Automation and control in high power pulsed NMR (original) (raw)
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A pulsed, broadband NMR spectrometer
Journal of Magnetic Resonance (1969), 1978
A pulsed nuclear magnetic resonance spectrometer suitable for measurements in solids is described. The spectrometer is phase coherent, and the pulse timing is synchronous with the operating frequency of the spectrometer. The apparatus uses a versatile pulse programmer and a gated broadband rf power amplifier which delivers 1.6 kW at 60 MHz with a 3-db bandwidth of 5 to 90 MHz. With the exception of the probe, the spectrometer does not contain any tuned elements. This permits short (0.5 psec) recovery times between the end of the rf pulse and the start of the signal. The spectrometer relies heavily upon the use of commercially available modules. A detailed description of the spectrometer construction and a discussion of typical operating characteristics are presented.
The Building of Pulsed NQR/NMR Spectrometer
International Journal of Electrical and Computer Engineering (IJECE), 2018
NQR spectrometer designed is composed of four modules; Transmitter, Probe, Receiver and computer controlled (FPGA & Software) module containing frequency synthesizer, synchronous demodulator, pulse programmer and display. The function of the Transmitter module is to amplify the RF pulse sequence to about 200 W power level into the probe (50 Ohm) which is a parallel resonance circuit with a tapped capacitor. The probe excites the nucleus and picks-up the signal emitted from the nuclei. The nuclear signal at the same frequency as the excitation, which is typically in the range of a few microvolts is amplified, demodulated and filtered (1 kHz to 100 kHz) by receiver module. 14 N NQR, 1 H and 2 H NMR signals are observed from the spectrometer.As the SNR of NQR signal is very low, NQR signal processing based on Adaptive Line Enhancement is presented.
Development of Low Frequency Pulsed NQR/NMR Spectrometer
Global Journal of Research In Engineering, 2016
An FPGA based NQR spectrometer has been designed for detection of N nuclei. The digital circuits required for NQR spectrometer i.e Pulse Programmer, DDS, digital receiver have been built inside FPGA. Combining FPGA chip with analog components, NQR spectrometer has been developed. N from NaNO2 is observed using same spectrometer. By adding a permanent magnet of uniform field NMR signal of proton as well as deuterium was also observed. Development of Low Frequency Pulsed NQR/NMR Spectrometer © 2016 Global Journals Inc. (US) G lo ba l J o ur na l of R es ea rc he s in E ng in ee ri ng ( ) V ol 13 Y e a r 20 16 F um e X V I I ss ue II V er si on I Preeti Hemnani , A. K.Rajarajan σ , Gopal Joshi, ρ & S. V. G Ravindranath Ѡ AbstractAn FPGA based NQR spectrometer has been An FPGA based NQR spectrometer has been designed for detection of N nuclei. The digital circuits required for NQR spectrometer i.e Pulse Programmer, DDS, digital receiver have been built inside FPGA. Combining FPGA chip w...
A computer-controlled pulse sequeneer for pulsed nmr experiments
Journal of Magnetic Resonance (1969)
A microprocessor-controlled pulse sequencer for diverse pulsed NMR experiments is described. The design is based on a first-in-first-out recycling memory which is loaded and triggered by computer software control. Sixteen output channels are provided for various synchronized functions.
The Fantastic Four: A plug’n’play set of optimal control pulses for enhancing nmr spectroscopy
2012
We present highly robust, optimal control-based shaped pulses designed to replace all 90 • and 180 • hard pulses in a given pulse sequence for improved performance. Special attention was devoted to ensuring that the pulses can be simply substituted in a one-to-one fashion for the original hard pulses without any additional modification of the existing sequence. The set of four pulses for each nucleus therefore consists of 90 • and 180 • point-to-point (PP) and universal rotation (UR) pulses of identical duration. These 1 ms pulses provide uniform performance over resonance offsets of 20 kHz (1 H) and 35 kHz (13 C) and tolerate reasonably large radio frequency (RF) inhomogeneity/miscalibration of ±15% (1 H) and ±10% (13 C), making them especially suitable for NMR of small-to-medium-sized molecules (for which relaxation effects during the pulse are negligible) at an accessible and widely utilized spectrometer field strength of 600 MHz. The experimental performance of conventional hard-pulse sequences is shown to be greatly improved by incorporating the new pulses, each set referred to as the Fantastic Four (Fanta4).
