A broadband pulsed radio frequency electron paramagnetic resonance spectrometer for biological applications

A time-domain radio frequency (rf) electron paramagnetic resonance (EPR) spectrometer/imager (EPRI) capable of detecting and imaging free radicals in biological objects is described. The magnetic field was 10 mT which corresponds to a resonance frequency of 300 MHz for paramagnetic species. Short pulses of 20–70 ns from the signal generator, with rise times of less than 4 ns, were generated using high speed gates, which after amplification to 283 Vpp, were deposited into a resonator containing the object of interest. Cylindrical resonators containing parallel loops at uniform spacing were used for imaging experiments. The resonators were maintained at the resonant frequency by tuning and matching capacitors. A parallel resistor and overcoupled circuit was used to achieve Q values in the range 20–30. The transmit and receive arms were isolated using a transmit/receive diplexer. The dead time following the trailing edge of the pulse was about 450 ns. The first stage of the receive arm contained a low noise,...

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