No abstract

No abstract

No abstract

Abstract:The paper discusses mathematical tools to evaluate novel noise spectroscopy based analysis and describes, via physical similarity, the mathematical models expressing the quantitative character of the modeled task. Using the Stefan-Boltzmann law, the authors indicate finding the spectral density of the radiated power of a hemisphere, and, for the selected frequency interval and temperature, they compare the simplified models with the expression of noise spectral density according to the Johnson-Nyquist formula or Nyquist's expression of the function of spectral density based on a derivation of Planck's law. The related measurements and evaluations, together with analyses of the noise spectroscopy of periodic resonant structures, are also outlined in the given context.

The paper is concerned with a comparison of the properties of RF coils of three configurations for MRI measurements on small animals. In comparison with the classical saddle coil the proposed modification of slotted-tube coil exhibits identical homogeneity of B 1 field in a larger space. The parallel-plate coil has a satisfactory homogeneity of B 1 field over the whole internal space. The signal-to-noise ratio measured for all three coils is roughly the same and is given by the magnitude of RF pre-amplifier noise. As the slotted-tube and parallel-plate coils have a lower inductance compared with the saddle coil, they can be tuned to resonance on the 200 MHz frequency even at larger dimensions. The results show that the parallel-plate coil has very good properties for the measurement of small animals.