scholarly journals RF Magnetic Signal Localization at Very High Magnetic Field Systems

2009 ◽  
Vol 3 (2) ◽  
Author(s):  
H. Yoo ◽  
L. Delabarre ◽  
A. Gopinath ◽  
J. T. Vaughan
Keyword(s):  
Magnetic Field ◽  
Convex Optimization ◽  
Human Head ◽  
Signal To Noise ◽  
Target Region ◽  
Field Systems ◽  
B1 Field ◽  
Suppression Region ◽  
Head Coil ◽  
Selection Of

The impetus of this work originated from the advent of high magnetic field magnetic resonance imaging scanners with B0 fields of 4T, 7T, and 9.4T. These ultrahigh magnetic field systems generally improve the signal to noise ratios. However, B1 field non-uniformity also occurs due to the increased RF field frequencies when wavelengths in the head become shorter than its size. As interest in multiple channel transmission line coils increases, the control of the amplitude and phase of individual coil elements is required in order to develop desired B1 field. The choice of the excitation of the coil elements may be determined by convex optimization. Convex optimization is used provides results very fast, when the problem is formulated globally. In addition, convex optimization provides better signal to noise (SNR) ratio when anatomic specific regions are investigated. In this paper, simulation and experimental results are discussed at 9.4T systems based on the number of elements. The primary objective of this study is to increase the signal in a specific target region and decrease the signal and noise in the outside region termed the suppression region. The convex formulations are minimizing the maximum field point in the suppression region while keeping the center of target maximum. Based on this min-max optimization criterion, an iteration method which modifies the selection of suppression fields is also performed to produce better results. The results of the localization on FDTD human data at 9.4T are shown in Fig. 1. In these figures, the axial slices of the center of human head model provided by XFDTD are used after manipulating with MATLAB and the 16 channel head coil is excited. Figure 1 shows an improvement of the homogeneity in the suppression region when the target region is at center. In Fig. 2, received signal localizations are obtained for three different regions of interest (ROI) after using the convex optimization. Note that the selection of ROI is limited by the geometric setting of phantom in the 8-channel TEM head coil. Convex optimization with an iterative method was performed on both the human head and phantom models with operating frequency 400 MHz to design coil channel excitation parameters. By applying the iterative method to the convex optimization, more homogeneous B1 fields are obtained in the suppression region for 9.4T system.

Nuclear magnetic resonance microscopy

1989 ◽  
Vol 47 ◽  
pp. 828-829
Author(s):  
Paul C. Lauterbur
Keyword(s):  
Magnetic Field ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Fields ◽  
Signal To Noise ◽  
Field Gradients ◽  
Useful Signal ◽  
Magnetic Field Gradients ◽  
Observation Times ◽  
Nuclear Magnetic

Nuclear magnetic resonance imaging can reach microscopic resolution, as was noted many years ago, but the first serious attempt to explore the limits of the possibilities was made by Hedges. Resolution is ultimately limited under most circumstances by the signal-to-noise ratio, which is greater for small radio receiver coils, high magnetic fields and long observation times. The strongest signals in biological applications are obtained from water protons; for the usual magnetic fields used in NMR experiments (2-14 tesla), receiver coils of one to several millimeters in diameter, and observation times of a number of minutes, the volume resolution will be limited to a few hundred or thousand cubic micrometers. The proportions of voxels may be freely chosen within wide limits by varying the details of the imaging procedure. For isotropic resolution, therefore, objects of the order of (10μm) may be distinguished.Because the spatial coordinates are encoded by magnetic field gradients, the NMR resonance frequency differences, which determine the potential spatial resolution, may be made very large. As noted above, however, the corresponding volumes may become too small to give useful signal-to-noise ratios. In the presence of magnetic field gradients there will also be a loss of signal strength and resolution because molecular diffusion causes the coherence of the NMR signal to decay more rapidly than it otherwise would. This phenomenon is especially important in microscopic imaging.