DAMARIS — a flexible and open software platform for NMR spectrometer control
Magnetic Resonance Imaging, 2007
Home-built NMR spectrometers with self-written control software have a long tradition in porous media research. Advantages of such spectrometers are not just lower costs but also more flexibility in developing new experiments (while commercial NMR systems are typically optimized for standard applications such as spectroscopy, imaging or quality control applications). Increasing complexity of computer operating systems, higher expectations with respect to user-friendliness and graphical user interfaces as well as increasing complexity of the NMR experiments themselves have made spectrometer control software development a more complex task than it used to be some years ago. Like that, it becomes more and more complicated for an individual lab to maintain and develop an infrastructure of purely homebuilt NMR systems and software. Possible ways out are:
Journal of Magnetic Resonance, 2000
This paper presents a software program, the Virtual NMR Spectrometer, for computer simulation of multichannel, multidimensional NMR experiments on user-defined spin systems. The program is capable of reproducing most features of the modern NMR experiment, including homo-and heteronuclear pulse sequences, phase cycling, pulsed field gradients, and shaped pulses. Two different approaches are implemented to simulate the effect of pulsed field gradients on coherence selection, an explicit calculation of all coherence transfer pathways, and an effective approximate method using integration over multiple positions in the sample. The applications of the Virtual NMR Spectrometer are illustrated using homonuclear COSY and DQF COSY experiments with gradient selection, heteronuclear HSQC, and TROSY. The program uses an intuitive graphical user interface, which resembles the appearance and operation of a real spectrometer. A translator is used to allow the user to design pulse sequences with the same programming language used in the actual experiment on a real spectrometer. The Virtual NMR Spectrometer is designed as a useful tool for developing new NMR experiments and for tuning and adjusting the experimental setup for existing ones prior to running costly NMR experiments, in order to reduce the setup time on a real spectrometer. It will also be a useful aid for learning the general principles of magnetic resonance and contemporary innovations in NMR pulse sequence design.
Modeling of NMR processing, toward efficient unattended processing of NMR experiments
Journal of Magnetic Resonance, 2007
Many alternative processing techniques have recently been proposed in the literature. Most of these techniques rely on specific acquisition protocols as well as on specific data processing techniques, the need for an efficient versatile and expandable NMR processing tool would be a particularly timely addition to the modern NMR spectroscopy laboratory. The work presented here consists in a modeling of the various possible NMR data processing approaches. This modeling presents a common working frame for most of the modern acquisition/processing protocols. Two different data modeling approaches are presented, strong modeling and weak modeling, depending whether the system under study or the measurement is modeled. The emphasis is placed on the weak modeling approach. This modeling is implemented in a computer program developed in python and called NPK standing (standing for NMR Processing Kernel), organized in four logical layers (i) mathematical kernel; (ii) elementary actions; (iii) processing phases; (iv) processing strategies. This organisation, along with default values for most processing parameters allows the use of the program in an unattended manner, producing close to optimal spectra. Examples are shown for 1D and 2D processing, and liquid and solid NMR spectroscopy. NPK is available from the site: http://abcis.cbs.cnrs.fr/NPK Ó
Matrix method for analysis of selective NMR pulses
Concepts in Magnetic Resonance Part A, 2005
The evolution of a single nuclear magnetic spin during the application of radiofrequency (RF) pulses is followed using the 3 ϫ 3 matrix solution to the Bloch equations. The effect of different pulses on the magnetization of spin-1/2 nuclei is described using this 3 ϫ 3 matrix. Simulations of the magnetization following a simple square pulse, amplitude and amplitude/frequency modulated pulses are represented as unit vectors in the rotating reference frame, and evolution of the magnetization can be followed at any time during the application of the pulse. Projection of these vectors onto the transverse plane of the rotating frame of reference is the magnitude of the various components of detectable magnetization. From these simulations, the peak amplitude required to drive the RF power output of linear amplifiers can be calculated accurately and directly related to experiment. In addition, the magnitude of magnetization for a range of frequency offsets within an NMR spectrum can be simulated with or without phase cycling. The simulations of shaped and adiabatic pulses are described. The accuracy of these simulations were readily verified by experiment so that implementation of new pulses into pulse sequences could be assessed by simulation prior to application and reduce the use of spectrometer time for optimization of RF pulses in NMR pulse sequences.