A Resonated Coil Driver for Rapid Scan EPR Richard W. Quine, 1 Deborah G. Mitchell, 2 Mark Tseitlin, 2 Sandra S. Eaton, 2 Gareth R. Eaton 2 1 School of Engineering and Computer Science, University of Denver, Denver, CO 80208 2 Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208 ABSTRACT: A resonated coil driver designed for rapid scan electron paramagnetic resonance (EPR) is described. Rapid scan EPR requires larger magnetic field coils and a more powerful magnetic field modulation than those designed for conventional continu- ous wave EPR. There are two advantages of a resonated coil driver: i) by resonating the scan coils the reactive components are removed, which allows the coils to be driven with much lower voltages, and ii) by resonating the coils a near-perfect sinusoidal scan is ensured. Performance of the coil driver is improved when Litz wire coils are used. With coil diameters between 3 and 3.5 inches, sweeps can be generated with widths up to about 80 G peak-to-peak and frequencies up to about 150 kHz, which permits sweep rates of more than 8 MG/s. The magnetic field is uniform over the sample length of a Bruker dielectric resonator. Enough detail has been presented for other laboratories to implement this design to perform rapid scan EPR. Ó 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 41B: 95–110, 2012 KEY WORDS: resonated circuit; rapid scan; sinusoidal field scan INTRODUCTION The design of the resonated coil driver is motivated by recent studies in our laboratory that demonstrate the advantages of rapid scan electron paramagnetic resonance (EPR) relative to conventional continuous wave (CW) EPR (1–3). The background literature on rapid scan NMR and EPR is discussed in Ref. 3. In conventional CW EPR, the signal is obtained by phase-sensitive detection at the magnetic field modulation frequency. In rapid scan EPR the signal is detected directly with a double balanced mixer, and phase-sensitive detection at a modulation fre- quency is not used (4). Rapid scan can be performed with magnetic field or microwave frequency sweep (5–7). Unless the resonator bandwidth is large rela- tive to the spectral range of interest, in frequency units, magnetic field scans are advantageous relative to microwave frequency scans. The magnetic field can be scanned at rates ranging from very slow to very fast relative to relaxation times. Instrumentally, the difference is in the scan coil driver and the detec- tor bandwidth. When the scan is slow relative to relaxation times, the final spectrum is detected (8). When the scan is fast, passage effects (9) in the relaxation-dependent spin response require deconvo- lution in postacquisition processing to obtain the slow-scan spectrum (3, 4, 10). This is a new regime for EPR, and new methodologies, instrumentation, and applications are being developed (11). We previously described a linear rapid scan driver (12). Because of hardware constraints, sinusoidal scans with resonated coils can be faster than linear scans. However, until recently, methods were not available to deconvolve the passage effects from rapid sinusoidal scans. Tseitlin et al. described and demonstrated a general approach to Fourier deconvo- lution to recover the slow-scan lineshape from Received 12 August 2012; revised 4 September 2012; accepted 18 September 2012 Correspondence to: Gareth R. Eaton; E-mail: geaton@du.edu Concepts in Magnetic Resonance Part B (Magnetic Resonance Engineering), Vol. 41B(4) 95–110 (2012) Published online in Wiley Online Library (www.interscience.wiley. com). DOI 10.1002/cmr.b.21222 Ó 2012 Wiley Periodicals, Inc. 95