ACTIVE SCREENING MAGNETIC FIELD SYSTEMS SYNTHESIS FOR SINGLE-CIRCUIT HIGH VOLTAGE POWER LINES WITH VERTICAL CONDUCTORS WITH SINGLE COMPENSATING COIL

2017 ◽  
Vol 25 (101) ◽  
pp. 402-408
Author(s):  
Boris B., Kobyljanskij ◽  
◽  
Valery V., Kolomiec ◽  
Boris I., Kuznetsov ◽  
Tatyana B., Nikitina ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Voltage ◽  
Power Lines ◽  
Active Screening ◽  
Field Systems ◽  
High Voltage Power Lines

scholarly journals Collecting Microplastics in Gardens: Case Study (i) of Soil

2021 ◽  
Vol 9 ◽  
Author(s):  
Zahra Sobhani ◽  
Yunlong Luo ◽  
Christopher T. Gibson ◽  
Youhong Tang ◽  
Ravi Naidu ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Point Of View ◽  
Signal To Noise ◽  
Statistical Point ◽  
Image Mapping ◽  
Noise Ratio ◽  
In The Beginning ◽  
Raman Image ◽  
Selection Of

As an emerging contaminant, microplastic is receiving increasing attention. However, the contamination source is not fully known, and new sources are still being identified. Herewith, we report that microplastics can be found in our gardens, either due to the wrongdoing of leaving plastic bubble wraps to be mixed with mulches or due to the use of plastic landscape fabrics in the mulch bed. In the beginning, they were of large sizes, such as > 5 mm. However, after 7 years in the garden, owing to natural degradation, weathering, or abrasion, microplastics are released. We categorize the plastic fragments into different groups, 5 mm–0.75 mm, 0.75 mm–100 μm, and 100–0.8 μm, using filters such as kitchenware, meaning we can collect microplastics in our gardens by ourselves. We then characterized the plastics using Raman image mapping and a logic-based algorithm to increase the signal-to-noise ratio and the image certainty. This is because the signal-to-noise ratio from a single Raman spectrum, or even from an individual peak, is significantly less than that from a spectrum matrix of Raman mapping (such as 1 vs. 50 × 50) that contains 2,500 spectra, from the statistical point of view. From the 10 g soil we sampled, we could detect the microplastics, including large (5 mm–100 μm) fragments and small (<100 μm) ones, suggesting the degradation fate of plastics in the gardens. Overall, these results warn us that we must be careful when we do gardening, including selection of plastic items for gardens.

scholarly journals High-Field Pulsed ENDOR with Intra-cavity Radiofrequency Coil

2020 ◽  
Vol 51 (11) ◽  
pp. 1433-1449
Author(s):  
G. Annino ◽  
H. Moons ◽  
M. Fittipaldi ◽  
S. Van Doorslaer ◽  
E. Goovaerts
Keyword(s):  
Magnetic Field ◽  
High Field ◽  
Conversion Factor ◽  
Signal To Noise Ratio ◽  
Model Systems ◽  
Signal To Noise ◽  
Radiofrequency Coil ◽  
W Band ◽  
Radiofrequency Current ◽  
Field Uniformity

AbstractThis study compares the performance of two coil configurations for W-band pulsed ENDOR using a setup with both a radiofrequency ‘hairpin’ coil internal to a microwave non-radiative resonator and Helmholtz-like coils external to the resonator. Evaluation of the different coil performances is achieved via the ENDOR study of two model systems. The efficiencies of the coil configurations are first investigated numerically, showing that a higher radiofrequency current-to-magnetic field conversion factor can be achieved with the intra-cavity coil, with a similar radiofrequency magnetic field uniformity. This result is then confirmed by the broadband ENDOR spectra acquired with the two coil arrangements. A gain in the signal-to-noise ratio enabled by the internal coil of about a factor 10 was observed. In some cases, the high conversion factor of the intra-cavity coil led to a saturation of the ENDOR transitions. The possibility to implement a similar intra-cavity radiofrequency coil configuration in higher field spectrometers is finally discussed.

