scispace - formally typeset
Search or ask a question
Author

Mohanasankar Sivaprakasam

Bio: Mohanasankar Sivaprakasam is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Computer science & Pulse wave velocity. The author has an hindex of 23, co-authored 243 publications receiving 2872 citations. Previous affiliations of Mohanasankar Sivaprakasam include University of California, Santa Cruz & Indian Institutes of Technology.


Papers
More filters
Journal ArticleDOI
TL;DR: In this article, a power transfer system with adaptive control technique to eliminate the power variations due to the loading or coupling coefficient changes is proposed, where a maximum of 250mW power is transmitted through an optimized coil pair driven by a Class-E power amplifier.
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.

437 citations

Journal ArticleDOI
TL;DR: The design procedure starts with the formation of equivalent circuits, followed by the analysis of the loss of the rectifier and coils and the H-field for induced voltage and current and an experimental power link is implemented with an overall efficiency of 67% at the optimal distance of 7 mm between the coils.
Abstract: This paper presents a design methodology of a highly efficient power link based on Class-E driven, inductively coupled coil pair. An optimal power link design for retinal prosthesis and/or other implants must take into consideration the allowable safety limits of magnetic fields, which in turn govern the inductances of the primary and secondary coils. In retinal prosthesis, the optimal coil inductances have to deal with the constraints of the coil sizes, the tradeoffs between the losses, H-field limitation and dc supply voltage required by the Class-E driver. Our design procedure starts with the formation of equivalent circuits, followed by the analysis of the loss of the rectifier and coils and the H-field for induced voltage and current. Both linear and nonlinear models for the analysis are presented. Based on the procedure, an experimental power link is implemented with an overall efficiency of 67% at the optimal distance of 7 mm between the coils. In addition to the coil design methodology, we are also presenting a closed-loop control of Class-E amplifier for any duty cycle and any value of the systemQ.

233 citations

Proceedings ArticleDOI
01 Feb 2008
TL;DR: The chip is composed of eight 16-channel front-end blocks, data serializing circuits, a DSP for on-chip spike sorting, digital MUX, encoder, UWB TX, and bias generators.
Abstract: The chip is composed of eight 16-channel front-end blocks, data serializing circuits, a DSP for on-chip spike sorting, digital MUX, encoder, UWB TX, and bias generators The chip operates in one of the two modes In sorting mode, a selected channel is connected to the on-the-fly spike sorting block and the extracted features of the spikes are transmitted for off-chip classification In streaming mode, all the sampled data from the 128 channels are recorded and transmitted without any additional processing

183 citations

Journal ArticleDOI
TL;DR: In this paper, a driver was proposed to generate bi-phasic (anodic and cathodic) current pulses for stimulating the retinal layer through electrodes which is part of a retinal prosthetic device for implants in blind patients affected by retinitis pigmentosa (RP) and age-related macular degeneration (AMD).
Abstract: This paper reports a driver circuitry to generate bi-phasic (anodic and cathodic) current pulses for stimulating the retinal layer through electrodes which is part of a retinal prosthetic device for implants in blind patients affected by retinitis pigmentosa (RP) and age-related macular degeneration (AMD). Dual voltage architecture is used to halve the number of interface leads from the chip to the stimulation sites compared to a single voltage supply. The driver circuitry is designed to deliver currents with six bit resolution for a wide range of full scale currents up to 600 /spl mu/A. To cater to the varying stimulus requirements among patients and different regions of the retina, variable gain architecture is used to achieve fine resolution even for a narrow range of stimulus. 1:8 demultiplexing feature is embedded within the output stage thus allowing one DAC for eight outputs. A novel charge cancellation circuitry with current limiting capability is implemented to discharge the electrodes for medical safety. Measurement results of a prototype chip fabricated in 1.5-/spl mu/m CMOS technology are presented.

175 citations

Journal ArticleDOI
TL;DR: A tradeoff between the power consumption of the system and the chip area in terms of the multiplexing ratio is investigated and the optimal number of channels per ADC is selected to achieve the minimum power-area product for the entire system.
Abstract: Power and chip area are the most important parameters in designing a neural recording system in vivo. This paper reports a design methodology for an optimized integrated neural recording system. Electrode noise is considered in determining the ADC's resolution to prevent over-design of the ADC, which leads to unnecessary power consumption and chip area. The optimal transconductance and gain of the pre-amplifiers, which minimizes the power-area product of the amplifier, are mathematically derived. A numerical example using actual circuit parameters is shown to demonstrate the design methodology. A tradeoff between the power consumption of the system and the chip area in terms of the multiplexing ratio is investigated and the optimal number of channels per ADC is selected to achieve the minimum power-area product for the entire system. Following the proposed design methodology, a chip has been designed in 0.35 mum CMOS process, with the multiplexing ratio of 16:1, resulting in total chip area of 2.5 mm times 2.0 mm and power consumption of 5.3 mW from plusmn1.65 V.

