Title: Narrow cavity low cost EPR spectrometer

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Abstract: An EPR spectrometer of high sensitivity and low cost particularly adapted for studying liquid samples of high dielectric loss such as water. A microwave cavity is employed oscillating either in the rectangular TE.sub.lOn or cylindrical TM.sub.lmO mode, where l, m, and n are integers. The cavity dimension corresponding to zero index is small, of the order of 2 mm for a spectrometer operating at 10 GHz, resulting in (1) the cavity frequency is unchanged (2) the cavity Q is unusually low (3) the cavity filling factor for 1 mm inner diameter cylindrical sample tubes is unusually high. The product of the Q and the filling factor, which product determines the EPR sensitivity, is as high a value as is found in larger high Q cavities. The requisite magnet gap is unusually small, thus greatly lowering the weight and cost of the magnet required. Rather noisy inexpensive low quality microwave sources can be used without degradation in sensitivity because of the low Q. Low Q lessens demodulation of microwave oscillator FM noise or enhancement of AM noise. An alternative aqueous cell of flat cuvette shape can be used oriented perpendicular to the cavity dimension corresponding to the zero index yielding improved sensitivity.


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