Improved Field Uniformity Research Articles

Spectral Reconstruction Improvement in a Cycloidal Coded-Aperture Mass Spectrometer.

Spatial aperture coding is a technique used to improve throughput without sacrificing resolution both in optical spectroscopy and sector mass spectrometry (MS). Previous work demonstrated that aperture coding combined with a position-sensitive array detector in a miniature cycloidal mass spectrometer was successful in providing high-throughput, high-resolution measurements. However, due to poor alignment and field nonuniformities, reconstruction artifacts were present. Recently, significant progress was made in eliminating most of the reconstruction artifacts with improved field uniformity and alignment. However, artifacts as large as 1/3 of the main peak were still observed at low mass (<17 u). Such artifacts will reduce accuracy in identification and quantification of analytes, reducing the impact of the throughput advantage gained by using a coded aperture. The artifacts were hypothesized to be a result of a mass dependent in curvature of ions in the ion source. Ions with higher mass (m/z > 17 u) and a larger curvature did not pass through all slits in the coded aperture. Therefore, when reconstructing with a system response derived from the aperture image from a higher mass m/z = 32 u ion, reconstruction artifacts appeared for m/z < 17 u. In this work, two methods were implemented to significantly reduce the presence of artifacts in reconstructed data. First, we modified the reconstruction algorithm to incorporate a mass-dependent system response function across the mass range (10-110 u). This method reduced the size of the artifacts by 82%. Second, to validate the hypothesis that the mass-dependent system response function was a result of differences in curvature of ions in the ion source, we modified the design of the ion source by shifting the coded aperture slits relative to the center of the ionization volume. This method resulted in ions of all masses passing through all slits in the coded aperture, a constant system response function across the entire mass range. Artifacts were reduced by 94%.

Improved field uniformity in EMC chamber for 6G communication

&lt;span&gt;This paper shows electromagnetic field uniformity in an electromagnetic compatibility (EMC) chamber that is used as a test facility for measuring electromagnetic interference and radiated immunity of 6G communication systems. While not defined yet, 6G radio frequency will work in the wavelength ranges above 95 GHz. With this reason, this paper designed a schroeder-type quadratic residue diffuser for 95 GHz to generate a uniform electromagnetic field in the EMC chamber and studied the field uniformity characteristics in it. To analyze the distribution of electromagnetic fields inside the EMC chamber, finite-difference time-domain (FDTD) numerical analysis method is used. The simulation results show that the EMC chamber with this diffuser satisfies the requirements of international standards and has improved the field uniformity in the chamber.&lt;/span&gt;

Bayesian Optimization of PCB-Integrated Field Grading for a High-Density 10 kV SiC Power Module Interface

An automated numerical optimization workflow using Bayesian optimization and a novel weighted point-of-interest (POI) cost function is proposed and demonstrated for PCB-integrated electric field grading structures. The traditional manual design techniques for high-density insulation systems involve simulating the electric field performance and manually assessing the performance characteristics, iterating until an acceptable design is achieved. The proposed technique improves on this by allowing for a fully automated workflow, based on a scalable, computationally efficient cost function that is readily implemented in commercial software and finite element method (FEM) packages. The workflow is demonstrated on PCB-integrated field grading structures, which are employed to alleviate field crowding, and improve field uniformity around the terminals of a high-density 10 kV SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> power module. The integrated field grading, in conjunction with the module housing, enables a power terminal spacing of 6 mm, while ensuring partial discharge (PD) free operation of the module. The proposed workflow accelerates design time by a factor of three when compared with a competing descent-based technique, and by a factor of 100 when compared with manual design techniques, with seven times lower convergence error. In addition, the optimized system performed 38% better than the previous manually designed version, experimentally demonstrating a PD inception voltage of 11.6 kV rms (16.4 kV peak). The proposed workflow is scalable to larger systems, making it applicable to a broad range of high-density, high-voltage insulation design problems.

