Browsing by Author "Gianluca Lazzi, Committee Co-Chair"

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    The Architecture, Design, and Electromagnetic and Thermal Modeling of a Retinal Prosthesis to Benefit the Visually Impaired
    (2003-05-19) DeMarco, Stephen Christopher; Wesley Snyder, Committee Member; Griff Bilbro, Committee Member; Gianluca Lazzi, Committee Co-Chair; Wentai Liu, Committee Co-Chair
    This dissertation describes the design and study of a retinal prosthesis for individuals who have suffered loss of vision from degeneration of the outer retina. Retinitis pigmentosa and age-related macular degeneration lead to blindness through progressive loss of retinal photoreceptors. Experiments reveal that direct electrical stimulation of remaining ganglion cells in degenerate retina elicits visual percepts in blind RP/AMD patients. This motivates research toward the development of a retinal prosthesis system involving an implantable stimulator microchip to compensate the defective photoreceptors. Many prostheses do not reside fully inside the body, but consist of an implantable stimulation unit and an external unit. This underscores a need in the retinal prosthesis to deliver power and support high-speed bi-directional communication with the implant wirelessly. The current progress in the types of non-invasive connections to bio-implants is reviewed as it relates to the power and communication needs of prostheses. The extraocular unit is a hardware-reconfigurable system based on FPGA technology which produces real-time instructions for the implantable micro-stimulator IC. The current retinal stimulator IC is designed to provide electrical stimulation to the remaining ganglion cells of post-degenerative retina. Also described is a design technique to significantly reduce the on-chip area of the stimulus circuits. This yields more output channels per chip area, thereby raising the stimulation resolution. Temperature elevation in the eye and head tissues associated with the retinal prosthesis is studied. A high resolution 2D human head and eye model is developed at 0.25mm spatial resolution with associated dielectric and thermal properties suitable for numerical simulations. The Finite Difference Time domain method (FDTD) with material independent absorbing boundary conditions is used to predict the specific absorption rate (SAR) induced from electromagnetic exposure to wireless inductive telemetry with the implant. A detailed heating pattern in the eye tissues due to the SAR and power dissipation in the implanted stimulator is computed using a time-domain numerical implementation of the bioheat equation.
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    A Multi-Channel Wireless Implantable Neural Recording System
    (2009-04-27) Yin, Ming; Paul Franzon, Committee Member; Gianluca Lazzi, Committee Co-Chair; Maysam Ghovanloo, Committee Co-Chair; Kevin Gard, Committee Member; Xiaoyong Zheng, Committee Member; Donald Woodward, Committee Member
    ABSTRACT YIN, MING. A Multi-Channel Wireless Implantable Neural Recording System. (Under the direction of Dr. Maysam Ghovanloo). This dissertation presents a multi-channel implantable wireless neural recording (WINeR) system for electrophysiology and behavioral neuroscience research applications. This system consists of two units: a system-on-a-chip (SoC) transmitter unit and a receiver unit built with off-the-shelf components. A novelty of the WINeR system is in its utilization of a wireless single-slope ADC technique by inserting a wireless link in between a pulse width modulator and a time-to-digital converter (TDC). This technique not only offers the WINeR system the benefit of a single-slope ADC, but also makes the WINeR transmitter unit very simple, low power, and small in regards to chip area. In addition, by directly transmitting pulse width modulation (PWM) signal, the pulse rate over the wireless link is reduced to the sampling rate, while a moderate system resolution can still be achieved. Another novelty of this system is that its transmitter uses an asynchronous (clockless) topology and achieves very low noise levels by eliminating the on-chip clock. Some of the other features of this system are the wideband FSK demodulator and FPGA-based TDC in the receiver unit capable of achieving high resolution, low noise, low power, low cost, and ease of implementation. A 32-channel WINeR transmitter prototype is implemented in a standard CMOS technology, and operates in the 900MHz ISM band. A prototype WINeR receiver is also built using off-the-shelf components with up to 75MHz bandwidth. A custom developed VC++ GUI running on a PC interface with the receiver unit through a USB port and facilitates data storage and visualization. In addition, detailed noise analysis is conducted both theoretically and experimentally to further characterize the performance of the system. Finally, the full functionality of the entire WINeR system has been validated from bench-top, and through in vivo experiments on rats.