Sudip Nag

Flexible Charge Balanced Stimulator With 5.6 fC Accuracy for 140 nC Injections

Electrical stimulations of neuronal structures must ensure net injected charges to be zero for biological safety and voltage compliance reasons. We present a novel architecture of general purpose biphasic constant current stimulator that exhibits less than 5.6 fC error while injecting 140 nC charges using 1.4 mA currents. The floating current sources and conveyor switch based system can operate in monopolar or bipolar modes. Anodic-first or cathodic-first pulses with optional inter-phase delays have been demonstrated with zero quiescent current requirements at the analog front-end. The architecture eliminates blocking capacitors, electrode shorting and complex feedbacks. Bench-top and in-vivo measurement results have been presented with emulated electrode impedances (resistor-capacitor network), Ag-AgCl electrodes in saline and in-vivo (acute) peripheral nerve stimulations in anesthetized rats.

Enabling Wireless Powering and Telemetry for Peripheral Nerve Implants

Wireless power delivery and telemetry have enabled completely implantable neural devices. Current day implants are controlled, monitored, and powered wirelessly, eliminating the need for batteries and prolonging the lifetime. A brief overview of wireless platforms for such implantable devices is presented in this paper alongside an in-depth discussion of wireless platform for peripheral nerve implants covering design requirements, link design, and safety. Initial acute studies on the performance of the wireless power and data links in rodents are also presented.

Implantable neurotechnologies: electrical stimulation and applications

AbstractNeural stimulation using injected electrical charge is widely used both in functional therapies and as an experimental tool for neuroscience applications. Electrical pulses can induce excitation of targeted neural pathways that aid in the treatment of neural disorders or dysfunction of the central and peripheral nervous system . In this review, we summarize the recent trends in the field of electrical stimulation for therapeutic interventions of nervous system disorders, such as for the restoration of brain, eye, ear, spinal cord, nerve and muscle function . Neural prosthetic applications are discussed, and functional electrical stimulation parameters for treating such disorders are reviewed. Important considerations for implantable packaging and enhancing device reliability are also discussed. Neural stimulators are expected to play a profound role in implantable neural devices that treat disorders and help restore functions in injured or disabled nervous system.

Current Excitation Method for

This paper presents a new highly sensitive (10 μV/ppm) bidirectional current excitation method for piezo-resistive sensor measurements, through excitation of two half bridges for ΔR measurement. The proposed circuit is insensitive to thermoelectric and stray noise effects since it measures the peak-to-peak value of the generated voltage. Measurement results using resistors show that variations as low as 0.3 ppm are measurable from 15°C to 80°C with resistors. As an experimental application, 40 parts per billion variation in gas concentration using piezo-resistive SU-8 microcantilevers is measured by the proposed circuit at room temperature.

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Stimulus artifacts inhibit reliable acquisition of biological evoked potentials for several milliseconds if an electrode contact is utilized for both electrical stimulation and recording purposes. This hinders the measurement of evoked short-latency biological responses, which is otherwise elicited by stimulation in implantable prosthetic devices. We present an improved stimulus artifact suppression scheme using two electrode simultaneous stimulation and differential readout using high-gain amplifiers. Substantial reduction of artifact duration has been shown possible through the common-mode rejection property of an instrumentation amplifier for electrode interfaces. The performance of this method depends on good matching of electrode-electrolyte interface properties of the chosen electrode pair. A novel calibration algorithm has been developed that helps in artificial matching of impedance and thereby achieves the required performance in artifact suppression. Stimulus artifact duration has been reduced down to 50 μs from the stimulation-cum-recording electrodes, which is ~6× improvement over the present state of the art. The system is characterized with emulated resistor-capacitor loads and a variety of in-vitro metal electrodes dipped in saline environment. The proposed method is going to be useful for closed-loop electrical stimulation and recording studies, such as bidirectional neural prosthesis of retina, cochlea, brain, and spinal cord.

Measurement in Piezo-Resistive Sensors With a 0.3-ppm Resolution

A widespread requirement exists for a low cost and reliable health monitor in the clinical as well as home environment. The e-jacket presented here is an example of a smart clothing system with multiple bioparameter acquisition of electrocardiogram (ECG), pulse oximetry, body motion/tilt and skin temperature. The battery operated circuit has an integrated graphic liquid crystal display (LCD) screen and a 2.4 GHz wireless link. An RS232 interface provides a plug-in port for easy accessibility to remote telemedicine applications. The system incorporates an efficient ARM7 microcontroller to coordinate a list of software tasks with associated time stamp. Comfort analysis and reliability aspects have been carefully studied along with intelligent power conservation schemes. A low cost and reliable tele-medical network is proposed using an innovative e-textile solution.

Sensing of Stimulus Artifact Suppressed Signals From Electrode Interfaces

The techniques of optogenetic stimulation and neural signal recording can be coupled together in order to realize a closed loop neural interface. An improved multifunction system has been presented that is able to generate single or multi-wavelength optical pulses as well as measure evoked neural potentials. The optical stimulator is based on blue (470 nm) and yellow (592 nm) LEDs. The neural recording amplifier consists of a low noise chip with an analog-to-digital converter (ADC), an impedance measurement hardware and a digital communication logic. In addition, wireless power and data transfer capabilities makes the system useful for a range of in-vivo studies. A safety feature against high temperature induced neural damage has also been incorporated. The entire system weighs approximately 4 gms and is packaged using an FDA-compliant biocompatible polymer for reliable and waterproof operation. In-vivo stimulation and recording experiments have been performed in the visual and motor cortices of transgenic CHR2 mice under anesthetized and partially awake conditions.

Wireless E-Jacket for Multiparameter Biophysical Monitoring and Telemedicine Applications

Restoration of motor function in cases of peripheral nerve injury is a challenging problem. Although peripheral nerves do regenerate, the time required for peripheral nerves to regenerate often causes atrophy to occur in the muscles before they can be re-innervated. This paper presents a solution through proximal recording of nerve signals and distal muscle stimulation. A fully implantable hardware architecture is described that can be operated by means of inductive power and MICS band data transmission schemes. Preliminary experiments and validation studies are reported with non-human primates based on recordings in the median nerve, stimulation of hand muscles, and task decoding and classification. This approach shows promise in creating a neural prosthesis capable of restoring hand movements in patients with upper limb peripheral nerve injuries.

Multi-function optogenetic stimulator and neural amplifier for wirelessly controlled neural interface

This paper presents an ultra-low-power current-mode ECG instrumentation amplifier, which is designed based on the current balancing technique and fabricated in TSMC 0.35 μm CMOS process. The instrumentation amplifier, which is presented here has three features. First, the instrumentation amplifier is a full-CMOS implementation of current-balancing technique applied for ECG signal conditioning. Second, the instrumentation amplifier is of ultra-low-power due to a power-oriented design methodology, which makes its power consumption very low compared to the earlier reported works for ECG recording applications. Third, integrated programmable bandpass filtering is implemented in the amplifier itself, which provides a compact solution for analog ECG signal conditioning. Measurement results show that the amplifier only draws 9 μA current from a 3.3 V lithium-ion battery, while CMRR of 100 dB and input voltage dynamic range of ± 6 mV are achieved. By considering trade-offs between input noise voltage and power, noise performance was compromised with power and area for ultra-low-power ECG signal conditioning applications. Measurement results show input referred noise voltage with a flicker noise corner frequency of 15 Hz at 9 μA dc current and small area, which is appropriate for the desired application. Measurement results meet the recommended specifications for signal conditioning of portable ECG monitoring devices. Design methodology, fabrication considerations, measurement setup, and experimental results are also explained in this paper.

Neural prosthesis for motor function restoration in upper limb extremity

A long‐term peripheral neural interface is an area of intense research. The use of electrode interfaces is limited by the biological response to the electrode material.