Sample Coil Research Articles

Magic angle spinning NMR with metallized rotors as cylindrical microwave resonators.

We introduce a novel design for millimeter wave electromagnetic structures within magic angle spinning (MAS) rotors. In this demonstration, a copper coating is vacuum deposited onto the outside surface of a sapphire rotor at a thickness of 50nm. This thickness is sufficient to reflect 197-GHz microwaves, yet not too thick as to interfere with radiofrequency fields at 300MHz or prevent sample spinning due to eddy currents. Electromagnetic simulations of an idealized rotor geometry show a microwave quality factor of 148. MAS experiments with sample rotation frequencies of ωr /2π=5.4kHz demonstrate that the drag force due to eddy currents within the copper does not prevent sample spinning. Spectra of sodium acetate show resolved 13 C J-couplings of 60Hz and no appreciable broadening between coated and uncoated sapphire rotors, demonstrating that the copper coating does not prevent shimming and high-resolution nuclear magnetic resonance spectroscopy. Additionally, 13 C Rabi nutation curves of ω1 /2π=103kHz for both coated and uncoated rotors indicate no detrimental impact of the copper coating on radio frequency coupling of the nuclear spins to the sample coil. We present this metal coated rotor as a first step towards an MAS resonator. MAS resonators are expected to have a significant impact on developments in electron decoupling, pulsed dynamic nuclear polarization (DNP), room temperature DNP, DNP with low-power microwave sources, and electron paramagnetic resonance detection.

Guide to Simulating Complex NMR Probe Circuits.

AbstractS‐parameter‐based circuit simulators are well suited to obtaining accurate solutions of even the most complex rf probe circuits. The basic theory necessary for determining the relative S/N of the probe circuit, based on B1/P0.5, from the voltage, current, impedance, and S‐parameter data that come from circuit simulators, is presented. Examples of simulator applications to circuits of increasing complexity are presented. A key requirement for effective utilization of circuit simulators in probe circuit optimizations is constructing an approximate analytical solution of the circuit, or an inverse simulation program, to accompany the direct circuit simulation, that calculates all the needed circuit component values based on minimal input data, such as B0, desired nuclides, sample coil description, and hardware options and details such as characteristics of various leads. A method of developing the needed inverse simulation program is presented for a simplified single‐coil HXY probe circuit. The inverse program is validated by the direct simulation itself. The methods are then applied to a detailed circuit that includes all significant leads, stray capacitances, couplings, and losses for a NB 28.2‐T 1‐mm HXYZ MAS probe. Similar HXY circuit models were validated by NMR experiments with rotor sizes from 0.75 mm to 3.2 mm at fields from 11.7 T to 21 T. Detailed HXYZ circuit model results at 11.7 T, including pulse widths, component values, voltages, and port isolations, agreed with experimental results within a few per cent. The 1200‐MHz HXYZ simulation predicted a 1H π/2 pulse of 1.3 μs at 25 W.

Preliminary Tests and Margin Estimate for a REBCO Insulated 10 T Insert Under High Magnetic Field

Our project is to build a high-temperature superconductor (HTS) insert generating 10 T in its center and expected to work inside a 20 T background field. In the first step, the background field is provided by a resistive magnet to avoid major coupling issues. Nevertheless, the final goal is to have the insert operating inside an LTS magnet to yield a 30 T-class all-superconducting magnet. The insert is designed as a stack of pancakes and double pancakes wound with REBCO tapes. Preliminary tests are performed on a deposited polyimide insulated coil, although design has started with metallic-insulation coils. This paper presents results obtained on a double pancake insulated HTS coil that was tested inside both a resistive coil at LNCMI and a superconducting magnet at Tohoku University. The electrical and mechanical behaviors of the sample coil are discussed, and margins are estimated taking into account the field distribution on each point of the coil. Results are encouraging as the coil passes 370 A (82.9% lc) self-field and 260 A (68.6% lc) under 8 T. Moreover, the coil is still working even after the outer magnet quench.

