NASA Tech Briefs, November 1993

Topics covered: Advanced Manufacturing; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences

Doctor of Philosophy

dissertationThe optimization of novel stretchable fingernail sensors for detecting fingertip touch force direction is introduced. The fingernail sensor uses optical reflectance photoplethysmography to measure the change in blood perfusion in the fingernail bed when the finger pad touches a surface with various forces. This "fingernail sensing" technique involves mounting an array of LEDs (Light Emitting Diodes) and photodetectors on the fingernail surface to detect changes in the reflection intensity as a function of applied force. The intensity changes correspond to changes in blood volume underneath the fingernail and allow for fingertip force detection without haptic obstruction, which has several applications in the area of human-machine interaction. This dissertation experimentally determines the optimal optical parameters for the transmittance of light through the human fingernail bed. Specifically, the effect of varying the wavelength and optical path length on light transmittance through the nail bed are thoroughly investigated. Light transmittance through the human fingernail is optimized when using green light (525nm) and when placing optoelectronic pairs as close together as possible. The optimal locations of the optoelectronic devices are predicted by introducing an optical model that describes light transmittance between an LED and a photodiode in the fingernail area based on optical experimentation. A reduced configuration is derived from the optimal optoelectronic locations in order to facilitate iv the fabrication of the optimized fingernail sensor without significantly compromising the recognition accuracy. This results in an overall force direction recognition accuracy of 95%. Using novel fabrication techniques, we successfully build a stretchable fingernail sensor prototype, which fully conforms to the two-dimensional fingernail surface and is independent of its geometry. Namely, we overcome the challenges of patterning conductive lines on a stretchable substrate, and embedding rigid optical components in a stretchable platform while maintaining electrical conductivity. A finite element analysis is conducted to optimize the electrical contact resistance between the optoelectronic components and underlying stretchable conductors, as a function of the bending curvature and substrate thickness. The functionality of the stretchable sensor is tested in relation to the design parameters. Finally, applications and potential impacts of this work are discussed

Analog VLSI circuits for inertial sensory systems

Supervised by Rahul Sarpeshkar.Also isssued as Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Includes bibliographical references (leaves 67-68).by Maziar Tavakoli Dastjerdi

Feature selection using enhanced particle swarm optimisation for classification models.

In this research, we propose two Particle Swarm Optimisation (PSO) variants to undertake feature selection tasks. The aim is to overcome two major shortcomings of the original PSO model, i.e., premature convergence and weak exploitation around the near optimal solutions. The first proposed PSO variant incorporates four key operations, including a modified PSO operation with rectified personal and global best signals, spiral search based local exploitation, Gaussian distribution-based swarm leader enhancement, and mirroring and mutation operations for worst solution improvement. The second proposed PSO model enhances the first one through four new strategies, i.e., an adaptive exemplar breeding mechanism incorporating multiple optimal signals, nonlinear function oriented search coefficients, exponential and scattering schemes for swarm leader, and worst solution enhancement, respectively. In comparison with a set of 15 classical and advanced search methods, the proposed models illustrate statistical superiority for discriminative feature selection for a total of 13 data sets

Thermal transport at the quantum scale

The aim of this thesis is to add new experimental insights to the knowledge of thermal transport physics at the scale of single atoms and molecules, where quantum effects become apparent. In particular a new instrument and measurement protocol to study heat transport at the nanoscale will be introduced, and the key experimental results on single molecules will be presented and compared to the outcomes of the latest theoretical predictions. Finally, possible technological perspectives and future directions of the fields will be reviewed and commented