Expanded test frequency band and improved field uniformity in a reverberation chamber for networked system by dual-band quadratic residue diffusers

Expanded test frequency band and improved field uniformity in a reverberation chamber for networked system by dual-band quadratic residue diffusers

Impact of third generation synthetic turf athletic field age on surface hardness and infill depth spatial variability

The use of synthetic turf (ST) has become a popular option for many athletic fields. Little is known about how surface hardness and infill depth spatial variability changes over time on third generation (3G) ST athletic fields. A research study was conducted to investigate the impact of field age on surface hardness and infill depth spatial variability from 12 3G ST athletic fields in Tennessee and Georgia (USA) between March 5, 2014 and April 8, 2014. The 3G ST athletic fields tested varied in fiber type including monofilament, slit film, and a combination of monofilament with slit film fibers. All 3G ST athletic fields were directly over gravel with no shockpad present. Surface hardness and infill depth were collected in the same location on all fields. Surface hardness was collected with the Toro Mobile Tester (400–450 samples/field) and infill depth was collected manually with a three-prong infill depth gauge (200–225 samples/field). As field age increased, surface hardness and spatial variability of the surface hardness increased significantly. Surface hardness and infill depth also had a significant negative relationship with one another. The increase in mean surface hardness and variability is partially attributed to infill depth loss and compaction of the remaining infill. Infill depth did not have a significant relationship with age, unless plots were outside the manufacturer’s recommendation for infill depth. Considering the nearly 3000 samples collected in this study, maintaining a minimum infill depth between 30 and 35 mm kept 90% of surface hardness data points below the National Football League limit of 100 Gmax. Results from this study highlight how 3G ST athletic fields can change with age, which may indicate the need for targeted infill applications and decompaction to improve field uniformity over time.

Expanded test frequency band and improved field uniformity in a reverberation chamber for networked system by dual-band quadratic residue diffusers

Expanded test frequency band and improved field uniformity in a reverberation chamber for networked system by dual-band quadratic residue diffusers

SCHEEPDOG: Programming Electric Cues to Dynamically Herd Large-Scale Cell Migration.

Directed cell migration is critical across biological processes spanning healing to cancer invasion, yet no existing tools allow real-time interactive guidance over such migration. We present a new bioreactor that harnesses electrotaxis-directed cell migration along electric field gradients-by integrating four independent electrodes under computer control to dynamically program electric field patterns, and hence steer cell migration. Using this platform, we programmed and characterized multiple precise, two-dimensional collective migration maneuvers in renal epithelia and primary skin keratinocyte ensembles. First, we demonstrated on-demand, 90-degree collective turning. Next, we developed a universal electrical stimulation scheme capable of programming arbitrary 2D migration maneuvers such as precise angular turns and migration in a complete circle. Our stimulation scheme proves that cells effectively time-average electric field cues, helping to elucidate the transduction timescales in electrotaxis. Together, this work represents an enabling platform for controlling cell migration with broad utility across many cell types.

A New Method to Improve Field Uniformity for Application to a Newly Developed 5 T EMPS Superconducting Magnet System

A 5 T low-temperature superconducting magnet is fabricated and tested for an EMPS (electro-magnetic property measurement system) whose sample space is 40 mm in diameter. Because the sample space is larger than that of conventional property measurement systems, it will be possible to measure the electro-magnetic properties of several samples simultaneously, thus reducing the measurement time. With a genetic algorithm incorporated with linear-programming, the optimal design of the 5 T LTS magnet was accomplished. A multi-coil 5 T EMPS magnet was fabricated according to the optimal design and tested in liquid helium. During current charging tests up to 43.5 A, the magnet voltage, current, and magnetic field were measured to monitor the magnet performance. Due to the manufacturing errors of the magnet, the field uniformity is usually worse than the design result. The concept of a newly proposed field uniformity improvement method was also introduced to compensate for field errors. The 5 T EMPS magnet system will be integrated with an EMPS console for electro-magnetic properties analyses.

Improving Field Uniformity Using Source Stirring With Orbital Angular Momentum Modes in a Reverberation Chamber

The orbital angular momentum (OAM) offers new degrees of freedom and finds application in communications and radar imaging. In this letter, the OAM is introduced for reverberation chamber (RC) measurements using OAM metasurfaces. Because of the space limitation of the used RC, the OAM source has to be located near a sidewall, which inevitably causes some degradation of the OAM purity. Nevertheless, our experimental results show that the field uniformity of the RC can be improved effectively by using the OAM metasurfaces.

