Magnetic field modulation

Considerations of the signal-to-noise ratio usually dictate the use of the technique of narrow-banding in nuclear resonance. The modulation magnetic field is reduced to small amplitude compared to the resonance line width as shown in Fig. 3. 

Fig. 28 Snapshot of shape change of a magnetoelast due to modulated magnetic field. The frequency of the field is 40 Hz...

Synchrotron (ondulator) sources are based on the bremsstrahlung radiation of the relativistic electrons in continuous magnetic fields (synchrotron sources) and space-time-modulated magnetic fields (ondulator sources). 

The importance of the generalized susceptibility function xi ) in the theory of magnetism in metals was discussed by many authors (see the review by Herring, 1966). Crudely speaking, xiq) is the approximate response function of the band electrons to a sinusoidally modulated magnetic field. The true response function contains the dipole matrix elements, but if they are approximated as constant or a simple function of q, the simple form of xi ) in eq. (3.69) follows. 

Hanna, T.M., Kohler, T, and Burnett, K., Association of molecules using a resonantly modulated magnetic field, Phys. Rev. A, 75, 013606, 2007. 

An interesting property of super paramagnetic systems is that they can be heated by periodically modulated magnetic fields. This feature allows drug release to be induced by an external stimulus. 

Flow which fluctuates with time, such as pulsating flow in arteries, is more difficult to experimentally quantify than steady-state motion because phase encoding of spatial coordinate(s) and/or velocity requires the acquisition of a series of transients. Then a different velocity is detected in each transient. Hence the phase-twist caused by the motion in the presence of magnetic field gradients varies from transient to transient. However if the motion is periodic, e.g., v(r,t)=VQsin (n t +( )q] with a spatially varying amplitude Vq=Vq(/-), a pulsation frequency co =co (r) and an arbitrary phase ( )q, the phase modulation of the acquired data set is described as follows ... 

Figure Bl.15.5. Effect of small-amplitude 100 kHz field modulation on the detector output current. The static magnetic field is modulated between the limits and The corresponding detector current varies between the limits 1 and/. The upper diagram shows the recorded 100 kHz signal as a fiinction of B. After [3].

Microwave power and its effect on the electrode/electrolyte interface, 439 Microwave region, Hall experiments, 453 Microwave spectroscopy, intensity modulated photo currents, 508 Microwave transients for nano crystalline desensitized cells, 514 Microwave transmission, as a function of magnetic field, 515 Minority carriers... 

Tjandra, N., Bax, A. Measurement of dipolar contributions to /ch splittings from magnetic-field dependence of J modulation in two-dimensional NMR spectra./. Magn. Reson. 1997, 124, 512-515. 

The essence of the DDIF method is to first establish a spin magnetization modulation that follows the spatial variation of the internal magnetic field within the individual pore. Such modulation is created by allowing spins to precess in the internal magnetic field. Then the diffusion-driven time-evolution (often decay) of such a modulation is monitored through a series of signal measurements at various evolution times tD. The time constant of this decay corresponds to the diffusion time of a molecule (or spin) across the pore and thus is a direct measure of the pore size. 

---