Diffracted Beam Monochromators for Powder Diffractometry

1970 ◽  
Vol 14 ◽  
pp. 38-56
Author(s):  
E. M. Proctor ◽  
T. C. Furnas ◽  
W. F. Loranger
Keyword(s):  
Preferred Orientation ◽  
Signal To Noise ◽  
X Ray ◽  
Direct Beam ◽  
Vertical Divergence ◽  
Oriented Samples ◽  
Efficiency And Effectiveness ◽  
Slit System ◽  
Bent Crystals ◽  
Selection Of

AbstractThe efficiency and effectiveness of diffracted beam x-ray monochromators used in powder diffractometry have been described in so many ways that much confusion exists regarding their true performance. Although significant improvements in signal to noise ratios are readily achievable, and they offer a solution to the sample fluorescence problem, it is not without sacrifice to total intensity or achievable resolution or both. This paper discusses and describes a series of comparisons between filtered direct beam, LiF and graphite monochromators.These comparisons include the considerations necessary for the appropriate selection of diffracted beam slit system, the effect of vertical divergence as a function of two theta for singly bent crystals, the effects of a non-uniformity of contribution over the length of the crystal, and the geometry necessary for the singly bent and doubly bent crystals. The total intensity and the resolution of LiF and graphite are discussed, in particular, it is noted that the performance of monochromators with randomly oriented samples is quite different than their performance with samples showing preferred orientation or grain effects.A new diffracted beam monochromator based on the Rowland focusing geometry is described.

scholarly journals VLA Polarization Observation of the Radio Arc at 15 Ghz

1989 ◽  
Vol 136 ◽  
pp. 269-274 ◽  
Author(s):  
M. Inoue ◽  
E. Fomalont ◽  
M. Tsuboi ◽  
F. Yusef-Zadeh ◽  
M. Morris ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Frequency ◽  
High Spatial Resolution ◽  
Intrinsic Polarization ◽  
Linear Feature ◽  
Field System ◽  
Polarization Observation ◽  
Field Systems ◽  
Relativistic Particles ◽  
Accelerated Particles

Polarization measurements of the radio Arc were made with the VLA at 15 GHz. High frequency polarimetry made with high spatial resolution minimizes Faraday depolarization and reveals polarized filaments which correspond to the predominant filaments of the radio Arc. We notice a peculiar linear feature in the polarization map (“thorns”) which suggests the presence of a second magnetic field system. The total intensity maps show no evidence for an interaction between the two field systems, so the thorns may be foreground magnetized structures. However, if the two magnetic field systems do interact, it would allow a model in which the acceleration of relativistic particles takes place at their intersection. The accelerated particles would flow toward both ends of the radio Arc, and account for the intrinsic polarization observed along the entire length of the system. Thermal electrons responsible for the Faraday depolarization occuring at longer wavelengths may be supplied by the interaction of the streams of relativistic particles with relatively dense, ambient thermal clouds.

Intelligent Symbiotic Relay Selection Technique for 5G Networks

2019 ◽  
Vol 43 ◽  
pp. 84-100
Author(s):  
Maryleen U. Ndubuaku ◽  
Kennedy Chinedu Okafor ◽  
Chidiebele Chinwendu Udeze ◽  
Omar Salih
Keyword(s):  
Relay Selection ◽  
Network Capacity ◽  
The Other ◽  
Link Quality ◽  
Support Vector ◽  
Second Phase ◽  
Signal To Noise ◽  
Relay Nodes ◽  
Geographical Locations ◽  
Selection Of

The growing demand for bandwidth and spectrum has inspired the ongoing efforts to establish the future 5G network supporting vertical sectors such as cyber-physical systems (CPS). Cooperative communication is one of the requisite techniques to improve coverage, network capacity and reduce power consumption in the network. In this paper, a symbiotic two-phase intelligent transmission is considered. The first phase occurs between the source and the candidate relays, and involves the selection of a set of “reliable relays”. The second phase occurs between the reliable relays and the destination, and involves the selection of the “best relay” for transmission. Dynamic relay selection using k-means clustering is used to detect the most significant correlation between all the channel state information (CSI) attributes in the system. The work identified the reliable relays while reducing the number of relay nodes for the second transmission phase. Contextual scenarios are created with typical network configuration using three geographical locations Coventry, Birmingham and London. An experimental validation is done with Omnet++ environment for the scenarios of three geographical locations. A natural grouping of mobile users is carried out leveraging the relay capabilities. The results are validated using support vector machine (SVM) classification algorithm. Considering urban environment deployment of relay nodes, metrics such as signal-to-noise-plus-interference ratio (SINR), attenuation, signal to noise ratio (SNR), link quality, k-means clustering, accuracy, and root mean square error (RMSE) are investigated for the Direct-2-Direct (D2D) capable relays. It was observed that the proposed technique both outperforms the other fixed-parameter relay selection techniques and improves with larger datasets unlike the other techniques.

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