I recently read again through Feher’s article on EPR sensitivity. After 61 years this article is still very important when building instrumentation for EPR or DNP. It explains many EPR concepts and the relevant instrumentation using simple, easy to understand concepts.
I must read for everyone working in the field of magnetic resonance instrumentation.
Feher, G. “Sensitivity Considerations in Microwave Paramagnetic Resonance Absorption Techniques.” Bell System Technical Journal 36, no. 2 (March 1957): 449–84.
https://doi.org/10.1002/j.1538-7305.1957.tb02406.x.
Within the past few years the field of paramagnetic resonance absorption has become an important tool in physical and chemical research. In many ways its usefulness is limited by the sensitivity of the experimental setup. A typical example is the study of semiconductors in which case one would like to investigate as small a number of impurities as possible. It is the purpose of this paper to analyze the sensitivity limits of several experimental set ups under different operating conditions. This was done in the hope that an understanding of these limitations would put one in a better position to design a high sensitivity resonance experiment. In the last section the performance of the different experimental arrangements is tested. The agreement obtained with the predicted performance proves the essential validity of the analysis. This paper is primarily for experimental physicists confronted withe the problem of setting up a high sensitivity spectrometer.