Nuclear Magnetic Resonance Sensor Research Articles

Towards Using NMR to Screen for Spoiled Tomatoes Stored in 1,000 L, Aseptically Sealed, Metal-Lined Totes

Nuclear magnetic resonance (NMR) spectroscopy is used to track factory relevant tomato paste spoilage. It was found that spoilage in tomato paste test samples leads to longer spin lattice relaxation times T1 using a conventional low magnetic field NMR system. The increase in T1 value for contaminated samples over a five day room temperature exposure period prompted the work to be extended to the study of industry standard, 1,000 L, non-ferrous, metal-lined totes. NMR signals and T1 values were recovered from a large format container with a single-sided NMR sensor. The results of this work suggest that a handheld NMR device can be used to study tomato paste spoilage in factory process environments.

A compact high-performance low-field NMR apparatus for measurements on fluids at very high pressures and temperatures

We discuss an innovative new high-performance apparatus for performing low-field Nuclear Magnetic Resonance (NMR) relaxation times and diffusion measurements on fluids at very high pressures and high temperatures. The apparatus sensor design and electronics specifications allow for dual deployment either in a fluid sampling well logging tool or in a laboratory. The sensor and electronics were designed to function in both environments. This paper discusses the use of the apparatus in a laboratory environment. The operating temperature and pressure limits, and the signal-to-noise ratio (SNR) of the new system exceed by a very wide margin what is currently possible. This major breakthrough was made possible by a revolutionary new sensor design that breaks many of the rules of conventional high pressure NMR sensor design. A metallic sample holder capable of operating at high pressures and temperatures is provided to contain the fluid under study. The sample holder has been successfully tested for operation up to 36 Kpsi. A solenoid coil wound on a slotted titanium frame sits inside the metallic sample holder and serves as an antenna to transmit RF pulses and receive NMR signals. The metal sample holder is sandwiched between a pair of gradient coils which provide a linear field gradient for pulsed field gradient diffusion measurements. The assembly sits in the bore of a low-gradient permanent magnet. The system can operate over a wide frequency range without the need for tuning the antenna to the Larmor frequency. The SNR measured on a water sample at room temperature is more than 15 times greater than that of the commercial low-field system in our laboratory. Thus, the new system provides for data acquisition more than 200 times faster than was previously possible. Laboratory NMR measurements of relaxations times and diffusion coefficients performed at pressures up to 25 Kpsi and at temperatures up to 175 °C with crude oils enlivened with dissolved hydrocarbon gases (referred to as "live oils") are shown. This is the first time low-field NMR measurements have been performed at such high temperatures and pressures on live crude oil samples. We discuss the details of the apparatus design, tuning, calibration, and operation. NMR data acquired at multiple temperatures and pressures on a live oil sample are discussed.

A MINI NMR SENSOR FOR MONITORING THE DEGRADATION OF FIRE-RESISTANT TURBINE OILS IN THERMAL POWER PLANT IN VIVO

Fire-resistant turbine oil is widely used in thermal power plant. As the service time increases, its lubrication and electrical characteristic degrade. This work proposes a mini NMR (nuclear magnetic resonance) sensor for assessing the degradation of the turbine oils used in real time and in vivo. Two magnetic discs with poles opposed were separated in a distance to generate a relative homogeneous static magnetic field between them. A solenoid coil was placed between the magnets as the RF coil. The dimensions of the sensor are 30 mm × 30 mm × 36 mm and the mass is 107 g. The T1 and T2eff of the turbine oils from two different power plants were measured. The results demonstrated that an increase of the service time of turbine oils clearly results in a decrease of T1 and T2eff . This method of monitoring degradation of turbine oils could lead to the use of NMR to assess the degradation level of turbine oils in service.

A Portable NMR Sensor Used for Assessing the Aging Status of Silicone Rubber Insulator

A portable nuclear magnetic resonance (NMR) sensor with an adjustable ‘clamp’ structure is constructed for the noninvasive measurement of the aging status of silicone rubber insulators used in the high-voltage power transmission. The Carr–Purcell–Meiboom–Gill sequence was employed to record the 1H NMR transverse relaxation curves of silicone rubber insulators with different service times. The decay curves were fitted to mono-exponential and bi-exponential functions. Further data processing of the decay curves was performed with the inverse Laplace transformation for one-dimensional T2 distribution analysis, focusing on the mean lifetime of the long T2 component (T2long mean). The results demonstrate that an increase in the aging level of the insulator clearly results in a decrease of T2long mean. For comparison, the relative permittivity of the insulator was also measured. It shows the same trend as that of T2long mean. This indicates that the T2long mean relaxation time obtained from our portable NMR sensor can reliably be used as an index to reflect the aging status of silicone rubber insulator.

