Development of a resonator with automatic tuning and coupling capability to minimize sample motion noise for in vivo EPR spectroscopy

EPR spectroscopy has been applied to measure free radicals in vivo; however respiratory, cardiac, and other movements of Living animals are a major so urce of noise and spectral distortion. Sample motions result in changes in resonator frequency, Q, and coupling. These instabilities limit the applica tions that can be performed and the quality of data that can be obtained. T herefore, it is of great importance to develop resonators with automatic tu ning and automatic coupling capability. We report the development of automa tic tuning and automatic coupling provisions for a 750-MHz transversely ori ented electric field reentrant resonator using two electronically tunable h igh Q hyperabrupt varactor diodes and feedback loops. In both moving phanto ms and living mice, these automatic coupling control and automatic tuning c ontrol provisions resulted in an 8- to 10-fold increase in signal-to-noise ratio. (C) 2001 Academic Press.