Electrofluidic pretreatment for enhancing essential oil extraction from citrus fruit peel waste

Pretreatment technologies make pressed fruit peel more valuable both nutritionally and economically. Robust electrofluidic systems, in particular, can facilitate clean and efficient production of valuable compounds from these byproducts. In this study, a multi-series system was designed with a combination of pipeline flow and induced electric field (IEF), then applied to pretreat citrus peel for enhancing the extraction of essential oils. The essential oil yield increased significantly from 0 V to 1 kV. There was a decrease in fluid impedance during the IEF-pretreatment period owing to the dissolution of cell contents, as well as a slight decrease in essential oil yield as frequency increased. Forty components were identified in the essential oils representing over 97% of the total GC peak areas for both procedures. We also observed significant effect on the essential oil yield between the IEF-pretreatments in different winding direction of the sample coils. High throughput was achieved by arbitrarily increasing the reactors within a compact system. In effect, the IEF-pretreatment is an effective, innovative, and ecologically sustainable technique for intensifying essential oil extraction without necessitating metal electrodes, thus avoids electrode surface corrosion, and heavy metal contamination.

In vivo imaging of electrical properties of an animal tumor model with an 8-channel transceiver array at 7 T using electrical properties tomography.

To develop and evaluate a technique for imaging electrical properties ((EPs), conductivity and permittivity) of an animal tumor model in vivo using MRI. Electrical properties were reconstructed from the calculated EP gradient, which was derived using two sets of measured transmit B1 magnitude and relative phase maps with the sample and radiofrequency (RF) coil oriented in the positive and negative z-directions, respectively. An eight-channel transceiver microstrip array RF coil fitting the size of the animal was developed for generating and mapping B1 fields to reconstruct EPs. The technique was evaluated at 7 tesla using a physical phantom and in vivo on two Copenhagen rats with subcutaneously implanted AT-1 rat prostate cancer on a hind limb. The reconstructed EPs in the phantom experiment was in good agreement with the target EP map determined by a dielectric probe. Reconstructed conductivity map of the animals revealed the boundary between tumor and healthy tissue consistent with the boundary indicated by T1 -weighted MRI. A technique for imaging EP of an animal tumor model using MRI has been developed with high sensitivity, accuracy, and resolution, as demonstrated in the phantom experiment. Further animal experiments are needed to demonstrate its translational value for tumor diagnosis. Magn Reson Med 78:2157-2169, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Factory Acceptance Tests: A Comparative Analysis to Establish a Baseline for Testing Data

Factory acceptances tests (FATs) of a new high-voltage (HV) rotating machine include comprehensive diagnostic tests of the finished stator winding insulation system. From these tests, the end user obtains the baseline data for the condition monitoring performed during the machine?s operating life. The design geometry of the stator windings and manufacturing processes used to produce them will affect the dielectric test results. There is a significant challenge in comparing the test results from different stators to obtain a statistically useful sample for an acceptance test database. This article compares the dielectric test results from the 14.4-kV windings of several new 1,800-r/min, 26.1-MW (35,000-hp) centrifugal compressor synchronous motor stators of identical design, built for two U.S. chemical plants. The results are compared with those from accompanying sacrificial coils. The stator diagnostic tests include the dissipation factor (DF) or tan delta, power factor tip up (PFTU) or delta tan delta, offline partial discharge (PD), corona inspection with an ultraviolet (UV) analyzer, and online PD. Sacrificial coils produced and processed alongside each stator receive the specified American Petroleum Institute (API) coil acceptance tests and corona inspection with a UV analyzer. The PD measurements on the sample coils were repeated at an elevated voltage, and the results were compared with the corona inspection observations. This article shares the comparative analysis of the stator and coil test results as an excellent example of the baseline FAT data.

