Microwave Probe Based on an Inverted Microstrip Line for Broadband Electron Paramagnetic Resonance Spectroscopy

This work presents a broadband inverted microstrip line (IMSL) as a microwave probe for electron paramagnetic resonance (EPR) spectroscopy, a technique used to detect unpaired electron spins in biological and chemical samples. The IMSL geometry enables sample placement in the most homogeneous region of the microwave magnetic field, overcoming limitations of standard coplanar and microstrip probes. Full-wave electromagnetic simulations and S-parameter measurements confirm broadband operation up to 67 GHz. EPR experiments show position-independent signal amplitude, reflecting substantially improved field homogeneity. The IMSL architecture therefore offers a compact, fabrication-efficient platform for broadband EPR sensing in biological and healthcare applications.