GENERAL-METHOD FOR ADJUSTING THE QUALITY FACTOR OF EPR RESONATORS

Instrumentation for remote control of the unloaded quality factor, Q(0 ), of a loop-gap resonator is described. The value of Q(0) can be lowe red by weak inductive coupling of the resonator to a loop of wire that contains a carbon resistor. Replacement of the resistor by a PIN diod e permits remote control. Theoretical analysis and experiments are car ried out in a context of electron paramagnetic resonance (EPR) spectro scopy at X band. Equivalent circuits are solved numerically and predic ted performance confirmed experimentally. Two applications are demonst rated: (a) superfine control of critical coupling of the incoming tran smission line to the resonator in excess of -80 dB, and (b) dynamic Q spoiling for reduction of the dead time after a microwave pulse, Possi ble degradation of EPR system performance by shot noise from the PIN d iode is considered. Scant literature suggests that it is very low, and noise from this source could not be detected experimentally. (C) 1995 American Institute of Physics.