Planar Measurements Research Articles

Planar Near-Field Antenna Measurements With a Uniform Step Larger Than Half-Wavelength

Planar Near-Field Antenna Measurements With a Uniform Step Larger Than Half-Wavelength

Reliability of 4D Flow MRI for Investigation of Fetal Cardiovascular Hemodynamics in the Third Trimester.

Purpose To provide reference values for four-dimensional (4D) flow MRI in healthy fetuses and evaluate reliability of fetal 4D flow MRI hemodynamics in third trimester fetuses with normal cardiovascular development or suspected coarctation of the aorta (CoA). Materials and Methods Pregnant patients with healthy fetuses or fetuses with echocardiographic concern for CoA were prospectively recruited between May 2021 and October 2023. Doppler US-gated fetal 4D flow MRI was performed at 3 T. Repeated 4D flow (time permitting) and two-dimensional (2D) phase contrast (PC) MRI data were acquired. Net flow was quantified, and the reliability of 4D flow measurement was evaluated by using precision across adjacent measurement planes, internal consistency based on conservation of mass, comparison of net flow from 4D flow MRI versus 2D PC MRI, and repeatability of 4D flow from separate acquisitions. Results Data were obtained in 34 pregnant participants (mean maternal age, 33 years ± 5 [SD]; mean gestational age, 35 weeks ± 2; n = 22 healthy fetuses and 12 fetuses with suspected CoA). Precision was high across all vascular segments (mean within-subject coefficient of variation = 7%). For mass conservation, there was an average difference of 19% ± 12 between ductus arteriosus plus isthmus flow versus descending aorta flow (r = 0.76). Net flow measured with 4D flow MRI correlated with that measured with 2D PC MRI (r = 0.51) but was underestimated relative to 2D PC MRI by approximately 34%. Hemodynamic parameters quantified from repeated 4D flow acquisitions had good agreement, with an intraclass correlation coefficient of 0.94 between test and retest data. Conclusion Hemodynamic measurements derived from fetal 4D flow MRI were reliable, showing good internal consistency, precision, and repeatability; however, as expected, 4D flow MRI underestimated absolute blood flow relative to 2D PC MRI. Keywords: Fetal MRI, Cardiac, Aorta, Hemodynamics/Flow Dynamics, Pulmonary Arteries Supplemental material is available for this article. © RSNA, 2024.

Inductance and penetration depth measurements of polycrystalline NbN films for all-NbN single flux quantum circuits

Abstract In this paper, we report on a systematic study of the inductance and magnetic field penetration depth (λ) of polycrystalline NbN superconducting thin films. By employing a four-metal-layer fabrication process specifically designed for all-NbN single-flux-quantum circuits, we constructed a superconducting quantum interference device loop composed of two parallel NbN SNS junctions, NbN microstrips, and NbN ground planes for precise inductance measurement. At 4.2 K, as the linewidth increases from 1 μm to 30 μm, the inductance per unit length (L u) of NbN microstrips significantly decreases, for example, the L u of 250 nm thick NbN microstrips drops from 0.907 pH/μm to 0.047 pH/μm. Compared to Nb, the L u of polycrystalline NbN microstrips is approximately two to three times that of Nb, offering an advantage for manufacturing smaller superconducting inductors. Furthermore, we conducted simulation analysis using InductEx software to extract the λ of NbN films of varying thicknesses. The results indicate that as the film thickness increased from 45 nm to 600 nm, λ initially decreased sharply and then stabilized, with values ranging from 430 nm to 323 nm. Notably, once the film thickness exceeded 200 nm, λ remained essentially constant, even at a temperature of 10 K, where it showed good stability, albeit with a slight increase (about 50 nm) compared to 4.2 K. This dependence of λ on thickness is reasonably explained by considering the effects of NbN film thickness on the superconducting critical temperature and residual resistivity. These research findings not only deepen our understanding of the characteristics of superconducting films but also lay a solid foundation for the future design and manufacture of more compact superconducting circuits at the higher temperature of 10 K.

Is the proper orthogonal decomposition suitable to validate simulation of turbulent wake?

