and dipole period spacing using a non-linear least squares fit. I used Monte-Carlo simulations of the non-linear least square fit to derive error bars for each parameter. Results. From the 44 subgiants studied, the automatic identification allows one to retrieve within 3 μHz, at least 80% of the modes for 32 stars, and within 6 μHz, at least 90% of the modes for 37 stars. The optimised and fitted gravity-mode period spacing and coupling factor are in agreement with previous measurements. Random errors for the mixed-mode parameters deduced from the Monte-Carlo simulation are about 30−50 times smaller than previously determined errors, which are in fact systematic errors. Conclusions. The period spacing and coupling factors of mixed modes in subgiants are confirmed. The current automated procedure will need to be improved upon using a more accurate asymptotic model and/or proper statistical tests.

Development of Method of Moment Based Programme to Analyze Cross Dipole Frequency Selective Surface and its Verification with Measured Results

Theoretical analysis of frequency selective surface comprising of cross dipole elements has been presented in this paper. Algorithm for theoretical analysis based on method of moment has been implemented by MATLAB programming. Theoretical, simulated and experimental results are compared. Simulated result is obtained by ANSOFT designer version 2.2 software. Experimental result is obtained by standard microwave test bench. Good parity in the results is observed. The presented FSS Structure has relevance in the field of mobile and satellite communication.

Interfacial polarization and tunable dielectric properties of coaxial SiC/CFs materials

Abstract To investigate the formation mechanism and influencing factors of interfacial polarization at the interface of materials with different conductivity. Semiconductor SiC and conductor carbon fibers are combined to prepare SiC/CFs coaxial structural materials with varying SiC nanoshell thickness by microwave heating. The results indicate that the electrical resistance of SiC/CFs material increases gradually as the SiC nanoshell thickness increased or materials filling ratio decreased. The dipoles form at the introduced interfaces and the ends of the one-dimensional materials. And the resonance frequency corresponding to the dipoles shifts as the electrical resistance value changes. So, we speculate that the resonance frequency of dipoles has a strong dependence on the electrical resistance of composites materials. Moreover, the SiC/CFs materials also exhibited a better impedance matching and electromagnetic wave absorption performance due to the introduction of SiC nanoshell. The minimum reflection loss of SiC/CFs materials was −31.6 dB at a sample thickness of 1.1 mm, which showed a stronger absorption property than that of CFs (−1.2 dB).