scholarly journals Topologically Optimized Magnetic Lens for MR Applications

2020 ◽  
Author(s):  
Sagar Wadhwa ◽  
Mazin Jouda ◽  
Yongbo Deng ◽  
Omar Nassar ◽  
Dario Mager ◽  
...  
Keyword(s):  
Numerical Optimization ◽  
Signal To Noise Ratio ◽  
Broad Band ◽  
Optimal Layout ◽  
Magnetic Lens ◽  
Resonator Design ◽  
Sample Shape ◽  
Field Homogeneity ◽  
Design Requirements ◽  
Resonance Detection

Abstract. Improvements to the signal-to-noise ratio of magnetic resonance detection leads to a strong reduction in measurement time, yet as a sole optimization goal for resonator design it would be an oversimplification of the problem at hand. Multiple constraints, for example for field homogeneity, and sample shape, suggests the use of numerical optimization to obtain resonator designs that delivers the intended improvement. Here we consider the 2D Lenz lens as a sufficiently broad-band flux transforming interposer between the sample and an RF circuit, as a flexible and an easily manufacturable device family with which to mediate different design requirements. We report on a method to apply topology optimization to determine the optimal layout of a Lenz lens, and demonstrate realisations for both low (45 MHz), and high frequency (500 MHz) NMR.

scholarly journals Topologically optimized magnetic lens for magnetic resonance applications

2020 ◽  
Vol 1 (2) ◽  
pp. 225-236
Author(s):  
Sagar Wadhwa ◽  
Mazin Jouda ◽  
Yongbo Deng ◽  
Omar Nassar ◽  
Dario Mager ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Numerical Optimization ◽  
Signal To Noise Ratio ◽  
Optimal Layout ◽  
Magnetic Lens ◽  
Resonator Design ◽  
Sample Shape ◽  
Field Homogeneity ◽  
Design Requirements ◽  
Resonance Detection

Abstract. Improvements to the signal-to-noise ratio of magnetic resonance detection lead to a strong reduction in measurement time, yet as a sole optimization goal for resonator design, it would be an oversimplification of the problem at hand. Multiple constraints, for example for field homogeneity and sample shape, suggest the use of numerical optimization to obtain resonator designs that deliver the intended improvement. Here we consider the 2D Lenz lens to be a sufficiently broadband flux transforming interposer between the sample and a radiofrequency (RF) circuit and to be a flexible and easily manufacturable device family with which to mediate different design requirements. We report on a method to apply topology optimization to determine the optimal layout of a Lenz lens and demonstrate realizations for both low- (45 MHz) and high-frequency (500 MHz) nuclear magnetic resonance.

scholarly journals Yebes 40 m radio telescope and the broad band Nanocosmos receivers at 7 mm and 3 mm for line surveys

2021 ◽  
Vol 645 ◽  
pp. A37
Author(s):  
F. Tercero ◽  
J. A. López-Pérez ◽  
J. D. Gallego ◽  
F. Beltrán ◽  
O. García ◽  
...  
Keyword(s):  
Radio Telescope ◽  
Signal To Noise Ratio ◽  
Broad Band ◽  
High Sensitivity ◽  
Lower Sensitivity ◽  
Molecular Chemistry ◽  
Long Baseline ◽  
New Instrumentation ◽  
Frequency Coverage ◽  
Technical Specifications

Context. Yebes 40 m radio telescope is the main and largest observing instrument at Yebes Observatory and is devoted to very long baseline interferometry (VLBI) and single-dish observations since 2010. It has been covering frequency bands between 2 GHz and 90 GHz in discontinuous and narrow windows in most cases in order to match the current needs of the European VLBI Network (EVN) and the Global Millimeter VLBI Array (GMVA). Aims. The Nanocosmos project, a European Union-funded synergy grant, has enabled an increase in the instantaneous frequency coverage of the Yebes 40 m radio telescope, making it possible to observe many molecular transitions with single tunings in single-dish mode. This reduces the observing time and maximises the output from the telescope. Methods. We present technical specifications of the recently installed 31.5−50 GHz (Q band) and 72−90.5 GHz (W band) receivers along with the main characteristics of the telescope at these frequency ranges. We observed IRC+10216, CRL 2688, and CRL 618, which harbour a rich molecular chemistry, to demonstrate the capabilities of the new instrumentation for spectral observations in single-dish mode. Results. Our results show the high sensitivity of the telescope in the Q band. The spectrum of IRC+10126 offers an unprecedented signal-to-noise ratio for this source in this band. On the other hand, the spectrum normalised by the continuum flux towards CRL 618 in the W band demonstrates that the 40 m radio telescope produces comparable results to those from the IRAM 30 m radio telescope, although with a lower sensitivity. The new receivers fulfil one of the main goals of Nanocosmos and open up the possibility to study the spectrum of different astrophysical media with unprecedented sensitivity.