Evolution of CPMAS under fast magic-angle-spinning at 100 kHz and beyond

This article describes recent trends of high-field solid-state NMR (SSNMR) experiments for small organic molecules and biomolecules using 13C and 15N CPMAS under ultra-fast MAS at a spinning speed (νR) of 80–100kHz. First, we illustrate major differences between a modern low-power RF scheme using UFMAS in an ultra-high field and a traditional CPMAS scheme using a moderate sample spinning in a lower field. Features and sensitivity advantage of a low-power RF scheme using UFMAS and a small sample coil are summarized for CPMAS-based experiments. Our 1D 13C CPMAS experiments for uniformly 13C- and 15N-labeled alanine demonstrated that the sensitivity per given sample amount obtained at νR of 100kHz and a 1H NMR frequency (νH) of 750.1MHz is ~10 fold higher than that of a traditional CPMAS experiment obtained at νR of 20kHz and νH of 400.2MHz. A comparison of different 1H-decoupling schemes in CPMAS at νR of 100kHz for the same sample demonstrated that low-power WALTZ-16 decoupling unexpectedly displayed superior performance over traditional low-power schemes designed for SSNMR such as TPPM and XiX in a range of decoupling field strengths of 5–20kHz. Excellent 1H decoupling performance of WALTZ-16 was confirmed on a protein microcrystal sample of GB1 at νR of 80kHz. We also discuss the feasibility of a SSNMR microanalysis of a GB1 protein sample in a scale of 1nmol to 80nmol by 1H-detected 2D 15N/1H SSNMR by a synergetic use of a high field, a low-power RF scheme, a paramagnetic-assisted condensed data collection (PACC), and UFMAS.

Analysis of the Current Charge and Discharge Characteristics of a Small-Scale Turn-to-Turn Soldered HTS Coil

A semipersistent current-mode operation with a high-temperature superconducting (HTS) coil is very useful for some applications, including maglev. An HTS coil for semipersistent mode operation includes at least one residual joint to make a closed-loop coil. A low current decaying rate is achieved by reducing the residual joint resistance. This paper suggests a winding method with a turn-to-turn soldering process. The turn-to-turn soldering process provides a wide flow path for the charged current in the HTS coil during the semipersistent mode operation. Therefore, the total equivalent residual resistance is reduced. However, this reduced residual resistance also prevents the current from participating in the charging process. Therefore, a new current charging method for the turn-to-turn soldered HTS coil needs to be tested. In this paper, a small-scale sample HTS coil with turn-to-turn soldering method is fabricated for testing. A simple charging-discharging experiment is performed on the sample coil. The time constant of the sample coil is calculated from the experimental results. A fast current charging sequence for the turn-to-turn soldered coil is also tested and analyzed from the perspective of power and energy consumption during the current charging operation.

Spin superradiance by magnetic nanomolecules and nanoclusters

Spin dynamics of assemblies of magnetic nanomolecules and nanoclusters can be made coherent by inserting the sample into a coil of a resonant electric circuit. Coherence is organized through the arising feedback magnetic field of the coil. The coupling of a magnetic sample with a resonant circuit induces fast spin relaxation and coherent spin radiation, that is, superradiance. We consider spin dynamics described by a realistic Hamiltonian, typical of magnetic nanomolecules and nanoclusters. The role of magnetic anisotropy is studied. A special attention is paid to geometric effects related to the mutual orientation of the magnetic sample and resonator coil.

Magnetic field dependent stability and quench behavior and degradation limits in conduction-cooled MgB2 wires and coils

Long lengths of metal/MgB2 composite conductors with high critical current density (Jc), fabricated by the powder-in-tube process, have recently become commercially available. Owing to its electromagnetic performance in the 20−30 K range and relatively low cost, MgB2 may be attractive for a variety of applications. One of the key issues for magnet design is stability and quench protection, so the behavior of MgB2 wires and magnets must be understood before large systems can emerge. In this work, the stability and quench behavior of several conduction-cooled MgB2 wires are studied. Measurements of the minimum quench energy and normal zone propagation velocity are performed on short samples in a background magnetic field up to 3 T and on coils in self-field and the results are explained in terms of variations in the conductor architecture, electrical transport behavior, operating conditions (transport current and background magnetic field) and experimental setup (short sample versus small coil). Furthermore, one coil is quenched repeatedly with increasing hotspot temperature until Jc is decreased. It is found that degradation during quenching correlates directly with temperature and not with peak voltage; a safe operating temperature limit of 260 K at the surface is identified.

