Probe Frequency Research Articles

Skin ultrasound for rheumatologists: Technical issues and challenges.

In several rheumatic diseases, the skin is involved and therefore it is an organ of interest which may be investigated by the rheumatologist. Ultrasound imaging has been proposed for assessing multiple skin conditions providing qualitative and quantitative information about different parameters in distinct skin layers. Our aim was to describe with a pictorial essay the main challenges that the ultrasound imaging may encounter when investigating the healthy skin in different body areas. Fourteen healthy subjects were submitted to skin ultrasound. The body areas that were investigated were decided following the 17 modified Rodnan skin score anatomical areas used in systemic sclerosis. Skin ultrasound was performed with a GE Logiq 10 with two probes (20 and 24 MHz). For an optimal quantification of the skin layers, the dermis interfaces either with the epidermis and hypodermis were investigated. The results of the ultrasound analysis are described and summarized in a pictorial essay which shows that some main factors may significantly influence the quality of the images of the skin layers. Specifically, age, scanning position, probe frequency, and the optimal positioning of some anatomical areas, in particular the hands and digits, emerged as factors that may have a relevance in influencing the quality of the imaging of the skin layers. Moreover, some technical suggestions are proposed to help optimizing and standardizing the performance of skin ultrasound assessment in healthy population. The pictorial essay we performed shows that the performance of skin ultrasound in healthy subjects still presents several issues that need to be addressed. The definition of the interface in different body areas is the first step which should be standardized before any measurement of the thickness of the skin layers is performed in rheumatic diseases.

A Mobius transformation-based liftoff effect reduction method for crack classification and prediction in eddy current testing

In eddy current (EC) defect evaluation, accurate determination of the crack depth is crucial. The lift-off signal on the complex impedance plane is not necessarily horizontal and mostly arc-shaped, which makes it difficult to separate from crack signals, which can have various orientations depending on probe characteristics and frequencies. Phase rotation is normally used to align the lift-off signal to the real axis and defect signal is read from the imaginary axis. However, this approach proves challenging to separate lift-off and defect signals within the complex plane in many cases.To address this issue, this study proposes and implements a Mobius transformation that linearizes the arc-shaped lift-off signals on the complex plane, enabling more accurate extraction of crack signals unaffected by lift-off signal height. Furthermore, it is demonstrated through k-nearest neighbors (kNN) that the transformed crack signals can still be effectively quantified.

Impact of ultrasonic probe type, frequency, and static pressure on large-scale graphene exfoliation

The ultrasonic liquid phase exfoliation method has emerged as an essential research direction for graphene preparation due to its cost-effectiveness and ability to minimize defects. However, this method faces challenges related to processing throughput when scaled up for industrial production. In this study, industrial grade ultrasonic homogenizers with different frequencies and probe types were evaluated for the preparation of FLG. In each experiment, 1.5 kg of graphite slurry was treated using a cyclic ultrasonic system. The results demonstrated that the 25 kHz dumbbell probe produced the thinnest FLG with the lowest defect density. Moreover, applying a static pressure of 0.2 MPa in the cycle system enhanced the cavitation-induced exfoliation of graphite sheets, effectively reducing the layer count and distribution range of FLG. This method improves the conductivity while minimizing defect density.

Electromagnetically induced grating via amplitude and phase modulations in a three-level V-type atomic medium

Abstract A probe laser beam can be completely absorbed in an atomic resonance frequency region, however, if a coupling laser beam is further applied to the atom, the atomic medium can exhibit electromagnetically induced transparency (EIT), i.e, the probe beam can be completely transmitted through the atomic medium. Thus, if the coupling beam is a standing wave field with nodes and antinodes, it will cause in space a periodic modulation of the transmitted spectrum of the probe field. This means that the probe field propagates through the atomic medium just as it passes through a diffraction grating which is called electromagnetically induced grating (EIG). Based on amplitude or phase modulation of transmission function, the absorption grating or the phase grating can be formed, respectively. In this work, based on controllable absorption and dispersion properties of a three-level V-type atomic system, we study the control of the absorption grating and the phase grating with respect to the intensity and the frequency of the laser fields. The absorption diffraction pattern at the two-photon resonance is obtained, while the phase diffraction pattern appears when there is a frequency shift of either the coupling frequency or the probe frequency compared to the corresponding atomic resonance frequency. By adjusting the coupling or/and probe laser frequency, the absorption grating can be converted into the phase grating and the high-order diffraction efficiency can also be improved.