Heterostructure engineering of quantum dots-in-a-well infrared photodetectors

Three of the most important characteristics of third-generation imaging systems are high operating temperature, multispectral operation, and large format arrays. The quantum dot infrared photodetector technology, owing to the three-dimensional confinement of carriers, the richness of the electronic spectra in quantum dots, and the mature III-V based fabrication technology, satisfy these requirements. This work focuses on quantum dots-in-a-well (DWELL) detectors in which InAs quantum dots are embedded in a compressively strained InGaAs-GaAs quantum well. Barriers separating two stacks of quantum dots can be GaAs, AlGaAs or a combination of different materials, with \u27smart barriers\u27. Motivation for this work is to improve the understanding and the performance of DWELL detectors to achieve high temperature operation and high signal to noise ratio for these detectors for given wavelength requirements, at applied biases compatible with CMOS technology. This aim has been pursued on three fronts: barrier designs, device designs and material systems. Smart barriers, such as resonant tunneling barriers have been demonstrated to improve the signal to noise ratio of the detector by reducing the dark current significantly, while keeping the photocurrent constant. A systematic experimental study has been conducted for understanding the effect of different types of transitions on the properties of DWELL detectors, which showed that bound to quasibound (B-Q) type of transitions optimize the device performance at moderate bias levels. The performance of B-Q type of architectures has been substantially improved by the use of confinement enhancing (CE) barriers that combine the advantages of high energy barriers, such as low dark current and high signal to noise ratio, with those of low energy barriers, such as high responsivity and longer peak wavelengths at low bias operation. A new type of detector, a quantum dot based quantum cascade detector, has been proposed and implemented. QD-QCD exhibits a strong photovoltaic action, leading to strong performance at zero bias, by the virtue of internal electric field generated by the quantum cascade action in the barrier. The zero bias operation, combined with record low photoconductive gains for any quantum dot detectors, makes QD QCD very attractive for focal plane array applications. For improved understanding, theoretical modeling of quantum dot strain, based on atomistic valence force field method as well as transport simulations of general heterostructure detectors with drift-diffusion model have been developed. The transport simulation results indicate the presence of a strong space charge region forming between the highly n-doped contact regions and non-intentionally doped barrier regions, which makes the internal electric field highly nonlinear in space. This has been verified by systematic experiments, in which effects of this electric field nonlinearity on the device parameters have been studied. This work would enable a device designer to choose different device parameters such as spectral response position and shape, photoconductive gain, response, signal to noise ratio, dark current levels, activation energies etc. This knowledge has been utilized in demonstrating highly sensitive FPAs, as well as high operating temperature imaging (at 140K) with DWELL detectors. State of the art performance has been obtained from different devices at different wavelengths, such as such as a detectivity of 4x1011 cm.Hz1/2W-1 at 77K in a bound to quasibound device with a cutoff wavelength of 8.5 μm, which is higher than that obtained from state of the art QWIPs. Although the dark current levels are substantially lower than standard QWIPs, and background limited photodetection is at much higher temperature, the focal plane array sensitivities are lower than those of the state of the art QWIPs, by around 10 mK, due to lower quantum efficiency (a factor of 2-3) and higher photoconductive gain. This difference can be eliminated by the use of gratings or shape engineering through the use of submonolayer quantum dots and with smaller photoconductive gains with DWELL detectors

Cyber defensive capacity and capability::A perspective from the financial sector of a small state

This thesis explores ways in which the financial sectors of small states are able todefend themselves against ever-growing cyber threats, as well as ways these states can improve their cyber defense capability in order to withstand current andfuture attacks. To date, the context of small states in general is understudied. This study presents the challenges faced by financial sectors in small states with regard to withstanding cyberattacks. This study applies a mixed method approach through the use of various surveys, brainstorming sessions with financial sector focus groups, interviews with critical infrastructure stakeholders, a literature review, a comparative analysis of secondary data and a theoretical narrative review. The findings suggest that, for the Aruban financial sector, compliance is important, as with minimal drivers, precautionary behavior is significant. Countermeasures of formal, informal, and technical controls need to be in place. This study indicates the view that defending a small state such as Aruba is challenging, yet enough economic indicators indicate it not being outside the realm of possibility. On a theoretical level, this thesis proposes a conceptual “whole-of-cyber” model inspired by military science and the VSM (Viable Systems Model). The concept of fighting power components and governance S4 function form cyber defensive capacity’s shield and capability. The “whole-of-cyber” approach may be a good way to compensate for the lack of resources of small states. Collaboration may be an only out, as the fastest-growing need will be for advanced IT skillsets