Evaluation of a mobile NMR sensor for determining skin layers and locally estimating the T2eff relaxation time in the lower arm

The nuclear magnetic resonance (NMR) mobile-universal-surface-explorer (MOUSE) was evaluated in a pilot study to determine its ability to detect physiological changes in human skin caused by physical or pharmacological interventions. The left lower arm skin thicknesses of ten male subjects were measured five times using a Profile NMR-MOUSE(®) ((1)H, 19 MHz) before and after a venous occlusion manoeuvre. In five of the subjects, the T(2eff) relaxation times were derived from a bi-exponential fitting and were determined in the dermis and subcutis before and after applying a salve containing capsaicin. The dermis (including the epidermis) showed rather homogeneous signal amplitudes. The subcutis was characterised by higher and more variable amplitudes. The full-skin thickness values were affirmed by ultrasound imaging. The NMR profiles did not show significant skin swelling due to venous occlusion. In the dermis, capsaicin caused significant (p < 0.05) decreases in both components of T(2eff) (100 ± 19 ms-19 ± 10 ms; 9.5 ± 0.5 ms-7.2 ± 1.6 ms). In the subcutis, the T(2eff) was not affected. In principle, NMR-MOUSE profiles are capable of detecting skin structure. However, precise measurements are jeopardised by poor reproducibility, long acquisition times, and incompatibility between the geometries of the sensitive area of the instrument and the non-planar structure of the skin. In the dermis, T(2eff) contrast could be used to detect the changes in tissue composition caused by inflammatory reactions.

Sensor design and implementation for a downhole NMR fluid analysis laboratory

This paper tries to build a multi-functional downhole nuclear magnetic resonance (NMR) fluid analysis laboratory that can evaluate fluid information in real time at reservoir conditions at a depth of several thousand meters. The aim is to monitor the pollution of the formation fluids and quantitatively evaluate NMR characteristics of the fluids. It focuses on the design of the structure and parameters of a sensor with zero stray fields. Two separate coils are designed to measure NMR characteristics of flowing or static fluids. A method is proposed to use the Bloch equation, to guide the optimization of the NMR sensor. Finally, the measured results confirm that the design is reasonable. There is a homogeneous static field (perpendicular to the axial direction) in the center of the sensor, and there are no stray external fields. The novel design of pre-polarization magnet improves the signal to noise ratio, while shortening the sensor length.

Assessment of moisture protective properties of wood coatings by a portable NMR sensor

We have evaluated the potential of nuclear magnetic resonance (NMR) spectroscopy based on small portable magnets for in situ assessment of moisture protective properties of wood coatings. Low field 1H NMR with a unilateral permanent magnet was used to monitor and map the local moisture content (MC) of wood specimens uncoated or coated with various types of commercial paint systems. The MC beneath a coating layer was measured with a penetration depth up to 5 mm and with a depth resolution of 0.2 mm. The method is quick, noninvasive, simple to perform, and does not require removing wooden parts from the structure.

