250 MHz passive Q-modulator for reflection resonators.

A simple scheme for dynamically switching the quality factor, Q, of a Loop-Gap Resonator (LGR); working at 250 MHz is presented. The addition of this Q-modulator resulted in 30% improvement in Electron Paramagnetic Resonance imager signal-to-noise ratio. During pulse excitation, this scheme lowered the Q, while higher Q was obtained during signal detection. These conditions favored the image acquisition. The Q-modulator is passive; the transition between different states was actuated by the radio frequency power itself.