116 citations


Cited by
More filters
Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal Article
TL;DR: This study is the first to establish reference and normal values for PWV, combining a sizeable European population after standardizing results for different methods of PWV measurement.
Abstract: Aims Carotid–femoral pulse wave velocity (PWV), a direct measure of aortic stiffness, has become increasingly important for total cardiovascular (CV) risk estimation. Its application as a routine tool for clinical patient evaluation has been hampered by the absence of reference values. The aim of the present study is to establish reference and normal values for PWV based on a large European population. Methods and results We gathered data from 16 867 subjects and patients from 13 different centres across eight European countries, in which PWV and basic clinical parameters were measured. Of these, 11 092 individuals were free from overt CV disease, non-diabetic and untreated by either anti-hypertensive or lipid-lowering drugs and constituted the reference value population, of which the subset with optimal/normal blood pressures (BPs) (n = 1455) is the normal value population. Prior to data pooling, PWV values were converted to a common standard using established conversion formulae. Subjects were categorized by age decade and further subdivided according to BP categories. Pulse wave velocity increased with age and BP category; the increase with age being more pronounced for higher BP categories and the increase with BP being more important for older subjects. The distribution of PWV with age and BP category is described and reference values for PWV are established. Normal values are proposed based on the PWV values observed in the non-hypertensive subpopulation who had no additional CV risk factors. Conclusion The present study is the first to establish reference and normal values for PWV, combining a sizeable European population after standardizing results for different methods of PWV measurement.

1,371 citations

Journal ArticleDOI
TL;DR: A review of recent advances in medical imaging using the adversarial training scheme with the hope of benefiting researchers interested in this technique.

1,053 citations

Patent
18 Dec 2008
TL;DR: The paper looks at the background to IPT and how its development was based on sound engineering principles leading on to factory automation and growing to a $1 billion industry in the process.
Abstract: A detection method for use in a primary unit of an inductive power transfer system, the primary unit being operable to transmit power wirelessly by electromagnetic induction to at least one secondary unit of the system located in proximity to the primary unit and/or to a foreign object located in said proximity, the method comprising: driving the primary unit so that in a driven state the magnitude of an electrical drive signal supplied to one or more primary coils of the primary unit changes from a first value to a second value; assessing the effect of such driving on an electrical characteristic of the primary unit; and detecting in dependence upon the assessed effect the presence of a said secondary unit and/or a foreign object located in proximity to said primary unit.

969 citations

Journal ArticleDOI
TL;DR: This work has analyzed the four-coil energy transfer systems and outlined the effect of design parameters on power-transfer efficiency, and a proof-of-concept prototype system is implemented and confirms the validity of the proposed analysis and design techniques.
Abstract: Resonance-based wireless power delivery is an efficient technique to transfer power over a relatively long distance. This technique typically uses four coils as opposed to two coils used in conventional inductive links. In the four-coil system, the adverse effects of a low coupling coefficient between primary and secondary coils are compensated by using high-quality (Q) factor coils, and the efficiency of the system is improved. Unlike its two-coil counterpart, the efficiency profile of the power transfer is not a monotonically decreasing function of the operating distance and is less sensitive to changes in the distance between the primary and secondary coils. A four-coil energy transfer system can be optimized to provide maximum efficiency at a given operating distance. We have analyzed the four-coil energy transfer systems and outlined the effect of design parameters on power-transfer efficiency. Design steps to obtain the efficient power-transfer system are presented and a design example is provided. A proof-of-concept prototype system is implemented and confirms the validity of the proposed analysis and design techniques. In the prototype system, for a power-link frequency of 700 kHz and a coil distance range of 10 to 20 mm, using a 22-mm diameter implantable coil resonance-based system shows a power-transfer efficiency of more than 80% with an enhanced operating range compared to ~40% efficiency achieved by a conventional two-coil system.

894 citations