To evaluate the suitability of the proper orthogonal decomposition (POD) for validating a simulated flow dynamics, we selected the flow in the wake behind a circular cylinder at Reynolds number of ≈5000 as a well studied canonical problem. The flow was simulated via k-ωSST detached-eddy simulation (DES) and, on selected planes of measurement (PoM), investigated experimentally by a time-resolved variant of the particle image velocimetry (PIV) and stereo-PIV methods. A standard model validation comprising, among other, comparison of the drag coefficient, or separation angle, and of the averaged flow properties and turbulence spectra, was carried out. Subsequently, both the PIV and the numerical data on the selected planes in the geometry were analyzed by POD, and a fully 3D POD analysis of the numerical data was used to evaluate the credibility of the planar POD as a tool for dynamic model validation.

Sensitivity of wavelet-based optical flow velocimetry (wOFV) to common experimental error sources

Abstract The influence of several potential error sources and non-ideal experimental effects on the accuracy of a wavelet-based optical flow velocimetry (wOFV) method when applied to tracer particle images is evaluated using data from a series of synthetic flows. Out-of-plane particle displacements, severe image noise, laser sheet thickness reduction, and image intensity non-uniformity are shown to decrease the accuracy of wOFV in a similar manner to correlation-based particle image velocimetry (PIV). For the error sources tested, wOFV displays a similar or slightly increased sensitivity compared to PIV, but the wOFV results are still more accurate than PIV when the magnitude of the non-ideal effects remain within expected experimental bounds. For the majority of test cases, the results are significantly improved by using image pre-processing filters and the magnitude of improvement is consistent between wOFV and PIV. Flow divergence does not appear to have an appreciable effect on the accuracy of wOFV velocity estimation, even though the underlying fluid transport equation on which wOFV is based implicitly assumes that the motion is divergence-free. This is a significant finding for the broader applicability of planar velocimetry measurements using wOFV. Finally, it is noted that the accuracy of wOFV is not reduced notably in regions of the image between tracer particles, as long as the overall seeding density is not too sparse i.e. below 0.02 particles per pixel. This explicitly demonstrates that wOFV (when applied to particle images) yields an accurate whole field measurement, and not only at or adjacent to the discrete particle locations.

Physics-informed data-driven reconstruction of turbulent wall-bounded flows from planar measurements

Obtaining accurate and dense three-dimensional estimates of turbulent wall-bounded flows is notoriously challenging, and this limitation negatively impacts geophysical and engineering applications, such as weather forecasting, climate predictions, air quality monitoring, and flow control. This study introduces a physics-informed variational autoencoder model that reconstructs realizable three-dimensional turbulent velocity fields from two-dimensional planar measurements thereof. Physics knowledge is introduced as soft and hard constraints in the loss term and network architecture, respectively, to enhance model robustness and leverage inductive biases alongside observational ones. The performance of the proposed framework is examined in a turbulent open-channel flow application at friction Reynolds number Reτ=250. The model excels in precisely reconstructing the dynamic flow patterns at any given time and location, including turbulent coherent structures, while also providing accurate time- and spatially-averaged flow statistics. The model outperforms state-of-the-art classical approaches for flow reconstruction such as the linear stochastic estimation method. Physical constraints provide a modest but discernible improvement in the prediction of small-scale flow structures and maintain better consistency with the fundamental equations governing the system when compared to a purely data-driven approach.

Target-free vision method for planar displacement measurement of structures subjected to out-of-plane movement by UAV

In the field of structural health monitoring, one of the essential tasks is to measure dynamic responses such as vibration displacement. With the recent advancement in computer vision, cameras are developed as alternative tools to traditional displacement sensors. Unmanned aerial vehicles (UAVs) offer mobility and can handle complex real-world situations. However, limitations of using UAVs, particularly self-motions, have hindered the accuracy in vibration displacement measurements. This paper proposes a target-free vision-based approach for measuring dynamic displacement responses using UAV. A series of videos of a beam subjected to planar motions are captured using a UAV. Stationary features on the background and target features on the structure are detected using features from accelerated segment test with adaptive threshold strategy and tracked using the Kanade–Lucas–Tomasi. UAV self-motions are estimated using motion-only bundle adjustment. Dynamic displacement responses of the structure are computed based on the displacements of target features and UAV self-motions. Results of the displacement responses and identified natural frequencies with different planar motion types and shooting angles are obtained. They are compared with those obtained by linear variable differential transducers, which demonstrates the accuracy of the proposed method for vibration displacement response measurement.

