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Electron paramagnetic resonance (EPR) is a powerful spectroscopic technique that allows direct detection and characterization of radicals containing unpaired electron(s). The development of portable, low-power EPR sensing modalities has the potential to significantly expand the utility of EPR in a broad range of fields, ranging from basic science to practical applications such as point-of-care diagnostics. The two major methodologies of EPR are continuous-wave (CW) EPR, where the frequency or field is swept with a constant excitation, and pulse EPR, where short pulses induce a transient signal. In this work, we present the first realization of a fully integrated pulse EPR spectrometer on-chip. The spectrometer utilizes a subharmonic direct-conversion architecture that enables an on-chip oscillator to be used as a dual-mode EPR sensing cell, capable of both CW and pulse-mode operation. An on-chip reference oscillator is used to injection-lock the sensor to form pulses and also to downconvert the pulse EPR signal. A proof-of-concept spectrometer IC with two independent sensing cells is presented, which achieves a pulse sensitivity of 4.6 x 10
Sun et al. (Fri,) studied this question.