Effects of ipsilateral, contralateral, and bilateral noise precursors on psychoacoustical tuning curves in humans

Cochlear tuning and hence auditory frequency selectivity are thought to change in noisy environments by activation of the medial olivocochlear reflex (MOCR). In humans, auditory frequency selectivity is often assessed using psychoacoustical tuning curves (PTCs), a plot of the level required for pure-tone maskers to just mask a fixed-level pure-tone probe as a function of masker frequency. Sometimes, however, the stimuli used to measure a PTC are long enough that they can activate the MOCR by themselves and thus affect the PTC. Here, PTCs for probe frequencies of 500 Hz and 4 kHz were measured in forward masking using short maskers (30 ms) and probes (10 ms) to minimize the activation of the MOCR by the maskers or the probes. PTCs were also measured in the presence of long (300 ms) ipsilateral, contralateral, and bilateral broadband noise precursors to investigate the effect of the ipsilateral, contralateral, and bilateral MOCR on PTC tuning. Four listeners with normal hearing participated in the experiments. At 500 Hz, ipsilateral and bilateral precursors sharpened the PTCs by decreasing the thresholds for maskers with frequencies at or near the probe frequency with minimal effects on thresholds for maskers remote in frequency from the probe. At 4 kHz, by contrast, ipsilateral and bilateral precursors barely affected thresholds for maskers near the probe frequency but broadened PTCs by reducing thresholds for maskers far from the probe. Contralateral precursors barely affected PTCs. An existing computational model was used to interpret the results. The model suggested that despite the apparent differences, the pattern of results is consistent with the ipsilateral and bilateral MOCR inhibiting the cochlear gain similarly at the two probe frequencies and more strongly than the contralateral MOCR.

Comparison of Skin Effects in Ferromagnetic and Nonferromagnetic Metals in Eddy Current Testing

ABSTRACT In eddy current (EC) testing, skin effect is a constraint factor of detecting subsurface defects and skin depth is an important parameter for probe design and frequency setup. This paper compares the skin effects in ferromagnetic and nonferromagnetic metals. It is well known that the high permeability of ferromagnetic metal makes the attenuation of EC faster due to the greater EC loss. In this paper, the other role of the high permeability of ferromagnetic metal on the skin effect is reported. The EC distributions in both the radial and depth directions in the two types of materials excited by pancake coils are computed. It shows that the EC is more dispersed in the radial direction in high-permeability material. More importantly, the high permeability of ferromagnetic metal makes the skin depth of EC under the excitation of pancake coil close to the standard skin depth of EC under the excitation of uniform magnetic field, whereas there is a big discrepancy in the skin depths of ECs under the two types of excitations. This difference is explained by the radial dispersion of EC based on the EC diffusion-cancellation theory. Finally, the EC distributions in ferromagnetic Q235 steel and nonferromagnetic brass are compared, and the simulation results are qualitatively verified by experiments.

First results of turbulence investigation on Globus-M2 using radial correlation Doppler reflectometry

The first results of investigation of the turbulence structure using Doppler backscattering (DBS) on the Globus-M2 tokamak are presented. A one-channel DBS system with a variable probing frequency within the 18–26 GHz range was installed to investigate the edge plasma at normalized minor radii 0.9–1.1. Radial correlation Doppler reflectometry was used to study the changes in turbulence eddies after the LH transition. Correlation analysis was applied to the phase derivative of complex in-phase and quadrature (IQ) signals of the DBS diagnostic as it contains information about the poloidal plasma rotation velocity. In L-mode, the radial correlation length L r is estimated to be 3 cm and after transition to H-mode reduces to approximately 2 cm. Gyrokinetic modelling in a linear local approximation using code GENE indicates that the instability with positive growth rate at the normalized minor radius 0.75 in L-mode and H-mode on Globus-M2 was the ion temperature gradient (ITG) mode.

