Digital detection and processing of multiple quadrature harmonics for EPR spectroscopy

Area of Science:

• Spectroscopy
• Electronics
• Signal Processing

Background:

• Electron Paramagnetic Resonance (EPR) spectroscopy is a powerful technique for studying materials with unpaired electrons.
• Traditional EPR receivers face limitations due to noise and nonlinearity from analog components.
• Accurate signal estimation is crucial for obtaining meaningful EPR data.

Purpose of the Study:

• To develop and report a novel quadrature digital receiver for L-band EPR spectroscopy.
• To present an associated signal estimation procedure for enhanced data acquisition and processing.
• To demonstrate the advantages of digital heterodyne processing and quadrature detection in EPR.

Main Methods:

• Implementation of a high-speed dual-channel analog-to-digital converter for direct digital down-conversion.
• Utilizing digital capture of the microwave reference signal for heterodyne processing, avoiding analog mixers.
• Development of a noise model for oscillator phase noise and a maximum-likelihood estimator for parameter estimation.
• Application of a convergent iterative algorithm for joint processing of in-phase and out-of-phase data.

Main Results:

• The digital receiver successfully acquires and processes multiple harmonics simultaneously.
• The proposed method avoids noise and nonlinearity issues inherent in analog mixers.
• Cramér-Rao bound analysis and simulations show a significant reduction in linewidth estimation error with quadrature detection.
• The system demonstrates robustness against varying levels of phase noise.

Conclusions:

• The developed quadrature digital receiver and estimation procedure offer a significant advancement for L-band EPR spectroscopy.
• This digital approach enhances accuracy and reduces errors in linewidth estimation, particularly in the presence of phase noise.
• The findings pave the way for more precise and reliable EPR measurements.