Batch-fabrication of novel nanoprobes for SPM

A micromachining method has been developed for fabricating 20µm tall silicon atomic force tips with flat tops less than 2µm wide suitable for defining nanosensors upon, and with low aspect ratio sides suitable for defining electrical connections to the sensor. Methods have been developed to allow flat substrate processing techniques to be applied to such non-planar micromachined substrates. This has necessitated the development of a novel resist-coating technique and the use of defocused electron-beam lithography. Methods for through-wafer alignment by electron-beam lithography and accurate alignment to the tips using micromachined alignment markers have also had to be developed. The fabrication process has been designed to enable a wide variety of sub-micron sensors to be defined on the atomic force probes, with little additional development beyond that of : sensors themselves. This flexibility has enabled very different sensors meant for very different scanning probe microscopy techniques to be designed without significant redevelopment of the underlying fabrication process. The main restrictions on the type of sensor that can be used are the physical dimensions of the sensor, the number of alignment levels necessary, the degree of alignment accuracy required and the choice of sensor materials. However, within these constraints it has been found that probes optimised for scanning near-field optical microscopy (SNOM), scanning thermal microscopy, modulation differential scanning calorimetry (MDSC) and scanning Hall-probe microscopy can be fabricated. For the SNOM probes three methods for fabricating sub-l00nm diameter apertures have been developed, analysed and compared with each other to evaluate both the process latitude. and, the size and reproducibility of apertures that can be fabricated, as a function of electron beam dose, pattern shape and size, and metallisation material and thickness. Two methods, both utilising multilayer 'resist' schemes have been found suitable for this purpose, one based on conventional electron-beam lithography with PMMA and a new dry etching process for titanium, and the other based on a novel electron-beam lithography technique utilising cross-linked PMMA for lifting off nichrome. A simple analytical model has also been developed for these probes allowing the effects of changes in the sensor design parameters on the light throughput to be compared qualitatively, if not quantitatively. For the scanning thermal probes a method for lifting-off sub-l00nm, thin-film thermocouple sensors on silicon tips without the loss of electrical continuity has been developed. For the MDSC probes, a similar method has been developed for defining thermal resistors. A method has also been presented for fabricating sensors for scanning Hall-probe microscopy based on an evaporated germanium sensing layer. This has been found to require annealing and optimisation of sensor design and geometry to reduce sensor resistance to acceptable levels

Considerations in Assuring Safety of Increasingly Autonomous Systems

Recent technological advances have accelerated the development and application of increasingly autonomous (IA) systems in civil and military aviation. IA systems can provide automation of complex mission tasks-ranging across reduced crew operations, air-traffic management, and unmanned, autonomous aircraft-with most applications calling for collaboration and teaming among humans and IA agents. IA systems are expected to provide benefits in terms of safety, reliability, efficiency, affordability, and previously unattainable mission capability. There is also a potential for improving safety by removal of human errors. There are, however, several challenges in the safety assurance of these systems due to the highly adaptive and non-deterministic behavior of these systems, and vulnerabilities due to potential divergence of airplane state awareness between the IA system and humans. These systems must deal with external sensors and actuators, and they must respond in time commensurate with the activities of the system in its environment. One of the main challenges is that safety assurance, currently relying upon authority transfer from an autonomous function to a human to mitigate safety concerns, will need to address their mitigation by automation in a collaborative dynamic context. These challenges have a fundamental, multidimensional impact on the safety assurance methods, system architecture, and V&V capabilities to be employed. The goal of this report is to identify relevant issues to be addressed in these areas, the potential gaps in the current safety assurance techniques, and critical questions that would need to be answered to assure safety of IA systems. We focus on a scenario of reduced crew operation when an IA system is employed which reduces, changes or eliminates a human's role in transition from two-pilot operations

2022 roadmap on neuromorphic computing and engineering

Modern computation based on von Neumann architecture is now a mature cutting-edge science. In the von Neumann architecture, processing and memory units are implemented as separate blocks interchanging data intensively and continuously. This data transfer is responsible for a large part of the power consumption. The next generation computer technology is expected to solve problems at the exascale with 10$^{18}$ calculations each second. Even though these future computers will be incredibly powerful, if they are based on von Neumann type architectures, they will consume between 20 and 30 megawatts of power and will not have intrinsic physically built-in capabilities to learn or deal with complex data as our brain does. These needs can be addressed by neuromorphic computing systems which are inspired by the biological concepts of the human brain. This new generation of computers has the potential to be used for the storage and processing of large amounts of digital information with much lower power consumption than conventional processors. Among their potential future applications, an important niche is moving the control from data centers to edge devices. The aim of this roadmap is to present a snapshot of the present state of neuromorphic technology and provide an opinion on the challenges and opportunities that the future holds in the major areas of neuromorphic technology, namely materials, devices, neuromorphic circuits, neuromorphic algorithms, applications, and ethics. The roadmap is a collection of perspectives where leading researchers in the neuromorphic community provide their own view about the current state and the future challenges for each research area. We hope that this roadmap will be a useful resource by providing a concise yet comprehensive introduction to readers outside this field, for those who are just entering the field, as well as providing future perspectives for those who are well established in the neuromorphic computing community