Methods for the robust computation of the long-period seismic spectrum of broad-band arrays

2020 ◽  
Vol 222 (3) ◽  
pp. 1480-1501
Author(s):  
Ross C Caton ◽  
Gary L Pavlis ◽  
David J Thomson ◽  
Frank L Vernon
Keyword(s):  
Signal To Noise Ratio ◽  
Spectral Band ◽  
Broad Band ◽  
Low Noise ◽  
Small Aperture ◽  
Transient Signals ◽  
Seismic Arrays ◽  
Low Snr ◽  
Long Period ◽  
Student’S T

SUMMARY We describe array methods to search for low signal-to-noise ratio (SNR) signals in long-period seismic data using Fourier analysis. This is motivated by published results that find evidence of solar free oscillations in the Earth's seismic hum. Previous work used data from only one station. In this paper, we describe methods for computing spectra from array data. Arrays reduce noise level through averaging and provide redundancy that we use to distinguish coherent signal from a random background. We describe two algorithms for calculating a robust spectrum from seismic arrays, an algorithm that automatically removes impulsive transient signals from data, a jackknife method for estimating the variance of the spectrum, and a method for assessing the significance of an entire spectral band. We show examples of their application to data recorded by the Homestake Mine 3-D array in Lead, SD and the Piñon Flats PY array. These are two of the quietest small aperture arrays ever deployed in North America. The underground Homestake data has exceptionally low noise, and the borehole sensors of the PY array also have very low noise, making these arrays well suited to finding very weak signals. We find that our methods remove transient signals effectively from the data so that even low-SNR signals in the seismic background can be found and tested. Additionally, we find that the jackknife variance estimate is comparable to the noise floor, and we present initial evidence for solar g-modes in our data through the T2 test, a multivariate generalization of Student's t-test.

scholarly journals Tips and tricks in linear imaging polarimetry of extended sources with FORS2 at the VLT

2020 ◽  
Vol 634 ◽  
pp. A70
Author(s):  
S. González-Gaitán ◽  
A. M. Mourão ◽  
F. Patat ◽  
J. P. Anderson ◽  
A. Cikota ◽  
...  
Keyword(s):  
Optical System ◽  
Signal To Noise Ratio ◽  
Broad Band ◽  
Good Control ◽  
High Signal ◽  
Tips And Tricks ◽  
Dual Beam ◽  
Instrumental Polarization ◽  
Imaging Polarimetry ◽  
Extended Sources

Context. Polarimetry is a very powerful tool for uncovering various properties of astronomical objects that otherwise remain hidden in standard imaging or spectroscopic observations. While common observations only measure the intensity of light, polarimetric measurements allow us to distinguish and measure the two perpendicular components of the electric field associated with the incoming light. By using polarimetry it is possible to unveil asymmetries in supernova explosions, properties of intervening dust, characteristics of atmosphere of planets, among others. However, the reliable measurement of the low polarization signal from astronomical sources requires a good control of spurious instrumental polarization induced by the various components of the optical system and the detector. Aims. We perform a detailed multi-wavelength calibration study of the FORS2 instrument at the VLT operating in imaging polarimetric mode to characterize the spatial instrumental polarization that may affect the study of extended sources. Methods. We used imaging polarimetry of high signal-to-noise ratio blank field BVRI observations during the full moon, when the polarization is expected to be constant across the field of view and deviations originate from the instrument, and a crowded star cluster in broad-band RI and narrow-band Hα filters, where the individual polarization values of each star across the field can be measured. Results. We find an instrumental polarization pattern that increases radially outwards from the optical axis of the instrument reaching up to 1.4% at the edges, depending on the filter. Our results are closely approximated by an elliptical paraboloid down to less than ∼0.05% accuracy, and ∼0.02% when using non-analytic fits. We present 2D maps to correct for this spurious instrumental polarization. We also give several tips and tricks for analyzing polarimetric measurements of extended sources. Conclusions. FORS2 is a powerful instrument that allows the linear polarimetry of extended sources to be mapped. We present and discuss a methodology that can be used to measure the polarization of such sources, and to correct for the spatial polarization induced in the optical system. This methodology could be applied to polarimetric measurements using other dual-beam polarimeters.

scholarly journals Design of an Indigenised Electronic Lock-In Amplifier

2000 ◽  
Vol 23 (1) ◽  
pp. 53-60
Author(s):  
Umesh Kumar
Keyword(s):  
Narrow Band ◽  
Signal To Noise Ratio ◽  
Broad Band ◽  
Power Line ◽  
Frequency Drift ◽  
Noise Power ◽  
Signal To Noise ◽  
Band Noise ◽  
Noise Ratio ◽  
Lock In

An indigenised lock-in amplifier is designed that enables the accurate measurement of signals contaminated by broad-band noise, power-line pick-up, frequency drift, or other sources of interference. It does this by means of an extremely narrow band detector which has the centre of its passband locked to the frequency of the signal to be measured. Large improvements in signal-to-noise ratio are achieved.

