Date of Award

Fall 2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical Engineering

Committee Director

Shu Xiao

Committee Member

Karl H. Schoenbach

Committee Member

Shirshak Dhali

Call Number for Print

Special Collections LD4331.E55 N338 2012

Abstract

The research of bioelectrics has expanded to subnanosecond pulse region and entered a new domain of biophysics of cell interaction with ultra-short and intense electric fields. As subnanosecond pulses may be delivered by antennas to the human body and is very attractive to the medical community, the study of subnanosecond pulse effects calls for exposure systems for both cells and tissues. Two systems were designed in the scope of this thesis, used for cells and tissues respectively. The exposure system designed for cell exposure is a cuvette consisting of two parallel aluminum gaps. This cuvette is placed in a coaxial transmission line which is terminated by a conical resistor array. The capacitance of the cuvette was designed to be on the order of 1-2 pf, so the risetime of the incoming pulses can be kept down to 100 ps for a 50 n transmission line. The electrode gap distance was designed to millimeter range in order to create a high intensity electric field. The important design issue is to increase the voltage holdoff of the terminating resistors. To serve that purpose, a number of lumped resistors were connected in series and further in parallel to form a resistor array, so the coaxial transmission line was designed with an intergap distance of 0.652 inches. A conical transmission was designed for allowing for a transition of a small-diameter dielectric coaxial cable to a large air-filled coaxial transmission line. Subnanosecond pulses (200 ps) with maximum voltage of 20 kV were delivered to the exposure system, and no resistor surface flashover was observed. The measurement of the reflected pulse amplitude shows a reflection coefficient of 27%. The simulation of the electric field using CST Microwave studio shows an average field of 450 V/m for a voltage of l V. The second exposure system designed for tissue exposure is a horn, which connects with a coaxial cable. From the center conductor of the coaxial cable extends a conical plate. The outer shield of the coaxial cable is mounted into an upside down pyramid. The other end of the conical plate is connected to a 50 n resistor, which further connects to the grounded pyramid, providing low frequency termination. The subnanosecond pulse energy is guided through the conical plate, acting like an antenna. The tissue sample can be placed inside the horn on top of a microwave-transparent Styrofoam. The measurement shows such a system has a reflection of 50%. For a location that is 2.5 cm from the center feed, the simulation of the electric field shows a field of 40 V/m for a voltage of I V.

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DOI

10.25777/6dsr-5f38

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