The interaction of top–down and bottom–up attention in visual working memory

Understanding the interplay between top–down and bottom–up attention in visual working memory (VWM) is crucial, although the specific challenges arising from this interaction remain ambiguous. In this study, we address this complexity by examining how cue informativeness and probe status of the salient items influence this interaction. Through three experiments, we manipulated top–down attention by varying probe frequencies using pre-cues and bottom–up attention by varying the visual salience of memory items. Experiment 1 explored cue informativeness at 100% and 50%, while Experiments 2 and 3 maintained cue informativeness at 80% and 50%. Additionally, Experiment 1 tested a few of the salient items, Experiment 2 excluded them, and Experiment 3 tested half of them in each cue condition. Across all experiments, we consistently observed cueing benefits for cue-directed items, albeit with costs to non-cued items. Furthermore, cue informativeness and the probe status of salient items emerged as critical factors influencing the interaction between top–down and bottom–up attention in VWM. These findings underscore the pivotal roles of cue informativeness and salient item relevance in shaping the dynamics of top–down and bottom–up attention within VWM.

Measuring the Electric Fields of Ions Captured in Crown Ethers.

Controlling reactivity with electric fields is a persistent challenge in chemistry. One approach is to tether ions at well-defined locations near a reactive center. To quantify fields arising from ions, we report crown ethers that capture metal cations as field sources and a covalently bound vibrational Stark shift probe as a field sensor. We use experiments and computations in both the gas and liquid phases to quantify the vibrational frequencies of the probe and estimate the electric fields from the captured ions. Cations, in general, blue shift the probe frequency, with effective fields estimated to vary in the range of ∼0.2-3 V/nm in the liquid phase. Comparison of the gas and liquid phase data provides insight into the effects of mutual polarization of the molecule and solvent and screening of the ion's field. These findings reveal the roles of charge, local screening, and geometry in the design of tailored electric fields.

Effect of stimulus duration on estimates of human cochlear tuning

Auditory masking methods originally employed to assess behavioral frequency selectivity have evolved over the years to infer cochlear tuning. Behavioral forward masking thresholds for spectrally notched noise maskers and a fixed, low-level probe tone provide accurate estimates of cochlear tuning. Here, we use this method to investigate the effect of stimulus duration on human cochlear tuning at 500 Hz and 4 kHz. Probes were 20-ms sinusoids at 10 dB sensation level. Maskers were noises with a spectral notch symmetrically and asymmetrically placed around the probe frequency. For seven participants with normal hearing, masker levels at masking threshold were measured in forward masking for various notch widths and for masker durations of 30 and 400 ms. Measurements were fitted assuming rounded exponential filter shapes and the power spectrum model of masking, and equivalent rectangular bandwidths (ERBs) were inferred from the fits. At 4 kHz, masker thresholds were higher for the shorter maskers but ERBs were not significantly different for the two masker durations (ERB30ms=294 Hz vs. ERB400ms=277 Hz). At 500 Hz, by contrast, notched-noise curves were shallower for the 30-ms than the 400-ms masker, and ERBs were significantly broader for the shorter masker (ERB30ms=126 Hz vs. ERB400ms=55 Hz). We discuss possible factors that may underlay the duration effect at low frequencies and argue that it may not be possible to fully control for those factors. We conclude that tuning estimates are not affected by maker duration at high frequencies but should be measured and interpreted with caution at low frequencies.

Exploring the Influence of Extended High-Frequency Hearing on Cochlear Functioning at Lower Frequencies.