Linear array arrangement using composite right‐/left‐handed transmission lines for magnetic resonance imaging

AbstractArray coils for magnetic resonance imaging have been used to improve field uniformity, improve signal‐to‐noise ratios, and increase imaging speed. Alternative radio frequency (RF) coils that use metamaterials, such as loop or microstrip coils, have recently been proposed and are expected to provide better performance than the traditional RF array coils. Transmission lines (TLs) based on metamaterials are known as composite right‐ and left‐handed (CRLH) TLs, which are artificially created by adding inductances and capacitances to a common TL. CRLH TLs have a zero‐order resonance mode, wherein wave propagation is independent of the TL's electrical length. Decoupling between array elements is important for obtaining the benefits of parallel imaging. In this study, we analyze the decoupling properties between two CRLH TLs. In addition, we design a linear array of four CRLH TLs to obtain a uniform magnetic (|B1|)‐field in the axial‐ and longitudinal‐direction at 7T for the corresponding frequency of 300 MHz.

Investigation of automotive testing in a reverberation chamber

Due to the increasing and urgent demands of automotive over-the-air (OTA) and electromagnetic compatibility (EMC) tests, it is necessary to evaluate the performance of a reverberation chamber (RC) loaded by a vehicle under test. Previous works mainly focus on qualitative analyses on the RC performance for a static vehicle. This article realises the idea of using rotated vehicles to improve field uniformity. Two methods are adopted to estimate the number of independent samples and to predict the uncertainty. In addition, the uncertainty is also estimated from many independent simulations. The estimated uncertainties show good agreements. It is shown that the uncertainty can be significantly improved by rotating the vehicle under test using a large turn-table platform. Authors’ results show that the bigger the volume of the vehicle is, the better the improvement is. Besides, the authors find that the restriction of the volume of the vehicle under test can be relaxed in automotive tests by utilising the vehicle as a rotating mode stirrer. In addition, it is found that the Weibull distribution provides the best fit to the field of RC working near the lowest usable frequency (LUF) for all the cases.

Effects of Magnetic and Electric Field Uniformity on Coded Aperture Imaging Quality in a Cycloidal Mass Analyzer.

Cycloidal mass analyzers are unique sector mass analyzers as they exhibit perfect double focusing, making them ideal for incorporating spatial aperture coding, which can increase the throughput of a mass analyzer without affecting the resolving power. However, the focusing properties of the cycloidal mass analyzer depend on the uniformity of the electric and magnetic fields. In this paper, finite element simulation and charged particle tracing were used to investigate the effect of field uniformity on imaging performance of a cycloidal mass analyzer. For the magnetic field, we evaluate a new permanent magnet geometry by comparing it to a traditional geometry. Results indicate that creating an aperture image in a cycloidal mass spectrometer with the same FWHM as the slit requires less than 1% variation in magnetic field strength along the ion trajectories. The new magnet design, called the opposed dipole magnet, has less than 1% field variation over an area approximately 62 × 65 mm; nearly twice the area available in a traditional design of similar size and weight. This allows ion imaging across larger detector arrays without loss of resolving power. In addition, we compare the aperture imaging quality of a traditionally used cycloidal mass spectrometer electric design with a new optimized design with improved field uniformity. Graphical abstract ᅟ.

Patch-Probe Excitation for Ultrahigh Magnetic Field Wide-Bore MRI

In this paper, we present the design of probe excitations for 7- and 10.5-T traveling-wave wide-bore magnetic resonance imaging systems. The probes are 297- and 447-MHz coaxially fed microstrip patches, designed to give a circularly polarized magnetic field when placed in the metallic bore waveguide. Images of a water phantom using the patch probes are obtained and compared with full-wave electromagnetic simulations. Additionally, periodic axial metal strip cylinders are inserted into the bore, resulting in improved field uniformity in a phantom with a simultaneous increase in SNR. The numerical analysis for nonquasi-static fields can be computationally intensive, and the numerical error for finite-element simulations is quantified using modified boundary conditions of the system. When the waveguide effects are taken into account, the mode content in the images compares well to full-wave simulations.

Total skin electron therapy in the lying-on-the-floor position using a customized flattening filter to eliminate field junctions.

