Abstract: A reverse magnetic field was added to a conventional ESR spectrometer in order to get a magnetic field scanning through zero, therefore the microwave signal of a sample at about zero field could be recorded. Two kinds of methods to add reverse magnetic field have been recommended, one is adding compensating Helmholtz coils, another is applying direct current to the rapid scan sweep coils of ESR spectrometer.

Key words: ESR spectrometer, Magnetic field scanning through zero, Low field microwave signal