Date of Award

Summer 2004

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical Engineering

Committee Director

Ravindra P. Joshi

Committee Member

Linda L. Vahala

Committee Member

Mournir Laroussi

Call Number for Print

LD4331.E55 C4336 2004

Abstract

Numerical simulations of electrical stimulation of frog gastrocnemius muscles have been carried out for pulse durations in the nanosecond regime. There are a number of potential advantages in using ultra-short pulses for neural stimulation, and no previous electro-stimulation work in the sub-microsecond regime has been reported. A timedependent, three-dimensional analysis model was developed and implemented for three distinct situations: (i) direct stimulation via electrode contact, (ii) indirect excitation based on electrodes immersed in a saline-filled bath, and (iii) remote electromagnetic stimulation through vacuum. The simulations yielded strength-dm ation (S-D) curves with pulse durations as short as 5 ns. Good agreement between the model predictions and experimental measurements was obtained. For example, with direct contact a peak current of about 30 A was predicted for the shortest pulse; the measured value was 34 A. The modeling also led to a demonstration of the non-thermal nature of electro-stimulation with nanosecond pulses, even with an applied voltage as high as 5 kV. Calculations of the S-D curves for both direct and indirect stimulation yielded a good match with the available experimental data. The verified model was used to investigate the effects of electrode placement and pulse shape, and a new anode-cathode-anode electrode scheme was developed for direct stimulation. A time constant of 160 μs was estimated for frog tissue stimulation; this value is indicative of a nerve-based response. Furthermore, it was shown quantitatively that inhomogeneities in the nerve geometry and size can affect the S-D curve. For electrical stimulation, the greatest potential for muscle twitching occurs at boundaries and within regions that have internal non-uniformity of nerve fiber size or potential distribution. For electromagnetic stimulation, the simulations demonstrated that the electromagnetic wave could not penetrate the muscle very effectively. However, nonuniformity of electric field distribution was observed, and this is a desirable pre-requisite for enhancing the activating function for a bio-response.

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DOI

10.25777/t5wd-qc42

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