Sample-accessible multi-resonance X-band EPR triple ring resonator

Micro-resonators downsize their resonating structures, reaching frequencies required for electron paramagnetic resonance (EPR) spectroscopy, thus allowing sensitive detection of mass-limited samples. Planar resonators provide accessibility of the sample space, allowing in situ and operando experiments for convenient characterization with access to environmental parameters such as UV radiation, gas and liquid flow, and better temperature gradient control. We report a novel triple-ring resonating structure that exploits the benefits of sample accessibility and its miniaturized structure. It offers three simultaneously operating X-band channels (8GHz to 11GHz) with a real-time accessible 50nL sample volume for each channel, with a maximum spin sensitivity of 1.18×10⁸ Spin/Hz^1/2. By cascading the ring resonators, we improve the quality factor of each resonance by reflecting and confining the electromagnetic energy by the neighboring rings. The Q-factor of the center resonance at 9.45GHz with the enhancement of 2 passive reflectors reaches 73. Three relative translations allow a wide range of tuning, matching, suppressing, and isolating the resonances. While the introduced resonator exhibits three resonances only, it can be readily upscaled to feature more resonances, thus opening the door to high-throughput parallel EPR spectroscopy.