Black-Out Test Versus UV Camera for Corona Inspection of HV Motor Stator Endwindings

As part of a factory acceptance test program for high-voltage (HV) motors, end users sometimes specify a black-out test. This is a traditional offline inspection where the stator is placed in complete darkness, each phase is energized to 115% of rated line-to-neutral voltage, and both ends of the stator are observed to determine the presence, location, and severity of endwinding surface partial discharges (PDs). The setup for the test may be complex and risky due to the need for observers to be standing in darkness close to the energized parts of the stator. The test results are qualitative and strongly depend on the observer's eyesight and individual perception. A safer and more accurate alternative is to use an ultraviolet (UV) camera or viewer. The observed PD activity may be observed in ambient lighting, recorded, and quantified through simultaneous offline PD measurements. This paper describes the two inspection techniques and presents experimental validation of the UV corona camera inspection method as a suitable replacement for a black-out test. Sample 13.8-kV coils were wound in a fixture simulating their relationship in a stator winding and subjected to high-potential tests while observed under black-out conditions and with a UV corona camera in ambient lighting. The stator windings from two HV compressor motors were inspected using the same camera. Recorded images of the observed discharges and measured PD activity in the sample coils and stator winding were used to compare the evaluation by each test method.

A Measurement Method of AC Losses in Superconducting Coils Using Poynting's Vector Method

A new measurement method to determine ac losses in superconducting coils has been proposed, and its validity confirmed experimentally. In this method, the ac losses in the coil can be obtained from measured Poynting's vectors around the coil windings. The Poynting's vectors can be obtained by local magnetic fields and electric fields around the coil. Local magnetic fields and electric fields are measured by pick-up coils and potential leads, which are mounted around the sample coil. These pick-up coil and potential lead pairs are arranged on the inner side, outer side, top, and bottom of the coil windings to cover the entire coil windings. This measurement method has the benefit that ac losses in a coil in a superconducting coil system consisting of multiple coils can be measured. Not only ac losses in the coils but also information on local electromagnetic phenomena in the coils can be obtained from profiles of the Poynting's vectors. In this paper, the details of the measuring method are described, and experiments using a coil wound with Bi-2223 multifilamentary tapes were carried out in liquid nitrogen to confirm the validity of the measurement method.

A simplified explicit model for determining the performance of a chilled water cooling coil

A simplified explicit model for the chilled water cooling coil was presented which could determine the performance of even a partially-wet coil without any need for iterative calculations. A quadratic correlation was derived for evaluating the dry portion of a partially-wet coil from the inlet chilled water temperature based on performance data generated from a validated numerical model for a sample coil over a range of operating conditions. By applying the present explicit model to simulate the performance of the sample coil, it was found that the errors in the calculated coil total capacities did not exceed 2.2% when compared with those based on the numerical model. The percentage errors in the simulated coil latent capacities varied widely from 100% for a just-slightly-wet coil down to 0.26% for a fully-wet coil. Nevertheless, the present model was considered an efficient and yet accurate approach for determining the performance of a chilled water cooling coil.

