Spin polarized beams are an essential tool in the study of nuclear physics using particle accelerators. Particle accelerators can produce spin polarized beams, but a technology is needed to continuously monitor, in real time and non-invasively, the beam's polarization direction and quality. Without this capability, there is no way to automate polarization quality optimization. The ring-coupled cavity resonator provides a mechanism to enhance the interaction between a cavity resonator and the spin of passing particles, and provides a method to determine and monitor, in real time and non-invasively, beam magnetization and longitudinal spin polarization direction and quality.