S.C. DeMarco

Bio: S.C. DeMarco is an academic researcher from North Carolina State University. The author has contributed to research in topics: Retina & Visual prosthesis. The author has an hindex of 6, co-authored 7 publications receiving 597 citations.

A neuro-stimulus chip with telemetry unit for retinal prosthetic device

Abstract: In this retinal prosthesis project, a rehabilitative device is designed to replace the functionality of defective photoreceptors in patients suffering from retinitis pigmentosa (RP) and age-related macular degeneration (AMD). The device consists of an extraocular and an intraocular unit. The implantable component receives power and a data signal via a telemetric inductive link between the two units. The extraocular unit includes a video camera and video processing board, a telemetry protocol encoder chip, and an RF amplifier and primary coil. The intraocular unit consists of a secondary coil, a rectifier and regulator, a retinal chip with a telemetry protocol decoder, a stimulus signal generator, and an electrode array. This paper focuses on the design, fabrication, and testing of a microchip which serves as the telemetry protocol decoder and stimulus signal generator. It is fabricated by MOSIS with 1.2-mm CMOS technology and was demonstrated to provide the desired biphasic current stimulus pulses for an array of 100 retinal electrodes at video frame rates.

Computed SAR and thermal elevation in a 0.25-mm 2-D model of the human eye and head in response to an implanted retinal stimulator - part I: models and methods

Abstract: Retinitis pigmentosa and age-related macular degeneration lead to blindness through progressive loss of retinal photoreceptors. Attempts are under way to construct a visual prosthesis to recover a limited sense of vision for these patients with the aid of implantable electronic devices. The function of these microchips is to provide electrical stimulation to existing viable retinal tissues - living ganglion and bipolar cells - using an array of on-chip stimulus circuits, while the dominant mechanism for power and data communication for these implanted devices has been wireless inductive telemetry using coils. This paper describes methods and models used to estimate the heating induced in the human eye and surrounding head tissues subject to the operation of this retinal prosthesis. A two-dimensional 0.25-mm high-resolution human head model has been developed with the aid of a new semiautomatic graphical segmentation algorithm. Finite-difference-based numerical methods for both electromagnetic and thermal modeling have been used to determine the influence of the specific absorption rate (associated with 2-MHz inductive coupling to the implant) and of stimulator integrated circuit (IC) power on tissue heating under different operational conditions and different hypothesis on choroidal blood flow and properties of the complex implanted circuitry. Results, provided in Part II of this paper, show that temperature increases of approximately 0.6 and 0.4/spl deg/C are induced in the midvitreous of the human eye in the absence and presence of choroidal blood flow, respectively, for a 60-electrode retinal prosthesis chip. Correspondent temperature rises of approximately 0.19 and 0.004/spl deg/C on the retina are obtained for these cases. Comparison with in vivo experimental measurements on intraocular heating in dog eyes shows good agreement.

An arbitrary waveform stimulus circuit for visual prostheses using a low-area multibias DAC

Abstract: Attempts are underway to construct a retinal prosthesis to recover limited vision for blind patients with retinitis pigmentosa using implantable electronic devices. These microchips provide electrical stimulation to damaged retinal tissues using an array of stimulus circuits. This paper describes improvements to conventional circuit designs with significantly decreased implementation area and the ability to support arbitrary stimulus waveforms where an array of such stimulus circuits is required. This yields greater spatial resolution in stimulation owing to more stimulus circuits per chip area. Also introduced are digital-to-analog converter gain prescalar and dc-offset circuits which tune the stimulus circuits to an optimally effective range due to variation in retinal degradation. The prototype chip was fabricated by MOSIS in 1.2-/spl mu/m CMOS technology.

Retinal prosthesis to aid the visually impaired

Abstract: In this retinal prosthesis project, a rehabilitative device is being designed to replace the functionality of defective photoreceptors in patients suffering from retinal pigmentosa and age-related macular degeneration. An implantable intraocular unit receives power and signal via a telemetric inductive link with an extraocular unit. The extraocular unit consists of a video camera and video processing board, a telemetry protocol encoder chip, an RF amplifier and a primary coil, while the intraocular unit consists of a secondary coil, a rectifier and regulator, a retinal chip with a telemetry protocol decoder and stimulus signal generator, and an electrode array. This paper describes the design and testing of the overall system components.