Low-field NMR logging sensor for measuring hydraulic parameters of model soils

Summary Knowing the exact hydraulic parameters of soils is very important for improving water management in agriculture and for the refinement of climate models. Up to now, however, the investigation of such parameters has required applying two techniques simultaneously which is time-consuming and invasive. Thus, the objective of this current study is to present only one technique, i.e., a new non-invasive method to measure hydraulic parameters of model soils by using low-field nuclear magnetic resonance (NMR). Hereby, two model clay or sandy soils were respectively filled in a 2 m-long acetate column having an integrated PVC tube. After the soils were completely saturated with water, a low-field NMR sensor was moved up and down in the PVC tube to quantitatively measure along the whole column the initial water content of each soil sample. Thereafter, both columns were allowed to drain. Meanwhile, the NMR sensor was set at a certain depth to measure the water content of that soil slice. Once the hydraulic equilibrium was reached in each of the two columns, a final moisture profile was taken along the whole column. Three curves were subsequently generated accordingly: (1) the initial moisture profile, (2) the evolution curve of the moisture depletion at that particular depth, and (3) the final moisture profile. All three curves were then inverse analyzed using a MATLAB code over numerical data produced with the van Genuchten–Mualem model. Hereby, a set of values (α, n, θr and θs) was found for the hydraulic parameters for the soils under research. Additionally, the complete decaying NMR signal could be analyzed through Inverse Laplace Transformation and averaged on the 1/T2 space. Through measurement of the decay in pure water, the effect on the relaxation caused by the sample could be estimated from the obtained spectra. The migration of the sample-related average 〈1/T2,Sample〉 with decreasing saturation speaks for a enhancement of the surface relaxation as the soil dries, in concordance with results found by other authors. In conclusion, this low-field mobile NMR technique has proven itself to be a fast and a non-invasive mean to investigate the hydraulic behavior of soils and to explore microscopical aspect of the water retained in them. In the future, the sensor should allow easy soil moisture measurements on-field.

Monitoring the Transesterification Reaction Used in Biodiesel Production, with a Low Cost Unilateral Nuclear Magnetic Resonance Sensor

The transesterification reaction used to produce biodiesel was monitored with 1H high-resolution nuclear magnetic resonance (HRNMR), conventional low-resolution NMR (LRNMR), and unilateral NMR (UNM...

Capacitor-based detection of nuclear magnetization: Nuclear quadrupole resonance of surfaces

We demonstrate excitation and detection of nuclear magnetization in a nuclear quadrupole resonance (NQR) experiment with a parallel plate capacitor, where the sample is located between the two capacitor plates and not in a coil as usually. While the sensitivity of this capacitor-based detection is found lower compared to an optimal coil-based detection of the same amount of sample, it becomes comparable in the case of very thin samples and even advantageous in the proximity of conducting bodies. This capacitor-based setup may find its application in acquisition of NQR signals from the surface layers on conducting bodies or in a portable tightly integrated nuclear magnetic resonance sensor.

Current-Distribution Measurement in Polymer Electrolyte Water Electrolysis Equipment and Polymer Electrolyte Fuel Cell Using NMR Sensor

In a polymer electrolyte fuel cell (PEFC), the current density through the polymer electrolyte membrane (PEM) is distributed along the electrode on the membrane electrode assembly (MEA). To increase the electric power density of a PEFC, it is necessary to locate local decreases in current density where electric power generation decreases due to a lack of hydrogen, flooding, and so on. Therefore, achieving a higher current density in a PEFC requires monitoring the local current density. We developed a new method to estimate the spatial distribution of current flowing through the MEA in a polymer electrolyte water electrolysis equipment (PEWEE) and a PEFC using Nuclear-Magnetic-Resonance (NMR) sensors. The magnetic field strength induced by current through the MEA in a PEWEE is acquired as the frequency shift of the NMR signal which is measured by the NMR sensor. The spatial distributions of the frequency shifts occurring along the MEA in a PEWEE and a PEFC was measured. In order to verify the method, the magnetic field strength induced by the current through the gas diffusion layer (GDL) in a PEWEE was analyzed theoretically under the assumption that the current through MEA was uniform. The frequency shift was then calculated as a function of the geometry of the GDL, current, and the position of the NMR sensor. From experimental and theoretical results, the frequency shift of the NMR signal is proportional to current density and depends on the position of the sensors. Using the measurement system, we also obtained the current distribution through the GDL in a PEFC generating electric power. In these studies, the experimental and theoretical results agree.

Least Squares Magnetic-Field Optimization for Portable Nuclear Magnetic Resonance Magnet Design

Single-sided and mobile nuclear magnetic resonance (NMR) sensors have the advantages of portability, low cost, and low power consumption compared to conventional high-field NMR and magnetic resonance imaging (MRI) systems. We present fast, flexible, and easy-to-implement target field algorithms for mobile NMR and MRI magnet design. The optimization finds a global optimum in a cost function that minimizes the error in the target magnetic field in the sense of least squares. When the technique is tested on a ring array of permanent-magnet elements, the solution matches the classical dipole Halbach solution. For a single-sided handheld NMR sensor, the algorithm yields a 640 G field homogeneous to 16 100 ppm across a 1.9 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> volume located 1.5 cm above the top of the magnets and homogeneous to 32 200 ppm over a 7.6 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> volume. This regime is adequate for MRI applications. We demonstrate that the homogeneous region can be continuously moved away from the sensor by rotating magnet rod elements, opening the way for NMR sensors with adjustable ldquosensitive volumes.rdquo

The RXRα C-terminus T462 is a NMR sensor for coactivator peptide binding

The C-terminal activation function-2 (AF-2) helix plays a crucial role in retinoid X receptor alpha (RXRα)-mediated gene expression. Here, we report a nuclear magnetic resonance (NMR) study of the RXRα ligand-binding domain complexed with 9- cis-retinoic acid and a glucocorticoid receptor-interacting protein 1 peptide. The AF-2 helix and most of the C-terminal residues were undetectable due to a severe line-broadening effect. Due to its outstanding signal-to-noise ratio, the C-terminus residue, threonine 462 (T462) exhibited two distinct crosspeaks during peptide titration, suggesting that peptide binding was in a slow exchange regime on the chemical shift timescale. Consistently, the K d derived from T462 intensity decay agreed with that derived from isothermal titration calorimetry. Furthermore, the exchange contribution to the 15N transverse relaxation rate was measurable in either T462 or the bound peptide. These results suggest that T462 is a sensor for coactivator binding and is a potential probe for AF-2 helix mobility.

Design of a Nuclear Magnetic Resonance Sensor Working in Inhomogeneous Magnetic Field

Design of a Nuclear Magnetic Resonance Sensor Working in Inhomogeneous Magnetic Field

Estimation of the apertures of water‐saturated fractures by nuclear magnetic resonance well logging

ABSTRACTFracture aperture is an important transport property in subsurface hydrology because it influences well productivity and the volume of the water resource. Nuclear magnetic resonance (NMR) well logging measures the hydrogen‐bearing fluid molecules in porous or fractured strata, and the NMR signal intensity increases with the amount of fluid in the sensed region of the NMR sonde. Fluid confined in a large fracture of &gt;&gt;0.2 mm in aperture has T2 (i.e. spin‐spin relaxation time) values as long as those of the bulk fluid. The bulk‐fluid porosity (i.e. porosity calculated using this long T2 component in a T2 histogram data) increases linearly with aperture. Therefore, NMR logging enables quantitative estimation of fracture apertures of &gt;&gt;0.2 mm using the bulk‐fluid porosity data if the calibration of the NMR sonde is performed adequately. We applied NMR logging to a borehole in a Holocene andesite lava at Sumikawa, Japan, to estimate the aperture of open fractures within the lava. A test well of 100 m depth and 20 cm diameter, filled with bentonite drilling mud, was scanned with an NMR sonde to obtain a profile of the porosity and the T2 histogram of the andesite. The bulk‐fluid porosity was calculated from the T2 histogram data, as the porosity at which the T2 value is larger than or equal to a threshold T2 of bulk bentonite mud. The bulk‐fluid porosity of a specific inclined fracture responsible for the total loss of circulation at 61.2 m depth during drilling was calculated assuming a threshold or T2 cut‐off of 33 ms, and again for a cut‐off of 100 ms. Calibration of the NMR sensor in a laboratory and measurement of the fracture dip angle by electrical microimaging logging enabled us to estimate the fracture aperture as 1.7 cm, assuming a T2 cut‐off of 33 ms, or 1.6 cm for a T2 cut‐off of 100 ms. The method of aperture determination described in this study is independent of fluid species and lithology, and is applicable to various hydrogen‐bearing borehole fluids (clean water, mud and oil) and geological settings.

