Date of Award

Spring 2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical and Computer Engineering

Committee Director

Shu Xiao

Committee Member

Shirshak K. Dhali

Committee Member

Chunqi Jiang

Call Number for Print

Special Collections LD4331.E55 R3555 2014

Abstract

Bipolar pulse generation has been studied using transmission line technology, which was mainly used for monopolar pulse generation. In this thesis, low impedance, high current, nanosecond pulse generators were designed, constructed and tested. Five transmission lines were connected in parallel, so the impedance was 10 n. The transmission lines were switched by a spark gap switch operated in air. The closing of the switch creates a matched condition on one side of the transmission lines and a short circuit on the other side of the transmission lines. When the transmission lines are precharged, one of the two waves in opposite directions propagating towards the matched load will result in a square pulse and the other wave reflected at short side will be negative in polarity, forming a bipolar pulse. Such an ideal description was found to be consistent with the actual experimental results for long nanosecond pulses such as 300+ 300ns, but was not the case for short nanosecond pulse durations, such as 5+5 ns. Finite rise time, transition from one polarity to the other, prolonged decay time, unequal amplitude of pulses, and significant tails were typically recorded in the pulses. The discrepancy is mostly caused by the parasitic inductance of the switch, or the finite loop length in the configuration of the cable connector. To alleviate the distortion of the pulses, the impedance of the transmission line can be increased. The inductance in our current configuration due to the finite current loop cannot be reduced due to the limited space. Biological testing of the bipolar pulses have shown that bipolar pulses are not effective in killing the cells, and the monopolar pulses with half of the pulse duration and energy are more effective in causing cell death. The modeling using PSPICE has shown that the membrane voltage charged by monopolar pulses can stay orders of magnitude as long as the pulse duration, but the membrane voltage charged by bipolar pulses is only stays as long as the pulse duration. The biological results suggest the effects induced by nanosecond pulses are reversible and energy-independent.

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DOI

10.25777/jy9q-e029

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