Spontaneous Laminar Separation Bubble Bursting on an Airfoil

An experimental investigation was conducted on a NACA 0018 airfoil at near-stall conditions, with stalled, stable laminar-separation bubble, and intermediate flow conditions were considered. Planar particle image velocimetry and surface pressure measurements were used to quantify the flow development at the midspan of the model. For the intermediate conditions, the airfoil is stalled in the time-average sense. However, conditionally averaged velocity field measurements reveal that reattachment of the separated flow and laminar separation bubble formation occur intermittently on the suction surface. The characteristics of the intermittently forming separation bubble and fully separated flow are analyzed based on conditional statistics, revealing variations in the transition process that may underpin the observed low-frequency flow oscillations. The growth rates of the most amplified wavenumbers in the separated shear layer vary with the angle between the separation streamline and the suction surface, leading to earlier transition when the separation angle increases. This change in transition location may play a role in spontaneous changes between fully separated and reattaching flow states.

A Simple and Effective Planar Near-Field Measurement Method With Sparse Nonuniform Sampling

A Simple and Effective Planar Near-Field Measurement Method With Sparse Nonuniform Sampling

Defect detection using spatial spectral entropy for noncontact acoustic inspection method

Inspection of concrete structures is important for maintaining social infrastructure such as tunnels and viaducts. Therefore, noncontact acoustic inspection method using acoustic irradiation induced vibration and a scanning laser Doppler vibrometer (SLDV) has been devised. Since this method uses flexural resonance, it can be said to be an alternative method for a hammering test. Using our method, internal defects of concrete can be detected up to a depth of about 10 cm from the surface of concrete, even at a distance of about 30 m. However, in a closed space such as an underground cavity, the signal-to-noise (S/N) ratio decreases due to reverberation from the surroundings, making it difficult to detect defects compared to open spaces such as viaducts. This problem can be solved by using spatial spectral entropy (SSE), which extends the concept of spectral entropy to the two-dimensional space of the measurement plane. In other words, by SSE analysis, the resonance frequency of both the defect and the SLDV can be detected and separated because of the difference in the spatial distribution characteristics of the vibration velocity spectrum for each the frequency. Therefore, it is possible to detect a defective part even in a place where the S/N ratio is not sufficient.

Characterization of droplet clusters in a turbulent multiphase gas cloud using a model cough simulator

This study aims to investigate the transport of droplets ejected from an artificial cough simulator, which releases a turbulent puff of droplets into the surrounding air, closely resembling the human coughing process. The focus is on understanding droplet clustering within the multiphase gas cloud across various operating conditions that emulate the wide variation in the spray characteristics in actual human subjects owing to infection severity, age, and gender. Time-resolved particle image velocimetry (PIV) technique was employed to measure the velocity of both droplet and gas phases. It also facilitates the identification and characterization of droplet clusters through Voronoi analysis of the PIV images. The area and length scale of individual droplet clusters were measured, and the degree of droplet clustering was quantified using the clustering index and relative droplet number density within the clusters. Additionally, the interferometric laser imaging for droplet sizing technique was utilized for planar measurement of individual droplet sizes. The range of Stokes number indicated partial to poor response of the droplets to the turbulent eddies. The results reported, for the first time, the presence of droplet clusters in the simulated coughing process. The wide spectrum of cluster size and self-similar evolution of droplet clusters unveil a multi-scale clustering phenomenon, shedding light on the intricate dynamics of the respiratory droplet dispersion process. The study comprehensively investigates the role of injection pressure on droplet clustering and the spatial development of the clusters, revealing some interesting findings, which are discussed.

Evaluating the impact of electrode planes on regional lung function assessment.

The aim of the study was to explore the influence of the measurement plane on regional lung function assessed via electrical impedance tomography (EIT). The forced vital capacity (FVC) maneuver was prospectively performed in 30 healthy male volunteers. Simultaneously, EIT measurements were conducted at the 3rd, 4th, and 5th intercostal spaces (ICS). The EIT-based spirometry parameters are calculated in a similar manner to their original definitions. The spatial and temporal distributions of the corresponding functional images were assessed and compared among the measurement planes. All subjects but one were able to perform the FVC maneuver according to the guidelines. Significant differences were found in 67% (6 out of 9) of the EIT-based parameters assessing the spatial and temporal distribution. The fEIT images were most homogeneous at ICS 4 compared to the other two measurement planes, except for the time required for 75% of FVC. The fEIT image FVCEIT distributed toward dorsal regions when the measurement planes moved from ICS 3 to ICS 5, whereas the identified lung areas became smaller. The spatial and temporal distribution of the regional lung function measured via EIT was influenced by the measurement planes. We recommend adhering to the same measurement plane for before-after comparison. ICS 4 was recommended for the sitting subjects performing lung function testing.