Planar integrated plasmonic mid-IR spectrometer

2013 ◽  
Vol 1510 ◽  
Author(s):  
Farnood K. Rezaie ◽  
Chris J. Fredericksen ◽  
Walter R. Buchwald ◽  
Justin W. Cleary ◽  
Evan M. Smith ◽  
...  
Keyword(s):  
Molecular Interaction ◽  
Broad Band ◽  
Interaction Region ◽  
Silicon On Insulator ◽  
Optical Methods ◽  
Ring Resonators ◽  
Design Parameters ◽  
Dynamic Simulations ◽  
Waveguide Modes ◽  
Resonator Design

ABSTRACTA compact spectrometer-on-a-chip featuring a plasmonic molecular interaction region has been conceived, designed, modeled, and partially fabricated. The silicon-on-insulator (SOI) system is the chosen platform for the integration. The low loss of both silicon and SiO2 between 3 and 4 μm wavelengths enables silicon waveguides on SiO2 as the basis for molecular sensors at these wavelengths. Important characteristic molecular vibrations occur in this range, namely the bond stretching modes C-H (Alkynes), O-H (monomeric alcohols, phenols) and N-H (Amines), as well as CO double bonds, NH2, and CN. The device consists of a broad-band infrared LED, photonic waveguides, photon-to-plasmon transformers, a molecular interaction region, dispersive structures, and detectors. Photonic waveguide modes are adiabatically converted into SPPs on a neighboring metal surface by a tapered waveguide. The plasmonic interaction region enhances optical intensity, which allows a reduction of the overall device size without a reduction of the interaction length, in comparison to ordinary optical methods. After the SPPs propagate through the interaction region, they are converted back into photonic waveguide modes by a second taper. The dispersing region consists of a series of micro-ring resonators with photodetectors coupled to each resonator. Design parameters were optimized via electro-dynamic simulations. Fabrication was performed using a combination of photo- and electron-beam-lithography together with standard silicon processing techniques.

Using Design Capability Indices to Satisfy Ranged Sets of Design Requirements

1996 ◽  
Author(s):  
Wei Chen ◽  
Timothy W. Simpson ◽  
Janet K. Allen ◽  
Farrokh Mistree
Keyword(s):  
Robust Design ◽  
Irrigation System ◽  
Signal To Noise Ratio ◽  
Successful Implementation ◽  
Signal To Noise ◽  
Statistical Process ◽  
Capability Indices ◽  
Design Requirements ◽  
Noise Ratio ◽  
Solar Powered

Abstract For robust design it is desirable to allow the design requirements to vary within a certain range rather than setting point targets. This is particularly important during the early stages of design when little is known about the system and its requirements. Toward this end, design capability indices are developed in this paper to assess the capability of a family of designs, represented by a range of top-level design specifications, to satisfy a ranged set of design requirements. Design capability indices are based on process capability indices from statistical process control and provide a single objective, alternate approach to the use of Taguchi’s signal-to-noise ratio which is often used for robust design. Successful implementation of design capability indices ensures that a family of designs conforms to a given ranged set of design requirements. To demonstrate an application and the usefulness of design capability indices, the design of a solar powered irrigation system is presented. Our focus in this paper is on the development and implementation of design capability indices as an alternate approach to the use of the signal-to-noise ratio and not on the results of the example problem, per se.

scholarly journals An Optimization of the Signal-to-Noise Ratio Distribution of an Indoor Visible Light Communication System Based on the Conventional Layout Model

2020 ◽  
Vol 12 (21) ◽  
pp. 9006
Author(s):  
Xiangyang Zhang ◽  
Nan Zhao ◽  
Fadi Al-Turjman ◽  
Muhammad Bilal Khan ◽  
Xiaodong Yang
Keyword(s):  
Visible Light ◽  
Communication System ◽  
Signal To Noise Ratio ◽  
Visible Light Communication ◽  
Optimal Layout ◽  
Signal To Noise ◽  
Ratio Distribution ◽  
Channel Quality ◽  
Reflected Light ◽  
Noise Ratio