Tomato quality evaluation by peak force and NMR spin–spin relaxation time

Throughout the fruit and vegetable processing industries, improving processing efficiency requires the development of in-line sensor technologies. The goal of this study was to determine if there is a basis to develop nuclear magnetic resonance (NMR) sensor technology based on spin–spin relaxation times to assist in quality sorting of processing tomatoes. The specific objectives were: to determine if firmness is an adequate indicator of maturity, to assess the effect of common defects on fruit firmness and NMR spin–spin relaxation time ( T 2) and to correlate firmness values and T 2 values. The study spanned three processing seasons and evaluated a number of standard processing varieties. To evaluate firmness, whole fruit compression tests were performed; NMR spin–spin relaxation times ( T 2) were determined using a CPMG pulse sequence and mono-exponential fitting. During the first season, a reasonable correlation was found between T 2 and peak force ( R 2 ≥ 0.75) using sound red fruit. Therefore, the study was expanded in 2005 and 2006 to include more processing varieties, maturity levels and common defects. Analysis of variance was performed on the responses, T 2 and peak force. In general, there were statistically significant differences in the mean values of the spin–spin relaxation times at the P = 0.05 level, yet these differences were small in magnitude. In addition correlation between NMR spin–spin relaxation time and fruit firmness in both 2005 and 2006 was poor. Neither of these experimental results supports continued development of an NMR sensor based on spin–spin relaxation time differences for in-line sorting of processing tomatoes.

Analysis of Characteristics of In-Line Magnetic Resonance Sensor

This study was performed to show the feasibility of nuclear magnetic resonance (NMR) techniques for quality evaluation of various agricultural and food products. A real-time in-line NMR quality evaluation sensor was designed, constructed and tested. The device consists of an NMR spectrometer coupled to a conveyor system and a data acquisition system. The conveyor was run at speeds ranging from 0 to 300 mm/s. An NMR signal can be detected when a sample is within ±50 mm of the NMR coil center. The response of NMR sensor was tested using several fruits. The results showed a feasibility of an NMR sensor for evaluating internal quality of various fruits.

Behavioral VHDL-AMS model and experimental validation of a nuclear magnetic resonance sensor

This paper describes the development for a model of a nuclear magnetic resonance spiral coil sensor using analog hardware description. Our procedure implies several steps with emphasis on model complexity reduction, identification of critical parameters and validation of experimental measurements. The proposed macro-model permits an extremely fast simulation while providing nearly finite element method accuracy. As a tool for coding the description of system level modeling we use analog hardware description language VHDL-AMS (Ashenden et al. in the system designer’s guide to VHDL-AMS, Morgan Kauffmann, 2002). In order to obtain the behavioral computation results, SYSTEM VISION simulation environment from Mentor Graphics® was employed. In our proposed model, the different parts of the sensor and the different effects involved (electrical parameters, physical and magnetic coupling, loss effects) can be modeled within the same tool, together with the sensor environment: electrical command and detection circuit, time dependent magnetic field, and so on.

High-Resolution NMR Spectroscopy with a Portable Single-Sided Sensor

We report construction of a portable nuclear magnetic resonance sensor with a single-sided open probe design. The resulting magnetic field inhomogeneity is compensated by a pulse sequence that takes advantage of parallel inhomogeneity in the applied radio frequency field. We can thereby acquire fluorine-19 spectra of liquid fluorocarbons with 8 parts per million resolution, surmounting the long-standing obstacle of obtaining chemical shift information with open probe instruments.

On the design of NMR sensor for well-logging applications

The magnetic fields of antenna and magnet used in inside-out nuclear magnetic resonance (NMR) well-logging tool are computed using a finite-element method (FEM). A typical operating frequency of such tools is 2 MHz, at which the skin depth is about 47 /spl mu/m for copper conductor. A direct application of FEM to evaluate power loss at such frequency, therefore, requires very fine discretization of the conductors, which, in turn, makes the problem numerically ill-conditioned. A perturbation technique along with FEM is used to evaluate the power loss in conductors that avoids the need for small discretization steps along the conductor thickness. The design of the magnet, on the other hand, is complicated by the fact that the model is nonlinear in nature because of the presence of ferrites and steel materials surrounding the magnet and because the size of the problem is usually quite large; quarter of a million unknowns is fairly common. A typical nonlinear FEM model requires about 35 h of central processing unit (CPU) time on a Sun Ultra 60 296 MHz workstation with one gigabyte of RAM. The magnet is built by stacking several magnet segments along the axial direction and the objective of the design is to magnetize these segments in such a way so as to produce a desired field profile in front of the magnet. It generally requires many executions of the nonlinear FEM model. An optimal control technique is used in conjunction with the FEM to speed up the design process. Very good agreement between the measured and computed antenna efficiency and magnetic field is obtained thus validating the numerical model.