Assessment of OH femtosecond thermally assisted fluorescence thermometry for hydrogen non-premixed flames

In this work, we further developed the planar temperature measurement method based on thermally assisted laser-induced fluorescence (TALF) with a single femtosecond (fs) laser and investigated the temperature distribution in the nitrogen-diluted oxygen–hydrogen cross-jet non-premixed flames at 1 kHz. Fs-TALF thermometry was firstly calibrated and assessed in a series of unconfined methane/air laminar flames at atmospheric pressure. In the calibration process, although the calibrated energy difference between OH v′ = 0 and 1 energy level was different from the theoretical value, the measured fluorescence ratio accurately reflected the temperature change from 1600 K to 2200 K in different methane flames. By comparing the calculated OH fluorescence spectrum, we believed that the main reason was the overlap of the OH (1-1) and (0-0) fluorescence bands. After the calibration, experiments were conducted with changing hydrogen flow velocity from 60 to 100 m/s and constant oxidizer flow velocity, where the dilution ratio, D varies from 0.46 to 0.7, and the equivalence ratio, ϕ, varies from 0.5 to 0.9. It is found, within the calibration range, fs-TALF thermometry can correctly measure the flame temperature. However, with ϕ further increases, the difference between the measured and theoretical temperatures gradually increases. At the same time, it was noted that the error in the measured temperature rises gradually as D decreases. In conclusion, fs-TALF thermometry can measure turbulent non-premixed hydrogen flames accurately in a range of temperature with acceptable temporal and partial resolution, while the errors within 200 K and spatial resolution is 170μm. The main error source should be the collisional effect due to the different local concentration of N2 and H2O. The results of this work will contribute to the further development the temperature measurement method hydrogen turbulent flames.

Assessment of planar array accuracy for 3D sound source reconstruction with Bayesian Focusing

As planar microphone arrays were initially designed for bidimensional sound source localisation, their use for three-dimensional acoustic imaging consistently suffers from a poor resolution along the normal axis. Such a statement is already well documented for beamforming approaches and their declensions. Bearing this in mind, this paper delves into the possibilities offered by inverse methods and especially iterative Bayesian Focusing to tackle this issue and deliver accurate source positions in three dimensions based on planar array measurements only. To this end, an experimental set up is designed: omnidirectional sources are mounted in a wooden mock-up featuring faces at different distances from an 81 MEMs planar array. Based on this measurements, a benchmark study of sound source reconstruction on a 3D mesh of the mock-up is conducted and compared to classical 2D acoustic maps set at different depths. The latter process is declined for various source correlation values and at extended frequency ranges. By doing so, the current paper delivers an overview of the ability to discriminate acoustic sources along the normal axis of a planar array, on a simple and well controlled test case, with a view to provide guidelines for further applications of 3D acoustic imaging on complex geometries.

Acoustic near field effects in distribution transformer noise measurement

This paper examines the near field effect, including the active and reactive acoustic field around a liquid-filled distribution transformer with heat-dissipating corrugated fins on the tank walls. The analysis was carried out on the basis of measurements of sound pressure and sound intensity levels along with acoustic maps including the phase correlation of acoustic waves. The acoustic field around the transformer was evaluated in the measurement planes showing normal direction radiation of up to 1,0 m distance. Discrete point measurements made with the PU (pressure - velocity) probe was used to obtain parameters such as particle velocity, active and reactive sound intensity as well as the transfer function associated with the reference microphone. The last parameter, the transfer function, allows to show the phase correlation between acoustic wave propagation, which contributes to a better understanding of acoustic near-field effects where energy circulates, creating a sound field that can have overestimated sound pressure and intensity levels.