Diminished basal cochlear function, as indicated by elevated hearing thresholds in the extended high frequencies (EHFs), has been associated with lower levels of click-evoked and distortion-product otoacoustic emissions measured at lower frequencies. However, stimulus-frequency otoacoustic emissions (SFOAEs) at low-probe levels are reflection-source emissions that do not share the same generation mechanism as distortion-source emissions. The primary objective of the present study was to examine the influence of hearing thresholds in the EHFs on SFOAEs measured at lower frequencies. SFOAEs were recorded from both ears in 45 individuals with normal hearing thresholds in the conventional audiometric frequencies (0.25-8 kHz). Hearing thresholds were also measured at EHFs (10, 12.5, and 16 kHz). SFOAE magnitudes and signal-to-noise ratios (SNRs) were averaged across 1, 2, and 4 kHz probe frequencies and also averaged for high-probe frequencies (2 and 4 kHz). SFOAE magnitudes and SNRs were significantly higher for ears with better EHF hearing relative to poorer EHF hearing, categorized based on the median split. In addition, hearing in the EHFs significantly contributed to the variance in all SFOAE measures, except for the high-frequency SFOAE magnitudes model. However, hearing thresholds at the probe frequencies did not significantly contribute to the variance in SFOAEs. The study findings suggest that alterations in the basal cochlea, as revealed by EHF hearing thresholds, could be associated with diminished cochlear functioning in relatively apical regions, shown by SFOAEs at lower frequencies, in individuals with normal audiograms. These findings underscore the significance of considering EHF thresholds in audiological evaluations, as alterations in these frequencies may reflect broader cochlear health status.

Amplitude Dispersion Compensation in Time-Reversed Lamb Waves for Enhanced Sensitivity in Damage Detection

In Lamb wave-based baseline-free damage detection employing the time-reversal method (TRM), the damage index (DI) is computed from the similarity between the main mode of the reconstructed signal obtained after the time-reversal process (TRP) and the input signal, both normalized. However, a perfect similarity with a zero DI value cannot be achieved for undamaged structures due to the amplitude dispersion of Lamb waves, which is not compensated in the TRP. Thus, a nonzero DI does not necessarily indicate the presence of damage. Even worse is the fact that the similarity and, therefore, the DI for the pristine structure depend on the probing frequency, making it difficult to estimate a unique threshold value of DI for damage identification. The imperfect reconstruction also significantly reduces the relative sensitivity of the DI to the presence of damage. In this article, we propose a method to compensate the amplitude dispersion in the main mode of the reconstructed signal for undamaged metallic plates to achieve a zero threshold of DI. First, the transfer function of the main mode of the reconstructed signal for an undamaged path (the path with the least DI for a network of sensing paths) is obtained by exciting the actuator with a broadband excitation and extracting the S0 and A0 modes from the forward response measured at the sensor. To compensate the amplitude dispersion in the TRP-generated main mode, the transfer function of the recorded signal of a path is divided by the transfer function of the main mode obtained for the undamaged path. A comprehensive numerical study shows that the DI computed with the compensated reconstructed signal has much higher sensitivity to damage than that without applying the proposed compensation at all frequencies, providing the flexibility to choose the probing frequency according to the desired damage size to be detected.

Human Olivocochlear Effects: A Statistical Detection Approach Applied to the Cochlear Microphonic Evoked by Swept Tones.

The human medial olivocochlear (MOC) reflex was assessed by observing the effects of contralateral acoustic stimulation (CAS) on the cochlear microphonic (CM) across a range of probe frequencies. A frequency-swept probe tone (125-4757Hz, 90dB SPL) was presented in two directions (up sweep and down sweep) to normal-hearing young adults. This study assessed MOC effects on the CM in individual participants using a statistical approach that calculated minimum detectable changes in magnitude and phase based on CM signal-to-noise ratio (SNR). Significant increases in CM magnitude, typically 1-2dB in size, were observed for most participants from 354 to 1414Hz, where the size and consistency of these effects depended on participant, probe frequency, sweep direction, and SNR. CAS-related phase lags were also observed, consistent with CM-based MOC studies in laboratory animals. Observed effects on CM magnitude and phase were in the opposite directions of reported effects on otoacoustic emissions (OAEs). OAEs are sensitive to changes in the motility of outer hair cells located near the peak region of the traveling wave, while the effects of CAS on the CM likely originate from MOC-related changes in the conductance of outer hair cells located in the basal tail of the traveling wave. Thus, MOC effects on the CM are complementary to those observed for OAEs.

