Magnet resolution

Instrumentation is appropriately different for the wide line case. The demands on magnet resolution and stability are reduced but those on data acquisition and transmitter and receiver recovery are increased. While most high resolution FT systems use digitizers that can digitize at a maximum rate of 50 kHz or less, a MHz or greater rate may be required for the spectra of solids. 

The quadripolar spectrometers whose resolution is limited to about 2000 are of simpler design than the magnetic sectors and are less costly. They are often used in conjunction with gas chromatography (see section 3.3) for purposes of identification. 

Brown, J.K. and W.R. Ladner Jr (1960), Distribution in coallike materials by high-resolution nuclear magnetic resonance spectroscopy . Fuel, Vol. 39, p. 87. 

A SQUID [2] provides two basic advantages for measuring small variations in the magnetic field caused by cracks [3-7]. First, its unsurpassed field sensitivity is independent of frequency and thus dc and ac fields can be measured with an resolution of better than IpT/VHz. Secondly, the operation of the SQUID in a flux locked loop can provide a more than sufficient dynamic range of up to 160 dB/VHz in a shielded environment, and about 140 dB/>/Hz in unshielded environment [8]. 

Sensitive parameters are necessary to compare several high resolution magnetic field sensors. Such parameters can be found with methods of signal theory for LTI-systems. The following chapter explains characteristic functions and operations of the signal analysis for linear local invariant systems and their use in non-destructive testing. 

So, a comparison of different types of magnetic field sensors is possible by using the impulse response function. High amplitude and small width of this bell-formed function represent a high local resolution and a high signal-to-noise-characteristic of a sensor system. On the other hand the impulse response can be used for calculation of an unknown output. In a next step it will be shown a solution of an inverse eddy-current testing problem. 

Main system parameters are shown in table 1. The fine field resolution is important. When operating in an unshielded space, however, at least such important is the high common mode rejection and the gradient rejection in order to suppress parasitic magnetic fields. 

Figure Bl.l 1.2 represents the essential components of a modem high-resolution NMR spectrometer, suitable for studies of dissolved samples. The magnet has a superconducting coil in a bath of liquid Fie, jacketed by...

Motion, and in particular diffiision, causes a further limit to resolution [14,15]. First, there is a physical limitation caused by spins diflfiising into adjacent voxels durmg the acquisition of a transient. For water containing samples at room temperature the optimal resolution on these grounds is about 5 pm. However, as will be seen in subsequent sections, difhision of nuclei in a magnetic field gradient causes an additional... 

Ahn C B and Cho Z H 1989 A generalized formulation of diffusion effects in pm resolution nuclear magnetic-resonance imaging Med. Rhys. 16 22-8... 

The low MW power levels conuuonly employed in TREPR spectroscopy do not require any precautions to avoid detector overload and, therefore, the fiill time development of the transient magnetization is obtained undiminished by any MW detection deadtime. (3) Standard CW EPR equipment can be used for TREPR requiring only moderate efforts to adapt the MW detection part of the spectrometer for the observation of the transient response to a pulsed light excitation with high time resolution. (4) TREPR spectroscopy proved to be a suitable teclmique for observing a variety of spin coherence phenomena, such as transient nutations [16], quantum beats [17] and nuclear modulations [18], that have been usefi.il to interpret EPR data on light-mduced spm-correlated radical pairs. 

Even for a single radical tire spectral resolution can be enlianced for disordered solid samples if the inliomogeneous linewidth is dominated by iimesolved hyperfme interactions. Whereas the hyperfme line broadening is not field dependent, tire anisotropic g-matrix contribution scales linearly with the external field. Thus, if the magnetic field is large enough, i.e. when the condition... 

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