Nonparametric Bayesian reconstruction of Galactic magnetic fields using information field theory

Context. Ultrahigh-energy cosmic rays (UHECRs) are charged particles with energies surpassing 1018 eV. Their sources remain elusive because they are obscured by deflections caused by the Galactic magnetic field (GMF). This challenge is further complicated by our limited understanding of the 3D structure of the GMF because current GMF observations primarily consist of quantities that are integrated along the line of sight (LOS). Nevertheless, data from upcoming stellar polarization surveys along with Gaia stellar parallax data are expected to yield local GMF measurements. Aims. This study is the second entry in our exploration of a Bayesian inference approach to the local GMF that uses synthetic local GMF observations that emulate forthcoming local GMF measurements, and attempts to use them to reconstruct its 3D structure. The ultimate aim is to trace back observed UHECRs and thereby update our knowledge about their possible origin. Methods. In this proof-of-concept work, we assumed as ground truth a magnetic field produced by a dynamo simulation of the Galactic ISM. We employed methods of Bayesian statistical inference in order to sample the posterior distribution of the GMF within part of the Galaxy. By assuming a known rigidity and arrival direction of an UHECR, we traced its trajectory back through various GMF configurations drawn from the posterior distribution. Our objective was to rigorously evaluate the performance of our algorithm in scenarios that closely mirror the setting of expected future applications. In pursuit of this, we conditioned the posterior to synthetically integrated LOS measurements of the GMF, in addition to synthetic local plane of sky-component measurements. Results. Our results demonstrate that for all locations of the observed arrival direction on the plane of sky, our algorithm is able to substantially update our knowledge on the original arrival direction of UHECRs with a rigidity of E/Z = 5 × 1019 eV, even without any LOS information. When the integrated data are included in the inference, the regions of the celestial sphere in which the maximum error occurs are greatly reduced. The maximum error is diminished by a factor of about 3 even in these regions in the specific setting we studied. Additionally, we are able to identify the regions in which the largest error is expected to occur.

Warping-Driven Greedy Method for Data Reduction in Planar Near-Field Antenna Measurements

Warping-Driven Greedy Method for Data Reduction in Planar Near-Field Antenna Measurements

Exponential Boundary Control for 2-D Spatial Distributed Parameter Systems Under Boundary Collocated and Planar Linear Measurements.

For a class of 2-D spatial distributed parameter systems (DPSs) with space-dependent diffusivity, this article aims to achieve exponential realization of their desired profiles. To reduce the number of required sensors and actuators, a planar output feedback boundary control strategy is proposed with combining two nonfull-domain measurement methods, boundary collocated measurement and planar linear measurement, in which only two boundaries of the considered 2-D spatial DPSs are controlled and a little output information is measured. Moreover, by employing the Poincaré-Wirtinger inequality and variable substitution dexterously, the final exponential convergence criteria of the error system can be obtained with method of "Diverse treatment for same term." Finally, we provide a general numerical example and an application example in 2-D heat conduction systems to illustrate the effectiveness and practicability of the proposed measurement and control schemes.

Three-Dimensional Nature of Low-Frequency Unsteadiness in a Turbulent Separation Bubble

Three-dimensional behavior of low-frequency unsteadiness in the incompressible turbulent separation bubble (TSB) produced by a wall-mounted hump is investigated using time-resolved planar and stereoscopic particle image velocimetry measurements at several planes across the separated region. The aspect ratio (wind tunnel width/separation length, Lz,WT/Lb=4.4) provides nominally two-dimensional flow for more than half of the spanwise extent of the test section. Analysis in the streamwise/wall-normal plane along the center of the test section shows low-frequency (St<0.1) large-scale motion of the separated region. The flowfield contains features of both geometry-induced and pressure-gradient-induced separation, but unsteady dynamics produce dominant frequencies closer to geometry-induced TSBs (St≈0.1) compared to purely pressure-gradient-induced TSBs (St≈0.01). Measurements along the spanwise direction and parallel to the initial shear layer development show strong evidence that the low-frequency motion is inherently three-dimensional, providing an additional dimension to the understanding of the flapping/breathing typically observed in planar streamwise/wall-normal measurements. Spectral proper orthogonal decomposition and low-order modeling identify spanwise undulations with wavelengths of the order of Lb and frequencies of St<0.1. The three-dimensional behavior causes a peak/valley formation along the span and a more localized expansion/contraction, leading to only small variations in the integral volume of the TSB.

On spectral eigenmatrix problem for the planar self-affine measures with three digits

On spectral eigenmatrix problem for the planar self-affine measures with three digits