Nathan M. Neihart

Bio: Nathan M. Neihart is an academic researcher from Iowa State University. The author has contributed to research in topics: Amplifier & CMOS. The author has an hindex of 13, co-authored 44 publications receiving 811 citations. Previous affiliations of Nathan M. Neihart include University of Utah & University of Washington.

Micropower circuits for bidirectional wireless telemetry in neural recording applications

Abstract: State-of-the art neural recording systems require electronics allowing for transcutaneous, bidirectional data transfer. As these circuits will be implanted near the brain, they must be small and low power. We have developed micropower integrated circuits for recovering clock and data signals over a transcutaneous power link. The data recovery circuit produces a digital data signal from an ac power waveform that has been amplitude modulated. We have also developed an FM transmitter with the lowest power dissipation reported for biosignal telemetry. The FM transmitter consists of a low-noise biopotential amplifier and a voltage controlled oscillator used to transmit amplified neural signals at a frequency near 433 MHz. All circuits were fabricated in a standard 0.5-/spl mu/m CMOS VLSI process. The resulting chip is powered through a wireless inductive link. The power consumption of the clock and data recovery circuits is measured to be 129 /spl mu/W; the power consumption of the transmitter is measured to be 465 /spl mu/W when using an external surface mount inductor. Using a parasitic antenna less than 2 mm long, a received power level was measured to be -59.73 dBm at a distance of one meter.

Memristive Behavior in Thin Anodic Titania

Abstract: A common material in creating memristors is titanium dioxide (TiO2), grown by atomic layer deposition, sputtering, or sol-gel process. In this letter, we study the memristive behavior in thin TiO2 films fabricated by brief electrochemical anodization of titanium. The effects of different anodization times and annealing are explored. We discover that inherent oxygen-vacancies at the bottom Ti/TiO2 interface naturally lead to memristive switching in nonannealed films. Annealing induces extra oxygen vacancies near the top metal/oxide interface, which leads to symmetric and ohmic current-voltage characteristics with a collapse of memristive switching. No clear dependence on anodization time was observed for times between 1 s and 1 min.

A two-stage sensing technique for dynamic spectrum access

Abstract: Dynamic spectrum access (DSA) is a promising approach for the more effective use of existing spectrum. Of fundamental importance to DSA is the need for fast and reliable spectrum sensing over a wide bandwidth. A model for two-stage sensing is described based on an analysis of the mean time to detect an idle channel. Simulation results show that it provides significantly faster idle channel detection than conventional single-stage random searching. Several system-level issues are also investigated including the settling time of the phase-locked loop (PLL) in the frequency synthesizer, which determines the channel switching time. Effects of the bandwidth of the coarse sensing block and the integration duration of the energy detector are also presented.

A Parallel, Multi-Resolution Sensing Technique for Multiple Antenna Cognitive Radios

Abstract: A parallel, multi-resolution spectrum sensing technique that is amenable to multiple-antenna cognitive radios is introduced. The authors show that for energy-detector-type spectrum sensors, the total sensing time due to FFT latency is reduced by 100 times using the proposed method versus the fixed-resolution, serial detection method employed in single-antenna systems. System-level tradeoffs such as the number of antennas, sensing bandwidth, and FFT size are also explored.

Analysis and Design of a Reconfigurable Multimode Low-Noise Amplifier Utilizing a Multitap Transformer

Abstract: This paper presents a reconfigurable multimode low-noise amplifier (LNA) capable of single-band, concurrent dual-band, and ultra-wideband operation. The multimode operation is realized by incorporating a switched multitap transformer into the input matching network of an inductively degenerated common source amplifier. The proposed LNA achieves single band matching at 2.8, 3.3, and 4.6 GHz; concurrent dual-band matching at 2.05 and 5.65 GHz; and ultra-wideband matching from 4.3 to 10.8 GHz. The power gain is 14.7-16.4 dB, noise figure is 1.9-4.7 dB, and third-order intermodulation intercept point is -2- + 0.4 dBm across all bands. The chip was fabricated in 0.13-μm CMOS, and occupies an area of 1.04 × 0.7 mm2, and has a power dissipation of 6.4 mW from a 1.2-V supply.

One-dimensional titanium dioxide nanomaterials: nanotubes.

Abstract: In the present review we try to give a comprehensive and most up to date view to the field, with an emphasis on the currently most investigated anodic TiO2 nanotube arrays. We will first give an overview of different synthesis approaches to produce TiO2 nanotubes and TiO2 nanotube arrays, and then deal with physical and chemical properties of TiO2 nanotubes and techniques to modify them. Finally, we will provide an overview of the most explored and prospective applications of nanotubular TiO2.

A Low-Power Integrated Circuit for a Wireless 100-Electrode Neural Recording System

Abstract: Recent work in field of neuroprosthetics has demonstrated that by observing the simultaneous activity of many neurons in specific regions of the brain, it is possible to produce control signals that allow animals or humans to drive cursors or prosthetic limbs directly through thoughts. As neuroprosthetic devices transition from experimental to clinical use, there is a need for fully-implantable amplification and telemetry electronics in close proximity to the recording sites. To address these needs, we developed a prototype integrated circuit for wireless neural recording from a 100-channel microelectrode array. The design of both the system-level architecture and the individual circuits were driven by severe power constraints for small implantable devices; chronically heating tissue by only a few degrees Celsius leads to cell death. Due to the high data rate produced by 100 neural signals, the system must perform data reduction as well. We use a combination of a low-power ADC and an array of "spike detectors" to reduce the transmitted data rate while preserving critical information. The complete system receives power and commands (at 6.5 kb/s) wirelessly over a 2.64-MHz inductive link and transmits neural data back at a data rate of 330 kb/s using a fully-integrated 433-MHz FSK transmitter. The 4.7times5.9 mm2 chip was fabricated in a 0.5-mum 3M2P CMOS process and consumes 13.5 mW of power. While cross-chip interference limits performance in single-chip operation, a two-chip system was used to record neural signals from a Utah Electrode Array in cat cortex and transmit the digitized signals wirelessly to a receiver

Design and Optimization of Resonance-Based Efficient Wireless Power Delivery Systems for Biomedical Implants

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.

Cochlear Implants: System Design, Integration, and Evaluation

Abstract: As the most successful neural prosthesis, cochlear implants have provided partial hearing to more than 120000 persons worldwide; half of which being pediatric users who are able to develop nearly normal language. Biomedical engineers have played a central role in the design, integration and evaluation of the cochlear implant system, but the overall success is a result of collaborative work with physiologists, psychologists, physicians, educators, and entrepreneurs. This review presents broad yet in-depth academic and industrial perspectives on the underlying research and ongoing development of cochlear implants. The introduction accounts for major events and advances in cochlear implants, including dynamic interplays among engineers, scientists, physicians, and policy makers. The review takes a system approach to address critical issues in cochlear implant research and development. First, the cochlear implant system design and specifications are laid out. Second, the design goals, principles, and methods of the subsystem components are identified from the external speech processor and radio frequency transmission link to the internal receiver, stimulator and electrode arrays. Third, system integration and functional evaluation are presented with respect to safety, reliability, and challenges facing the present and future cochlear implant designers and users. Finally, issues beyond cochlear implants are discussed to address treatment options for the entire spectrum of hearing impairment as well as to use the cochlear implant as a model to design and evaluate other similar neural prostheses such as vestibular and retinal implants.