Using of Digital Demodulation of Multiharmonic Overmodulated EPR Signals to Improve EPR Oximetry Reliability |
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Authors: | Mark P Tseitlin and O A Tseitlin |
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Institution: | (1) Kazan Physical–Technical Institute, Russian Academy of Sciences, Kazan, Russian Federation |
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Abstract: | Overmodulation of electron paramagnetic resonance (EPR) lines is routinely used in EPR oximetry in order to increase the signal-to-noise
ratio and thus to improve the accuracy with which the line width of a spin probe can be measured. For a known probe type,
the line width is easily translated into the oxygen partial pressure. A standard EPR spectrometer uses the analog phase-sensitive
detection (PSD) to demodulate the EPR signal. PSD imposes the restriction that only one spectrum is measured at a time, which
is normally the first-harmonic EPR line. Information about EPR signals centered at the other harmonics of the modulation frequency
is irreversibly destroyed by PSD. The question is raised whether this information can be utilized for EPR oximetry, for overmodulation
enhances the second- and the other harmonic spectra, so that they approach the first-harmonic spectrum in intensity. To find
an answer, numerical simulation and experimental measurements have been conducted. The experiment required modification of
the detection scheme, so that all EPR-related information in the overmodulated signal is preserved. This permits measuring
of the multiharmonic EPR spectrum, which when fitted to a set of the corresponding theoretical lines produces more accurate
results in comparison with the standard overmodulation method. |
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