Improving a low frequency EPR spectrometer using field-programmable gate array enabled direct digital detection

Abstract

Field-programmable gate array (FPGA) enabled direct digital detection (DDD) at higher frequencies is becoming increasingly available and popular due to the high-speed real-time signal processing. Consequently, it is opening up new possibilities for digital rather than analog demodulation, filtering, quadrature detection, and general signal processing that can reduce the spectrometer noise associated with thermal drift, aging, and layout of the equivalent analog detection chain. This article presents the result of a comparison of the low-frequency electron paramagnetic resonance (LFEPR) signal-to-noise ratio for a DPPH standard on the electron paramagnetic resonance (EPR) mobile universal surface explorer (MOUSE) by two signal detection schemes. The first utilized the classic analog detection and demodulation scheme of a LFEPR spectrometer and the second utilized the Zurich Instruments ultra-high frequency lock-in (UHFLI) amplifier, which replaces most of the analog components in the LFEPR spectrometer. The UHFLI spectrometer configuration improved the signal-to-noise ratio by a factor of two, reduced the baseline drift to one eighteenth, reduced the instrument volume by 70 %, and reduced the instrument weight by 50 % compared to the values with the classic analog system.