Johnson-noise-limited cancellation-free microwave impedance microscopy with monolithic silicon cantilever probes

Microwave impedance microscopy (MIM) is an emerging scanning probe technique for nanoscale complex permittivity mapping and has made significant impacts in diverse fields. To date, the most significant hurdles that limit its widespread use are the requirements of specialized microwave probes and high-precision cancellation circuits. Here, we show that forgoing both elements not only is feasible but also enhances performance. Using monolithic silicon cantilever probes and a cancellation-free architecture, we demonstrate Johnson-noise-limited, drift-free MIM operation with 15 nm spatial resolution, minimal topography crosstalk, and an unprecedented sensitivity of 0.26 zF/√Hz. We accomplish this by taking advantage of the high mechanical resonant frequency and spatial resolution of silicon probes, the inherent common-mode phase noise rejection of self-referenced homodyne detection, and the exceptional stability of the streamlined architecture. Our approach makes MIM drastically more accessible and paves the way for advanced operation modes as well as integration with complementary techniques.

High-field/high-frequency electron spin resonances of Fe-doped β−Ga2O3 by terahertz generalized ellipsometry: Monoclinic symmetry effects

We demonstrate detection and measurement of electron paramagnetic spin resonances (EPR) of iron defects in β−Ga2O3 utilizing generalized ellipsometry at frequencies between 110 and 170 GHz. The experiments are performed on an Fe-doped single crystal in a free-beam configuration in reflection at 45∘ and magnetic fields between 3 and 7 T. In contrast with low-field, low-frequency EPR measurements, we observe all five transitions of the s=5/2 high-spin state Fe3+ simultaneously. We confirm that ferric Fe3+ is predominantly found at octahedrally coordinated Ga sites. We obtain the full set of fourth-order monoclinic zero-field splitting parameters for both octahedrally and tetrahedrally coordinated sites by employing measurements at multiple sample azimuth rotations. The capability of high-field EPR allows us to demonstrate that simplified second-order orthorhombic spin Hamiltonians are insufficient, and fourth-order terms as well as consideration of the monoclinic symmetry are needed. These findings are supported by computational approaches based on density-functional theory for second-order and on ligand-field theory for fourth-order parameters of the spin Hamiltonian. Terahertz ellipsometry is a way to measure spin resonances in a cavity-free setup. Its possibility of varying the probe frequency arbitrarily without otherwise changing the experimental setup offers unique means of truly disentangling different components of highly anisotropic spin Hamiltonians. Published by the American Physical Society 2024

A polarization-improved dual-beam spin-exchange relaxation-free magnetometer with reflection-assisted pumping

The highly sensitive SERF magnetometers hold exciting prospects for magnetocardiography and magnetoencephalography, and the accuracy of medical measurements depends largely on the performance of the magnetometers. A double-pass configuration is used to obtain uniform polarization and constructed by adding a mirror to retro-reflect the pump light. The transmission model of the reflected light which takes the effect of forward light into account is proposed, and the improved polarization is experimentally verified. The essential operation parameters of the magnetometer are optimized. The theoretical framework is established outlining the relationship between pump power, probe frequency, and signal response, and the optimal values for these parameters are experimentally determined. With the appropriate selection of probe power and operating temperature, the double-pass configuration achieves a sensitivity of 5.81 fT/Hz1/2, a bandwidth of 110 Hz, and represents a 17% improvement in stability compared to the single-pass configuration. The optimized magnetometer exhibits reduced susceptibility to laser conditions and enhanced stability, attributed to the reflection-assisted polarization improvement and better uniformity. This configuration efficiently utilizes the pumping laser, and its miniaturization offers significant benefits for magnetoencephalography and other biomagnetic measurements.

