The period variation of a relaxation oscillator due to a low intensity microwave field

The oscillations period increase of a discharge tube relaxation oscillator placed in a low intensity microwave field is reported. The experimental setup consists of a miniature neon lamp inserted into a relaxation oscillator circuit. The microwave field is generated using a low power transmitter operating at 2.412 GHz. The average period of the relaxation oscillations as a function of the dc supply voltage has been measured in two cases, namely, in the presence of microwave field and in the absence of the microwave field, respectively. The oscillation period has been measured as the time interval between two consecutive flashes produced by the neon lamp and observed using a photocell. The maximum relative variation of the oscillations period due to the microwave field was about 13% at 10 mW transmission power. This effect can be used to detect the microwave fields. A similar principle has been described to detect the optogalvanic effect. Variation of the breakdown voltage and minimum voltage necessary to maintain the discharge as an effect of the microwave field is discussed.