For an actual visible light communication system, it is necessary to consider the uniformity of indoor illumination. Most of the existing optimization schemes, however, do not consider the effect of the first reflected light, and do not conform to the practical application conventions, which increases the actual cost and the complexity of system construction. In this paper, considering the first reflected light and based on the conventional layout model and the classic indoor visible light communication model, a scheme using the parameter Q to determine the optimal layout of channel quality is proposed. We determined the layout, and then carried out a simulation. For comparison, the normal layout and the optimal layout of illumination were also simulated. The simulation results show that the illuminance distributions of the three layouts meet the standards of the International Organization for Standardization. The optimal layout of channel quality in the signal-to-noise ratio distribution, maximum delay spread distribution, and impulse response is obviously better than the optimal layout of illumination. In particular, the effective area percentage of the optimal layout of channel quality is increased by 0.32% and 6.08% to 88.80% as compared with the normal layout’s 88.48% and the optimal layout of illumination’s 82.72%. However, compared with the normal layout, the advantages are not very prominent.

Selective-phase Ion Cyclotron Resonance Spectroscopy

1974 ◽  
Vol 52 (10) ◽  
pp. 1997-1999 ◽  
Author(s):  
Melvin B. Comisarow ◽  
Alan G. Marshall
Keyword(s):  
Cyclotron Resonance ◽  
Signal To Noise Ratio ◽  
Broad Band ◽  
Resonance Spectroscopy ◽  
Ion Cyclotron Resonance ◽  
Linear Phase ◽  
Band Frequency ◽  
Absolute Value ◽  
Ion Cyclotron ◽  
Absorption Mode

In-phase ("dispersion"), 90° out-of-phase ("absorption"), and "absolute-value" (square root of the sum of the squares of the "absorption" and "dispersion") ion cyclotron resonance (i.c.r.) spectra of CH3+ and CH4+ have been obtained by broad-band frequency-swept r.f. irradiation of an ionized methane sample, followed by broad-band detection, digitization of the transient i.c.r. response, Fourier transformation using a digital computer (1), and application of a linear phase correction across the F.t.-i.c.r. spectrum. The "absorption" spectrum is the same as would be obtained by conventional marginal-oscillator field-sweep i.c.r. detection and provides a means for identifying spurious "foldover" peaks; the "dispersion" response is not observable with a marginal oscillator detector. The principal advantages of the new "absolute-value" display are (1) the signal-to-noise ratio is significantly better than for the conventional "absorption" mode, at the expense of a slight broadening of the i.c.r. spectral line shape; and (2) "absolute-value" display will very likely be the method of choice in frequency-sweep F.t.-i.c.r. spectroscopy (2), in order to circumvent the complicated non-linear phase corrections which may otherwise be required to obtain an "absorption" mode display.

scholarly journals Cusp-latitude Pc3 spectra: band-limited and power-law components

2002 ◽  
Vol 20 (10) ◽  
pp. 1539-1551 ◽  
Author(s):  
P. V. Ponomarenko ◽  
B. J. Fraser ◽  
F. W. Menk ◽  
S. T. Ables ◽  
R. J. Morris
Keyword(s):  
Solar Wind ◽  
Power Law ◽  
Signal To Noise Ratio ◽  
Broad Band ◽  
Mhd Waves ◽  
Noise Power ◽  
Magnetometer Data ◽  
Back Ground ◽  
Band Limited ◽  
Effective Signal

Abstract. This work attempts to fill a gap in comparative studies of upstream-generated Pc3–4 waves and broad band ULF noise observed at cusp latitudes. We performed a statistical analysis of the spectral properties of three years of cusp-latitude ground magnetometer data, finding that the average daytime Pc3–4 spectra are characterized by two principal components: an upstream-related band-limited enhancement (‘signal’) and a power-law background (‘noise’) with S(f ) a  f -4 . Based on this information we developed an algorithm allowing for the deconvolution of these two components in the spectral domain. The frequency of the signal enhancement increases linearly with IMF magnitude as f [mHz] ~ 4.4 | BIMF | [nT], and its power maximizes around IMF cone angles qxB ~ 20 and 160° and at 10:30–11:00 MLT. Both spectral components exhibit similar semiannual variations with equinoctial maxima. The back-ground noise power grows with increasing southward Bz and remains nearly constant for northward Bz . Its diurnal variation resembles that of Pc5 field-line resonance power, with a maximum near 09:00 MLT. Both the band-limited signal and broad band noise components show power-law growth with solar wind velocity a V 5.71sw and a V 4.12sw, respectively. Thus, the effective signal-to-noise ratio increases with in-creasing Vsw. The observations suggest that the noise generation is associated with reconnection processes.Key words. Magnetospheric physics (magnetopause, cusp, and boundary layers; MHD waves and instabilities; solar wind magnetosphere interactions)

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