Searching for axion resonances in vacuum birefringence with three-beam collisions

We consider birefringent (i.e., polarization changing) scattering of x-ray photons at the superposition of two optical laser beams of ultrahigh intensity and study the resonant contributions of axions or axionlike particles, which could also be short lived. Applying the specifications of the Helmholtz International Beamline for Extreme Fields (HIBEF), we find that this setup can be more sensitive than previous light-by-light scattering (birefringence) or light-shining-through-wall experiments in a certain domain of parameter space. By changing the pump and probe laser orientations and frequencies, one can even scan different axion masses, i.e., chart the axion propagator. Published by the American Physical Society 2024

Shear-Wave Elastography of the Achilles tendon: reliability analysis and impact of parameters modulating elasticity values.

Shear wave elastography (SWE) has seen many advancements in Achilles tendon evaluation in recent years, yet standardization of this technique is still problematic due to the lack of knowledge regarding the optimal way to perform the examination. The purpose of this study was to evaluate the effects of ankle position, probe frequency and physical effort on the shear modulus of the Achilles tendon, but also to determine the intra and inter-observer reliability of the technique. 37 healthy volunteers were included; SWE protocol was performed by two examiners. We analyzed the shear modulus of the tendon with the ankle in neutral, maximum dorsiflexion and maximum plantar flexion using two different high frequency probes. Afterwards, the subjects performed a brief physical exercise and SWE measurements were repeated. The L18-5 probe showed the highest ICC values (ICC = 0.798, 95% CI 0.660-0.880, p < 0.001) when positioned at 2cm from the calcaneal insertion with the ankle in a neutral state. Conversely, utilizing the same L18-5 probe at 1cm from the insertion during maximum plantar flexion of the ankle resulted in the lowest ICC (ICC = 0.422, 95% CI 0.032-0.655, p = 0.019). Significant variations in elasticity values were noted among different ankle positions and probe types, while no significant changes in elasticity were observed post-physical exercise. Ankle position and probe frequency are factors that influence elasticity values of the Achilles tendon. An ankle position between 10 and 20 degrees of plantar flexion is the most suitable for SWE evaluation. However, more research focusing on Achilles tendon SWE is essential due to the challenges encountered in standardizing this region.

High-resolution spectroscopy of liquid water with dispersive atomic vapor prism cell

This article presents an experimental demonstration of a spectroscopic method based on the dispersion of the scattering spectrum from laser-illuminated liquid water collected through a rubidium atomic vapor prism cell. Resonant absorption at 780 nm suppresses Mie/Rayleigh scattering and the steep gradients in refractive index near the 780 nm absorption lines separate Brillouin scattering from Raman scattering in liquid water. The opposing spatial displacements of the Stokes and Anti-Stokes shifted Brillouin peaks yield a measurement of their spectral shifts and thus the temperature or salinity of the water. Performance of the prism cell was mapped with a frequency tunable laser for frequency offsets from the center of the rubidium absorption feature of between −15 GHz and 15 GHz and at rubidium cell temperatures between 148 °C and 177 °C. The experimental results are compared with a numerical model and show good agreement with the scattering peak displacements within experimental uncertainties of probe frequency and cell temperature. In the present configuration, the minimum detectable frequency shift is estimated to be 15.5 MHz. Experiments were conducted in water demonstrating the utility of this method for the measurement of water temperature. Liquid water LiDAR was suggested as one of the possible applications for this method and several ways to improve the experimental setup and cell temperature stability were identified.

Inducing torque on molecular magnets via Laguerre Gaussian beams

This theoretical study delves into the induction of torque by light beams carrying orbital angular momentum on single-molecule magnets (SMMs). The investigation explores the impact of decay rates, detunings, and control field intensities on the generation of light-induced torque and the resulting current flow in a ring formation. The results highlight the crucial role of the control field, showcasing its efficacy as a tool to manipulate and amplify torque at different frequencies. Detuning is identified as a critical parameter influencing the shift, slope, and emergence of multiple peaks in the torque profile. The interplay between detuning, control field intensity, and decay rates introduces a control mechanism for fine-tuning torque at distinct probe frequencies. These findings underscore the potential applications of the control field and detuning as robust tools for tailored manipulation of torque in SMMs, paving the way for advancements in controlled current flow dynamics with ring structures.