Resonance gyromagnetic

Microwave Ferrites. Microwave devices employing ferrites make use of the nonreciprocal propagation characteristics that are close to or at a gyromagnetic-resonance frequency at ca 1—100 GHz. The most important devices are isolators and circulators (see Microwave technology). 

The precessional motion can be maintained by a suitable radio frequency field superimposed on the steady field. For example, in Fig. 9.38(b), when a steady field Hz is applied along the z axis and a radiofrequency field //,., is applied in the x-y plane and rotates in the same sense and at the same frequency as the precession, resonance occurs. Gyromagnetic resonance as outlined above is in principle the same as ferrimagnetic resonance referred to earlier (Section 9.3.1), except that in the former case the material is magnetically saturated by a strong applied field. In practice the steady field, which determines the Larmor frequency, is made up of the externally applied field, the demagnetizing field and the anisotropy field, and is termed the effective field He. Figure 9.39 shows the He values at which resonance occurs in some of the important communications and radar frequency bands. 

Unlike the case of the Faraday rotation isolator, even an elementary description of the operational principle of the circulator is not easy, involving as it does the dimensional resonance of the microwave field within the ferrite cylinder. In this context the word resonance does not signify gyromagnetic resonance but a standing-wave resonance determined by the dimensions of the... 

These internal modes can be individual movements which are easily detectable (for example, in the case of magnetic materials at high frequency there is a magnetic spin resonance called gyromagnetic resonance ). Many others (collective modes) should be noted, whether by physical intuition or by response calculation of heavily coupled systems (relaxation of magnetic domains at low frequencies wall relaxation ). Such collective modes are also observed in the case of heterogeneous materials based on conductive inclusions. They are due to capacitive effects and induced currents. 

The majority of double-resonance solid-state NMR experiments involving spin-1/2 nuclei use transfer of nuclear polarization via dipolar cross polarization (CP) to enhance polarization of the diluted spins S with small gyromagnetic ratio ys and significant longitudinal relaxation time T at the expense of abundant spins I with large y, and short 7 [215]. Typically, CP is used in combination with MAS, to eliminate the line broadening due to CS A, as well as with heteronuclear decoupling. To achieve the / S CP transfer, a (n/2)y pulse is applied at the I spin frequency,... 

The effect of deuteration, for the needs of sequence-specific resonance assignments using triple-resonance experiments, was first demonstrated by Bax and co-workers on the 19.7 kDa protein calcineurin B in 1993.56 By replacing the H spin with deuterium, the transverse relaxation time of 13C spin is increased by nearly an order of magnitude due to the 6.5 times smaller gyromagnetic ratio of 2H in comparison to in.52,56 Not surprisingly, deuteration was utilized for the aid of structure determination of several... 

In a conventional NMR instrument the resonant magnetic induction of a nuclide immersed in a field with magnetic induction B occurs at the Larmor frequency coi = jB, where y is the gyromagnetic ratio of the nuclide. Since the NMRD profiles cover several orders of magnitude of the field value B, they necessarily include sections with very low B values. 

The imaging of conversion within the fixed bed was achieved by using a distortionless enhancement by polarization transfer (DEPT) spectroscopy pulse sequence integrated into an imaging sequence, as shown in Fig. 44. In theory, a signal enhancement of up to a factor of 4 (/hZ/c 7i is the gyromagnetic ratio of nucleus i) can be achieved with DEPT. In this dual resonance experiment, initial excitation is on the H channel. Consequently, the repetition time for the DEPT experiment is constrained by Tih (< T lc) where Tn is the Ty relaxation time of... 

Since the microwave frequency and gyromagnetic ratio are constant, changes in the applied stress will result in a shift in the resonant magnetic field. Indeed, the shift equation is... 

From the gyromagnetic ratio we are able to calculate that the resonance frequency of the chlorine is 188.255 MHz. Therefore between the two nucleii there are 200 - 188.255 = 11.745 MHz. 

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