In this paper,the dielectric barrier discharge fingerprint acquisition technique isintroduced.The filament discharge phenomena were observed in the process of fingerprint ac-quisition.The filament discharge reduced the quality of fingerprint images.Obviously,it wasnecessary to eliminate streamer discharges in order to get good fingerprint images.The streamerdischarge was considered to be the cause of the filament discharge in the experiment.The rela-tionship between the critical electric field and the discharge gap was calculated with the Raether'smodel of streamer discharge.The calculated results and our experiment proved that it would bedifficult for the streamer discharge to occur when the discharge gap was narrow.With a narrowdischarge gap,the discharge was homogeneous,and the fingerprint images were clear and largein area.The images obtained in the experiment are very suitable for fingerprint identification asthey contain more information.
Using a unipolar pulse with the rise time and the pulse duration in the order ofmicrosecond as the primary pulse,a nanosecond pulse with the repetitive frequency of severalkilohertz is generated by a spark gap switch.By varying both the inter-pulse duration and thepulse frequency,the voltage recovery rate of the spark gap switch is investigated at differentworking conditions such as the gas pressure,the gas composition as well as the bias voltage.Theresults reveal that either increase in gas pressure or addition of SF6 to the air can increase thevoltage recovery rate.The effect of gas composition on the voltage recovery rate is discussed basedon the transferring and distribution of the residual space charges.The repetitive nanosecond pulsesource is also applied to the generation of large volume,and the discharge currents are measuredto investigate the effect of pulse repetition rate on the large volume streamer discharge.
A Rogowski coil is developed to detect the nanosecond pulse signals of the dischargecurrent with a wide bandwidth of 800 kHz to 106 MHz and high sensitivity of 2.22 V/A. Perfor-mance tests show that the Rogowski coil has both excellent dynamic and static characteristics.Calibrating results and the comparison between the standard current shunt and the developed Ro-gowski coil for the measurement of nanosecond discharge pulses demonstrate that the developedRogowski coil can reproduce the actual waveform of the discharge current accurately.