Fiber Bragg Grating Sensors for Strain Measurement at Multiple Points in an NbTi Superconducting Sample Coil

Multipoint stress/strain measurement in a simple single layered Niobium Titanium wire wounded superconducting sample coil (SSC) was carried out using fiber Bragg grating sensors (FBGs) at low temperature (4.2 K) and at high background magnetic field (8 T) excited by power supply. Ten gratings with different spatial period were fabricated at various positions along a single mode fibre (SMF). The grating location in the SMF sensing array was then mounted at the measuring points on the SSC using stycast 2850 FT. The change in the strain in the SSC. This induced strain, changes the Bragg wavelength of the mounted FBG sensor, which was then recorded using a FS5100 Bragg meter. Experimental results showed that the FBG sensor array was highly reproducible with error of ±0.8 μm/m for high external magnetic field and high current. Also the Young's modulus of the SSC at 900 A, 8 T, and 4.2 K was calculated to be ~ 117 GPa, which is below to the average Young's modulus of the NbTi/Cu superconducting composite wire, which is in the range of 130 GPa at 4.2 K. The loading and unloading characteristic curves of the SSC exhibit reversible behavior without any hysteresis in the operated range. This ensures that the SSC operates linearly within the elastic limit for the applied current and magnetic field. In this paper, we report the behavior of each single turn of the single layered SSC and its corresponding strain due to Lorentz force. The FBG sensing principle is validated by executing various modes of SSC excitation.

Two-dimensional NQR using ultra-broadband electronics

We have recently developed an ultra-broadband instrument that can effectively excite and detect NMR and NQR signals over a wide frequency range. Our current system operates between 100kHz and 3.2MHz using an un-tuned sample coil. The major benefits of this instrument compared to conventional NQR/NMR systems include increased robustness, ease of use (in particular for multi-frequency experiments), and elimination of the need for tuning adjustments in the hardware. Here we describe its use for performing two-dimensional (2D) scans, which allow improved interpretation of complex NQR spectra by detecting the connected resonances. Our method relies on population transfers between the three energy levels of spin-1 nuclei (such as 14N) by using multi-frequency excitation and a single RF coil. Experimental results on pure samples and mixtures are also presented.

A new device for formaldehyde and total aldehydes real-time monitoring

A new sensitive technique for the quantification of formaldehyde (HCHO) and total aldehydes has been developed in order to monitor these compounds, which are known to be involved in air quality issues and to have health impacts. Our approach is based on a colorimetric method where aldehydes are initially stripped from the air into a scrubbing solution by means of a turning coil sampler tube and then derivatised with 3-methylbenzothiazolinone-2-hydrazone in acid media (pH = -0.5). Hence, colourless aldehydes are transformed into blue dyes that are detected by UV-visible spectroscopy at 630 nm. Liquid core waveguide LCW Teflon® AF-2400 tube was used as innovative optical cells providing a HCHO detection limit of 4 pptv for 100 cm optical path with a time resolution of 15 min. This instrument showed good correlation with commonly used techniques for aldehydes analysis such as DNPH derivatisation chromatographic techniques with off-line and on-line samplers, and DOAS techniques (with deviation below 6%) for both indoor and outdoor conditions. This instrument is associated with simplicity and low cost, which is a prerequisite for indoor monitoring.

Electrical measurements of AC losses in high temperature superconducting coils at variable temperatures

Measurements of AC losses in high temperature superconducting (HTS) coils wound from two different types of YBa2Cu3O7 (YBCO) coated conductors are reported. AC loss measurements by different arrangements of voltage loops and pick-up coils were investigated to propose accurate and convenient techniques to measure the AC losses in HTS coils, especially for large coils with the measurement signals significantly higher than the input range of typical lock-in amplifiers. A new and simple sub-cooling technique with an open liquid nitrogen bath was developed to measure AC losses in the sample coils at variable temperatures between 65 and 77 K. The temperature dependence of the losses in these coils was qualitatively explained based on the data on transport and magnetization AC losses in isolated tapes at variable temperatures.

