This study presents methods for understanding, modeling and control of tele-operated pneumatic actuators for rehabilitation in Magnetic Resonance Imaging (MRI). Pneumatic actuators have excellent MRI-compatibility as opposed to conventional electro-mechanical systems; however, the actuator and the system drivers cannot be co-located due to the MRI-compatibility requirements. The actuators are driven via long transmission lines, which affect the system dynamics significantly. Methods provided in this work produced accurate pressure estimation and control by accounting for the pressure dynamics in the lines, which has been neglected by previous work in this area. The effectiveness of the presented modeling and control methods were demonstrated on tele-operation test setups. This research also includes the design of necessary system components for the developed algorithms. An MRI-compatible optical sensor was developed for force feedback and its design was analyzed for high precision. Directions and opportunities for future research are discussed.

No description available.

published_or_final_version / Electrical Engineering / Doctoral / Doctor of Philosophy

No description available.

The general expressions for finding the network functions, e.g., the immittance and the scattering parameters, of a general, uniformly coupled n-line structure in an inhomogeneous medium are derived in terms of the normal mode parameters of the system. These are used to compute or to derive the explicit expressions for the elements of the immittance matrix in terms of normal mode parameters. The scattering parameters of a general non-symmetrical directional coupler with arbitrary terminations are derived in terms of the known scattering parameters with a specified set of terminations such as characteristic non-mode converting terminations. The formulation is quite general and can be applied to various coupled guided wave systems, including coupled microstrip lines, slot lines, comb lines, dielectric waveguides and various other uniformly coupled transmission systems. The results obtained are used to present the procedure to determine the optimum terminations for directional couplers and sensitivity of various multiports, including couplers, to changes in terminations. It is shown that the coupler performance can be optimized in terms of the terminating impedances. The analysis and design procedure for both symmetrical and nonsymmetrical four-port coupled structures consisting of the symmetrical three lines in an inhomogeneous medium such as microstrips are presented. Tables and charts for the design of three-line structure are based on the closed form expressions for the immittance parameters. The analysis and design procedure for open-circuited interdigital multiple coupled microstrip line structures for applications as wideband DC blocks and filters are also presented. As in the case of the other microstrip structures, the initial design is based on the TEM assumption and the final geometry is then determined by the exact computation of the frequency response of the two ports. For larger numbers of lines, the design is based on the equivalent even- and odd-mode parameters of the n-line system. For this case, the TEM design equations, derived in terms of even- and odd-mode impedances of a pair of lines, can be translated into a physical configuration by using published results on coupled lines. / Graduation date: 1983

Coplanar microstrip structures placed on dielectric substrates are used as high frequency electro-optic modulators. The method of lines, a mathematical technique for solving partial differential equations, has been applied to solve for the propagation characteristics of such a configuration. It has been determined that simple transmission line models are adequate to describe this system. The propagation characteristics are expressed in terms of the equivalent impedance and the phase velocity of the signal on the microstrip. In order to maximize the effective bandwidth of the modulator, the impedance is matched to that of the surrounding dielectric substrate, and the difference in the phase velocities of the two signals is minimized. The numerical technique developed here allows for the analysis of inhomogeneous dielectric substrates, so that trench structures for tuning the propagation characteristics to their desired values can be modelled. The numerical results for typical structures are presented, and suggest that the method of lines is a viable one for analyzing these modulator structures. / Graduation date: 1991

In this thesis a numerical technique to model general microstrip asymmetric and multiple step discontinuities is presented. The method is based on a magnetic wall waveguide model that is assumed to be valid for describing the electromagnetic fields associated with the microstrip line and in the vicinity of microstrip discontinuities. The fields are expanded in the uniform regions and the mode-matching method is applied at the discontinuities to analyze for the frequency dependent transmission properties of the multi ports. The generalized scattering matrix technique is used to model cascaded interacting discontinuities and is used to compute the properties of double-step and multi port structures. The generalized scattering matrix formulation takes into account the scattering phenomena of the dominant and all of the higher-order modes including evanescent ones. The validity of this model has been discussed extensively, and it is shown that the model can be used to describe the microstrip discontinuities with acceptable accuracy. The technique is applied (1) to study the transmission characteristics of asymmetric step discontinuities; (2) to design a filter for a desired frequency range using interacting asymmetric double step micros trip line; and (3) to design a new nominal 3db power devider of large bandwidth consisting of a three port rectangular patch. The techniques and models presented can be used in computer-aided analysis and design of such circuits. / Graduation date: 1993

Thesis (M.S. in Systems Engineering (Electronic Warfare))--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Atwater, Harry A. Second Reader: Janaswamy, Rama. "September 1990." Description based on title screen as viewed on December 29, 2009. DTIC Identifier(s): Suspended striplines, microstrip lines, equivalent circuits, program listings, theses. Author(s) subject terms: Suspended-microstrip line, step discontinuity, equivalent circuit model, step-change. Includes bibliographical references (p. 60). Also available in print.

Thesis--Ph. D., University of Hong Kong, 1979.

The studies of the designs on true-time-delay lines (TTDLs), n-bit digital phase shifters and wideband switched-line phase shifters using composite right/left-handed transmission-line (CRLH TL) unit cells are presented in this thesis. To simplify these designs, a symmetrical CRLH TL unit cell having equal input and output impedance is proposed. In the design of TDDLs, the symmetrical CRLH TL unit cell with higher time-delay efficiency helps achieve a size reduction of 67.9%, compared with the TTDL designed using right-handed transmission line (RH TL). The symmetrical CRLH TL unit cell is further modified to a compact CRLH TL unit cell to further reduce the size by 58%. For performances comparison, the TTDLs using the compact CRLH TL unit cells, symmetrical CRLH TL unit cells and RH TL are studied using computer simulation and measurement. Results show that the TTDLs using the compact CRLH TL unit cells can achieve much longer time delays. The TTDLs designed using CRLH TL unit cells have narrow bandwidths because CRLH TL unit cells have narrow bandwidths. In this thesis, a wideband unit cell obtained by rotating the CRLH TL unit cell by 900is proposed in the design of TTDLs. Simulation and measurement show that the TTDL using wideband unit cells can achieve a time delay about 3 times and 6 times longer than that of the periodic microstrip line (PML) and RH TL, respectively. A 2-bit, 3-bit and 6-bit phase shifters using symmetrical CRLH TL unit cells are designed using computer simulation. In these designs, positive-intrinsic-negative (PIN) diodes mounted on the fingers of the CRLH TL unit cells are used as switches to control the phase response at the output. Different phase shifts are achieved using different switching states determined by controlling bits. The phase shifters are fabricated and measured. Simulated and measured results agree very well. Power-handling capability is also analyzed using surface-current density on the CRLH TL unit cells. Results show that the phase shifters have much higher power-handling capabilities than that of the PIN diodes. A wideband 1800-switched-line phase shifter using symmetrical CRLH TL unit cell is proposed. The switched-line phase shifter employs a symmetrical CRLH TL unit cell as the reference arm and a RH TL as the delay arm to produce a constant phase shift across a wide frequency band. For comparison, a traditional 1800-switched-line phase shifter using RH TLs for both reference and delay arms is also designed. To reduce the size, the CRLH TL unit cell is realized using lump elements (LEs). Wideband 900-and 1800-switched-line phase shifters using LE-CRLH TL unit cells are studied and compared with the traditional 900-and 1800-switched-line phase shifters. Simulated and measured results show that the proposed designs using symmetrical CRLH TL unit cells and LE-CRLH TL unit cells have very constant phase shifts with smaller variations compared with the traditional designs. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy