Twin LC Resonator System for EPR Measurements Operating at Radio-Frequency

Abstract

Two LC resonant circuits resonating at the same frequency (245 MHz) faced each other with reverse polarity (twin electron paramagnetic resonance (EPR) resonator). For the inductor of the LC circuit, a square single-turn one-loop coil (width, 38 mm) was fabricated. Each LC circuit was independently tuned using mechanical variable capacitors. A cylindrical phantom (diameter, 25 mm) including a 1 mM nitroxide radical physiological saline solution was located at the center of two coils (distance between these coils, 50 mm). Two resonant frequencies (the lower and the higher ones) were observed at each LC circuit of the twin EPR resonator with termination of the other LC circuit. The lower resonant frequency alone was observed when the powers from two LC circuits of the twin EPR resonator were combined by a 180° combiner. On the other hand, the higher frequency alone was observed when they were combined by a 0° combiner. EPR signals could be obtained using the 180° combiner (lower frequency) but not the 0° combiner (higher frequency).