A total skin electron (TSE) floor technique is presented for treating patients who are unable to safely stand for extended durations. A customized flattening filter is used to eliminate the need for field junctioning, improve field uniformity, and reduce setup time. The flattening filter is constructed from copper and polycarbonate, fits into the linac's accessory slot, and is optimized to extend the useful height and width of the beam such that no field junctions are needed during treatment. A TSE floor with flattening filter (TSE FF) treatment course consisted of six patient positions: three supine and three prone. For all treatment fields, electron beam energy was 6 MeV; collimator settings were an x of 30 cm, y of 40 cm, and θcoll of 0°; and a 0.4 cm thick polycarbonate spoiler was positioned in front of the patient. Percent depth dose (PDD) and photon contamination for the TSE FF technique were compared with our standard technique, which is similar to the Stanford technique. Beam profiles were measured using radiochromic film, and dose uniformity was verified using an anthropomorphic radiological phantom. The TSE FF technique met field uniformity requirements specified by the American Association of Physicists in Medicine Task Group 30. TSE FF R80 ranges from 4 to 4.8 mm. TSE FF photon contamination was ~ 3%. Anthropomorphic radiological phantom verification demonstrated that dose to the entire skin surface was expected to be within about ±15% of the prescription dose, except for the perineum, scalp vertex, top of shoulder, and soles of the feet. The TSE floor technique presented herein eliminates field junctioning, is suitable for patients who cannot safely stand during treatment, and provides comparable quality and uniformity to the Stanford technique.PACS number: 87

Unconventional Purcell filter in superferric magnets in the Facility for Antiproton and Ion Research

For the magnets used in beam lines, especially in high resolution applications, the field quality ΔB/B is a very important factor which determines the quality of the beam after passing through the magnets. End-shaping of the poles and introduction of Purcell filters improve field uniformity. However, in most applications, what matters is the uniformity in the total field integrated along the beam path (Δ(∫Bdl)/∫Bdl). With this criterion in mind, we have used unconventional partially penetrating Purcell filters in designing wide aperture highly uniform dipole and quadrupole magnets for the large acceptance low energy beam line in the Super Fragment Separator of the upcoming Facility for Antiproton and Ion Research (FAIR) at Darmstadt. The weight of dipole magnets decreases by the use of such filters.

利用多馈源激励改善混响室的场均匀性

利用多馈源激励改善混响室的场均匀性

Mode-Stirred Reverberation Chamber Characteristic to Stirrer Parameter and Usefulness Evaluation

This paper analyzes optimal stirrer parameter to improve field uniformity in a mode-stirred reverberation chamber. Stirrer parameter is varied about stirrer height and stirrer angle. Also we analyze quality factor, number of excited modes and stirrer efficiency that affect field uniformity. The results show good performance as higher as stirrer height. Isotropic field distribution is formed at stirrer angle. When stirrer angle varies, scattering characteristic of incident wave are changed. So electric field distribution in a mode-stirred reverberation chamber is also changed. Therefore, it affect field uniformity. The results expect to help that designs stirrer for get better field uniformity. Immunity test performed designed mode-stirred reverberation chamber for semiconductor that categorized by technology. Test result shows that good recurrence compared wave-guide immunity test.

Modeling of linear carbon nanotube nanotriodes with improved field uniformity

A linear array of gated carbon nanotubes (CNTs) is proposed for improving the array electron emission properties by controlling the electric field conversion factor and its uniformity. The CNT emission current has been computed according to a previously developed model that takes into account the low dimensionality of the CNT electronic system. The CNT field conversion factor (for single CNT and linear array gated CNTs) has been numerically derived using the OPERA3D/TOSCA software and then expressed analytically. For better performance, controlling the parallelism of the CNTs in the array is not a strong requirement, but controlling their height is. The position of the CNT array emission current optimum depends on the value of parameters chosen, but generally it is obtained for array packing density ratio a∕hn (array pitch/CNT height) taking value in the range of 0.5–1.

Comments on "Investigation of the field uniformity of a mode-stirred chamber using diffusors based on acoustic theory"

In the above paper [see ibid., vol. 41, p. 446-51, 1999] a particular type of reflection grating, viz., Schroeder diffusers of the quadratic-residue type (QRDs), was proposed with the aim of improving field uniformity inside mode-tuned or mode-stirred reverberation chambers. While an improvement of the field homogeneity (but not necessarily the field isotropy) was demonstrated, some facts about the design and application of this type of pseudorandom diffractor (PRDs) appear to have been overlooked.

Simulations on field uniformity in a triangular reverberation chamber

This article presented the results of an electromagnetic field analysis inside a rectangular and triangular reverberation chamber being attached to the Schroeder Quadratic Residue Diffusers (QRD). Simulation results showed that a triangular chamber, which had more mode distribution than the rectangular chamber in the defined volume, had advantages of producing improved field uniformity. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 198–205, 2002.