Parallel resonant radio frequency magnetic probe tuned by symmetric capacitor

This paper provides a comparative analysis of signal amplification principles between series and parallel radio frequency (RF) magnetic probes, underscoring the superior performance of the parallel configuration in measuring time-varying magnetic fields within RF plasma environments. To address inherent limitations of conventional parallel RF probes, particularly electrical asymmetry in compensation capacitors, an enhanced design incorporating a fully symmetric variable capacitor is proposed. Experimental results demonstrate that the upgraded probe amplifies differential mode (DM) signals from less than 300 mV to 1.2 V at 13.56 MHz while suppressing common mode (CM) signals below 700 μV. The fully symmetric variable capacitor design not only resolves thermal hazards from high-current conditions in series LC circuits but also enhances the probe's signal amplification capability across a broadband range, while achieving significant CM signal suppression through its symmetric architecture.