Highly tunable cryogenic resonance circuit for radio frequency magnetic field generation using in situ switch-bank...

This study presents a cryogenic resonant radio frequency (RF) transmitter coil design for magnetic field generation that utilizes electromechanical switches to match and tune the resonance frequency with capacitor banks in situ. The design enables magnetic field generation at any frequency across a wide frequency range of 25-140 MHz (560% tuning range) while operating at 1.5 K. Magnetic field generation efficiencies ranged from 10 to 15 μT/mW up to 70 MHz using a coil volume of 5.4 cm3. An average loaded Q-factor of ∼50 was achieved in the lower frequency range, with a gradual performance degradation observed toward higher frequencies. The circuit design is discussed to outline the main design choices, followed by results on circuit characteristics, tunability, and magnetic field generation efficiency. By mapping usable configurations at cryogenic temperatures, we show that overlapping resonances enabled by capacitor banks permit magnetic field generation at any frequency within the range of interest. This is achieved by allowing for slight detuning of the RF drive to bridge the gaps between discrete configurations. The use of capacitor banks also enables selection of the operating range, making the system highly flexible.