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# Decoupling (electronics)

About: Decoupling (electronics) is a(n) research topic. Over the lifetime, 10395 publication(s) have been published within this topic receiving 100706 citation(s). The topic is also known as: decoupling (electronics).

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TL;DR: It is found that a stepwise variation of the phase angle in the TPPM sequence offers even better results, and the application of this new method to a liquid crystalline compound and a solid, L-tyrosine hydrochloride, is reported.

Abstract: Recently we developed an efficient broadband decoupling sequence called SPARC-16 for liquid crystals ?J. Magn. Reson. 130, 317 (1998). The sequence is based upon a 16-step phase cycling of the 2-step TPPM decoupling method for solids ?J. Chem. Phys. 103, 6951 (1995). Since then, we have found that a stepwise variation of the phase angle in the TPPM sequence offers even better results. The application of this new method to a liquid crystalline compound, 4-n-pentyl-4'-cyanobiphenyl, and a solid, L-tyrosine hydrochloride, is reported. The reason for the improvement is explained by an analysis of the problem in the rotating frame.

1,535 citations

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Abstract: Traditional modulation methods for broadband proton decoupling (1-4) have now been superseded by modern pulse techniques (5) using sequences of composite 180” pulses (6). Initial progress was achieved with the MLEV decoupling sequences (7-9) and guided by coherent averaging theory (10). This approximate analysis showed that longer and more effective decoupling “supercycles” could be constructed from primitive decoupling sequences according to an inductive “expansion procedure.” Waugh’s exact theory of periodic decoupling (II) further clarified the role of expansion procedures (12) in terms of the net rotation induced by the sequence of pulses. The particular merits of the exact analysis were that it provided a simple criterion for good decoupling, allowed prospective sequences to be evaluated by computer simulation, and isolated the effects of instrumental shortcomings. The WALTZ decoupling sequences (13, 14) resulted from careful attention to the influence of these imperfections, in particular the accuracy of the radiofrequency phase shifts. Applied to carbon13 spectroscopy, WALTZ16 decoupling produces residual splittings of less than 0.1 Hz over a range of decoupler offsets aB = +&. In routine applications splittings as large as 1 Hz can go unnoticed due to coarse digitization in the frequency domain and line broadening produced by sensitivity enhancement functions. However, for more demanding applications, including the investigation of small isotope shifts, of couplings to other nuclei, or of carbon-carbon couplings in natural abundance (15), WALTZ16 has definite advantages. A number of modified broadband decoupling sequences, all broadly based on the WALTZ16 scheme, have been introduced recently (14-19). At 2 Hz carbon-l 3 linewidths, the best of these promises to deliver a 40% improvement in bandwidth over WALTZ-16. In fact this sequence, dubbed PAR-75, gives a bandwidth comparable to an earlier sequence based on composite pulses incorporating short periods of free precession (20). These sequences do not restrict the pulsewidths to multiples of 90” and therefore require more sophisticated pulse programming, but the additional complexity may be justified for certain applications, such as 19F decoupling, where extremely wideband operation is required. The present communication demonstrates that sequences with extremely wide bandwidths may be devised by further relaxing the requirement of programming simplicity. For windowless decoupling sequences a figure of merit (20)

1,084 citations

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Abstract: Progressive improvements in broadband decoupling performance have recently been achieved with the pulse sequences known as MLEV-4, MLEV-16, MLEV-64, etc. (Z-5). Applied to carbon-13 spectroscopy, such sequences permit operation with a much lower radiofrequency power. A common feature of these and related experiments (6) is that their effectiveness can be improved by combining different versions of the primitive cycle into extended “supercycles” in which some of the residual pulse imperfections are compensated in a manner reminiscent of the folklore of solid state NMR. The original treatment of these experiments was based on average Hamiltonian theory (7) which, although it provides insight into the mechanism of error compensation, can be rather cumbersome in its application (5). An elegant new theory has recently been proposed (6, 8) which represents the effects of the proton irradiation sequence by means of a train of spin rotation operators, the overall effect at the end of the cycle being calculated by explicit matrix multiplication. The offset dependence of this proton response then determines the residual splitting of the carbon-13 resonance and hence the effectiveness of the decoupling. A particular virtue of this treatment is that it provides a simple mechanism for testing new decoupling sequences by computer simulation, and it acts as a guide to the intuitive approach. The principal criteria for decoupling performance are (a) wide effective proton bandwidth for a given power dissipation, (b) residual splittings of carbon-13 small compared with the line width, (c) insensitivity to pulse length error or

994 citations

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Abstract: A new scheme for low-power broadband heteronuclear decoupling is described, based on the use of a composite radiofrequency pulse sequence 90°(+ X ) 180°(− X ) 270°(+ X ), incorporated into a repeated cycle or supercycle. Its principal attribute is that the residual splittings on the observed resonances (usually carbon-13) are very small (less than 0.1 Hz) for a wide range of decoupler offsets (approximately − B 2 ΔB B 2 ). Existing theories of broadband decoupling are used to calculate the effects of various possible instrumental imperfections on decoupling performance. It is concluded that spatial inhomogeneity of the B 2 field has a perceptible influence near the extremes of the decoupler bandwidth. Only 180° shifts of the radiofrequency phase are used, and the performance is remarkably insensitive to the exact setting of this phase shift. Any decoupler which employs a systematic modulation scheme runs the risk of introducing “cycling sidebands” into the observed spectrum; it is demonstrated that with the proposed sequence these sidebands are very weak, particularly when the decoupling cycle and the signal acquisition processes are not synchronized. As an illustration, the broadband-decoupled carbon-13 spectrum of an aniline derivative is recorded showing natural-abundance carbon-13 satellite signals but no appreciable cycling sidebands. The circuit for a practical implementation of this decoupling sequence is described.

720 citations

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TL;DR: A new series of broadband heteronuclear decoupling sequences, called the DIPSI sequences, which give better quality decouplings of protons from carbon-13 than previous sequences like WALTZ-16 when there is scalar coupling among the protons.

Abstract: We extend the idea of iterative schemes from the single-spin to the two-spin-case. As an application we derive a new series of broadband heteronuclear decoupling sequences, called the DIPSI sequences. They give better quality decoupling of protons from carbon-13 than previous sequences like WALTZ-16 when there is scalar coupling among the protons. In the absence of such coupling, the DIPSI sequences offer the same high standard of performance as WALTZ-16, but over somewhat smaller bandwidths.

719 citations