Simulated temperature increase in a head/eye model containing an intraocular retinal prosthesis

Abstract: We study electromagnetic power deposition and temperature elevation in the human head due to an implantable intraocular retinal prosthesis designed to restore limited vision to individuals suffering blindness from outer retinal degeneration such as Retinitis Pigmentosa and Age-related Macula Degeneration. We have developed a high-resolution 2D human head and eye model at 0.25 mm spatial resolution in order to numerically simulate temperature elevation in the eye and surrounding tissues. A 2D finite difference time domain method (FDTD) with material independent absorbing boundary conditions is used to predict with high detail the specific absorption rate (SAR) induced via inductive powering and telemetry with the implant. A highly detailed heating pattern in the eye tissues due to SAR and power dissipation in the implanted stimulator is computed using a 2D time-domain numerical implementation of the bioheat equation.

Analyte Monitoring Device And Methods Of Use

Abstract: An analyte monitor includes a sensor, a sensor control unit, and a display unit. The sensor has, for example, a substrate, a recessed channel formed in the substrate, and conductive material disposed in the recessed channel to form a working electrode. The sensor control unit typically has a housing adapted for placement on skin and is adapted to receive a portion of an electrochemical sensor. The sensor control unit also includes two or more conductive contacts disposed on the housing and configured for coupling to two or more contact pads on the sensor. A transmitter is disposed in the housing and coupled to the plurality of conductive contacts for transmitting data obtained using the sensor. The display unit has a receiver for receiving data transmitted by the transmitter of the sensor control unit and a display coupled to the receiver for displaying an indication of a level of an analyte. The analyte monitor may also be part of a drug delivery system to alter the level of the analyte based on the data obtained using the sensor.

Design and analysis of an adaptive transcutaneous power telemetry for biomedical implants

Abstract: Inductively coupled coil pair is the most common way of wirelessly transferring power to medical implants. However, the coil displacements and/or loading changes may induce large fluctuations in transmitted power into the implant if no adaptive control is used. In such cases, it is required to transmit excessive power to accommodate all the working conditions, which substantially reduces the power efficiency and imposes potential safety concerns. We have implemented a power transfer system with adaptive control technique to eliminate the power variations due to the loading or coupling coefficient changes. A maximum of 250mW power is transmitted through an optimized coil pair driven by Class-E power amplifier. Load shift keying is implemented to wirelessly transfer data back from the secondary to primary side over the same coil pair, with data rate of 3.3 kbps and packet error rate less than 10/sup -5/. A pseudo pulsewidth modulation has been designed to facilitate back data transmission along with forward power transmission. Through this back telemetry the system transmits the information on received power, back from implant to primary side. According to the data received, the system adjusts the supply voltage of the Class-E power amplifier through a digitally controlled dc-dc converter, thus varying the power sent to the implant. The key system parameters are optimized to ensure the stability of the closed-loop system. Measurements show that the system can transmit the 'just-needed' power for a wide range of coil separation and/or loading conditions, with power efficiency doubled when compared to the uncompensated link.

Optimal Frequency for Wireless Power Transmission Into Dispersive Tissue

Abstract: RF wireless interface enables remotely-powered implantable devices. Current studies in wireless power transmission into biological tissue tend to operate below 10 MHz due to tissue absorption loss, which results in large receive antennas. This paper examines the range of frequencies that will optimize the tradeoff between received power and tissue absorption. It first models biological tissue as a dispersive dielectric in a homogeneous medium and performs full-wave analysis to show that the optimal frequency is above 1 GHz for small receive coil and typical transmit-receive separations. Then, it includes the air-tissue interface and models human body as a planarly layered medium. The optimal frequency is shown to remain in the GHz-range. Finally, electromagnetic simulations are performed to include the effect of load impedance and look at the matched power gain. The optimal frequency is in the GHz-range for mm-sized transmit antenna and shifts to the sub-GHz range for cm-sized transmit antenna. The multiple orders of magnitude increase in the operating frequency enables dramatic miniaturization of implantable devices.

Retinal prosthesis

Abstract: A prosthesis device is designed to replace the functionality of defective photoreceptors in patients suffering from Retinitis Pigmentosa and age-related Macula Degeneration. The circuit designs include a telemetry link used for power transmission and a bidirectional data communication bus. The 28.9mm/sup 2/ IC dissipates 50mW and is fabricated in 1.2/spl mu/m technology. Experimental results on human subjects are included.