AC Loss Measurement of High-Tc Superconducting Coils Wound With Stacked Conductors

In order to elucidate the ac loss characteristics of high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconducting coils wound with stacked conductors, we measured ac losses of Bi-2223 sample coils under the various electromagnetic conditions by a nitrogen boil-off method. The sample coils were wound with stacked conductors, which were composed of two Bi-2223 tapes. Each tape of stacked conductors was wrapped with polyimide tape, and the ends were made into the open circuit or short circuit. The coils with transposition and the coils without transposition were prepared as sample coils. We measured the magnetic amplitude dependence and the frequency dependence of ac losses of sample coils under external magnetic fields, and evaluated the magnetization losses and coupling current losses. Measured data were compared with theoretical values. Based on the obtained results, ac loss characteristics of high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconducting coils wound with stacked conductors under external magnetic fields were discussed.

An online monitoring system for atmospheric nitrous acid (HONO) based on stripping coil and ion chromatography

A new instrument for measuring atmospheric nitrous acid (HONO) was developed, consisting of a double-wall glass stripping coil sampler coupled with ion chromatography (SC-IC). SC-IC is featured by small size (50 × 35 × 25 cm) and modular construction, including three independent parts: the sampling unit, the transfer and supporting unit, and the detection unit. High collection efficiency (> 99%) was achieved with 25 μmol/L Na2CO3 as absorption solution even in the presence of highly acidic compounds. This instrument has a detection limit of 8 pptv at 15 min time resolution, with a measurement uncertainty of 7%. Potential interferences from NOx, NO2+SO2, NO2+VOCs, HONO+O3, HNO3, peroxyacetyl nitrite (PAN) and particle nitrite were quantified in laboratory studies and were found to be insignificant under typical atmospheric conditions. Within the framework of the 3C-STAR project, inter-comparison between the SC-IC and LOPAP (long path liquid absorption photometer) was conducted at a rural site in the Pearl River Delta. Good agreement was achieved between the two instruments over three weeks. Both instruments determined a clear diurnal profile of ambient HONO concentrations from 0.1 to 2.5 ppbv. However, deviations were found for low ambient HONO concentrations (i.e. < 0.3 ppbv), which cannot be explained by previous investigated interference species. To accurately determine the HONO budget under illuminated conditions, more intercomparison of HONO measurement techniques is still needed in future studies, especially at low HONO concentrations.

Measurements of ambient HONO concentrations and vertical HONO flux above a northern Michigan forest canopy

Abstract. Systems have been developed and deployed at a North Michigan forested site to measure ambient HONO and vertical HONO flux. The modified HONO measurement technique is based on aqueous scrubbing of HONO using a coil sampler, followed by azo dye derivatization and detection using a long-path absorption photometer (LPAP). A Na2CO3-coated denuder is used to generate "zero HONO" air for background correction. The lower detection limit of the method, defined by 3 times of the standard deviation of the signal, is 1 pptv for 1-min averages, with an overall uncertainty of ±(1 + 0.05 [HONO]) pptv. The HONO flux measurement technique has been developed based on the relaxed eddy accumulation approach, deploying a 3-D sonic anemometer and two HONO measurement systems. The overall uncertainty is estimated to be within ±(8 × 10−8 + 0.15 FHONO) mol m−2 h−1, with a 20-min averaged data point per 30 min. Ambient HONO and vertical HONO flux were measured simultaneously at the PROPHET site from 17 July to 7 August 2008. The forest canopy was found to be a net HONO source, with a mean upward flux of 0.37 × 10−6 moles m−2 h−1. The HONO flux reached a maximal mean of ~0.7 × 10−6 moles m−2 h−1 around solar noon, contributing a major fraction to the HONO source strength required to sustain the observed ambient concentration of ~70 pptv. There were no significant correlations between [NOx] and daytime HONO flux and between JNO2 × [NO2] and HONO flux, suggesting that NOx was not an important precursor responsible for HONO daytime production on the forest canopy surface in this low-NOx rural environment. Evidence supports the hypothesis that photolysis of HNO3 deposited on the forest canopy surface is a major daytime HONO source.